Outdoor sound system (not for movies)

[Mike Blakesley]

I am in charge of a local July 4 fireworks display, along with a friend of mine. It started as a backyard thing for just our families, but we started getting more and more spectators who started giving us contributions to help with paying for the show.

In 2015 we purchased an electronic firing system to automate our show. It was the best thing we ever did, making the show better and faster, and safer for us in the bargain, since now we can watch it instead of having to fire it. This led to even more spectators, to the point where we are now putting on our town's "official" fireworks display. Since 2022, it's been held at our local fairgrounds on the carnival midway, which is about a 200 x 700' space. The field is covered in grass so it's a perfect place for watching fireworks.

At some point we decided to add music to the show. Since we're on a tight budget, I resurrected the sound equipment that I used back in the '70s and '80s when I was a mobile DJ. The equipment consists of four Cerwin-Vega PD-18B 3-way speakers, and two amps: A "home" model by Pioneer, and a "pro" model by Crown. (I was on a tight budget then, too.) Both are in the 40+ years old range.

The system has worked well, and the speakers still sound great (amazingly), but that Pioneer amp, which is totally not suited to what it's being used for, is super clunky. So we have decided, after this year's show in which the Pioneer decided not to play at the last minute, to replace these two amps with two new matching ones. We'll keep the Crown for a spare.

My questions for any of you sound experts here are:

1. What kind of amps should I use? Those PD-18B speakers have an "EIA Power Handling Capacity" of 300W. I've always heard that more power is better than not enough, as long as you avoid clipping, so should I get something that puts out more than 300w RMS? Keep in mind, these amps won't be used frequently and yes, I'm still on a tight budget, so while we're not looking to cheap out, we don't want to break the bank either. Something in that sweet spot. I've been looking at the Rockville brand - they offer a pro line of products that are really affordable. Has anyone had any experience with that company?

2. The other question involves our proposed setup. I'll add a photo of the area to this post. Is it better to have the amplifiers up front with the preamp unit and run long speaker wires, OR is it better to have an amp on each side with each pair of speakers and run long RCA cables from the pre-amp to each amp? I'm guessing the first option would be best, given what I know from the theater -- our amps are all in the booth, with long wires leading to the stage. But, if the other way would be better, I'd like to know. We use 12-gauge speaker wires.

Given the size of the field, I'm planning to put two speakers in front of the crowd and two more to the left and right. We don't need to cover the entire length of the field. So the "home base" will be in the middle front, and then the speakers about 100' away on each side, and the second pair about another 150' down the line from the first pair. The photo is pretty self explanatory -- red dots are speakers, and the blue dot is where the control center is, although it doesn't have to be right there.

Any comments, ideas or suggestions would be greatly appreciated! I have 11 months now to work this out... for once in my life I'm planning ahead instead of rushing around at the last minute.

Fireworks-shoot-area.jpg

[Scott Norwood]

Do you actually need to buy this stuff? At first glance, it would seem to make more sense to rent what you need for a once-per-year event, and take some advice from the rental company about what to use.

If you actually do want to buy amplifiers, there are plenty of new-ish QSC and Crown models on Ebay that should be fine. What is the efficiency rating for your speakers and what sort of SPL do you need?

[Bobby Henderson]

With big outdoor events in large fields, I usually see speakers in line array configuration set up in elevated positions (often well above the stage). For instance, here in Lawton the US Army will organize large outdoor concerts on Fort Sill's Polo Field. They usually have a pair of big vertical line arrays mounted above the stage and possibly additional columns of speakers to the left and right. Line arrays are the only thing that can provide consistent audio coverage for that kind of space. The bottom speakers aim down at the people closer to the stage while the top speakers are aimed to the crowds way in the distance.

[Mike Blakesley]

I'm not sure if it would be practical to rent anything, because there are no companies in this area that rent this kind of stuff... but I have to admit I've never checked on that option, I'll look into it.

This doesn't need to be concert level sound, it just needs to be decent sounding.

