摘要:

A general statistical theory is developed for the masking effect of reverberation on the intelligibility of words. Speech is considered a series of discrete pulses distributed statistically over a 30‐db range in sound pressure level in a given frequency band. The articulation index is calculated as a function of reverberation time, using preliminary values of speech pulse lengths and spacings obtained fromVisible Speechspectrograms. The percent articulation for words is then calculated from the articulation index and is compared with Knudsen's experimental values. The theoretical values agree precisely with the measured values at reverberation times less than two seconds and differ by less than 17 percent out to six seconds. The calculations are extended to include a combination of background noise and reverberation.

ISSN:0001-4966    

DOI:10.1121/1.1906551

出版商:Acoustical Society of America    

年代:1949

数据来源: AIP

摘要:

A six‐foot grand piano has been studied for the change of its tuning with relative humidity. During nearly two years of observations in the living room in which the piano is located, the relative humidity varied between 20 and 70 percent. The change of tuning lagged the rise and fall of humidity as if the structure were characterized by a “time constant” of the order of 15 days. The relative humidity weighted according to this time constant varied only between 35 and 62 percent. Within the three central octaves, the tuning of this 40‐year old piano rose on the average 5 cents (0.3 percent in frequency) for each increase of 10 percent in weighted relative humidity. A working hypothesis is developed by which to organize the experimental results.

ISSN:0001-4966    

DOI:10.1121/1.1906552

出版商:Acoustical Society of America    

年代:1949

数据来源: AIP

摘要:

A musical scale is a sequence of musical intervals in a certain range, such as an octave; a mode is a cyclic permutation of a scale; a key is a mode at a certain pitch‐level; a raga is a melodic pattern of a key. There are 66 heptatonic scales, 462 heptatonic modes, and 5544 heptatonic keys. For each key there are thousands of possible ragas, or a total of many millions of ragas.Most writers, confusing scales and modes, have listed comparatively few of the possible scales. The older writers were further limited by harmonic considerations. Slonimsky's scales and melodic patterns (1947) are mostly ragas, in which, as with Schillinger (1946), symmetry is paramount; Slonimsky's pentatonic and heptatonic scales are actually modes.The inverse of a scale contains the same intervals in reverse order. The complement of a scale contains all the notes of an octave not in the scale itself. A scale may be measured by the total mean‐square deviation of all its intervals.The notation of a heptatonic scale as a harp scale (with seven letter names) agrees with the deviation index. However, the function of notes in the scale may often be expressed by fewer than seven letter names or by two different names for the same note. For the composer, the intensive study of individual scales will be more rewarding than the listing of thousands of keys or millions of ragas.

ISSN:0001-4966    

DOI:10.1121/1.1906553

出版商:Acoustical Society of America    

年代:1949

数据来源: AIP

摘要:

The advent of “slow‐speed” records with fine grooves has resulted in the introduction of 3‐speed phonographs which are unduly complex in operation. A great simplification in their mechanical complexity and in turn in the operating procedure can be obtained if the problem of changing the needle for the various types of records is eliminated. With a universal stylus, the phonograph may be designed with one‐tone arm, one cartridge and the only additional operation required of the user is the selection of the correct speed. Several solutions to the problem of a universal stylus will be presented.

ISSN:0001-4966    

DOI:10.1121/1.1906554

出版商:Acoustical Society of America    

年代:1949

数据来源: AIP

摘要:

A study was made of solo and ensemble performance of the same musical material as related to systems of intonation postulated by certain acoustical, musical, and psychological theories. In particular, it was desired to check earlier findings that unaccompanied performance and listener preferences approximate Pythagorean intonation and to extend a similar line of investigation to ensemble performance.Solo and ensemble performances by 24 well‐trained string quartet players were recorded from which stratified random samples of tones were obtained for frequency analysis. This analysis was made through the use of 16‐mm sound‐on‐film loops with a chromatic stroboscope (Stroboconn).The results confirm earlier findings for unaccompanied melodies and indicate that Pythagorean intonation is also most typical of ensemble performance. This tendency appears to dominate any “cultural conditioning” which may exist for equi‐tempered intonation.

