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lukeamdman

Luke's basic amplifier tests

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lukeamdman    154

EDIT: The testing methodology was updated to use a non-reactive load (water heater elements).

I purchased 10 of these (Camco 6000w 240v low watt density):

https://www.amazon.com/Camco-Screw--Foldback-Heater-Element/dp/B000PSB3B2/ref=sr_1_1?ie=UTF8&qid=1468811988&sr=8-1&keywords=camco+6000w+240v

Each was measured and the resistance was either 9.9 or 10ohms, so with 5 wired in parallel for each channel the resistance came to almost exactly 2.0ohm. 2ohm stereo or a single 4ohm load utilizing all 10 can easily be wired.  Utilizing just four of these elements per channel I can wire two 4ohm loads ((2) in parallel + (2) in a series).

 

3r0i5nK.jpg

iRR7pS6.jpg



Testing Summary


1.  For the CEA-2010 burst tests I use REW as the signal generator and a Rigol DS1054Z oscilloscope with a 10x probe to measure Vpp. The amps are pushed as far as possible while still being able to produce a clean CEA-2010 wave form.

2.  The second test is 12 seconds in duration at 20hz at maximum clean output.



** What these tests do not reveal! **

- Efficiency (I'm not measuring current draw from the wall)
- Distortion/THD
___________________________________________________________________________________________

Crest CC4000 - Bridged

Crest CC4000 - Stereo

Crown XLS 2500 - Bridged

SpeakerPower SP2-12000

Lab Gruppen IPD 2400

Behringer iNuke NU4-6000 - Bridged

Behringer iNuke NU4-6000 - Stereo - 4ohm

Behringer iNuke NU4-6000 - Stereo - 2ohm

"Cube Amp" - Stereo - 4ohm

 

____________________

** These tests below were performed with my (8) sealed 21" drivers as the load. I no longer have these amps so I can't re-test with the latest method **
____________________

Crest CC5500

Peavey CS 4080HZ

 

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LTD02    6

neat.  if i'm interpreting the result correctly, the ipal's can't handle the current and compressed out almost all the power gains afforded by the sp amp?

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lukeamdman    154

neat.  if i'm interpreting the result correctly, the ipal's can't handle the current and compressed out almost all the power gains afforded by the sp amp?

 

It's a little hard to tell since the frequency wasn't the same.

 

The bridged amps were tested at 32.9hz, and the SP was tested at 27.5hz.  The excursion minimum on the Othorn is 30hz, so both were close to that.

 

The SP amp was definitely harder on them thermally, since it was ~6kw per driver compared to ~5500w shared between the two, but even so, excursion was surprisingly high with the bridged CC5500. 

 

I was really impressed with the Crest, and I let the sine wave continue at 1db into clipping to see how long it would go.  It maintained a steady 154v until it tripped its magnetic circuit breaker (the power switch) at ~4-5 seconds in. 

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LTD02    6

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.

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lukeamdman    154

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.

 

I had already done the math for the amperage, so I knew it was more of pretty much everything with the SP amp ;)

 

The only caveat is the frequency difference between the tests.  I could re-run the SP test at 32.9hz to find out?

 

In a few months I'll have (8) sealed FTW-21 in addition to the Othorns, so that will open the door to some lower frequency testing as well. 

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LTD02    6

i wasn't suggesting that you hadn't done it or didn't know.  i was just laying out my logic.  on second thought, in this test, doubling the current and doubling the power are looking at the same thing. [they probably always are, but with amps and speakers frequently folks refer to the "watts" as the volts/dc r not the actual, and varying, impedance.]

 

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!

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lukeamdman    154

Wait what? You dumping the GH and just going sealed and Othorns? Or adding in the sealed to the 4 total horns? Wild son! 

 

Every fiber of my being wants to keep the GH and just add the FTWs to the four horns, but doing so would require me to move the TV and L/C/R speakers forward 2ft and they're already way to close to the front row as it is.  My room is just too small for that. 

 

The other issue is the funds...  To keep the GH I'd need to buy even more amps! 

