Crest CA-9 vs. QSC PLX2502 (PLX2 Series)

[Passinwind]

You have to get past what you can measure to see if the listening is different than the measurement.

Whoa! The idea here is to first see if you can hear a difference between two gain-matched amps. If not, game over. If so, you could move on to quantifying why you hear a difference.

Fdeck's software is very simple. You won't need meters, or dummy loads.

Assuming you find a reason to use an analyzer program (see above), don't hook up a 2KW amp to a standard soundcard input directly, unless you like smoke.

 

[bongomania]

...don't hook up a 2KW amp to a standard soundcard input directly, unless you like smoke.

Details, Charlie, details...

 

[seamonkey]

Whoa! The idea here is to first see if you can hear a difference between two gain-matched amps. If not, game over. If so, you could move on to quantifying why you hear a difference.

See here I don't agree. If it takes just a slight tweak of tone to make up the difference, then why dismiss one amp over another. I'm only talking about micro adjustments here. Not major EQ swings. And not adjustments at every listening level.

If this was medical testing, and one amp put out a gas that made you sleepy, then to make things equal, you'd put out a similar gas while testing the other amp. Just so you didn't clue off the sleepiness as being the first amp.

If you don't measure first, Amp manufacturers are going to add built in eq curves to fool people otherwise.

Crown has added a subharmonic generator to their DSP. Turn this on and beat out every other amp on subjective bass response.

Assuming you find a reason to use an analyzer program (see above), don't hook up a 2KW amp to a standard soundcard input directly, unless you like smoke.

I did say using a measuring mic. Use the speaker you're going to be using and a mic to measure it.

 

[bongomania]

If it takes just a slight tweak of tone to make up the difference, then why dismiss one amp over another.

Because the point of the test is to determine whether two amps perform differently, not whether they can be processed into similarity.

I'm only talking about micro adjustments here. Not major EQ swings. And not adjustments at every listening level.

Any such adjustments, even at the micro level, would invalidate the test IMO.

 

[Kindness]

Because the point of the test is to determine whether two amps perform differently, not whether they can be processed into similarity.

Any such adjustments, even at the micro level, would invalidate the test IMO.

+1 and +1

 

[pickles]

+1 and +1

And another +1

If a power amp has a built-in EQ curve that you think makes it sound better, why not use it? I don't plan to add an extra EQ to my rig to make up for pre-shape in a power amp ... ever. The amp sounds the way it sounds with my pre -- and that is what the test is all about.

 

[seamonkey]

Then use the EQ on your preamp to equal out the test.

In any case, if you don't measure, I for one won't believe your results. If the output levels aren't the same, and you're using your ears to say they're the same, it's not going to be anymore than another opinion.

Read up on Blind testing, it does setup equality before the tests.

Might as well test heads with the knobs set straight up. Every head has a different weighted curve.

In the end - all the amps are sonically essentially the same. Maybe the on board preamp part of the amp slightly differs - enough that some may claim some amp is superior with the preamp knobs set flat, but only a little tweak is all it takes to make them objectively equal.

Enter the Crown Xti and all the pro-sound amps that do or will include signal processing (DSP). This kind of processing going to be common place and doesn't seem to affect the relative price. I guess these will all be superior. Good for progress.

 

[tripb19]

This thread was handy for about 4 pages

 

[Kindness]

Then use the EQ on your preamp to equal out the test.

In any case, if you don't measure, I for one won't believe your results. If the output levels aren't the same, and you're using your ears to say they're the same, it's not going to be anymore than another opinion.

Read up on Blind testing, it does setup equality before the tests.

Might as well test heads with the knobs set straight up. Every head has a different weighted curve.

In the end - all the amps are sonically essentially the same. Maybe the on board preamp part of the amp slightly differs - enough that some may claim some amp is superior with the preamp knobs set flat, but only a little tweak is all it takes to make them objectively equal.

Enter the Crown Xti and all the pro-sound amps that do or will include signal processing (DSP). This kind of processing going to be common place and doesn't seem to affect the relative price. I guess these will all be superior. Good for progress.

The scientific method is not improved by adding variables.

The test is supposed to measure whether there is any INHERENT tone differences between the two amps. If you EQ the signals going to the two amps differently, you've completely invalidated the test.

 

[pickles]

Then use the EQ on your preamp to equal out the test.

In any case, if you don't measure, I for one won't believe your results. If the output levels aren't the same, and you're using your ears to say they're the same, it's not going to be anymore than another opinion.

Read up on Blind testing, it does setup equality before the tests.

