lukeamdman

Ha, for what, a THIRD sp2-12k?!?

Yeah I can do that. On the XLS, even without a load connected the most voltage I can get out of it was ~100v. On the SP2, both 20hz and 40hz are clipping and are beyond the voltage specs listed. I did get more voltage at 40hz than 20hz on the CC amps though.

Unfortunately I sold the 7.5 so I can't do any further testing. However, I do have a NU4-6000 I'll be testing. No problem man! Is it still the voltage that seems off, or the current? On the XLS, the voltage at 20hz can only be maintained for 1 second or so, which I think is misleading since all the other voltages can be maintained for much longer. I'll take another impedance sweep. Should I take it from a single cabinet, or all 4 wired to a single 1.5ohm load like I used for most of the testing?

Yeah that's a nice feature! I also see he updated the spec sheets which lists a more accurate frequency response and also power output numbers for the 240v amps running on 120v.

Looks like Brian has lowered prices across the board and now offers the DSP option to everyone: http://www.speakerpower.net/order.html

This time I ignored the clip lights and watched for any distortion in the wave form. At 5hz it can only maintain that power for about a second, and that's not long enough to get a low/high range of the fluctuation.

Crest CC5500

Crest CC4000

I re-ran the testing for the XLS 2500, this time using the scope to measure Vrms and also letting the sine waves run a little longer at 5/10hz to capture the range of current across the resistor.

Excellent information, Josh! Your goal of getting the most output out of the same size enclosures was definitely met. The RFs look better in every way for your application.

Interesting.

I'm also going to do more testing with the differential probe. The "noise floor" was too high to get impedance measurements at levels of only 1-3 volts (it reads ~12-14mV even when not connected to anything), but once the load exceeds ~2A across the resistor (20mV) it should be accurate but I need to put it through it's paces.

I did some comparisons between the scope and the fluke meters with no load connected to the amp. I did this from the sub output, but I raised the XO to it's highest setting of 250hz. The time in between the lowest and highest readings on the Fluke was 2-3 seconds at 5hz/10hz, so it's not oscillating very quickly. However, when doing actual power testing, I don't let the sine wave run for that long, so my 5hz/10hz readings so far haven't been accurate since I don't know if I was taking the number from the high or low end. However, things got more interesting when I raised the voltage: The readings were always identical between the Fluke 117 and the Fluke 115, however, the higher the voltage got, the more the scope read a higher voltage than the Flukes, and that gap slowly gets larger the higher the voltage is. My thoughts are that I should use the scope to measure Vrms directly off the amps, and use a fluke to measure voltage across the resistor (I actually have no choice since the scope can't do this as I mentioned a few days ago). The voltage across the resistor, which will never exceed ~650mv doesn't fluctuate very much at all even at 5hz. Thoughts? Also, during my first comparison while the amp was in stereo I took some screenshots from the scope at each frequency:

I re-ran the 40hz testing on the XLS and got the same result. Pushing past clipping, 100-101v is like a brick wall and the amp will lower itself to ~95v after a second. I checked the signal on the scope and pushing passed 95v does show distortion at the top of the sine wave, so it does appear the amp is reaching it's limit. I'll do the same on the SP2 to see if I can squeeze anymore out of it.

Yeah...you're right... What the heck is up with that? There's never any wiring changes or anything when going from 40hz to 20hz for any amp test, and I was running the CC4000 through it's paces last night and it also did the same thing. Could my system resonance around 35-36hz somehow hinder the amps performance near there? The 40hz numbers across the board for the 3 amps I've tested do look a little on the low side.

Here's a couple amp frequency response comparisons I took today. The CC5500 is always the red line: CC5500 vs SP2-12K: CC5500 vs. XLS 2500: CC5500 vs. NU4-6000: CC5500 vs. LG IPD 2400:

It would throttle down after about 1 second at 5hz. I recall a post from Brian a few years ago saying the amp would reach the full 6kw down to 20hz, but by 12hz it was down to ~4,800w or something.

In order for the amp to lose power, voltage from the mains has to drop below 200v. In my testing, I haven't got the voltage to drop more than 2-3v, so it stays right at 240v or above. Voltage output was the same whether two channels were driven or one. This amp is basically two of the 6kw torpedo's in a single chassis.

SpeakerPower SP2-12000 (1ch driven) Once the clip lights were on I didn't push any further, and at 5hz it wouldn't have made any difference. However, I've read several things that indicate on this specific amp, once the clip lights are seen, there's still 1-2db left before actual clipping occurs. It's possible there was some power left in the tank.

Crown XLS 2500 (Bridged/Bypass mode with clip limiting turned off) Even though the clip limiters were off, once clipping started the voltage wouldn't increase even when turning up the main volume. At 10hz and lower, rather than seeing clip lights, the subs would start "pulsing" rapidly. I've seen similar behavior from my Lab Gruppen IPD 2400.

As for which frequencies to test, I'm thinking 10, 20, and 40hz? Think 5hz is also worth while?

I'll test the XLS 2500 first and try to get it done by this weekend.

Non-bridged. For non-bridged amps I could have just moved the resistor to the ground side and it'd work just fine, however, since bridged amps don't have a "ground level" connection I'd run into the same issue again. A solution for this grounding issue is a differential probe, which I did try and it works, BUT, the "noise floor" of the scope+differential probe were too high to get mV numbers I trust to be accurate.

Here's the new rig:

Dang.