70V system puzzle

[egnlsn]

While we're on the subject of 70V speakers, I've got a quick question:

I put in a paging amp with two horns. Now they want to put in another horn 1000' from the amp. How critical is voltage drop in this kind of application?

The stuff I installed can be set up for 70V, 35V, and various impedances (amp has mulitple outputs, horns have built-in xformer and selector switch) Am I correct in assuming that 70V is the best for long distances?

Definitely 70 Volt.

 

[mdshunk]

Yeah, I can't really do anything with the house amp, since that's not even in the same building as this tenant's space. All I have to work with is a Muzak feed at 70V, 70V ceiling speakers with their requisite mounted transformers, and wall attenuators. I was just hoping there'd be a trick gadget ready-made off the shelf rather than putting together my own transformer and three double-throw switch.

That Lowell gadget is neat, though. I like to know about weird stuff like that.

 

[iwire]

I guess it boils down to do it properly or just do it in a way that sort of gets the job done.

I have yet to see anyone post that the simple switch idea is wrong.

Not a good idea to put a speaker level signal (especially 70 Volt) on the same switch as a line level connection. Pretty good chance of bleed thru from the speaker to the line level input.

And in this particular configuration that would cause what?

 

[egnlsn]

Yeah, I can't really do anything with the house amp, since that's not even in the same building as this tenant's space. All I have to work with is a Muzak feed at 70V, 70V ceiling speakers with their requisite mounted transformers, and wall attenuators. I was just hoping there'd be a trick gadget ready-made off the shelf rather than putting together my own transformer and three double-throw switch.

That Lowell gadget is neat, though. I like to know about weird stuff like that.

Not talking about the house amp -- the tenant's amp. The Muzak 70V feed into that Lowell matching XFMR. From there into an A/B switch, with the tenant's CD player connected to the other input. The output of the A/B switch into the tenant's amp. A/B switch selects whether they listen to their CD player or Muzak.

 

[egnlsn]

I have yet to see anyone post that the simple switch idea is wrong.



And in this particular configuration that would cause what?

A 70V signal bleeding into a 1V line. Inductive coupling is the term.

 

[hbiss]

How critical is voltage drop in this kind of application?

This is one of the reasons 70.7v exists. Use the 70.7v output and the 70.7 volt taps on the transformers. Just remember that you don't want whatever you set your wattages for on the speakers to exceed more than about 80% of the rated amp power.

For that 1000' run with a usual paging horn set at 35 watts #12 will be fine. Voltage drop is not critical with most 70 volt paging systems because you can just use higher wattage tap on the speaker at the end of the line if the volume isn't loud enough.


The Muzak 70V feed into that Lowell matching XFMR. From there into an A/B switch, with the tenant's CD player connected to the other input. The output of the A/B switch into the tenant's amp. A/B switch selects whether they listen to their CD player or Muzak.

Why go through all that trouble?

Not a good idea to put a speaker level signal (especially 70 Volt) on the same switch as a line level connection. Pretty good chance of bleed thru from the speaker to the line level input.

And why would you need to use a 3PDT switch with line level audio on it also? All you need to do is switch the speakers between the house feed and the customer's amp. DPDT.

I have yet to see anyone post that the simple switch idea is wrong.

It's not and that's the way I would do it.

-Hal

 

[mdshunk]

I have yet to see anyone post that the simple switch idea is wrong.

It's not and that's the way I would do it.

-Hal[/QUOTE]

Every once in a while, I guess I have a decent idea. I hope that if some manufacturer reads this, they'll make a one-piece solution to this.

 

[hbiss]

They don't because each situation is always different. Multiple program sources feeding a 70v speakers is nothing new. If you look in Lowell as well as Atlas Sound you will see that they have 2 pole 6 position rotary switches and two gang combo (selector switch and volume control) wall plates to do exactly what you are going to do only for six sources.

Muzak used to use those in all their installatons many years ago when their programming was delivered from separate receivers or over telephone lines. They just used six separate amplifiers and brought the outputs over to the wall selector switch and from there to the speakers. That was the way the customer was able to change the type of music. Now of course it's a satellite receiver with almost 100 channels so it's easy enough just to change the channel on the receiver. And by the way, Muzak isn't elevator music any more. Every type of music by the original artists, it's all there.

That brings up another question, is this an old building and Muzak installation? I haven't seen a "centralized" system like that since those I was talking about above. Normally each business gets their own receiver and amp.

-Hal

 

[iwire]

A 70V signal bleeding into a 1V line. Inductive coupling is the term.

