<html> Ric, It is hard to make a convincing demonstration using ultrasonic tones.  The problem is that you are producing relatively low frequency resultant tones using very low-energy, high frequency tones.  The acoustic power of a 20,000 Hz tone and a 20500 Hz tone combined together would be very small, even if the volume is 100 db.  The resulting 500 Hz tone would be very weak.  If you drive the high frequency pitches loud enough to make the resultant tone more audible, you might end up with only a splitting headache and burned out tweeters! In organ pipes, they have large pipes moving a lot of air on, say, 32hz and 48hz, and you will hear (or feel) a 16 Hz. tone.  The church in San Diego I used to go to had a great organ, and it did this so well that the building would shake at 16 hz when playing the resultant low C (C0 in piano terminology). Resultant tones are created, very simply, by the beating of the two pitches. The variation in volume we hear as a beat becomes a pulse, then once it passes 20hz or so we begin to hear it as a separate pitch. You sometimes can hear resultants in tenor notes of the piano if you play two notes together.  The difference can be heard as a deep pitch that, if you try, you can identify as you work up and down the scale.  You have to listen for it. The question as to whether it is really a vibration in the air or not becomes rhetorical - you can hear it, you can measure it, so it is there.  It is the same as asking if strings at 440 and 441 are creating a beat or not - that beat is a 1 hz pitch, it is just so slow that we hear it as a variation in loudness.  That variation in loudness, if it happens fast enough, is perceived as a tone by our ear. Back to your original question, Ric. I made a recording for you, and you can hear the resultant tone.  I made a wav file of 20K and 20.5K tones, one in each ear.  Then I combined them into a single mono file.  If you play it in good headphones and turn up the volume loud, you can just hear the 500hz tone as a pitch. I made a zipped copy of the mono recording with the resultant tone.  Anyone who wants a copy, please write to me off-list at this address and I will send the files to you privately.  I don't want to clog the list up with an attachment for all the people with dial-up connections that don't want the file.  In zipped format it is about 700K.  After it is unzipped, it played in Windows Media player fine. Don Mannino RPT At 10:24 PM 12/2/2002 -0600, you wrote: <blockquote type=cite class=cite cite>----- Original Message ----- From: Clyde Hollinger <cedel@supernet.com> To: Pianotech <pianotech@ptg.org> Sent: Monday, December 02, 2002 6:06 AM Subject: Re: audible resultant from two supersonic frequencies? > Ric, > > I am confused by your question.  First, do you really mean >supersonic,  defined as greater than the speed of sound waves?  I >think you may mean ultrasound, defined as sound with a frequency >greater than 20,000 Hz, which is approximately the upper limit of >human hearing. Clyde,     You had me doubting for a second, thanks for the point out.     I am using the definition as given by Webster's 3rd New International. "Supersonic 1: having a frequency above the audibility range of the human ear or greaterh than about 20,000 cycles per second --- used of waves and vibrations; compare infrasonic, sonic. "     Yes "supersonic flight" is definition number two.  And yes then I mean "ultrasound" since I see it is defined as. ":a wave phenomenon of the same physical nature as sound but with frequencies above the range of human hearing--- also called supersound".    There is also "ultrasonics" ":the science of ultrasonic phenomena : supersonic " >What > would be the point of experimenting with sounds we can't hear? The question is,  are there AUDIBLE resultants, which is a sound we CAN HEAR, that is produced from two frequencies we can't hear such as 20,440 - 20,000 hz which gives on paper 440 hz  or A440 which certainly we can hear.   An experiment has to be conducted to determine if this is true.   I am wondering if this has ever been done, and if not how might it be done?   I need two audio frequency generators?   Can the computer give hz over 20,000? How bout tune lab? Would I need two?     ---rm   (the "r" stands for 'ric' and the "m" stands for "M") _______________________________________________ pianotech list info: <a href="https://www.moypiano.com/resources/#archives" eudora="autourl">https://www.moypiano.com/resources/#archives</a> </blockquote></html>