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from Behringer to QSC...the difference!

post #1 of 43
1/26/07 at 12:41pm
Thread Starter 
I don't know if it's the Powerlight Technology or just the added power but i just installed a PLX3102 for the sub...3 dB of THD headroom @ 10 Hz (104 dB for behringer and 107 dB for the QSC...17% THD) and a 2-3 dB output improvement...the sub "seems" more visceral and detailed now...or maybe it's just the placebo effect...regardless...i went through M&C and WOTW (26:21 laser scene)...something "feels" different on both these discs, especially the lightning strikes on WOTW...also the QSC is quieter than my laptop...the ep2500 is MUCH louder...so now i can throw the ep2500 on the extra 15" box and finish the bass end of things...overall i'm glad i made the switch
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post #2 of 43
1/26/07 at 1:11pm
My Led Zeppelin view on this issue "The Song Remains the Same"...

* Placebo effect is real and is a variable.
* Published specifications can and usually is different once in an application, for better or worse.
* If the improvement is not placebo, then it's just more power. There is no magic.

There is a reason why proamps have a 'food chain' level I'm sure if you
climbed higher, you'd get more power and eventually your subwoofer would
be the bottleneck and not the amplifier. Most people will bottleneck their
amplifier at about the same time they bottleneck the woofer, but having the
extra amplifier 'umph' is sweeter.
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post #3 of 43
1/26/07 at 1:47pm
I wonder what kind of results you would have got with dual EP2500's...?
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post #4 of 43
1/26/07 at 3:17pm
Congrats on the switch, and if your ears tell you its better .. just believe em . The powerlight series amps have always seemed more "controlling" of woofers to me vs. K2s and plate amps that I have used. They are also nice and quiet too
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post #5 of 43
1/26/07 at 6:24pm
Thread Starter 
Quote:
Originally Posted by jjw350z View Post

Congrats on the switch, and if your ears tell you its better .. just believe em . The powerlight series amps have always seemed more "controlling" of woofers to me vs. K2s and plate amps that I have used. They are also nice and quiet too

are you referring to the damping factor?
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post #6 of 43
1/26/07 at 6:58pm
Quote:
Originally Posted by kramskoi View Post

I don't know if it's the Powerlight Technology or just the added power but i just installed a PLX3102 for the sub...3 dB of THD headroom @ 10 Hz (104 dB for behringer and 107 dB for the QSC...17% THD) and a 2-3 dB output improvement...the sub "seems" more visceral and detailed now...or maybe it's just the placebo effect...regardless...i went through M&C and WOTW (26:21 laser scene)...something "feels" different on both these discs, especially the lightning strikes on WOTW...also the QSC is quieter than my laptop...the ep2500 is MUCH louder...so now i can throw the ep2500 on the extra 15" box and finish the bass end of things...overall i'm glad i made the switch

I know ssabribo/Shervin had a similar observation in comparing the different Behringer EP amps to the K2 he found for a steal. On complex material the budget amplifiers simply begin to clip much sooner than the lesser regarded amps, even if alleged power ratings aren't all that different. Another curious comparison is the RMX2450 to a similar sized PL series. The RMX HD amps fair better with typical subwoofer loads. I suspect the most tangible of these differences come from more robust power supplies, where there are similar consistent differences in plate amplifiers under real use.

The good news is that the Behringer and other low-buck amps work rather well if you have more than enough power for your application and keep them out of clipping.
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post #7 of 43
1/26/07 at 8:58pm
The QSC 1450's pack quite a punch.It was night and day between my old Adcom GFA-555mkII's bridged and the QSC's bridged.

It's rather lite duty with one QSC per Tumult. It was a little unfair.....the Adcoms were never meant to drive 4ohms bridged, and subwoofers weren't part of their design forum.

I've got two Behringer A500's to run the four surround speakers.We'll see how they sound with music.Make sure you set the switch to stereo on the back side before listening ...it makes setup a little easier.

