TH-18 Flat to 35hz! (Xoc1's design) - Page 107 - diyAudio
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Old 28th September 2012, 12:09 AM   #1061
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Quote:
Originally Posted by weltersys View Post
I think you may gain far more by switching amps rather than speakers.

I have QSC PLX 3602 amplifiers (1250 w@4 ohm, 1800 at 2 ohm) rated for slightly more power than the PLX 3402 (1100 @4, 1700 @2).

I have compared them to my Crest CA 9 (800 @4, 1000 @2), the CA9 measures more musical LF output than the PLX 3602.
Of note, the CA-9 does not sound bad in the LF when the clip light illuminates, but the PLX-3602 seems to get "iffy".
Lest anyone thinks I'm just a Crest fanboy, I tested the Crest CC-2800 (965 @4, 1400@2) and it had 5 dB less musical bass output than the CA 9!
The CC-2800 sound goes to crap when the clip light illuminates, I found a TH cabinet that I thought the speakers were crapping out sounded way better (and 5 dB louder) when I used another amp (the SP 4000) for testing.

Interestingly enough, above 100 Hz, the PLX 3602 has noticeably more output than the CA 9. The same can't be said about the CC-2800..

I have been using the CA-9 bridged in to the B&C18SW115-4, no problems with either amp or speaker.

Another great sounding amp is the SpeakerPower SP4000 mono plate amp, (2400w @ 4, 4000 @2) which only weighs 7 pounds, and runs cool while the PLX-3602 at the same output feels like a hair dryer.
The CA-9 bridged mono has just a little more musical LF output than the SP4000, but weighs 44 pounds, and sucks more AC power.

Although all the amps mentioned will bench test at their rated specifications, doing side by side comparisons of amps with music played in to speakers was an eye /ear opener for me, the differences were far greater than I would have thought possible.

Art Welter
Great info, Art! I really enjoy reading these types of findings.

The SpeakerPower SP4000 option is fantastic. Maybe not ideal for my situation, but I was just looking for a high power plate amp w/XLR in for another project. Speakon out is a definite plus.

Have you any experience with the Crown I-T8000? There's a sound engineer a couple hundred miles from me who switched to those from his PLX's. He runs (4) TH-118 off of one I-T8000 and reports much more LF content without the notes dying off quickly like his previous amps.

Last edited by CRESCENDO; 28th September 2012 at 12:12 AM. Reason: found pricing
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Old 28th September 2012, 12:14 AM   #1062
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Have you (or anyone else here) tried this?
Fighting For Power
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Old 28th September 2012, 01:51 AM   #1063
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Quote:
Originally Posted by CRESCENDO View Post
Have you (or anyone else here) tried this?
Fighting For Power
It works and some amps are built like this from the factory now.
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Old 28th September 2012, 03:08 AM   #1064
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"It only works on certain types of amps and is tied to how the power supply is handled.* Amps with a sperate power supply for each channel will not generate any more power.

Yes it inverts the B channel with respect to the A channel.* And ties the B channel input to the A channel input.* This only works if you are sending the same signal to both outputs-which is not the case in stereo.

So you would need 2 amplifiers with 4 loudspeakers hookedup to do this in stereo."

-Ivan Beaver
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Old 28th September 2012, 05:42 AM   #1065
NEO Dan is offline NEO Dan  United States
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Quote:
Originally Posted by CRESCENDO View Post
So you would need 2 amplifiers with 4 loudspeakers hookedup to do this in stereo.
-Ivan Beaver
Not when the amp is actually built with an inverted channel, IPR series 1600's and 3000's for example.
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Old 28th September 2012, 05:53 AM   #1066
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Yeah, Dave responded to those objections on another message board here. He gives examples and also states how much more power he was able to extract between a few amplifiers.
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Old 28th September 2012, 07:12 AM   #1067
djk is offline djk
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"It works and some amps are built like this from the factory now. "

It makes a fraction of a dB difference and can have a downside of dynamic woofer off-set going in opposite directions in a stereo amplifier.

It has been tried in the past in many commercial designs, and then abandoned.

It is touted as being a fix for power supply pumping in half-bridge class D designs, but that remains to be seen.
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Old 28th September 2012, 06:57 PM   #1068
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Quote:
Originally Posted by CRESCENDO View Post
Great info, Art! I really enjoy reading these types of findings.

