Measuring Amplifiers - Page 28 - AVS Forum
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post #811 of 1918 Old 05-17-2008, 10:26 AM
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Steve,

Your making your argument based on an assumption not currently in fact. If the crown can produce its rated output power @ 20 hz albeit at a greater than advertised THD then your argument would be one to consider. However, at this point that is merely an assumption. However, the rollof we are seeing with this amp below 50 hz is something we have never seen to this degree and certianly at least suggests something is amuck. While it may indeed perform admirably in "real world" conditions for which the amp was designed for (PA use) the major driving force for the scrutiny of indvidual amps and how they peformed as related to this thread is for home audio sub-woofer duty. And for the time being,and until (and if) further testing on this amp is done, it would appear that better options for less money are available for that specific duty.

And the chinese gave us:

Tainted wheat glutten dogfood
Lead paint on childrens toys
and all of these wonderfull amps
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post #812 of 1918 Old 05-17-2008, 12:17 PM
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Quote:
Originally Posted by clueless View Post

Your making your argument based on an assumption not currently in fact. If the crown can produce its rated output power @ 20 hz albeit at a greater than advertised THD then your argument would be one to consider. However, at this point that is merely an assumption.

Quote:
Originally Posted by chasw View Post

If you read the 20 Hz distortion level at 8 ohms, you will see that it is above 2.X% THD to achieve its power. This is why I took the path of using stated THD figures on the 4 ohm and 2 ohm measurements.

He did distortion limited testing - seeing how much power the amp would produce without exceeding a certain distortion level. Upon second glance, I see that at 2.6% distortion it was still a bit short of claimed specs, but that doesn't mean the amp didn't have more to give, albeit at a higher distortion level.

I tend to agree with the statement from Dayton Audio - again, Chuck's tests are great for an apples to apples comparison of amp A to amp B or trying to verify a manufacturer's claims, but not the greatest testament to real usage.
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post #813 of 1918 Old 05-17-2008, 01:39 PM
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I think someone made a joke to chase and send him a fake amp, not too sure but sound fishy to me

Warning to prevent risk of injuries, you should always be smarter than the equipment you are about to use.
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post #814 of 1918 Old 05-17-2008, 02:03 PM
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Given what I have seen of amplifier performance so far, I have learned that nothing is what it seems until the hardware is analyzed and the unit is tested. The Crappinger EP2500's suddenly look pretty good now don't they? Very low distortion, much higher output, much lower cost, why do people come down on them again?
Hmm, the CE4000's are not rated huge (barely above an EP2500) yet they produce far more output in the real world, you wouldn't get this from the spec sheet, even if you factor in the PFC, they just dish out massive amounts of power, actually over spec, this is very impressive.


Just because and amp has a high price tag doesn't mean the performance or even quality will be there, we shouldn't be surprised when we see stuff like this, if you look at other amp tests done in cyber, you will see similar anomalies. Why do we get so angry when we see amps like the buttkicker, dayton plate amp and XTI perform different from the spec sheet. Ultimately, a spec sheet means very little to nothing in terms of real world output until we see what the amp has inside it and how it performs. There is no other way to insure quality, it doesn't matter WHO makes the amp, there is just no guarantee it will perform as the spec sheet indicates. I have seen low end receivers outperform higher end ones in the same product lineup under the same testing conditions, why? There is just no safe brand or testing standard that will line up with the posted specs every time.
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post #815 of 1918 Old 05-17-2008, 02:08 PM
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There is a difference between the 8 ohm and 4/2 ohm test. Because of the 'clipping' behavior of this amplifier, I was able to run the 8 ohm test at full power and then see where the distortion was. For the 2 & 4 ohm tests, I had to run the amp up to its factory rated distortion and then measure power level. The amp is rated for 0.5% THD at 8 ohms and 4 ohms, and then rated at 1% THD for 2 ohms. When this amplifier clips at 4 or 2 ohms it does not really 'clip' in the classic sense, i.e. square off the waveforms, it goes into oscillation. At 2 ohms the amp would run at 0.1% THD and then jump to 10% THD and produce no more voltage. I did not want to damage the amp so I just ran it up to before oscillation and measured from there at 2 ohms. As a side note, while testing at 2 ohms, it took less than 90 seconds for the amplifiers thermal lights come on but the amp did not shut down nor was the case very warm to the touch. I am going to let the amp cool down and rest before doing 8 & 4 ohm mono tests.

Steve
As I said, your making an assumption, but the way the amp behaved on the bench suggests otherwise.
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post #816 of 1918 Old 05-17-2008, 02:28 PM
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EAR,

While you're doing some low freq sine, how about hooking up the Acoupower and see if it's as mechanically quiet at high excursion as claimed?

