atcomsystems.ca/forum Forums Wiring - Telecom Carriers - Trunks & Services Security, Alarms and Paging Large PA system installation

We have been approached to quote a very large PA system for a government building. Although it sounds a bit excessive, they have indicated that we'll need to furnish 150 speakers on each of six floors (900 total). We'll propose a 70 volt system with a separate amplifier (or more) per floor. A single zone controller will allow access.

For simplicity in troubleshooting, we'll propose putting no more than ten speakers on each cable run.

The problem is that they want us to reuse the existing speaker enclosures and just replace the speakers/transformers themselves. The existing wall mount enclosures are fairly well made of steel, so I can see why they want to keep them. The problem is, I was hoping to find a source for 8" speakers with transformers without any kind of grille or enclosure. I'm not having much luck. I'd hate to buy ones with grilles just to take them apart. Any ideas?

Atlas has them like that. Nothing is excessive for the gov.

Wow. Round up the usual suspects. https://www.quamspeakers.com/product-pages/transformers.shtml

I don't envy you the labor of changing out however many 100's of speakers and transformers.

Carl

Ed -

Atlas, for sure, 8" speakers are readily available. if you have a problem locating them let me know and I'll see what I can do.

Also what I did on my last big PA job (JFK -AA. 5,000+ speakers) was, when we had a large grouping of speakers instead of looping them all (as the plans called for) or setting up individual runs, I had the guys run one feed to a central location, mount a 3 or 4 gang electrical box and then bring individual runs out to logical clusters. As long as the splice point is marked on the prints, troubleshooting is very easy.

And with that many speakers, you'll want the two most important pieces of test gear available - an impedance meter and an iPod. With those two you can get anything working.

Sam

I have to ask. What do you use the IPOD for?

Presumably use it as an audio source to check the speakers for volume. Beats having a guy doing "Pete Moss to the Garden Center" all day long.

I have some test tones that I downloaded onto the iPod. Set on "repeat" it allows you to test a large group of speakers easily. When your'e done with the stress tests, pipe music through the speakers and if they sound good - they are good!

Sam

I have a couple audio apps on my iPhone, most notably Tone Gen Pro.
I also have a db meter and a few others.


PS, "Pete Moss to the Garden Center"...love it!

Two excellent suggestions Sam. I'd also second Atlas Sound for a source of 8" speakers without grilles. The model C5AT70 is probably exactly what you are looking for.

Your local Dukane Sound dealer is Life Safety Solutions (https://tlglss.com/educational.asp) and I am sure they'd be happy to quote you on the model 5A607 speaker which is exactly what you need!

Couple of things that come to mind here Ed. First, about the existing wiring. Most large amps require Class 1 wiring. Is what's there suitable- is it in conduit or other Chapter 3 wiring method? Are the amps you are contemplating Class 1? (Remember, if it doesn't say Class 2 or Class 3 wiring by the output is MUST be assumed as Class 1.)

The second question: is this a life safety system? If so you probably aren't qualified to install it and there are all kinds of design considerations way beyond a PA system.

-Hal

Hal -

You're absolutely correct about Class 1 wiring. Usually most Amps 100watts or larger require class1 for the 70Volt output. 25 volt output does not require class 1 but will require substantially bigger amplifiers.

Class 1 wiring can be installed in flex (mc,bx) and does not necessarily have to be installed in conduit.

As far as life safety systems - I'm not familiar With the code in DC or Virginia, but in my experience that's usually associated with the fire alarm system.

Sam

Wow, good point, Hal. Their specs state that this PA system is not planned to be used for everyday paging; more of an emergency announcement system. I'm not sure if that falls into the category of a life safety system, but I'll surely be asking the question first thing on Monday.

This is a 100 year-old building where we have been maintaining for their ISDN system for several years. We never paid any attention to the existing PA system since that wasn't within the scope of our support contract. The building is being gutted, but since it is a historical building, they won't allow any new drilling, etc. This is why we have to re-use the existing speaker enclosures, Wiremold and conduits. Since they gutted all of the voice cabling, I'm sure that they did the same with the PA cabling too. Even if there's anything left, I'm sure that it would be cheaper to replace it all rather than to hunt through the remnants.

My plan is to use multiple 60 watt amplifiers, one in each of the three closets on each floor. It appears that CL2 wiring will be OK for this environment.

I do have to ask a question about NEC requirements on this: It states that the code does not apply to federal government installations. This building is owned by the Feds. Does this stipulation apply to installations by federal employees or to installations within federal buildings by outside contractors? Should we discuss this with Mr. Holt's people?

Geez, I'd be happy if I knew half of what you forgot.

Ed, I did quite a bit of work in Federal buildings. I was always told that they fell under the National, not the local building codes. So in NYC, the less stringent National Electrical Codes were used, not the more stringent NYC codes.

If that's the case then the NEC would apply.

