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How could i blow 2 mid range speakers at the same time ? PA Equipment.


syzsounds

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Hi guys,

I've been passed onto this forum over from the AV forums as they said you might be able to help me out better than they can ,

 

On a mobile setup im using I have blown 2 of the mid/bass speakers at the same time.

Im using the OHM RWS subs and the OHM RW3 top cabs.( matched set)

Running from an inter m 3200 amplifier.

Coming from a Kam 960 setup and a KAM gmx mk2 ..( old I know .but they do the job !)

 

What happened was I was using them at a car show and they just started to sound terrible so knocked the system off and had a check ..nothing found so carried on.

There was a smell coming form one of the top cabs but no sound change at all.

 

My thinking maybe is that there wasnt enough power to run the amp from the generator I was using.

Would I be right in thinking that not enough power could blow the 2 speakers ?

Its very strange as the 2 subs seem to be fine and the 2 bullet style tweeters are fine too.

 

Any help would really be appreciated as its starting to get expensive.

If you need to know anything please ask away.

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Simon,

 

<disclaimer> It is impossible to know exactly what occoured without examining the equipment and without having taken tests on site.</disclaimer>

 

<speculation>Looking at the paper specifications of your setup. Your amplifier is capable of providing 1200W per side into a 4hom load. The RWS and RW3 cabs appear to be 300W each at 8 ohm. Making another assumption about the efficiency of the passive crossover you are using, this gives you 600W per cab. In theory this isn't a huge problem It does depend on the material you are putting through the system though. With heavily compressed DJ music I would be less happy with a 2:1 ratio of amplifier power over speaker power than I would with live music, however each to their own. If you have used this system regularly without blowing drivers then it is unlikely that the setup has caused this problem.

 

I suspect you are right in suspecting the generator. Basicaly your amplifier is capable of 37dB of voltage gain.

 

If you start off with a 0dBu input (0.775vRMS) after 37dB gain your amplifier will trying to producing something like 55vRMS which would require voltage rails something like +/- 75v

 

IF your mains voltage is low, then the power voltage rails in the amplifier might be running low, So when the amp is trying to produce 75v, and the power rails are sitting at 65v then all your waveforms will clip at 65v - much lower than normal.

 

Cliped waveforms coming out of amplifiers are very bad news for speakers.

 

If you know what you are doing, it might be worth measuring the output of the generator next time you use it.....

 

Apologise for the huge assumptions here,

 

James

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Thanks James,

 

What I forgot to mention is that we have had one speaker blow before but I put this down to old age and heavy useage.

The amp is now going in to be looked at ..its the PSR 3200 and they dont make them anymore :)

 

Anyhow , Im changing the sub box speakers into the tops to make them a mid/bass, Looking at the specs they should be fine.

 

Now im on the hunt for some suitable subs to replace them.

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Hey

I used my system awhile back and I ran it to hard with no protection except for the clip on the amp,

they were in the sun and were clipping allot, when I was finished I went to pack up the system and the boxes smelt of burning.

When I tested them I found a rattle in one of the 15" drivers (it sounded like a wire taping or rubbing against the cone, it was independent to loudness).

That was a couple months ago, I have used the speakers scence on a festival and successfully managed to fry the speakers and they don't work.

 

Things that come to mind that you might want to check/look at:

-Was the Generator producing a true sine wave (50Hz if you are in Australia)?

-The frequency's that you are putting through the speakers, can they handle them?

-How dead the drivers are, depending on the price you can get them fixed.

-Peak limiting equipment to stop the amp from peaking in the first place, I got a compressor DBX 166XL

 

If your system is running of one Amp then to me it sounds like the drivers are taking frequencies they cant handle and then are burning out.

I also agree with "Clipped waveforms coming out of amplifiers are very bad news for speakers."

 

Im not sure if this experience helps but hopefully it did...

maXim

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I used my system awhile back and I ran it to hard with no protection except for the clip on the amp,

:)

It's the amp clipping that you want to protect your speakers from! Do you mean your amp has some form of anti-clip device built in? These can help but are not a substitute to having a big enough amp in the first place.

