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Re: Insert earphones for neurophysiology


A quick calculation to find the wavelength of 20 kHz in Air shows :

lambda= v/f = 331/20e3 = 16.5 mm

This is a wavelength of 1.65 cm ... as the diaphragm is modulating with 
maximum velocity, we are most probably interested in the half wavelength 
: lambda = 8.3 mm

The 20 kHz notch must have something to do with the size of the earphone 
... it is quite possible that it is very difficult to correct for this 
problem ... although that statememnt is not proven by any means.

I remember that one of the companies I was working for brought out 
powered monitors (speakers) ... they chose tweeters which were embedded 
in the centre of the mids ... they had the same proble, but with a 
lower frequency of about 10 or 15 kHz (as lambda was larger).


On Tue, Dec 05, 2006 at 02:24:13PM -0500, Ewan A. Macpherson wrote:
> On 5 Dec 2006 at 12:58, Dan Tollin wrote:
> > Has anybody out there tried to use some of the new insert earphones for
> > auditory neurophysiology studies?  I am thinking of phones such as the
> > Etymotic ER-4 (or 6) or the Shure E series.
> A couple of years ago, I did quick, free-field measurements (with a 
> reference mic a couple of inches from the earphone) of the transfer 
> functions of the ER-4s and one of the Shure E models. They both seemed 
> to have a very deep notch at around 20 kHz, so perhaps not so good for 
> cats etc.
> --
> Ewan Macpherson, Ph.D.  <emacpher@xxxxxxxxx>
> Research Investigator, Central Systems Laboratory
> Kresge Hearing Research Institute, U. Mich.
> http://www-personal.umich.edu/~emacpher


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