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Author Topic: power compression on not the amp for the job  (Read 7518 times)

Nathan Schwarzkopf

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power compression on not the amp for the job
« on: April 18, 2004, 10:59:43 AM »

 Embarassed Mildly embaresed because I should know this.
I had a techno show to set up for using a friends gear.  The Question lies on the subs.  HE runs a CE2000 amp and jbl mpro 255s subs.  When i speced them I saw they were a touch underpowered. (ce2000 660 stereo 4ohm, jbl 500rms 4ohm cab)  He had some ce 1000 he was going to use for tops and monitors so I bridged the 1000's and gave each one to a sub witch sould have gave it 1100w.  I have never used the ce1000 bridged or for subs(only on monitors) so I didn't know how they would preform.  The 1000's did not do well, the 2000 stereo had more spl and a fuller bottom.  Ive heard power compression tossed around alot but I have not found anything to read up on it so I don't exactly know what it means.  my questions is could it be power compression(any info you have on it would be nice).  Or is the ce 1000 just not the amp for the job(sorry but i don't have much exp. with the 1000).  The crown web site says there pretty much the same amp.
thanks for all the help guys.
AL K.
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Fred Garrett

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Re: power compression on not the amp for the job
« Reply #1 on: April 18, 2004, 12:42:31 PM »

As I understand it, power compression occurs when a speaker's voice coil heats up to the point where the coil's thermal state actually increases the working impeadence of the speaker.  Basically, the coil gets hot enought were it goes from being 8 ohm nominal to 10 ohm or 12 ohm or whatever.  In that situation, the  more you push the fader up, the hotter the coil  gets and the less the speaker produces.  To cure this you need to back off the volume and let the coil cool down. I believe this is the reason for the "vented gap" designs in the JBL woofers.

I have never confirmed this info, so if I am off the mark, someone please correct me.

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Andy Peters

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Re: power compression on not the amp for the job
« Reply #2 on: April 18, 2004, 03:04:59 PM »

AL wrote on Sun, 18 April 2004 07:59

The Question lies on the subs.  HE runs a CE2000 amp and jbl mpro 255s subs.  When i speced them I saw they were a touch underpowered. (ce2000 660 stereo 4ohm, jbl 500rms 4ohm cab)


For techno running full tilt -- yeah, it's underpowered.  WAAY underpowered.  You probably want more subs, too.

Quote:

He had some ce 1000 he was going to use for tops and monitors so I bridged the 1000's and gave each one to a sub witch sould have gave it 1100w.  I have never used the ce1000 bridged or for subs(only on monitors) so I didn't know how they would preform.  The 1000's did not do well, the 2000 stereo had more spl and a fuller bottom.


Well, the 2000s are somewhat more powerful.  You're right -- the CE1000 ain't an amp for  subs.

Quote:

Ive heard power compression tossed around alot but I have not found anything to read up on it so I don't exactly know what it means.  my questions is could it be power compression(any info you have on it would be nice).  Or is the ce 1000 just not the amp for the job(sorry but i don't have much exp. with the 1000).


As Square says, power compression occurs when the voice coils heat up, which causes their impedance to go up, which means the speakers get quieter, so you crank up the output, which heats 'em up more, which makes 'em get quieter.  You see where this leads.

Power compression arises either when you have too much power going to a driver that's not adequately cooled, or if the amp is clipping.  In the latter case, the harmonics that clipping produces can't be reproduced by the speaker, so that energy is dissipated as heat in the voice coil.

Having said all of that: the CE1000 ain't an amp you want to use for subs -- it's just tooooo small.  You simply need a lot more power.  

Quote:

 The crown web site says there [sic] pretty much the same amp.


yeah, 'cept as I said, the 2000 is somewhat bigger.  The CE4000 is a different story.

--a
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Rob Dellwood

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Re: power compression on not the amp for the job
« Reply #3 on: April 18, 2004, 03:13:53 PM »

The 1000's did not do well, the 2000 stereo had more spl and a fuller bottom. Ive heard power compression tossed around alot but I have not found anything to read up on it so I don't exactly know what it means. my questions is could it be power compression(any info you have on it would be nice). Or is the ce 1000 just not the amp for the job(sorry but i don't have much exp. with the 1000). The crown web site says there pretty much the same amp.
thanks for all the help guys.
AL K.


