Page 55 - Master Handbook of Acoustics
P. 55
Example 4 Line Amplifier Output Voltage
A line amplifier has an input impedance of 600 Ω and output impedance of 600 Ω. It has a gain of
37 dB. With an input of 0.2 V, what is the output voltage?
Example 5 General-Purpose Amplifier Gain
An amplifier has a bridging input impedance of 10,000 Ω and an output impedance of 600 Ω. With a
50-mV input, an output of 1.5 V is observed. What is the voltage gain of the amplifier?
It must be noted that this is not a power-level gain because of the differences in impedance.
However, a calculation of voltage gain may serve a practical purpose in certain cases.
Example 6 Concert Hall Calculations
A seat in a concert hall is 84 ft from the tympani. The tympanist strikes a single note. The sound-
pressure level of the direct sound of the note at the seat is measured to be 55 dB. The first reflection
from the nearest sidewall arrives at the seat 105 msec after the arrival of the direct sound. (A) How
far does the reflection travel to reach the seat? (B) What is the SPL of the reflection at the seat,
assuming perfect reflection at the wall? (C) How long will the reflection be delayed after arrival of
the direct sound at the seat?
(A)
(B) First, the level L, 1 ft from the tympani, must be estimated:
