Distributed Audio PA systems paper I wrote

[Tony Bandiera Jr]

Wrote this for my new business endeavor tell me what y'all think. (It is quite a large document so I will break it into two posts.)PAS logo.jpg

OUTDOOR P.A. SYSTEMS:



This document will provide information on outdoor Public Address Systems, as used for motor sports tracks, arenas and other large outdoor areas. Each system designed and installed by PAS utilizes some or all of the equipment and technologies discussed here. Actual equipment used will vary depending on a number of factors and is unique to each installation. Technical terms will also be explained, starting with:

• What is a “Distributed Audio” P.A. System?

Unlike a typical home stereo, car audio, or meeting room P.A., a Distributed Audio system uses multiple horn type speakers spread out over a large area to provide a uniform coverage of sound in that area. Normally, with the first three methods, you’d use very large speakers in just a few locations, which results in the sound being ear-bleed loudness near the speakers, with a rapid fall off in volume as you move away. Further, there is a “hole in the middle” effect where virtually no sound is heard between the speakers. For music, that is sometimes ok, and you can also have the benefit of lots of bass (if you are willing to have very large subwoofers and very powerful amplifiers). As an example, to cover a stadium with loud, full range sound (like at a Supercross Race), it takes dozens or even hundreds of large speakers being driven with well over 1-5 MILLION watts of audio power. (Your average home stereo is around 300-500 watts per channel max.) A rock concert uses even more power and speakers. As you can imagine, this requires a LOT of cabling and a massive electrical service. The costs of the equipment alone can easily top 2+ million dollars. Not a practical amount to spend for most situations like local motor sports or rodeos.


The other issue is driving multiple speakers from one amplifier. Most typical amplifiers can handle speaker loads of 4-8 ohms (A measure of how much resistance/impedance the speaker has), and they drive the speaker more with current (watts) than volts output. If you try to connect more than one speaker per amplifier channel, things get tricky. You must calculate connections (in series or parallel, or a combination) to make sure the total impedance is not lower than 4 ohms. This connection scheme means complex wiring, more wire needed, and if any one speaker blows out (or is disconnected), it can take out some or all of the rest. And loads lower than the rated capability of the amplifier can cause it to overheat, shut down on protection mode, or burn out.

But the equipment and design of Distributed Audio systems solves these problems in a unique way, with a few tricks:

1. The amplifier drives the speakers at a higher voltage (25, 70.7, 100 or 140 volts).
2. Each speaker has a transformer that converts the higher voltage down to drive the speaker at a fixed maximum wattage.
3. You spread the smaller speakers out to cover a larger area.
4. A simple single wire run that loops to each speaker is used.

The electrical theory is a bit complex and to explain it fully will take too much time. But put simply, the higher the voltage used, the more power in watts can move through a given wire size, at a longer distance, with minimal losses. For a large system where a big space needs to be covered, hundreds or thousands of feet of wire is needed. Reducing the wire size required and quantity needed (not making complex series/parallel connections) results in a huge savings in wire costs.

Now as for the horn speakers, they offer some big advantages and a minor drawback:

1. They produce high levels of sound in a compact form factor;
2. They are durable and weatherproof;
3. Most (including the ones PAS uses) have selectable wattage (thus volume);
4. They are directional and minimize sound “spillover” to areas where sound is not wanted;
5. You can have as few or many horns as you want, up to the power output of the amplifier.

The minor drawback? They are optimized for voice and have little to no bass response.
This is ideal for most uses we cater to, as you want a clearly heard announcer rather than a rock concert level of boom. This is also a HUGE savings in wire size, amplifier size and power use. (Remember the Supercross track?)

So the idea is to spread the sound over a large area, using multiple speakers with simple wiring and no fussy connection voodoo to deal with. The selectable wattage at each speaker means we can tailor the sound level of each horn to just the right level to not blow people’s ears out.
A typical system PAS designs uses 6.5”x11” horns, with up to 32 watts selectable at each horn. Horns that have to throw sound across an open area use 32 watts, ones up close (grandstands for example) use the 16 watt taps to avoid being too loud. Our typical systems are two zones, with amplifier ratings from 300 watts per zone (channel) to 1,200 watts per zone. We usually oversize the amplifier to the next larger size so it runs cooler and with less stress.

