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Old 19th February 2013, 12:03 PM   #1
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Lightbulb Building a new PA from old - HELP!!

Hello Guys,

I am looking to upgrade some old PA cabinets/enclosures with new loudspeakers and compression drivers if possible. At present I have 2 x EV Stage 200ís (full range 12Ē driver, 300w, 8ohm) I would use for the tops/vocals. I also have a pair of Peavey HiSys 5XT (full range 15Ē driver, 500w, 8ohm) for click track backing music, drum kit etc. I have a few mixers, probably either use a Behringer 12 channel or a Soundcraft folio 16 channel. For a power amp I have an American Audio 1500 (500w RMS @ 8ohms, 750w RMS @ 4ohms).

What I was going to do is run the EVís with the American Audio power amp flat-out at 750w @ 4ohms. Then buy a Crown/Behringer etc to run the Peaveys at 1000w @ 4ohms. Could anyone recommend a good system controller for the PA?

I was looking to replace the drivers in the EVís from the 300w to a more powerful Precision Devices PD.125SB30 - 400w or Eminence Kappa Pro 12 Ė 500w for added protection and headroom, as the old drivers were having issues when being driven. Would it be a simple drop-in job? I donít want to damage the compression drivers or crossovers with the new powerful driver?

Same goes for the Peaveys Ė was looking at replacing the old black widows with Eminence Kappa Pro 15LF-2 (600w @ 8ohms). Again, I donít want to blow the comp drivers or damage the crossover. I just need a more powerful, reliable PA system for my band without worrying if the cabs are being overdriven.

Any advice would be grateful?

Thanks!
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Old 19th February 2013, 02:15 PM   #2
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What sort of bear are you?

Yes, you are overdriving your PA.

Here's why.
Consider the total power of your guitar amps on stage. Sum them. Now figure that they run at ~10% THD or more. Consider the SPL that they produce. In order for the PA to produce clean sound at the same SPL you need <1%THD (roughly speaking) or it starts to sound like total poop. That's a lot more power than what the guitar amps produce. But wait, add in the drums. Are you running your drums into the PA? In simple terms, you can't get away with this. Why? because the peak output of the drums exceeds the peak available power and SPL headroom in your PA by many dB, maybe 20dB uncompressed. You don't have 20dB OVER the average level the band plays at. Now let's talk vocals, the vocals need to be undistorted, plus they need to be heard at an average level that most bands mix above the average music level the band is playing at. Plus the average level of vocals is low compared to a guitar, especially one with any crunch or distortion.

So you've got a max SPL and max power issue with the typical small band PA that can not be overcome.

The only solutions come in using various tricks that include compression and limiting, selectively.

A bit depends on how loud you play, and exactly what is going into the mics that feed the PA. That's the other part. That and using EQ cleverly. Boost is your enemy. Headroom is your friend.

Behringer sells cheap and usable boxes that do various tricks that bands need. Used is cheaper still.

Clipping is your enemy. Never clip the PA amps. Period.

Ur best bet is probably Bi-amping.
Use high slopes on the HP for the compression drivers.
Limit the "sizzle" on the highs - it's mostly trash and hash above 10Khz in a typical band setting.

Eminence is certainly dollar wise a good value.
You should do a box simulation to see which drivers give the best results given the existing cabinets.

In a biamp situation you'd run the compression drivers directly, with a soft knee limiter before the amp to absolutely prevent the compression drivers from being over driven, and use an amp that is maybe 2x the rated power of the compression drivers. Always use a single cap in series to prevent DC destruction and accidental LF from doing damage.

The other trick is a small lightbulb in series with the compression drivers, that can act as a slow compression/protection scheme. Typically auto backup bulbs work.

Use the highest power, highest sensitivity drivers you can manage, imo.

250watt class D amp modules are dirt cheap from Parts Express, btw... they do need a power supply though. One might consider putting one of them on each speaker, for example... don't think they can be bridge though... Class D amps are sure cheap and powerful today...

Hope this give a few ideas...

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Old 19th February 2013, 04:49 PM   #3
JMFahey is offline JMFahey  Argentina
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Agree and add.
If you will replace speakers and add new power amps, it means you are only "saving" on the *empty* cabinets.
Not much logic to it, huh?
Plus you are planning to overpower every single component by at least 2X .
Not much logic either.

To better use what you already have, I'd drive the 500W 8r Peaveys with the American Audio 500W 8r per channel AA1500 (perfect match), and get another 200/250W per channel amp for the EV (also a perfect match), and add a couple good limiters between mixer and Power Amps.
As Bear (1) says, clipping is your enemy.
This way, best bang for the buck and .... a realistic goal.

