Your Test for "Dynamic Headroom"

gregz

gregz

Full Audioholic
I've typically measured the maximum dynamic output of my amplifiers (and prospective amplifiers) at 60Hz steady state for 1 second. I use an oscilloscope to measure visible distortion or clipping.

I know that there have been attempts to standardize general guidelines for defining dynamic headroom, but musical peak duration and frequency can vary greatly with the type of music. A Beethoven crescendo can last much longer than the fast, repeated drum hits in a rock song.

What do you use to determine an amplifier's dynamic headroom? (Or do you just buy a big enough amp not to worry about it?)
 
Francious70

Francious70

Senior Audioholic
Buy big enough to not worry about it.

Paul
 
gregz

gregz

Full Audioholic
...I hope y'all realize that your cavalier answers mean more money out of MY pocket...

Ah, I s'pose so. Right now, I'm planning on borrowing several of a friend's DJ amps by several manufacurers. They're impressive on paper, but I have to deal with quieting the fans and possible sonic inferiorities.... But if one of them works, then I'm looking at a WHOLE lot of power for under $400.

Wish me luck!
 
Francious70

Francious70

Senior Audioholic
Look into a Crown. I like the way they sound.

Paul
 
gregz

gregz

Full Audioholic
Paul, now you've got my attention! Which series of Crown amps, the XLS series by chance? The Crown XLS402A can be had for barely over $300. Do you have one of these in your own home setup?

In an earlier search through these forums, I had found an old thread where somebody had brought up the question of using pro amps in home application. But that thread never really went anywhere except for a bunch of people chiming in on why it seemed like a good or bad idea in theory.
 
WmAx

WmAx

Audioholic Samurai
The only issue with many pro amps is fan noise -- or rather finding one that has a variable adjustable speed fan or adding a control for the fan.

-Chris

gregz said:
Paul, now you've got my attention! Which series of Crown amps, the XLS series by chance? The Crown XLS402A can be had for barely over $300. Do you have one of these in your own home setup?

In an earlier search through these forums, I had found an old thread where somebody had brought up the question of using pro amps in home application. But that thread never really went anywhere except for a bunch of people chiming in on why it seemed like a good or bad idea in theory.
 
anamorphic96

anamorphic96

Audioholic General
Gregz,

I have used a couple of QSC (1400,1700,MX1500a) amps in a home set up and was not very pleased. They seem to have a very bright balance. However bass sounded tremendous. Very tight and deep with great authority. It was the mids and highs I could not deal with. Very irritating.

If your going to use one of these to drive those subs your building I would say go for it.

Cheers,
Glenn
 
gregz

gregz

Full Audioholic
Hmmm.... QSC and Crown were the two brands to which I had narrowed my choices down... If all the amps I try sound bad like that, I guess I COULD always go back to bi-amping. That would bring the price down because I'd need less of an amp to drive my strictly 4 ohm subwoofers.

I've been resisting bi-amping to make my eventual upgrade to surround sound easier. If I have a surround sound receiver + two amps for mains, that'll be a big stack-'o-power. I guess there are worse things. The line level crossovers would be a snap.

The brands of pro amps I'll be able to borrow from my friend to try out are: Behringer, Samson, Mackie, Crown, and Yamaha. I'll let you know what comes of it in either the Amps, Pre-pros & Receivers or Write Your Own Review section.
 
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anamorphic96

anamorphic96

Audioholic General
From the looks of your system I think it would rock. We use bi-amping to a great degree in the cinema end of things. I think think bi amping opens things up a great deal. Things get more natural and effortless. The QSC amps are very reliable and work well under stress. They never seem to flinch. Plus that Denon your running sounds pretty stout. What year is it ? Sounds like a perfect match to those NHT's.
Also with a big fat QSC or Crown amp driving those subs. YOU WOULD HAVE SOME SERIOUS DEEP BASS. Especially with those NHT drivers.

I cant wait until I get my Studio 40's bi amped and in a larger room again. Then I can let things fly.

Cheers,
Glenn
 
gregz

gregz

Full Audioholic
Thanks, Glenn. I picked up that Denon in the mid nineties for a song when Denon was discontinuing all its high end stereo products to make way for the new emphasis on HT. They definitely don't make them like that anymore! The beast weighs 24 lbs, and has an 8A fuse, and is rated at 0.015% THD at 100W X2 from 20 to 20. It'll go to 130W/ch steady state before clipping.
 

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anamorphic96

anamorphic96

Audioholic General
Now Thats An Amplifier !!!

Nice Amplifier. :eek:
I see 8 output stages, nice sized heat sinks, beer can sized capacitors an enclosed toroidal transformer. Why cant Denon build like this anymore. That amp has got to sound nice with those NHT's. :) I have a always liked there products. One of the few compnanies that has very neutral speakers.

I hope you end up bi amping. Sounds like the way to go in this case. Those subs will hit hard with a dedicated amp. :p :D :) :eek:

Cheers,
Glenn
 
Francious70

Francious70

Senior Audioholic
260W total before clipping?? That seems a little low. Especially with 120AC 8A goin to it. Hell, with 12DCV 8A some car amps will put out 300W.

Paul
 
annunaki

annunaki

Moderator
Paul,

Remeber efficency. That amplifier is probably only about 30% efficent or so. If it indeed draws near 8 amps to make 130 per channel. However, the 8 amp fuse may be there in the need to drive 4 ohm loads to around 200-220 watts unclipped. That being the case it would have pretty typical efficency around the 50% range for a class A/B. If not, (capable of 200-220 into 4 ohms) I would assume a Class A bias resulting in lowered efficency.


By the way, 8 amps (of current) at 12 volts only allows for 96 watts at 100% efficency. With a realistic efficency of 50% (for class A/B) it is more like 48 watts. 67 watts if it were a typical class D amplifier (usually about 70% efficent).

Sorry to be the "nitpicker". :)
 
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Francious70

Francious70

Senior Audioholic
annunaki said:
Paul,

Remeber efficency. That amplifier is probably only about 30% efficent or so. If it indeed draws near 8 amps to make 130 per channel. However, the 8 amp fuse may be there in the need to drive 4 ohm loads to around 200-220 watts unclipped. That being the case it would have pretty typical efficency around the 50% range for a class A/B. If not, (capable of 200-220 into 4 ohms) I would assume a Class A bias resulting in lowered efficency.


By the way, 8 amps (of current) at 12 volts only allows for 96 watts at 100% efficency. With a realistic efficency of 50% (for class A/B) it is more like 48 watts. 67 watts if it were a typical class D amplifier (usually about 70% efficent).

Sorry to be the "nitpicker". :)
Yea, that was my bad, it was late and I did some mis-calculations. And remember what kind of a load you are driving. A subwoofer wired at 2-ohms, bridged on a class-d amp, will drive near 250-300 watts on a high-end amp (typically 80%+ efficient).

Paul
 
WmAx

WmAx

Audioholic Samurai
Francious70 said:
Hell, with 12DCV 8A some car amps will put out 300W.

Paul
How do you manage 300 watts with 12VDC at 8 amperes current?(V*I=P)

A magical amp? I see, you were just tired. hehehehe :D

-Chris
 
gregz

gregz

Full Audioholic
Hmm... Looking at the UL specs, power consumption is listed at 5.7A. Although I know the amp clips at 130W/ch steady state, it's conservatively rated for only 100W/ch.

My suspicion is that it is A/B, but overbuilt in every way. It originally sold for $850 before it was discontinued, so Denon was pretty proud of it considering it's just a two channel receiver. The extra oomph is probably there to handle dynamic peaks and 4 ohm loads.

Actually, from the looks of things, the Denon can probably handle everything on its own...

...But I have a weakness....

The more capable and effective something is, the more I'm likely to pamper it because of its value to me. In the knife collecting world, it's called "too pretty to use" complex. But why would I beat up an amp that's no longer even made just to save the $299 a subwoofer pro amp would cost me? I should take anamorphic's advice and bi-amp regardless.

I think I need a therapist.
 
annunaki

annunaki

Moderator
The power consumtion is probably stated for normal use. Meaning 130 watts x 2 or both channels driven to clipping (ear splitting levels). That would suggest about 38% efficency or so. I could be wrong however. Maybe the consumption is taken at 10% thd or something, who knows. Either way it doesn't matter. It is a good amplifier, enjoy it. :)
 
toquemon

toquemon

Full Audioholic
Greg, i think Mudcat has everything connected with proamps and he says it sounds pretty good. Ask him.
 
R

Richard Black

Audioholic Intern
Just for the record, you can measure dynamic headroom most easily on a storage oscilloscope, preferably an analogue one (no, really!). This enables you to look at the envelope of the waveform as the amp is slightly overloaded. You'll see a brief (few ms) portion where the envelope is bigger than in the later part, and a few rough calculations will give you the dynamic headroom. But it's not a very useful statistic because by my reckoning it almost never holds up for long enough to help you much. Go by steady-state power ratings. Buy a big NAD or something - they put out quite a lot of nice clean power.

Richard
 

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