whence we see that 
9 7 9) 
Doe = (ODS +IDS)/2. (5) 
or % : 
a 2 2 V/2 
Doe = {(on, + ID; v2 | : (6) 
Putting in the applicable numbers tor NRAP, we find it: effective piston diameter 
to be 
? ? 1/2 
Doe = [22 ar, 1.252)/2| 
= 11.631 inches. (7) 
= 
2. Hunter (ref B1) gives the power output formula for a small circular piston generating 
low frequency sound as 
P = 213 (p/c)f4 (A-s)-, (8) 
where 
P = average radiated acoustic power In ergs per second 
E % 9 
p = water density in g/cm? 
c¢ = velocity of sound in cm/s 
f = frequency in Hz 
: : ? 
A = piston area in cm7 
s = amplitude of piston motion in cm. 
For two pistens operating in phase in the breathing mode in a projector whose 
dimension is small compared to the wavelength of the output sound, as in NRAP, the A-s 
products for the two pistons must be added before using the result in equation (8). 
3}, Inserting the numbers for the NRAP operating at Lake Pend Oreille into equation (8), 
we get 
P = 29 1/1.435(10)° | (1594 | (n/4) (11.6317 2.547) (0.391/2) (2.54) (2)]? (9) 
1.0139( 10)! ergs per second 
BY Acoustics, by JL Hunter, Prentice Hall, 1957, p 147. 
1.0139 watts. 
