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We blew 4no. PD1850's

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Hemisphere View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Hemisphere Quote  Post ReplyReply Direct Link To This Post Posted: 25 June 2018 at 4:56pm
Some recent threads on power compression in FLH designs suggests that this would be more likely than overexcursion failure. Hot day, running long and hard, small sealed chamber, long horn path, tight throat etc (in other words almost as badly ventilated as a driver can be) could be done in by 800 clipped Watts.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote rosssss224 Quote  Post ReplyReply Direct Link To This Post Posted: 25 June 2018 at 4:56pm
Originally posted by levyte357- levyte357- wrote:

Originally posted by rosssss224 rosssss224 wrote:

This weekend we took the rig to a free party. We used 4no. super bass horns loaded with pd1850's.

genny: 20kVA diesel
amp: proline 3000
xover: 30-78hz
LMS: ultradrive
Limiters: -24dB w/ 4000ms release


This was always going to end in tears.

Even if you used Void 8MK2, you would still have lost drivers.

SBH Outputs far more 60hz+, than 40hz+, so you are basically not really gonna hear any of the 40hz notes, never mind 30hz.

Use HR to model SBH with PD1850, take a look at displacement graph, and tell me what driver displacement is, with 800W input.


While I sort of agree with what your saying they were used in a stack of 4 which will have levelled the response somewhat.(the ultradrive was also set up by Toasty on here)

Plenty people use sbh 30hz and up to good effect without destroying drivers.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Conanski Quote  Post ReplyReply Direct Link To This Post Posted: 25 June 2018 at 5:01pm
Don't jump to conclusions pull the drivers to see if the cones are destroyed or coils fried. Shredded cones suggests highpass and/or EQ errors leading to over excursion.. or the drivers are just all wrong for the cab. Burnt coils = overpowering but I doubt that is what you will find, I think the crunching sounds you were hearing is a good hint.


Edited by Conanski - 25 June 2018 at 5:02pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote rosssss224 Quote  Post ReplyReply Direct Link To This Post Posted: 25 June 2018 at 5:02pm
Originally posted by Conanski Conanski wrote:

Don't jump to conclusions pull the drivers to see if the cones are destroyed or coils fried. Shredded cones suggests highpass and/or EQ errors leading to over excursion.. or the drivers are just all wrong for the cab. Burnt coils = overpowering but I doubt that is what you will find.

Had a quick look at the cones and they were in tact and dont think they were rubbing. Mates having a look later properly so will try get some pictures. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Hemisphere Quote  Post ReplyReply Direct Link To This Post Posted: 25 June 2018 at 5:16pm
PD1850's are only rated as 800W AES, but that will be in optimally vented conditions - if not literally free air rating. Close off the entire rear half of the driver and put the other half at the end of a maze of tunnels on a hot day and don't be surprised if it drops to 300W AES, or even less. Like sound energy, heat energy also builds up in enclosed (or heavily walled in) spaces.

I think you just gave them too much power. Assuming 6dB dynamic range music, 800W 3dB into clip is equivalent to 1600W peaks or 400W AES, and those drivers will take less than that much long term average power in an SBH before failure. 

If the loading arrangement causes the heat to dissipate twice as slowly as it would in free air, then the AES rating is 400W, four times, 200W. Not an easy figure to calculate, I wouldn't even know where to begin with a guess, but I'm sure someone better educated could make one.


Edited by Hemisphere - 25 June 2018 at 5:23pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote daavneeq Quote  Post ReplyReply Direct Link To This Post Posted: 25 June 2018 at 5:20pm
crap mixer, pops & clicks certainly won't have helped matters either. 
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Post Options Post Options   Thanks (1) Thanks(1)   Quote snowflake Quote  Post ReplyReply Direct Link To This Post Posted: 25 June 2018 at 5:28pm
clipping an amp when playing music rather than sinewaves puts large amounts of DC into the speaker. this will make the coil hit the backplate and/or move the coil out the airgap and stop it cooling properly.

there's a big difference between a clip limiter light that tells you the amp has automatically reduced the gain to stop clipping the output stage and a clip indicator light that tells you the amp is clipping and your drivers may already be damaged. it's not clear from the manual which of these the proline has.


