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Author Topic: seeking Crest 10001 wizards  (Read 8914 times)

Cliff Fuller

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seeking Crest 10001 wizards
« on: May 26, 2011, 10:47:52 AM »

I'm currently using Crest 10001 amps to push some subwoofers. The subs present a 1 ohm load to the amplifier. I am experiencing amp channels going into protect without clipping or being over-driven. I've looked at the damping of the speaker/cable system as a culprit but can't reproduce the problem at the shop. It occurred to me that perhaps through cone excursion the load may be dropping below the 1 ohm tolerance of the amp? Does anybody have any ideas they could throw at me?

Thanks for your time ...
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Tim McCulloch

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Re: seeking Crest 10001 wizards
« Reply #1 on: May 26, 2011, 11:00:05 AM »

I'm currently using Crest 10001 amps to push some subwoofers. The subs present a 1 ohm load to the amplifier. I am experiencing amp channels going into protect without clipping or being over-driven. I've looked at the damping of the speaker/cable system as a culprit but can't reproduce the problem at the shop. It occurred to me that perhaps through cone excursion the load may be dropping below the 1 ohm tolerance of the amp? Does anybody have any ideas they could throw at me?

Thanks for your time ...

The amp doesn't like 1 ohm loads.  Does Crest rate the amp for this use? No, they don't, and it's unimaginable to me that a user would expect them to function as they would with a 4 ohm or even 2 ohm load.  That said....

Impedance is not a constant number, but a value that changes with frequency.  I suspect there is a significant difference in program material between field and shop tests.  Sine wave sweeps may be more revealing.
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Cliff Fuller

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Re: seeking Crest 10001 wizards
« Reply #2 on: May 26, 2011, 11:40:09 AM »

The amp doesn't like 1 ohm loads.  Does Crest rate the amp for this use? No, they don't, and it's unimaginable to me that a user would expect them to function as they would with a 4 ohm or even 2 ohm load.  That said....

Impedance is not a constant number, but a value that changes with frequency.  I suspect there is a significant difference in program material between field and shop tests.  Sine wave sweeps may be more revealing.

Tim, I really respect your experience and knowledge but ... The spec sheet from Crest old school states "5000W 1Ω Stereo Power".

The impedance idea is something that I started to consider also. There's nothing like an open low bass string to make your sub system work  ;D Thanks for the sine wave suggestion...
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Tim McCulloch

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Re: seeking Crest 10001 wizards
« Reply #3 on: May 26, 2011, 01:16:49 PM »

Tim, I really respect your experience and knowledge but ... The spec sheet from Crest old school states "5000W 1Ω Stereo Power".

The impedance idea is something that I started to consider also. There's nothing like an open low bass string to make your sub system work  ;D Thanks for the sine wave suggestion...

I suppose a specification implies manufacturer's endorsement of such use, but I think you now see the folly of such.

For professional use I suggest you purchase another amp or 2 or 3 or figure out how to convince clients that "it worked on the bench" somehow makes an in-show failure acceptable.

Power is incredibly cheap these days.  When the Pro001 series came out, that was not so... back then the watts-per-dollar standard was Peavey's CS800, at about $1/watt.  Today even Crown's I-Techs hit that price point.

Have fun, good luck.

Tim Mc

ps.  There is also the distinct possibility that you have some component-aging issues with the protection circuit that have it kicking in prematurely.
« Last Edit: May 26, 2011, 01:18:20 PM by Tim McCulloch »
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Marty McCann

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Re: seeking Crest 10001 wizards
« Reply #4 on: May 26, 2011, 02:24:31 PM »

I suppose a specification implies manufacturer's endorsement of such use, but I think you now see the folly of such.

For professional use I suggest you purchase another amp or 2 or 3 or figure out how to convince clients that "it worked on the bench" somehow makes an in-show failure acceptable.

Power is incredibly cheap these days.  When the Pro001 series came out, that was not so... back then the watts-per-dollar standard was Peavey's CS800, at about $1/watt.  Today even Crown's I-Techs hit that price point.

Have fun, good luck.

Tim Mc

ps.  There is also the distinct possibility that you have some component-aging issues with the protection circuit that have it kicking in prematurely.

to add to what Tim posted, I would suggest that you look closely at the impedance curve of your Subs.  Loudspeaker Impedance is a "nominal" rating.  Many bass reflex (ported) enclosures have an impedance dip that goes well below published nominal.  I have also seen these dips as wide as an octave or more.

Also for the brief time that a voice coil may leave the gap, it reverts to it DCR impedance. 

And, speakers will work with a couple of shorted turns, but the amp has to work harder.
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Art Welter

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Re: seeking Crest 10001 wizards
« Reply #5 on: May 26, 2011, 03:47:44 PM »

The amp doesn't like 1 ohm loads.  Does Crest rate the amp for this use? No, they don't, and it's unimaginable to me that a user would expect them to function as they would with a 4 ohm or even 2 ohm load.  That said....

Impedance is not a constant number, but a value that changes with frequency.  I suspect there is a significant difference in program material between field and shop tests.  Sine wave sweeps may be more revealing.

Tim, I really respect your experience and knowledge but ... The spec sheet from Crest old school states "5000W 1Ω Stereo Power".

The impedance idea is something that I started to consider also. There's nothing like an open low bass string to make your sub system work  ;D Thanks for the sine wave suggestion...
As Marty mentions, bass reflex (ported) enclosures have an impedance dip that goes well below published nominal, often that dip will be as low as the DC resistance of the speakers.
When you get down to a one ohm load (or possibly .5 or .75 ohm), speaker cords can't be to short or too large.

I used to run Crest 8001 at 2 ohms, the difference between long fly cabling and the usual  15' of #12 was quite pronounced.

You may find a series parallel arrangement, though on paper delivering less power, will actually "sound" much louder and have better definition than running the same compliment of speakers at 1 ohm.

This may require running the amp in mono to get the maximum power transfer  to the load.

Art Welter



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Greg_Cameron

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Re: seeking Crest 10001 wizards
« Reply #6 on: May 26, 2011, 05:10:02 PM »

You may find a series parallel arrangement, though on paper delivering less power, will actually "sound" much louder and have better definition than running the same compliment of speakers at 1 ohm.

This may require running the amp in mono to get the maximum power transfer  to the load.

+1

I'm running my double 18s with series drivers for a 16 ohm nominal load. Up to 4 boxes are run off of a single bridged Crest 7001. It sounds tight and the amps can run all day like that at full output.

Greg
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Pascal.Pincosy

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Re: seeking Crest 10001 wizards
« Reply #7 on: May 27, 2011, 04:37:45 AM »

to add to what Tim posted, I would suggest that you look closely at the impedance curve of your Subs.  Loudspeaker Impedance is a "nominal" rating.  Many bass reflex (ported) enclosures have an impedance dip that goes well below published nominal.  I have also seen these dips as wide as an octave or more.
One of the venue's I work at has a bunch of 10001's that run up to six 8 Ohm drivers per channel with no issues, presenting a nominal load of 1.3 Ohms. They have been running in this configuration for many years now with only very occasional age-related reliability issues. I'd suggest that maybe you just hang 1 or 2 fewer subs off each channel and see how that works for you.
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Re: seeking Crest 10001 wizards
« Reply #7 on: May 27, 2011, 04:37:45 AM »


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