JP2024000668A5 - - Google Patents

Description

The present invention relates to an audio device that is used in an audio device in which the user prepares a speaker system and an amplifier separately and uses them in combination, and that allows even a person with little acoustic or electrical expertise about speakers and amplifiers to easily flatten, improve, or adjust the frequency characteristics of the low-frequency sound pressure generated by the speaker.

As the first background technology, we will explain the patents obtained by the inventor of this invention.

Patent No. 6699957

According to Patent Document 1, a speaker unit in which resonance in the low frequency range is mechanically suppressed by an acoustic resistance material composed of, for example, an elastic body having small holes such as urethane foam, or a flexible fiber material compressed at an appropriate density, is incorporated into a box, and the insufficient low frequency sound pressure is corrected by an equalizer circuit having a frequency-to-gain characteristic that increases the gain at a rate of 6 dB/oct from the frequency at which the sound pressure begins to become insufficient toward lower frequencies to 0.5 to 2 times the lowest resonance frequency of the speaker, and any sound pressure at low frequencies that is still insufficient after correction is compensated for by a resonance means of the enclosure, for example, the bass reflex resonance of a bass reflex box, thereby making it possible to configure an acoustic device that can reproduce unprecedented low frequency sounds even with a small speaker unit and a speaker system using that speaker unit.

However, unless this type of audio equipment is provided as a set consisting of a speaker unit, a box, and an amplifier including an equalizer circuit as part of a complete, integrated product, such as a television or radio receiver, it will not provide sufficient performance for general users without specialized knowledge.

In addition, even in audio equipment in which speaker systems, amplifiers, CD players, and other devices are provided separately and users combine them according to their personal preferences, it is not possible to guarantee uniform playback sound pressure from low to high frequencies, unless at least a speaker system incorporating the above-mentioned mechanically resonance-suppressing speaker unit and an equalizer device that corrects the lack of low-frequency sound pressure for the speaker system are provided as a set.

This is because the compensation characteristics of the compensation circuit must be adjusted according to the specifications of the speaker unit of the speaker system used for bass sounds, the box in which it is installed, the degree of resonance suppression, etc., and adjustment of these compensation characteristics can only be done by someone with specialized knowledge and the skills to use appropriate measuring equipment.

On the other hand, there is a group of people among the general public who do not have the specialized knowledge or skills , known as DIY enthusiasts, who refer to published examples of construction and manuals, purchase speaker units and box boards as components, and assemble their own speaker systems.

However, for the reasons mentioned above, even for such so-called DIY enthusiasts, it is considered difficult to create an equalizer that effectively flattens the frequency-to-sound pressure characteristics in the low-frequency range or to adjust the correction characteristics in audio equipment such as that described in Patent Document 1.

The second background art is a well-known technology not related to Patent Document 1, namely, a speaker system that uses a normal speaker unit and box that does not suppress resonance, i.e., a general bass reflex speaker system or a general sealed speaker system.

They are used in combination with an amplifier, but if the parameter design of the speaker unit and box is inappropriate and the frequency vs. sound pressure characteristics in the low-frequency range are undesirable, it is possible to improve the characteristics by using a frequency vs. gain characteristic adjustment device such as a graphic equalizer on the amplifier side. Even in this case, it is difficult to address the issue without the appropriate expertise and the ability to use measuring equipment , and it takes a considerable amount of time to address the issue.

Therefore, the objective of the present invention is to provide an acoustic equalizer device that enables easy flattening and improvement of the frequency-to-sound pressure characteristics in the low-frequency range emitted by a speaker system in a bass-reflex speaker system that uses a speaker unit that suppresses the low-frequency resonance of the speaker unit, or in other conventional general bass-reflex or closed speaker systems, even for DIY enthusiasts with little specialized knowledge of acoustics and electricity, or even for those who are not enthusiasts but who are trying to build a speaker system for the first time by purchasing a speaker unit and box construction kit.

Another object of the present invention is to provide an acoustic equalizer device that enables even a person with specialized knowledge and skills to easily flatten and improve the frequency -to-sound pressure characteristics in the low-frequency range.

In order to solve the above-mentioned problems, claim 1 provides an acoustic equalizer device that controls the frequency vs. sound pressure characteristics of a speaker unit in the low-frequency range, wherein at frequencies A and B where A<B, the gain at frequency A is greater than the gain at frequencies B or higher, and the gain between frequencies A and B has a frequency vs. gain characteristic that changes at 6 dB/oct, and a frequency vs. gain characteristic of a BEF (band elimination filter) centered on frequency C where C<B, and is characterized by having means for uniquely setting, selecting or adjusting frequencies A, B and C based on the aperture of the target speaker unit.

In order to solve the above-mentioned problems, in claim 2 , there is provided an acoustic equalizer device according to claim 1 , further comprising a means for adjusting the gain of the BEF at frequency C centered on frequency C.

As a result, in claim 1, frequencies A, B, and C of the acoustic equalizer device can be appropriately set only from the diameter information of the speaker unit, regardless of whether or not one has specialized knowledge or measurement techniques , without knowing the values of frequencies A, B, and C which are determined from the specifications of the speaker unit and box used in the speaker system, thereby easily improving the frequency-to-sound pressure characteristics of the speaker system in the low-frequency range.

In claim 2 , the peaks and valleys of sound pressure at frequency C can be precisely adjusted according to the degree of suppression of mechanical resonance of the speaker unit , and furthermore, the frequency-to-sound pressure characteristics in the low-frequency range can be easily improved even in speaker systems that use speaker units that do not suppress mechanical resonance.