KG
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post #8 of 43
1/26/07 at 9:08pm
Quote:
Originally Posted by kgveteran View Post

It was a little unfair.....the Adcoms were never meant to drive 4ohms bridged, and subwoofers weren't part of their design forum.

KG

Some of the only amps that I have run into in this category that like subwoofers are NAD's 216THX and 218THX .... both of them will run down to 2ohms bridged (although you can cook on em in 2 ohms), I was only able to shut down the 216 on an AV15 in a sealed box at insane levels. Very powerful and controlled amps .... usually about $375-$600 on ebay ... I snatch them up when I find em....a lot of friends use them for subs now as well.
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post #9 of 43
1/27/07 at 12:17am
Yeah, with my 4 subs + BASSIS setup I went from 2 Crown XLS-402s to 2 QSC PLX3402s. Perhaps not surprisingly, it made a difference. The interesting thing was that, even though I always made sure that the 402s weren't being pushed into clipping, when I played them loud, with a stressful input (think WOTW), I had to be careful not to 'bottom' out the subs (sealed 12" Dayton Titanic MkIIIs); or, at least, I thought it was bottoming, because when I went to the 3402s the 'bottoming' ceased. I assume that what I thought was bottoming out, was just some nasty distortion.

With respect to the Titanics, I have been really impressed, because even after upping the system to four 3402s (1 per sub), they (the subs) show not the least signs of stress. My guess is that, at [my] reference listening level, they're receiving peaks at their limit of 700 watts or so (each).

Also, I decided to relieve my B&K receiver of most of its amplification duties, by using pro amps for the L, C, and R (leaving the surrounds, and back surrounds to the B&K). I first tried 3 of the Behringer A-500s (bridged), but, after getting 2 bad ones (out of a total of 4 that I tried), I decided to just bite the bullet and go with 3402s all the way. So now there's 7 of those puppies in my rack (nice rack!). The difference in the LCRs, even with the A-500s, from my B&K (125wpc) was substantial. My three front speakers are rated at 250 watts, and apparently the B&K never could make them really perform. Used to be, when I turned up the volume, there was a point at which I started feeling uncomfortable. Now, it's like the more I give them, the more they want.
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post #10 of 43
1/27/07 at 1:16am
I've been following the 'amplifier issue' for decades. After looking at amplifier designs,
playing with amplifiers, reading other user testimonials, doing some of my own amp
testing, reading other people's amp testing, looking at ABX information, filtering out
marketing propaganda, there is only one conclusion why people feel the way they do
regarding amps driving woofers.

Answer is: Power.
Upgrading to more power is always perceived as better when it comes to driving woofers.

Published specs are ballpark numbers. How the amp performs in your application
will be different. There are amps that loose almost 1/2 their power on a bad installation
and even if the installation was proper, the tested data can still be off from published.

The damping factor issue is ancient history because the modern amps we use today has
plenty and more, extra doesn't bring anything to the party.

Rumors:
RMX 1850HD is a RMX2450 amp with lower rail voltage. A good trick to keep the amp
from going into thermal overload too early when driving a demanding load like a subwoofer. It won't drive your sub better than the 2450, it will just give you less power
and probably run longer before getting hotter.

The QSC 1450's pack quite a punch.It was night and day between my old Adcom GFA-555mkII's bridged and the QSC's bridged.

The 1400w QSC better pack a punch compared to the 600w Adcom. /hehe
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post #11 of 43
1/27/07 at 1:25pm
I use a Crest CPX 2600,and have been very happy with it....the thing weighs in a 50 pounds compared to the EP2500's 40..

I am powering 2 Tempests in an IB configuration and soon adding 2 more.


I would have loved if the Crest had more(300) damping power...the more expensive amps have more than 600 + DF.
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post #12 of 43
1/28/07 at 4:00am
Thread Starter 
Quote:
Originally Posted by Kanaris View Post

I use a Crest CPX 2600,and have been very happy with it....the thing weighs in a 50 pounds compared to the EP2500's 40..

