I have made an ultrasonic pest repeller based 555 IC(it has a volume for changing the freq).
As you know these devices work with ultrasonic sensors or tweeters,
but I connected the output of 555 via a capacitor into a common 4 or 8 ohm loudspeaker; just to see what will happen(I knew that the diaphragm is not suitable for ultrasonic frequencies),
I had an audible sound(like whistel) at ultrasonic frequencies too!
Can anybody explains the reason?
Ok, the diaphragm is not suitable, but why any sound at that freq???!
If your circuit has an adjustable frequency then what frequency was it? Maybe it was an audible frequency, not ultrasonic.
Why don't you attach the schematic of your circuit so we can calculate the frequency of the 555 oscillator, check to see if it has a supply bypass capacitor and to see if the 555 is overloaded by the high current in the speaker.
If your circuit has an adjustable frequency then what frequency was it? Maybe it was an audible frequency, not ultrasonic.
Why don't you attach the schematic of your circuit so we can calculate the frequency of the 555 oscillator, check to see if it has a supply bypass capacitor and to see if the 555 is overloaded by the high current in the speaker.
I'm suspecting them even more after reading **broken link removed**.
An integer submultiple or fraction of a FUNDAMENTAL. Whereas the HARMONIC SERIES consists of integer multiples of the fundamental, the subharmonic series consists of pitches related to the fundamental by ratios: 1/2, 1/3, 1/4, 1/5, 1/6, ...
Subharmonics do not normally occur in natural sounds, although the subharmonic f/2 may be generated by the cone of a LOUDSPEAKER.
You are probably right, on second thoughts sub-harmonics are unlikely to be the cause because the 1/2 harmonic of the frequency range is still ultrasonic.