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Feedback: Where did the 1 kHz tone come from?

Hi list

Many thanks to all those who responded to my question.  For those
interested, here is a summary of the feedback I had:

(1) The phenomenon is well documented.
(2) The audible f2-f1 DP is unlikely to arise from within the auditory
system and is measurable in the room using standard techniques.
(3) The most likely sources are (a) transducer distortion and/or (b)
non-linearities within the air, producing a DP with a highly position
specific amplitude.  The latter source has been exploited in commerical
audio equipment.  The impression I got is that the SPL of the primaries
required to produce a significant 1 kHz DP is much higher than implied
in the desciption my colleague here originally brought to my attention,
which is partly why we initially dismissed the transducer distortion.  I
had no idea the air was sufficiently non-linear at high SPLs to produce
audible intermodulation distortion!  Many thanks for all the feedback.

Best wishes


Daniel Rowan MSc
Research Student
Institute of Sound and Vibration Research
University of Southampton
University Road
Southampton SO17 1BJ
England, UK
Tel: 023 80594968
Email: dr@isvr.soton.ac.uk