摘要:

The accepted system of tuning divides the octave into a succession of twelve tones, of which the frequency relations are such that if n be any tonen : n + 1 = 1 : 2112from which also it follows thatn : n + 12 = 1 : 2This system, however, is purely artificial and was adopted in the eighteenth century in order to effect a practical compromise between the growing demand for freedom of tonal combination, and the limitations of a keyboard which had fastened itself upon practical musical performance. The paper discusses the nature of the musical scale and the anomalies which arise when an attempt is made to evoke intervals and chords in accurate relations of frequency with only twelve separate tones available in each octave. Some of the acoustical defects of equal temperament are pointed out especially in relation to music as heard. A thorough reconsideration of the subject is suggested for the general benefit of the reproducing arts and of the future of Music as a living form of expression.

ISSN:0001-4966    

DOI:10.1121/1.1901909

出版商:Acoustical Society of America    

年代:1931

数据来源: AIP

摘要:

The voice teachers of the past and the present have been trying and are tying to standardize their work in teaching the control of the human voice. Without a standard of measurement this was not possible. The acoustical scientists have evolved a standard of measurement in the art of the reproduction of the human voice. The speaker through practical demonstration believes he can prove that the same standard of measurement can be applied to the training of the human voice in speech and in song. With this end in view the speaker has evolved and applied in his teaching an acoustic measuring apparatus with which the student of voice can hear his own voice amplified and measure the right pressure of the vowel continuant through the deflection of a sensitive meter.

ISSN:0001-4966    

DOI:10.1121/1.1901913

出版商:Acoustical Society of America    

年代:1931

数据来源: AIP

摘要:

If the crooks for the first, second, and third valves of a brass instrument are made of the proper lengths to produce respectively a tempered whole tone, a tempered half tone, and a tempered tone and a half, then the notes produced by the simultaneous use of any two or more valves are sharper than the corresponding tempered intervals. The problem of tempering the scale of a valve instrument thus becomes a matter of making each valve crook too long for tempered intervals when the valves are used singly, so that the sharpness of notes produced by the combined use of valves shall be reduced as much as possible. The precise lengths of the several valve crooks for minimizing discrepancies of intonation in a valve instrument appear to be unknown both to writers on acoustics and to makers of valve instruments. The paper presents the method of minimizing such discrepancies.

ISSN:0001-4966    

DOI:10.1121/1.1901914

出版商:Acoustical Society of America    

年代:1931

数据来源: AIP

摘要:

In order to determine noise specifications in absolute units for a certain type of large reduction gear measurements were made of the sounds produced by ten machines in operation at a large central generating station. An average weighted total intensity, and a frequency analysis were made of the noise of each machine. It appears that these data are suitable and sufficient for absolute noise specifications on this type of machine.It was found that 1 db. represents an important difference in loudness in these machines which places quite rigorous requirements on the apparatus and the methods of measurement in order to eliminate errors due to wave patterns, location, load, speed, etc. Data on these points are given.A very close check was obtained between the observed frequencies of the various notes, and the movements of certain parts of the machine. By a comparison of the frequency analyses of the different machines it was possible to locate which part of the machine was responsible for the noise, and something of the nature of the defect producing the noise.

ISSN:0001-4966    

DOI:10.1121/1.1901918

出版商:Acoustical Society of America    

年代:1931

数据来源: AIP

摘要:

In constructing a model for demonstration of the function of the cochlea two assumptions are what we ought to keep clearlyoutof our mind: (1) that the living cochlea might containdeadbuilding material of such physical properties as vulcanized rubber or tensile metal, (2) that the cochlea might containcontractiletissue, muscle tissue, that is, building material, which, in itself or in the supports in which it is inserted, could, from time to time at least, actively produce any stresses.A mechanical theory must recognize four salient features: (1) that any sound pervades the cochlea no matter whether the window flexibility is considered in theorizing or put down as negligible in theorizing or is actually (pathologically) impaired—just as any sound pervades any building with all its rooms and partititions, and that such aprimitive functionis almost certain to have at least a weak and otherwise limited stimulating effect; (2) that the main andmore adequate(but not exclusive) stimulating effect in mammalian animals (having an elongated cochlea tube) is likely to result from displacements of the phragma due to pressure differences between the windows, which are unsymmetrical to the meatus; (3) that thebulgeformed by the displaced phragmacan not travel, but can only lengthen itself, as is demonstrated by inspection of the hydraulic model; (4) that the formation of a bulge on either side of the average location of the phragma issucceededby the development ofstressin the phragma, as is demonstrated by inspection of the hydraulic model.