I am powering 2 Tempests in an IB configuration and soon adding 2 more.


I would have loved if the Crest had more(300) damping power...the more expensive amps have more than 600 + DF.

it would'nt place too much faith into damping factor...wire guage and length, nominal impedance of the speakers (which is highly variable) all determine the final damping factor...and usually damping factor is given at 8 ohms...AETS, it is generally held that 20 DF is sufficient for accurate reproduction of the input signal...meaning anything higher is inaudible...of course, this will vary with the individual...it does seem that high damping factor has a negative effect on system Qtc:

"The point I'm trying to make is that the actual amplifier damping factor specification has little to do with the damping factor seen by a typical woofer...unless the woofer is welded directly to the output terminals of the amplifier ... there could be a patent here. :-)

Many audio engineers are of the opinion that an amplifier damping factor of 10 or greater is adequate. Those sky high damping factors seen on the spec sheets of some amps are frequently just inventions of the marketing department and are irrelevant to actual system performance. The effect of higher source impedances (lower damping factors) is the same as adding series resistance in the speaker cable. Ultimately, the effect is a micro equalization of the frequency response as the voltage drive to the speaker becomes non-flat due to the frequency dependant impedance of the speaker. (adding series resistance creates a small peak at the speaker's own impedance peak...often on the order of 0.25 dB or so) The effect of the series resistance of the "damping" of the speaker is difficult to see when the problem is viewed this way.

The Q(tc) of a closed box speaker is increased by the addition of a series resistance. Here is the formula for this increase in system Q:

Q(tc) = Q(tco) ( (Re + Rg)/ Re )

where:
Q(tc) is the final Q of the speaker system
Q(tco) is the Q of the speaker with zero Ohms source impedance
Re is the DC resistance of the speaker
Rg is the added series resistance


Example 4:

Say we have a speaker system with Q(tco) = 0.707 and DC resistance Re = 6.5 Ohms.
We add 0.25 Ohms of series resistance by way of our amp, speaker cable and crossover.
The net Q of the speaker then becomes:

Q(tc) = 0.707 ( (6.5 + .25) / 6.5 ) = .707 (6.75/6.5) = .734

So the effect of 0.25 Ohms series resistance is really to raise the Q of the speaker from .707 to .734. We could calculate the damping factor...but who cares! We are really only concerned with our net system response. Yes, you could say the "lower damping factor" has affected the transient response of the speaker for the worse. We've all heard the mysterious explanation that "the cone keeps moving after the signal has stopped". But I prefer to look at the problem in terms of the speaker's Q(tc). We can all relate to the speaker Q much better than "the cone keeps moving...". So I prefer to move any discussion of amplifier damping factor away from the mysterious "cone keeps moving..." and into the much better understood arena of speaker system Q.

As you can see there is much more to the issue of "speaker damping" than just the amplifier's damping factor. In many systems the amp's DF will be irrelevant to the final system response because of the series resistance added by the speaker cable and the passive crossover components (see Example 3 above). Speaker designers should always be aware of the source impedance from which their speakers will be driven so that they can compensate for the source impedance in their design. If in fact your goal is to design a speaker system that will have a net response Q(tc) = .707 then you will need to anticipate the Rg (source impedance) the driver will "see" and design the enclosure for some lower Q(tco) such that the Rg will raise the NET Q(tc) to the targeted 0.707.

Regards,

John

/////////////////////////////////////
John L. Murphy
Physicist/Audio Engineer
True Audio
http://www.trueaudio.com
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post #13 of 43
1/28/07 at 8:24am
Thanks a lot for the above post, I learned a little something about subs in the process. About a month ago I finally decided to switch the Ep1500 over to power the Natalie P's. The difference is a lot like what you describe. detail, bass, output were all improved. I too initially came to the conclusion that the higher damping factor was the overall determing factor. This is an assumption but I am pretty confident in saying the HK's internal amp wasn't meant to drive a 4ohm load. So, the combination of having an already low damping factor at 4ohms plus everything else mentioned above would probably yield a much higher final Qtco in my system in comparison to what the Ep1500 does.
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post #14 of 43
1/28/07 at 10:29am
The audible improvement from HK to EP was more power.
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post #15 of 43
1/28/07 at 12:24pm
I understood the meaning of DF before the post, and still understand DF....maybe you didn't understand my post.
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post #16 of 43
1/28/07 at 1:07pm
Quote:
Originally Posted by Exocer View Post

....maybe you didn't understand my post.

