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what is headroom???


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#1 of 23 OFFLINE   PeterK

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Posted July 20 2005 - 09:53 AM

sorry for the dumb question, but I don't know what it means/is or the consequences of having not enough/too much of it. It somehow affects the speakers I gather, but thats about all I know
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#2 of 23 OFFLINE   Victor Ferguson

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Posted July 20 2005 - 11:44 AM

Per google search results: The amount of additional signal above the nominal input level that can be sent into or out of an electronic device before clipping distortion occurs.

#3 of 23 OFFLINE   Kenneth Harden

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Posted July 20 2005 - 12:33 PM

Think of it as an extra reserve of power you have on hand. Less distortion, amp works easier, loud sounds are not compressed, etc.

#4 of 23 OFFLINE   Kevin C Brown

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Posted July 20 2005 - 01:22 PM

This number used to be a lot more "published" in the 80's, but not so much now.

My rule of thumb was always: 2 dB or better: pretty good headroom. Less than 1 dB: not so good at all.

And here's the real world example. If you want to increase you listening level by 3 dB, you have to double the power of the amp you have. So now you can see the importance of headroom. A less powerful amp with more headroom can actually do better with transients than a more powerful amp with less headroom.
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#5 of 23 OFFLINE   Edward J M

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Posted July 21 2005 - 12:52 AM

You can also view headroom as the reserve of SPL available from a speaker or subwoofer before it is driven into audible distortion or compression.

For example, if your current playback levels are peaking at 105 dB, and your system is capable of playing at 110 dB before distorting or exhibiting compression, you have 5 dB of headroom available at your current playback level.
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#6 of 23 OFFLINE   FeisalK

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Posted July 21 2005 - 02:21 AM

Max
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#7 of 23 OFFLINE   Kevin C Brown

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Posted July 21 2005 - 12:51 PM

EJM- Good point. I had always thought of it in reference to amplifiers, but you can also look at it in reference to speakers or a sub.
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#8 of 23 OFFLINE   PeterK

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Posted July 24 2005 - 12:44 PM

ok, so it's the number of dB you your reciever can max put out less the dB your reciever is putting out when normally listening, or the amount your speakers can handle compared to what you listen at. And, having headroom of only 1 or 2 dB means you run the risk of damaging the receiver and/or speakers and/or distorting the sound coming out of the speakers.
thanks

P.S. Fiesal thanks for your helpful insight! Posted Image
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#9 of 23 OFFLINE   FeisalK

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Posted July 25 2005 - 03:09 AM

Peter, LOL there was an image but it wont show Posted Image
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#10 of 23 OFFLINE   Kenneth Harden

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Posted July 25 2005 - 05:27 AM

Have you ever heard about the joke where the car salesman tells you the tilting steering wheel in a new car gives you more headroom?

Posted Image

#11 of 23 OFFLINE   james_pierce

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Posted July 25 2005 - 07:34 AM

Ken had it nailed with his first post. More headroom will differentiate the quieter passages and louder passages better. Also complex passages will be better rendered. But this is usually in regards to how well the amp can control the speakers assuming the speakers are up to the task! The rsult will be a much cleaner sound. I have a NAD AV pushing somewhat difficult speakers and would happily welcome more headroom for my Dyn's.
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#12 of 23 OFFLINE   Kenneth Harden

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Posted July 25 2005 - 09:03 AM

Thanks James!

Litening to a Denon 1705 and 3805, even on really cheap speakers, you can hear how effortless the 3805 sounds, where the 1705 is a bit 'closed in', it goes above sound quality, just the fact there is SOO much more current on the bigger Denon.

#13 of 23 OFFLINE   ChrisWiggles

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Posted July 25 2005 - 09:30 AM

Quote:
A less powerful amp with more headroom can actually do better with transients than a more powerful amp with less headroom.

What are you talking about? "Headroom" is not an attribute of the design that is distinct from the power. Your statement is nonsensical.

