Tables 146-149 



TABLE 146. — A Fundamental Tone, its Harmonics (Overtones) and the Nearest Tone 

 of the Equal-tempered Scale 



l 93 



Characteristics of Speech, Music, and Noise 



(See Kaye, Nature 128, 253, 1931; Fletcher, Rev. Mod. Phys., 3, 258, 1931) 



Average ear perceives frequencies 20-20,000 cycles/sec Upper limit less with increasing 



age. Ordinarily attention largely restricted to 50-5,000 for speech, 35-7,000 in music 

 Matching of sounds. — Average ear detects 10 per cent difference of energy when two 



notes of medium loudness sound alternately without break; doubled if interval of silence; 



ordinarily 25 per cent holds. 

 Weber-Fechner law. — When sound sensation advances arithmetically, physical intensity 



advances geometrically (Kingsbury). Frequencies, 700-4,000 c/sec, relation between 



loudness and intensity independent of frequency. Lower frequencies, loudness increases 



proportionally more rapidly than intensity. 



TABLE 147.— The Bel and the Decibel 



Bel, Decibel. — One bel is 10-fold increase in power or energy. 

 Intensities differing as r to 1 differ by log r bels. 



Ratio intensities 1 10 100 1,000 10,000 io 13 



Number decibels, 10 log r o 10 20 30 40 130 db 



Least perceptible change in loudness of a sound of medium loudness under various con- 

 ditions = 1 db (0.2 to 9 db according to frequency and loudness). Threshold of audibility 

 taken as zero (see Table 148). Pure sounds of medium frequency: range of audibility be- 

 tween threshold and sensation of "feeling" of the sound about 130 db. 



If intensity levels of two pure sounds is the same,then if each is increased by the same 

 amount of energy they no longer give an equal sensation of tone. Standard for mixed sounds 

 may be taken as a pure note. Frequency about 1000 cycles/sec. Threshold value (zero) = 

 about 1 millidyne/cm 2 . 



TABLE 148. — Loudness Levels of Various Noises 



Source 



Average 

 Distance decibels 

 ft. above 



threshold 



Quiet whisper 5 10 



Quiet garden 30 



Ordinary talk 3 50 



Express train Pullman 60 



Steamship siren . . . 1,500 60 



Busy traffic, N. Y.. . . 72 



Police whistle 15 80 



Lion roaring, Zoo. .18 85 



Note 



6 

 1 



6 

 4 



3 



2 



3 



3 



Source 



Average 

 Distance decibels 

 ft. above 



threshold 



Lindbergh applause.. Street 90 



Pneumatic drill 20 90 



Elevated R.R., N.Y. 20 90 



N. Y. subway Int. 95 



Riveting... 35 95 



Steamship siren 115 95 



Airplane cabin Int. 80-110 



Airplane engine 18 115 



Note 



(1) Davis, Journ. Roy. Aeron. Soc, 1931. (2) Free. (3) Gait. (4) Parkinson, Journ. Acoust. Soc. Amer., 1930- 

 (5) Fletcher. (6) Kaye. 



TABLE 149. — Peak Power in Watts of Musical Instruments (Fortissimo) 



(Sivian, Dunn, White, Journ. Acoust. Soc. Amer., Jan. 1931.) 



Trombone 6 Piccolo 0.08 



Piano 0.4 Flute 0.06 



Trumpet 0.3 Clarinet 



Bass tuba 0.2 



Bass viol 0.16 



Peak powers, fortissimo playing. Orchestra of 75 pieces. Both peak and average powers of orchestra 

 are about 10,000 times such for conversational speech. Violin played as softly as possible, 4 microwatts. 

 Threefold peak power 20,000,000 times this. 



Smithsonian Tables 



75-piece orchestra 70 



Large bass drum 25 



Pipe organ 13 



Snare drum 12 



Cymbals 'o 



French horn 0.05 



Triangle 0.05 



