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Luke's basic amplifier tests


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#21 Ricci

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Posted 14 October 2015 - 09:27 AM

 as for testing the same freq., that might make some sense as the contribution from the room (and possibly the sensitivity of the horn?) may be a little different at the two different frequencies.
 
with that much power compression, i'd be worrying about cooking the drivers.  don't want to see that!


Can't tell much if anything about power compression with this data. The tests being at 2 frequencies nearly 1/3rd octave apart can easily account for 2.5dB itself. Not to mention one has a much lower impedance than the other. Not really apples / apples at all.

Luke even as strong as those drivers are Id be careful with doing this type of stuff. You may cook one. Use as many drivers as possible so they don't get heated as much.
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#22 lukeamdman

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Posted 14 October 2015 - 01:57 PM

Can't tell much if anything about power compression with this data. The tests being at 2 frequencies nearly 1/3rd octave apart can easily account for 2.5dB itself. Not to mention one has a much lower impedance than the other. Not really apples / apples at all.

Luke even as strong as those drivers are Id be careful with doing this type of stuff. You may cook one. Use as many drivers as possible so they don't get heated as much.

 

Agreed.  The SP amp tests were definitely hard on the drivers. 

 

Any other testing with the SP amp will have to be with all eight FTW-21s or a pair of IPALs on a single channel. 


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#23 BeastAudio

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Posted 14 October 2015 - 02:38 PM

Great data. Sad for my poor little 7.5 :D



#24 lukeamdman

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Posted 14 October 2015 - 02:48 PM

Great data. Sad for my poor little 7.5 :D

 

Based on your experiences with the 7.5 and 7500 I knew how the 2ohm stereo test was going to turn out :angry:

 

I bought mine for the sole intention of 4ohm stereo and it's awesome for that.



#25 Infrasonic

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Posted 14 October 2015 - 04:42 PM

I've noticed a recurring trend with most of these class-D type amps that they produce far greater output numbers (and more stability) with just one of two channels driven.

 

Is this behavior simply tied to a PS that can not provide good solid current enough for two channels with these kind of high output numbers?



#26 BeastAudio

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Posted 14 October 2015 - 04:49 PM

I've noticed a recurring trend with most of these class-D type amps that they produce far greater output numbers (and more stability) with just one of two channels driven.

 

Is this behavior simply tied to a PS that can not provide good solid current enough for two channels with these kind of high output numbers?

 

That's my exact guess. By process of elimination, and talks with one of the peavey/crest designers, it is the only thing that you could attribute to the shutdowns basically. It ain't line sag....



#27 lukeamdman

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Posted 14 October 2015 - 05:26 PM

I've noticed a recurring trend with most of these class-D type amps that they produce far greater output numbers (and more stability) with just one of two channels driven.

 

Is this behavior simply tied to a PS that can not provide good solid current enough for two channels with these kind of high output numbers?

 

 

That's my exact guess. By process of elimination, and talks with one of the peavey/crest designers, it is the only thing that you could attribute to the shutdowns basically. It ain't line sag....

 

My guess is that it would have to be an inadequate power supply.  If I understand the Crest/Peavey 7.5/7500 amps correctly, similar to the SP amps each channel is already a "bridged" amp, which is why they can't be bridged again into a single channel.  If rail voltage were the issue, one channel driven would also be limited to ~57v into a ~2ohm load as well which obviously isn't the case. 

 

The Crest CC series will also output more at 2ohm with 1 channel driven vs. 2 channels, but it's not nearly as dramatic of a difference and it's more forgiving (it'll actually show clip lights instead of simply power cycling without warning). 



#28 Infrasonic

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Posted 14 October 2015 - 05:44 PM

In some cases then it seems like an actually good idea to buy the amp with the intention on using only one channel at a time.

 

Arguably less value but then the price/performance needs to be weighed in and compared to other products in the same price range. Even with ~$800 amps it gets pretty dang close to a single Speaker Power amp. Not sure what the range is on their prices. I've seen $2,500 touted as a general price for one or all of them though I doubt they all cost the same.

 

But... get a single Crest or Peavey and use just one channel (assuming you need at least two or more) and the price goes up pretty quick.



#29 Bossobass Dave

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Posted 14 October 2015 - 06:57 PM

again, i'm a little foggy this morning, but i think you have to check the current for heating not the watts.

 

6148 w into 1.2 r is 86.5 v.  86.5 v divided by 1.2 r is 71 amps.  one channel per driver so 71 amps through each driver.

 

5310 w into 4 r is 145.7 v.  145.7 v divided by 4 is 36 amps.  drivers in series so 36 amps through each driver.

 

with almost twice the amps, the spl at the listening position was 0.4db louder despite more than twice the watts, indicating almost total power compression past 36 amps.  at least that is what i was thinking.

 

Trying to figure out your math here...

 

There's "almost twice the amps", but less than 1dB more watts, not "more than twice the watts". Very little compression in dBSPL clocked. Am I missing something?

 

The key here is the "more than twice the amps" part. Two things happen as the load increases (impedance is lowered); 1) THD increases and 2) efficiency drops (more heat).

 

I think a repeat with SL running would show the difference in THD. Although approximate, the relative difference might be noteworthy, IMO.



#30 BeastAudio

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Posted 14 October 2015 - 07:38 PM

In some cases then it seems like an actually good idea to buy the amp with the intention on using only one channel at a time.

