JPH01165300A - Method for measuring characteristic of loudspeaker system - Google Patents

Abstract

PURPOSE:To obtain the acoustic characteristic of a loudspeaker system with high accuracy by calculating the acoustic characteristic of the system by using three kinds of the acoustic characteristics. CONSTITUTION:The acoustic characteristic found by integrating the surface acoustic pressures on a virtual spherical surface, with a loudspeaker to be measured at the center, in the operating state of an enclosed type loudspeaker system while the passive acoustic output section of the loudspeaker system to be measured is closed tight and the passive operation is checked is represented by A1 and the acoustic characteristic measured in a state where a microphone is brought nearer to the loudspeaker to be measured while the enclosed type loudspeaker system is an operating state is represented by A2. Moreover, the acoustic characteristic found by integrating the acoustic pressures on a virtual spherical surface, with the loudspeaker system to be measured at the center, in a state where the passive acoustic output section of the loudspeaker system to be measured is in an operating state is represented by A3. The acoustic characteristic of the loudspeaker system is calculated by subtracting a correcting characteristic S which is obtained by subtracting the characteristic A2 from the characteristic A1, from the acoustic characteristic A3. Therefor, the acoustic characteristic, especially in a low frequency range, can be measured with high accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for measuring the acoustic characteristics of a speaker system having a passive acoustic output section, and particularly to a method for measuring low frequencies with high accuracy.

[Prior art]

Conventionally, the acoustic characteristics of a system beaker system have generally been measured in an anechoic chamber with a configuration as shown in FIG.

As shown in the figure, the speaker system 2 to be subjected to measurement is installed inside an anechoic chamber 81, and a microphone 82 is installed in the anechoic chamber 81 to face the speaker system 2. Then, the output signal of the sine wave oscillator 83 is amplified by a signal amplifier 84 to drive the speaker system 2, and the acoustic output of the speaker system is detected by the microphone 82, amplified by the microphone amplifier 85, and recorded on a recorder 86. .

The characteristics measured in the anechoic chamber 81 are shown in FIG. 991, and compared with the characteristics 92 obtained in a completely free sound field (an environment where the sound pressure level decreases by 6 dB when the distance from the sound source is doubled). Errors occur in the low-frequency characteristics.

This is because the free sound field of the anechoic chamber 81 is no longer established at low frequencies.

If you want to establish a free sound field at 20Hzt, the − side should be 2.
This requires an anechoic chamber with a large space with a length of 0 m or more, making the equipment very expensive.

Regarding low-frequency measurements, there are two ways to obtain free-field characteristics without using an anechoic chamber: (1) Measuring by placing a microphone close to the speaker system (2) Determining f of the impedance characteristics of the speaker system
o and Q. Method (8) Using another speaker system, place it close to the speaker system under test, alternately use one speaker system as a microphone to measure the acoustic output of the other speaker system, and calculate using the reciprocity theorem. There is.

[Problem that the invention seeks to solve]

However, when the speaker system under test has a closed lid and the low-frequency sound output section is located solely on the buckle surface of the cabinet, the above-mentioned low-frequency measurement method uses a free sound field as shown in Figure 10 101 and 102. A characteristic similar to characteristic 103 can be obtained, but as shown in FIG. 11, for example, a bass reflex type speaker system 2 having a structure in which the opening 111 of the boat is installed in the rear plate causes a large error.

The method described above is to measure by placing the microphones close together (
This is because the calculation method (3), which uses the equation 1 and the reciprocity theorem, does not allow measurement including the acoustic output of the boat of the bass reflex type system. In addition, method (2) of calculating from impedance characteristics requires complicated calculations of a multiple resonance system including phase characteristics, and furthermore, the calibration of the sound level must be calculated using another method, which is troublesome.

The present invention enables low-frequency free sound field of a speaker system having a passive acoustic output section such as a bass reflex, a passive radiator, a backload horn, etc., without using expensive equipment such as an anechoic chamber, for example, in a boat fishing room. The present invention provides a method for measuring characteristics with high precision.

[Means for solving problems]

The present invention seals the passive acoustic output section of a speaker system under test having a passive acoustic output section to prevent passive operation, and when the closed-lid speaker system is in operation, a virtual spherical surface centered on the speaker system is formed. Acoustic characteristic A obtained by integrating surface sound pressure; Acoustic characteristic A2 measured by bringing a microphone close to the speaker in the operating state of the sealed lid speaker system; and a passive acoustic output section of the speaker system to be measured. is in an operating state, and the acoustic characteristic A3 obtained by integrating the surface sound pressure on a virtual spherical surface centered on the speaker system is used to subtract the acoustic characteristic human from the acoustic characteristic human to obtain a correction characteristic. S and
The free sound field characteristics of the system speaker system are measured by subtracting the correction characteristic S from the acoustic characteristic A to calculate the acoustic characteristics of the speaker system under test having a passive acoustic output section.

