Physics 2010 HW7
1. To what must the decay variations in Everest figure 7-8 be attributed?
a. Any differences must be attribute to the random nature of the noise signal, everything
else was constant.
2. What assumptions are implied when we speak of a reverberation time?
a. When speaking of a reverberation time it can be assumed the decay is measured as the
source is interrupted. The decays at the modal frequencies are decay rates characteristic
of individual modes not of the room as a whole. Long reverberation time implies low
absorbance while short reverberation time implies high absorbance.
3. What is an “electroacoustically coupled” space
a. An electroacoustically coupled space is what is used to describe the overall reverberant
effect when sound picked up from a studio having one reverberation time is reproduced
in a listening room having a different reverb time. The combined reverb time is greater
than either room alone.
4. What does Everest recommend for the reverb time of a recording studio, as compared to the
living room where the music is likely to be enjoyed?
a. The optimum reverb time for a recording studio
is around half a second depending on volume
(refer to Fig 7-15, Everest 153).
b. The optimum reverberation time for a living
room is about .3 seconds (Everest 154 -155)
5. In artificial reverberation devices…
a. What is the single ingredient of every form of
reverberation device?
i. Delays
b. The introduction of what feature adds to the
“lifelike” character?
i. The return of successive echoes in a
space is the ingredient of natural
reverberation.
6. You want to beef up the bass absorption of your foam absorber, to increase its absorption
around 100 Hz. How far from the wall should you
mount it?
a. A common density for acoustical foam is
2 lb/ft2
b. 100Hz=170/(2*d)1/2
c. (170/100)2/2=d
d. 1.445 inches
7. Briefly explain the physical principles by which porous absorbers absorb sound.
a. Sound energy is dissipated as heat in the interstices of the fibers.
