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Old 30th January 2013, 07:25 PM   #1
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Location: Chichester, UK
Default PA Speaker Design Help

Hi, I have a few questions for designing a couple of PA speakers and subs to go with them.The Drivers I am planning to use are linked to below. If there are any better alternatives, please say. Thanks for any answers given.
- Eminence Alpha 10a as Mid driver
Speaker Detail | Eminence Speaker
- Eminence ASD1001 as HF Driver
Driver Detail | Eminence Speaker
- Eminence Alpha 15a as Sub driver
Speaker Detail | Eminence Speaker

Does anybody know if these drivers are OK with each other? I'm planning to run them with an active crossover-3 way. A 4 core cable to each Top cab, with the outputs from two amps going to two separate drivers in the same cabinet. No passive crossover at all. Sorry if this doesn't make sense. I was going to use a 400w/side 8 Ohm amplifier for the 10a, 500w/side 8 Ohm for the 15a, and a 100w/side 8 Ohm for the compression driver. I am trying to keep this as cheap as possible for the band I play with. Preferably under about 120 per cabinet. This is because I am still at high school, so cannot get much money in.
My other question was will it be worth building the amplifiers? I have found a couple of designs that have fairly good feedback across the 'net, for instance, 400W MOSFET Amplifier Circuit With IRFP448 for the 10a driver. I am fairly happy with a soldering iron etc..
Sorry for the long post, and thanks again for any answers.
Ollie Nye
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Old 31st January 2013, 03:58 AM   #2
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DarkDerp
not to discourage a fellow d.i.y.'er from such a noble quest but are you simply choosing to build in order to save money? i don't know your skill level and please don't take this the wrong way but are you sure you can build the stuff in a timely fashion. your bandmates may get impatient if your to busy to rehearse 'cause your building amps?
your speaker project is the one area that may well be but cost effective and rewarding.
building amps can take both time and money (when mistakes are made) and from a reliability standpoint if you feel you can build as good as you can buy used, have at 'er buddy
after a quick look at your amp schematic of choice i'd recommend you find something that has output protection you wouldn't like toasting your new Eminence's(in those lovingly built boxes) testing your newly minted amps!
p.s. what x-over do you have?
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Old 31st January 2013, 07:16 AM   #3
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Thanks for the reply!
I am choosing to build over buy for the cost savings, but also because I would like to have a go a building something that is used mostly every week. We do have a small set of guitar amps being used at the moment, but as I use an electric drum kit, these cannot cope with the kick. I generally play into headphones, then use a splitter for the other three people. As you can imagine, there is quite a lot of cable all over the place.
The crossover I would be using is the one linked to below. Built again, as it doesn't seem too hard to have a go at. +/-15v power supply I believe.
- Crossover
Linkwitz-Riley Electronic Crossover
Thanks again!
Ollie Nye
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Old 31st January 2013, 09:39 AM   #4
JMFahey is offline JMFahey  Argentina
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That 400W amplifier has some important errors, (noobie design), which *no* commercial amp designer would make.
No output protection to begin with, as noted by Turk 182 , no Zobel network (which shows me this amp may "simulate" good, but die when actually built and driving real world speakers), Q11 *must* be a PNP and not NPN as shown , plus emitter and collector must be swapped, R4 and R5 must go to ground and not to +V , etc.
And to boot, it's a heavy and expensive amplifier, which will sooner or later kill the speakers (as duly noted) even *if* you manage to make it work.
Looks like one more example of the "1000W amps" so popular in beginner's Forums .
Oh well.
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Old 31st January 2013, 11:35 AM   #5
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the crossover you your looking at is stereo two way but if i'm not mistaken your planning a three way system aren't you?
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Old 31st January 2013, 12:58 PM   #6
Xoc1 is offline Xoc1  United Kingdom
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Hi DarkDerp
Please fill in your location on your profile Speaker recomendations are often based on what is available at a good price where You are located on the planet!
The HF driver looks to be OK
Have you a suitable HF horn in mind they add conciderably to your budget!
For the best bang for the buck maybe concider a 12" driver for the mid.
An Eminence Beta 12CX Coaxial with an adaptor could get you efficient quality mid up to 2Khz and save you some money!
For the Bass driver you will need to spend a bit more to get a decent driver.
On the eminence website check out the cabinet designs for the Alpha 15 - note the recommended power (100W) The Alpha 15 is also not very efficient.
If you want something that really rocks maybe look at the SS15 design on the Subwoofer forum and save up for one of the budget drivers that would work in that cabinet.
I would not recommend you to build your own amps. Instead buy some secondhand ones that work and save some cash!
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Old 31st January 2013, 01:23 PM   #7
JMFahey is offline JMFahey  Argentina
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Sensible recommendations.
People buys "new/modern" stuff and discard "old" stuff like the incredibly robust Peavey CS power amps and many others same vintage.
Yes, they are large, heavy, use old fasioned transformers instead of SMPS ...
You can have them quite cheap, not only at pawnshops or Craigslist but in the "used" section or GC and such.
Or maybe a DJ or Sound guy has them in his garage and needs the space.
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Old 31st January 2013, 02:33 PM   #8
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Thanks again for all the replies.
For the crossover, further down the webpage contains a mono, three way crossover. Obviously, I would need to build two of these.
As for using used gear, I did think about it, but after asking around in the local area, and searching eBay for a few months, nothing is nearby enough for me to get.
Thanks for the sub woofer thread too!
Does anyone know of a different amp design, with recommended features? I'm not too fussed about the weight, as it will be built into a rack mount on wheels that we have already got.
Thanks again,
Ollie Nye
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Old 31st January 2013, 02:47 PM   #9
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Quote:
Originally Posted by DarkDerp View Post
Thanks for the reply!
I am choosing to build over buy for the cost savings, but also because I would like to have a go a building something that is used mostly every week. We do have a small set of guitar amps being used at the moment, but as I use an electric drum kit, these cannot cope with the kick. I generally play into headphones, then use a splitter for the other three people. As you can imagine, there is quite a lot of cable all over the place.
The crossover I would be using is the one linked to below. Built again, as it doesn't seem too hard to have a go at. +/-15v power supply I believe.
- Crossover
Linkwitz-Riley Electronic Crossover
Thanks again!
Ollie Nye
Go look at the speakerplans forums. They are a UK site with very busy wanted and for sale forums, and will give you a flavor of real pro audio DIY.........