You'll have *now* an excellent system for a Club situation without spending too much.

You want a larger system?
Fine, add up to this basic one (which you will then use as sidefills and monitors) and add whatever you like, but in a modular way, matching Cabinets and Power Amps.

Because if you have 5000W amps and 1000W speakers, you have a 1000W system.
A dangerous to use one, by the way.
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Old 19th February 2013, 05:45 PM   #4
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Thanks guys!

I'm not actually using this setup at the moment. It's just a project I'm going to do. I think I'll use the AA power amp with all the said cabinets. I'm going to put 500w 8ohm drivers into the EV's and keep the Peavey's as they are. I'm going to use one side of the amp to run the EV's at 4ohm, the amp will be pushing out 750w @ 4ohm (according to the spec), and use the other side to drive the Peaveys at 4ohm. That way I think there will be enough headroom for vocals and music tracks. We don't usually mic up guitar amps or drums depending on the venue. But I will have to get a system controller for the setup. Could you advise on one for the gear I got? The driverack looks cool.
Also I need to know if I will damage the crossover/comp drivers if I choose this option?
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Old 21st February 2013, 01:33 AM   #5
JMFahey is offline JMFahey  Argentina
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Quote:
Also I need to know if I will damage the crossover/comp drivers if I choose this option?
Probably, because you will upgrade woofers but not crossovers or drivers.
And you will end having no more than 1500W.
I suggest you set up a system like I mentioned, which needs only a relatively inexpensive 250/250 power amp, you'll still have 1500W , end everybody will be happy.
In either case, you'll need a couple *good* limiters.
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Old 23rd February 2013, 04:35 AM   #6
JackNZ is offline JackNZ  New Zealand
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Very important to know that the original EV speakers are of very high sensitivity because of a light moving structure. So the crossover in the box is tuned to match this driver to the tweeter. An other driver with more watts will probably not be loud enough and the speaker will be missaligned.
One other thing is that if you start modifying P.A. speakers without meassuring what is happening, you end up with a random crossover region that gives you funny lobes of directivity and cancelled out angles. So moving around with a mike will be dangerous and prone to feedback out of trhe blue. Only a P.A. speaker with a smooth amplitude response will handle easy and give you maximum use of your system.
So if you can setup a somehow working meassuring setup or a friend of yours can, than i would suggest changing the 12" in the EV's for something stronger. Emmi would work, but better go for B&C or such.
I would keep the hi range driver, they are not bad. You might have to adjust HF damping or maybe use a speaker processor, with meassuring(!) can lead to a good system and has limiters.
Then don't be afraid overpowering (electricly) a modern 12" driver. They have much more peak power than a old design like the EVM 12 L or S.
They will not break so fast (my experience).
I would leave the Peavey's alone. They are optimized and will sound better if you add new speakers, x-over and a new cabinett, know what I mean?
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Old 23rd February 2013, 04:50 AM   #7
JackNZ is offline JackNZ  New Zealand
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Your American Audio amp is much likely to put out some 400 Watts on 8 Ohms to the EV's. This is not too much as long as you don't see the red light on the amp or try to play back some HipHop sound loud.
Still swapping the EV for a decent Emminence would help. I see no need going for a PD chassis. If you re ready to spend that much, rather go for a Italian neo speaker. Will make your speakers some 6 Kilos lighter as a sideeffect. The EV 12" will break anyway as time goes by. They don't even have to be overpowered.
Processors: DBX Driverack P.A. is the minimum. I would not go for a Behringer processor. They are not very reliable and tend to having issues soundvise.
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Old 26th February 2013, 10:04 AM   #8
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Thanks again guys.

I understand about the point of tuning of components within an enclosure. So would a direct EVM 12L/S be an obvious replacement? I thought that modern speaker builds would be more than adequate especially since the Stage 200 series was from the early ‘80s. Can you recommend a modern replacement instead of the EVM 12L/S with the correct spec for the crossover/tweeter? Or at least get close to it. PD was mentioned to be pointless, can you explain why? I’m all for reliability at the moment as I’ve had a rough time with PA gear as of late. It’s beginning to fry my brain! Ha ha.

It seems through my experience, the only thing that breaks down on the Stage 200’s is the drivers. I’ve had no problems with the tweeters or crossovers.

For basics guys, have you any information on the frequency ranges of passive/cabinet loaded crossovers I would need for a 12” full range cabinet, 15” cabinet etc?
I hope it’s not that difficult to knock together cabinets.