• How many speakers can you put on one system?

On a Distributed Audio system, the sky’s the limit (based on amplifier output power).

For example, we use a 70.7 system, and we’ll say it is a 300 watt per channel amplifier.
Each channel can handle any combination of :
(300) 1 watt horns, (150) 2 watt horns, (100) 3 watt horns........ (9) 32 watt horns (actually 10 ) and so on. And we can mix and match them as long as the total of ALL of the horns on a channel does not exceed 300 watts (or whatever the amplifier is rated for.)

The system can also easily be expanded at any time by adding horns. If the existing amp doesn’t have the power a simple amp swap will take care of it at minimal cost.

Bigger places like Indianapolis Motor Speedway used 140 volt systems with multiple 10,000 watt amplifiers and over 450 horns. They have since upgraded to a full range system using 150 full range outdoor speakers and digital controls.

• Why not use full-range speakers every time?

One word: cost. Fully weatherproof outdoor full range speakers are very expensive. Yes, many models can cover a given area in fewer numbers than multiple horns, but each full range speaker still costs 7-30 times more than the equivalent number of horns to cover that same area. You also need much heavier wiring to drive full range speakers and much more powerful amplifiers. PAS will design and install full range systems on request, but the costs can easily approach high five figures even for a medium system. (Smaller rodeo arenas can be designed for full range at much lower costs, but still a lot more money than horns.)

For motor sports like motocross, asphalt and dirt track cars, etc. full range P.A. Systems aren’t really beneficial, as vehicle and bike noise will drown out most of the bass response anyway. It also muddies the sound, making voices harder to hear.
Multi purpose venues like fairgrounds should always strive to do a full range system with enough power capability to amplify bands and other performers. (Some fairgrounds still prefer horn-based systems and let artists provide their own P.A. for music.)
So should you go for a full range system? It will depend on intended use, sound levels desired, and of course, your budget.

• What about background music?

Background music is not a problem, and the mixer PAS uses has a feature called “Ducking” in the Mic 1 input. Ducking means the music mutes when someone is talking, and returns as you stop talking. This avoids the dreaded “dead air” that most announcers hate. The mixer can also select between two music player sources with a simple button push. Each stereo music input has its own level control, so you can balance the music levels to your liking. Each Mic input also has adjustable gain, which is preset during system testing and rarely needs to be changed. The fidelity of the music will depend on the speakers used, so horns will be lacking bass. If your venue wants to use the P.A. For live music or video performances, it is strongly suggested you opt for a full-range system. Oh, and choose your playlist carefully, make sure it is appropriate for your audience!

• Does PAS offer FM Radio transmitters?

Yes we do. There are a few caveats with FM transmitters however:

1. You must be careful not to “step on” any local or fringe commercial stations when choosing your FM frequency;
2. You must get a quality FM transmitter, not a typical cheap one from online. Cheap transmitters are unreliable, often drift from the set frequency, and tend to have poor range and audio quality;
3. Use of an FM (or AM, not recommended as per below) transmitter requires the use of a compressor/limiter on the audio to avoid overdriving the FM signal. It must also be set correctly, or you will get a lot of customer complaints;
4. A quality FM transmitter is expensive, and the only type we will provide. If you choose to use one that you provide, we will not warranty it or its performance.

And a word of advice: NEVER use an AM transmitter! Not only is the audio quality poor, but AM radio is very prone to static pickup from a lot of things like bike or vehicle ignitions, two-way radios used by track crews, weather (lightning), and nighttime AM station signal spread (AM travels very far at night and a frequency that is quiet during the day can get multiple stations picked up at once, resulting in annoying whistling, fading and flutter.)

If you do a transmitter, remember: Clear signals, not too loud (or soft), avoid cheap units and NEVER do AM radio. Otherwise all you’ll end up doing is annoying your paying customers and sponsors.



