Tuesday, October 13, 2009

HSS Speakers - A New Tool for our Arsenal?

This is not a review of an article, it is a summary of a white paper on a new technology called HyperSonic Sound developed by Elwood G. Norris. After the summary you will find my thoughts on how this technology might be useful to music+brain people like us. I'd like to hear your thoughts as well.


HSS speakers emit ultrasonic waves at frequencies around 200 kHz which is far beyond the range of human hearing (also beyond the range of dogs and cats). Unlike conventional speakers, these ultrasonic waves travel through the air as a highly focused beam of energy (i.e. a "column" of sound) over relatively long distances (over 200 meters!).

To create sound we can hear, HSS speakers use the principle of combination tones. Combination tones are the result of interference between two waves of different frequencies. These 'new' tones are equal to the sum and difference of the two orginial tones. For example, a 2000 Hz sine wave and a 1800 Hz sine wave played simultaneously will result in two combination tones: 200 Hz and 3800 Hz. In HSS technology, the two original waves are very high (e.g. 200,000 Hz and 200,100) but one of the combination tones is in the audible range (in this case, 100 Hz). Using this technique, HSS speakers are able to emit audible sound through ultrasonic carrier waves.

Some of the benefits of HSS:

1) Ultrasonic frequencies are of very high energy so sound can be transmitted over very long distances.

2) HSS speakers use piezoelectric transducers instead of magnets. They can be very small and cause no electromagnetic interference.

3) Sound is emitted from a single point source. There is no distortion in sound caused by the typical of multiple speaker setup.

4) The beam of sound from HSS speakers can be highly focused. This means that a person standing 200 yards away can hear the music you are transmitting as clearly as if they were wearing headphones. Not only that, their friend standing 2 ft away from them hears nothing!

5) HSS have an incredible frequency response - from below 10 Hz to 30 kHz at up to 120 dB!

I can immediately think of a few ways that HSS could be useful to neuroscientists and music+brain people:

1) They could be used at the lab at Baycrest since HSS speakers use no magnets.

2) HSS provides a compact way to deliver very low frequency sounds at high SPL. You may not need a chair with transducers, or a giant speaker system with big subwoofers, only tiny speakers with a BIG punch. I imagine an HSS speaker moving its focused beam of low frequency sound over your body would have a similar effect as Lee's chair.

3) Studies could be done using only 'pure' sound. With normal speakers, the room itself has an effect on the sound (reverb and delay). Since HSS can be so tightly focused, the effects of the room on sound would be minimal (very little reverb or delay). Headphones also present a problem since they distort the ear. With HSS, headphones are unnecessary.

I would like to get my hands on some HSS speakers, to fully explore their possibilities. They are just becoming available on the market starting at over $1000.

Anyone have any other ideas for how we could use these speakers?

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