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Old 10th April 2004, 01:03 PM   #1
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Default Building a set of PA speakers, any help appreciated.

My uncle plays with a jazz band and at the moment they play gigs where people supply the gear. However the time has come when he wants his own set up so he can advertise that they have it to hepfully get more work.

He asked my advice on what he needed to buy as he didnt really have a clue. So I was going through the peavey catalogue he had looking at the stuff and thought that the amps were quite reasonable. £600 for a 2*600watts 4ohm RMS 9 channel mixer. But it was the speakers that looked too costly so I offered to build the whole shebang (speakers) for him.

He needs to play sound to about 100 ppl and remember this is jazz and not a disco or night club thing so the demands for overall SPL are probably not going to be as high.

I recommended two 18" subs that have the monitors on top of them. Using 12" bass/miss in them with a compression driver for the topend. So in other words two bass bins with those "top hat" things with metal poles supporting the top bit.

Something like Eminence Omega Pro-18 18" for the bass bin, Delta Pro 12 for the bass/mid in the top bit, with a suitable high freq driver. I dont know anything about compression drivers so dont know where to start with regards to whats good and whats not, recommendations needed otherwise im shooting in the dark with what to choose.

Also whats the deal with power at these things. I would have thought active would be the best, but this adds on more amplifiers, if I were to go active how much power would be recommended for each driver?. I am no stranger to active xovers so building one is not going to be hard, but is it necessary. Do I want to design this as a three way using the sub bit just for bass duty? or a two way and a sub where both the 12" and the 18" do bass. Is baffle step necessary?

I am a very confident person when it comes to xover design and my ability to build the speakers etc, thats not the hard part. I just want to know what basic requirements are needed to make a good sounding PA set of speakers that will fill a 100 ppl space with jazz music.

So I want driver recommendations, if the mid and bass units I have selected are fine then thats no problem. Just the tweeter is needed again I dont have a clue with regards to that.

Active or passive - how much power would be needed with each 6*200 watts? active thats gonna get very loud with 95dB speakers. I would also be buying the amplifiers, I am confident in making them its just Im not confident they would be able to survive a PA environment. My speakers on the other hand you could jump on them and they woudnt break.

Thanks in advance Matt
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Old 10th April 2004, 01:23 PM   #2
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The sub / mid drivers will be fine. If you wanted to go all Eminence, then the PSD2002 1" compression driver is fine on a constant dirctivity flare (not sure what models Eminence have to offer here. Alternatively some of the P.Audio drivers would be ok, or the Peavey 22XT.

I would be inclined to run the top box passive, with a crossover around the 2 or 2.5kHz mark (with bulb type horn protection), and use active crossover to the sub boxes. Don't be tempted to let the 12s carry the same signal as the subs - crossover here could be around 150Hz or so.

Somehere around 400 - 450W per channel amp for top boxes, and 700 - 750W / channel for subs would work well

The metal pole between top hats is a good arrangement, and lets you couple the subs to the floor while still getting the top boxes up. The spacing will not be a problem in practise with a low crossover point.

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Old 10th April 2004, 01:46 PM   #3
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I take it we are talking 400/700 watts into 8ohms and not 4ohms. Having a look at PA amps they all seem to mainly specify the 4ohm rating as the main spec, I know this is probably just marketing hype but still. Its just to me 400/700 seems like an awful lot. Our school had a peavey set up like I described, and this ran off a 200 watt sereo amp and filled the room which was about 15*30 meters. I would have thought something like 250 on the top and say 400 on the bottom would be enough. Obviously Im not in any position to really talk about this. 4*80 and 2*200 gets my room cooking 3*4 meters, and this is with 83dB sens speakers.

If I really will need all that power then just tell me and I'll tell him, but I dont think the kit they have been using is anywhere near as "powerful" as that.
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Old 10th April 2004, 01:47 PM   #4
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Hi Matt.

