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Another perfectly good speaker damaged from underpowering


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Here's an example of a BW driver that was damaged being powered at just slightly more than the RMS level (about 400 watts) and the sound guy had an unfortunate kick drum accident without proper high pass filtering and the VC exited the gap, came back in but missed the gap by a few thousandths and destroyed the bobbin.

 

The owner was sure the problem was caused by not enough power :facepalm:

 

This kind of stuff happens all the time. In this case, the motor structure was ruined, the re-entry caused the VC to enter at a diagonal and the wire seperated from the bobbin. Since the pole piece is undercut, the whole thing got jammed and all the tricks in the book couldn't save it.

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Just to be clear, this is a 350wrms rated Peavey Black Widow? You're saying it is impossible to pull the remains of the voice coil from the magnet structure? Even with a dental pick? I've got a couple of these myself and this is the first time I've ever heard of one of their magnet structures being rendered unreuseable :eek:!

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Here's an example of a BW driver that was damaged being powered at just slightly more than the RMS level (about 400 watts) ...

 

 

At first read this seems very, very misleading. It make it sound like powering the speaker at 50 watts over it's thermal rating is or is part of the failure problem when the real damage mechanism is excursion related. If that's the case then that 400W of power is more likely 4-8 times over the rated power depending on exactly what an "unfortunate kick drum accident" is as the power rating that low is probably on the order of 50 to 100 W.

 

I'm afraid too many readers will walk away with the wrong conclusion. The power mentioned 350 & 400W doesn't really have much to do with anything.

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At first read this seems very, very misleading. It make it sound like powering the speaker at 50 watts over it's thermal rating is or is part of the failure problem when the real damage mechanism is excursion related. If that's the case then that 400W of power is more likely 4-8 times over the rated power depending on exactly what an "unfortunate kick drum accident" is as the power rating that low is probably on the order of 50 to 100 W.


I'm afraid too many readers will walk away with the wrong conclusion. The power mentioned 350 & 400W doesn't really have much to do with anything.

 

Right.

 

Nothing was mentioned as to what box it was in,eqing,or what the accident was.

 

If the speaker had been in a ported box and the eq was boosted allot below the box tuning freq then this would/could have happened. The power handling

drops way down below box tuning. A 350 watt speaker would be torn apart with with a 5hz signal at 400 watts. I would have labled the post "The importance of a low cut filter". A 350 watt BW speaker will take 400 watts all day every day "Within Its Stated Useable Freq.Range" in a correct box. It was not 400 watts that killed this speaker. It was 400 watts of power NOT in its designed freq range.

 

Dookietwo

 

Saddly this post will be deleted. :facepalm:

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The way I look at it, such accidents are in part owing to a lack of proper driver engineering. The motor should be designed such that the voice coil cannot move beyond the gap, or be able to hit the back plate. This would, I should think, involve a deeper voice coil (so it can't reach the end of the gap), and much deeper gap (so the deep coil cannot hit the back plate).

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The way I look at it, such accidents are in part owing to a lack of proper driver engineering. The motor should be designed such that the voice coil cannot move beyond the gap, or be able to hit the back plate. This would, I should think, involve a deeper voice coil (so it can't reach the end of the gap), and much deeper gap (so the deep coil cannot hit the back plate).

 

 

 

 

That's easily and often done.

 

I mean, just so long as you are good with the horrible efficiency in more important band ranges versus comparable drivers.

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I have heard this nonsense before from the mouths of countless sales people. If you under power your speakers, you will blow them :facepalm:

:rolleyes:

 

I think that ignorance has damaged more speakers than any other problem ever encountered in live sound ;)

 

Issues like bad crossover settings, lack of limiters (or not setting them up properly if they are part of your amp), not using low frequency cut off on your amps (when present), and simply running your system above its capacity are the things I have seen cause speaker failure.

 

The Engineering Officer on my submarine had a saying:

...And the STUPID shall be punished

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Yes, you guys are understanding the problem accurately... no HPF, a D112 set up with a couple of channels reversed and the gain was way too high. Gate was on and open, as soon as the drummer kicked, the gate closed nand now there was sufficiient gain to insure the signal was slammed rail to rail at very low frequency. The driver was acousticly unloaded due to box tuning and the excursion exceeded Xmech, VC jumped the gap and re-entered catching the bottom of the bobbin, folded it inwards and the other side continued inwards. Then, everything got hot and came apart with the wire and a substantial part of the bobbin wedged in and under the pole piece return. Because of the way it was wedged and the bits and pieces stuck under the pole piece, the magnet structure (motor) was not salvageable. Complete loss. Generally, I's really good at clening things up (years of experience with JBL D series and 2202/5/20 series drivers).

 

Shows you that even powering at RMS can bee too much.

 

Yes, designing with larger Xmech is possible but there are some significant tradeoffs in sensitivity, cost and performance as Don mentioned.

 

There was indeed sarcastic intent in the title!

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Thanks for the clarification! Now that I think about it one of the things that saved us in the bad old days was that the crapped out SM58 you threw in the kick didn't pick up the real low stuff so we didn't need no stinkin' HPFs
:lol:
.

 

Just as important, the amps were not as big.

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In this case it was only 400w - same as the CS800's we useta run around 1980 into each 4 ohm 300w(?) CV 18". Never lost one of those - but we just had one of them $50 RadioShack mics (remember those?) stuck in the kick.

 

 

Yeah, some amps were big enough, but most were not. The CV drivers were pretty robust mechanically but failed thermally due to the aluminum bobbin. Also, most 18" CV drivers were 8 ohm, yielding a speaker that was pretty resistant to damage by knuclkeheads. Also, the impedance curves were higher than typical, also reducing real power delivered to the driver. Somewhat self-protecting.

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