Yes but in this case I do not see it as a making one bit of a problem.

To each their own, often the simple works and many times audiophiles like to make things much more complicated then they have to be.

 

[mdshunk]

That brings up another question, is this an old building and Muzak installation? I haven't seen a "centralized" system like that since those I was talking about above. Normally each business gets their own receiver and amp.

-Hal

Yeah, originally built in the early 70's. Pretty nice office campus though.

 

[hbiss]

Which goes to answer you question. Today you would use an amp with multiple inputs. Turn the Muzak down on CH 1 and turn up the CD player on CH 2. With some amps those controls can be remoted with a volume control or a switch.

-Hal

 

[mdshunk]

what sort of amp has 70v inputs?

 

[hbiss]

70v inputs? No such thing and what for. Inputs are line level or balanced. A Muzak receiver has a line level out. (It has no amp to drive speakers.) You would use the line level outs on your other sources as well. If you had to you could use a pad or transformer to match a 70v line to a line input but that is rarely done and if it is it would only be of a temporary nature. You never want to take the speaker output of an amp and use it to continue a chain. The output stage is designed to provide the power to drive the speakers and unfortunately power and lowest noise/lowest distortion can't be had at the same time. While the amps today can be very good, it's still as it always has been, nearly all of the signal degradation takes place in the output stages.

-Hal

 

[iwire]

This is the amp / mixer we use with one of our chain store customers

The amp comes with no inputs

http://aa.peavey.com/modularmixeramps/mma8752_8152.cfm

You pick and choose what you need for input or processing modules. http://aa.peavey.com/modules/ This system makes it easy to pick and choose which input can take over the other inputs for paging.

 

[Speedskater]

Two good sources for 70 Volt audio parts and pieces are:

www.markertek.com 70V Commercial Sound
www.parts-express.com Pro Audio 70V Commercial

 

[hbiss]

The amp comes with no inputs

Those are modular amps and several manufacturers have them- Bogen and TOA off the top of my head and you just gave me Peavy (who I wouldn't bother with). They all have a selection of separately purchased plug-ins that allow you to choose your inputs and some functions. I find them expensive for most applications because you have to buy that big amp even if you only need two or three inputs. If you need nine inputs then it's a different story.

-Hal

 

[iwire]

Those are modular amps

No kidding

and several manufacturers have them- Bogen and TOA

Yes sometimes we use TOA as well, the modules will interchange fine between them.

off the top of my head and you just gave me Peavy (who I wouldn't bother with).

Then I guess we will stop using them as well .

I find them expensive for most applications because you have to buy that big amp even if you only need two or three inputs. If you need nine inputs then it's a different story.

Our customer has a number of different types of inputs and priority requirements.

It is without a doubt much more then Marc needs, just putting it out there so folks might see what is available.

 

[egnlsn]

The Muzak 70V feed into that Lowell matching XFMR. From there into an A/B switch, with the tenant's CD player connected to the other input. The output of the A/B switch into the tenant's amp. A/B switch selects whether they listen to their CD player or Muzak.

Why go through all that trouble?

Not a good idea to put a speaker level signal (especially 70 Volt) on the same switch as a line level connection. Pretty good chance of bleed thru from the speaker to the line level input.

And why would you need to use a 3PDT switch with line level audio on it also? All you need to do is switch the speakers between the house feed and the customer's amp. DPDT.

I have yet to see anyone post that the simple switch idea is wrong.

It's not and that's the way I would do it.

-Hal

The input on the same switch as the speakers was what was suggested in post #4, which I was referencing.

Switching ONLY the speakers between the Muzak system and the tenants system would be fine with one drawback. There would be no control over the Muzak level. If that is of no concern at all, fine. If the tenant would like to be able to adjust the level of the Muzak, not so fine.

 

[egnlsn]

Yes but in this case I do not see it as a making one bit of a problem.

To each their own, often the simple works and many times audiophiles like to make things much more complicated then they have to be.

No audiophile here, but I do hate hearing things between tracks of a CD (Muzak in the midst of Zeppelin?).

 

[egnlsn]

If you had to you could use a pad or transformer to match a 70v line to a line input but that is rarely done and if it is it would only be of a temporary nature.
-Hal

Done often in stores where various departments have their own systems that are fed from a master system. Store music and paging goes everywhere, and each department has just about exclusive control over the loudness of the music in their own domain. No worries about cable distance, where line level would pretty much disappear over a couple thousand feet.