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Old 21st December 2008, 09:58 AM   #1
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Default Compact PA system - comments please?

Im looking at building a compact PA system for small pub gigging. It would have two vocals and two acoustic guitars going through it I sometimes tune the bass E string down to D which is 70odd Hz so I wouldnt need anything below that. What does the idea of 2 Eminence Beta 8-CX per side (with an APT-50 in one of them) sound like? Id use the Dayton 2.5K crossover and probably drive each side with 250 watts ish Ive been looking at Rod Elliotts 200w Mosfet amp.

The bass response is dropping off a bit by 70Hz in Bass Box, but by using a 12db/octave high pass filter at 58Hz, I can get it back up to something acceptable, although giving it 250w, the excursion is up to 7mm at 80Hz (Xmax 3, Xlim 13.2). (Rod Elliot also has a 36db/octave rumble filter which will tune to 58Hz).

Any comments on the general idea, or on specifics? Thanks.
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Old 21st December 2008, 03:40 PM   #2
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I doubt 2 x 8" per side will be enough for a pub PA. Best bet is to look around the PA suppliers sites and see what types of speaker they recommend, then DIY your own version.

Rob.

FWIW I'd probably go for something similar to the JBL Eons with a sub running ~35 - 80Hz.

I'd also get a decent EQ for the system.
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Old 21st December 2008, 06:02 PM   #3
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I personally think something like this is your best bet, whether you build it yourself or you buy it.

http://www.parts-express.com/pe/show...number=248-642

http://www.parts-express.com/pe/show...number=248-830

Basically, a 10", 12", or 15" woofer crossed over to a compression horn.

I've chosen these particular speaker just for the photos, you'll have to do a little research to determine which works best for you. These are stand mountable, and in a small venue that is usually an advantage.

Also, when you need to expand the PA, you just go to four instead of two.

If you want to kick it up a notch, consider these -

http://www.parts-express.com/pe/show...number=248-839

http://www.parts-express.com/pe/show...number=245-814

or

http://www.parts-express.com/pe/show...number=245-805


These two are TWO 15" (or two 12") woofers and a compression horn. One of these on each side should do the job nicely for venues big and small.

Again, I'm not necessarily endorsing the specific speakers, they just had nice photos.

Notice that in both cases, these ready-made speakers are relatively cheap. You have to decide whether that is a good thing or not.

In any case, this probably demonstrates the best design for compact PA systems - buy them or build them yourself.

Steve/bluewizard
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Old 23rd December 2008, 03:22 PM   #4
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I don't recommend either of the dual-15" two- or quasi-three-way designs, or anything with a plastic box. They always end up sounding thick and woofy, or like musical Tupperware. A 12" or single-15" two-way speaker ought to serve the OP's purposes just fine.

My suggestion is a pair of these: http://www.directproaudio.com/produc...directid=58931

These will be real workhorses. They're a fair bit nicer than Yamaha's Club series, which have been the de facto standard for bar bands for years and years. The major differences are:

- A nicer HF driver than the Yamaha Club series - a low-compression mylar ring-radiator (Community UC-1)

- A smoother-sounding fiberglass HF horn, which doesn't ring as enthusiastically as Yamaha's plastic HF horn

- Birch plywood construction, which is significantly lighter than the MDF cabinets of the Yamaha Club series and can stand up to quite a bit more abuse.

- HF driver protection circuitry

- Painted finish that won't come off in ribbons like Tolex or absorb liquids, smoke, mold, or odors like Ozite carpet.

They're not the very cheapest speakers out there, but they're competitively priced for the advantages they offer, and they also sound excellent. They'll smack the low-end Peavey and JBL JRX stuff around, and also provide a fair improvement upon the latest Yamaha Club series, ever since Yamaha quit loading their Club cabinets with Eminence drivers. The other bit of good news is their 102dB 1W/1m sensitivity, which means you won't need to push your amps as hard to fill a larger space. Community also has matching powered subwoofers in that model range that are about to hit the stores next year.
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Old 23rd December 2008, 07:27 PM   #5
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Speakers for pub and other small venue gigs have some special considerations that sets them apart from another PA speakers that is often overlooked by professional speaker companies but a diy'er can succesfully incorporate.

What you want is a point source that sound well both up close and father away. As you mention there's also really no reason to go lower than 50-60 Hz. Most PA speakers designed for this purpose use a 12" or 15" woofer combined with a large compression horn. This design makes the distance between the acoustical centers of each driver rather large, and the larger the distance is the lower the compression horn has to go in order to summarize at closer distances.

The problem is that most professional speaker companies do not take this into consideration as lower cut-off on the horn requires larger and more expensive horn drivers.

As a diy'er you can just use a coax speaker and avoid the problem altogether as you have also correctly assumed in your original idea, though I fear that 8" is probably too small for any venue other than a recording studio or small caf. I often find that 15" drivers are too large and that they often sound unbalanced, whether this is because of pure difference in force factor and that the gap between the usable range of the woofer and horn driver becomes too large to bridge in these I can't really say but that's my impression after having heard tons of them over the years. In my opinion 15" woofers require cross-overs at no higher than 1Khz but doesn't generally sound good over roughly 400-500 Hz, so they're better suited for 3 or more way systems.