Sam

Actually you just did, I just came from over there. The answer is to ask the AHJ what codes apply. There should also be something in the RFP specs that you got from them. There is nothing in the NEC that exempts federal buildings but the feds might exempt themselves from the NEC in whole or in part I would assume.

This does sound like a life-safety system from what you said. Is there a design for this or did they just dump it on you to do a design-build? If so what do the specs say? I believe Life-Safety is covered by NFPA 101 (The NEC is NFPA 70). Something also to talk over with the AHJ and fire marshal. What is required in govermental buildings? If it is Life-Safety it's probably best to sub it out to a company who has experience in that area.

-Hal

They did just dump it on us as a sub for the new prime contractor. We've been given very sketchy specifications since this was apparently an oversight on the agency's part. There was a pre-bid conference held on-site and one of the potential bidders noticed the existing speakers. The agency quickly scrambled together an addendum that basically states "the existing paging system shall be replaced using existing speaker enclosures, conduits and other wiring pathways". All of the original wiring and amplifiers have apparently been removed as a part of the gut job. That hardware is probably already listed on E-Bay as we speak.

This job is starting to stink to high heaven. As a sub of a sub for the prime contractor, I see this as becoming a huge problem. My boss will insist that we bid on it anyway. It is a huge job, but laced with many unknown issues and potential liabilities. I really dislike federal government projects for this exact reason.

Well then in the absence of anything else that is what I would bid on. Just make sure you write an ironclad contract with specs for them to sign before you do any work. Then if they decide to do something else they can't blame you and it becomes a change order.

-Hal

It would be handy if they'd left the old cable as you could probably have used it for drawing new cable through the conduits.

Multiple 60 watt amps per floor means you will have to distribute audio at line level to multiple locations, as well as switching signals for zone switching, local source over-ride etc - and it will make using a UPS much harder.

Much better to cable back to a central amplifier room. If you can do 3 zones per floor, put in 1 amp per floor, sized for 1.5x floor load. Then when one amp fails, you can split that floor's zones across three other amps.

You also have everything close to hand in one room and can carry out all testing and maintenance without having to go onto the office floors.

70V wiring will run happily over 100s of metres (miles if you lump-load the lines to compensate for cable capacitance): here's the control room of a Bultin's holiday-camp installation by Messrs. Tannoy.

Driving 150 speakers per floor with a 60w amp! You need to rework that math. Recently had a project requiring some special audio considerations and Parts Express helped me out. The customer was extremely satisfied with the end product.

No, we are proposing three 60 watt amplifiers per floor, one per closet. The more realistic count of speakers per floor is about 90 at most, so roughly thirty speakers per amplifier. Set at 1/4 watt taps, we'll be fine. Thanks for the concern though!

I ended up going with a 100% Bogen solution. The price came out right and the customer didn't even flinch when we presented it. It took my breath away personally, but I'm not used to pricing projects into the six figures.

That's government pricing for you.

Ed -

1/4 Watt per speaker is kind of low. is this all "quiet" office space? Is the system for general announcements or for more serious stuff? What's the spacing on the speakers?

sam

Sam, yes it is very quiet office space with very few hard surfaces. The speakers are ridiculously close to each other in my opinion, but that is what they want. In most areas, they are no more than 25 feet apart. The system will never be used for general daily paging; it will only be used on very rare occasions.

90% of the offices are modular furniture, so the space is almost all open.

The similar setup in one of their other buildings has never been used in ten years except for monthly testing.

OK. Usually we set small closed offices for 1/4 watt and open "bull-pens" went for 1 Watt. (At JFK we had the bathrooms set at 2 Watts, the Gates at 4, Corridors at 8 and outdoors, machine rooms and whatever went 15W. Speakers out by the runways went at 30W!)

Wall mount speakers generally don't project farther then 25 feet, so the spacing is good (These are wall mount, right?) Horns might push 35' but have practically no bass and sound like sh*t.

One important thing with wall mount speakers is that they should not be directly facing each other. If you have them on opposite walls then they should be staggered. Usually we try to keep them pointing in the same direction.

For ceiling speakers, the rule of thumb we used was: Twice as far apart as the distance from the speaker to the ground - for ADEQUATE coverage (10' ceiling=20' apart). For BETTER coverage we used twice as far apart as the distance from the speaker to the ears of the person hearing it (10' ceiling in classroom=13' apart. 10 ceiling in hallway=9' apart).

Hope this makes sense.

Sam

Reading all this reminds me of the "good old days," when this site was a lot busier.

I have learned more from this one thread than all the other "media" I ingested in the past week combined.

You guys are awesome.

As B/4,
Jim

I agree with you, Jim. I've learned a lot here in a short period of time. When my boss presented me with this project for pricing, I scoffed at it. Then I thought, let me check with my friends here and get their feedback. Now I'm not so concerned about it. Besides, if I get into a pinch, I can drag Sam out of retirement to come down and manage it for me!