GB2184542A

GB2184542A - Acoustic measuring device

Info

Publication number: GB2184542A
Application number: GB08628717A
Authority: GB
Inventors: Michael Stanley Novak; Nicholas Anton Kantoch
Original assignee: ELECTROMUSIC Ltd
Current assignee: ELECTROMUSIC Ltd
Priority date: 1985-12-02
Filing date: 1986-12-02
Publication date: 1987-06-24
Anticipated expiration: 2006-12-02
Also published as: GB2184542B; GB8628717D0

Abstract

Received sound frequencies are analysed by a sound receiver whose response can be varied in a continuous manner by a fader slide 12 and an indication is made of the amplitude in a given frequency band using LEDs 13. A signal generator 20 may be provided in the same unit, but direct signal transmission to the receiver is prevented, so that the apparatus indicates the response in a selected band of the surroundings to the generated signals. Choice of frequency band is made by touch-sensitive control 14 and indicated by LEDs 14a. <IMAGE>

Description

SPECIFICATION Acoustic measuring device In order to analyse the frequencies of sound, it has been proposed to divide the sound spectrum into a series of channels, for example each extending over one third of an octave, and to provide a detector for each channel, the output of each detector operating an indicatortoindicatetheamplitudeofsound within the corresponding band offrequencies. Such an arrangement is cumbersome, since a large number of detectors and indicators has to be provided.

According to the present invention, there is provided an acoustic measurement device comprising a sound receiver, means for varying the frequencies to which the receiver is sensitive in a continuous manner, and an indicator responsive to the output of the receiver. With this arrangement, only one receiver and only one indicator has to be provided and the operator can concentrate on the frequency bands of interest by adjusting the frequencies to which the receiver is sensitive accordingly, either in a single sweep ofthewhole audio band or in sweeps of decade bands for greater resolution.

An example of the invention will now be described with reference to the accompanying drawing which is a plan of an acoustic measurement device. This device is intended for measuring the frequency response of a room, and therefore includes an elec tronicsignal generatorintheform of a white noise generator20 operable overthefull frequency band of interest as well as a sound receiver in the form of a condenser microphone 10 located behind an ac oustic window liThe frequency to which the micro- phone and filter are sensitive is adjusted by means of afaderslide 12, which has scales calibrated for a choice offrequency ranges, the choice being made by touch-sensitive control 14 and indicated by LEDs 14a.A series of light emitting diodes 13 are provided, connected to a filter circuit in the output of the microphone 10, to indicate the amplitude of that output. In the illustrated example,the light emitting diodes 13 are calibrated in decibels, at 1 dB intervals, though a larger spacing could be used if this resolution is not required, eg 3dB.

The device is operated by directing the acoustic window 11 in the direction of interest, adjusting the control 14to the frequency band of interest, adjusting thefrequency in the band bythefader 12 and observing the light emitting diodes 13totakea measure ofthe amplitude of sound in the frequency band of interest being received by the microphone 10. Sound may be received by the instrument after transmission through the sound system into which the noise signal is being injected, although the apparatus will also analyse externally generated sounds.When a measurement has been made in one frequency band, further measurements may be made in other frequency bands by adjusting the control 14. A plot of the frequency response may then be ascertained by sweeping the complete audio spectrum.

The choice of frequency band made by the control 14 when in the scan mode. This may for example be in the band of 20Hz to 22kHz (full range), 20Hzto 220Hz, 200Hzto 2.2kHz and 2kHzto 22kHz. Various weighted responses, such as linear, A, C, and D weightings (known to the skilled operator), are available in the SPL meter mode; one such weighting which may be used mimics the response of the human earatlowto medium sound pressure levels.

The instrument's sensitivity can be adjusted by the control 16 and indicated by LEDs 1 6a. The speed of response of the apparatus can be adjusted by the control 17. It is possible to vary the type of display by the light emitting diodes, for example, either illuminating the one diode adjacent the decibel level ofthe frequency band of interest being received (dotdisplay wherein the diodes are arranged in a line, increasing amplitudes being indicated by the illumination of a single diode at an increasing distance along the line.), or illuminating all the light emitting diodes from the lowest level to that level (bar display wherein the diodes are arranged in a line, increasing amplitudes being indicated by an increasing number of consecutive diodes in the line being illuminated.) by the control 18.The former display saves battery power, butthe latter display may be more easily assimilated by the operator.

An equalizer circuit can be incorporated in the de vice housing to compensate for any non-linear re- sponseofa condenser microphone.

When the apparatus is required to measure externally generated sounds, clearlythe internal signal generator is not employed.

The apparatus described differs from a sound level meter witch optional filter sets and from a system of microphone, pre-amplifierand sweep filter by: The filter frequency is continously variable for very accurate frequency resolution - not at pre-set, fixed centre frequencies.

The unit is self-contained with its own electronically synthesised signal source.

The unit is battery operated, compact and thereforcefully portable.

The internal circuitry is electronically gated orvoltage-controlled allowing forthe later addition of automatic sweep facilities etc and, with extra circuitry, automatic resonance search facilities which, linked to frequency-locked programme filters, could provide very basic automatic room or system equalising potential inthefuture.

Various embodiments ofthe invention may be used for measuring amplitudevsfrequency char- acteristics of electro-acoustic systems such as sound reinforcement systems, telephone or radio communication systems etc, acoustic emitters such as industrial machines, vehicles, air-conditioning plants etc and acoustic environments such as auditoria, studios, and public buildings.