Quote:
As a follow-up, I'd like to say I’m concerned by some here that immediately assume this amplifier is “bad”, especially in light of the fact that this is a tracking amplifier that's designed to deliver high voltage into reactive loads (ie, loudspeakers). They are not optimized for fully resistive load banks. So much of this talk in this thread is not relevant to driving woofers. These hi-tech amps can put a ton of power into the actual woofer and cannot be fully tested using standard non-inductive resistant loads. That being said, we'll post additional information as soon as we complete our internal testing.

I don't think I buy this. The heaviest load on an amp is at Fb in a vented box and at the low end for a sealed box, where in both cases the impedance approaches Re and is nearly purely resistive.

Noah
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post #817 of 1918 Old 05-17-2008, 02:38 PM
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I wonder if that was a stock response by Crown.... LOL. I agree that some amps will put out more power into a reactive load than a resistive load, but those designs are usually class D, like the QSC PL380. It's damping factor increases as you go lower in frequency.

"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 #818 of 1918 Old 05-17-2008, 02:50 PM
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Quote:


As a follow-up, I'd like to say I’m concerned by some here that immediately assume this amplifier is “bad”, especially in light of the fact that this is a tracking amplifier that's designed to deliver high voltage into reactive loads (ie, loudspeakers). They are not optimized for fully resistive load banks. So much of this talk in this thread is not relevant to driving woofers. These hi-tech amps can put a ton of power into the actual woofer and cannot be fully tested using standard non-inductive resistant loads. That being said, we'll post additional information as soon as we complete our internal testing.

Yeah, I don't buy that 'explanation' from Dayton either. A resistive load is the easiest load you can give an amp. Performance and stability can only get worse with reactive loads.

Dennis H
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post #819 of 1918 Old 05-17-2008, 03:20 PM
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We're still waiting for "tests" (proof) from Dayton and/or Parts Express which will show how their amps perform up to their advertised specs. My guess is that manufacturers aren't about to be cajoled into making fools of themselves on this performance oriented site. They'd be fools to do that. The way it is now, they can claim or lead us to believe (like Crown has) that their amps perform better than they do . . . . "in real life" under (real usage conditions) just by making those wonderful sounding and carefully worded advertising brochures and spec sheets.
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post #820 of 1918 Old 05-17-2008, 04:12 PM
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Quote:
Originally Posted by noah katz View Post

EAR,

While you're doing some low freq sine, how about hooking up the Acoupower and see if it's as mechanically quiet at high excursion as claimed?

The first thing I noticed when I saw my first video of acoupower drivers in action was "Dang! they don't have ANY mechanical noise!" even when pushed to their excursion limits they sound excellent, much better than any other high excursion driver I have used. I would say that are even better than the dayton reference series subs, and the acoupower's can do over twice the excursion at higher frequencies and still sound phenomenal.
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post #821 of 1918 Old 05-17-2008, 05:21 PM
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I would love to see a Face Audio test. It could be any amp (I have a personal vested interest in seeing a F500TS test as that is what I have) in their lineup. It would be interesting to see how a model from them and a comparable model from Crown and QSC stack up. It would also be interesting to see the insides of a TX model and see what the differences are between them and a TS model. I am thinking larger toroid, more power transistors, more and larger PS caps (perhaps from Panasonic or Nippon), and larger heatsinks.

I am surprised about the XTi. I had it before the Face Audio. I liked it, but the DSP raised the noise floor and hissing came from the tweeters from my RF-7s. I wonder how much better my F500TS is in terms of 2ohm performance due to the 2.8ohm dip with the RF-7s.
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post #822 of 1918 Old 05-17-2008, 06:10 PM
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Penngrey,

Here is what I did.

1) Recalibrated my sound card and loaded that file with REW
2) Ran a test tone through my Denon 3803 with the sub adjustment in the receiver set to 0, receiver volume at -20 and the Crown level set to about 3 o'clock. These gave me a reading of right around 75 db
3) I than ran a calibrate through REW and had to adjust the receiver volume to 10 to get close to 75db.
4) I than ran the generator for a 20HZ sine way and was reading way down in the 80db range (with the receiver at -10 and the Crown at 3 o'clock).
5) I than turned the level control on the Crown fully clockwise. Ran the 20HZ sine way again. Even with turning the receiver volume control on the receiver as far as I could go I only read 92db.


The one thing about this test is I cannot guarantee the Denon is producing a 1.4 volt signal the amp needs to go to full power.
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post #823 of 1918 Old 05-17-2008, 07:56 PM
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Exo, my guess is you came pretty close to what the XTi (1000) will do at 20HZ.