FIG. 1 is a diagram showing an example of a speaker system disclosed in Patent Document 1. FIG. 2 is a diagram showing the frequency vs. sound pressure characteristic of the speaker system shown in FIG. 1. FIG. 2 is a block diagram showing the configuration of an electric circuit device for driving the speaker system shown in FIG. FIG. 1 is a diagram showing an embodiment of a circuit of an equalizer device according to the present invention. FIG. 5 is a diagram showing the frequency vs. gain characteristic of the equalizer circuit 603 shown in FIG. 4. FIG. 6 is a diagram showing the frequency vs. sound pressure characteristic when the frequency vs. sound pressure characteristic shown in FIG. 2 is corrected by the frequency vs. gain characteristic shown in FIG. 5 . 5 is a diagram showing the frequency vs. gain characteristic of the BEF circuit 605 shown in FIG. FIG. 8 is a diagram showing the frequency vs. sound pressure characteristic when the frequency vs. sound pressure characteristic shown in FIG. 6 is corrected by the frequency vs. gain characteristic shown in FIG. 7. FIG. 5 is a circuit diagram showing another embodiment of the equalizer device shown in FIG. 4. FIG. 10 is a circuit diagram showing another embodiment of the equalizer device shown in FIG. 4 and FIG. 9. FIG. 1 shows an example of a typical bass reflex speaker system. A diagram showing the frequency vs. sound pressure characteristics when a valley in sound pressure occurs between the resonance frequency due to the speaker unit and the volume of the internal space of the box in the bass reflex speaker system of FIG. 11 and the bass reflex resonance frequency due to the bass reflex duct and the volume of the internal space of the box. FIG. 13 is a diagram showing the frequency vs. sound pressure characteristic when the frequency vs. sound pressure characteristic of FIG. 12 is corrected by the frequency vs. gain characteristic shown in FIG. 5 . FIG. 14 is a diagram showing the frequency vs. sound pressure characteristic when the frequency vs. sound pressure characteristic of FIG. 13 is corrected by the frequency vs. gain characteristic shown in FIG. 7. FIG. 15 is a diagram showing the frequency vs. sound pressure characteristic when the strength of bass reflex resonance is set to an appropriate level in the frequency vs. sound pressure characteristic of FIG. 14 . FIG. 1 shows an example of a typical closed speaker system. FIG. 17 is a diagram showing the frequency vs. sound pressure characteristic of the speaker system shown in FIG. 16 . FIG. 18 is a diagram showing the frequency vs. sound pressure characteristic when the frequency vs. sound pressure characteristic of FIG. 17 is corrected by the frequency vs. gain characteristic of FIG. 5 . FIG. 19 is a diagram showing the frequency vs. sound pressure characteristic when the frequency vs. sound pressure characteristic of FIG. 18 is corrected by the frequency vs. gain characteristic of FIG. 7. FIG. 17 shows the frequency vs. sound pressure characteristics when the volume of the inner space of the box is set incorrectly for the speaker unit specifications in the speaker system shown in FIG. 16, causing a peak in the sound pressure. FIG. 18 is a diagram showing the frequency vs. sound pressure characteristic when the frequency vs. sound pressure characteristic of FIG. 17 is corrected by the frequency vs. gain characteristic of FIG. 5 . FIG. 19 is a diagram showing the frequency vs. sound pressure characteristic when the frequency vs. sound pressure characteristic of FIG. 18 is corrected by the frequency vs. gain characteristic of FIG. 7.

First, we will explain an embodiment of the equalizer device of the present invention based on Patent Document 1, in which a speaker unit with mechanical resonance suppression is applied to a bass reflex speaker system.

Figure 1 is an explanatory diagram of one embodiment in which a speaker unit 1 with mechanical resonance suppression is attached to a bass reflex box 2. An acoustic resistance material 3 is arranged on the side of the diaphragm 101 of the speaker unit 1 facing the box internal space 201, and the acoustic resistance material 3 is covered with a partition wall 4 so that only a part of its surface 301 is exposed to the box internal space 201, and the air vibrations caused by the diaphragm 101 are transmitted to the box internal space 201 only through the surface 301 of the acoustic resistance material 3 by the partition wall 4. A bass reflex duct 202 is also provided in the box 2.

In addition, in claim 3 of Patent Document 1, the resonating means of the enclosure is described as "due to a combination of the equivalent mechanical stiffness of the main space of the enclosure and an equivalent mechanical mass provided separately," and is not limited to a bass-reflex box as explained in the present patent, but will be explained using a bass-reflex box as a representative type.

In addition, Fig. 1 corresponds to the embodiment of Fig. 24 in Patent Document 1, but the "means for suppressing mechanical resonance by damping the vibration of the diaphragm of the speaker unit" in claim 1 of Patent Document 1 corresponds to the sound absorbing materials 23 and 24 in Fig. 24 of Patent Document 1, and the acoustic resistance material 3 in Fig. 1 of the present patent. Furthermore, in claim 2 of Patent Document 1, "the means for suppressing mechanical resonance includes the rear surface of the diaphragm of the speaker unit and an opening at a predetermined distance from the rear surface of the diaphragm, and an acoustic resistance material having breathability and sound absorption is arranged between the diaphragm and the opening in a small space in which air vibrations caused by the vibration of the diaphragm are transmitted to the main space inside the enclosure only through the opening" corresponds to the sound absorbing materials 23 and 24 arranged in the wall 20 constituting the small space and the opening 2101 of the small space in Fig. 24 of Patent Document 1, but in Fig. 1 of the present patent, the acoustic resistance material 3 is covered with a partition wall 4 leaving its surface 301.

Fig. 2 shows the frequency vs. sound pressure characteristics when the voice coil (not shown) of the speaker unit 1 of the speaker system shown in Fig. 1 is driven with a uniform voltage at each frequency. In Fig. 2, frequency A is a frequency in the vicinity of the lowest mechanical resonance frequency fo of the speaker unit 1 in Fig. 1 (0.5 to 2 times fo in Patent Document 1), frequency B is the frequency at which the low-pitched sound pressure starts to drop below the high-pitched sound pressure when the fo resonance of the speaker unit used is suppressed , frequency C is the resonance frequency of the speaker unit 1 and the box internal space 201 when the speaker unit 1 is attached to the box 2, and frequency D is the resonance frequency of the box internal space 201 and the bass reflex duct 202, which is empirically set to about 1/2 of fo.

In Figure 2, (A) shows the frequency vs. sound pressure characteristics when the resonance of the speaker unit 1 is completely suppressed by the acoustic resistance material 3. Starting from frequency B, which is a parameter of the aperture of the speaker unit described later, the sound pressure decreases at 6 dB/oct toward lower frequencies, but at frequency A, the decrease stops due to the overlap of the peak of sound pressure (B) caused by the bass reflex resonance of the bass reflex duct 202 and the box internal space 201, centered at frequency D.

(C) shows the frequency vs. sound pressure characteristics when the acoustic resistance material 3 is omitted and the resonance of the speaker unit 1 is not suppressed. At frequencies above the resonance frequency C determined by the volume of the internal space 201 of the speaker unit 1 and the box 2, the sound pressure is almost constant, but below the frequency C, the sound pressure theoretically decreases at 12 dB/oct toward lower frequencies.

Here, the resonance of the speaker unit 1 is equal to the resonance of the resonance frequency C determined by the volume of the internal space 201 of the speaker unit 1 and the box 2. In other words, the lowest mechanical resonance frequency fo of the speaker unit 1 is the resonance frequency when the speaker unit 1 is not attached to a finite box, and when it is attached to a finite box, the resonance frequency rises above fo. This resonance frequency is frequency C in Figure 2. To explain this in yet another way, the acoustic resistance material 3 in Figure 1 suppresses the mechanical resonance of the speaker unit 1, but this resonance suppression is the suppression of resonance by the internal space 201 of the speaker unit 1 and the box 2.

(B) is the frequency vs. sound pressure characteristic when the mechanical resonance of the speaker unit 1 is not completely suppressed by the acoustic resistance material 3, and is between (A) and (C), but approaches either (A) or (C) depending on the degree of resonance suppression.

FIG. 3 is a block diagram of an electrical circuit device that drives the speaker system shown in FIG. 1, in which reference numeral 5 is a well-known sound source device such as a CD player, 6 is the equalizer device of the present invention, and 7 is a well-known power amplifier connected to the speaker system.