We use a CE2000 and in order to bridge them (with bridge switch engaged)you must use a specially wired speakon cable to get the bridged output.  Using a standard speakon cable even with bridge switch engaged will only give you the standard stereo output. If the CE1000 has the same requirement, this could explain your problem. You may have only been getting 450 watts from them, instead of 1100.   Hope this helps.   -RobD
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Tim Padrick

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Re: power compression on not the amp for the job
« Reply #4 on: April 19, 2004, 02:37:51 AM »

A CE1000 bridged into a 4 ohm box is rated 1100w <i>at 1kHz.  A CE4000 can pretty much do it's 1kHz rated power at sub frequencies, but it's possible that a CE1000 cannot. However I think it likely that you ran into the connection problem that RobD mentioned.  I'd have a look at that.

Michael 'Bink' Knowles

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Re: power compression on not the amp for the job
« Reply #5 on: April 19, 2004, 09:32:55 PM »

Quote:

The CE4000 is a different story.


Dontcha know it. Even though I'm not done putting all the flesh on the Amp Shootout website bones I have this one little gem of a GIF to post. It shows the CE4000 low frequency response at 20Hz. Left side shows input level, middle section is 117vac supply and right section is 96vac supply. The CE4000 delivers a lot of clean power then kind of tops out and stays at a certain ceiling in terms of output level. This is a good thing for NOT burning up your voice coils, in my opinion. Also, the very slight drop in output power at sagging supply voltages means your amp will keep chugging away. Many other amps dropped significantly when faced with sagging wall power. The CE4000 doesn't get fazed either way.
index.php/fa/21//

Too bad I don't have any info on the CE1k and CE2k little brethren.

-Bink
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Michael 'Bink' Knowles
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Ray Abbitt

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Re: power compression on not the amp for the job
« Reply #6 on: April 19, 2004, 09:52:52 PM »

Bink wrote on Tue, 20 April 2004 02:32

Quote:

The CE4000 is a different story.

Too bad I don't have any info on the CE1k and CE2k little brethren.


Well the 2k was there. Of course the problem was that you needed 2 months, not 2 days to get through all of the amps that were there.

But my understanding is that the 4k is completely different than the 1k/2k. And although I own both 1000's and 2000's, I really can't imagine using the 1000 on subs. Nice for running the horns on a bi/tri amped system though.

-ray
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Michael 'Bink' Knowles

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CE2000 vs. CE4000
« Reply #7 on: April 20, 2004, 10:31:46 AM »

Yeah, Ray, two months would have been about right. Rolling Eyes  
Your CE2000 should have been tested, you are right about that. It isn't the same beast as a CE4000 by any stretch but the CE2000 has its own merits, for sure. What is yours used for?

I wonder if the CE2000 responds the same way to low freqs as its big brother...

I just used a CE2000 last night for a vintage dance event. Sounded fine, though I didn't feed it anything below 50Hz. Barely adequate DJ-style MI-level speakers responded well enough to my parametric tweaks and delivered the goods. I had the CE2000 input attenuators at about 10 o'clock because I like to run all the upstream gains pretty hot and there was plenty of 'go' for the crowd of 100. Subwoofers would have been nice, though.

The design of the CE4000 is very different. Crown could have given it a completely different model number and saved us all the confusion.

-Bink

P.S. Ray, did you lose a pair of banana-banana cables at the Amp Shootout? Clear plastic sheathing showing the copper inside? Yellow e-tape on one and green e-tape on the other? Somebody left them behind and I don't know who.

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Michael 'Bink' Knowles
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Michael 'Bink' Knowles

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Re: CE2000 vs. CE4000
« Reply #8 on: April 20, 2004, 10:34:50 AM »

Quote:

...though I didn't feed it anything below 50Hz.


We're all good now!

-Bink  Rolling Eyes
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Michael 'Bink' Knowles
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Ray Abbitt

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Re: CE2000 vs. CE4000
« Reply #9 on: April 20, 2004, 12:20:26 PM »

Bink wrote on Tue, 20 April 2004 15:31

Yeah, Ray, two months would have been about right. Rolling Eyes  
Your CE2000 should have been tested, you are right about that. It isn't the same beast as a CE4000 by any stretch but the CE2000 has its own merits, for sure. What is yours used for?

Nothing too demanding. For the last couple of years I've been running bi-amped SP2XT's, CE1000 for horns (1 or 2 per channel), CE2000 for the 15's (once again 1 or 2 per channel) and another one for subs (a pair of Yamaha club 18's usually connected to a single channel). Crossover freqs vary with the venue and with the program material.  
Quote:

I wonder if the CE2000 responds the same way to low freqs as its big brother...

