Measuring Amplifiers - Page 33 - AVS Forum
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post #961 of 1917 Old 05-23-2008, 10:19 AM
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Quote:
Originally Posted by catapult View Post

Anyone who has read this thread knows Chuck uses a variac to keep the voltage at 120. And I think Chuck has been doing this electronics stuff long enough that he knows an oscillation when he sees it on the scope. He was seeing it up at 1kHz so it has nothing to do with DC or undervoltage, it's just a really nasty form of clipping that he was trying to avoid. And a resistor is the easiest load you can drive despite what Crown says. Loudspeakers are harder to drive than a resistor.




Sure, but how much current was being drawn by the amplifier when he did the 20 Hz test for the XTI-1000? If power supply limiting occured, then the current use by the amplifier should drop a lot as compared with the testing of higher frequencies!
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post #962 of 1917 Old 05-23-2008, 10:44 AM
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Quote:
Originally Posted by thylantyr View Post

When it comes to subwoofers, the gap narrows from the sine
wave world to the real world.

Example: In car audio where people are playing tones for SPL
display, the sine wave test = real world

In HT audio, perhaps movie special effects, are there any effects
that may represent a continuous tone, even for a fraction of a second? If so, then the sine wave test = real world.

When I listen to some Slayer where Kerry King is making some
crazy guitar noises using feedback, is that close to a continuous
tone, but at a higher frequency range? if you think it may be,
then the sine wave test @ 1khz = real world



BTW, I have blown my circuit breakers on those guitar moments
as it was punishing my amplifiers



If anyone uses the XTI amplifier with a subwoofer and plays a DVD that has a 20 Hz signal (or lower) that limits the output power to 90 watts, the end user would know it just by listening.

We still do not know if the XTI-1000 that was tested if a good unit either. In addition I wonder how that same XTI-1000 amplifier behaves with the use of wide band pink noise as a test signal?

Just as a note, I hope to learn something here about testing these newer style amplifiers. Is that specific amp a bad unit, is the XTI design bad, or is the test bad?
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post #963 of 1917 Old 05-23-2008, 11:15 AM
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Quote:


If anyone uses the XTI amplifier with a subwoofer and plays a DVD that has a 20 Hz signal (or lower) that limits the output power to 90 watts, the end user would know it just by listening.

Several pages back, Exojam did a test......

http://www.avsforum.com/avs-vb/showp...&postcount=823

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post #964 of 1917 Old 05-23-2008, 11:23 AM
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Question: Exactly HOW is an amplifier going to differentiate between driving a resistor and a loudspeaker load.... ? Heck, some main loudspeakers drop below 3 ohms in the bass region, like the Klipsch RF-7, and RF-83.

"You take the blue pill - the story ends, you wake up in your bed and believe whatever you want to believe. You take the red pill - you stay in Wonderland and I show you how deep the rabbit-hole goes."
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post #965 of 1917 Old 05-23-2008, 11:27 AM
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Quote:
Originally Posted by J_Palmer_Cass View Post

If anyone uses the XTI amplifier with a subwoofer and plays a DVD that has a 20 Hz signal (or lower) that limits the output power to 90 watts, the end user would know it just by listening.

We still do not know if the XTI-1000 that was tested if a good unit either. In addition I wonder how that same XTI-1000 amplifier behaves with the use of wide band pink noise as a test signal?

Just as a note, I hope to learn something here about testing these newer style amplifiers. Is that specific amp a bad unit, is the XTI design bad, or is the test bad?


The 'RMS test method' works for any style of amplifier

The only thing cool about this new platform design is
the DSP. The class AB part isn't a good idea for the
higher powered models. You can check out how QSC has
executed the concept of the "universal platform" better than
Crown, but QSC is not a golden child either. lol



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post #966 of 1917 Old 05-23-2008, 11:28 AM
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Quote:
Originally Posted by michael hurd View Post

Question: Exactly HOW is an amplifier going to differentiate between driving a resistor and a loudspeaker load.... ? Heck, some main loudspeakers drop below 3 ohms in the bass region, like the Klipsch RF-7, and RF-83.


Speaker loads varry,they go up and down ...up and down. A resistor is much more constant.

Ask yourself mortal , do you have as much displacement as me ? The answer is no unless you have a Windmere fan sub.
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post #967 of 1917 Old 05-23-2008, 11:33 AM
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I know Arthur.... LOL... but do you want your FR going up and down too?! May as well get out the SE OTL monoblocks with big bottles on them to drive your sub.