I'd recommend a 10" coax possibly with an auxilary 10" woofer, or even better just a good 12" coax. Something like the P.audio BM12CX38 which sound incredibly well but for nearly $400 a piece it comes with a hefty pricetag. The P.audio BM12CXA is a little more reasonably priced at $250 each and does retain most of the qualities of it's more expensive sibling.
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Old 24th December 2008, 12:57 AM   #6
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Default 2x8 with tweeter

labougie,

I have been using Eminence Alpha 8" and the APT in my stage monitors for about six years. I replaced Eminence 15" and 1" cabinets at the time. Two 2x8" are about the same output as the 15" and horn, but I prefer the mid range and the sparkle of the tweeter.

The cabinets loaded only weigh 26 pounds.

The APT should not be crossed much lower than 3.5 K, but the 8" still have adequate dispersion, output and sound quality at that point.

I run the cones in series. The sensitivity runs around 101 dB from 80 HZ up. For what it is worth, I just did some SMAART testing between the Alpha 8, the Alpha 8A and the Beta 8, and in my cabinets they read almost exactly alike.

The Beta will take twice the power of the Alpha, which is in real life a bit less than 3 dB.

I would consider the 2x8" to be a little ahead in terms of output to a 10", and right around where a 12" would get you. The advantage of a slimmer, lighter cabinet with more coherent mid hi outweigh the slight output advantage of the 12".

With a pair of the Eminence 2x8" and APTs, you can hit around 123 dB at one meter with only 250 watts. At 50 feet outside, you can still hit 110 dB SPL. That would be very loud for an acoustic guitar act.
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Old 24th December 2008, 02:47 PM   #7
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One important factor, that should be discussed, but apparently hasn't is Price? How much money are you willing to spend in this project?

I'm recommending, or at least showing pictures of, speakers in the in the $200 to $300 range, Taterworks is recommending speakers in the $600 range. I'm sure his $600 speakers sound great, but are you in a position to spend $1200 on a two PA speakers?

I do agree though, that having two single woofer boxes is better than one box with two woofers. And it is also an advantage from a cost and flexibility perspective, in small venues, as I said, you can use one on each side, then in bigger places, two on each side. In really big venues, you can have FOUR on each side.

As to using coaxial speaker, that would be great if you could find speaker that will actually stand up to PA use. As someone mentioned in this thread (or another?) you have to de-rate HiFi speakers by about a factor of about 2 or 3.

So, you either magically come up with coaxial PA speakers, which I haven't seen, or you come up with extremely high power HiFi speakers.

I have seen dual cone PA/musical instrument speakers; that is, a single speaker that has a 'whizzer' cone for high frequencies. But even these don't have great high end response, and typically, they have a very uneven high end response.

However, the idea of running two 8" or two 10" woofers in series is not a bad idea. Two speaker in series aren't any louder than a single speaker for a given amount of power, but, and this is the real advantage for PA use, each speaker only has half the normal cone excursion. You can push a series pair of speakers PRETTY HARD before you reach the mechanical limit of cone excursion.

Also, two 8" are somewhere between a single 10" and a 12". Two 10" are somewhere between a 12" and 15" speaker in terms of relative cone size. Still, for a small club PA speaker, two 8" would probably do a good job.

Another advantage is that the cabinets could be built more like HiFi tower speaker, which would make the very compact and easy to haul around. The overal size and shape and ease of transport is important for a PA speaker.

As to the horns, one doesn't necessarily have to use big high compression horns. There are plenty of Pro-Audio tweeter, horn and otherwise, that are more compact. In the case of this PA speaker, I'm assuming a moderately high crossover, so smaller tweeters should still get the job done, especially if you gang a couple of them together. In adding two 4"x4" horns in series, you gain the same advantage as the woofers in series. It isn't louder, but it will go much louder before you reach the mechanical limits of the horns.

Though I'm sure some will shout me down for suggesting it, you could consider ganging some piezo horn tweeters. These things are DIRT CHEAP, like $2 each, and sound pretty good. Typically they do not need a crossover, but they do needs some resistance in series to assure the impedance doesn't drop too low, and to lower the volume. They are typically relatively loud for such a small device. Personally, I put a resistor in parallel with them, and use them with a standard crossover.

Also, just so we are clear, the photos I linked to weren't specifically recommendations for those speakers, they were simply demonstrating a style of speaker that the original poster could build. They served as illustrations of a style of speaker.

So, I think, we need to establish a budget which will allow us to make some more realistic recommendations.

Just a thought.

