CN204539472U - A kind of microphones sensitivity measure system of method based on the comparison - Google Patents

Abstract

The utility model discloses a kind of microphones sensitivity measure system of method based on the comparison.The method of measurement of conventional microphone sensitivity is to measuring condition and equipment requirement harshness, and method is complicated.The utility model comprises standing wave tube, microphone standard component, oscilloscope, signal generator and loud speaker; Loud speaker is arranged on one end of standing wave tube, and coaxial with standing wave tube; The other end of standing wave tube is fixed with metallic plate; Microphone standard component is arranged on the central authorities of metallic plate, coaxial with standing wave tube; Tested microphone is vertically mounted on standing wave tube outer wall, and position determines by measuring wavelength: when the wavelength of sound wave is greater than standing wave tube length, the axial distance of tested microphone and metallic plate is less than 1/4 wavelength; When wave length of sound is less than standing wave tube length, the axial distance of tested microphone and metallic plate is greater than 1/4 wavelength; Microphone standard component is all connected with oscilloscope with tested microphone.The utility model is applicable to the less demanding microphones sensitivity of certainty of measurement.

Description

A kind of microphones sensitivity measure system of method based on the comparison

Technical field

The utility model belongs to acoustic measurement field, is specifically related to a kind of microphones sensitivity measure system of method based on the comparison.

Background technology

Microphone, as a kind of transducer acoustical signal being converted to the signal of telecommunication, is widely used in the numerous areas such as aero-acoustics, architecture, environmental acoustics.An important parameter of microphone property is receiving sensitivity, and in the measurement and experimental analysis of acoustical signal, sensitivity of microphone is the key ensureing measurement and result accuracy.

Along with the extensive use of acoustic measuring technique, the demand of microphone is increasing, and what such as auditory localization technology was applied realizes supervisory control system, speech recognition system, spatial sound field transformation technology etc., general is all adopt the form of microphone array to realize, and therefore microphone quantity required gets more and more.In array structure, the consistency of the sensitivity of microphone is also the accuracy key ensureing to measure simultaneously.Therefore the measurement of sensitivity of microphone has very important meaning.The method of measurement of sensitivity of microphone, main employing pistonphone method, static excitation method, coupler reciprocal method etc.Along with the development of laser interferometry techniques, digital technology, pistonphone method calibration microphone becomes focus, the displacement using laser interferometry techniques to measure piston in the design of modern piston generator, laser interferometry techniques can ensure that in pistonphone, the precision of displacement measurement reaches micron order more.Pistonphone research domestic is at present still based on commercialization.Static excitation method can be measured the relative change of the sensitivity of microphone with frequency, generally in conjunction with pistonphone method and static excitation method, namely the pressure sensitivity of microphone of a certain frequency is calibrated with pistonphone, then static excitation method measures the frequency response of this pressure sensitivity of microphone, and the method process is more complicated.From the forties in 20th century, people have done large quantifier elimination to coupler reciprocal method, reach higher accuracy, and more than the frequency 20Hz that is aligned in of current microphone generally adopts coupler reciprocal method calibration as the standard method of microphone absolute calibration.Coupler reciprocal method signal to noise ratio when low frequency can be deteriorated, and can cause sound leakage for the capillary of all pressing, because of which limit it the low frequency sensitivity of microphone measure in application.

No matter be in conjunction with pistonphone and static excitation method, or the coupler reciprocal method of the standard of employing, although certainty of measurement can reach very high standard, but the requirement of its surveying work to equipment and condition is all harsher, the a lot of occasion of practical application can not reach this measuring condition, nor needs to reach very high precision, and above method can cause higher cost.Therefore design a kind of structure simple, easy to operate, cost is low, and the measuring system that can meet the sensitivity of microphone of general measure requirement is necessary.

Summary of the invention

The purpose of this utility model is for traditional measurement method measuring condition and equipment requirement harshness, the shortcoming of method of measurement complexity, a kind of microphones sensitivity measure system of method is based on the comparison proposed, according to standing wave theory, structure is simple, with low cost, be applicable to the measurement to the less demanding microphones sensitivity of certainty of measurement.

The utility model is achieved through the following technical solutions:

The utility model comprises excitation sound source, standing wave tube, microphone standard component and oscilloscope; Described excitation sound source comprises signal generator and loud speaker; Described loud speaker is arranged on one end of standing wave tube, and coaxial with standing wave tube; The other end of standing wave tube is fixed with metallic plate; Microphone standard component is arranged on the central authorities of metallic plate, coaxial with standing wave tube; Tested microphone is vertically mounted on standing wave tube outer wall, and position determines by measuring wavelength: when the wavelength of sound wave is greater than standing wave tube length, the axial distance of tested microphone and metallic plate is less than 1/4 wavelength; When wave length of sound is less than standing wave tube length, the axial distance of tested microphone and metallic plate is greater than 1/4 wavelength; Described microphone standard component is all connected with oscilloscope with tested microphone.

The diaphragm surface of described loud speaker at least blocks 2/3 of standing wave tube cross-sectional area.

Described standing wave tube adopts PVC pipe.

The inner hole centreline of described standing wave tube is straight line, and cross section is everywhere the circle that radius is equal.

The length of described standing wave tube is 4m, and internal diameter is 152mm, and pipe thickness is 4mm; The thickness of described metallic plate is 10mm, and tested microphone is arranged on the position of distance metallic plate 0.56m; The measuring frequency scope of described standing wave tube is 50Hz ~ 1000Hz.

The length of described standing wave tube is 0.75m, and internal diameter is 46mm, and pipe thickness is 2mm; The thickness of described metallic plate is 10mm, and tested microphone is arranged on the position of distance metallic plate 0.15m; The measuring frequency scope of described standing wave tube is 200Hz ~ 4000Hz.

The beneficial effects of the utility model: structure is simple, workable, can meet the measurement to the less demanding microphones sensitivity of certainty of measurement.

Accompanying drawing explanation

Fig. 1 is structural representation of the present utility model.

Fig. 2 is the sensitivity curve of tested microphone when adopting 4m standing wave tube to measure.

Fig. 3 is the sensitivity curve of tested microphone when adopting 75m standing wave tube to measure.

In figure: 1, encourage sound source, 2, standing wave tube, 3, microphone standard component, 4, oscilloscope, 5, tested microphone, 6, signal generator, 7, loud speaker.

Embodiment

Below in conjunction with drawings and Examples, the utility model is further described.

As shown in Figure 1, a kind of microphones sensitivity measure system of method based on the comparison, comprises excitation sound source 1, standing wave tube 2, microphone standard component 3 and oscilloscope 4; Excitation sound source 1 comprises signal generator 6 and loud speaker 7; Loud speaker 7 is arranged on one end of standing wave tube 2, and coaxial with standing wave tube 2; The diaphragm surface of loud speaker 7 at least blocks 2/3 of standing wave tube 2 cross-sectional area; Standing wave tube 2 adopts PVC pipe, and inner hole centreline is straight line, and cross section is everywhere the circle that radius is equal, and endoporus hole wall is smooth, firm, and enough closely knit, there is not resonance at standing wave tube working frequency range; The other end of standing wave tube is fixed with metallic plate, as acoustic reflection end face; Microphone standard component 3 is arranged on the central authorities of metallic plate, coaxial with standing wave tube; Tested microphone 5 is vertically mounted on standing wave tube outer wall, position determines by measuring wavelength: when the wavelength of sound wave is greater than standing wave tube length, the axial distance of tested microphone and metallic plate is less than 1/4 wavelength, when wave length of sound is less than standing wave tube length, the axial distance of tested microphone and metallic plate is greater than 1/4 wavelength; Microphone standard component 3 is all connected with oscilloscope 4 with tested microphone 5.

