We blew 4no. PD1850's |
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Hemisphere
Old Croc Joined: 21 April 2008 Status: Offline Points: 2272 |
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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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rosssss224
Registered User Joined: 25 July 2012 Status: Offline Points: 447 |
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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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Conanski
Old Croc Joined: 26 January 2006 Location: Ottawa, Canada Status: Offline Points: 2515 |
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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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rosssss224
Registered User Joined: 25 July 2012 Status: Offline Points: 447 |
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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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Hemisphere
Old Croc Joined: 21 April 2008 Status: Offline Points: 2272 |
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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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daavneeq
Registered User Joined: 25 June 2012 Status: Offline Points: 36 |
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crap mixer, pops & clicks certainly won't have helped matters either.
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snowflake
Old Croc Joined: 29 December 2004 Location: Bristol Status: Offline Points: 3118 |
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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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Hemisphere
Old Croc Joined: 21 April 2008 Status: Offline Points: 2272 |
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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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toastyghost
The 10,000 Points Club Joined: 09 January 2007 Location: Manchester Status: Offline Points: 10920 |
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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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Conanski
Old Croc Joined: 26 January 2006 Location: Ottawa, Canada Status: Offline Points: 2515 |
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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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snowflake
Old Croc Joined: 29 December 2004 Location: Bristol Status: Offline Points: 3118 |
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"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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Hemisphere
Old Croc Joined: 21 April 2008 Status: Offline Points: 2272 |
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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.
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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