1. An acoustic measurement device comprising a sound receiver, means for varying the frequencies to which the receiver is sensitive in a continuous manner, and an indicator responsive to the output of the receiver.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Acoustic measuring device In order to analyse the frequencies of sound, it has been proposed to divide the sound spectrum into a series of channels, for example each extending over one third of an octave, and to provide a detector for each channel, the output of each detector operating an indicatortoindicatetheamplitudeofsound within the corresponding band offrequencies. Such an arrangement is cumbersome, since a large number of detectors and indicators has to be provided. According to the present invention, there is provided an acoustic measurement device comprising a sound receiver, means for varying the frequencies to which the receiver is sensitive in a continuous manner, and an indicator responsive to the output of the receiver. With this arrangement, only one receiver and only one indicator has to be provided and the operator can concentrate on the frequency bands of interest by adjusting the frequencies to which the receiver is sensitive accordingly, either in a single sweep ofthewhole audio band or in sweeps of decade bands for greater resolution. An example of the invention will now be described with reference to the accompanying drawing which is a plan of an acoustic measurement device. This device is intended for measuring the frequency response of a room, and therefore includes an elec tronicsignal generatorintheform of a white noise generator20 operable overthefull frequency band of interest as well as a sound receiver in the form of a condenser microphone 10 located behind an ac oustic window liThe frequency to which the micro- phone and filter are sensitive is adjusted by means of afaderslide 12, which has scales calibrated for a choice offrequency ranges, the choice being made by touch-sensitive control 14 and indicated by LEDs 14a.A series of light emitting diodes 13 are provided, connected to a filter circuit in the output of the microphone 10, to indicate the amplitude of that output. In the illustrated example,the light emitting diodes 13 are calibrated in decibels, at 1 dB intervals, though a larger spacing could be used if this resolution is not required, eg 3dB. The device is operated by directing the acoustic window 11 in the direction of interest, adjusting the control 14to the frequency band of interest, adjusting thefrequency in the band bythefader 12 and observing the light emitting diodes 13totakea measure ofthe amplitude of sound in the frequency band of interest being received by the microphone 10. Sound may be received by the instrument after transmission through the sound system into which the noise signal is being injected, although the apparatus will also analyse externally generated sounds.When a measurement has been made in one frequency band, further measurements may be made in other frequency bands by adjusting the control 14. A plot of the frequency response may then be ascertained by sweeping the complete audio spectrum. The choice of frequency band made by the control 14 when in the scan mode. This may for example be in the band of 20Hz to 22kHz (full range), 20Hzto 220Hz, 200Hzto 2.2kHz and 2kHzto 22kHz. Various weighted responses, such as linear, A, C, and D weightings (known to the skilled operator), are available in the SPL meter mode; one such weighting which may be used mimics the response of the human earatlowto medium sound pressure levels. The instrument's sensitivity can be adjusted by the control 16 and indicated by LEDs 1 6a. The speed of response of the apparatus can be adjusted by the control 17. It is possible to vary the type of display by the light emitting diodes, for example, either illuminating the one diode adjacent the decibel level ofthe frequency band of interest being received (dotdisplay wherein the diodes are arranged in a line, increasing amplitudes being indicated by the illumination of a single diode at an increasing distance along the line.), or illuminating all the light emitting diodes from the lowest level to that level (bar display wherein the diodes are arranged in a line, increasing amplitudes being indicated by an increasing number of consecutive diodes in the line being illuminated.) by the control 18.The former display saves battery power, butthe latter display may be more easily assimilated by the operator. An equalizer circuit can be incorporated in the de vice housing to compensate for any non-linear re- sponseofa condenser microphone. When the apparatus is required to measure externally generated sounds, clearlythe internal signal generator is not employed. The apparatus described differs from a sound level meter witch optional filter sets and from a system of microphone, pre-amplifierand sweep filter by: The filter frequency is continously variable for very accurate frequency resolution - not at pre-set, fixed centre frequencies. The unit is self-contained with its own electronically synthesised signal source. The unit is battery operated, compact and thereforcefully portable. The internal circuitry is electronically gated orvoltage-controlled allowing forthe later addition of automatic sweep facilities etc and, with extra circuitry, automatic resonance search facilities which, linked to frequency-locked programme filters, could provide very basic automatic room or system equalising potential inthefuture. Various embodiments ofthe invention may be used for measuring amplitudevsfrequency char- acteristics of electro-acoustic systems such as sound reinforcement systems, telephone or radio communication systems etc, acoustic emitters such as industrial machines, vehicles, air-conditioning plants etc and acoustic environments such as auditoria, studios, and public buildings. CLAIMS

2. Apparatus as claimed in claim 1 comprising a signal generator arranged to generate signals over the whole band of frequencies to which the receiver can be made sensitive, the generator being arranged to project signals away from the receiver so that the receiver does not receive signals directly from the generator, but only after reflection by an outside body.

3. Apparatus as claimed in claim 1 or claim 2 wherein the indicator comprises a series of lightem- itting diodes.

4. Apparatus as claimed in claim3whereinthe diodes are arranged in a iine, increasing amplitudes being indicated byan increasing numberofconsecutive diodes in the line being illuminated.

5. Apparatus as claimed in claim 3 wherein the diodes are arranged in a line, increasing amplitudes being indicated by the illumination ofa single diode at an increasing distance along the line.

6. Apparatus as claimed in any one of the preceding claims wherein the varying means comprises means to select a band of frequencies and to vary the frequencies continuously within that band.

7. Apparatus as claimed in claim 6 wherein the varying means comprises means to select aweigh- ted band offrequencies.

8. Apparatus as claimed in any one ofthe preceding claims comprising touch-sensitive controls.

9. Apparatus as climed in any one of the preceding claims wherein the receiver comprises a microphoneandanequalisertocompensateforanynonlinear response ofthe microphone.

10. Acoustic measurement apparatussubstanti ally as herein described with reference to and as il iustrated in the accompanying drawing.