Roadtonowhere08, That's an interesting statement you make about the XTi DSP raising the noise floor. If that's a common trait of that amp then even it's best area of performance is failing.
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post #824 of 1918 Old 05-17-2008, 10:59 PM
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Quote:
Originally Posted by noah katz View Post

EAR,

While you're doing some low freq sine, how about hooking up the Acoupower and see if it's as mechanically quiet at high excursion as claimed?

Noah,

Have you searched for "Acoupower" on Youtube lately?

Yes, they are quiet when the pole vent is not blocked and kick off quite a breeze. I didn't crank it way up without a better means to monitor excursion. The test was a basic functional check, nothing more. Carlos never claimed that the pole vent itself was quiet, in fact he warns that it is noisy. It was designed to pump air through the voice coil as a primary goal. He will be the first to tell you that you do NOT want to point the pole vent directly into a port as sunosubs do. I didn't think they made too much noise for as much as I've pushed them. He offers a "salt shaker" diffuser cap as well as the standard one. I have a picture of it at home. I would also assume you'd never want to reverse mount these drivers. I'll have an Acoupower thread started soon where I'll have a decent collection of data I've been acquiring.

Dr V
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post #825 of 1918 Old 05-18-2008, 12:27 AM
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Quote:
Originally Posted by LINEARX View Post

Exo, my guess is you came pretty close to what the XTi (1000) will do at 20HZ.

Roadtonowhere08, That's an interesting statement you make about the XTi DSP raising the noise floor. If that's a common trait of that amp then even it's best area of performance is failing.

Well, the chip doing the ADC-DAC is pretty good based on what Cirric Logic specs it as. I suspect it (the cause for the hiss) is somewhere in the chain, but it definitely has a constant hiss independent of the volume. If they nailed the execution of the design and intent, I could see this amp being a huge hit with the HT crowd, what with the DSP and balanced passthrough for subs. I really wanted to like the amp, but the hiss was a deal breaker. I would have even forgiven the fact that they DSP cannot ever be truly bypassed.
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post #826 of 1918 Old 05-18-2008, 12:46 PM
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"Have you searched for "Acoupower" on Youtube lately?"

Now I have

In the 10 Hz test what was the chirping noise when you tipped it sideways?

"Carlos never claimed that the pole vent itself was quiet, in fact he warns that it is noisy. "

Can't remember where I saw it, but he did say something to the effect that they're essentially mechanically silent at up to 90% of max excursion.

Noah
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post #827 of 1918 Old 05-18-2008, 01:55 PM
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That chirping noise was odd. Was something rubbing on the floor?
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post #828 of 1918 Old 05-18-2008, 02:33 PM
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I guess that's the sound of air rushing through the pole venting???
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post #829 of 1918 Old 05-18-2008, 07:42 PM
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I'll have to revisit that. Offhand I'd say its pole vent noise, as the sound went away when I sat the driver down, thus blocking the vent. I tested 2 drivers and 2 amps, so I'm not sure if they both did that or not. It seems much louder in the video than I remembered in person. The Ear could also try the same test. I sent Carlos a heads up.

Dr V
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post #830 of 1918 Old 05-18-2008, 08:01 PM
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Wow, talk about fast customer support!

"Yes, that noise is there by design and is the result of turbulence….which is critical for heat dissipation. It will not be audible from the front of the driver. This is why I have mentioned to you and others that it is not a good idea to have the opening of a large port tube near the rear of an Acoupower driver and that you should use fiberglass, fiberfill, or acoustic wedge panels to prevent a direct sound path from the rear of the driver to the opening of the port tube.



Now you know why!



Please don’t be too concerned about this. Just work at what I say above, and the sound of this outside the box will not be audible….especially with any kind of program material. Remember that a vented box is not just a resonator, but also an acoustic low pass filter. Just put lots of fiberglass in the box and prevent a direct path from the rear of the driver to the inside port tube opening, and you will be fine.





Carlos"
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post #831 of 1918 Old 05-18-2008, 08:54 PM
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The air venting from the acoupower is phenomenal. On the acoupower website videos you can see a child holding a plastic bag and filling it up with air even after moving some 6 feet away from the driver.

Still waiting for further driver test results with the XTi, we have the first one in from exojam....hey its already past Sunday over in US of A for you guys!
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post #832 of 1918 Old 05-18-2008, 08:58 PM
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Quote:


hey its already past Sunday over in US of A for you guys!

?? Its only 11 pm here

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post #833 of 1918 Old 05-19-2008, 09:33 AM
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Sorry about the wait...I have been on vacation......My girlfriend got a tic and a nice engagement ring so very eventful for me.

