At your own risk. High intensity sound can irreversibly damage hearing.
Needed for this experiment:
2 sinewave oscillators each driving a tweeter in the same room.
This experiment was done on around 1995 at Napier University - Edinburgh. It can't be recalled what the 2 frequencies were. But it should work with many or any combinations.
When one generator is emitting in the room an adult with good hearing will hear up to about 16KHz.
The hypothesis is that if 25KHz and 26KHz are input to a non linear system then not only harmonics are produced by intermodulation tones such as 26KHz-25KHz=1KHz.
These are also called Tartini tones. Tartini was one of the fist who observed them on the violin.
Since the ear mechanism is non linear if the ultrasonic frequencies are high enough in intensity, the non linear byproducts should be heard.
And this is what happened.
It was not loud but a frequency inside the audible spectrum could be heard.
The experiment should not be difficult to be repeated but caution should be exercised for ear protection.
References:
The definition of linear systems, superposition principle or f(x1)+f(x2)=f(x1+x2) which rarely if ever happens on nature which is non linear. Usually f(x1+x2) give additional multiple combinations of f(x1) and f(x2).
Radio Engineering - Terman - McGraw Hill
Tartini tones - Wikipedia
Needed for this experiment:
2 sinewave oscillators each driving a tweeter in the same room.
This experiment was done on around 1995 at Napier University - Edinburgh. It can't be recalled what the 2 frequencies were. But it should work with many or any combinations.
When one generator is emitting in the room an adult with good hearing will hear up to about 16KHz.
The hypothesis is that if 25KHz and 26KHz are input to a non linear system then not only harmonics are produced by intermodulation tones such as 26KHz-25KHz=1KHz.
These are also called Tartini tones. Tartini was one of the fist who observed them on the violin.
Since the ear mechanism is non linear if the ultrasonic frequencies are high enough in intensity, the non linear byproducts should be heard.
And this is what happened.
It was not loud but a frequency inside the audible spectrum could be heard.
The experiment should not be difficult to be repeated but caution should be exercised for ear protection.
References:
The definition of linear systems, superposition principle or f(x1)+f(x2)=f(x1+x2) which rarely if ever happens on nature which is non linear. Usually f(x1+x2) give additional multiple combinations of f(x1) and f(x2).
Radio Engineering - Terman - McGraw Hill
Tartini tones - Wikipedia
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