Headroom is just the "extra capability" more than you need, which can be useful. If you own a porsche, and you're driving 30mph next to a ford festiva, you have a lot more headroom than the festiva, if you need it. Besides buying a more powerful amp, or more efficient and better-powerhandling speakers, a great way to get more headroom is just to turn down the volume... Posted Image

Just as you don't want to be pushing the capability of your car all the time, you don't want to push the capability of your stereo. By having more-capable components with more 'headroom' then everything is sort of working easier and stressing components (like drivers, power supplies, etc) less and sounding a bit better. Obviously if you are at the extreme edge of your systems capability and clipping etc, then you're really actively *worsening* the sound, rather than just it being not quite as good as if you had a little bit more potent amp, etc.

#14 of 23 OFFLINE   Greg Bright

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Posted July 25 2005 - 10:00 AM

I discovered headroom when I was given a 350wpc power amp to plug in between my 100wpc receiver and my main speakers. The difference in sound quality is difficult to describe. Cleaner, more open, less congested. One doesn't notice these things until real power is there. Funny thing, playing at levels that I did before POWER I can still light up those LEDs on the power amp almost to the top. That tells me that most people who listen loud hear distortion of some sort, like it or not. Now I don't think doubling power is worth a hoot. Triple or quadruple is the way to go.
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#15 of 23 OFFLINE   Kevin C Brown

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Posted July 25 2005 - 12:42 PM

Quote:
Your statement is nonsensical.
Wow. What did I ever do to you?


Every power amp review that I used to read long time ago in Stereo Review and Audio magazine (and even High Fidelity way back when) tested for power output and headroom. Separately.

There *is* a difference between how power amps react to a constant signal demand vs transients.

I will try to dig up a recent example of this, just so you can apologize.
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#16 of 23 OFFLINE   Kevin C Brown

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Posted July 25 2005 - 12:58 PM

Just for Chris:

http://www.octasound....d_solution.pdf

Read the section on Power Amplifier Headroom.

And here:

http://www.crownaudi....much_power.htm

http://www.audiovide....ctionaryid=246

http://www.audiovide....ctionaryid=450

And here is a very crisp technical explanation:

http://www.alleged.com/info/dsl3/

"The headroom voltage is the difference between the supply voltage rail and the maximum output voltage swing, both positive and negative, for a given load current."

And that "difference", re: V, I (and R) => W, which then can be translated into dB.

And here's a really good one:

http://forum.ecousti....79/109459.html

"The problem with many amplifiers and A/V receivers designed for economy (the most watts for the dollar) is that they make the transformer just big enough to produce the voltage output they need [to meet sustained power output measurements into an 8-ohm load], and just big enough capacitors to supply the sustained, continuous voltage and current they need for continuous power, and then the amplifiers quit, so those amplifiers have no real headroom. "

I'm sure you can find other examples.

So ... the dynamic headroom of an amplifier is an intrinsic part of the design, separate from its rated output.

One simple example:

Amp A: 200W per channel into 8ohms, with 0.387 dB of headroom.

Amp B: 175W per channel into 8ohms, with 2.231 dB of headroom.

Amp B *will* have an easier time with transients than Amp A.
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#17 of 23 OFFLINE   ChrisWiggles

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Posted July 26 2005 - 03:49 AM

sorry, didn't mean to sound grumpy, but it didn't make any sense at all, but i see what you meant now, between constant power and peak power. But this isn't really synonomous to "headroom." you are right though, just it was confusing.

#18 of 23 OFFLINE   ChrisWiggles

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Posted July 26 2005 - 03:55 AM

anyway, let me take a little longer than 5 seconds to explain my point:

the headroom of the system is one that you should design in, essentially. You don't want to have just barely enough power for your task, continuous. You'll be driving things hard, and if ever you wanted just a little more volume, you wouldn't have that capability. If you are in this situation, you really do want to have that extra transient headroom briefly, but you also would want to increase the capability continuous as well. So headroom should really be continuous power as well, rather than just transient 'extra space.' IMO, if you have a system where you're at the edge so far that you're actually into that transient headroom beyond the continuous capability of the amp, you really don't have much headroom in the system left and you're pushing things too hard for comfort.

#19 of 23 OFFLINE   PeterK

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Posted July 26 2005 - 10:07 AM

so how do you know when the headroom limit is reached?
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#20 of 23 OFFLINE   ChrisWiggles

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Posted July 26 2005 - 10:10 AM

when you have no more headroom left Posted Image

i.e. when you are clipping, or otherwise trying to exceed the capabilities of your system.





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