Perhaps, so I edited the reply.
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post #17 of 43
1/28/07 at 1:17pm
I went back and re-read my post. I see why you would think I missed the point. I should've been a lot more clear
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post #18 of 43
1/28/07 at 6:16pm
Quote:
Originally Posted by Richard Mayer View Post

I wonder what kind of results you would have got with dual EP2500's...?

That's what I would like to know!
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post #19 of 43
1/28/07 at 9:00pm
Thread Starter 
Quote:
Originally Posted by crackyflipside View Post

That's what I would like to know!

...having three 2.4kW amps operating on a 20 amp circuit that is'nt dedicated may be asking for trouble...the third amp would power the third 15" i will be adding to the system shortly...

power is'nt the only reason why i bought the QSC...there's a difference between Behringer and QSC PLXII/Crown K amplifiers...damping factor, signal to noise, powerlight voltage supply, fan noise, weight and build quality...operating without highpass filtering, i would prefer not to risk running 4.5-5kW through even these drivers...not at $900 a pair...
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post #20 of 43
1/28/07 at 9:07pm
Quote:
Originally Posted by kramskoi View Post

i would prefer not to risk running 4.5-5kW through even these drivers...not at $900 a pair...

Some people simply have no sense of adventure....
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post #21 of 43
1/29/07 at 8:15am
Thread Starter 
Quote:
Originally Posted by Thomas-W View Post

Some people simply have no sense of adventure....

I hear ya TW but the whole idea is not to overdrive the equipment.

The QSC adds more VLF detail and once the third 15" goes in the extra box "everything bass" will be complete, given the available space...2x15 for music and 3x15 for HT...
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post #22 of 43
1/29/07 at 10:36am
Quote:
Originally Posted by kramskoi View Post

given the available space...2x15 for music and 3x15 for HT...

You need to visit those Bass Anonymous meetings
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post #23 of 43
1/29/07 at 10:48am
and all this time I though if you level matched everything correctly, all amps "sound" the same.....LMAO!!!!!
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post #24 of 43
1/29/07 at 11:09am
Quote:
Originally Posted by ssabripo View Post

and all this time I though if you level matched everything correctly, all amps "sound" the same.....LMAO!!!!!

If you want to test two amps at their highest power level then you
have to level match the highest amp to the lowest amp, ie

1000 watt amp vs. 100 watt amp.

Match the 1000w amp to operate at 100w so you can compare 100w from
brand 'A' to the 100w from brand 'B'.

Here's more comedy. Lets get two of the same amplifier and mis-match them
to see what might happen.

Flips a coin -> I chose Crown K2 as the example.

Test condition:
Lets run K2 #1 in bridge mode with an 8 ohm woofer with 1% THD at 117VAC [under full load]
Expect about ~1400w.

Lets run K2 #2 in bridged mode with an 8 ohm woofer with 1% THD at 96VAC [under full load]
Expect ~900w.

Play a 20hz test tone on both rigs.