ISSN:0001-4966    

DOI:10.1121/1.1906555

出版商:Acoustical Society of America    

年代:1949

数据来源: AIP

摘要:

A general theory of passive linear electroacoustic transducers for which the surface velocity distribution is independent of the manner of excitation of the transducer is developed and applied to the calculation of important practical parameters of the transducer. A proof of the electroacoustic reciprocity theorem for such transducers is included. Another important theorem, the available acoustic power theorem, which states that the maximum power which can be absorbed by such a transducer from a plane wave sound field is given by the product of the intensity of the wave and the quantity λ2δR/4π where λ is the wave‐length of the wave and δRis the receiving directivity factor of the transducer relative to the direction of incidence of the wave is also proved. The paper concludes with a discussion of the available power efficiency of a transducer and its relation to the threshold pressure of the transducer.

ISSN:0001-4966    

DOI:10.1121/1.1906556

出版商:Acoustical Society of America    

年代:1949

数据来源: AIP

摘要:

The application of sound of known intensity and a frequency of 12.7 kc to a laminar propane‐air flame is found to produce a shift in the stability limits of the flame. The sound alters the flashback limit so that the flame becomes more stable and the blowoff limit so that the flame becomes less stable. It is shown that the normal burning velocity is not changed with the application of sound and that the flow‐velocity profile in the tube is likewise unchanged. From the Lewis and von Elbe theory of flame stabilization it is then concluded that the “penetration distance” must be increased. The “penetration distances” are calculated from the flow‐velocity distribution and the normal burning velocity and, near stoichiometric, are found to increase about 20 percent at the maximum sound intensity of 10 milliwatts/cm2. Sound at a frequency of 18.3 kc is found to affect the blow‐off limit in a similar manner as the lower frequency but no appreciable effect is noted on the flashback limit.It is concluded that these results in combination with further experimental studies should yield useful information about the nature of the “penetration distance” and flame holding in general, but that sound at these low frequencies does not offer a useful tool for studying flame propagation. It is recommended that the effects of sound on practical burners be given careful study because the results presented indicate that the maximum quantity of energy that can be released in a given burner volume may be limited by the sound level in the combustion chamber.

ISSN:0001-4966    

DOI:10.1121/1.1906557

出版商:Acoustical Society of America    

年代:1949

数据来源: AIP

摘要:

An ultrasonic beam (frequency, 1.145 mc/sec.; wave‐length, 0.13 cm) produced in water by a quartz crystal is scattered by various liquid cylindrical obstacles (diameter, 1.3 cm). These obstacles are composed of methyl and amyl alcohols, ethyl alcohol‐H2Osolutions,NaCl‐H2Osolutions, and diethylaniline. They provide a range of values of acoustic impedance, acoustic velocity, and ratio of obstacle diameter to wave‐length. Pressure amplitude distributions are measured over various cross sections of the scattered beam for a fixed position of the obstacles relative to the source. The scattered wave fronts are also obtained. These two types of measurements lead to the conclusion that the scattering is diffractive rather than ray acoustical. Other evidence is given which exhibits the presence of a scattered wave.

ISSN:0001-4966    

DOI:10.1121/1.1906558

出版商:Acoustical Society of America    

年代:1949

数据来源: AIP

摘要:

Pressure distribution in the acoustical field excited by a vibrating circular plate clamped at the edge in an infinite wall is calculated for the points the distance of which from the center of the plate is greater than 10–20 times its radius. For completeness a short survey of the theory of forced vibrations of plates is given in this paper too.

ISSN:0001-4966    

DOI:10.1121/1.1906559

出版商:Acoustical Society of America    

年代:1949

数据来源: AIP

摘要:

The Applied Physics Laboratory of Johns Hopkins University, operating under contract with the Bureau of Ordnance of the U.S. Navy, set up during the war a testing laboratory for ram jet motors at Forest Grove, Maryland, short distance outside of Washington, D. C., in a location surrounded by open country. Postwar building in the neighborhood made it necessary to quiet this installation if operation were to continue at the same location, and the Kellex Corporation undertook design of the revisions. Since very large volumes of air and hot gases had to enter and leave the test cells, it was necessary to design a duct system which offered extremely low resistance to gas flow, but high attenuation to sound. This paper gives a brief description of the resulting construction which has allowed the laboratory continue operation in the midst of a residential community.

ISSN:0001-4966    

DOI:10.1121/1.1906560

出版商:Acoustical Society of America    

年代:1949

数据来源: AIP