Signal generator 6 and loud speaker 7, as sound source 1, are measured the acoustic pressure of standing wave tube end by microphone standard component 3, another some place acoustic pressure measured by tested microphone, and in stationary field, 2 sound pressure levels all import oscilloscope 4 into; Using the sound pressure sensitivity of microphone standard component 3 as with reference to value, according to the functional relation of 2 place's acoustic pressures in stationary field, the receiving sensitivity of tested microphone can be drawn.Theory deduction is as follows:

In plane wave, the acoustic pressure at any point x place is:

P (x)=Ae ^-ikx+ Be ^ikx(1), in formula, x is the distance of point on standing wave tube central axis direction and loud speaker 7; A is magnitudes of acoustic waves, and B is the phase difference of sound wave forward and negative line feed; Wave number k=ω/c ₀, c ₀for the velocity of sound in air, ω is angular frequency.

According to equation of particle motion

$\frac{\∂p}{\∂x}=-\mathrm{i\ρ\ωu}\left(x\right)---\left(2\right)$

In formula, ρ is density, ω=kc ₀, obtaining particle vibration velocity is

$u\left(x\right)=\frac{{\mathrm{Ae}}^{-\mathrm{ikx}}-{\mathrm{Be}}^{\mathrm{ikx}}}{\mathrm{\ρ}{c}_0}---\left(3\right)$

In formula, the value of A, B can be solved by following two boundary conditions: when standing wave tube length is l, is 0, obtains Ae by the particle vibration velocity of x=l ^-ikx=Be ^ikx; At x=0 place, particle vibration velocity u (0)=U, obtains ρ c ₀u=A-B.Therefore, in standing wave tube, the acoustic pressure of any point x is

$p\left(x\right)=-\mathrm{i\ρcU}\frac{\cos \left(k(l-x)\right)}{\sin \left(\mathrm{kl}\right)}---\left(4\right)$

The position of tested microphone is at the x place of standing wave tube, and the acoustic pressure relation between standing wave tube end microphone standard component meets formula

$\frac{p_{\mathrm{prob}}}{p_{\mathrm{ref}}}=\cos \left(k(l-x)\right)---\left(5\right)$

In formula, p _probfor the acoustic pressure of tested microphone, p _reffor the acoustic pressure of microphone standard component.

The sensitivity of tested microphone is

$S_{\mathrm{prob}}=\frac{p_{\mathrm{prob}}}{p_{\mathrm{ref}}}\·\frac{1}{\cos \left(k(l-x)\right)}\·S_{\mathrm{ref}}---\left(6\right)$

In formula, S _reffor the sensitivity of microphone standard component.

The operating frequency range of this microphones sensitivity measure system of method based on the comparison:

The condition that only there is plane wave in standing wave tube is lower than cut-off frequency f _csound wave be plane wave, namely when frequency of sound wave is greater than cut-off frequency, in standing wave tube, sound field is no longer one dimension.The computing formula of cut-off frequency is as follows:

$f_c=\frac{1.84c_0}{\mathrm{\πd}}---\left(7\right)$

In formula, d is the internal diameter of standing wave tube.

The lower-frequency limit that standing wave tube can be measured, is determined by the length of standing wave tube, that is:

$f_s=\frac{c_0}{2l}---\left(8\right)$

In formula, f _sfor the lower-frequency limit normally measured.

Because measuring frequency is by the restriction of standing wave tube length, the measurement that two kinds of physical dimensions realize different range frequency can be designed: a kind of standing wave tube length is 4m, internal diameter is 152mm, pipe thickness is 4mm, standing wave tube one end plate thickness is 10mm, tested microphone 5 is arranged on the position of distance metallic plate 0.56m, and the measuring frequency scope of this standing wave tube is 50Hz ~ 1000Hz; Another kind of standing wave tube length is 0.75m, and internal diameter is 46mm, and pipe thickness is 2mm, and the thickness of standing wave tube one end metallic plate is 10mm, and tested microphone 5 is arranged on the position of distance metallic plate 0.15m, and the measuring frequency scope of this standing wave tube is 200Hz ~ 4000Hz.

