Re: In a loud club, will I be able to hear a spoken voice if I plug my ears?

Here's some facts to consider and a hypothesis:

First, there's a psychoacoustic effect called masking, which allows loud 
noises to "drown out" quieter ones, especially those that are near in 
frequency.  See http://is.rice
.edu/~welsh/elec431/psychoAcoustic.html
for an introduction to auditory masking.  As the web page discusses, the 
masking effect is dependent on frequency, amplitude, and time separation.

By the way, masking is the principle that allows audio data compression to 
work with minimal perceived impact to sound quality.  For example, the 
popular MP3 coding used to store music and audio uses so-
called "perceptual coding" to throw away relatively unotticeable parts of 
the instantaneous audio spectrum, reataing only data representing that 
part of the audio spectrum which dominates the sensation of hearing for 
the moment. 

Thus, in a dance club setting, the loud noise from the band or audio 
system "drowns out" conversation from people nearby.  Ever notice that 
when the music stops while you're conversing with someone, chances are 
you've been shouting?

Second, I'd venture that the attenuation caused by plugging your ears is 
frequency dependent.  Here's some data on ear plugs, showing clearly that 
high-frequency sounds are attentuated substantially more than lower 
frequency sounds. http://www.aearo.c
om/pdf/hearingcons/earlog13.pdf

My hypothesis: plugging your ears caused a differential attenuation of the 
dance club's ambient music and crowd noises, with more attenuation at 
frequencies above the speech band than in the speech band (most human 
voice energy is concentrated in a fairly narrow band, as compared to the 
broadband spectrum of noise and music.  That's why voice through a 
telephone sounds OK, but music sounds terrible.)  The music/noise was 
causing masking of speech; plugging your ears attenuated your girlfriend's 
voice, but it attenuated EVEN MORE of the much louder amplitude 
music/noise spectrum.  In other words, the total power reduction of the 
ambient music/noise was greater than the power reduction of your 
girlfriend's voice, because it had greater effect at the higher 
frequencies, where the ambient music/noise spectrum has energy, but your 
girlfriend's voice doesn't.  By differentially reducing the sound power 
reaching your eardrums of the dance club's ambient music/noise as compared 
to your girlfriend's voice, the masking effect of the dance club's 
music/noise was reduced, making your girlfriend's voice more easily 
perceivable.  

Of course, that's just my opinion, I could be wrong :-)

Dr. Steve