What is Headroom? - Home Theater Forum and Systems - HomeTheaterShack.com

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post #1 of 9 Old 06-04-08, 02:06 PM
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What is Headroom?

This may be a stupid question that I should certainly have a firm grasp on by now - but heh, I've gotta reach my 10 post quota somehow, and I really have been confused here.

What is headroom, in reference with a sub? And rather, why is it important? I think I'm confusing myself the more things I read randomly in places mentioning it, so I thought it might be best to just come out and ask. Is it the difference between what my sub is *capable* of, and what I'm actually running it at? And if so, is the importance to keep the sub from bottoming out? Do things just sound better if there's more headroom (I'm supposing in order to give certain frequencies a chance for higher output if that's what's recorded)?

I've got a PB12/+2 at home, had it for about 2 months now. My room's fairly large (~2800 cubic ft with two small hallways and an opening to a kitchen coming off of it), and I'm running the svs at about half gain in 20hz tuning. It sounds nice to me, but sometimes doesn't pressurize the room quite as much as I'd like. But I read about most people only having this thing on 1/4 gain, so I'm weary of turning it up more. Thanks for any info, whether general or specific!

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post #2 of 9 Old 06-04-08, 02:59 PM
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Re: What is Headroom?

Hello Maxx:

The simple answer is the difference between the noise when no signal is present and the maximum signal before over driving the amp (clipping) or the speakers (bottoming out). I don’t usually hear this associated with speakers alone in any meaningful sense unless it might be applied to the minimum applied signal to be heard and the maximum signal before over drive occurs.

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post #3 of 9 Old 06-04-08, 03:22 PM
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Re: What is Headroom?

I typically hear it in the context of adding another sub to a room for more headroom. But why? When I was ordering my pb12/2 I was originally looking at a PC+ and it seemed a big issue whether it would have enough headroom in my room. I didn't not order the PC+ (but instead the pb12/2) because of that issue, but for other reasons - so I never further investigated it at the time. But now I'm curious. So where does Gain factor in? The higher the gain would mean a lower input signal before overdriving either the amp or speaker, correct? So that would mean... less headroom? (confused still) :\

I appreciate the help though!
post #4 of 9 Old 06-04-08, 03:24 PM
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Re: What is Headroom?

Headroom is simply the ability to play louder, still cleanly...without running out of driver excursion or amp power.
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post #5 of 9 Old 06-04-08, 03:25 PM
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Re: What is Headroom?

Sometimes, the easiest way to find a definition is Wikipedia
See here: Headroom

I see headroom as power reserve: more headroom for your sub will allow it to be able to play louder (but not saturate) when required (in action scenes for instance).

I think that the Wikipedia graphic shows very well what it is: if your sub cannot play louder than say 120dB and you're already playing at 100dB then everything than 20dB louder will be clipped and distorted.

Hope it helps !

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post #6 of 9 Old 06-04-08, 03:51 PM
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Re: What is Headroom?

All of the posts above have very good points, May I add that Headroom is simply the db level you like to listen to at its loudest with no distortion but still having room to go louder if required during peaks in the soundtrack.
THX guidelines state that a system should be able to maintain 95db with peaks of 115db so in theory you should be able to go above 115db without any clipping or distortion in the signal weather it be the amps power output or the speakers output. That would be your so called "headroom"

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post #7 of 9 Old 06-04-08, 04:07 PM
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Re: What is Headroom?

Gain is just how many times the amplifier increases the signal. Usually when talking about amplifiers we talk about voltage gain, if an amplifier has a gain of 10 and I apply 1 volt to its input I would get 10 volts on its output. So more gain just means I need a smaller signal to start with. There is also what is referred to as room gain which is somewhat more complex but amounts to how much louder a speaker is in a closed space like a listing room as than it is outdoors. More room gain means less power needed for the same volume. Room gain is not the same at all frequencies and is affected by speaker placement, room shape and size etc.
So, no, more gain does not mean less headroom it more often than not means more headroom.
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post #8 of 9 Old 06-04-08, 10:12 PM
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Re: What is Headroom?

maxx233 wrote: View Post
... I'm running the svs at about half gain in 20hz tuning. It sounds nice to me, but sometimes doesn't pressurize the room quite as much as I'd like. But I read about most people only having this thing on 1/4 gain, so I'm weary of turning it up more.
Need to post more often, Right???

Half gain ... that's nothing; mine is almost at 100% (let's say 90-95%) ... but, I'm using Velodyne VRP1000 and TSS750 ... I'm for better subs ... SVS, HSU, DIY ...
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post #9 of 9 Old 06-05-08, 10:28 AM
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Re: What is Headroom?

I'm pretty happy with mine so far. I have a pretty decent size room, and it's definitely not optimal acoustically... the svs fills it pretty well. Since I got a new receiver I've had a hard time getting it to sound right, but I think I'm almost there. I'm waiting for my BFD to show up tomorrow (first one was defective) to get it tweaked just right hopefully. The reason I'm wondering about the headroom is because I want to know how much tweaking I can do with this as far as increasing some frequencies (or overall gain). While this thing sounds great, I go into my roommate's room and have some hint of jealousy for element's of his sound (but... he's in a 750 cubic ft room with a bandpass box, so I just keep telling myself it's not comparable.)




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