[Tony Bandiera Jr]

Mike, any good QSC amplifier rated at least 400w/ch will do well with your speakers. There are lots of used QSC available at cheap prices on fleabay and Reverb (an excellent site that I have bought some gear from recently.) Reverb also has an excellent mixer for your application, Beheringer ZMX 8210/8210v2 that has several mic inputs, two stereo line ins, and an additional mono AUX output. https://reverb.com/marketplace?query=beheringer%20zmx8210

Note: The link results says "No results found", but if you look at the related items below that you will see the results anyways. Might be a glitch on Reverb's page.) Availability at that low price is limited, so grab one now.

That mixer also has "Ducking" on the Mic 1 input, so the music mutes when speaking, then fades back up when you stop talking. I have used several of these for my motocross P.A. systems with great results. For $150 it is hard to beat.

EDITED TO ADD: Reverb also sells new and used Pro Audio speakers at decent prices, if you want to upgrade.

Back to the amplifiers, any of the QSC line CX, PL, PLX, RMX, etc, will work well and there are several examples on Reverb as well as fleabay. I found a CX302 (300w/ch) for under $200. Plus the CX is essentially the same as the DCA Series, light weight and built well. QSC is the ONLY amp brand I have found that will take all the abuse a portable setup throws at it, and I haven't had a single one fail despite heat, extreme dust, being dropped, and getting rained on. Out of over 2,000 QSC units I have installed, both in cinema and live sound, nothing beats them.

My current permanent MX system has 16 horns in two zones, and covers a very large area with enough volume to overpower 30 dirtbikes. It is the 8210 mixer with a CX302 (with outboard 70.7v driver transformers) for 600w total power. (Of course, the horns are meant for voice and have no bottom end, but you get the idea.) My portable MX P.A. system uses 6-12 horns (depending on location) with same mixer and a CX302V (direct output at 70.7v) in a 3RU road case, the whole case is just under 30lbs. I will be doing a thread in Film Yak about both systems in the near future.

As for the 40y old Crown, I wouldn't trust that thing farther than I could throw it. It is on borrowed time, and when it lets go, it WILL send the full DC rails to your speakers. Put it on the shelf as a display, or better yet, use it as a boat anchor.

Stay away from Rockville, Peavey and especially Pyle! Those "bargain" brands are not worth the money, as they often lie about power ratings, and the build quality is crap. Since your events are "one-offs", you want reliability as you don't get a second chance to do the show over if something fails. Plus I am willing to bet that none of those brands has a better featured mixer and more stable amp than the combo I recommended above. (And will probably cost more.)

tldr; Don't buy unknown, economy brands. You can easily find quality brands like QSC online, and the Behringer 8210 is an excellent bargain mixer for live sound applications. And get the Crown retired before it retires your speakers.

[Harold Hallikainen]

I like having the amplifiers at the speakers or use of powered speakers as opposed to very long speaker lines. But, long unbalanced low level lines (like those with RCA connectors) are inviting ground loop hum. If the mixer has a balanced audio output and the amplifiers have balanced audio input, long lines will work fine (we used several mile twisted pair telephone lines in broadcast). If balanced lines cannot be used, I'd stay with the long speaker wires.

Good luck!

Harold

[Marcel Birgelen]

Billings is "next door" isn't it?

I agree with Bobby and Scott, it's far more usual to rent this kind of stuff for a once-a-year show than to buy it. The only problem you may face is that the 4th of July may be a challenging day to get anything rented.

For outside setups, we only use line array setups, which are all active systems. Line arrays have the distinctive advantage that you can really aim them at the crowd and avoid leakage into the neighborhood as much as possible.

Professional sound will not use RCA cables, but XLR. To reduce wire gauge, amps are usually pretty close to the speakers or like far more common those days for temporary setups: Speakers are active speakers. Running unbalanced (RCA) cables for more than 50 ft. will get you into trouble, while XLR can go up to 1000ft, at least theoretically. Because audio signals have the tendency to degrade over long distances, digital transport is becoming more common those days.