Although not shown in Figure 3, devices commonly called preamplifiers or control amplifiers are used between 5 and 7 to select and switch connections between sound source devices and recording devices, adjust volume, and adjust bass and treble levels (commonly known as tone control) in a different sense to the equalizer device of this invention. However, as these are not necessary for explaining this invention and are well known, for the sake of convenience, they are not shown in the figure and are not explained here.

Figure 4 shows an embodiment of the detailed circuit of the equalizer device 6 of the present invention in Figure 3, which is composed of analog circuits centered around an operational amplifier. In Figure 4, 601 is a variable resistor for level adjustment, 602 is an amplifier, 603 is an equalizer circuit using C and R, 604 is a buffer amplifier, and 605 is a BEF (band elimination filter) circuit that attenuates gain within a frequency band.

In the figure, the order of processing the frequency vs. gain characteristics of the input signal is the equalizer circuit 603, followed by the BEF circuit 605, but the order of other amplifier circuits, buffer amplifiers, etc. can be changed as necessary.

Furthermore, the basic circuits 602, 603, 604, and 605 are well known as operational amplifier and filter circuits, and we believe there is no need to explain their detailed operation again, but the frequency-gain characteristics of the CR equalizer circuit 603 are as shown in Figure 5, where gain below frequency A is greater than gain above frequency B, and the rate of change between frequencies A and B is 6 dB/oct. For convenience of explanation, frequencies A and B in Figure 5 correspond to frequencies A and B in Figure 2 and are in the same relationship, but in reality, some deviation is allowed, as described below.

Frequency A and frequency B are determined by R1, C1, and R2 in the circuit as frequency A = 1/(2π(R1+R2)C1) and frequency B = 1/(2πR2C1), but in the circuit of this embodiment, by switching C1 connected by SW1 to C11 to C13, both frequency A and frequency B can be switched in stages as a set, and frequency A can be adjusted with variable resistor r1 in R1 and frequency B can be adjusted with variable resistor r2 in R2. The reason for this will be explained later.

FIG. 6 is a diagram for explaining the correction effect of the equalizer circuit 603 on the frequency vs. sound pressure characteristics shown in FIG. 2. The sound pressure characteristics (a) to (d) shown in FIG. 2 become the sound pressure characteristics (a') to (d') by correcting the frequency vs. gain characteristics shown in FIG. 5.

When correction is made using the frequency-gain characteristic shown in FIG. 5, if the suppression of mechanical resonance by the acoustic resistance material 3 is not complete, that is, if the characteristic before correction is as shown in (b) or (c) in FIG. 2, then after correction in FIG. 6 , a peak in sound pressure will appear at frequency C as shown in (b') or (c') compared to the flat characteristic (a').

The BEF circuit 605 in Figure 4 is generally used in devices known as graphic equalizers. In a typical graphic equalizer, the circuit section within the dotted frame is arranged for multiple bands of different center frequencies, for example 30, 60, 120, 250, 500... Hz, allowing the gain at the center frequencies to be reduced or increased.

The equalizer device of the present invention requires only one band whose center frequency is C and whose gain can be set in a decreasing direction. For convenience of explanation, the center frequency C of the band is assumed to have the same relationship as the center frequency C in Fig. 2, but in practice, some deviation is allowed as described later. Also, the gain of the center frequency C can be adjusted as shown in Fig. 7 by using the variable resistor r3 in the figure.

In a normal graphic equalizer, R3 and r3 are only r3 (or the resistance value of R3 is zero), and the slider (variable terminal) position of r3 connected to C2 is the midpoint of the resistance, and the gain change at frequency C is zero (i.e., there is no increase or decrease in gain) . When the resistance value below the slider in the figure is zero, the gain at frequency C is minimum (gain attenuation is maximum), and when the resistance value above the slider in the figure is zero, the gain at frequency C is maximum (or the gain increase is maximum). However, in this invention, the resistance value of R3 may be set within the range from 0 (zero) to r3 . It is preferable to set R3=r3, and in that case, when the slider position is at the top end position of r3 in the figure, the gain change at frequency C is zero, and when it is at the bottom end position, the gain is minimum (gain attenuation is maximum). In this specification, the resistance value of R3=r3 is described.

The center frequency C is determined by C2, C3, R4, and R5 in the figure, as shown by the formula: center frequency C = 1/ ( 2π√(C2C3R4R5) ) , but the SW2 in the figure switches in stages between sets such as C21 and C31, C22 and C32, and C23 and C33. The reason for this will be explained later.

Frequency C can be adjusted just like frequency A and frequency B. In this case, it is possible to provide a variable resistor r5, but r5 is not a required component.

As mentioned above, FIG. 7 shows the frequency vs. gain characteristic of the BEF circuit 605. As mentioned above, the BEF band center frequency C is the same as frequency C in FIG. 2 and FIG. 6, and the bandwidth of the attenuation characteristic is appropriately set by the circuit constant so as to roughly correspond to frequencies D and B in FIG. 6.

The degree of gain attenuation at center frequency C is adjusted by r3 in FIG. 4, as described above . The amount of adjustment is at most about the difference in sound pressure between (C') and (A') at frequency C in FIG. 6, and at least zero , but normally the r3 slider is adjusted so that the degree of attenuation is halfway between the maximum and minimum. Hereinafter, the adjustment position of the slider at this time will be described as the central position of gain adjustment . In other words, it is assumed that the degree of attenuation can be adjusted with r3 from the normal middle to the minimum or maximum, and the circuit constants are set so that (C") in FIG. 7 has the inverse characteristic of the difference (C'-A') between (C') and (A') in FIG. 6, and (B") in FIG. 7 has the inverse characteristic of the difference (B'-A') between (B') and (A') in FIG. 6.

The characteristic (a'') in FIG. 7 represents zero gain attenuation, which is realized by setting R3=r3 in the circuit diagram of FIG. 4 and adjusting the slider for r3 to the uppermost position in FIG.

Now, for the equalizer device of the present invention configured as described above, a more detailed explanation is required regarding the relationship between the frequencies A, B, and C in the frequency vs. sound pressure characteristic of the speaker system in Fig. 2 and the switching of the switches SW1 and SW2 in Fig. 4. In fact, in the speaker system configured as in Fig. 1, the representative values of the frequencies A, B, and C in Fig. 2 are roughly determined by the diameter of the speaker used, and in the equalizer device, the representative values of the frequencies A, B, and C in Fig. 7 are used for each diameter, and when an adjustment range is provided, the representative values can be used as the central values .

To explain this in terms of frequency B, first, for a speaker with a nominal diameter of 10 cm, the frequency B is about 1000 Hz, and for a speaker with a diameter of 20 cm, it is about 500 Hz. This is because the equation Ka = 2πa/λ (a: radius of the disk, λ: wavelength) is generally known as the relational expression that expresses the radiation impedance of a disk, and it is said that when Ka is 1 or less, the effective radiation impedance decreases, and when the diaphragm vibrates with the same amplitude, the sound pressure decreases in proportion to the decrease in impedance. The frequency at which Ka becomes 1 is about 1000 Hz for a disk diameter of 10 cm (radius a ≒ 5 cm), and about 500 Hz for a diameter of 20 cm (radius a ≒ 10 cm). In reality, even if the nominal diameter of speaker units on the market is the same, the radius of the diaphragm varies slightly from product to product, and frequency B also varies slightly. However, in general, a representative value for frequency B can be determined uniquely based on the diameter of the speaker used, and if there is an adjustment range, the representative value can be used as the central value .