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post #968 of 1917 Old 05-23-2008, 11:51 AM
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Driving a loudspeaker can be much more difficult than driving a resistor for an amplifier, even if the minimum impedance of the loudspeaker is higher than the resistor. This has a lot to do with how the amplifier is designed and what type of motor the loudspeaker has.

A reactive loud, such as a loudspeaker, means that for a portion of the AC cycle, the load draws much more current from the amplifier than the impedance suggests from Ohms law and that for a portion of the AC cycle the load draws less current than the impedance suggests. Some switching amplifier designs will detect the current flow during the low impedance portion of the waveform, and current limit of shut down to keep from exceeding the SOA of the output devices even though you may really be at 1/2 of the amplifiers RMS power output on a full cycle basis.

Remember that the impedance curve of a loudspeaker is a measurement usually made at one drive level. When you are driving a subwoofer with a 3" or 4" VC that has 10-20mh of inductance, as the VC is moving in and out of the gap, it is creating a huge back EMF that is trying to drive the voltage at the amplifier terminals where it wants to. Some amplifier designs are not going to like this. From this standpoint, a loudspeaker creates a much more difficult load than it appears from a simple impedance and phase curve. The reactance changes radically with drive level.

Some power amplifier SMPS are designed to output full rated power for 30 minutes, some are only designed to do it for a few seconds. This behavior is all over the map and depends on the particular design. It varies a lot even within one companies product line.

Jack Hidley
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post #969 of 1917 Old 05-23-2008, 12:03 PM
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Quote:


Sure, but how much current was being drawn by the amplifier when he did the 20 Hz test for the XTI-1000? If power supply limiting occured, then the current use by the amplifier should drop a lot as compared with the testing of higher frequencies!

Sorry, if the amp thinks 20 Hz is DC and starts limiting power, it's a bad design, especially for powering a subwoofer. Crown has acknowledged as much in their own testing although they use a lot more words (CYA) to admit they messed up. Maybe Crown will fix it someday and it will become a good design. Until then....

Dennis H
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post #970 of 1917 Old 05-23-2008, 12:04 PM
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We agree on why driving a loudspeaker is harder than driving a resistor. The only thing is if an amp does a poor showing driving a resistor, will it do OK in the real world for driving a reactive load. Some amp designs yes, class D amps like the PL 380 would benefit from driving a reactive load, like a horn or a reflex box.

Others... well not so good. As mentioned drivers create voltage when the coil is moved through the magnet assembly ( remember that inductance thing.... ) and is continually fighting the amplifier to push current into and out of the output stages.

Bottom line to remember.... huge high power motor needs a big amp.

"You take the blue pill - the story ends, you wake up in your bed and believe whatever you want to believe. You take the red pill - you stay in Wonderland and I show you how deep the rabbit-hole goes."
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post #971 of 1917 Old 05-23-2008, 12:43 PM
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Quote:


We agree on why driving a loudspeaker is harder than driving a resistor.

All these comments about loudspeakers vs. resistive loads is
misleading, skewed or wrong.

I stopped myself from posting on this issue earlier
as it could open up a new can of worms. Sorry, this
will be PM conversation only



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The perfect setting for things to come......

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post #972 of 1917 Old 05-23-2008, 02:08 PM
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Quote:
Originally Posted by thylantyr View Post

All these comments about loudspeakers vs. resistive loads is
misleading, skewed or wrong.

I stopped myself from posting on this issue earlier
as it could open up a new can of worms. Sorry, this
will be PM conversation only

I demand a huge barrel O worms. Sadly I have a feeling the Ex tea eye may be flawed and no updates to any software or minor hardware mods may correct the poor performance.

The Ex tea eye has this suspicious look inside,besides the output stage transistors and some regulation...there is very little beef. Look at the QSC PLX and PLX2 series,there is beef to calm the hunger and deliver.

I know amps are getting smaller and more efficient,but there is a limit and compromise grows as they lean these amps too much(money saving mesures and after...weight saving).

Ask yourself mortal , do you have as much displacement as me ? The answer is no unless you have a Windmere fan sub.
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post #973 of 1917 Old 05-23-2008, 02:23 PM
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Amps need not be heavy and jammed full of components to have massive power output. Look at the CE4000 only 34lbs, or the Bink's test data for the Crest 9200. It weighs less than 25lbs.

Seems like XTI is either not a very good design, or Chuck had a faulty unit.
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post #974 of 1917 Old 05-23-2008, 02:39 PM
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Quote:
Originally Posted by Ricci View Post

or Chuck had a faulty unit.






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Now that this is out of the way...

I have a very strong feeling the low cost Crown XLS series are much better suited for subwoofer duty.The only downside(and not a real on e in stationary home use)...weight.

