Interference on Speakers

[TechSupp]

Problem 1:

Got a Smartboard installed with a separate speaker mounet either side at the top. Got a problem now that through the speaker can be heard music (had this before in another classroom where it was a taxi firm we heard!) not that you are not supposed to nhear music through a speaker but this is when none is being played via the PC! How can I stop or cut down this problem? Should I use one of those ferrite rings on the cable or just try and re route the cable (difficult as there is not much spare).

 

Problem 2:

Similar thing but this time its a crackle etc comming from the speakers when the room hearter kicks in or the lights are switched on. Was OK untill Xmas when the sparkies added some extra sockets to the system but apparently not on the same ring. They suggest its to do with the eddy currents and "nowt to do with our work, we've checked it!"...just coincidence then!

 

My answer was it must be the flux capacitance then captain...didn't help much but it made me feel better! Once again any ideas for a solution?

[smadison]

I ran into this before. Try using the speakers with a laptop with and without the power pack on. If you get feedback with the power pack plugged in and not when it is running off the laptop battery check the grounding on your speakers.

[Andrew_C]

It is more likely that the interference is "getting in" through the signal cables. If the screening is poor, or connectors corroded. That said, if the speaker cables are just the right length they may be acting as a tuned aerial if the amplifier is of poor design.

 

You could try a the ferrite, or change the cable length. If you can work out which radio station, you may find that the existing cable is 1/2, 1/4 or some fraction of the wavelength that they transmit on.

 

It will probably be an @rse to cure. New amplifier may be the easiest route. Grounding of speakers is a red-herring.

[Azhibberd]

I ran into this before. Try using the speakers with a laptop with and without the power pack on. If you get feedback with the power pack plugged in and not when it is running off the laptop battery check the grounding on your speakers.

 

Strangely enough i ran into the same problem around 3 months ago really threw me of but sorted it with a replacement power supply.

 

But ye "Problem 2:" try just getting an extension lead and putting them into another mains ring, although also try changing your input cables I've seen interference been picked up by really cheap cables.