Dead compression drivers - anyone for toast?

[Chris L]

Hi

 

Looks like my compression drivers have gone, and I need to replace them.

I have (all Peavey):

1x PV1500 power amp

2x pro-sub (15")

2x pro-15 (15" + 1")

More info on www.peavey-eu.com for the speakers and www.peavey.com for the amp. I know it's a Peavey system but I think it's good for the price :) .

It's a good amp which I've had no problems with and has a nice feature called DDT compression, which stops the output clipping (Peavey said so ;) ). I run this at 2ohms a side, which seems ok, it's never had a heat problem and I sometimes put a desk fan behind the air input just to make sure. Peavey recommend this amp for these speakers.

 

I don't know what the comp. drivers in there at the moment are, as they give no model number, just an impedance, a date and 2 serial codes on the back of them, which when googled do nothing useful.

What I'm wondering is if anyone knows anything about these speakers and if I can replace these with Peavey RX-22 drivers (ie, whether they'll physically fit/attatch to my horn) as I can't work it out from pictures I've found or the spec. sheet on the Peavey website.

 

Also, I'm trying to work out how I blew them, as I use them from the passive crossover in the pro-sub. I have never turned off the DDT and this amp is the recommended one for the speakers. I'm careful not to send a peaking signal through, but I do push the system fairly hard. I never turn the amp up above +29dB and it gets a signal of just less than +12dBu. I'm careful not to let the DDT active LEDs light more than in time with the music.

Hopefully someone can tell me what I did wrong.

Peavey have some tech notes on their site and I don't think I broke any of these "rules".

 

Any help would be much appreciated as I like my compression drivers rare :D .

 

Thanks

Chris

[Mark Payne]

Hi Chris

 

Sorry to hear that.

 

DDT compression will not ultimately save your HF drivers. No simple limiting system will do this.

HF drivers have two main modes of failure. They either get destroyed mechanically and the diaphragm dome or its mounting is shaken apart and breaks down ... or ... the voice coil gets too hot and burns out. What has happened to yours?

 

With DDT clip limiting or any simple crossover limiter, we prevent the squared off waves that do the mechanical "shake it and break it" damage but as we push into the limiter threshold, we are still increasing the amount of energy being sent and the voice coil temperature can still kill the driver.

 

The fact that you mention something like "I only allow the DDT lights to flash with the music" indicates to me that you are limiting on LF content in the amplifier. There may not be any limiting on HF peaks taking place at all.

 

I you are pushing DDT like a disco light then your system is not up to the SPL you are wanting to generate. And now Mr Peavey has found a second way to communicate this fact to you because you ignored his first warning :-o

 

There are systems out there that protect the speakers more fully by modelling the voice coil temperature, cone excursion and peak limiting all at the same time and controlling output based on all three, making for bullet proof PA.

 

Oh... where you run the amp gain controls is irrelevant. Knocking 3dB off the amp will have you popping it up at the mixer. We already know that you want more noise that your system can generate. Stop doing that. Just turn them all the way up (0dB).

 

Hope this helps.

 

Mark

 

 

 

Hi

 

Looks like my compression drivers have gone, and I need to replace them.

I have (all Peavey):

1x PV1500 power amp

2x pro-sub (15")

2x pro-15 (15" + 1")

 

..... stuff deleted.................

 

Thanks

Chris

[mal421]

I've got a PRO15 with the same problem on my bench at the moment . Personally I want to donate to a local bonfire but the owner insist that I repair it . I also have another peavey compression driver labelled Peavey 22A if this is the RX 22 compression driver then it won't fit the PRO15 cab, it's just too big to fit in the space provided . Sorry I can't be more helpful .

[Rob_Beech]

HF Peaks are a big problem with speaker cabinets using passive crossovers. If you have an amp rated at 500watts its possibly to put all of that 500watts into the HF driver with the right signal. this of course will not do it any good at all and you'll probably end up in the situation you are in now. A smaller compression driver such as that may only be rated at 40watts so you can see where problems will occur. There is a little bit of protection from the crossover as often these can fail first under such a load. there is sometimes some protection on the speaker itself which brings me to the next point. I am not a peavey user but I am aware of some of the older cabinets having a protection lamp in them, which would be run in series with a compression driver. These will blow if the signal gets too high to save blowing the driver. Its not a bomb proof protection but it helps. maybe this is all that needs replacing?

 

Rob

[Chris L]

I'd looked inside and they have burnt out, one still works a little bit.