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I used my system awhile back and I ran it to hard with no protection except for the clip on the amp,

:)

It's the amp clipping that you wan to protect your speakers from! Do you mean your amp has some form of anti-clip device built in? These can help but are not a substitute to having a big enough amp in the first place.

 

hey,

sorry, yes you are correct (about the amp clipping) thats why I got the DBX 166XL to limit unexpected peaks because I don't have enough headroom,

The amp was the Behringer EP2500 (not proud of it either).

the system was also way to small for the venue

 

luckely in the end insurance payed for me to upgrade to the Yamaha C115 from my old dead peavey 215's

maXim

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luckely in the end insurance payed for me to upgrade to the Yamaha C115 from my old dead peavey 215's

maXim

 

What are you saying? that the the speakers you clipped were insured against damage and the insurance company paid for you to upgrade them?

 

Confuzed?

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The amp is 1400 watt RMS per side ... the speakers work out around 300-350 RMS per cab and I run 4 of them.

This has been fine for ages until the generator problem ( Which James sort of confirmed )

The amp is now in for a full diagnosis at CIE .

 

I just want to replace the subs now ...with what though I havent a clue.

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Just a thought here but was the generator you were using (as you suggest it was on the small side) actually regulated or was it a site generator with an unregulated output?

An unregulated generator with amp would cause the problems you describe....

 

Poppadom

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replacing subs...

umm look on the used market if you want cheap... (eBay?)

 

I know about some active subs, so I can recommend the dynacord "M18", but this is expensive RRP: $4999AU. Mackie ONLY IF they arnt made in china. & RCF

 

As far as passive iv'e heard that that the Yamaha c118 is decent

-FBT, EV, Dynacord, Yamaha are worth a look at in the expensive range.

-Peavey "PV® 118 Subwoofer" is at the cheaper end and good if you don't push them to hard.

 

1400W at what ohms?

if you manage it right you could get 2 sets of dubble 18" like the yamaha c215. To me these sound like they have more of a bottom end to them.

 

whatever you choose unfortunately it isnt gonna be cheap =[

http://www.musiciansfriend.com/live/naviga...N=100001+304616 might help

 

hopefully my limited knowledge helps.

maXim

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As many will know - the power rating of a speaker unit is very difficult to specify in a form that can be clearly understood. Essentially there is a trade off between actual power applied to the drive unit and the length of time this signal is applied. So most speakers can comfortably handle brief bursts of very high power - essential for transients of course.

 

In the situation described above I think that the generator is innocent - and the problem is simply too loud for too long.......!

 

John

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As many will know - the power rating of a speaker unit is very difficult to specify in a form that can be clearly understood. Essentially there is a trade off between actual power applied to the drive unit and the length of time this signal is applied. So most speakers can comfortably handle brief bursts of very high power - essential for transients of course.

 

In the situation described above I think that the generator is innocent - and the problem is simply too loud for too long.......!

 

John

Well had everything apart and the amp in for a checkover .... The genny was at fault ( after much digging to find out which one was used) Not voltage regulated and it was poorly too ... Great !

 

Although to be fair these speakers get about 8-10 hours use at a time outside ... not the ideal situation I know.

But,

Today I won some scoops on ebay ... time for some fane collosus methinks....

 

Thanks guys ( and girls ?) for your help.

 

Sy

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The only time I've ever lost a driver was when systems get abused. Usually unintentionally, but on a couple of occasions I've heard the drivers in distress and got to the amp racks to see everything that should have been green - red. Shortly after one goes. The person with the hand on the faders pushes further to make up the lost level and another dies very soon after. Since then, the systems that go out without me (rare now) had a limiter in the rack, with a covered front panel, with those nice security bolts. One came back and stupidly, I didn't check it until just before the next job, when I found one driver dead and the limiter out of circuit - they'd pulled out the cables and repatched at the back!

 

The point is that in most cases, the speakers sound bad as they are heating up, meaning you can back off a bit. I have never lost a driver when I'm mixing. I think many people have a "never mind the quality, feel the volume" attitude and take driver failures as just one of those things.

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