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[Joel North]

Hello! long time reader, first time poster..

Seeking advice after I've had two woofers at the club blow in the last month and I've been recommended to check my amp before having them re-coned.

The speakers are EV QRx 115. As part of a 3-way, tri-amped system, the woofers are only taking above 100Hz and being driven with 550w each from a QSC PLX3002. Maybe a little underpowered, but the amp is not pushed too hard into limiting/clipping.

I've had a temporary speaker in place for about a month, which is fine. And I put a temporary woofer in the second speaker which is fine. They aren't blowing up instantly. And, the two woofers that are blown did not smoke, they don't smell burnt. They are just giving an infinite resistance reading when measured.

It's funny that they both went in a relatively close time frame, but I just attributed to it being in a club and they would eventually fail, given the amount of heat in the club I'm sure that makes the woofers less efficient. I'm very careful with the system, and even though a DJ takes over after I leave, I still monitor things closely and I personally don't feel that the system was being pushed beyond it's limits or into distortion.

Is it possible the amp could be responsible for this in some way, ie; DC? The QSC has automatic DC protection so I am doubtful of that. What would the amp do that could cause the speakers to burn out (although not both at the same time)? And are there any sort of tests I could perform to make sure my amp is OK?

Any other ideas or speculations?


Thanks in advance

[Stuart Pendleton]

If it were the amp, I would expect the failures to be much faster than you indicate.  Prerecorded music generally lacks dynamics. Because of that, speakers are derated when used for that purpose.  Although the QRX115 says 400 watts, and 550 watts would be OK for live music, it is above the safe threshold for a DJ.  Secondly, DJs are fairly notorious for causing red lights. Being in a club is actually one of the intended environments for these cabinets so I don't think that has anything to do with the failures.

My best guess when reading this thread (with limited background to go on,) is that the DJ is blowing up your speakers by running prerecorded music with little dynamics too loud for the gear. In this situation, a limiter is your friend, and the only sure way to protect the speakers.

QRX is a good speaker series (I own quite a few of them) and they are not prone to failure unless driven past their ratings.  QSC amps are good amps with enough history that I would not make that my first thought.  DJs are prone to overpowering, gear failure, and have a known history with most live sound professionals.  That is where I would start my corrective actions after replacing the speakers with OEM 15s, or having the originals reconed.

[Joel North]

Thanks for the insight, Stuart. You may be right, perhaps they were just driven too hard. The DJ's do abuse them, and maybe this abuse week after week has caused them to die, rather than the normal "blow ups" I am used to seeing in speakers.

I'm also considering to push for a DriveRack (unfortunately, there is no speaker protection now aside from the amp limiters - and common sense - which is not used after I leave the building!).. the money to buy new woofers could nearly buy a DriveRack!

Also, another great clue here that I forgot to mention, but will make the DJ look guilty.. A couple of months ago, shortly after I began the job at this place, I fixed an issue where the amps were tripping a breaker if the volume got too loud. This acted sort of like a "natural limiter" in that the DJ had to be careful of the volume. Now without that in place they are free to push the system as hard as they want, and probably the added strain on the woofers is what caused them to die.

We really need a processor / limiter in a club situation. DJ's push and push, crank the bass, crank the volume. Really need the limiter in place to take care of things, though I was hoping the amp limiters would have been enough in the meantime! If I am going to lobby for $$ to buy a processor, I want to make sure the woofers don't blow again in a month!

[Stuart Pendleton]

Somewhere on here (or the original LAB) was a thread that was interesting.  Someone used a compressor on the main outputs for a DJ.  Whenever the appropriate level was exceeded, the compressor kicked in hard, dropped the level WAY down, and held it there for a while. DJs realized that if they went too high, they actually shot themselves in the foot by reducing the audible level substantially.  Just a thought.

[Fernando Lopez]

Somewhere on here (or the original LAB) was a thread that was interesting.  Someone used a compressor on the main outputs for a DJ.  Whenever the appropriate level was exceeded, the compressor kicked in hard, dropped the level WAY down, and held it there for a while. DJs realized that if they went too high, they actually shot themselves in the foot by reducing the audible level substantially.  Just a thought.