[John Eickhof]

i would recommend a 70v line system, i provided the wide area sound for the fireworks here, for over two decades covering several acres w/ 2-3000 in attendance, is on our high school track, i use a sure mono mixer tied to a qsc 900 with outputs bridged, feeding a qsc ot-300 output transformer,i use 12 30 watt 70v pa speakers long throat with 20" dia horns, they are military surplus made by electro-voice or altec, spacing is approx 40ft in a single line array on 6ft tripods the listening field is from 40ft in front of the array to 80ft with minimal loss of level , even well audible over the sound of the fireworks. i have less than $1500 total in this system and it has been working fine for 3 decades here! coverage is great with no time delays needed. i have done larger systems for parades, etc. mike, i can help you design a system and direct you to where you can get the components, 70v line affords you low lioss on long speaker feeds where pre amp {or line level) feed over distances is not recommended

[Harold Hallikainen]

Good point! I had forgotten about 70V line systems. I used to use them to distribute audio around offices. Is it really practical at high power levels? It seems like you'd need a pretty big transformer at the speaker.

[Mike Blakesley]

Billings is "next door" isn't it?

It is, but I figure by the time we rent equipment, drive there to get it (and take it back), it might only take a couple or 3 years before we'd pay for owning stuff. Depending on how much we wind up spending, that is.

Thanks for all the above info, I always knew there was a lot I didn't know about sound but this thread is really getting informative.

[John Eickhof]

years ago when i worked at altec service, we were well trained in large area arrays, for auditoriums, stadiums, hotels, casinos and even prisons, in actuality, the transformer at the speaker is relatively small and most speakers are tappable for impedance and wattage, older professional amps like altec, rca, ampex and others utilized transformer outputs, a large number of speakers could be driven off one amp, for example drive in theatres, 500-600 or more speakers off one 250 watt amp! also pa and paging systems, you have to know how to calculate load vs coverage, altec was the forefront of the large area arrays back then, these amps had 4,6,8, 16 ohm outputs for ordinary use ie single two or thee way speaker and 25v (250 ohm) and 70v (500 ohm) taps for large arrays, newer solid state amps like QSC do not have the higher impedance levels so they utilize an outboard transformer to boost the 8-16 ohm level to 25 or 70v line, the beauty of this system is that you will not get impedance variations between speakers as they operate plus, in the case of drive-ins, you could have a user volume control that would only effect that speaker. like you would with low impedance systems, plus you can tap each speaker at a different power rate depending on volume levels are required for that speakers coverage. overall its a very efficient way to cover a very large area with good sound and less dark areas, the most important rule is to make sure the total speaker wattage load does not exceed the amplifier power...as the amplifier will overload, runaway or severe distortion will result! I have seen shorts at the post in drive-ins literally arc apart with some of the old vacuum tube amps! my favorite was the altec A-287W a 275 watt amp it was indestructible! Ballentyne made a powerhouse 200 watt amp back then too, plus if more power is needed amps could be paralleled easily without phasing issue unlike low impedance! I have a pair of altec horns with 288 drivers that i set up for parades that are clearly audible for 6 blocks and have altec driver transformers and I us a single 35w amp to feed them! the important thing is the speaker line are less susceptible to pick up outside noise, static, or line loss due to the 70v line carrier then low impedance or low signal level line impedance wiring. Harold, the secret to large array is proper coverage, altec utilized a lot of components similar to their voice of the theatre speakers for their large array systems at 70V line, of course the drive-ins were more economy minded thus the inexpensive speakers and fairly limited range of sound, and of course mono soundtrack! however the larger 2 way systems sounded better but of course were not as good as a nice indoor with good acoustics!

[Tony Bandiera Jr]

Guys, line arrays are indeed the BEST solution, but far too expensive to even rent for this kind of event. (Plus many line arrays will require towers and rigging, yet another expense and complexity.) The space is only 200x700 feet, big, yes, bot NOT line array big. He is also not looking for true concert level SPLs. It IS possible to cover that space well enough with standard passive speakers. Using powered speakers means running power to each of his speaker locations, PLUS a balanced audio line. With total speaker wire lengths not over 200-250 feet, 12 or 10ga. speaker lines will work, with minor losses. Also, I don't like the idea of having 120v power cords laying on grass accessible to the public. That said, it IS an option, but Mike's goal is to do it for minimal cost, and powered speakers of decent size are expensive.