Might as well test heads with the knobs set straight up. Every head has a different weighted curve.

You're confusing issues. I'm going to gain match using a dummy load (thanks passin!) and a 1khz sine wave to make the test fair, then see if the amps sound any different. Thats all that matters in the context of actually using the amp. The fact that you could, with an extensive enough EQ circuit and a lot of time, make one sound like the other is not relevant IMO.

I've been reading a lot about blind testing, and you're the first person I've seen suggest this method.

 

[bongomania]

Then use the EQ on your preamp to equal out the test.

What?? How un-scientific can you get?

all the amps are sonically essentially the same.

The POINT of this whole thread is to find out the truth of that assertion, and everything else you are adding about EQ, opinion, and DSP is just derailment from that point. I suspect intentional derailment. I would also say you are contradicting yourself. If they are "sonically essentially the same", then why would anyone use EQ to "equal out the test"?

 

[Jeff A]

What?? How un-scientific can you get?



The POINT of this whole thread is to find out the truth of that assertion, and everything else you are adding about EQ, opinion, and DSP is just derailment from that point. I suspect intentional derailment. I would also say you are contradicting yourself. If they are "sonically essentially the same", then why would anyone use EQ to "equal out the test"?

+1000000

 

[Passinwind]

In the end - all the amps are sonically essentially the same. Maybe the on board preamp part of the amp slightly differs - enough that some may claim some amp is superior with the preamp knobs set flat, but only a little tweak is all it takes to make them objectively equal.

You do realize that this thread is about power amps and not bass heads, right?

 

[seamonkey]

Maybe you don't need any EQ, but you need to measure it first.
If you measure it and find a small difference, no sense stopping the test, go ahead and EQ it out, and complete the test.
Go from quiet to loud while you test - how do they compare with a little EQ if needed. Power amps have little preamps in them, they are rated in some fractional db frequency response that if you listen hard - you could hear (but could easily eq out).
Nothing too radical.

 

[blowinblue]

While y'all are going round and round and round about amps, I've been sitting in front of my amps playing, practicing, enjoying. And gigging a few times per week. I may be having more fun than you guys, but don't be jealous. I'm sure you'll get all this sorted out...eventually.

Yes, I am teasing you! Cheers.

M. M.

 

[el_Kabong]

While y'all are going round and round and round about amps, I've been sitting in front of my amps playing, practicing, enjoying. And gigging a few times per week. I may be having more fun than you guys, but don't be jealous. I'm sure you'll get all this sorted out...eventually.

Yes, I am teasing you! Cheers.

M. M.

yeah and I drank the knob creek too.....

 

[pickles]

While y'all are going round and round and round about amps, I've been sitting in front of my amps playing, practicing, enjoying. And gigging a few times per week. I may be having more fun than you guys, but don't be jealous. I'm sure you'll get all this sorted out...eventually.

Yes, I am teasing you! Cheers.

M. M.

Dude these threads are like catnip for hobby geeks and techno nerds.

I've said many times about the PLX that even if it sounded as much thinner as I may or may not have perceived it, there is still nothing about it that would prevent your from getting great sound on a gig.

But we're geeks, so we test and we optimize

 

[Bob Lee (QSC)]

Sorry, I've been out sick for a couple days. (It sucks getting a cold in the summer. Actually, it sucks getting a cold.)

You shouldn't change EQ between amps for a double-blind comparison. Both amps have a high input impedance that is almost entirely resistive. The preamp would have to have a bizarre high output impedance that varies wildly across the frequency spectrum in order to cause a significant difference between them.

 

[pickles]

For anyone else who's off the deep end, I found a cool blog on topics of audio testing by a guy that seems to have significant cred:

Invalid Link Removed

There are lots more on the same site if you poke around.

 

[oddio]

For anyone else who's off the deep end, I found a cool blog on topics of audio testing by a guy that seems to have significant cred:

Invalid Link Removed

There are lots more on the same site if you poke around.

Thanks for the link. I enjoyed reading these. If you wade through a few, the author properly credits Dr. Floyd Toole for his pioneering efforts in this area. I was fortunate enough to participate in several of these tests when Dr. Toole was based here at the NRC and conducting tests in the anechoic chamber. When the (acoustically transparent) curtain was lifted at the end of the testing, it was always astonishing to discover that those tiny Yamaha studio monitor speakers were shaming refrigerator-sized Tannoys in double blind tests (for example), as determined by a majority of listeners. Anyhow, I'm drifting off topic here so I'll wander off in search of some coffee...