Probably not, but until I get some different subs, I'm not likely to find out either. But I'm probably going to be building Lab subs, so the 2000's probably aren't going to make it there. (Somehow visions of 8 amps to drive 4 subs makes my back hurt)
Quote:

I just used a CE2000 last night for a vintage dance event. Sounded fine, though I didn't feed it anything above 50Hz. Barely adequate DJ-style MI-level speakers responded well enough to my parametric tweaks and delivered the goods. I had the CE2000 input attenuators at about 10 o'clock because I like to run all the upstream gains pretty hot and there was plenty of 'go' for the crowd of 100. Subwoofers would have been nice, though.

That's pretty much how I run mine most of the time too. I work pretty small venues most of the time so it works well. Trouble is that because it sounds good, I keep getting good offers for jobs that are bigger than I feel comfortable with until I do some upgrading.
Quote:

P.S. Ray, did you lose a pair of banana-banana cables at the Amp Shootout? Clear plastic sheathing showing the copper inside? Yellow e-tape on one and green e-tape on the other? Somebody left them behind and I don't know who.

Nope. Not me. I don't have anything with banana plugs.

-ray
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Andy Peters

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Re: CE2000 vs. CE4000
« Reply #10 on: April 20, 2004, 04:57:42 PM »

Bink wrote on Tue, 20 April 2004 07:34

Quote:

...though I didn't feed it anything above 50Hz.


Spell check doesn't catch this sort of idiocy. I meant to say "anything below 50Hz" as you probably guessed.

-Bink Confused


Hey, Bink,

Ya know you can edit your own posts, right?

After it appears, you'll see an "edit" button on the bottom of the box that surrounds your post.  You can make all of your idiocy go away!!!
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Michael 'Bink' Knowles

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Editing leaves pieces here and there...
« Reply #11 on: April 20, 2004, 07:06:12 PM »

Editing? Yeah, I can see it now. Thanks for the heads up, Andy.

You know, since both you and Ray quoted me, my editing job isn't at all complete. Try and revise history and you'll have to burn all the history books... Rolling Eyes

-Bink
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Michael 'Bink' Knowles
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John Roberts {JR}

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Re: Editing leaves pieces here and there...
« Reply #12 on: April 20, 2004, 09:19:10 PM »

Bink wrote on Tue, 20 April 2004 18:06

Editing? Yeah, I can see it now. Thanks for the heads up, Andy.

You know, since both you and Ray quoted me, my editing job isn't at all complete. Try and revise history and you'll have to burn all the history books... Rolling Eyes

-Bink


Footprints have some value on those rare occasions we might find reason to correct a post Cool . Not only could it make the smart-ass doing the correcting look bad, but it could really confuse folks trying to make sense of the thread after the fact.

JR
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Ray Abbitt

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Re: Editing leaves pieces here and there...
« Reply #13 on: April 21, 2004, 02:54:56 AM »

JR wrote on Wed, 21 April 2004 02:19

Bink wrote on Tue, 20 April 2004 18:06

Editing? Yeah, I can see it now. Thanks for the heads up, Andy.

You know, since both you and Ray quoted me, my editing job isn't at all complete. Try and revise history and you'll have to burn all the history books... Rolling Eyes

-Bink


Footprints have some value on those rare occasions we might find reason to correct a post Cool . Not only could it make the smart-ass doing the correcting look bad, but it could really confuse folks trying to make sense of the thread after the fact.

 JR

Besides, we all knew what he meant.
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RobertOziemkowski

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Re: power compression on not the amp for the job
« Reply #14 on: April 21, 2004, 08:55:22 AM »

Bink wrote on Tue, 20 April 2004 02:32

Quote:

The CE4000 is a different story.


Dontcha know it. Even though I'm not done putting all the flesh on the Amp Shootout website bones I have this one little gem of a GIF to post. It shows the CE4000 low frequency response at 20Hz. Left side shows input level, middle section is 117vac supply and right section is 96vac supply. The CE4000 delivers a lot of clean power then kind of tops out and stays at a certain ceiling in terms of output level. This is a good thing for NOT burning up your voice coils, in my opinion. Also, the very slight drop in output power at sagging supply voltages means your amp will keep chugging away. Many other amps dropped significantly when faced with sagging wall power. The CE4000 doesn't get fazed either way.

-Bink


Bink,

Did you by chance give the CE4000 more than 200v? According to Crown the amp is designed to function on voltages from 100-240v.
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Michael 'Bink' Knowles

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CE4000 at higher voltages
« Reply #15 on: April 23, 2004, 02:53:06 AM »

No, Rob, I didn't have time to set up a second test for higher AC supply voltages. I bet that for the CE4000 as well as Crown's MA5000, it would be a lot like gilding the lily. The low end performance is already there and now you have a touch more to play with...

-Bink
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