There's a glass tube with a filament in and a code starting IN in there, which says diode to me but that's def in one piece in both of them.

What I want to do is replace the HF drivers with higher power ones, which will hopefully stop me from breaking any more. I'm probably going to give Peavey a ring tomorrow and see if they can recommend or source a higher power replacement.

What I'm thinking of doing when I want to/can afford to upgrade is to buy new drivers which are higher power/louder etc for all the speaker cabs. Is this a good idea or will the cabinets then be the wrong shape to get a decent sound? Or should I add another pair of speakers to my system, bearing in mind that storage space (my bedroom) is running in fairly short supply. Going to get a second amp + active crossover when I can afford it too.

Still think it's a good system, not the best, but at £130 a speaker for the pro-15s and the subs I think it's good value for money.

 

Thanks for your replies

Chris

[rob.d]

HF Peaks are a big problem with speaker cabinets using passive crossovers. If you have an amp rated at 500watts its possibly to put all of that 500watts into the HF driver with the right signal.

 

ie loud HF feedback. I dont think you mentioned what your application was? Like Rob says, the correct signal will cook a compresion driver in a flash- if the comp driver is rated at 40w continuous, 80w peak, its very easy to see how a 500W amp can generate a signal capable of frazzling the comp driver in a millisecond- and nearly 10dB more before the DDT steps in!

 

As per your query re replacing drivers-

 

Personally, I'd recommend chucking the lot on ebay. Its not because Peavey's bad or whatever (though I'm not a fan- I work for a dealer...)- the reason being this. If youve ever built a sub, youll be aware of Thiele-Small parameters- which are basically a series of measurements of a stock loudspeaker driver , which can be used to determine the relative effect of acoustical loading on electrical loading (ie what sort of sound it will make, given different frequencies, in different size cabs- as the cone moves back and forth, consider the effect that the air pressure inside the box has on the cones movement- suck, squash, suck, squash etc etc. the bigger the box the lesser this effect.), and visa versa. For convenience, we'll forget that you can "tune" a box to a frequency (eg 45hz) with ports where air can get in and out of the back of the cab.

 

Given the correct calculations, you can use the TS parameters to design a box which is the best shape and size for the specifics of the loudspeaker driver. (alternatively use something like winISD, which does it for you and draws a nice frequency response graph on your comp). If you turn this around, you can see that finding a set of TS parameters (of which there are 10-20 and vary ad infinitum) to match your Peavey boxes is likely to be a mission- though you could perhaps check out if they'll work or not if you find something you take a shine to.

 

Incorrectly matching a cab to a box might mean it, at best sounds all wrong, or at worst lets the driver overexcurt and your back in your shop before you know it, ordering replacements for drivers with shagged suspension. As an example, the Eminence Kappa 15 is rated for about 800 watts (if I remember..)- but to make it reproduce any meaningful bass frequency youve got to load the bugger in a 200 litre + capacity box. Thats huge- thats into most manufacturers double 15" size box territory. On the flip side a little Delta 12 will want maybe(?) a 60-80 litre box, just to stop it from rattling against its own suspension stops.

 

The moral of this particular story being- go with something engineered into place by a pro. RCF can build a speaker to match a prescribed box, but they manufacture their own drivers anyway and have a massive R&D department to do it.

 

Hope this helps

 

Rob

[greenalien]

Replacing HF drivers in passive 2-way cabs is par for the course, I'm afraid.

Show me a DJ who doesn't push everything into the red, particularly towards the end of their set...

This problem can be reduced by incorporating a compresser/limiter between mixer and amp. This can simultaneously reduce HF peaks, give a subjective overall increase in volume, and provide a 'brick wall' that reduces any signal above, say, +6db, and thus stops fader abuse by DJ's - and all for under £100. :)

[Chris L]

I knew the cabinet's pretty important, but it's THAT important then, thanks <_<

Just trying to find a "cheap way out" as I don't have a huge amount of cash.

 

The next thing I'm going to buy is a compressor to go between the FOH EQ and amp, especially if that's gonna help. Probably the Behringer autocomp or composer 2-channel one, I forget which I liked more. Oh, and buy some new diaphragms :D

 

thanks for the Help

Chris

[The Boogie Man]

When the funds allow, as well as a comp/limiter for evenining out the dynamics of the sound and limiting the overall peak to the amp, keep an eye out for another amp and put a two way stereo x/over in the line. that will give you a lot more flexibility setting up the sound and give the tops only the frequencies that they want to hear.

cheers

baz