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In Reply to: But why? posted by tlyyra on April 19, 2007 at 17:12:27:
Well, hearing ultrasonic frequencies is controversial, to say the least. It takes more than just the signal being present and people being able to detect a difference. What seems to happen is that when when the ultrasonic frequencies can intermodulate with other frequencies in the speaker driver and produce intermodulation distortion (difference tones) in the audible range.-Audio Engineering Society Convention Paper 5401, presented at the 110th Convention, 2001 May 12-15, Amsterdam, The Netherlands:
"Detection threshold for tones above 22 kHz," by Ashihara Kaoru and Kiryu Shogo, National Institute of Advanced Industrial Science and Technology 1-1-4 Umezono Tsukuba, Ibaraki 305-8568, Japan.
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"Opposition brings concord. Out of discord comes the fairest harmony."
------Heraclitus of Ephesis (fl. 504-500 BC), trans. Wheelwright.
Follow Ups:
It seems as if the Oohashi studies are ok in this respect since they have used bi-channel systems with filter set at 26 kHz (170 dB/octave). However, audio systems as they are used in reviews and homes don't have electronic x-overs and multiamping. So, once again, the results obtained in listening tests using such systems are questionable, at best.
I am not at all certain Oohashi was able to remove the IM distortion, although they did make an effort. They say they eliminated the IM between the high frequency content and the lower frequency contentn by using two drivers. But since the IM would be difference tones, the tones in the speaker used for the high frequency content could very well have produced IM distortion products in the audible range. Measurements could have shown whether there were or not. Kaoru and Shogu showed graphs showing very clearly whether the IM products were present or not.
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"Opposition brings concord. Out of discord comes the fairest harmony."
------Heraclitus of Ephesis (fl. 504-500 BC), trans. Wheelwright.
Good research work Pat D
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Richard BassNut Greene
Subjective Audiophile 2007
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