Next, as mentioned above, frequency A is considered to be in the range of 0.5 to 2 times the fo of the speaker unit, but for speaker units currently on the market, this fo is similar to frequency B , depending on the diameter, for example, about 80 Hz for a 10 cm speaker unit, about 50 Hz to 70 Hz for a 12 cm to 16 cm speaker unit, and about 40 Hz for a 20 cm speaker unit (this is intended only for products on the market that are fully designed for audio use and are often used for DIY ). Therefore, frequency A is determined as a representative value in the range of 0.5 to 2 times the average fo for each diameter of the speaker unit used, and if there is an adjustment range, the representative value can be used as the central value .

Furthermore, for frequency C, a representative value may be set according to the diameter of the speaker unit used, such as approximately 1.5 times fo for 10 cm and approximately twice for 20 cm.

This is because, as mentioned above in Patent Document 1, which was explained as the first prior art, the resonant frequency of the bass reflex duct of the bass reflex box, i.e., frequency D, is empirically set to approximately 1/2 of the f0 of the speaker unit being used. The resonant frequency of the bass reflex duct at this time is calculated from the cross-sectional area and length of the duct and the internal volume of the box, so that once the desired bass reflex resonance frequency is determined for each caliber of the speaker unit, the internal volume of the box will naturally be concentrated to a similar size by setting a practical duct cross-sectional area and length.

Furthermore, the speaker unit of the diameter being used must be able to be installed within the box with an adequate fit in terms of external dimensions ; these two constraints mean that the reasonable and practical internal volume of the box is concentrated within a certain range for each diameter of the speaker unit.

For example, when the speaker unit has a diameter of 10 cm and fo is 80 Hz, the design of the internal volume of the box is concentrated in the range of about 3L to 10L due to the above constraints. The resonance frequency C of the speaker unit and the internal space of the box in this case is calculated by a formula (not shown ) to be about 130Hz (about 1.6 times fo) at 3L, about 110Hz (about 1.4 times fo) at 5L, and about 100Hz (about 1.3 times fo) at 10L, but the magnification of the resonance frequency C with respect to fo is set to about 1.5 times (120Hz) as a unique representative value, and if there is an adjustment range, the representative value can be used as the central value .

Similarly, when the speaker unit has a diameter of 20 cm and fo is 40 Hz, the internal volume of the box is often designed to be in the range of about 15 L to 40 L for the same reasons as in the case of a 10 cm diameter. In this case, the resonance frequency C of the speaker unit and the internal space of the box is 100 Hz (about 2.5 times fo) at 15 L, 80 Hz (about twice fo) at 20 L, and 65 Hz (about 1.6 times fo) at 40 L, but the magnification of the resonance frequency C with respect to fo is set to approximately twice (80 Hz) as a unique representative value, and if there is an adjustment range, the representative value can be used as the central value .

This means that in the explanation of frequency C above, there is a slight frequency shift between the frequency C on the equalizer side using a representative value and the actual frequency C on the speaker system side, but if we examine the effect of this shift on the frequency vs. sound pressure characteristics, we find that when the ratio of frequency C on the speaker system side to frequency C on the equalizer device side, i.e. (frequency C on the speaker system side)/(frequency C on the equalizer device side), is 0.5 or 2, a sound pressure step of up to 6 dB occurs near frequency C in the frequency vs. sound pressure characteristics. This is because the sound pressure difference between the characteristics (c) and (a) in Figure 6 is 6 dB/oct except at the position of frequency C, and the sound pressure difference when the frequency changes by a factor of two is 6 dB.

However, among the above mentioned cases, the worst condition where (frequency C on the speaker system side)/(frequency C on the equalizer device side) is at its maximum is when the aperture is 20 cm and the box volume is 15 L, and the ratio is 100 Hz/80 Hz = 1.25. The effect on the sound pressure at that time is only 1/4 of 6 dB, that is, a sound pressure step of 1.5 dB appears near the frequency C. In the frequency vs. sound pressure characteristics of speaker systems actually on the market, it is common for there to be unevenness of ±6 dB to ± 10 dB within the reproducible frequency range, which is still within the normal range, so the sound pressure step of 1.5 dB is not so large. Therefore, it does not matter if there is a slight frequency difference between the actual frequency C on the speaker system side and the frequency C on the equalizer side determined by its representative value.

For the same reason, the equalizer may use a representative value for each diameter of the speaker unit used for frequencies A and B. In the explanation, the representative value is replaced with the center value because, in addition to switching between SW1 and SW2, frequencies A, B, and C also take into account the presence of adjustment means using r1, r2, and r5, and it is assumed that a center position is set in the adjustment range and that the frequency becomes the representative value when the adjustment is at that position. Of course, it goes without saying that the sound pressure difference caused by the difference between the representative value and the actual frequency, as explained above for frequency C, can be eliminated by adjusting the adjustment means.

From the above, it is possible to set unique representative values for frequencies A, B, and C using only the diameter of the speaker unit being used.

Therefore, in the equalizer device of the present invention, for example, if a change-over switch indicating the diameter of the speaker unit being used is provided in the equalizer device, and frequencies A, B, and C are switched to their representative or central values within the equalizer device depending on the change-over position of the switch, the user can simply select by turning the knob of the equalizer device's change-over SW to the position indicating the diameter of the speaker unit being used, and can set each frequency appropriately without knowing frequencies A, B, and C themselves, which should actually be set by calculation or experiment from the specifications of the speaker unit, box size, etc.

In the embodiment of the present invention, SW1 and SW2 correspond to changeover switches according to the diameter of the speaker unit. The circuit example in FIG. 4 shows only the circuit for one side of the L or R stereo CHs, and for just one side of the circuit, SW1 needs a 1-circuit, 3-contact switch, and SW2 needs a 2-circuit, 3-contact switch. Therefore, to switch and select both L and R CHs at once, SW1 needs a 2-circuit, 3-contact switch, and SW2 needs a 4-circuit, 3-contact switch. SW1 and SW2 may be independent, or may be combined into one with 6 circuits and 3 contacts. SW2 may also be provided separately on the C2 side and C3 side, and there is no problem as long as the switching position can be specified by the diameter of the speaker unit. The number of contacts can be increased or decreased depending on the type of diameter of the speaker unit to be applied.

Furthermore, the surface of the equalizer device indicates the SW switching position only by symbols or frequency notation, and even if the instruction manual or the like shows a table showing the correspondence between the diameter of the speaker unit and the SW switching position, i.e., the symbols and frequencies , frequency A, frequency B, and frequency C can be set and selected uniquely from the diameter information.

In the equalizer device of the present invention as described above, when the diameter of the speaker unit to be used is selected by switching SW1 and SW2, and frequencies A, B, and C are switched internally according to the diameter of the speaker unit, as described above, the frequency vs. sound pressure characteristic of the original speaker system shown in Figure 2 will be in the range (i') to (iii') between frequencies D and B in Figure 6 due to the frequency vs. gain characteristic of the equalizer circuit 603 shown in Figure 5.

Next, when the frequency vs. sound pressure characteristic between frequency D and frequency B in FIG. 6 is in the range of (i') to (iii'), the frequency vs. sound pressure characteristic is corrected to that in FIG. 8 by the frequency vs. gain characteristic of the BEF circuit 605 shown in FIG. 7, and the details of this will be described below.

If the acoustic resistance material 3 of the speaker system shown in Figure 1 does not completely suppress the mechanical resonance of the speaker unit 1, and the frequency vs. sound pressure characteristic shown in Figure 2 is as shown in (B), which is centered between (A) and (C), then by setting the slider r3 of the BEF circuit 605 to the center position for gain adjustment, the peak (B') in the sound pressure at frequency C in the frequency vs. sound pressure characteristic shown in Figure 6 can be flattened as shown in Figure 8 (A) by simply switching between SW1 and SW2.

If the mechanical resonance of the speaker unit 1 in the speaker system shown in Figure 1 is nearly completely suppressed by the acoustic resistance material 3, and the frequency vs. sound pressure characteristic shown in Figure 2 is close to (I), then simply switching SW1 and SW2 with the r3 slider of the BEF circuit 605 at the center of the gain adjustment will result in a sound pressure valley at frequency C (I') in the frequency vs. sound pressure characteristic shown in Figure 6, as in Figure 8 (b). In that case, by adjusting the r3 slider to adjust the frequency vs. gain characteristic in Figure 7 to the (I") side, it is possible to approach (a).

Conversely, if the acoustic resistance material 3 of the speaker system shown in Figure 1 is barely effective in suppressing the mechanical resonance of the speaker unit 1 and the frequency vs. sound pressure characteristic shown in Figure 2 is close to (C), then simply switching SW1 and SW2 with the r3 slider of the BEF circuit 605 at the center of the gain adjustment will result in a peak in sound pressure (C') at frequency C in the frequency vs. sound pressure characteristic shown in Figure 6, as shown in Figure 8 (c). In that case, adjusting r3 to adjust the frequency vs. gain characteristic in Figure 7 to the (C") side will make it possible to approach (a).

This adjustment can be done precisely using measuring equipment, but it may also be done appropriately so that the person making the adjustment feels comfortable, based solely on the auditory sense of the musical tones , regardless of the frequency characteristics .

The reason why such an adjustment is necessary is that in practical mechanical resonance suppression, the frequency vs. sound pressure characteristic has to be located between the characteristic curves (C) and (A) as shown in Figure 2 (B), and the degree of suppression varies depending on the speaker unit and acoustic resistance material used, as well as the compression state of the acoustic resistance material, and the position between (C) and (A) cannot be limited, so this adjustment is essential if you want to precisely flatten the frequency vs. sound pressure characteristic . If resonance could be completely suppressed, such an adjustment would not be necessary, but to completely suppress resonance, the flow of air going back and forth inside the acoustic resistance material must be suppressed to the extent that the vibration of the diaphragm of the speaker unit is stopped, and if that is the case, the vibration of the diaphragm due to the original driving electric signal will also be suppressed, and the essential sound generation will also be suppressed, so mechanical resonance suppression will naturally have its limits and will be incomplete.

The characteristic shown in Figure 2 (c) is the frequency vs. sound pressure characteristic when the speaker unit does not have any mechanical resonance suppression measures in place using acoustic resistance materials, and the sound pressure remains almost constant from frequency B up to the resonance frequency C, which is determined by the speaker unit and the internal spatial volume of the box, and decreases at a rate of 12 dB/oct from frequency C.

Therefore, if the gain at center frequency C of the BEF circuit 605 in Figure 4 described above is set to about 1/2 of the sound pressure difference between (C) and (A) at frequency C in Figure 2, and the remaining ±1/2 is allowed to be adjusted, it will be possible to accurately match the characteristics of (A) by adjusting the remaining ±1/2 in accordance with the degree of mechanical resonance suppression of the speaker system produced by implementing realistic mechanical resonance suppression in the speaker unit.

This suggests that even if a speaker system is constructed by excluding the mechanical resonance suppression means using acoustic resistance material 3 from the constituent elements of Patent Document 1 described in the first prior art, it is possible to construct a small-sized acoustic device with the same bass reproduction capabilities as the speaker system of that patent in which mechanical resonance is suppressed by gain adjustment at the center frequency C of the BEF circuit 605.

That is, as explained in FIG. 2, by setting the bass reflex resonance frequency of the bass reflex box to approximately 1/2 of the f0 of the speaker unit, and then adjusting frequency A to approximately 0.5 to 2 times the f0 of the speaker unit being used as a basic value, it is possible to obtain a small-sized acoustic device that can reproduce a frequency of approximately 1/2 of the f0 of the speaker unit being used by using the equalizer device of the present invention , even without mechanical resonance suppression by the acoustic resistance material 3.

However, in this case, the diaphragm and the internal space of the box are connected without any acoustic resistance material. Therefore, when the box is constructed as a parallelepiped, resonance that occurs according to the distance between the parallel walls inside the box is transmitted directly to the diaphragm, and the resonance sound propagates from the diaphragm to the external space of the speaker system. In other words, it is impossible to eliminate the disadvantage that the resonance sound, known as box resonance, is easily emitted outside the box.

The above-mentioned adjustment of frequency A and frequency B may be performed by using a measuring device to adjust the frequency to an optimum point, or by simply adjusting the frequency to a position that the user finds most comfortable to hear . The same applies when an adjustment means is provided for frequency C.

The adjustment of frequency A and frequency B can be set so that the adjustment range continuously covers the frequencies at adjacent switching positions by SW1. For example, in the adjustment of frequency A, when the switching by SW1 indicates 10 cm, 13 cm, and 20 cm in diameter, and frequency A is set to 80 Hz at the 10 cm diameter position and 60 Hz at the 13 cm position as the center value, if the adjustment at the 10 cm position is configured to be approximately 10 Hz on the negative frequency side and the adjustment at the 13 cm position is configured to be approximately 10 Hz on the positive frequency side, frequency A can be adjusted almost continuously between the 10 cm and 13 cm diameters. The same applies between 13 cm and 20 cm.

Furthermore, it is very preferable to configure the frequency A so that it can be adjusted from 1/2 to 2 times the central value of fo. This is because in Patent Document 1, the frequency A is set to 0.5 to 2 times the fo of the speaker unit used, so if the central value of the adjustment is set to 1 time of fo and the adjustment range can be adjusted from 0.5 to 1 time on the negative side and 1 to 2 times on the positive side from the central value and the central value is always set, it is possible to first set the frequency A to fo of the speaker unit used by simply switching SW1, and then adjust the frequency A to a maximum of 0.5 times on the negative side and a maximum of 2 times on the positive side for each aperture , which is optimal as the equalizer device of Patent Document 1.