A guy I know of regularly buys empty cabinets from eBay and installs crossovers, drivers and tweeters into them. They sound great and punchy, if only I had the knowledge I guess….ha.
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Old 27th February 2013, 03:10 PM   #9
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To really build good sounding speakers, IMHO, you need a flat response mike, a measuring device (scope or AC VOM or sound card computer) a sine wave frequency generator. An an-echoic chamber is used by the manufactures to test in but you can use the outdoors (if it is quiet). I had a friend that assembled drivers from the catalog in 1970, his 4 driver enclosure sounded awful. Whereas the 2 driver speakers I bought at the store sounded good. Good drivers does not equal good sound, IMHO. Every bit of foam and wood brace changes things. More and better info is on the speaker thread of this forum.
Datasheets on what drivers you buy can give you some information on where to put the crossover frequencies. You can build crossovers out of inductors and capacitors, or op amps and drivers IC's for biamp setups. I would a lot rather calculate the knee of a crossover from parts specs, than 3 driver speaker performance.
Bass only enclosures are the easiest, those 4 driver 15" rigs the main calculation is where to put the reflex port and how big. That you can copy by looking to a certain extent. Full frequency voice or even worse keyboard is a lot more difficult because of the way high frequencies bounce around and cancel-reinforce.
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Last edited by indianajo; 27th February 2013 at 03:16 PM.
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Old 27th February 2013, 03:38 PM   #10
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Quote:
Originally Posted by The Bear2013 View Post
Thanks again guys.

I understand about the point of tuning of components within an enclosure. So would a direct EVM 12L/S be an obvious replacement? I thought that modern speaker builds would be more than adequate especially since the Stage 200 series was from the early ‘80s. Can you recommend a modern replacement instead of the EVM 12L/S with the correct spec for the crossover/tweeter? Or at least get close to it. PD was mentioned to be pointless, can you explain why? I’m all for reliability at the moment as I’ve had a rough time with PA gear as of late. It’s beginning to fry my brain! Ha ha.

It seems through my experience, the only thing that breaks down on the Stage 200’s is the drivers. I’ve had no problems with the tweeters or crossovers.

For basics guys, have you any information on the frequency ranges of passive/cabinet loaded crossovers I would need for a 12” full range cabinet, 15” cabinet etc?
I hope it’s not that difficult to knock together cabinets.

A guy I know of regularly buys empty cabinets from eBay and installs crossovers, drivers and tweeters into them. They sound great and punchy, if only I had the knowledge I guess….ha.

Not knowing anything about the specifics of your existing cabinets, it is impossible to even guess at what would be reasonable as a driver replacement. So, first step is to spec the cabinet dimensions, the internal volume and what the cabinet is NOW set up as (sealed, ported, other...) and how it is tuned in the case of a ported cabinet.

Next determine the T/S params for the existing EV.


Next determine the xover frequency for the tweeters (whatever they are, that would be useful to know too)

Now you are just about ready to figure out what you need or want to do.

That assumes a direct replacement with no changes.

IF you want to buy or build cabinets, then you have a wide open field and the choices are quite wide and varied. An advantage is that you can definitely build a very high performance system DIY. But you need to either follow existing plans correctly OR you need to be able to make your own design choices (don't think ur up to that just yet)

The PD is hyper overpriced (assuming it's the driver company I am thinking of...) - for that much money ur better off buying more of something else, or adding more speakers/cabinets, or buying an existing PA cabinet rather spending $$ on a premium priced driver.

The "knowledge" is pretty simple on one level:

download some freeware bass/enclosure speaker simulation software, plug in the T/S params of your existing speaker into the appropriately entered box volume and (presuming here) port dimensions and see how it looks in the bass end. Compare to the specs of other available woofers. This will tell you how it will come out *approximately* on the bass end.

next is the rest of the response - that can be seen to some extent by the mfrs published curves, if there are any. The driver needs to cover to the xover point and beyond a bit (in most cases) and not have objectionable deviations (peaks and valleys)

You need to consider impedance, that effects xover frequency and slope, as well as amplifier load.

You need the most sensitivity you can find, and the most power handling, that's a balance: power vs. SPL vs. xmax/excursion.

It's all a big compromise. Finding the best compromise is the game.

Worst case you build/modify something, and it sucks, so you sell the parts and go at it again with the knowledge you gained, not much loss $$ wise.

There is lots of information in the forum here on just this sort of thing, ur not the first to want to do this. So, read up. There are really almost endless possibilities and variations to consider and try.

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Last edited by bear; 27th February 2013 at 03:43 PM.
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