ISSN:0001-4966    

DOI:10.1121/1.1915836

出版商:Acoustical Society of America    

年代:1936

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.1915837

出版商:Acoustical Society of America    

年代:1936

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.1915838

出版商:Acoustical Society of America    

年代:1936

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.1915839

出版商:Acoustical Society of America    

年代:1936

数据来源: AIP

摘要:

A loudspeaker may be tested by removing its horn and loading it acoustically with an air column of variable length in a closed tube. In this way one can measure the acoustic impedance of the horn and the sound power output of the speaker, under the assumption that the air chamber in front of the diaphragm can be regarded as an addition to the tube of an equivalent lengthrdetermined by experiment. Under this assumption the air load impedanceZAat the diaphragm is given byZA = −j(A12/A2)ρc cot kxwhereA1is the diaphragm area,A2, the cross section of the tube, andxthe total length, i.e., actual length plusr. An analytical treatment leads to the formulaZA = −j cos2 kr[(A12/A2)ρc cot kx] −j(A12/A2)ρc sin kr cos kr. Eq. (1) leads to correct results for the measurement of acoustic impedance of the horn and sound power output, but cannot be extended to determine the mechanical impedance of the diaphragm. Eq. (2) is the basis of a new treatment which is more general. It is expressed in terms of a parameterrwhich can be calculated theoretically at low frequencies, or determined empirically at higher frequencies. The theory has been verified experimentally.

ISSN:0001-4966    

DOI:10.1121/1.1915840

出版商:Acoustical Society of America    

年代:1936

数据来源: AIP

摘要:

High quality reproduction of recorded music is possible only if the speeds of recording and reproducing machines are maintained constant within very narrow limits. As improvements are made in these machines greater refinement in measurement of the variations is required in order that the progress may continue. The development of an improved “Wow‐meter” for such measurements is described, and various alternative schemes are discussed. The securing of a standard record, itself sufficiently free from imperfections, presents one of the most serious difficulties. For testing turntables a toothed steel wheel was built, in which special precautions were taken to minimize indexing and other possible errors. The current generated by means of this wheel is supplied to an electric circuit so arranged that variations in frequency cause deflections of a galvanometer, which are registered on a photographic film. The principle employed, namely, a resonant circuit slightly off tune, has been used in earlier devices. In the meter described a push‐pull arrangement has been adopted to reduce the likelihood of errors due to variations in voltage. A frequency meter of this type has certain inherent limitations in its ability to register very rapid fluctuations. Certain measures have been adopted to make the meter satisfactory in this respect, and the possibility of going further in this direction if necessary is given consideration.

ISSN:0001-4966    

DOI:10.1121/1.1915841

出版商:Acoustical Society of America    

年代:1936

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.1915842

出版商:Acoustical Society of America    

年代:1936

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.1915843

出版商:Acoustical Society of America    

年代:1936

数据来源: AIP

摘要:

The American Standards Association Sectional Committee Z‐24 on Acoustical Measurement and Terminology has under it a Subcommittee on Fundamental Sound Measurements. The Subcommittee during the past few years has been considering definitions and test procedure pertaining to the calibration of microphones. The following report is the result of its work. At a recent meeting of the Sectional Committee it was voted to submit this work to the interested scientific bodies for publication in their journals with the thought of promoting constructive criticism and discussion. The Subcommittee made use of considerable material from the tentative report of the I.R.E. Standards Committee on Electro‐Acoustic Devices, and this is gratefully acknowledged.

ISSN:0001-4966    

DOI:10.1121/1.1915844

出版商:Acoustical Society of America    

年代:1936

数据来源: AIP