As mentioned above, the resonant frequency D of the bass reflex duct and the space inside the box should basically be set to about half the fo of the speaker unit being used, but for speaker units with a diameter of about 5 cm, fo is about 200 Hz. From experience with prototypes of such speaker units, it has been shown that the frequency vs. sound pressure characteristics can be successfully flattened even when the resonant frequency D is set to 70 Hz and frequency A is adjusted to around 130 Hz.

In this experiment, frequency D is 0.35 times fo of the speaker unit used, and frequency A at this time is 0.65 times fo, and this frequency A can be adjusted within the range of 0.5 to 1 times fo.

In addition, when using a speaker unit with a diameter of 10 cm and fo of 80 Hz, it has been found that the frequency vs. sound pressure characteristic can be successfully flattened by adjusting frequency D to 40 Hz and frequency A to the vicinity of 160 Hz. In this case, frequency D is 1/2 of fo of the speaker unit, and frequency A at that time is twice fo, and this frequency A can be adjusted on the plus side of fo, that is, within the range of 1 to 2 times. In this way, adjustment of frequency A can be used.

On the other hand, the adjustment range of frequency B does not need to be as wide as that of frequency A, because, as mentioned above, a unique value for frequency B is calculated from the diameter of the speaker unit's diaphragm. However, it is considered sufficient if the adjustment can be made up to 0.5 to 1 times on the negative side and 1 to 1.5 times on the positive side with respect to the center value calculated for each diameter.

This adjustment function, to repeat what has already been mentioned, has the advantage that if the adjustment positions of r1 and r2 for frequency A and frequency B and r5 for frequency C are first set to the center point of the adjustment range as the representative value, and r3 is set to the center position of the gain adjustment, then even a person lacking specialized knowledge or measurement techniques can generally set frequency A, frequency B, and frequency C appropriately to flatten and improve the frequency-sound pressure characteristics by simply switching SW1 and SW2 according to the caliber information. In addition, if the relationship between the specifications of the speaker unit used, such as the caliber, degree of mechanical resonance suppression, box volume, and duct resonance frequency, and the adjustments of frequency A, frequency B, and frequency C is described in the device's instruction manual, a person with specialized knowledge or measurement techniques will be able to adjust frequency A, frequency B, and frequency C more precisely in relation to the frequency-sound pressure characteristics, and further, regardless of the presence or absence of knowledge or technique, or the flattening and improvement of the frequency-sound pressure characteristics, the adjuster can make adjustments that they feel are more preferable based solely on their hearing.

Figure 9 shows an embodiment of a circuit for an equalizer device different from that shown in Figure 4. The difference between Figure 9 and Figure 4 is that the switching between frequency A and frequency B of the equalizer circuit using C and R is performed by the values of R1 and R2, not by switching the capacitance of C1. It is also possible to simply use the entire R1 and the entire R2 as variable resistors to change the frequency continuously, or to switch in stages.

When R1 and R2 are switched continuously, the change in frequency A and frequency B does not result in a point-by-point change, but if a symbol related to the diameter or diameter of the speaker unit is displayed at the position indicated by the variable resistor knob at the position where the resistance of R1 and R2 becomes the required resistance value, it can be treated like a switching switch.

At this time, R1 and R2 change continuously, and therefore frequency A and frequency B also change continuously by adjusting R1 and R2. However, frequency A = 1/(2π(R1 + R2)C1) and frequency B = 1/(2πR2C1), so when C1 is a fixed value, frequency A is determined by the value of (R1 + R2), and frequency B is determined by the value of R2.

Therefore, first, the knob position of R2 is indicated at the resistance value where frequency B is the representative value, then the resistance value when the knob is set to the display position of each caliber is substituted for R2 in (R1+R2) where frequency A of each caliber is the representative value, and the remaining knob position R1 is indicated at the resistance value required to set the representative value of each caliber by indicating the caliber or a symbol related to the caliber, so that the representative values of frequency A and frequency B can be set by adjusting R1 and R2. Moreover, since the relationship between frequency A and frequency B is frequency A<<frequency B, the relationship between R1 and R2 is R1>>R2, and frequency A mainly depends on the value of R1, so the knob position of R2 does not need to strictly match the display position of the caliber.

As another method, as shown in FIG. 10, a set of C1, C2 and C3 (C2 & C3) can be configured as plug-in parts, and multiple types of these plug-in parts can be provided for each diameter of the speaker unit. If the plug-in parts can be interchangeably connected on the equalizer device side, the user can select the plug-in part according to the diameter of the speaker unit and attach and connect it to the equalizer device, thereby enabling frequencies A, B and C to be set appropriately and uniquely .

As yet another method, instead of switching or selecting C1, C2, and C3, the frequencies A, B, and C of the equalizer device may be fixed to representative values uniquely determined from a single type of diameter , and the equalizer device itself may be configured and provided according to the diameter of the speaker unit, for example, for a 10 cm diameter, for a 20 cm diameter, etc. This method also allows the frequencies A, B, and C to be set uniquely according to the diameter of the speaker unit.

Next, we will explain the improvement in frequency-to-sound pressure characteristics using the equalizer device of the present invention for a typical bass reflex speaker system in which a speaker unit that does not suppress mechanical resonance is combined with a bass reflex box, as explained in the second prior art, and a typical closed speaker system in which a speaker unit that does not suppress mechanical resonance is combined with a closed box.

FIG. 11 shows the structure of a typical bass reflex speaker system, as explained in the second prior art, and FIG. 12 is a diagram illustrating the frequency vs. sound pressure characteristics of an example of a poorly designed speaker system.

This failure example occurs when the resonant frequency (frequency D') of the bass reflex duct 202' is set too low compared to the resonant frequency (frequency C') of the speaker unit 1' and bass reflex box 2' in Figure 11 in a typical bass reflex box design, resulting in a valley in sound pressure between frequency C' and frequency D' in the composite sound pressure characteristic (G) of the sound pressure characteristic (E) that does not take the bass reflex duct into account and the sound pressure characteristic (F) of the bass reflex duct in Figure 12.

In such a case, when using the equalizer device of the present invention to improve the frequency vs. sound pressure characteristics, first connect the equalizer device of the present invention to the position shown in Figure 3, then set SW1 and SW2 to the aperture of the speaker unit. At that time, leave frequency A at the center value without adjustment. Next, adjust the gain adjustment of frequency C to minimum gain (maximum gain reduction). After that, adjust the overall sound pressure balance by listening to it or using a measuring device while adjusting the degree of bass reflex resonance by filling the bass reflex duct with an acoustic resistance material such as glass wool, and adjust frequency A.

This adjustment will be described in detail with reference to Figures 12 to 16. In Figure 12, the sound pressure characteristic (E) is such that, due to the resonance between the speaker unit and the space inside the box, the sound pressure at the center frequency C' of the resonance is raised to the same level as the sound pressure at frequency B', and the sound pressure drops sharply at frequencies lower than the center frequency C'. It is generally said that the drop in sound pressure at frequencies lower than frequency C' occurs at 12 dB/oct.