Speaking of radio and transmitters....

[Tony Bandiera Jr]

Part 2:

• What about wireless mics?

Wireless mics are one of the best things you can have, especially for motor sports announcing. It gives the announcers freedom to move around, in the stands or track side for winner circle interviews. Rodeo announcers can often get good use of a wireless as well.

Here’s the funny thing about wireless systems: cheap ones are rarely any good (no surprise), and the most expensive ones can be bad as well (shocking). As the owner of PAS, (and an announcer), I have personally used all types of systems from around $150 to well over $700. A disturbing number of the high end models worked with good to excellent range, but added an annoying delay or echo to the audio. The cheap ones had bad range or were very noisy and prone to dropouts. But a few of the less expensive ones performed surprisingly well.

Our current single handheld mic we offer has proven to be pretty reliable, able to withstand the abuse of outdoor work, and has decent range. It is also reasonably priced.

Most announcers prefer a handheld mic, but we offer headset and lav (the tiny mics news people use) options. Which is best will depend on the venue. Bike and car tracks should use only handhelds. Rodeo arenas and similar venues can use any of the options. There are also systems available that can handle multiple mics so you can mix and match if desired. Keep in mind with multiple mic systems ONLY 1 Mic will have the music “ducking” option available (due to the mixer.)

All that said, be aware that even the best wireless system can still suffer from limited range or dropouts, due to a variety of reasons:

1. Atmospheric conditions (Sunspots, solar flares);
2. Other nearby radio devices;
3. Commercial transmitters (rarely);
4. Weak transmitter batteries;
5. Antenna placement. (PAS uses only external, roof mount antennas to minimize this issue.)

As such, be aware that PAS does NOT warranty range or 100% dropout free performance of ANY wireless system.
Speaking of which:

• Why not use wireless (Bluetooth) speakers?

We get asked this a lot, and it is not a dumb question. But for many reasons, wireless or battery operated portable speakers are not practical:

1. Power. They need power, by batteries (which will ALWAYS die at the worst possible moment) or power for a charger or AC adapter. Running AC power wiring is very costly and introduces safety hazards at each speaker location.
2. WiFi or Bluetooth signals are very flaky;
3. Bluetooth signals can easily be “hijacked” by anyone with a smartphone. (You don’t want someone’s NSFW music playlist on your P.A. System);
4. Bluetooth/ WiFi can be subject to atmospheric blocking;
5. They are easy to steal or damage;
6. Most portable speakers are not designed for extended exposure to heat, sun or rain.

For temporary use for a show, band or side event wireless speakers are great, but not for a professional P.A. System. PAS does not sell or recommend any types of wireless speaker.

• OK, so wired it is. What are the best practices for wiring speakers?

There are a few things to consider when installing a wired 70.7 volt (or higher) system. Most PAS systems are Class 2, 70.7 volts.

First, the type and “Class” of wiring. For audio systems, you have Class 3 (low voltage, <50 volts); Class 2 (>50 volts up to 99 volts) and Class 1 (100 volts and up). Class 1 and Class 2 wires, per the National Electrical Code (NFPA) must be installed with specific protections (conduits, etc.) and be listed and approved for use as such. This to avoid shock and fire hazards. The wire must be marked as suitable for the Class it is used for, keeping in mind that a wire rated Class 1 can be used for all three Classes, Class 2 wire can only be used for Class 2 OR Class Three, and Class 3 Wire can ONLY be used for Class 3 audio.

Direct burial is the preferred method with the best balance of cost and durability for outdoor P.A. Systems. Care must be taken to route DB wires away from other electrical lines (crossing at an angle, never run directly alongside), buried at a minimum of 24” or more, and sleeved with pipe or conduit when crossing any roads, pathways or areas subject to digging or ripping. Wires running up speaker poles (especially in Class 2 or Class 1 systems) MUST be in conduit (or run inside the pole ) and protected from physical damage.

Handholes or splice boxes should be provided at each speaker pole, and every 200 feet of wire run.

