ISSN:0001-4966    

DOI:10.1121/1.1901431

出版商:Acoustical Society of America    

年代:1929

数据来源: AIP

摘要:

The paper reports the results of an experimental study of the Reverberation Method. The assumptions made in the Reverberation Theory are critically examined. The fundamental equationat1 = 9.2Vv log10 4Eaı̣vaffords two independent means of measuring the change produced in the quantityafor a given room, using a source whose acoustic power may be varied in known ratios. Outstanding differences in the experimental results of the two methods, are reported and possible explanations therefor are discussed. Effects of size and shape of test sample, and quality of test tones on measured values of the absorption coefficients are reported.For detailed account of some of the matter reported reference may be made to Journal of the Franklin Institute for March 1929. Later work included experimental verification of a linear relation between the amplitude of vibration of the electrically driven piston source and the magnitude of the driving current.

ISSN:0001-4966    

DOI:10.1121/1.1901863

出版商:Acoustical Society of America    

年代:1929

数据来源: AIP

摘要:

A description is given of the normal vocal tract and the action of the vocal cords in generating sound waves from the steady flow of air from the lungs. For persons whose larynx has been removed the flow of air from the lungs is changed into sound by a device external to the body and this sound is converted into speech by introducing it into the mouth and carrying on the ordinary speech‐producing motions with the lips, tongue, teeth, etc. A description is given of a recently developed vibrating reed type of artificial larynx for accomplishing the above. While using this instrument for producing a sustained vowel the rate of expulsion of air is about 125 cc per second and the excess pressure in the lungs is about .005 atmospheres, giving the rate at which the lungs do work as .06 watts. Using Saccia's measurements of the rate of radiation of acoustic energy from the lips of a speaker it is calculated that of the energy used by the lungs in forcing air through the glottis only about 0.17% is converted into useful acoustic energy.

ISSN:0001-4966    

DOI:10.1121/1.1901866

出版商:Acoustical Society of America    

年代:1929

数据来源: AIP

摘要:

In the acoustical treatment of rooms, an accurate knowledge of sound absorption coefficients is necessary. Test data on Type B Acousti‐Celotex from seven different laboratories is presented showing a variation from .40 to .47 in values obtained by the reverberation method and from .23 to .40 by the “tube” method. The values .23, .40 and .47 were all obtained on the same samples shipped to the different laboratories. The desirability of standardizing test methods is apparent.To determine which absorption values should be used in engineering work, a study was made of a large number of completed installations. A small 512 cycle organ pipe was calibrated for acoustic output both at the University of Illinois and at the Bureau of Standards. The 3A Audiometer was used to determine the amount of noise, if any, in the rooms and it was found possible to correct the measurements for the threshold shift caused by the noise. From the data, 45 installations are selected as typical. Using .47 as the coefficient, the total absorption in each room was calculated. In 24 of the rooms the test absorption was greater than the calculated absorption by an average of 9.7%. In 21 of the rooms the test absorption was less than the calculated absorption by an average of 12.1%.

ISSN:0001-4966    

DOI:10.1121/1.1901868

出版商:Acoustical Society of America    

年代:1929

数据来源: AIP

摘要:

A summary is given of the quantitative effects of loudness, reverberation, noise and the shape of an auditorium upon the hearing of speech in auditoriums. The average loudness of speakers is found to be about 50.7 db in small auditoriums (27,200 cu. ft.) and 45.7 db in large auditoriums (240,000 cu. ft.). The loudness of spech in large auditoriums is therefore at a critically low level, so that slight disturbances from reverberation or noise suffice to make hearing conditions unsatisfactory. The percentage articulation in an auditorium is ascertained by means of the formula,Percentage Articulation = 96k1kτknks, wherek1,kτ,knandksare the reduction factors owing to diminution of loudness, reverberation, noise, and shape of auditorium, respectively. Methods and data are given for determining these reduction factors. A study of the combined effects of loudness and reverberation yields the optimal times of reverberation for the hearing of speech in auditoriums of different sizes. Thus, the optimal time for a room of 25,000 cu. ft. is found to be .80 second. The optimal time increases to .90 second for an auditorium of 100,000 cu. ft., and to 1.00 second for an auditorium of 400,000 cu. ft. It is shown that artificial amplification of speech is imperatively needed in auditoriums larger than 400,000 cu. ft., and is desirable in auditoriums larger than 100,000 cu. ft. A series of curves indicates the probable percentage of speech‐articulation in auditoriums varying in size from 25,000 cu. ft. to 1,600,000 cu. ft. and having times of reverberation between .5 and 8.0 seconds. The results of the investigation make it possible to assign a quantitative rating to the acoustic quality (for the hearing of speech) of any auditorium, or to determine the physical requirements of an auditorium which is to attain a specified degree of excellence.

