Dead drivers? |
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odc04r
Old Croc Joined: 12 July 2006 Location: Sarfampton Status: Offline Points: 5482 |
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Gradually getting quieter and quieter sounds like potentially overheating. What DC resistance are the coils?
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cravings
Old Croc Joined: 30 January 2007 Location: Ireland Status: Offline Points: 7442 |
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what was your processor? what was doing the limiting?
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Sypa
Young Croc Joined: 21 February 2013 Location: Croatia Status: Offline Points: 921 |
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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.
Would blame the amplifier or source before the drivers themselves . When I play they are ran very hard almost full tilt for hours of sub heavy material of a k20.
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PolymorphicMark
Registered User Joined: 27 May 2004 Location: United Kingdom Status: Offline Points: 444 |
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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.
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Free to do what i WANT
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re-production
Registered User Joined: 16 February 2017 Location: Suffolk UK Status: Offline Points: 176 |
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I haven't put a multimeter on them but nominal resistance is 8ohms
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re-production
Registered User Joined: 16 February 2017 Location: Suffolk UK Status: Offline Points: 176 |
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Limiter was a DBX which I thought should have had good limiters on it, however running the amp into the threshold of clipping is not a sustainable way to run the system. We are changing to linea soon so we should have the headroom needed
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re-production
Registered User Joined: 16 February 2017 Location: Suffolk UK Status: Offline Points: 176 |
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Yeah lesson learnt here, not going to leave a system unattended again
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Earplug
Old Croc Joined: 03 January 2012 Location: Europe Status: Offline Points: 7216 |
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You need to take (at least) one out and see if it´s open circuit, rubbing, etc. Then pop out the VC and look at the damage. That will tell you a lot.
Also, check that the amp is ok. I´m not sure about your model, but I had a couple of the AB Precedent Series 1100A´s and really wasn´t too impressed with their performance. I remember something in the amp´s blurb about using a small transformer, but large reservoir caps to compensate - but for me that just resulted in a weak PSU and clipping when pushed. |
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Earplugs Are For Wimps!
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re-production
Registered User Joined: 16 February 2017 Location: Suffolk UK Status: Offline Points: 176 |
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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.
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wires
Young Croc Joined: 21 May 2009 Status: Offline Points: 1365 |
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Quick way; Connect a speakon leads to the input of the cab, multimeter the other end.
Will at least tell you if it is open circuit or not. |
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toastyghost
The 10,000 Points Club Joined: 09 January 2007 Location: Manchester Status: Offline Points: 10919 |
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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!
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 |
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Contour
Young Croc Joined: 03 March 2004 Status: Offline Points: 623 |
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Very good post! Thanks.
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