That is a good answer Stuart,

Has the op considered a pair of subs? Since you are only sending 100Hz and above to the tops I would assume that the DJ is cranking the low frequency on the mixer and thus that could be the culprit

[Jonathan Betts]

If there is no RMS limiting and you are running that rig into the red (DJ music)then it is only a matter of time before they die. I like to set my RMS limiters at half the rated RMS power of my cabinets.

[Joel North]

Interesting thought about the compressor but probably wouldn't be good for my situation. I work closely with the DJ's and am friends with them, so they'd probably ask me to "fix it".. I wouldn't want to explain "well it's a punishment until you learn to behave!"  .. If this weren't the situation I'd definitely implement that compressor.. great idea!

Everything below 100Hz is already handled by a set of QRx218S's. Now those I am surprised are not blown. DJ's aren't happy till the red lights are on, and I can hear the subs bottom out sometimes. But they keep on kicking!

Jonathan, thanks for that tip. Now that you guys point it out, it seems reasonable that they blew.


I don't mean to sound irresponsible here. The club has been dealing with these problems long before I arrived and it's just how things roll. Same thing in all most places around here. No limiters, not really enough Tops, everyone wants it louder, speakers blow because they're "junk", buy replacements, etc.. I operate the system responsibly but once I leave is when the problems happen.

I'm curious why it took this long for things to blow (since they are pushed about the same each weekend) but like I guessed already, perhaps they've just been getting progressively worse as time went on. A limiter is needed or it sounds like we'll be needing repairs again soon!

[Stuart Pendleton]

As far as the compressor, tell the DJ the new speakers are prone to power compression but they won't blow as easy. Just back off before they compress!!!!    ;-)

Get a limiter and be done with the issue.  A Driverack limiter will help but it isn't a brick wall.  Look on eBay for something like an Aphex Dominator.  You can't even hear it when it hits the threshold, but it is a brickwall limiter that stops everything from getting past it.  Other limiters don't play as nice, or work as well generally.

You can find the Aphex for $200-300 usually if you look carefully and bide your time a little.

http://www.ebay.com/itm/Aphex-Dominator-II-Broadcast-Radio-Limiter-720-/250891084708?pt=LH_DefaultDomain_0&hash=item3a6a4623a4#ht_500wt_1411

[Jonathan Betts]

Interesting thought about the compressor but probably wouldn't be good for my situation. I work closely with the DJ's and am friends with them, so they'd probably ask me to "fix it".. I wouldn't want to explain "well it's a punishment until you learn to behave!"  .. If this weren't the situation I'd definitely implement that compressor.. great idea!

Everything below 100Hz is already handled by a set of QRx218S's. Now those I am surprised are not blown. DJ's aren't happy till the red lights are on, and I can hear the subs bottom out sometimes. But they keep on kicking!

Jonathan, thanks for that tip. Now that you guys point it out, it seems reasonable that they blew.


I don't mean to sound irresponsible here. The club has been dealing with these problems long before I arrived and it's just how things roll. Same thing in all most places around here. No limiters, not really enough Tops, everyone wants it louder, speakers blow because they're "junk", buy replacements, etc.. I operate the system responsibly but once I leave is when the problems happen.

I'm curious why it took this long for things to blow (since they are pushed about the same each weekend) but like I guessed already, perhaps they've just been getting progressively worse as time went on. A limiter is needed or it sounds like we'll be needing repairs again soon!

The speakers voice coil probably went. Since you have a 100 hz HP filter on the cabinets it probably wasn't mechanical damage. Let us know when you replace the speakers what the damage was. This is good info to know for people reading this thread.

[Jonathan Betts]

Speaking of limiters, does anyone have any experience with the dbx 1066. I found one for cheap and was considering using it with my QSC 4050hd setup. Are the limiters good in these? I like the fact that they have compression, gate and limiters all in one unit.

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