Electronics > Beginners

Why is my subwoofer demodulating the treble?

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tggzzz:

--- Quote from: testtube44 on June 03, 2020, 01:16:22 pm ---
--- Quote from: magic on June 03, 2020, 09:01:27 am ---No expert but I imagine that there ought to be a crossover somewhere, to keep treble out of the sub. Speaker transducers as such are nonlinear so I think they shouldn't even be allowed opportunity to create such problems in the first place :-//

--- End quote ---
I think it's definitely the amplifier. If the speaker was causing distortion it would be obvious, that only requires a single tone to sound bad, this takes 2. I've also had this thing accept microwave frequencies and produce pulsing sounds. That was when I held the wifi card of an xbox close to the headphone jack bypass and volume knob, perhaps more evidence that it's something "nonlinear".

--- End quote ---

That is a completely different non-linear effect: EMI/EMC.

The front-end semiconductor junctions are rectifying the RF power, and that causes a DC voltage shift. If the variations in RF power occur at audio frequencies, the DC shift will change at audio frequencies, and will be amplified.

Classic example is with a GSM cellphone. When a call starts you hear the ba-da-dah ba-da-dah ba-da-dah (call setup messaging) followed by the brrrrrrrrrr (voice call) of the 217Hz TDM signal.

The only solution is to prevent the RF entering the front end, which requires EMI/EMC shielding/filtering.

testtube44:
clearly they didnt rf shield it either, but is that suprising considering the obvious quality problems elsewhere in this mess? just the other day my iphone was creating audible interference from 4ft away!

tggzzz:

--- Quote from: testtube44 on May 28, 2024, 11:20:25 am ---clearly they didnt rf shield it either, but is that suprising considering the obvious quality problems elsewhere in this mess? just the other day my iphone was creating audible interference from 4ft away!

--- End quote ---

Consider whether it is worth removing the input cables, and seeing whether the EMI/EMC persists. If the EMI/EMC is no longer present, then it may be entering the cables, in which case external filtering may help.

I wouldn't hold my breath, though!

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