Therefore, when the frequency interval between frequency C' and frequency D' is wide, the sound pressures in the overlapping parts of sound pressure characteristic (E) and sound pressure characteristic (F) are both low, so the combined sound pressure characteristic has a valley in sound pressure between frequency C' and frequency D' as shown in (F).

When the equalizer device of the present invention is used, the frequency vs. sound pressure characteristics of the speaker system in FIG. 12 are first corrected as shown in FIG. 13 by the frequency vs. gain characteristics shown in FIG. 5 of the equalizer circuit 603 in FIG. 4 inside the device.

In this case, as mentioned above, frequency B' in Figure 12 depends almost entirely on the diameter of the speaker unit, so if the diameter is the same, frequency B in Figure 5 will also be the same, and the equalizer device of the present invention can be applied as is to a general bass reflex speaker system.

Next, the frequency vs. sound pressure characteristic of Fig. 13 is corrected as shown in Fig. 14 by the frequency vs. gain characteristic of the BEF circuit 605 of Fig. 4 shown in Fig. 7. At this time, by adjusting the gain at center frequency C by r3 of the BEF circuit 605 to the minimum gain (maximum gain reduction), the peak of sound pressure at frequency C' in Fig. 14 can be flattened for the same reasons as those explained in Figs. 6 to 8.

As shown in Fig. 14, the frequency C of the equalizer device does not strictly match the frequency C' of the general bass reflex speaker system to be improved, as mentioned above . This is because the fo of the speaker unit used varies slightly depending on the product, and because there is a difference in the setting of the internal space volume of the box due to the difference in the concept of the configuration between a general bass reflex box and the bass reflex box shown in Patent Document 1 described in the first prior art .

The example in Figure 14 explains the case where frequency C is slightly higher than frequency C', but generally, the difference in the resonant frequency between the speaker unit and the volume of the box's internal space due to differences in the volume of the box's internal space is only a few tens of percent, as mentioned above, and the resulting sound pressure difference between frequencies C and C' is only a few dB, so the mismatch between frequencies C' and C has almost no effect on the frequency vs. sound pressure characteristics, and the sound pressure peak at center frequency C' can be largely corrected by the BEF circuit at center frequency C.

In FIG. 14, the peak sound pressure of the bass reflex resonance sound pressure (F') at center frequency D' due to the bass reflex duct 202' and the box internal space 201' is expected to be higher than the corrected sound pressure at frequency C' in FIG. 14 due to the correction by the equalizer circuit 603 and BEF circuit 605 in FIG. 4.

Therefore, if the sound pressure of the bass reflex resonance becomes higher than the corrected sound pressure at frequency C' as in Figure 14, it is necessary to lower this peak of sound pressure appropriately. Figure 15 shows how this is done, by adjusting the sound pressure peak (F') at resonance frequency D' in Figure 14 to a weaker degree of resonance by filling the bass reflex duct 202' in Figure 11 with an acoustically resistant material such as glass wool, and also adjusting frequency A to lower the height of the peak as shown (F"). This adjustment can also be done with a measuring device, or simply by adjusting appropriately based on hearing.

As explained above in Figures 11 to 15, even in the case where there is a valley in sound pressure between frequency D' and frequency C' in a general bass reflex speaker system as in Figure 12, it is relatively easy to improve the situation by using the equalizer device of the present invention to eliminate the valley in sound pressure as in Figure 15. If the equalizer of the present invention is not used, it would be necessary to change the speaker unit, redesign the box to lower the resonant frequency C', or shorten the duct length of the bass reflex duct to raise the resonant frequency D', or in any case, to redo the mechanical structure, which would require considerable effort.

This is the effect of flattening out the mechanical resonance caused by the speaker unit with center frequency C' shown in Figure 12 and the space inside the box using the electrical correction means BEF circuit 605 and equalizer circuit 603 shown in Figure 4, and reconstructing the characteristics, so that the mechanical structure can be left as is and only the characteristics can be improved.

Although the adjustment of frequency B and frequency C has not been described in the explanation of FIG. 11 to FIG. 15, it goes without saying that the correction can be made more precise and appropriate by making appropriate adjustments according to the situation.

From the above, although it requires the time-consuming adjustment of the degree of resonance of the bass reflex duct at frequency D' using an acoustic resistive material, or the adjustment of frequency A, in a conventional bass reflex speaker system, if the parameter design fails, it is possible to improve characteristics using less labor-intensive electrical means without having to make labor-intensive physical changes to the box volume or the cross-sectional area or length of the duct.In addition, improvements can be easily made using the equalizer device of the present invention, which can uniquely set frequencies A, B, and C from the diameter information of the speaker unit.

To put it the other way around, in a conventional general bass-reflex speaker system, even if the box internal volume is intentionally set smaller than normal, the equalizer device of the present invention can obtain the same low-frequency reproduction capability as with the proper setting, and in a general bass-reflex speaker system with an internal volume properly set, the bass-reflex duct of the speaker system can be modified to be longer to lower the bass-reflex resonance frequency D', intentionally creating a valley in the frequency vs. sound pressure characteristics as shown in Figure 12, and the equalizer device of the present invention can be applied there to expand the low-frequency reproduction frequency of the general bass-reflex speaker system at hand. This is similar to the case in the first prior art patent where the speaker unit was not provided with a mechanical resonance suppression means using an acoustic resistance material.

FIG. 16 is a structural diagram of the speaker system using a sealed box explained in the second prior art, and FIG. 17 is a diagram explaining its frequency-sound pressure characteristics.

In Figure 17, frequency C" is the resonant frequency of speaker unit 1" and box internal volume 201", and is theoretically higher than fo of speaker unit 1". However, if internal volume 201" is appropriately selected for fo and Q of speaker unit 1", sound pressure can be flattened at frequencies above frequency C" as shown in Figure 17.

When the equalizer device of the present invention is applied to such a closed speaker system, and the switching positions of SW1 and SW2 are adjusted to match the diameter of speaker unit 1", first, the correction characteristics of the equalizer circuit 603 shown in Figure 5 will cause a peak in sound pressure at frequency C" as shown in Figure 18 (H'), and then, by using the correction characteristics of the BEF circuit 605 shown in Figure 7, the characteristics can be improved to be flat up to frequency A as shown in Figure 19 (H").

As mentioned above, in Figures 18 and 19, there is no problem if frequency C" is replaced with frequency C and frequency B" is replaced with frequency B, so here we will explain it as C" ≒ C and B" = B.

In this case, if frequency A is set to the same as or lower than the fo frequency of speaker unit 1", the limit of the bass frequency that can be reproduced at the same sound pressure as the mid-high tones can be improved from frequency C", which is higher than the fo frequency of speaker unit 1", to frequency A, which is lower than the fo frequency. For example, when a speaker unit with a diameter of 10 cm and fo of 80 Hz is installed in a 5 L sealed box, frequency C" will be around 120 Hz, but this can be improved to below 80 Hz.

