PrinceGaz wrote:
> Question: what sort of speaker did they use to send sounds in (presumably)
> the 15-30KHz region. Unless they used specialised ultrasonic transducers
> there is little knowing what you were hearing. [Gaz is tempted to mention
> sub-harmonics but thinks that is bull and thinks he is in enough trouble with
> the ongoing Linux thread]. Me thinks their speakers were c**p, or rather
> incapable of reproducing a clean 22KHz or higher signal.
I think that is probably a very silly statement. These are professional doctors
working in
a specialist centre of which there are only a few in the country. Their equipment is
highly specialised and probably very very expensive. We're not talking about some DIY
bloke with a Radio Shack function generator and a couple of 4ohm tweeters, this is
high-specification medical equipment.
> There is a reason any hifi speaker has 2 or 3 (at least) elements-- each can only
> give good reproduction over a limited frequency range. Anyone taking these
> "how high can we hear" tests should ask
> a) what speakers they use
> b) how high they crank up the sound pressure level with frequency
> c) couldn't we all hear a tone of 25KHz if blasted at 150dB
If it was a test done in a HiFi shop or at a local "What HiFi" convention, yes I would
have doubts about te equipment. Perhaps if I explain *why* I have the tests you may
understand a little better.
There's a trait that runs in our family that effects hearing. The ear drum thickens
prematurely, so that by about 40 most men in my family are almost profoundly deaf. Dad
was
lucky enough not to have been effected as badly, although his hearing has gone a bit. I
take a test every 4 years to monitor my hearing which has been found to be quite in
excess
of the average person my age. So far I am pleased to say it looks like my hearing is
not
going to deteriorate much more than average, but they are surprised that my auditory
range
is so wide. They don't use a Hi-Fi speaker at all, but several sets of headphones,
speakers etc. which are designed to reproduce sound within a specific frequency range
to a
very high degree of accuracy.
When I say I go to have my hearing tested, I don't mean I go to the Hi-Fi shop and
listen
to a copy of "Test Signals Greatest Hits", I mean I take a medical test under
controlled
conditions.
--
Magic
Location : Portsmouth, England, UK
Homepage : http://www.mattnet.freeserve.co.uk
EMail : mailto:[EMAIL PROTECTED]
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