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Deep Canal Fittings

Angelo Campanella acampane at postbox.acs.ohio-state.edu
Sat Jul 1 17:00:03 EST 1995

In article <3sp8ne$ct3 at lastactionhero.rs.itd.umich.edu> mstaben at umich.edu (Matthew S. Staben) writes:
>>In a later posting you noted that you have shortened the canals for a
>>matter of comfort.  I've found that I can simply narrow the end of the
>>CIC slightly by grinding and buffing.  I have solved the discomfort and
>>seemingly had no adverse results such as feedback.

What I have found, in wearing earplugs for noisy environments (small 
airplane cockpits, etc.. 90-100 dBA, chiefly low frequency noise) is that 
earplug fit, which I am comparing to hearing aid fit, is very variable.  
If the plug is too firm, then jaw, chewing and speaking movements 
invariably encompass a range where firm plugs will unseat, breaking the 
seal, or hurt, adding to fatigue and general disgust in usage.  The best 
earplugs are quite compliant, allowing for 20-30% in size from one 
jaw extreme to another (a subjective estimate on my part).  The worst 
earplugs are those that are firm and especially cylindrical.  I don't 
think very many ear canals are circular.. rather they are probably quite 
eliptical.  Furthermore, I don't think that many canals are straight, but 
rather they are arced..

One of the more useless earplugs I have ever had was a pair that was 
especially maolded for me by an audiologist.  If I sat with my mouth 
closed (a rare event!), they would seal.  But as soon as I talked or 
especially opened my mouth widely, they would unseat.  I never used them 
in practice.  They would bend, but they would not expand or shrink in 
crossectional area as is desparately needed to maintain a good sound seal.

Now, considering the above enviroment, (and I have not been following your 
dialogue very closely... so forgive me if I have misinterpreted the problem 
extant) use of a long and deep cylinder, looking for a firmer interior 
base is quite likely to cause discomfort if the full dynamic range of 
flesh motion is not accounted for.  Your beveling of corners and length 
trimming actions seem to properly (to me) address this dynamic problem.  
Fortunately, the closeness of fit for hearing aids need not be as tight as 
that needed for high attenuation earplugs, so there is good hope that you 
can achieve your goal..

I envision a standard itinerary of jaw movements and maybe spoken words that 
will allow you to survey the fit.. and - much as a dentist trims the seat of 
fillings and caps while asking you to do specific jaw clenching actions - 
you will be able to 'home in' on the best dynamic fit .. one that the user 
can enjoy far into the future..


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