 

Arguably less value but then the price/performance needs to be weighed in and compared to other products in the same price range. Even with ~$800 amps it gets pretty dang close to a single Speaker Power amp. Not sure what the range is on their prices. I've seen $2,500 touted as a general price for one or all of them though I doubt they all cost the same.

 

But... get a single Crest or Peavey and use just one channel (assuming you need at least two or more) and the price goes up pretty quick.

 

Which is exactly how I have mine set up. Left corinthian is on a single channel of the peavey, Right corinthian on the single channel of the crest, and then the nearfields on the other channel of the crest. Which now has me thinking should I bust out a third amp of some sort for the nearfields, or get a 5500 and bridge the corinthians to 4 ohm mono and call it a day? 



#31 3ll3d00d

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Posted 14 October 2015 - 07:56 PM

Two things happen as the load increases (impedance is lowered); 1) THD increases and 2) efficiency drops (more heat).

I think a repeat with SL running would show the difference in THD. Although approximate, the relative difference might be noteworthy, IMO.

What sort of difference in thd have you seen from going to increased loads?

This sort of data (thd vs freq at different output and under different loads) seems almost completely absent from published specs so I am curious to know what sort of real world impact is.

#32 LTD02

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Posted 15 October 2015 - 01:04 AM

Trying to figure out your math here...

 

There's "almost twice the amps", but less than 1dB more watts, not "more than twice the watts". Very little compression in dBSPL clocked. Am I missing something?

 

...

 

the cc5500 was ~5300 watts both channels driven (bridged) through two drivers in series.

the sp12000 was two channels each cranking 6148 watts for about 12,300 watts total through one driver per channel.

the cc5500 hit 138.6db output.

the sp12000 hit 139.0 output.

 

those were the numbers that initially led me to conclude the ipal may be completely compressed out.  but on second review and as others have pointed out the frequency was a little different.  the low corner on the cab is right around there too, so it wasn't an apples to apples comparison.



#33 MemX

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Posted 15 October 2015 - 11:58 AM

What sort of difference in thd have you seen from going to increased loads?

This sort of data (thd vs freq at different output and under different loads) seems almost completely absent from published specs so I am curious to know what sort of real world impact is.

 

It would be good to have some empirical data on this - after all, our vocal friend on AVF asserts it is common knowledge ;) lol



#34 lukeamdman

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Posted 15 October 2015 - 10:39 PM

Lab Gruppen IPD 2400 - 2ohm stereo:

 

lg-2ohm_zpshs2i948k.jpg

 

 

At the voltages listed above, it was fine for ~2 seconds and then it seemed like the frequency all of the sudden doubled and was pulsing?  Clip lights never came on for any of this, but trying to go any higher in volume made this behavior happen even faster. 

 

I expect the 4ohm test to have much better results. 



#35 Infrasonic

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Posted 15 October 2015 - 10:46 PM

You're only using this amp for your mid/hi section though, right? In your case, no big deal and "plenty" of power for the application at hand.



#36 lukeamdman

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Posted 15 October 2015 - 10:58 PM

You're only using this amp for your mid/hi section though, right? In your case, no big deal and "plenty" of power for the application at hand.

 

Yeah, it's powering a pair of BMS 4594ND (8ohm) that are 118db sensitive....no issues to report for this application :D



#37 lukeamdman

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Posted 16 October 2015 - 05:20 PM

Lab Gruppen IPD 2400 - 4ohm stereo:

 

lg-4ohm_zpsrqbwihqv.jpg

 

 

I was really expecting this to do better at 4ohm, but I still couldn't get this amp to output more than 500w RMS one channel driven or over 250w RMS with both driven.

 

Perhaps LGs power ratings are a pure burst/peak ratings and it simply can't sustain that kind of power for over a second?

 

 

 

 

Lab Gruppen IPD 2400 - 5.5ohm stereo:

 

lg-5.5ohm_zpsgpoej5gc.jpg

 

 

Due to results at 2ohm and 4ohm stereo with the horn subs, I thought I would change it up a little and this time I used my ported AE TD18H+ drivers.

 

Even at 5.5ohm and 80hz, trying to increase even 0.5db above these levels resulted in the strange pulsating tones after ~2 seconds into the sine wave.  Still no clip/limiter lights for any test.   



#38 NWCgrad

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Posted 16 October 2015 - 09:30 PM

Great thread Luke. I was pricing out a CC4000 the other day, measurements look good.

#39 LTD02

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Posted 18 October 2015 - 11:51 PM

Not sure what to say Luke.  The specs on the website and in the manual sure seem to indicate 1200 watts per side at 4R and specifically stated are voltage and current limits that exceed that spec.  I'm sure you checked, but maybe worth double checking again for any limiter that may be engaged?



#40 lukeamdman

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Posted 19 October 2015 - 04:20 AM

Not sure what to say Luke.  The specs on the website and in the manual sure seem to indicate 1200 watts per side at 4R and specifically stated are voltage and current limits that exceed that spec.  I'm sure you checked, but maybe worth double checking again for any limiter that may be engaged?

 

I checked again and the limiter is set to the maximum voltage, which is 98v for each channel.  I also have the channels "linked", so whatever settings I change on one channel are mirrored to the other (things like input gain, EQ, XO, phase, limiter voltage). 

 

Even if it were the voltage limiter doing this, it still wouldn't explain how I get more voltage with one channel driven vs. two channels driven, right?






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