[Effect]

In other words, in the low range with long wavelengths in the free field, the cabinet of the speaker system does not affect the characteristics due to diffraction effects, so it is non-directional, and the distance of radius R (m) from the center of the speaker system is The acoustic characteristics obtained by integrating the surface sound pressure on a virtual spherical surface as shown in Fig. 2 b-, and the position at a distance R [m] facing the center of the acoustic output radiation surface of the speaker system, Fig. 2 a The acoustic characteristics measured by installing a microphone in the same area show the same characteristics. Furthermore, the closed-lid speaker system that has a single low-frequency sound output in a general room described above can be measured using method (1) in which a microphone is placed close to the speaker system or f of the speaker system. Similar characteristics are also exhibited by method (2), which is calculated from +Q, and method (3), which uses the reciprocity theorem.

On the other hand, the sound was measured by installing a microphone in a position facing the sound output radiation surface of a general speaker system! Temporality is a major characteristic of peaks and troughs, which receive a large amount of interference between reflected waves from indoor walls and direct waves.

Furthermore, slight changes in the installation position of the microphone or speaker system will cause the interfering frequencies to change, resulting in poor reproducibility. Since the effects of the above-mentioned interference are averaged out, the acoustic characteristics are smoothed and have high reproducibility.

Utilizing these properties, the free field acoustic characteristics of a speaker system having a back-up acoustic output section can be obtained in a general room. I will explain based on this. 1st
The figure is a basic measurement system diagram showing the same embodiment. In the same figure, a speaker system 2 to be measured is installed using a speaker stand 3 approximately 1 m above the floor of the room to be measured approximately in the middle of a room 1 to be measured whose wall surface has a length of 2.5 m or more on one side. .

The microphone 4a is located at a distance rm close to a position opposite to the center of the diaphragm surface of the bass speaker of the speaker system 2.
to be installed. The distance r will be described in detail later.

The microphones 4b to 4e form a microphone array, and in order to integrate the sound pressure of a virtual hemisphere centered on the speaker system 2, the microphone positions defined in JI8Z8732 are set at a radius so that the microphone position can be measured at the position shown in Fig. 2b-. 1m
The microphone array is installed on the vertical circumference of the microphone, and the microphone array is rotatably moved in the horizontal direction to obtain acoustic characteristics at a predetermined position.

After the output of the sine wave oscillator 5 is amplified to a predetermined signal level by the amplifier 6, it is applied to the speaker system 2 under test. The sound output is detected by the microphones 4a to 4e, and displayed as a sound pressure level by the sound measuring device 8 via the changeover switch 7.

A measurement example of a bass reflex type speaker system 2 having the above configuration and having a bass reflex boat opening 111 in the rear plate shown in FIG. 11 will be explained. (The opening 111 of the slave port is sealed with a wooden board to put the sealed lid speaker system into operation. Then, the sine wave oscillator 5 transmits a continuous sine wave signal of a specific frequency in the desired frequency band to the amplifier 6. to the speaker system 2 via the microphone 4a, and detecting the acoustic output of the speaker system by the microphone 4a;
The sound pressure level L a [dB] is obtained by the sound measuring device 8 whose sound pressure level has been calibrated. The distance r between the speaker system 2 and the microphone 4a at this time was 10 crn. Distance r 10 (20Hz to 200Hz near m)
As shown in Figure 3, an inverse square characteristic indicating a free sound field is established up to the vicinity, and the measurement can be performed with almost no influence from the location where the measurement is being made, so the following equation can be used to calculate It can be converted into sound pressure level LAI (dB).

FIG. 441 shows the characteristics obtained by calculating the sound pressure level L, 1 of each frequency in the frequency range to be measured.

Next, using the microphone arrays 4b to 4e, JIf!
The sound pressure level at each measurement position in FIG. 2b designated by 3Z8732 is measured, and the integrated value LA2 (dB:l) of the surface sound pressure of the virtual hemisphere is calculated using the following equation.

Here, L and ti are the sound pressure levels at each measurement position,
N represents the number of measurement points.

The calculated sound pressure level LA includes the sound pressure level IJI at a microphone distance of 1 m and the influence of the measured indoor environment. FIG. 42 shows the characteristics obtained by calculating the sound pressure level LA2 of each frequency in the frequency range to be measured.