To be honest, I find the 18" way overkill.
A good 15" will suffice, and Your uncle will prefere the size and price of the 15" to the 18" !!
It's only about 100 ppl, not a stadium ;o) (yet)
A cheap but good and capable supplement, capable of making it on it's own, could be a 60 litre box, tuned to 40hZ, with a Beyma 12G125 and a Bayma CP-385 Nd/TD245, with an asymetric (6dB/oct. LP - 18dB/oct. HP) x-over at around 2,5kHz.
I have good experience with the 12G125 in this configuration, although with another "tweeter", but the CP-385 Nd has revieved very good reviews lately.
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Old 10th April 2004, 01:50 PM   #5
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The general PA rule of thumb is around 6W to 10W per person in the audience when spec-ing a system, so you should have loads of headroom with your planned system and Centauri's suggestions. However, as this is for a Jazz band, I think you could probably get away with just the one sub per side. Stick with the two top boxes per side as this will be useful for spreading the sound around in difficult venues.
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Old 10th April 2004, 02:07 PM   #6
Bull is offline Bull  United Kingdom
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The Eminence Omega pro 18 will be fine for sub bass/bass or even better the Magnum 18LF.
If you want a smaller more portable sub use the Kappa pro 15LF or the Omega pro 15.
The Delta Pro 12 is fine for midrange.
I personally don't like the PSD2002 comp driver so a Fane/Beyma/B&C compression driver would be better.

Build the cabinets out of 18mm birch plywood and use something like hammerite matt black paint.And also brace the cabinets well,and put metal ball corners on them,and the cabinets will last decades!

The mixer amp would be underpowering them as the Omega is 800w rms,Delta 12 is 400w rms,and 1 inch horns are around 40w-100w rms depending on how high you cross them over.

So you could use the mixer/amp to power the mid/highs and buy a seperate amp to drive the lows like the Crown Macrotech MA3600VZ OR MA5000VZ [get them 2nd hand as they are expensive new].

Also if you use an active crossover,still use a high pass passive filter on the tweeter horns.As they are easy to blow,and even switch on thumps can fry them.Thats why you use a passive high pass filter to protect the HF in an active system.


Good luck!!!!!!

And a picture of the amps
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Old 10th April 2004, 02:09 PM   #7
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JMO here for some things to consider :

First you need to ascertain what will be going through the PA,
if the whole band is miked up including drums and bass or
sometimes for smaller venues are they unPA'd.

If so ideally the sub should be optional, IMO a good 15" would
be fine. The main speakers a good 12" and good medium sized
horn c/o at 1.5Khz should be fine.

Also note a 9 channel mixer is not much at all when
you are miking up a drum kit, so check on this also.

Your microphone set up, cables and stands is not going to be cheap.

You also need to consider monitoring requirements, ask them if
they need them, how many, and whats put through them.

IMO baffle step is neccessary and is usually ignored, as is the
tendency for PA drivers to have excessive midrange. You should
be able to build a far nicer sounding "rig" than the run of the mill
stuff if you stick to basic loudspeaker principles.

You could consider a 4 ohm MTM 10" 2 way with BSC, c/o ~ 1.5Khz,

sreten.
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Old 10th April 2004, 02:10 PM   #8
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MA3600VZ
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Old 10th April 2004, 02:24 PM   #9
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OK there will be no drums its a gypsy jazz style thing as per matin taylor or django.

This will incluse a sax, two guitars, keyboards and a bass. Nothing over the top. I also had a chat to him about this and I didnt fully understand his requirements. This is not to play as a concert, its music for events to provide live music whilst people can talk.

Also quite a lot of the time it will just be my uncle and a mate playing two guitars, as in no bass. So I thought that it would make sense to use the two way top thing as a full range so for the smaller venues they could just use that on a stand. But when the whole lot let together use the bass bins and an active xover to take the bass off the two way and the mids off the bass.

Yes you are right an 18" will probably be ovekill and he will be much happier using a 15" with regards to size. All this has to fit in an esate ford mondeo.

So now im thinking the same 12" I originally stated, a good compression device as per recommendations and a 15" driver to do bass.

Sreten you have a good point when mentioning monitoring, he did mention something about this. He is going to ask the guy he usually gets equipment off when he needs to about the spec of that to give me some idea of the requirements with regards to SPL. Again I dont think 400 + 700 watts is needed for background music at events.
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Old 10th April 2004, 02:43 PM   #10
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In that case, I would go for a pair of 15" plus horn boxes passively crossed over, driven by a 2x300w amp. Keep it simple and small. If they need some more bottom end, you could build a couple of extra 15"s at a later date.

If you build the top boxes wedge shape, you could build a couple identical extra as monitors.
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