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PHSJason
03-01-2005, 09:39 PM
We have a job where we specced in in-ceiling speakers for the side speakers in a 7.1 system due to room layout. We are using the Sonance SRS-1 dipole surround speakers (http://www.sonance.com/subs/product_details_specs.php?product_id=313) and due to budget reasons, we are not using back boxes. When we arrived today to start the pre-wire, we found that the electricians had run all the main home-runs right across where the speaker goes. We have a choice of moving the speakers higher into the ceiling to keep them away from the line voltage, or we can keep the locations and try to shield them.
1) how much shielding do back boxes made out of 5/8" MDF provide?
2) is there an available cl rated product that we can use to shield the speaker locations from interferance?
3) is there a cost-effective version of product #2?
4) realistically, has anyone experienced ac hum in in-cieling/wall(passive) speakers from the speakers being in close proximity to ac lines?

We are trying to have this system buttoned up by friday. I took some pictures, but haven't up-loaded them yet.

Jason

djnorm
03-01-2005, 10:25 PM
I've only had problems with BX - Armored Cable. A couple of times, we installed a speaker in contact with BX, and had BAD noises coming out of them... It usually touched some solder point on the crossover... We put foam pipe insulation over the BX...

Sorry for the non-answer... :wink:

Shadowman68
03-01-2005, 11:01 PM
Ihad a similar circumstance. I went into a job blind. Didnt do the prewire, or the trim. He wanted some his inceiling speakers installed. Once I had the first hole cut out. I notice a run of 14/2 down the stud about 3 inches away from the speaker hole and headed for the pot light about 2 feet away. Not having anything directly on hand, I installed the speaker as is and fired up the system, It sounded fine until you turned the light on, then there was a very audible hum. The next day after making a few phone calls I headed to the hardware store and bought myself a bicycle inner tube. I cut through the tube to make it a length, then cut a slit down the length and wrapped the rubber around the lumex. It made its way around about 3 times and made a nice sheath. I wrapped it heavily in black tape and popped the speaker back in. After firing the system back up again, I could not hear the hum anymore. not to say that it got rid of the problem entirely, but the hum was not audible. At least to my ears anyway.
So now I always carry a car inner tube in my truck. When ever I have to cross a 110 or 240 or cannot avoid being within 16 inches of it in a stud bay or floor joist I wrap the power in rubber tubing.
Seems to work for me.

LarryFine
03-01-2005, 11:38 PM
Jason,

1) None.
2, 3, & 4) There should be no interference, as speaker signals are of high-enough current that induced noise should still be inaudible. Just don't bundle the speaker wire with the power wires.



Shadow,

The rubber should have had zero effect. The difference must have been a result of how you moved the power wire. However, if it continues to work for you, don't complain; it's cheap enough.

Shadowman68
03-02-2005, 12:16 AM
Hmm better to be lucky than good sometimes.

PHSJason
03-02-2005, 08:41 AM
Larry,

The speaker wires will be away from the line voltage. I am woried about the speaker itself sitting 1" from a dozen runs of 12-2/3 etc. Can the 110 produce enoug EMI to cause the speaker to hum?

Jason

LarryFine
03-02-2005, 12:31 PM
Shouldn't, although extreme currents could radiate a lot of magnetism. By extreme, I mean hundreds of amps.

Crazyone
09-12-2005, 10:01 PM
Depends alot of the loads on those circuits as well. Usually the inducted noise is caused by parallel runs with the speakers cable not the 120 volts stuff crossing over the speakers. What reciever or equipment are you using?

Edit Larry covered my answer before me =)..

Brandon