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What Has Caused this Damage?

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AJ113 View Drop Down
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    Posted: 21 October 2018 at 1:48pm
This is a 450-watt Eighteen Sound 15 inch driver - it's not marked, but my super-sleuth detective skills have narrowed it down to a 15w700.

It was in what seems to be a very-nicely built 6th order bandpass cabinet; as I understand it, made by Apart as a prototype.

Obviously I gave it too much juice. I was running a 700-watt amp. It was live music so I figured it would be ok, but the kick drum was triggered and I had the bass guitar quite high up in the mix, I guess I pushed it over the edge.

So my question is: the loudspeaker voicecoil is fried, obviously thermal overload, but I don't understand fully what has caused it. I have never seen a speaker looking like that before, just through excessive power being fed to it. Has the compression within the cabinet restricted the speaker's excursion and caused thermal overload, or has the excess power fried the voicecoil and the ripped cone is a result of that somehow?

The reason I ask is because I want to replace the drivers (yes, I blew two :( ) but not necessarily with Eighteen Sounds, and I want to understand what has happened here so that I can pick suitable products.




Edited by AJ113 - 21 October 2018 at 1:49pm
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Post Options Post Options   Thanks (1) Thanks(1)   Quote valve head777 Quote  Post ReplyReply Direct Link To This Post Posted: 21 October 2018 at 1:57pm
Kick or excess bass ripped the cone allowing the voice coil to then move out of the magnetic gap causing it to burn? Cone must have ripped before the VC damage. How does the spider look?
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Post Options Post Options   Thanks (1) Thanks(1)   Quote Mircea Bartic Quote  Post ReplyReply Direct Link To This Post Posted: 21 October 2018 at 2:11pm
high loading on the cone, cone too thin for the loads applied. Probably no highpass or incorect DSP settings.

also not a 15W700. suspension is different on that


Edited by Mircea Bartic - 21 October 2018 at 2:12pm
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Post Options Post Options   Thanks (1) Thanks(1)   Quote ceharden Quote  Post ReplyReply Direct Link To This Post Posted: 21 October 2018 at 2:39pm
As above, looks like the cone isn't designed to take the high loading you get in a bandpass.

A driver with a heavier, straight-sided cone might be a good place to start narrowing down your choices.
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Post Options Post Options   Thanks (1) Thanks(1)   Quote studio45 Quote  Post ReplyReply Direct Link To This Post Posted: 21 October 2018 at 5:48pm
The thing is, bandpass cabs are quite reliant on the driver parameters being just-so, to arrive at the correct tuning for the driver+cabinet system as a whole. So putting another driver in there might work, or it might not.

You may have just discovered why this was a prototype - did it actually go into production? Maybe Apart had this problem, and could not solve it other than by re-designing.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AJ113 Quote  Post ReplyReply Direct Link To This Post Posted: 22 October 2018 at 7:32am
Originally posted by valve head777 valve head777 wrote:

Kick or excess bass ripped the cone allowing the voice coil to then move out of the magnetic gap causing it to burn? Cone must have ripped before the VC damage. How does the spider look?
That's my 2p's worth...


Yes that makes sense, thank you. The spider looks fine to me.
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AJ113 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AJ113 Quote  Post ReplyReply Direct Link To This Post Posted: 22 October 2018 at 7:44am
Originally posted by Mircea Bartic Mircea Bartic wrote:

high loading on the cone, cone too thin for the loads applied. Probably no highpass or incorect DSP settings.
The amps are high passed to 30Hz and I had a 40Hz HPF on the masters. Of course, that still may not have been enough.

Quote also not a 15W700. suspension is different on that
I'm 99% certain it is. I've checked every minute detail I can think of, they all match up to library images of a 15w700.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AJ113 Quote  Post ReplyReply Direct Link To This Post Posted: 22 October 2018 at 7:54am
Originally posted by studio45 studio45 wrote:

...You may have just discovered why this was a prototype - did it actually go into production? Maybe Apart had this problem, and could not solve it other than by re-designing.


Good point. As far as I know it never went into production. On the other hand I've used these boxes many times on hires and they've always been rock solid, so I think it's more likely to be user abuse.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AJ113 Quote  Post ReplyReply Direct Link To This Post Posted: 22 October 2018 at 8:01am
Quote also not a 15W700. suspension is different on that
Quote I'm 99% certain it is. I've checked every minute detail I can think of...


...except the suspension! Very good point!

Looks like the chaps at Apart have reconed it at some point.


Edited by AJ113 - 22 October 2018 at 8:02am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AJ113 Quote  Post ReplyReply Direct Link To This Post Posted: 22 October 2018 at 8:10am
Could anyone advise what characteristics and parameters I need to check for a loudspeaker to be suitable for a 6th order bandpass cab please?
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Post Options Post Options   Thanks (1) Thanks(1)   Quote odc04r Quote  Post ReplyReply Direct Link To This Post Posted: 22 October 2018 at 9:24am
Tough stiff cone that does not flex easily, higher mms might be an indication.
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Post Options Post Options   Thanks (1) Thanks(1)   Quote studio45 Quote  Post ReplyReply Direct Link To This Post Posted: 22 October 2018 at 4:03pm
Originally posted by AJ113 AJ113 wrote:

Could anyone advise what characteristics and parameters I need to check for a loudspeaker to be suitable for a 6th order bandpass cab please?

Can you measure the chamber volumes and port sizes? Because you need a driver suitable for *this* BP6 cabinet. They're not as forgiving as a reflex cabinet. If the driver parameters are not suitable the response will be less than optimal, possibly to the point of complete rubbishness.

A strong cone is a good start, but the rest of the numbers need to be right too. If you can measure up the box, you can simulate various drivers in WinISD and arrive a a good solution.
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