Below in conjunction with experiments of measuring data, the utility model is further described.

When frequency is lower than 1000Hz, get c ₀=340ms, under axial symmetry sound source condition, plane wave existence condition is f _c=1000HZ, then in pipe, sound wave is the standing wave tube internal diameter d=199mm of plane wave, and therefore internal diameter is the standing wave tube of 152mm sound wave when can ensure that frequency of source is less than 1000Hz in pipe is plane wave.Standing wave tube length is 4m, can be obtained the lower-frequency limit f measured by formula (8) _s=42.5HZ, measuring range can be decided to be 50Hz ~ 1000Hz.Fig. 2 is the sensitivity curve of tested microphone when adopting 4m standing wave tube to measure, frequency corresponding to figure medium sensitivity maximum is by the determining positions of tested microphone, microphone is placed in the position of distance standing wave tube end 56cm, and the frequency that therefore sensitivity maxima is corresponding is:

$f=\frac{1}{4}\·\frac{c}{l-x}=151.8\left(\mathrm{Hz}\right)$

When frequency of sound wave is less than 4000Hz, in standing wave tube only there is the condition of plane wave and be in sound wave, standing wave tube internal diameter d < 49mm, therefore internal diameter is 46mm, length is the standing wave tube of 75m, and the frequency of sound wave scope that can measure is 200Hz ~ 4000Hz.Fig. 3 is the sensitivity curve of tested microphone when adopting 75m standing wave tube to measure, frequency f=566Hz that figure medium sensitivity maximum is corresponding.

Claims (6)

1. a microphones sensitivity measure system for method based on the comparison, comprises excitation sound source, standing wave tube, microphone standard component and oscilloscope, it is characterized in that:

Described excitation sound source comprises signal generator and loud speaker; Described loud speaker is arranged on one end of standing wave tube, and coaxial with standing wave tube; The other end of standing wave tube is fixed with metallic plate; Microphone standard component is arranged on the central authorities of metallic plate, coaxial with standing wave tube; Tested microphone is vertically mounted on standing wave tube outer wall, and position determines by measuring wavelength: when the wavelength of sound wave is greater than standing wave tube length, the axial distance of tested microphone and metallic plate is less than 1/4 wavelength; When wave length of sound is less than standing wave tube length, the axial distance of tested microphone and metallic plate is greater than 1/4 wavelength; Described microphone standard component is all connected with oscilloscope with tested microphone.

2. the microphones sensitivity measure system of a kind of method based on the comparison according to claim 1, is characterized in that: the diaphragm surface of described loud speaker at least blocks 2/3 of standing wave tube cross-sectional area.

3. the microphones sensitivity measure system of a kind of method based on the comparison according to claim 1, is characterized in that: described standing wave tube adopts PVC pipe.

4. the microphones sensitivity measure system of a kind of method based on the comparison according to claim 1, is characterized in that: the inner hole centreline of described standing wave tube is straight line, and cross section is everywhere the circle that radius is equal.

5. the microphones sensitivity measure system of a kind of method based on the comparison according to claim 1, is characterized in that: the length of described standing wave tube is 4m, and internal diameter is 152mm, and pipe thickness is 4mm; The thickness of described metallic plate is 10mm, and tested microphone is arranged on the position of distance metallic plate 0.56m; The measuring frequency scope of described standing wave tube is 50Hz ~ 1000Hz.

6. the microphones sensitivity measure system of a kind of method based on the comparison according to claim 1, is characterized in that: the length of described standing wave tube is 0.75m, and internal diameter is 46mm, and pipe thickness is 2mm; The thickness of described metallic plate is 10mm, and tested microphone is arranged on the position of distance metallic plate 0.15m; The measuring frequency scope of described standing wave tube is 200Hz ~ 4000Hz.