Steve/bluewizard
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Old 24th December 2008, 04:00 PM   #8
HK26147 is offline HK26147  United States
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Yes Budget...
and What are the limitations - as far as weight, size, and transportability?
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Old 24th December 2008, 09:55 PM   #9
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Thanks for all the input guys. Some background:

Were an acoustic guitar and a mandolin, two vocals, playing acoustic bluegrass/country style music and as such, massive volume isnt a requirement. The gigs are to 50-60 people in a small room. My current PA is a tri-amped affair, 300w mono into one 12 Celestion 1225e (300w) per side, crossed over at 250hz into 2 x Eminence Alpha 6s per side with a piezo, poled up above the 12s and driven by 75w a side. This will run at much higher volumes than we would ever use and is also big and cumbersome. Im 60 and humping gear about has lost any charm it might have ever have had!

Someone mentioned in a Parts Express review of the Beta8CX that two per side with a single APT50 would make a better-than-expected compact pa and Im really just researching this idea. The reviewer said:

This device is extraordinary. It outperforms other speakers in this range. Combined with an APT-50 tweeter (which is excellent) and a good crossover, you can create a stunning little PA system in a tiny box that beats many of the top name-brand speakers by a mile for a LOT less $$$. Tip: Put two in each box in a vertical array. You can mount the tweeter on one speaker for a super compact design, or place the tweeter (with a wide dispersion horn; APT-150 for example) in between the two speakers for a quasi D'Appolito array. Either way, you will get beautiful imaging, superb off-axis response and amazing clarity throughout the musical frequency spectrum. No matter what tweeter you choose, youll find this driver excels for the range from about 100Hz to 2.5 kHz. There are several finished crossovers here on the PE website that would work for this: (Dayton XO2W-2.5K 2-Way for instance)

The problem would be getting that additional 30Hz at the bottom end and hence the idea of a 36db/octave rumble filter at 60Hz. I cant model that in Bass Box it just gives a 12db/octave high pass but the excursion result for 2 x 8cx in 25 litres driven by 100w (output is around 120db plenty!) with a high pass at 60Hz is 5mm.

Xmax on these is 3mm, Xlim is 13mm. My question is simply: How audible will be the distortion produced by going up to 5 or 6mm of excursion at 70 odd Hz? If it's not going to work, I'll look around at other alternatives but I'd like to cross this off the list (or not!) first. Thanks.
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Old 25th December 2008, 04:16 AM   #10
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Yeah, sorry, but I don't think that reviewer is quite right in his assessment. Well, he may be right on his quality assessment, but he is wrong on a few details.

The Eminence coaxial Beta-8CX is really only good to about 5khz according to this spec sheet -

http://www.parts-express.com/pdf/290-500s.pdf

Meaning the claimed rating of 20khz is not quite accurate.

Further the reviewer recommends the Dayton off-the-shelf crossover, crossing over at 2.5khz, when the minimum frequency of the super tweeter (APT-50) is 3.5khz. Also, the APT-150 is just the APT-50 with a horn on the front. It too must crossover at 3.5khz or higher, and must have at least an 18db/octave slope.

I quote from the spec sheet -

Specifications: * Power handling: 45 watts RMS (crossover frequency 3.5 kHz, 18 dB/octave), 85 watts RMS (crossover frequency 5 kHz, 18 dB/octave) * Impedance: 8 ohms * Useable range: 3,500-20,000 Hz * Fs: 2,500 Hz * Recommended crossover: 3,500 Hz *

From the rated sensitivity of 92db, the frequency response rises to 95db at one point and falls to 88db at another. This is what I said was typical of coaxail speakers. They aren't very stable across their full rated specturm.

One thing I was going to address before was, where is the best place to crossover for this application?

Generally, voice is considered to be in the 300 to 3000 hz range (based on telephone/spoken voice). Though more accurately spoken voice is closer to 80hz to 1000hz, and lead guitar is 80 to about 1400hz. Violin can go up closer to 3200hz. This is all approximate and only considers fundimental. And the top note on a piano is just under 4000hz.

So, does a 3500 or 5000hz crossover really make sense?

Actually, I don't know the answer, but I think it is something that must be considered. Do you want the crossover in the low voice range so the horn handles the bulk of mid and highs? Do you want it in the middle of the voice range, so the load is shared by the bass speaker and horn? Or do you want the cone speaker to handle it all, and only count on the horn for overtones and harmonics?

This must be considered regardless of which speakers you choose.

Now as a bass/midbass speaker, this (Beta-8CX) might actually be a very good speaker, but it is lacking as a full range.

Now here is a 4"x4" Selenium compression horn that goes down to 1500hz, that might allow a 2000hz or 2500hz crossover.

http://www.parts-express.com/pe/show...number=264-240

I'm not necessarily recommending this, just pointing it out as more likely than what was suggested in the review.

Again, I'm raising questions, not answering them. Choosing matching speakers is a difficult task, and without question, rated frequency response simply can't be trusted. You need to see a spec sheet that shows a sample frequency response curve to have any worth while information, and to be able to reach any worth while conclusions.

I'm sure that is no help at all, but I think there are a few things to consider here.

Steve/bluewizard
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