John, I agree and disagree with your approach in this case. Again, the relative area to be covered is small enough that 12 or 10ga speaker cables will handle the demands here. A 70.7 volt system is also overkill (and good luck nowadays finding speaker transformers that can handle reasonable low frequencies without costing a fortune). Since most fireworks shows are set to music, you need full range fidelity, and that gets very spendy in 70v land. You may personally have the right transformers and so on, but we are trying to keep this simple and inexpensive, yet still perform up to snuff. Now for what I have been doing, with the racetrack PAs, 70.7v is the ONLY right way to do it. Many horns, each at sensible power levels, and fed with 12 ga direct burial cable good for up to 1,000 feet before any significant losses happen. But of course the fidelity is voice-only, virtually no low freq below 500hz.

QSC DOES make direct 70/100 drive amplifiers (in the now discontinued CX series, the CX 204v, 302v, 602v) and they have a new line (Check the Q-sys website, they are under Power Amplifiers) the MP-A20v, 40v, 80v 2,4,8 channel x200w) that can do 70 or 100v (bridged) systems directly. There is also the CX-Q Series all-singing, all dancing models which can drive lo-z, 70 or 100v in any combination.

To be clear, I am NOT bashing anyone for the suggestions, and all of this is what makes this forum so good, we all have great ideas for solutions to problems. But my time spent doing live sound for concerts and events has taught me that sometimes, simple is better.

[Marcel Birgelen]

I agree that a "concert style" line array setup would be complete overkill for an "extended garden party", although line arrays come in many shapes those days and there are small, easily portable and easy to deploy systems that come with their own "rigging", that don't break the bank. The advantage of those systems is that they're pretty power-efficient, by not wasting too much energy on shooting soundwaves to places you don't want them anyway. Another advantage is that you can keep the setup simple: put two small line arrays, each about a quarter from the edge of the field in front of the audience, and you'll cover most of the field with a good stereo image and you reduce cable running lengths to a minimum. With only two audio sources, one for each channel, you also won't get nasty interference. But, certainly, I didn't want to suggest that Mike's solution would be getting L-Acoustics on the hook for some major dance or rock-concert setup.

Personally, I don't think I'd go with a 70v system though. It depends really on the availability in your region, but around there it's really hard to find GOOD equipment for decent prices at those power levels. A lot of it is old and really sounds horrid, as it will not handle low and very high frequencies very well. I'd rather consider a 70v system when I'd to cover an entire street with some background music on a budget.

I'm all for rigging your own stuff, especially if you know what you're doing or if you want to spend the time to learn what you're doing. You can get quite a mileage with some used QSC CX amps and a bunch of passive cabinets, especially if you can source them cheaply. But if you don't have the knowledge or simply don't want to put in the time, I don't think it's a bad idea to try and rent some stuff. There's usually all kinds of rental out there, ranging from big concerts to your garden variety party, the latter ones usually not having concert-style-audio-budgets, but something that can be rented for a few hundred bucks an evening. In the end, you'll only need two sufficiently sized active speakers and some decent XLR wiring. If your PA mixing doesn't have balanced outputs, get an isolation transformer for a few bucks. If you arrange for transport yourself, the price should still be reasonable.

[Carsten Kurz]

If you can feed balanced audio to the remote amps from e.g. a mixer, I would use amps local to the speakers. It is better to feed AC over long runs. If potential rain is an issue, it's probably safer to keep the amps near the mixer, and covered by a tent, and just cover the speakers.

I guess you can get these older QSC USA series for very little money now. 20 years ago, every cinema had them. They are very solid, and some owners would even donate them for free. I got a few for free.

[Scott Norwood]

Is anyone really dong 70v systems where sound quality matters? I tend to think of it is being for Muzak-style paging and background-music systems, not for foreground music. The first theatre where I worked actually had a 70v system for the surround channel, but that was installed in the 1950s, and I have not seen anything like that in newer installations.

Anyway, I'm still on the side of renting equipment for a once-yearly event and making all of this someone else's problem. Which has the benefit of not requiring maintenance, not having to worry about liability if someone trips on a cable, and being able to do something different next year if this year's setup is sub-optimal (or if the requirements change).