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chrapladm    46

Real world problems I guess. :D

 

I couldnt tell what what amount of compression was going on with the different frequencies measured in the end. It would look like there was quite a bit of compression with double the "wattage," and only minimal gains. BUT again its not exactly apples vs apples. Still a great test though.

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Infrasonic    153

Every fiber of my being wants to keep the GH and just add the FTWs to the four horns, but doing so would require me to move the TV and L/C/R speakers forward 2ft and they're already way to close to the front row as it is.  My room is just too small for that. 

 

The other issue is the funds...  To keep the GH I'd need to buy even more amps! 

 

Worries about funds, orders eight FTW21's.

 

You're lucky I'm at work or that would have been a good meme made as we've got several pics of you in varying degrees of amusement non-amusement. :D

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lukeamdman    154

 

Worries about funds, orders eight FTW21's.

 

You're lucky I'm at work or that would have been a good meme made as we've got several pics of you in varying degrees of amusement non-amusement. :D

 

LOL!

 

The only way I can afford those FTW is by selling the Ghorns...and also because of the group buy price they have going on right now!

 

I already have a solid buyer for the Ghorns, and if he had his way, they would have been in his basement well over a month ago  :D

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Infrasonic    153

Okay, I see what you're up to. Honestly, I'd probably do just this. Swap out the Ghorns for massive sealed displacement. You've got the "goods" with dual Othorns doing the major lifting and with a sick sealed system you finish off the rest of the bandwidth with ease. Especially in a room like yours (mine is about as big).

 

Though... I don't want to nor feel comfortable persuading you to sell off the Ghorns. They are just too cool and I know you really love yours. Honestly surprised to see you do it but ... it's not a lateral move doing big time sealed. It's the end game.

 

I can make all sorts of suggestions but I'd rather be a fly on the wall and see what happens. Very interesting.

 

Excuse me. Master of OT here.... I'll let this get back to the tests. :)

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lukeamdman    154

Okay, I see what you're up to. Honestly, I'd probably do just this. Swap out the Ghorns for massive sealed displacement. You've got the "goods" with dual Othorns doing the major lifting and with a sick sealed system you finish off the rest of the bandwidth with ease. Especially in a room like yours (mine is about as big).

 

Though... I don't want to nor feel comfortable persuading you to sell off the Ghorns. They are just too cool and I know you really love yours. Honestly surprised to see you do it but ... it's not a lateral move doing big time sealed. It's the end game.

 

I can make all sorts of suggestions but I'd rather be a fly on the wall and see what happens. Very interesting.

 

Excuse me. Master of OT here.... I'll let this get back to the tests. :)

 

The (8) FTW will be in 4 large dual-opposed boxes, and they'll be placed exactly where the Ghorns are today with the Othorns sitting on top of them.

 

The plan is to wire the two drivers in each cabinet in parallel (FTW/UXL are not DVC), and then wire two cabinets in a series for something around a ~4ohm load.

 

The pair of CC5500 I'll have sitting around that are currently powering the Ghorns should be perfect for the job.

 

If the CC5500's don't work out for whatever reason (not sure what their sub 10hz performance is like), there's always the SP2-12000 to try as well.  

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Infrasonic    153

Not a bad idea. I'd hook up each enclosure to some amp or amp channel for the long run but that wiring scheme should work okay.

 

This would be quite an upgrade, methinks. SPL might be pretty dang close in the 12.5-32hz range just cuz of your current brute force application of heavy hitting low tuned horns. But below 15hz or so.... you'll have a massive increase in sensitivity and output.

 

Sounds like fun!

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lukeamdman    154

Crest Pro-Lite 7.5

 

7.5_zpsbskkjhz2.jpg

 

 

When driving a 2ohm load, it was either completely fine or power cycling.  Even with one channel driven, 81v for 2-3 seconds was no problem.  Trying to go up even .5db resulted in an immediate power cycle.  Same behavior with 2 channels driven.

 

It may reach its specs at 2ohm stereo at 1khz, but definitely not in in the bass region. 

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Ricci    652

 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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lukeamdman    154

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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lukeamdman    154

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.

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Infrasonic    153

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?

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