If overhead runs between speaker poles are necessary, there are some precautions that need to be observed:

1. Minimum clearances over fences, people, roadways or equipment access points. Take the highest piece of equipment (with booms, buckets, beds or implements fully raised) measure that to the ground, and ADD a minimum of ten feet. That will be the height the wire must be to avoid getting snagged, with an air temperature below 80 deg. F. The wire WILL sag lower in hotter temperatures, and if loaded with snow or ice in winter. Where only people can cross under, a minimum height of 10 feet above ground level is sufficient.
2. NEVER, EVER CROSS OVER, OR HANG WIRE WITHIN, 15 FEET OF A MOTOCROSS/ENDURO TRACK! (Crossing over a car, truck or kart track is ok with a minimum height above the highest point of track surface of 20 feet., but is not recommended. );
3. Wire used for overhead must be rated for extended sun and weather exposure, have a steel support wire built in, or must be a suitable wire type secured to a steel guy wire,1/8’ minimum, securely fastened at each end. The speaker wire must be secured to the guy wire with UV rated cable ties or suitable tape, not more than 12” apart.;
4. NEVER secure speaker wire to ANY other electrical cable, and maintain a minimum 12” clearance for all electrical cables. Position speaker wires below electrical cables when possible.

• What type of wire is suitable for speaker systems?

Unlike standard 60hz AC power, the type of wire used for speaker systems is important. At frequencies higher than 100 hz or so, a phenomenon known as “Skin Effect” takes over. The electrons at higher frequency will travel mainly on the outer part of the copper, ignoring the solid center part. This causes a loss of efficiency and on longer runs and higher power systems, can result in losses well over 30-50%

Solid wire is NOT to be used with speaker systems!!
Only stranded, copper conductors are used by PAS for our systems. Most of the time we use OFC (Oxygen-Free Copper) to improve efficiency and minimize losses. Regular copper wire is ok for shorter (under 300 foot) runs. DO NOT use CCA (Copper Coated/Covered Aluminum) for Direct Burial or outdoor use, it will fail with the slightest moisture intrusion.

Wire Gauge (size) is important too. Even though a 70.7 system requires the speakers to be driven with less current to the speakers, there is still a fairly high current involved and it is very important to minimize voltage drops over the length of the run. Voltage drop will cause the speakers near the end of the run to have less output (volume) if the drop is excessive. It is very difficult (and expensive) to get a voltage drop less than a few percent, so we calculate our wire sizes to try to get no more than 5-6% drop at the last speaker in the line.

A heavier gauge wire is also less subject to physical damage.The absolute smallest wire gauge we use is #14 for extremely short runs, and sometimes as a riser wire up a pole. #12 and 10 are used on most systems.

• And finally, what about electrical power requirements?

For the majority of our systems, a single 120v, 15 (or 20) amp receptacle is all that is needed. Larger systems with two or more amplifiers will require 2 or more 20 amp, 120v receptacles. We can also, in larger systems, require 120/240 volts and 30 amps or more.

It is up to the customer to have a properly wired receptacle at the equipment location. PAS can recommend an electrician to provide or upgrade receptacles on request.

It is possible to operate a PAS system on a generator, but be sure it is an inverter type with “clean” power to avoid equipment damage (not covered under warranty) or system noise. Most large rental generators of 15kw and higher are considered as “clean” power. Try to avoid connecting the P.A. system to the same generator powering any type of discharge (Sodium, Metal Halide, etc.) lighting as those types of lighting produce a lot of AC power noise.

Equipment racks we provide will be equipped with surge protection and quick disconnects to the speaker lines.

If you made it this far, thanks for taking the time to read up on how a professional Distributed Audio P.A. system comes together.



(Contact info Redacted)

[Steve Guttag]

Tony, have you ever worked with Steve Durr?

[Tony Bandiera Jr]

Tony, have you ever worked with Steve Durr?

No I haven't and the name is not familiar.

Like as was true of most of my career, I got tossed headfirst into troubleshooting and repairing these types of P.A. systems with no help or advice other than maybe a schematic or amp spec sheet. They weren't too hard to figure out, and I had to learn the hard way not to service them with the amp powered up (they bite harder than a regular audio system.)