The SpeakerPower SP4000 option is fantastic. Maybe not ideal for my situation, but I was just looking for a high power plate amp w/XLR in for another project. Speakon out is a definite plus.

Have you any experience with the Crown I-T8000? There's a sound engineer a couple hundred miles from me who switched to those from his PLX's. He runs (4) TH-118 off of one I-T8000 and reports much more LF content without the notes dying off quickly like his previous amps.
I have no direct experience with the Crown I-T8000, but am not a fan of extreme current limiting, the amp puts out 4000 watts per channel at 4 ohms (good for single high powered 4 ohm speaker or two lower powered 8 ohm speakers) but only 3500 watts at two ohms, not enough power to get the most out of a pair of four ohm DSL TH-118 per side.

One of the excellent features of the SP4000 is it's low frequency performance at really low impedances. I have used it with four Lab 12 in parallel, at Fb that is only a 1 or 1.5 ohm load, and the amp still kicked hard, though it would be possible to kick it's breaker if leaned on too hard for too long.

That said, on paper the I-T8000 would have 3 dB more output in to a four ohm load than the SP4000, whether it would actually make a particular sub sound louder is a question only answered by an A/B test, my investigation of just four amps revealed large differences that don't correspond to specifications.

Of note, the old school heavy metal Crown PSA 2 (weighs 8 times what the SP-4000 weighs), rated for only 460 watts at 4 ohms, and 700 at 2 ohms, put out 1 dB more output in to a BC18SW115-4 than the Crest CC 2800, rated at 965 watts at 4 ohms, and 1400 at 2 ohms, almost exactly double the paper rating of the PSA-2.
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Old 28th September 2012, 11:26 PM   #1069
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Quote:
Originally Posted by weltersys View Post
I have no direct experience with the Crown I-T8000, but am not a fan of extreme current limiting, the amp puts out 4000 watts per channel at 4 ohms (good for single high powered 4 ohm speaker or two lower powered 8 ohm speakers) but only 3500 watts at two ohms, not enough power to get the most out of a pair of four ohm DSL TH-118 per side.
Not that it means all the difference in the world, but just to clarify - I believe he's using the 8 ohm versions. So, 4 ohm load/4000W per channel, 2000W per TH-118.

The prices for these amps have reduced a little bit due to new versions coming out. I saw the amp as a more powerful (yet lightweight) upgrade from what I'm currently running (DSP being a bonus). I have found some used Crest CA-9 and CA-12 amps for enticing prices - I just don't know how I'd enjoy quadrupling my rack weight :P The I-T8000 seemed a decent compromise. I'm loving the knowledge I'm reading from you all, so I'm not asking for that to stop
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Old 29th September 2012, 07:14 AM   #1070
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Quote:
Originally Posted by NEO Dan View Post
Measurement sweep setup suggestion:
  • Attach multimeter to amp terminals or wire ends, speaker is not attached at this point.
  • Use the REW generator to play a 60Hz sine wave and set amp output voltage, 4Ω: 2v/1m, 10v/5m, 20v/10m. Note the REW generator output level setting, and do not go higher than -12 to avoid digital clipping. Ensure there is no clipping elsewhere in the signal chain.
  • Start measurement sweep dialog, set output level to the same value previously used in the generator, set frequency of sweep to 20-300Hz and select the shortest/128k sweep length and set the number of sweeps to 2.
  • Click the start measuring button, if you have too much or too little input signal make corrections at the mic/input level side only.
Before I click "Start Measuring" I clicked "Check Levels" to be sure everything was still even - yet, it popped up with "Level is Low" before audio was heard through the sub
So, the measurement process stops, but the 2 sweeps continue to play.
I get this dialog box (attached) before any audio is played


Quote:
Originally Posted by NEO Dan View Post
Note:
If you use a C-weight SPL meter to calibrate your setup with the 60Hz sine wave the actual level is ~.9dB higher than indicated due to the roll off of the C-weight filter.
When I enter the SPL Meter for calibration, it supplies a filtered pink noise signal, not sine wave choice. When I enter the Signal Generator, it doesn't show an incoming signal, just outgoing and "RMS Level dB FS" adjustment. Where do I need to be and what do I need to do to get this done properly?
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