Next, remove the wooden block of the sealed bass reflex opening 111 of the speaker system 2 to be measured, set it to the desired operating state, and measure the sound pressure level in the same environment and under the same measurement conditions in which the sound pressure levels L and 2 were measured. The integral value of the surface sound pressure of the virtual hemispherical surface "A3" is calculated using the following equation.

Here, I' A 3 i represents the sound pressure level at each measurement position.

This sound pressure level L A II is equal to the sound pressure level L,!
This includes the influence of the surrounding measurement environment and the desired sound pressure level LM. FIG. 5 shows the characteristics obtained by calculating the sound pressure level L A 3 of each frequency in the frequency range to be measured.

Then, the sound pressure level that has changed from the free sound field depending on the environment in which it was measured is corrected and calculated using the following equation.

L, = L Todoroki 2 Li (ctB
Figure 6 shows the characteristics obtained by calculating the correction amount for each frequency in the frequency range to be measured.

Sound pressure level L obtained from correction scale and sound pressure level LA3
, 4 are calculated using the following formula.

LA4=L, 3-L, CdB:] FIG. 77 shows the characteristics obtained by calculating the sound pressure level LA4 of each frequency in the frequency range to be measured. The characteristic 71 is the same as the characteristic 72 measured in a free sound field. Note that the present invention may digitize the above embodiments and perform measurement, calculation, and control using a high-speed 7-lier converter and a computer. In that case, an impulse or random noise is appropriate as the signal source, and if you use a method to calculate the frequency response from the transfer function between the applied signal of the speaker system and the detected signal of the microphone, you can use an unsteady continuous signal. is also possible.

Another method for obtaining the sound pressure level LcL (dB) is to obtain f of the impedance characteristic of the speaker system.

The method (2) of calculating from ,Q, or the method of calculating using the reciprocity theorem (3) may be used. In addition, in the case of method (1), in which the microphone is placed close to the speaker system for measurement, the distance between the diaphragm and the microphone may be set close enough to avoid contact due to the amplitude of the diaphragm, or the inverse square characteristic can be established. In addition, the microphone distance R when measuring the surface sound pressure on the virtual hemispherical surface may be set within the range of distance R.
(m) may be increased depending on the size of the speaker system to be measured and the size of the room to be measured.

As described above, the present invention can be implemented with various modifications without departing from the spirit thereof.

〔Effect of the invention〕

According to the invention, without using an anechoic chamber, for example - in a membrane chamber,
This is extremely useful in practice since it is possible to obtain acoustic characteristics with high accuracy even in a speaker system having one or a plurality of passive acoustic output parts in any direction.

[Brief explanation of the drawing]

Fig. 1 is a measurement diagram showing an embodiment of the present invention, Fig. 2 is a virtual spherical diagram showing the microphone position to be measured, Fig. 3 is a characteristic diagram showing the inverse square characteristic in a general room, and Fig. 4 Fig. 7 is a characteristic diagram explaining the present invention, Fig. 8 is a measurement system diagram showing a conventional measurement method, Figs. A cross-sectional view of the speaker system is shown. 1... Room to be measured 2... Speaker system to be measured 81... Anechoic chamber Patent applicant Nippon Columbia Co., Ltd. Japan, 1986 Patent Application No. 324359 2 Name of the invention Method for measuring characteristics of speaker system 3 Relationship with the case of the person making the amendment Patent applicant address Postal code 107 4-14-1 Akasaka, Minato-ku, Tokyo
No. 4 Name (4161 Nippon Columbia Co., Ltd. Representative Director Kazuo Mochizuki 4 Agent Address Zip Code 210 5-1 Minato-cho, Kawasaki-ku, Kawasaki-shi, Kanagawa Prefecture Nippon Columbia Co., Ltd. Kawasaki Factory Details page 1 line 3 "Speaker system Characteristic measurement method”
Toro is corrected to read "method for measuring characteristics of speaker systems."

Claims (1)

[Claims] The passive sound output part of the speaker system under test having a passive sound output part is sealed to prevent passive operation, and the surface sound pressure on a virtual sphere centered on the speaker system is measured in the operating state of the sealed lid speaker system. Acoustic characteristic A_1 obtained by integrating , Acoustic characteristic A_2 measured by bringing a microphone close to the speaker with the sealed lid speaker system in the operating state, and the passive acoustic output part of the speaker system to be measured in the operating state. Then, using the acoustic characteristic A_3 obtained by integrating the surface sound pressure on a virtual spherical surface centered on the speaker system, the above acoustic characteristic A_
A method for measuring characteristics of a speaker system, in which the acoustic characteristic A_2 is subtracted from 1 to obtain a correction characteristic S, and the correction characteristic S is subtracted from the acoustic characteristic A_3 to calculate an acoustic characteristic of a speaker system to be measured having a passive acoustic output section. .