Like the QSC RMX series these lower cost,more classic amps could be quite interesting.

I will go grab the largest XLS ,the XLS5000 and XLS802.These look like capable low cost amps.

Ask yourself mortal , do you have as much displacement as me ? The answer is no unless you have a Windmere fan sub.
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post #976 of 1917 Old 05-23-2008, 03:29 PM
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Quote:
Originally Posted by thylantyr View Post

I don't really buy into their explanation. Whether a
speaker or resistor is connected won't matter in a
proper design. If it does, it's a bad design.

HERE HERE!!!!

Most of us don't get to test manufacturers clams very often.
When was the last time you put (inset what the max towing capacity of your truck here) behind your truck and tried to pull it?
But when Car and Driver does it and that model of truck can't pull what the manufactures says it can, would you buy an explanation like.......

"the Car and Driver test used a 2 axle trailer with a boat on it, our test was a single axle loaded with bricks......"

I think not. If the weigh the same I call BS. This is another annoying car metaphor but come on people. Resistor or reactive load......I just don't buy that argument.

Perhaps a bank of robust 8"dvc subwoofers could be used instead of the water heater elements. Although I think it might be a little out of budget for this FREE testing.

"There is no greater mistake than the hasty conclusion that opinions are worthless because they are badly argued."
-- Thomas H. Huxley
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post #977 of 1917 Old 05-23-2008, 03:50 PM
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Quote:
Originally Posted by TheEAR View Post

Now that this is out of the way...

I have a very strong feeling the low cost Crown XLS series are much better suited for subwoofer duty.The only downside(and not a real on e in stationary home use)...weight.

Like the QSC RMX series these lower cost,more classic amps could be quite interesting.

I will go grab the largest XLS ,the XLS5000 and XLS802.These look like capable low cost amps.

Crown inherited XLS from C-audio when Harmon purchased
that company. XLS version A thru C looks anemic inside,
but good enough for light duty work. Amazing, Crown did
an fresh update to this series, version D looks better, but
the guts still look like they hired a high school kid to do
circuit board layout. Oh well. I have not seen the guts
of the new XLS5000.



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post #978 of 1917 Old 05-23-2008, 05:32 PM
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Quote:
Originally Posted by Jack Hidley View Post

When you are driving a subwoofer with a 3" or 4" VC that has 10-20mh of inductance, as the VC is moving in and out of the gap, it is creating a huge back EMF that is trying to drive the voltage at the amplifier terminals where it wants to. Some amplifier designs are not going to like this.

Hmm...sorry to take the thread on a detour, but perhaps another reason why low-inductance subwoofers always seem to sound better?

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post #979 of 1917 Old 05-23-2008, 05:34 PM - Thread Starter
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Here are some tests of the new Elemental Designs eQ.2 subwoofer processor.





Continued below.
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post #980 of 1917 Old 05-23-2008, 05:35 PM - Thread Starter
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20 Hz Subsonic Filter


30 Hz Subsonic Filter


50 Hz Parametric EQ


100 Hz Parametric EQ
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post #981 of 1917 Old 05-23-2008, 05:37 PM - Thread Starter
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Commentary:
All in all for $100 this is a pretty good unit. The frequency response is flat +-0.5dB, the filters do what they say they will, S/N ratio is quite good, and the price is right!

If you look at the input voltage versus the output voltage, it appears to be limited in output. The unit never puts out more than 2.5 volts. The worst part of it is that the THD rises exponentially higher when the output voltage gets past 2 volts. I believe this could be solved with some changes in the output circuit and the choice of IC's. Maybe in version II.

Other than the low output voltage and the associated distortion, I would also like to see a balanced XLR output and reduce the height of the unit to a rack standard 1 3/4". Then they could offer accessory rack mount kits for it to satisfy users with 19 inch racks.

Chuck
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post #982 of 1917 Old 05-23-2008, 05:46 PM
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Quote:
Originally Posted by thylantyr View Post

I stopped myself from posting on this issue earlier
as it could open up a new can of worms. Sorry, this
will be PM conversation only

Right, only 9 posts in 4 hours

Noah
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post #983 of 1917 Old 05-23-2008, 06:26 PM
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All right Chuck! Thanks for changing the subject.

Dennis H
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post #984 of 1917 Old 05-23-2008, 09:22 PM
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Quote:
Originally Posted by noah katz View Post

Right, only 9 posts in 4 hours

I only have 1 post on that issue and technically it's 0 posts as I didn't
express my feelings. But I don't think you know what the issue is, you
have to read the whole thread to keep up



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post #985 of 1917 Old 05-23-2008, 09:31 PM
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Chuck,
try REW. It's a very cool measurement tool, and FREE.


Regards,
Dan
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post #986 of 1917 Old 05-24-2008, 04:25 AM
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Quote:


Commentary:
All in all for $100 this is a pretty good unit. The frequency response is flat +-0.5dB, the filters do what they say they will, S/N ratio is quite good, and the price is right!

If you look at the input voltage versus the output voltage, it appears to be limited in output. The unit never puts out more than 2.5 volts. The worst part of it is that the THD rises exponentially higher when the output voltage gets past 2 volts. I believe this could be solved with some changes in the output circuit and the choice of IC's. Maybe in version II.

Other than the low output voltage and the associated distortion, I would also like to see a balanced XLR output and reduce the height of the unit to a rack standard 1 3/4". Then they could offer accessory rack mount kits for it to satisfy users with 19 inch racks.

Awesome, Im happy to own one I agree on the height and the 19 rack needs.. I have no where to put it right now inside my AV rack other then on top of my amp.

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The QSC RMX manual states "The HD designation on the RMX 1850HD designates this model as "heavy duty". The RMX 1850HD is superior to all other RMX models for driving 2 ohm loads for extended periods. The RMX 1850HD is perfectly suited for subwoofer-type applications"
What makes the 1850HD better than the 2450 for sub duty? The 2450 has 33% more output, they both have class AB+ H output circuits, same weight...???
Is the 1850HD just a 2450 with less gain?
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Quote:


The QSC RMX manual states "The HD designation on the RMX 1850HD designates this model as "heavy duty". The RMX 1850HD is superior to all other RMX models for driving 2 ohm loads for extended periods. The RMX 1850HD is perfectly suited for subwoofer-type applications"
What makes the 1850HD better than the 2450 for sub duty? The 2450 has 33% more output, they both have class AB+ H output circuits, same weight...???
Is the 1850HD just a 2450 with less gain?

Bridged my 1850HD and it sucks in driving even two of my 18" subs which should be easy to drive, it also really couldnt drive one of my 15" TC2K ported subs, which was shocking.

Im Not happy at all with its performance. Its heavy, its noisy, its ugly and does even come close too either the eD LT/1300 or the Velodyne SC-1250 when compared side by side. I was very disappointed this weekend, I had the gain on it 100% and I had to turn down my SC-1250 to about 35% to equal out the SPL on both subs. Obviously the one problem is the voltage differences between the pre and the pro amp (-10 dB vs +4 dB) but we dont want to debate that once again.

Chuck is getting one fo my SC-1250s this week so its going to be great seeing the test numbers from these amps. I love them so far, they are the best amps I have owned for subs so far beating my LT/1300, Dayton 1000, QSC1850, EP2500. Im definitely not a pro amp fan at all.

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post #989 of 1917 Old 05-24-2008, 06:16 PM
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A little quick update on my crude testing of the XTi2000 and 4000 with TC Sounds TC3000 and LMS-Ultra(both in sealed 3cu ft cabinets).

Today I really pushed both amps driving these very capable sub drivers to the point clipping lights flashed!

The XTi2000 was driving one TC3000 15(one channel in use,no bridge),it gor seriously loud and the driver's cone was moving some serious air,the clipping lights came only on passages where bass in the 20-30HJz was making the cone move what was like 1.5-2inches of excursion! The amp was on a 30A line,not lack of current here.Keep in mind one channel was driven.

With the XTi4000 the clipping light never lit or flashed,it was very loud...again the driver's cone doing serious pumping. When it was time to let the LMS-Ultra work,I made the clip light flash faintly again when the cone was what looked like ~2-2.5inches of excursion.

For what these amps will be used,I will not even push them half as hard. So they pass my primitive test.

Then for fun I tried the test with my QSC PL380 and Crown iTech6000...HOLLEEE These amps are monsters,both could push the drivers into monster excursion and where the walls came alive with their own excursion! The iTech and PowerLight are the real deal in my view.

For something like a Acoupower,TC2000/REVO and up,SDX15 I woulpd recomed using a QSC PLX2 3000+ series.Not the XTi's

As most here have one or two subs and use them in much larger spaces than my 700 "cabin" .

Ask yourself mortal , do you have as much displacement as me ? The answer is no unless you have a Windmere fan sub.
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post #990 of 1917 Old 05-24-2008, 06:38 PM
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Hmmm... I was reading from the manual that came with my RMX 1450 (for mains). Covered the other models too.
1850HD:
input sensitivity 1.16v(+3.5dBu)
1800w 4ohms bridged mono
Turn off the filters and clip limiters?
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