Do you see the comedy on why one person may perceive the K2 to
be sweet for their sub, and another person might think it's weak. It's
the same amp using a different electrical install, but all other variables are
the same.
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post #25 of 43
1/29/07 at 11:22am
even more comedy for you:

run amp "A" with the same source (117AC) under full load, and run the same setup with amp "B" using an A/B non-delay switch.

amp A "measures" 600 watts RMS into 4 ohms, 20-20Khz, .005% THD, and 118 db S/N ratio.
amp B "claims" 650 watts RMS into 4 ohms, 20-20Khz, .1% THD, and 98-100 db S/N ratio.

with the meter reading 70 SPL or higher, every single person heard a difference.....guess which one it was
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post #26 of 43
1/29/07 at 12:19pm
Quote:
Originally Posted by ssabripo View Post

even more comedy for you:

run amp "A" with the same source (117AC) under full load, and run the same setup with amp "B" using an A/B non-delay switch.

amp A "measures" 600 watts RMS into 4 ohms, 20-20Khz, .005% THD, and 118 db S/N ratio.
amp B "claims" 650 watts RMS into 4 ohms, 20-20Khz, .1% THD, and 98-100 db S/N ratio.

with the meter reading 70 SPL or higher, every single person heard a difference.....guess which one it was

You auditioned two amps with a switch box non level matched and people
chose a winner. I don't see the comedy. lol
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post #27 of 43
1/29/07 at 2:31pm
When you measure the AC current....how do you get 96 volts?

Could you explain to a dummy like me..?


Quote:


Test condition:
Lets run K2 #1 in bridge mode with an 8 ohm woofer with 1% THD at 117VAC [under full load]
Expect about ~1400w.

Lets run K2 #2 in bridged mode with an 8 ohm woofer with 1% THD at 96VAC [under full load]
Expect ~900w.

Could you have done the same test with a 2,4 or 8 ohm woofer?
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post #28 of 43
1/29/07 at 3:03pm
When you measure the AC current....how do you get 96 volts?

Someone tested that particular amplifier under 117VAC and 96VAC conditions
and measured the wattage at 1% THD+N @ 20hz. The output power was
less with 96VAC vs. 117VAC input. That scenario I posted is a real one.

The reason a 'sagging' AC line test was performed was because this is a real
world scenario. People assume their house voltage is sweet but there is
losses at high power. Those losses can cause the amplifier to output less power
and you may not realize it. Some amplifiers are designed where they are not
affected too much by line sags and continue to output the same power.

Many amplifier are designed for 120VAC and tested at 120VAC to get the power
ratings. But in a real world situation, most people don't have 'low loss' home
electrical systems so they realize voltage drops or sags.

I tested my proamp on my home wiring to see what happens with my electrical system.
Pluggin my proamp into the ordinary wall socket on 20A breaker yielded a
voltage drop from 120VAC to under 100VAC, playing a test tone at full power
using the lowest rated impedance load, in which case the proamp turned off right away because the AC line voltage sag was too great
and the proamp protection circuit enabled.

I did another test where I ran 8 awg romex from the main breaker box {200A)
from the back of house, to the garage, and redid the test. Even using oversized
wire, I still got a 10VAC voltage drop, from 120VAC to 110VAC. The amplifier
worked, but maximum power was not realized. You really need to look at
over engineering your home wiring alot if you want to run a bunch of monster
amplifiers. You can cripple your amplifier's maximum performance ability
even if you had an electrical install the proper wiring, even installing 'overkill'
wiring had too much voltage loss.

After this experience, I made plans to install 2 awg wiring for my HT with subpanel with less than 50 feet of travel. Gotta keep the losses low.

Could you have done the same test with a 2,4 or 8 ohm woofer?
You can do the same tests with any impedance as long as it doesn't go outside
the amplifier's specifications.

If you were to run the K2 at 4 ohm bridged, it will draw more current, and
you will have more output power but you will also have more AC line losses.
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post #29 of 43
1/29/07 at 3:11pm
That is very interesting... I checked my house voltage and it's at 124 volts...
I will recheck it when playing my Crest 2600 at full load ... I have a dedicated 12 gauge 20 amp circuit for it.


Now you got me thinking..
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post #30 of 43
1/29/07 at 3:15pm
Quote:


You auditioned two amps with a switch box non level matched and people
chose a winner. I don't see the comedy. lol

Again man, there's magic I tells ya!
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