ISSN:0001-4966    

DOI:10.1121/1.1901869

出版商:Acoustical Society of America    

年代:1929

数据来源: AIP

摘要:

Prof. Wallace Sabine's method of determining reverberation periods was used. Organ pipes in the tabernacle organ served as the source of sound. By opening and closing doors and windows the absorbing power of the building was found to be 630 open window units. The period of reverberation increased from 1.63 seconds for a note of 16 v.p.s. to a maximum of 5.21 seconds for 348 v.p.s. thence decreasing to 0.97 seconds for 8368 v.p.s. The constant of decay of sound, the mean free path, the paramoterk, and the volume of the building were determined by observing the variations produced in the reverberation by variations in the intensity of the sound.The intensity of the sound was determined throughout the building and expressed in terms of the intensity meter from the source. It was found to vary from 100 per cent at near stations to 4.2 per cent at remote distances.Articulation tests showed the percentage of syllables accurately received varied from 39 per cent for normal conversation voice to 59 per cent for preaching voice, to 80 per cent for electrically amplified voice. When the reverberation was reduced from 5 seconds for the empty building to 2.3 seconds when 3100 people were present good hearing increased from 52 per cent to 59 per cent for preaching voice in spite of presence of additional noises caused by audience.

ISSN:0001-4966    

DOI:10.1121/1.1901870

出版商:Acoustical Society of America    

年代:1929

数据来源: AIP

摘要:

The usual method of measuring the period of reverberation with organ pipe and stop watch is uncertain, due to extraneous noises, variation in sensitivity of the ear, and other difficulties. Attempts to determine the period through measurements of the sound intensity level established by a calibrated source were unsuccessful.A new method is here described in which a regular succession of equally timed and constant strength sounds are emitted. At desired instants in the intervals between the emission of sound the intensity is measured. From this data the period of reverberation is determined astp = 6t′/log10 (Eave/E′ave), wheret′ is the time in which the intensity decays fromEavetoE′ave, these three quantities being directly observable.Chief of the advantages listed is the elimination of errors due to variations in the observer's acuity of hearing. The method is also applicable to the measurement of the sound‐absorption coefficients of materials.

ISSN:0001-4966    

DOI:10.1121/1.1901872

出版商:Acoustical Society of America    

年代:1929

数据来源: AIP

摘要:

The paper is chiefly concerned with the important speech power quantities—frequency spectra, distributions of instantaneous, average, syllabic and peak amplitudes, etc.—as they obtain in actual speech for a large range of voices, talking levels, and subject matters. The analysis is not nearly so complete nor so fine‐grained as that which, in principle, can be derived from oscillographic records of individual speech sounds. Its advantage is in the speed with which data can be secured, under widely varying conditions and on a scale which warrants statistical conclusions. Some of the methods in use for measurements of this type are described. These include forms of apparatus developed prmarily for use in telephone plant work, as well as those developed for detailed laboratory investigations. The data discussed are mainly those obtained in the laboratory with an integrator and with a peak meter. The former gives the average value of the instantaneous sound amplitudes; the latter gives the magnitude and frequency of occurrence of the peak values. The distribution of average and peak amplitudes in the frequency spectrum is obtained in addition to their values in the entire sound wave. Illustrative results are given for samples of speech, music and noise.

ISSN:0001-4966    

DOI:10.1121/1.1901875

出版商:Acoustical Society of America    

年代:1929

数据来源: AIP

摘要:

This paper presents some results of a study of the words used in telephone conversations. These show that many words have a much higher relative occurrence in conversation than in written matter, and that conversation in general is characterized by a more intensive use of its commonest words than written matter. Curves are presented showing the number of different words found among a given total number of words, not only in individual conversations but also in samples as high as 10,000 total words. Finally the paper shows the distribution of the fundamental sounds of speech in conversation and shows the differences in the relative occurrence of the speech sounds in conversation as compared with written matter, in nouns as compared with verbs, adjectives, etc., and in the few frequently used words as compared with the many infrequently used words. The results are based on about 80,000 recorded words.

ISSN:0001-4966    

DOI:10.1121/1.1901877

出版商:Acoustical Society of America    

年代:1929

数据来源: AIP

摘要:

This chronograph was developed for use in recording the loudness of blows from piano hammers as an artist is making an Ampico record. It records accurately the velocity of each hammer at the moment it strikes the strings.The chronograph, which is of the spark type, records on either stationary or slowly moving paper. A cylindrical drum with a spiral conductor distributes the time interval sparks at right angles to the motion of the paper.A new method of making visible the spot, where the secondary spark punctures the paper, is described. This method permits the use of a very feeble current. A secondary spark energy sufficient to puncture the paper is all that is needed. The punctured spot may be made visible regardless of its size.A simplified electrical circuit for producing the secondary spark is described.Curves and data are given showing the relationship between the velocity of the hammer and the loudness of the piano tone in sesation units.The chronograph with its auxiliary system of recording feeble sparks is applicable to many fields of scientific investigation.

ISSN:0001-4966    

DOI:10.1121/1.1901879

出版商:Acoustical Society of America    

年代:1929

数据来源: AIP