摘要:

For the experimental evaluation of the acoustical impedance of a termination by the impedance‐tube method at low frequencies, the length of the impedance tube is a problem. In the present paper, the method of exact analysis of standing waves developed by the authors for the stationary medium as well as for mean flow, has been extended for measurement of the acoustical impedance of a termination at low frequencies. The values of the tube attenuation factor and the wave number at the low frequency of interest are established from the experiment conducted, with the given impedance tube, at a higher frequency. Then, exciting the tube at the desired low frequency it is sufficient to measure sound pressure at three differenct locations (not necessarily the minima) in order to evaluate reflection coefficient and hence the impedance of the termination at that frequency.

ISSN:0001-4966    

DOI:10.1121/1.381546

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

The transmission‐line or the impedance‐tube method for the measurement of the acoustic impedance of any termination involves a search for various minima and maxima of pressure. For this purpose, arrangement has to be made for the microphone to travel along the length of the impedance tube, and this complicates the design of the tube considerably. The present paper discusses a method which consists in evaluating the tube attenuation factor at any convenient frequency by making use of measured SPL’s at two (or more) fixed locations with a rigid termination, calculating the tube attenuation factor and wave number at the required frequency of interest with or without mean flow (as applicable), and finally evaluating the impedance of the given termination by measuring and using SPL’s at three (or more) fixed locations. Thus, the required impedance tube is considerably smaller in length, simpler in design, easier to manufacture, cheaper in cost and more convenient to use. The design of the tube is also discussed. Incidentally, it is also possible to evaluate the impedance at any low frequency without having to use a larger impedance tube.

ISSN:0001-4966    

DOI:10.1121/1.381547

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

A vibration pick‐up‐type ear microphone was developed as an alternative to the conventional sound‐pressure‐type ear microphone. It was evaluated and compared to other conventional microphones with the following results: It is possible to obtain remarkable sensibility without closing the ear canal and to obtain speech intelligibility scores of over 95%. There was no significant difference between voice intelligibility with a mask and without a mask. Speech intelligibility of the vibration pick‐up‐type ear microphone in high ambient noise is much higher (110 dB—96%, 125 dB—84%) than that of a noise canceling microphone (110 dB—87%, 125 dB—77%) and of a sound‐pressure‐type ear microphone with ear muff (110 dB—85%, 125 dB—68%). By using the two‐way communication device it is possible to talk and to listen simultaneously since the ear canal is not obstructed. The vibration pick‐up‐type ear‐insert microphone can be used (1) for voice communication in high ambient noise, (2) in a mask, (3) for hands‐free operations, and (4) it will not howl due to excessive feedback. Communication systems using the vibration pick‐up‐type ear microphone have been evaluated in various environments.

ISSN:0001-4966    

DOI:10.1121/1.381548

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

The low‐frequency voltage–pressure sensitivity of piezoelectric right circular cylinders is derived for three common polarization schemes. The acoustic pressure on the three major surfaces is considered variable, thereby allowing for any configuration of shielding. Derived sensitivities are illustrated for a common piezoelectric ceramic material (Clevite PZT 4).

ISSN:0001-4966    

DOI:10.1121/1.381549

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

This is an addendum to an already published article [J. Acoust. Soc. Am. 59, 1361–1370 (1976)].

ISSN:0001-4966    

DOI:10.1121/1.381550

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

The authors’ reply to comments by D. G. Browningetal. [J. Acoust. Soc. Am. 60, 369–374 (1977)].

ISSN:0001-4966    

DOI:10.1121/1.381552

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

Two experiments on forward masking are described. Probe threshold were measured using a two‐interval forced‐choice technique. In experiment I the masked threshold for a 1‐kHz probe was measured as a function of masker level for three maskers; a 1‐kHz tone, a 1/3‐, and a 1/1‐octave noise band centered at 1 kHz. At medium and high masker levels, maskers equated for energy in the critical band around 1 kHz did not produce equal amounts of masking. The tone was the most effective masker, and the 1/1‐octave noise the least. In experiment II the threshold for a 1‐kHz probe was measured for a 1‐kHz masker at levels ranging from 26 to 76 dB SPL, and for maskers ranging from 800 to 1100 Hz at levels of either 76 or 61 dB SPL. The effect of adding to each of these a 1.2‐kHz tone at 81 dB SPL was also determined. The 1.2‐kHz tone produced a significant reduction in probe threshold for masker frequencies within 50 Hz of that of the probe, but had little effect for maskers outside this range. The results are discussed in relation both to lateral suppression and to cues arising from qualitative differences between masker and probe.

ISSN:0001-4966    

DOI:10.1121/1.381553

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

The attack and release times were measured on each of three samples of 27 different models of compression‐type hearing aids using the test conditions specified in ANSI Standard S3‐22 (1976). The results indicate that almost all of the hearing aids tested have attack times less than or equal to 10 ms. A little more than half of the hearing aids had release times of 50 ms or less. The range of the attack times varied from 1 to 23 ms and the release times from 5–600 ms.

ISSN:0001-4966    

DOI:10.1121/1.381554

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.381555

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.381682

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP