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

[Horny Toad]

Yup, that seems to be the case.

So you need to either deal with the weight of the CA-9 or hire a roadie.

 

[Tony G]

If room acoustics and your EQ curve didn't change, then you have a valid observation.

It should be mentioned that a better test would be to alternate between both setups at the same gig. It's possible that on the recent gig your bandmates were using different EQ curves that allowed your bass to sit in the mix a little better.

I will do this exact thing tomorrow as I am playing that same bar again tomorrow night. I planned on doing UL502 alone for the first set, UL502 into CA-9 for the second set, and back to the UL502 alone for the third set.

 

[Tony G]

So you need to either deal with the weight of the CA-9 or hire a roadie.

Wanna make 5 bucks?

 

[Fuzzbass]

I will do this exact thing tomorrow as I am playing that same bar again tomorrow night. I planned on doing UL502 alone for the first set, UL502 into CA-9 for the second set, and back to the UL502 alone for the third set.

Excellent!

 

[Horny Toad]

Wanna make 5 bucks?

Dude, I spend more than that on gas pulling out of my driveway.

 

[pickles]

Louder would give you more fullness (see "equal loudness").

That just is not true, it would make the signal louder. When you turn the amp up, the mids and highs get louder as well, and then you sound "too loud" Not "fuller" or "fatter".

AGAIN I will ask you what the percentage increase in perceived LF response (relative to the rest of the signal) is between say 100db and 102db?

 

[pickles]

This statement doesn't fit in with my most recent experience though, so maybe you can help me understand whats up. At a club I've played a number of times just using my UL502 at gig level, it has sounded very good for the most part. Most recently, I played this same venue adding the CA-9 into the equation, but while my overall volume was a touch lower than usual, my tone seemed overall fuller. Am I misunderstanding something occurring here?

IME, no, you are not misunderstanding anything. You're just getting better tone.

 

[pickles]

you haven't taken a close enough look or learned enough of the physics behind it to reach the same conclusions I have or ... I believe science teaches us one thing ...

Where is this science? If you can't explain it, can you provide references?

Science doesn't teach anyone anything if it is not presented properly.

 

[seamonkey]

...
Is it possible that lead sleds perform better than switching amps when voltage is lower than expected?

Chances are the switching amp has a regulated power supply. The rail voltage inside the amp is going to remain stable even if the supplied line voltage varies. (within reason)

I would doubt that a lead sled would have this.

 

[Kindness]

Where is this science? If you can't explain it, can you provide references?

Science doesn't teach anyone anything if it is not presented properly.

I can't in the course of one post teach you, but what I am specifically referring to is: (1) Fletcher-Munson curves and other biological factors that influence "tone"; (2) double blind testing methods and the psychological effects associated therewith; (3) the design and operation of amplifiers and other equipment in the signal chain; and (4) the operation of testing equipment.

 

[Bob Lee (QSC)]

That just is not true, it would make the signal louder. When you turn the amp up, the mids and highs get louder as well, and then you sound "too loud" Not "fuller" or "fatter".

AGAIN I will ask you what the percentage increase in perceived LF response (relative to the rest of the signal) is between say 100db and 102db?

Actually, it is true. One of my posts that you perhaps didn't read links to an explanation of equal-loudness contours.

This is a psychoacoustic phenomenon, not one that occurs in electronics. You turn up the volume by some amount, and the mids get louder while the lows and upper highs also get louder, but disproportionately so.

This phenomenon is why many stereo systems have a "loudness" switch that boosts the lows and highs to somewhat resemble the human auditory system's frequency response at higher sound pressure levels.

If you're going to reject this knowledge too, then you're bucking against a great deal of scientific discovery.

If you want fuller bass or whatever without loudness, then you have to EQ, and your choice of power amp will not help you there as a general rule they are extremely flat. Even the CA amps don't have bass boost, and the PLX amps don't have bass cut (aside from the selectable 30 or 50 Hz high-pass filters).

 

[tombowlus]

and the PLX amps don't have bass cut (aside from the selectable 30 or 50 Hz high-pass filters).

I just wanted to say that this is one feature that I really like about the QSC amps!

Tom.

 

[Bob Lee (QSC)]

This statement doesn't fit in with my most recent experience though, so maybe you can help me understand whats up. At a club I've played a number of times just using my UL502 at gig level, it has sounded very good for the most part. Most recently, I played this same venue adding the CA-9 into the equation, but while my overall volume was a touch lower than usual, my tone seemed overall fuller. Am I misunderstanding something occurring here?

I don't know. It might or might not have been fuller in tone, and it might not might not have been lower in volume. Your perception may or may not have changed from one time to another. The surest way to compare is with a side-by-side test, preferably a double blind one.

 

[pickles]

Actually, it is true. One of my posts that you perhaps didn't read links to an explanation of equal-loudness contours.

This is a psychoacoustic phenomenon, not one that occurs in electronics. You turn up the volume by some amount, and the mids get louder while the lows and upper highs also get louder, but disproportionately so.

This phenomenon is why many stereo systems have a "loudness" switch that boosts the lows and highs to somewhat resemble the human auditory system's frequency response at higher sound pressure levels.

If you're going to reject this knowledge too, then you're bucking against a great deal of scientific discovery.

If you want fuller bass or whatever without loudness, then you have to EQ, and your choice of power amp will not help you there as a general rule they are extremely flat. Even the CA amps don't have bass boost, and the PLX amps don't have bass cut (aside from the selectable 30 or 50 Hz high-pass filters).

I haven't even hinted at rejecting it. I have understood it for many years and have read a lot about it.

I'm asking you to quantify it at the tiny differences in loudness that you are claiming spoil all of our listening tests, but you've again ignored my direct question.

Fuller bass without EQ is exactly what some people hear when switching from a PLX to a CA. It is the very core of the discussion.

 

[Bob Lee (QSC)]

I haven't even hinted at rejecting it. I have understood it for many years and have read a lot about it.

I'm asking you to quantify it at the tiny differences in loudness that you are claiming spoil all of our listening tests, but you've again ignored my direct question.

Fuller bass without EQ is exactly what some people hear when switching from a PLX to a CA. It is the very core of the discussion.

Okay, maybe you're not rejecting it, but you're pretending it doesn't exist.

You can quantify the phenomenon yourself at the article I cited. Compare a 6.7 dB difference in gain, such as the difference between a PLX and a CA9.

Fuller bass without EQ = louder, unless the "fuller bass" is imagined.

 

[pickles]

Okay, maybe you're not rejecting it, but you're pretending it doesn't exist.

You can quantify the phenomenon yourself at the article I cited. Compare a 6.7 dB difference in gain, such as the difference between a PLX and a CA9.

Fuller bass without EQ = louder, unless the "fuller bass" is imagined.

But you're pretending we're stupid. We're not out here A/Bing with both amps "on 4" (at least I'm not). We accept that gain matching is important. We match listening levels as closely as we can by ear when A/Bing. I feel safe in saying that I was within 2db during any A/B test I've ever performed.

So what is the F-M effect of a 2db gain increase when you're already well along the curve? And could that possibly be responsible for an audible difference in "fullness"?

The actual way these tests typcially go down is that we play with our band. If we turned up, we'd be deemed "too loud" by our bandmates.

 

[Chef]

XGabrielle;
I'm running an Aggie DB680 into a qsc/plx 2402. To me, this is the best of both worlds.
All the harmonics and musicality of a great tube pre section; and the DB680 brings some heft too! The plx 2402 will do 2400 watts bridged into 4 ohms, 700 watts per side into 4 ohms, 1200 watts per side into 2 ohms...so you could drive two 4 ohm cabs off each side if you needed to!
All this in a Roady Ready 4 space rack is under 60 lbs.
Tube color, harmonics, big beefy eq, fast reacting SS power, relatively light package, big flexible power.

YMMV;
alan

 

[Bob Lee (QSC)]

But you're pretending we're stupid. We're not out here A/Bing with both amps "on 4" (at least I'm not). We accept that gain matching is important. We match listening levels as closely as we can by ear when A/Bing. I feel safe in saying that I was within 2db during any A/B test I've ever performed.

So what is the F-M effect of a 2db gain increase when you're already well along the curve? And could that possibly be responsible for an audible difference in "fullness"?

The actual way these tests typcially go down is that we play with our band. If we turned up, we'd be deemed "too loud" by our bandmates.

I'm not pretending anyone's stupid. If you want to really compare amps, you have to match the gains and not just accept that it's important but not do it.

Maybe you're within 2 dB. Maybe you're not. Your results suggest that you're not.

 

[Bob Lee (QSC)]

How far below?

Maybe the problem for me all along was that the 1602 only puts out the 350-odd watts that Bink's test shows it is capable of at 20hz. And then maybe I'd have better results with a PLX that had more headroom?

I had no desire to be any louder, just wanted more fullness.

Anything below clipping qualifies as "below clipping."

Headroom can be useful, but if you don't use it, it doesn't add anything to the sound. It's better than clipping, though.

 

[pickles]

If I were within 2db. What would the difference be?

What about 3 or 4 db.

Isn't there an equation we could use to put some perspective on the effect? If you don't know, then how can you claim it is a significant factor?

I've got the chart in front of me but its almost impossible to eyeball what the difference would be. At 10 phons the curve is very steep and at 120 phons it is much flatter ... but trying to see the difference between 90 and 91 phons is tough. I've been googling and can't find equations.