An update and a question for all.
Talked to partsexpress (Eric over there at ext.111). He used a dummy load(read a monster 4 ohm resister) and got 57 volts (frequency unknown). Eric said he had tested the amplifier himself and it made 800+ watts (if memory serves 845watts). He also mentioned a veriac as well as other very similar testing methodologies.

So I really don't know what to say about this one. Bid Chuck says one thing partsexpress says another.

Should I just go for the ep2500 and deal with the fan noise? I am leaning towards full external dsp so the parametric eq is not really that important to me?
I am really confused as to what to do.
4 15" woofers......either will power them fine 580watts or the ep2500.....your (everyone's) thoughts?

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post #834 of 1918 Old 05-19-2008, 09:50 AM
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If you get an EP2500, fan mod it.

YID DIY
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post #835 of 1918 Old 05-19-2008, 09:58 AM
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Did anyone notice that the specs for the Dayton amp on the website have been changed? Now it only states 1000W at 4 ohms mono, no THD spec.

jimstewart, did Eric state the distortion? Before they were claiming 1024 W at .153% distortion in the manual. Eric says 845 W at an unknown level of distortion and the specs on the amps page now state 1000W at an unknown level of distortion.
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post #836 of 1918 Old 05-19-2008, 10:11 AM
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No distortion number given. At least not that I remember. He seemed to think the amp was running perfectly. Perhaps someone else will send Chuck there 1000watt(clears throat) pe amp for testing. But Eric did seem perfectly satisfied that the amp was performing to spec.

Whats 57volts at 4.4ohms equal in watts?

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post #837 of 1918 Old 05-19-2008, 10:25 AM
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Quote:


Perhaps someone else will send Chuck there 1000watt(clears throat) pe amp for testing. But Eric did seem perfectly satisfied that the amp was performing to spec

You PMed me about mine but I actually still use it regardless of posted test results here.

I might send it later to Chuck but I doubt it matters because I believe the test results will be similar.

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post #838 of 1918 Old 05-19-2008, 10:46 AM
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Quote:


An update and a question for all.
Talked to partsexpress (Eric over there at ext.111). He used a dummy load(read a monster 4 ohm resister) and got 57 volts (frequency unknown). Eric said he had tested the amplifier himself and it made 800+ watts (if memory serves 845watts). He also mentioned a veriac as well as other very similar testing methodologies.

So I really don't know what to say about this one. Bid Chuck says one thing partsexpress says another.

If you read the beginning of this thread onward, we discuss
the issues with loads for amplifier testing, to build a good
load to ensure proper results, hence Chucks amplifier load
is a real monster load not some crummy resistor(s) like these from Partsexpress.

http://www.partsexpress.com/webpage....n&WebPage_ID=3

You can still use these if you know what you are doing,
but most novice amplifier testers don't seem to understand
that resistors change their value when heated and when
they record their test results, they still assume the load is
stable, unbeknownst to them it maybe have shifted a few
ohms.

Fun exercise;
Lets say you used a crummy resistor that was really
6 ohms during the test and you read 57 volts. When you
do the math, you use 4 ohms in the formula and get about
812 watts. If the load was really 4 ohms, you won't read
57 volts because there is more loading than a 6 ohm load,
therefore lets say you read 45 volts, that's 506 watts.
You can see how the load plays a big role in getting proper
scores.

There is nothing wrong with Chuck's test



The storm was gone, but dark clouds still hung around
The perfect setting for things to come......

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post #839 of 1918 Old 05-19-2008, 11:13 AM
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I have read every page of this thread multiple times......

I be leave that chuck has done everything possible to get an accurate test method.

I am not an amateur amplifier tester.
Thats y I sent it to a semi pro with a heater element array.

I also have to be leave that Eric understands this issue with heating of a resistive load.
During our conversation he mentioned to me that he had repaired this very style of amp in question multi times. (read if he is soldering components inside of amps he might know a thing or 2 about how they work......)

Not to mention that "resistor" you linked to would light up like a x-mas tree it you dropped 800watts on it......da


I am totally on chucks side on this one. He has showed anyone interested in looking how he has done his tests. What materials and methods he used. I have seen no documentation on how PE did there tests.

That being said I don't think that anyone is trying to pull anything here, I am interested in understanding the differences between how PE and chuck got there numbers, but I doubt that I will get the information i.e. photos and docs on there testing.

Still interested in peoples opinion on pe or behringer.
(can some one pm me the link to the fan mod)

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post #840 of 1918 Old 05-19-2008, 11:33 AM
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Quote:
Originally Posted by jimstewart View Post

Still interested in peoples opinion on pe or behringer.
(can some one pm me the link to the fan mod)

The fan mod is easy. I really should have taken pictures. There is a sticky on it at HTS in the DIY sub section. I did two 12v fans as opposed to one 24v fan though.

YID DIY
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