http://forum.speakerplans.com/forums.html

You need a used powered mixer and some used 1x15" pa cabs that should be able to produce kick. That will get you up and running for a few hundred pounds, then you can tweak, mod and build from there. You do not need to build some crazy setup that will probably be unreliable, your bandmates will not like that.

There are multiple reasons your current DIY plan is not viable for pro audio PA.

Last edited by turbodawg; 31st January 2013 at 02:52 PM.
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Old 31st January 2013, 03:21 PM   #10
JMFahey is offline JMFahey  Argentina
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I've checked apexaudio designs here at DIY, because they seem to be popular and early prototypes sem to have been working for years, *but* the "simple" one does have no short protection, and the "complex" one, besides being too much for a beginner, has only a relay short protection which many times is not fast enough.
If they were for a fixed (Dance hall, etc) installation, fine, but PA implies cables in the floor where somebody can trip on them (don't ask ) , connectors, setting up and dismounting of PA system, drunk/stoned/dog tired assistants, etc. , where regular shorts are *expected* often.
In fact, (personal opinion) the *main* difference between Pro PA amps and all others lies in robustness and tolerance of abuse (mechanical, thermal and electrical).
Tons of "Audiophile" Amps easily beat Pro PA types on "quality" but not on "strength", by a long way.
Search for Pro type Power amp Kits available where you live and post them here for review.
They will make your life easier, *specially* the PCB design, plus parts availability from a single supplier, a big plus.
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