sundance-communications.com/forum Forums Wiring - Telecom Carriers - Trunks & Services Cabling Telephones Systems Wiring 44 speakers at car dealership...

I would definitely disagree on this. If you called Valcom to ask for their assistance, I am sure they would tell you the same. I have a group of waste water treatment plants that I have installed paging systems in. These include outside horns as well as horns installed in connecting tunnels. We are talking over 20,000 feet of distance, 75 powered horns. I would never be able to do it with any kind of 70volt system, yet with Valcom powered speakers, I am able to use the existing phone wire infrastructure and a number of large power supplies distributed throughout the facility.

I do agree that for music, a 70volt system sounds better than a self powered speaker, even though there is a tremendous low frequency loss due to that damn transformer.

A car lot is an ideal candidate for powered speakers. It is much easier to tailor the volume level in different outside areas. One area may be larger while another area may need to be quieter due to neighbors, etc.

I Just installed a bunch of the 2X2 Valcom High Fidelity lay in speakers V-1422 and they have very good sound.

I was taught...not to use shielded.

Same here. I actually had the owner of a large sound contracting company, in trying to see how much I knew, try to trick me on that very subject a long time ago. He said "so, for a 70 volt system you always use shielded cable, right?" No was my reply as he smiled in agreement.

The only time I have ever had a problem with a speaker line picking up anything was with a single speaker on one home run that was tapped at something like 1/8 watt. The single run was combined into a multi-pair cable with other similar runs that all went back to a simple zone switcher. When the zone was "off" the line was simply left open and floating. What happened was you could still hear audio on the speakers due to crosstalk in the multi-pair cable. Remember, the 1/8 watt tap on a 70 volt transformer is an impedance of 40K which is high enough to pick up noise all by itself when hanging on a run of wire that is open at the other end. The remedy here was to change the switcher configuration so that all switches in the off position short the speaker lines. Note that this is NOT a usual installation.

You're not going to have this problem with higher wattage taps or where multiple speakers, even tapped at fractional wattages are all bridged on the same line. This is normally what you are going to have and the combined impedance is quite low so noise pickup should not be an issue. Certainly not from "crossing data cables" or even electrical wiring at any rate.

Now that you have shielded cable, the issue of what to do with the shield becomes a question. It will have to be grounded on one end or one point for it to be of any use. It will have to be spliced together at each speaker so it is uninterrupted to the the last run as your wiring is daisy-chained along.

I do agree that for music, a 70 volt system sounds better than a self powered speaker, even though there is a tremendous low frequency loss due to that damn transformer.

Another subject for another thread. We need to talk about choosing speaker line matching transformers, speakers and 70.7 volt amplifiers that themselves do not have output transformers. If you know what you are doing the results can very much equal that of driving a single 8 ohm speaker directly.

I do agree with you about Valcom. Your example certainly could have been done with a 70 volt system- using multiple amplifier locations and distributing line level audio to each, which could be done by a variety of methods even VoIP.

The question is then what do you have to work with and what is economical. As you said Valcom is designed to work with the existing telecom infrastructure and you are only worried about voice so the choice was pretty clear.

-Hal

Another subject for another thread. We need to talk about choosing speaker line matching transformers, speakers and 70.7 volt amplifiers that themselves do not have output transformers. If you know what you are doing the results can very much equal that of driving a single 8 ohm speaker directly.

I agree, and there's lots to learn here on this topic and I don't mean to hijack Marlon's thread, but we all seem to be doing it different.

One thing that amazed me and I did not realize until you guys pointed it out here, was that some of the manufactures actually recommend shielded wire. I was very surprised that Bogen did. While searching Bogen I found some of their literature said to use it and some said not to. Very inconsistent.

Electronically that goes against the grain not only for frequency response but as Hal pointed out, what do with it. If it is done wrong, you have either created an attraction to noise or a ground loop.

I still have a real problem running shielded outside for paging speakers, such as lamp poles. Shielding has a bad habit of attracting lightening.

Here is a great article on WHAT the differences are between unbalanced and balanced and when and why you would go balanced or non balanced.

https://www.bogen.com/support/pdfs/Installs.pdf

TP, You are very correct about the lightning.

Scenario --- auto dealership with powered bullhorns on the light poles, interior ceiling speakers, and zones for the shop, waiting room, offices, or all page.

Lightning hits power pole main feeder for the commercial area on the edge of the lot. Gets the Nortel across the street at the sign shop. Blows the paging amp, speaker power supply, and the zone controller along with five powered speakers.

The sign shop is another story. The paging was a Lucent install about ten years old. IW only. Spare leads not grounded. Replaced everything, the zone control, the amp, and the power supply for the powered speakers, and ALL speakers outside. Couldn't pull out the wiring. Used as was.

GROUNDED everything I could find. Got rid of "HUM" and back-feed that used to show up on the inside speakers.

My part of the thread hijack!

You know I've seen that article before Coral Tech but I just reread it. There's a perfect example of Bogen being inconsistent. On page 9, they are talking about the possibilities of noise, such as electrical wiring, causing hum so they tell you how to run a balanced configuration. Not shielded, just balanced.

On the next page, they are talking about the 70volt bleeding out and they use the example of a school intercom system. They run balanced using shielded. Notice the shielding is to contain the signal so it doesn't radiate out, not because it picks up noise. Also notice how they are shielding/balancing, using the center tap (CT), which IMO is the only way to do it properly. Unfortunately, not many amps have the CT terminal.

KLD, had the same thing. It was a construction company yard with speakers on the lamp poles. I didn't do the initial installation, just took over servicing them. The original company ran shielded wiring, lamp poles kept getting hit with lightening and it would take out the entire paging system. It did this 3 times and I finally unhooked the shielding (it was the quickest, least resistance path to ground for the lightening) and I have not had a problem since.

After the second strike, they had an electrician rewire copper grounding on the poles to ground stakes and since that didn't help for the 3rd strike, I unhooked the shielding at the amp completely and hooked it up on the tower just so it is at least grounded to something (rather than being an antenna).

This may seem a little dumb to some, but here's what I do with outdoor speakers. The only ones I have are being fed with aerial drop wire, between the aerial drop and the speaker I take some 26 gauge wire and wrap it around my screwdriver about 10-15 times making a coil, I do this on both ends of the aerial drop, on the feed side also. Since lightning likes to travel in a straight line, it will blow through the coil. I've never lost a speaker or equipment this way, because of lightning. (knock on wood) I learned this many years ago from an old phone guy.

TP, that is WHY I insist on Bogen amps.