As for designing them, that was some trial and error until I had a few systems built and tweaked to what got the job done.

A sidebar: I got into cinema service in the military. I was a projectionist on the base theatre, and we were upgrading out old Peerless Magnarcs (with 1k Xenon conversions) to a 2k LP Assoc. lamphouse and rectifier. I first had to dig up a three phase breaker for the booth panel (stole an unused one from the stage panel) and then, after the AAFES tech got pulled into an extended troubleshooting phone call, had to wire the second lamphouse and install the bulb myself. (We had a show that night and it was 1700 hours.) I had also had to figure out why the sound was always so horrible there. (They had a relay in the rack that turned on only the side wall speakers for music, and only the Big Altec A7 for film.) That relay was bypassed so all three were driven that the same time always, which not only stressed out the amplifier but created a horrible time alignment issue, made worse by the very live room. Once I corrected that (and noted the higher fader setting for film) everyone raved about how great the sound was.

After I left Active Duty and signed up for the Air National Guard I worked at the UA 8 Buena Park where I met an RCA tech who suggested I work for them. The rest is history.

[Steve Guttag]

Steve Durr has the Indianapolis Motor Speedway as one of his clients (at least, historically...things may have changed over time). You mentioned that venue so I was curious if you crossed paths. I met him at the Library of Congress in Culpeper, VA where was the acoustic guru for them on their various listening rooms and even the Packard theatre at that facility. I gather that recording studios and other high-end listening spaces are his specialty.

[Tony Bandiera Jr]

Steve, thanks for the reply. I might have run into his name in some of the research on the IMS P.A. system. I really wanted to find the Crown paper on their install at IMS, I think it was with MacroTech amps, they had cool photos of the twistlock speaker patch bays, the power supply layout (3 phase 208v) and other tidbits. That was from long ago, I might have the printed copy in storage somewhere.

I have done a couple of the systems I am offering at a few tracks out here, and have another track wanting a bigger system this coming spring.

I have also started repairing QSC CX/DCA amplifiers, got one CX 302v which was a 120v configured amp connected to 240v. Destroyed the main filter caps and blew the 25 amp fuse, but no other damage that I have found so far. I've been too busy to test it and see how the repair went. I plan to video that power up just in case things go sideways,, lol. I have a CX 1202v with both channels locked in protect that is next up on the bench. (I hope to get that one resolved for the upcoming install.) Sadly, my connection with QSC is no longer there and I forgot my former password to get to the service manuals. I have found schematics and some other info online.

[Steve Guttag]

Yeah...the way QSC handled 120V on the CX/DCA line was to run it through a voltage doubler circuit. So, hooking up 200-240 could end up trying to nail the poor power supply with 480V...as Uecker would say...that's "just a bit outside" of its operating range. Note, since this is how QSC did their power supply, you are often better, in the US to run them at 120V rather than 208 as your power rails will get a little higher. In residential, where you have 240 coming in, it's a wash.

Even if you still had your credentials, QSC has changed things so much you'd have to reapply anyway and they seem to have less and less interest in anyone but regular repair houses doing the work. Trying to explain to them that in cinema, we try to do field repairs as much as possible (to not take theatres down) is a thing, has been challenging. As an example, the DCP line touchscreen used to be a dealer orderable part. Now it is a service center only part. So, is the theatre supposed to just shut down while a field serviceable unit is changed? If you are a big chain, yeah, you can have spare units. What about singles? It makes no sense to me. It's not a safety thing either...Dealers can still get power switches, fans input attenuators...etc. So, it isn't like you can't get things that would expose the fool to lethal power.

QSC used to sell "Repair Kits" that took a steamroller approach to repairs. They knew, statistically, what the likely failure points were on their products. If one put in a repair kit, they likely would repair the product by changing those parts (and likely quite a few that were just fine).

You could also buy a pre-populated board set. Snap the input and output boards off (like saltines) and change out the guts but keep the metal work, transformer, fans, power cord...etc.

