Re: ultrasonic hearing via bone conduction

[Lars Bramsløw <lab@xxxxxxxxx>]

Hi Rob,

I think the audio equipment manufacturers are trying to sell us something we
don't need with 96 and 192 kHz sampling frequency.  When it comes to
air-conducted sound I haven't seen a blind study where subjects could
discriminate a 20 kHz and a 40 kHz bandlimited signal.  

In hearing aids, on the contrary, we are not trying to sell something not
needed :-)  For air-conducted hearing aids, we see little reason to go
beyond 10 kHz, which is probably going to be the limit for some time.  After
all, most losses tend to increase with frequency, and we don't have
audiometric data beyond 8 kHz from ordinary clinical practice. The earmould
and real-ear characteristics is also very difficult to control at these
small wavelenghts.

There is another related issue in hearing aids and that is to protect
against ultrsonic sounds from movement detectors, e.g. burglar alarms,
automatic doors etc. These devices produce large SPL's starting from say 50
kHz, and this can cause saturation and intermodulation in the hearing aid
front-end, which is audible.

The boneconduction aspect is interesting but I still wonder if the
audibility is due to intermodulation or off-frequency listening rather than
'ordinary' hearing.  If anyone has any scientific papers on the topic,
please share them with us.

Regards

Lars



Lars Bramsløw
 
Audiology
Oticon A/S
Kongebakken 9
DK-2765 Smørum
Denmark
 
+45 39 13 85 42 Direct
+45 39 17 71 00 Main
lab@xxxxxxxxx
http://www.oticon.com


-----Original Message-----
From: AUDITORY Research in Auditory Perception
[mailto:AUDITORY@xxxxxxxxxxxxxxx] On Behalf Of Maher, Rob
Sent: 23. november 2005 23:21
To: AUDITORY@xxxxxxxxxxxxxxx
Subject: ultrasonic hearing via bone conduction

I recently received a query from a colleague about bone-conducted ultrasonic
hearing in humans.  I also found a prior thread from a couple years ago
about ultrasonic perception here in the AUDITORY list.  Based on the
published literature it seems clear that humans can get a hearing sensation
from ultrasonic vibrations coupled to bone.

Anyone able to share their experience working with this phenomenon?  Any
commercial hearing aids in this realm?

It is also interesting that some audio equipment manufacturers are starting
to spec their loudspeakers into the ultrasonic range based on these
findings.

Thank you,
Rob Maher


* * *

A few relevant references are:

Lenhardt, Skellett, Wang, and Clarke, A.M., "Human ultrasonic speech
perception," Science 253 (1991) 82-85

And more recently:
"Where'd you get those ultrasonic peepers?"
http://www.acoustics.org/press/150th/Lenhardt.html 

Fujimoto, Nakagawa, and Tonoike, "Nonlinear explanation for bone-conducted
ultrasonic hearing," Hearing Research 204 (2005) 210-215
http://www.h6.dion.ne.jp/~fff/documents/pdf/heares.pdf