Edited by snowflake - 25 June 2018 at 5:28pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Hemisphere Quote  Post ReplyReply Direct Link To This Post Posted: 25 June 2018 at 5:37pm
Originally posted by snowflake snowflake wrote:

clipping an amp when playing music rather than sinewaves puts large amounts of DC into the speaker. this will make the coil hit the backplate and/or move the coil out the airgap and stop it cooling properly.
So once the coil reaches the clipped top of the waveform, instead of 'resting' there it just keeps on going until the signal indicates it should pull back, since no amp can control a cone that well, right?

So you're saying the lack of control during that period causes the cone to keep moving (substantially?) further than it would have done if the amp had had the headroom available to take the signal where the clip was indicating it would go, For as far as it's able to travel before the signal pulls it back again..up to xmech or so potentially but without the damage since the amp isn't forcing it to push past it?

Makes sense that this could impact on cooling capacity, combined with the loading effects even 10-20% could make a big difference. 200W AES really wouldn't be so surprising, and it sounds like nothing for a PD1850, but as Timebomb posted recently it's rare that dance music actually has lower than 8dB dynamic range, so that 200W AES wouldn't be a noticeable limitation with the SBH as it runs out of  excursion before you get there.. but then if you're clipping your amp you're probably running your drivers past xmax too.


Edited by Hemisphere - 25 June 2018 at 5:48pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote toastyghost Quote  Post ReplyReply Direct Link To This Post Posted: 25 June 2018 at 6:22pm
Originally posted by snowflake snowflake wrote:

clipping an amp when playing music rather than sinewaves puts large amounts of DC into the speaker. this will make the coil hit the backplate and/or move the coil out the airgap and stop it cooling properly.

there's a big difference between a clip limiter light that tells you the amp has automatically reduced the gain to stop clipping the output stage and a clip indicator light that tells you the amp is clipping and your drivers may already be damaged. it's not clear from the manual which of these the proline has.



Music is sine waves? Just layered ones...

Clipping will be either too much long term average power causing thermal failure or too much peak voltage with distortion characteristics pushing drivers to over excursion / mechanical damage. It’s much better to talk in these terms regarding failures as a result.

Take the drivers out and assess them before we speculate much more about the exact cause and how to prevent it in future.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Conanski Quote  Post ReplyReply Direct Link To This Post Posted: 25 June 2018 at 10:23pm
Originally posted by snowflake snowflake wrote:

clipping an amp when playing music rather than sinewaves puts large amounts of DC into the speaker.


No... sorry snowflake that is just another internet myth, no properly functioning amp allows any appreciable amount of DC to pass to the speaker outputs. When it comes to subs in particular clipping an amp just raises the average signal level, and if this average is sustained and happens to be more than the the drivers can handle long term then VC damage results.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote snowflake Quote  Post ReplyReply Direct Link To This Post Posted: 25 June 2018 at 10:42pm
"Music is sine waves? Just layered ones..."

by music I meant layered sine waves rather than a single tone.

clipping an asymetric waveform inevitably leads to dc and a voice coil offset.

http://sound.whsites.net/clipping.htm


Edited by snowflake - 25 June 2018 at 10:59pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Hemisphere Quote  Post ReplyReply Direct Link To This Post Posted: 25 June 2018 at 11:47pm
The article ypu linked to makes clear in the introduction that an amplifier that produces DC output (or anything close enough to behave similarly) is a special case and it's referenced as such throughout.
Quote 3.0 - Conclusion

There is no doubt that a clipped asymmetrical waveform will generate a DC component in the output of an amplifier. There is equally no doubt (as evidenced above) that a fully DC coupled power amp is the worst possible case. Since there is no requirement whatsoever for an audio amplifier to reproduce DC, it follows that designs that are fully DC coupled are of no benefit to the listener, and indeed may cause far greater problems than they are supposed to 'solve' (according to those who insist that DC reproduction is somehow 'better').

I think it's safe to say the amp powering your system will not be DC coupled, which sounds like something reserved for bizarro-audiophile setups.

The article is also full of completely open ended terms like 'given enough clipping the driver may be damaged' (well, yea, but how much is 'enough'?), and 'will generate a DC component'. Again, sure, but how much? A fraction of a milisecond? More than a milisecond? The mention of voice coils hitting the backplate was made with reference to a DC coupled amp driven to heavy clipping.



Edited by Hemisphere - 25 June 2018 at 11:55pm
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