QSC also used to sell "Renew Kits" which merely changed out those parts that aged (e.g. capacitors) so one could preemptively keep things going.

You could keep your QSC product going at the level (and price point) you were willing to spend. That's all gone now. You have factory and authorized service center repairs for everything from major parts to hang nails. And that is for things that they will repair! I just had an "Atterotech" wall plate (Dante) fail. Atterotech is a brand that QSC acquired to augment their Q-SYS line up. They don't repair those...just a bad PoE power supply board (available at Mouser) and it is up and going again for a lot less than new. The world has definitely changed! I wonder how many of these wall plates (That are in the $800 range) have been junked when a repair, where the labor to unsolder/solder is the bulk of the cost) could have kept them going. I thought the world was supposed to get more green.

Lately, we've been repairing the Crown DSi amplifiers (DSi 1000s, in particular). They have a heat problem near the power switch caused by some precision resistors being near a capacitor that dries out. And, is typical of Crown, they also live life on the edge on their ratings...that capacitor is 35V...as is the voltage that can hit it! Swap it with a 50V and up it to a 105C...its chance of survival goes way up.

[Tony Bandiera Jr]

Steve, that voltage doubler tripped me up. As a first test doing the repair I was looking for shorts, and had thought the bridge rectifier was bad (The two AC inputs legs are shorted together when it is wired for 120v) I found that when I got the schematic. I also learned that a few simple wire swaps and you can convert it to run on 240.

The situation at QSC is disheartening....I have no idea why decades old designs are held under double-secret probation and you have to pledge the frat to get info....it makes no sense. Now in the cases of their DSP and software based hardware, I can understand that. But for analog technology that even someone like me can figure out, why be so secretive? I haven't asked yet, but I wonder if QSC Service will still even repair the CX line? Or DCA for that matter.

The power supply parts cannon kits are still available, as are a few of the replacement "modules" with the saltine boards. I have had to select new IGBT's as the old IR ones they used are NLA. ( found some with higher voltage and current but mostly matching gate and other specs) I did find some NOS TOP 210 and 221 chips.

Crowns, ugh. I hated working on those overpriced and overrated POS. Remember the TOA amplifiers with the protect board that had a power resistor cooking a critical cap? Dennis S. from RCA had to even modify the factory fix to get them to finally work right. I had a few of those modded boards as part of my service parts, now gone since John passed.

As for green,, without veering into a political commentary, we can say it is obvious that adding all the technology (which takes massive amounts of components and energy to build) only to end up with goods that fail in unrepairable (uneconomical ways to repair) ways, only to toss them out...we have gone billions of tons of waste in the wrong direction. Example? D Cinema projectors and servers that go out of date and end up being tossed. Film equipment was pretty much easily recyclable and would last 40-50 years or more. Ya progress!

[Steve Guttag]

DCA amps are current production. So, they're fully repairable by QSC or one of their authorized service centers. And, by extension, so are CX, PLX and others that used the same motherboards but different front and rear. The CX line JUST left production as the pro audio people aren't using linear amps anymore. Plus, the "Dataport" connector is becoming a cinema exclusive. This allowed them to conserve those parts to the DPM/DCA line of equipment.

[Tony Bandiera Jr]

That's good to know, so EOL for CX should pretty much run until DCAs are also, at least as far as mainboards are concerned. I'd guess (haven't cross referenced that far down the rabbit hole) only chassis panels, labels and other such nonsense should be the only things NLA.

I guess I got spoiled back in the day with my easy access to parts and service manuals and bulletins. From what you said, me as a small fry doing P.A. work they probably won't grant me the same level of credentials as before (though I was able to buy some parts online from them.)

[Steve Guttag]

All I can say is you'll have to try the waters yourself and see what happens. Don't be surprised if you get the cold shoulder. It's a very different company than it was a few years ago. You might find that even getting spare parts to be difficult. They may have moved them to dealer-only (with a restricted selection) and service center only for the rest.

[Tony Bandiera Jr]

Yeah once I gear things up a notch I'll try again, so far I have been able to get what I need from them (other than a CX specific service manual.)