Next, we will explain an example where the characteristics of a speaker system using the same sealed speaker box were improved by using the equalizer device of the present invention when the design was unsuccessful. An example of the frequency vs. sound pressure characteristics in this case is shown in Figure 20. In this example, with a typical sealed box, the specifications of speaker 1" and the box internal volume 201" were unreasonably selected, resulting in a bass frequency C" that was higher than the desired frequency and a peak in sound pressure centered around frequency C".

This type of situation occurs when the box size is designed to be smaller than the fo, aperture, diaphragm mass, and Q of the speaker unit being used, and is particularly likely to occur with speaker units that have a light diaphragm mass and a large Q.

In such a case, to improve the frequency vs. sound pressure characteristics using the equalizer device of the present invention, the negative (gain decreasing) adjustment range of the gain adjustment at frequency C of the BEF circuit 604 in Figure 4 must be set wider than described above. This requires setting the circuit constants to increase the Q of the BEF resonant circuit accordingly, but this explanation is based on the assumption that the constants of the other CR elements, including C2, C3, R4 and R5 of the BEF circuit 605, have already been set in this way.

Connect such an equalizer device to the position shown in Figure 3, and first set SW1 and SW2 to the aperture of the speaker unit. At that time, leave the adjustment of each frequency at the center position . Next, adjust the gain adjustment of frequency C to the maximum on the negative side.

This will be described in detail with reference to Figures 20 to 22, but ultimately, it is the same as the case of Figures 17 to 19 except that the gain adjustment range at frequency C of the BEF circuit of the equalizer device is expanded to the negative side.

In Figure 20, the sound pressure characteristic (H) is such that the sound pressure at center frequency C'' is raised to a level higher than the sound pressure at frequency B'' due to resonance between speaker unit 1'' and the box internal space 201'', and the sound pressure drops sharply at frequencies lower than center frequency C''.

When the equalizer device of the present invention is used in this case, the frequency vs. sound pressure characteristics become as shown in Figure 21 due to the correction characteristics shown in Figure 5 of the equalizer circuit 603 in Figure 4 inside the device.

Then, the frequency vs. sound pressure characteristic of FIG. 21 is corrected as shown in FIG. 22 by the correction characteristic of the BEF circuit 605 shown in FIG. 7.

In other words, by using the equalizer device of this invention, not only can the bass frequencies that can be reproduced by a closed speaker system be expanded downward, but it can also improve the peak in sound pressure in the bass range that occurs when the speaker unit and box internal volume are not properly set.

In the above, the settings of the center values of frequency A, frequency B, and frequency C are merely examples, and if the settings and switching adjustment operations can be performed based only on the diameter information of the applicable speaker, it will be considered to be within the scope of the rights.

In addition, while the description of the embodiment shows the equalizer device being configured with an analog circuit, the scope of the patent also includes a digital filter configured using a computer system, whereby the settings for frequency A, frequency B, and frequency C can be made using the aperture information of the applicable speaker unit.

To summarize the above explanation, the acoustic equalizer device of the present invention is equipped with means for setting, selecting, or adjusting frequencies A, B, and C of the equalizer device to representative values that are uniquely based on the diameter of the speaker unit used. Therefore, even if there is a slight deviation between frequencies A, B, and C of the equalizer device and the frequencies A, B, and C strictly required for a speaker system that uses the speaker unit, the user can easily set frequencies A, B, and C by setting, selecting, or adjusting the equalizer device based only on the diameter information of the speaker unit used, without knowing the required frequencies A, B, and C, and it becomes possible to flatten and improve the frequency-to-sound pressure characteristics in the low-frequency range of the speaker system.

The setting, selection, or adjustment operation of the diameter of the speaker unit of frequency A, frequency B, and frequency C can be performed by a collective or individual switching SW or by replacing parts by plugging in, or by a continuous adjustment operation means with diameters or symbols.It is also possible to switch to an equalizer device at all, and to select the equalizer device itself by making the diameter of the speaker unit and the equalizer device correspond one-to-one without any means for replacement or adjustment operation.

In this case, even if the equalizer device has fixed frequencies A, B, and C as representative values without any adjustment means, it is possible to generally flatten and improve the frequency vs. sound pressure characteristics in the low range as described above, but if an adjustment range is to be provided, an adjustment means with a clearly defined representative value position (center value) can be provided. If such an adjustment means is provided, the adjustment means first selects the speaker diameter at the center value position , and then the adjustment means is adjusted by measurement , making it possible to flatten and improve the frequency vs. sound pressure characteristics more precisely , and the adjustment can be made so that the adjuster feels that the musical sound is more preferable when listening to it.

The value of the adjustment means is great at frequency A. This is because in Patent Document 1, there is a range of appropriate magnifications of frequency A to fo depending on the diameter of the speaker unit used, fo, the frequency of the bass reflex resonance, and the peak of the sound pressure, and while Patent Document 1 sets frequency A to 0.5 to 2 times fo, the present patent does not limit it to the range of Patent Document 1, nor does it fix the central value (reference value) to 1 time fo.

The attenuation of the BEF circuit at frequency C can be fixed at a constant value if the target speaker system is restricted to a certain extent. For example, according to Patent Document 1, if the use is limited to a speaker system in which mechanical resonance is suppressed by acoustic resistance in the speaker unit, the attenuation can be fixed as (B") between (A") and (C") in Figure 7, or (C") can be moved closer to (A") or (C") depending on the expected degree of mechanical resonance suppression. If the use is limited to a conventional general bass reflex speaker system, the attenuation can be fixed at (C") in Figure 7.

However, if there are no restrictions on the speaker system to be used, it is possible to make the attenuation amount of the BEF circuit adjustable. In this case, the adjustment amount can be set to a central value roughly halfway between (A") and (C"), as in (B") in Figure 7, and can be adjusted within the range from (A") to (C"). Of course, there is no restriction on this central value and adjustment range.

This provides an equalizer device for use in industries that provide audio equipment when a speaker system is made by hand, or when only the speaker system of the audio equipment shown in Patent Document 1 is to be commercialized.

1, 1', 1"...Speaker unit 101...Diaphragm of speaker unit 1 2, 2', 2"...Box 201, 201', 201"...Inner space 202 of box 2...Bass reflex duct 3...Acoustic resistive material 301...Surface of acoustic resistive material 3 arranged in inner space 201 4...Partition wall 5...Sound source (signal generation) device 6...Equalizer device of the present invention 601...Signal level adjustment 602...Amplification circuit 603...Equalizer (CR filter) circuit 604...Buffer amplifier 605...BEF circuit

Claims (2)

An acoustic equalizer device that controls the frequency-to-sound pressure characteristics of a speaker unit in the low-frequency range, characterized in that, for frequencies A and B where A<B, the gain at frequency A is greater than the gain at frequencies B or higher, the gain between frequencies A and B varies at 6 dB/oct, and the frequency-to-gain characteristics of a BEF (band elimination filter) are centered on frequency C where C<B, and the device is equipped with means for uniquely setting, selecting, or adjusting frequencies A, B, and C based on the aperture of the target speaker unit. 2. The acoustic equalizer device according to claim 1 , further comprising a means for adjusting a gain at frequency C of the BEF centered on said frequency C.