Dead drivers?

Gradually getting quieter and quieter sounds like potentially overheating. What DC resistance are the coils?

xb1500 user here  i burned 2 out of 8 i have and those were run off an bridged qsc 5050. I suspect clip limiter was turned off on accident which burned them to a crisp. 

I haven't put a multimeter on them but nominal resistance is 8ohms

Yeah lesson learnt here, not going to leave a system unattended again

I will have a look but trouble is I don't have any time to open up the cabs before the next gig so we are having to get another pair and replace them. But for safety we are borrowing some MC2 amps for this gig so we should be ok.

fatfreddiescat wrote: If these were loaded in a small sealed chamber then you could easily halve their long term rated power. I once made the mistake of assuming no harm would come to a pair 600W 15XB's driven with a 300 Watt p/ch amp with hi/lo pass and clip limiters, came back toast - bloomin mashed ravers, were loaded in Martin 115 horn bins.

That applies to every single driver, ever. For most speakers, if you actually give them 1/4 to 1/3 of their AES rated power for an extended duration, they will burn up. For example, if you actually measure the thermal limit of your boxes to determine the maximum input voltage they can sustain (https://www.prosoundtraining.com/2013/11/22/the-loudspeaker-toaster-test-revisited/ - anyone can do this their own boxes using this guide) then you'll find the same.

Powersoft recommend 1/3 of AES rated power for TruePower limits if the manufacturer has not provided a preset, for example. A Danley DBH218 has a thermal limit set in their DNA amps (OEM Linea 44M) of just 50v, despite it being loaded with 2x B&C 18SW115 which are rated at 1700W AES, 3400W continuous program - as a 2 ohm nominal box, that's 1250W long term, or 625W per driver. A TH118, which has really good cooling of the magnet due to the placement of the driver at the mouth of the horn, with a single 18SW115, is rated at 40v - 4 ohm box, so that's just 400W long term.

This goes hand in hand with many people not really knowing how much power they're putting into their boxes on shows. I still hear people saying 'I gave my bins 2000W all night' but you're often really, really not. Sure, when the music is super compressed and crest factor is low, you're going to find it easier to burn up coils but unless you're actually keeping an eye on the output voltage and current against the impedance curve, you won't know for sure. It's pretty common to actually be getting the output you need with average power of a few hundred watts and high peaks - again, the issue here is that some boxes need more current for a given voltage to get moving due to their impedance curve, and that causes additional heating and thermal compression and then the vicious cycle of turning it up to compensate for the loss in output…

I strongly recommend people actually test their boxes to find the thermal limit, especially on subs, and then set their limiters from this value - especially if you're going to be doing bass heavy events for long periods of time!

PolymorphicMark wrote: Sounds like the DJ's rinsed it into the reds and possibly clipped the mixer putting intermittent DC across the drives. Happened to me along time ago on some PD 1850's, Left the club for a short time to come back to 3 toasted drivers.

An old myth that refuses to die. Clipping does not produce DC. It does however keep up the long term average power, but so does sitting in limiters all night.


Edited by toastyghost - 23 April 2018 at 6:31pm