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Topic:
70v speaker system and network crosstalk
This thread has 7 replies. Displaying all posts.
Post 1 made on Tuesday October 15, 2013 at 17:08
joebernardo
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I recently installed a 70v speaker system in a newly constructed office space. I am also installing cat 6 wiring for 150 desks at the same lication. While completing the data wiring I was using a tone generator and an inductive amplifier to find an unmarked cat 6 wire when I started hearing the music through the toning speaker... I am obviously worried about this because we should not have interference on the data network. I used shielded cable for the speaker systen install and don't understand why there is stray voltage in the data lines. In addition I made sure not to lay the speaker wires near the data wires. One thing i am concerned about is the fact that i have volume controls in the walls where wires may be near eachother. By reading through this forum I found something about the drain wire on the shielded cable which I did not use. I am going to try to hook that up to ground and see if that helps . In the meantime What would cause this? What are possible solutions? Does it even matter considering data runs at different mhz ? Help
Post 2 made on Tuesday October 15, 2013 at 19:46
highfigh
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Shielding works best when the shield is grounded correctly but it's usually done on low level signal-carrying cabling.
My mechanic told me, "I couldn't repair your brakes, so I made your horn louder."
Post 3 made on Tuesday October 15, 2013 at 22:59
Ernie Gilman
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You'll hear the music not only when you're near the hot lead of a 70V signal, but if the wire is small in gauge (say 18 or smaller) you might even hear the music on the ground because of the resistance of the wire. Ask if you need an explanation.

It's not good practice to run data and audio next to one another, but mostly low level audio and data, because data can leak into the audio cable. That's the reverse of the problem you fear.

You're not likely to have a data problem. See, you're not measuring for audio on the data wire when the data wire is connected. Connecting adjacent wires to ground or to the equipment they normally go to will greatly reduce the amount of music you hear when you're near the speaker wires. Toners spray an electric field all over the place and nearby grounding lessens it.
A good answer is easier with a clear question giving the make and model of everything.
"The biggest problem in communication is the illusion that it has taken place." -- G. “Bernie” Shaw
Post 4 made on Wednesday October 16, 2013 at 02:29
pilgram
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I wouldn't worry about it.

My toner has picked up music playing on return air vents that were metal all of the way back to the unit.

I don't have an absolute reason why but I do know that it has never effected my LAN lines in an installation even though I could "hear music" when toning them out.
Every day is a good day.......some are just better than others!

Proud to say that my property is protected by a high speed wireless device!
Post 5 made on Wednesday October 16, 2013 at 23:48
DeuceTrinal
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Unshielded (shield needs to be grounded at the amp to be effective) 70V speaker wire can radiate signal a toner wand on high volume can pick up for 3-5 feet. How far away were you from speaker wiring? I've never seen an issue with this if normal best practices (don't run speaker wire and data in the same bundle) are followed.
More zip ties!
Post 6 made on Thursday October 17, 2013 at 09:09
Ernie Gilman
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A toner wand is specifically designed to pick up and amplify very small radiated signals. All the data wiring we use is specifically designed not to pick up very small radiated signals, or to be more precise to pick them up in a way that results in them being picked up in a common mode way, which good data circuitry does not respond to. Line or mic level cabling is also designed to reject such noise. Speaker level wiring rejects such noise by its low impedance and high voltage characteristics. You're worried about signal characteristics that the wand exploits and that everything else is built to reject. Don't.
A good answer is easier with a clear question giving the make and model of everything.
"The biggest problem in communication is the illusion that it has taken place." -- G. “Bernie” Shaw
Post 7 made on Thursday October 17, 2013 at 09:18
jimstolz76
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My favorite story like this is from a house right off of I-95 that has a major trunk of underground communication lines right behind the community. Every single house would hear a radio station through their phones, through speakers, through everything. You could walk around the house with your toner wand and clearly listen to the radio.

The worst one was in a house where I was walking between rooms with my phone butt set in my hand. The wires were dangling and definitely not connected to or touching anything at all. The radio station started playing out of the butt set...with nothing connected to it.
Post 8 made on Thursday October 17, 2013 at 16:53
Ernie Gilman
Yes, That Ernie!
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A friend I've known for thirty years, but with whom I had lost contact, called me to root out a problem. He had bought a condo about 1500' from a transmitting tower that broadcast a Spanish language religious station and he was getting interference in everything. That included a loudspeaker connected to a McIntosh power amp...when the amp was turned off.

I usually have some ideas, but this stuff was insidious and I couldn't make more than a tiny bit of improvement.

The surprise was that this was happening at all, because it was an FM station. FM signals are always at exactly the same level of power but they vary the frequency of transmission to put the sound onto the carrier. AM makes total sense for such interference as AM is simply a radio signal that goes up and down in volume (i.e. power), so anything that can filter out the RF (not hard) and one side of the carrier (not too hard) will give you signal. We could not figure out AT ALL what was able to convert varying frequencies around 100 mHz into audio!
A good answer is easier with a clear question giving the make and model of everything.
"The biggest problem in communication is the illusion that it has taken place." -- G. “Bernie” Shaw


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