Re: ear defenders/sound attenuation

[Mike Ravicz <Mike_Ravicz@xxxxxxxxxxxxxxxx>]

Hello Gerry,

It's been a few years since I've looked at this, but...  My  
recollection is that the performance among inexpensive commercial  
dielectric earmuffs/ear defenders with both large and small earcups  
is all pretty similar at moderate and high frequencies (above 500 Hz  
or so) but that earmuffs with smaller earcups were worse at low  
frequencies: 2-5 dB less attenuation at a few hundred Hz.  By looking  
in a handful of industrial and laboratory supply catalogues we found  
a wide variety of choices - maybe 12-15 different models.  Such  
catalogues usually give just a frequency-average NRR value, but a  
little poking around on the Web can usually provide attenuations at  
different frequencies.

Keep in mind that anything to disrupt the seal between the earmuff  
cushion and the subject's skin will degrade performance (e.g., hair,  
glasses, prominent jaw, etc.).  Some people have looked at heavier  
gel cushions - I think they provide more attenuation (and perhaps a  
better seal) at low freqs.
	- Mike Ravicz

Mike Ravicz, Eaton-Peabody Lab., Mass. Eye & Ear Inf., Boston MA  
02114 USA
+1 (617) 573-5591; FAX +1 (617) 720-4408; mike_ravicz@xxxxxxxxxxxxxxxx
"Are you going to come quietly, or do I have to use earplugs?" -  
Spike Mulligan