ISSN:0001-4966    

DOI:10.1121/1.1901923

出版商:Acoustical Society of America    

年代:1931

数据来源: AIP

摘要:

The distinction between pressure and free wave calibration of the microphone will be brought out and two or three methods using electrostatic actuator, thermo-phone and piston-phone will be described. Experimental precautions required in use of each of these will also be given.

ISSN:0001-4966    

DOI:10.1121/1.1901925

出版商:Acoustical Society of America    

年代:1931

数据来源: AIP

摘要:

The difference between microphones whose action depends on the pressure and those whose action depends on the pressure gradient in the sound wave is pointed out, and illustrations are given of each type. The characteristics of the pressure gradient in a complex sound field is discussed. It is shown that under certain conditions the pressure gradient gives a measure of the particle velocity in the sound wave. Illustrations and experiments are described which show how the vector characteristics of the pressure gradient may be used to advantage in making acoustic measurements.

ISSN:0001-4966    

DOI:10.1121/1.1901929

出版商:Acoustical Society of America    

年代:1931

数据来源: AIP

摘要:

Present electrical sound equipment has little output below about 100 cycles. An electrical device of large output in the range 30 to 200 cycles would afford new musical effects not hitherto possible.From a review of existing literature it is concluded that an acoustic output of at least one watt should be provided. Ten watts would be desirable. The result can be attained in several ways and the amount of equipment required with various arrangements is calculated. The results should serve as a guide in the design of installations.

ISSN:0001-4966    

DOI:10.1121/1.1901902

出版商:Acoustical Society of America    

年代:1931

数据来源: AIP

摘要:

P. Sabine and E. Meyer have noted that for frequencies above 2,000 d.v. the rate of absorption of sound in a room increases as the relative humidity decreases. The writer has investigated and confirmed this effect during the past year and has obtained some quantitative data which have a bearing upon problems in architectural acoustics and sound signaling. Assuming that the intensity of a plane wave in air diminishes in accordance withe—mct where c is the velocity t the time and m the absorption coefficient in the air the reverberation formula becomes (in British units)t = .049V−S loge (1 − a) + 4mV.By making reverberation measurements, under different conditions of humidity, in two rooms having the same boundary material (painted concrete) but different mean free paths, it is possible to determine both m andaas functions of the frequency and humidity of the air. For frequencies below 512 d.v., m is negligible. It increases approximately with the square of the frequency. At 4,096 d.v., m increases from about .0015 at 70 per cent relative humdidity (21°C) to .0033 at 20 per cent relative humidity. At frequencies above 6,000 d.v., the absorption in the air in a room may be greater than the absorption by the boundaries. The absorptivity of painted concrete remains nearly constant above 512 d.v., and has a value of about .016.

ISSN:0001-4966    

DOI:10.1121/1.1901905

出版商:Acoustical Society of America    

年代:1931

数据来源: AIP

摘要:

This paper is the result of a careful comparative study of the coefficients obtained by various methods used for the measurement of absorption coefficients employing the equations of the reverberation theory. Both organ pipes and an electro-dynamic loud speaker were used as sources of sound. With the latter, both steady tones and flutter tones were employed. Absorbing power was measured by determining the rate of decay from measurements of the reverberation time for known relative values of the steady state intensity, using the loud speaker source. The results indicate that a loud speaker operated at a fixed value of the input current sets up a steady state intensity that is constant, independently of the absorbing power of the room. The measurements with the organ pipes confirmed the assumption that the latter acts as a source of constant acoustical power output, setting up a steady state intensity that is inversely proportional to the total absorbing power of the room.Comparison of the results using steady and flutter tones shows that with a frequency range of a semitone above and below the mean frequency the measured values agree within the limits of experimental error. As between the organ pipe and the loud speaker, the former shows consistently higher values on four materials tested at the tone 512 vibrations per second, although the difference is only slightly greater than the experimental error. At other frequencies there is no consistent difference.The experiments showed that although total absorbing power scan be measured with a precision of the order of 2% or 3% yet errors of this magnitude, if cumulative, may result in variations of about 10% in the value of the absorption coefficient, computed from the difference in absorbing powers of the reverberation chamber with and without the test sample present.Comparison of results with result on identical samples tested in other laboratories show that at the frequency 512, the agreement between different laboratories is within the limits of accuracy of the methods so far developed.

ISSN:0001-4966    

DOI:10.1121/1.1901907

出版商:Acoustical Society of America    

年代:1931

数据来源: AIP