What's the fuss with headroom?

[Grant Bunter]

I see plenty of use of "headroom" in posts.

Sometimes the reference is regarding gain structure before the amp, other times it's in reference to amps themselves.
I've even used the term myself.

Not understanding it as well as I might, I've been looking into headroom for some time.
From what I gather, headroom, in a nutshell, is having the ability to cope with transients in a system without introducing distortion when a level increases and you approach clipping.

Before the amp, I perfectly understand. Particularly in live music, it's impossible to hit a drum with the same intensity every time, or strum a guitar with the same force on every chord, etc etc.
So a system that can't handle that adequately would be less than desirable.

Where I come undone is when it comes to amps, relative to Bill's designs.
Most particularly in subs, in every set of (pro audio) plans there is a blurb on transient peaks, and setting a voltage with a steep slope/ brick wall limiter specifically to protect against transients and thus protect drivers. That makes perfect sense.

You set up your system to prevent the amp going over a specified voltage (and ideally that setting up involves a structure that has minimal clipping at everything running to max before your amp).

So in setting a limiter to control an amp, have you taken away the headroom the amp may have otherwise had???
If this is the case, why is headroom important with amps???

[Ryan A]

So in setting a limiter to control an amp, have you taken away the headroom the amp may have otherwise had???
If this is the case, why is headroom important with amps???

Not really...if the maximum output voltage of your amplifier is close to the voltage limiter for your speakers, then you haven't taken away much headroom.

The way I see it, headroom is how much overhead your system is capable of during a particular program. If your program is played at say 25 volts average, and the speakers are hard-limited at 50 volts, then you have 25 volts of headroom, or whatever that works out to in db. This means that dynamic transients will be reproduced faithfully up to the 50 volts.

[CoronaOperator]

So in setting a limiter to control an amp, have you taken away the headroom the amp may have otherwise had???

The limiter is definately putting a leash on the amplifier. If your speakers can't handle the extra tansients without destruction then why risk putting them though. If your playing close to the limiter then you need more rig for the gig. That limiter kicking in will protect your speakers but absolutely squashes the sound.

[ripNdeb]

Actually, headroom is a term which is loosely applied to having extra amp than you need. OR something like that.

Technically, head room is better explained here:

http://www.soundonsound.com/sos/apr98/a ... cture.html
http://www.rane.com/note135.html
http://www.prosoundweb.com/article/usin ... rformance/

[Gregory East]

Amp excess capacity gives you an amp with excess cooling capacity, thus your amp can be expected to run cool and live longer than one running flat out.

I think of headroom as the extra dynamic range you have past your average level.

[Radian]

If your program is played at say 25 volts average, and the speakers are hard-limited at 50 volts, then you have 25 volts of headroom, or whatever that works out to in db.

It's simple really. That's obviously 6 dB.

[BrentEvans]

Without quoting a bunch of stuff..

Amp headroom (specifically, clean voltage output beyond the stated voltage limit) for Bill's subs is technically unnecessary, but having a little extra capability helps keep the amp running cool, which never hurts.

The tops are a different story. If you have a 250w driver in the top, that driver can handle peaks of quite a bit more (say, 500w). This is only 3db, but if you set a limiter to 250w, you'll cut out the transients above that, and the hard limit becomes quite audible with tops as you approach it. Having 3-6 db of headroom in your amp for tops is usually pretty safe, as the driver can handle the excursion and thermal load, and the drivers typically won't break up audibly on only transients. This nets you several db of clean dynamic output you wouldn't have if you limited yourself to the RMS voltage from the driver spec. I drive my Beta loaded DR200s with 450 watt amps for the woofers, and the amps can go all the way up to DDT limit (about 60v) with no audible distortion. The drivers run cool and the cabs scream.

[Grant Bunter]

Thanks guys

Keeping the amp cool wasn't something I had considered, and a couple of you pointed that out.

Brent,
Brilliant answer. And now more obvious to me why you bi amp...

[BrentEvans]

Brent,
Brilliant answer. And now more obvious to me why you bi amp...

You're too kind.

I biamp my DRs for a different reason, which is the sensitivity differential in the ribbons I use. However, in general, I find that when you're pushing mid drivers (especially smaller ones) with a sufficient amount of power, a strong surge in the low midrange will affect intelligibility. This happens because a surge of power in the low mids seems to introduce distortion in the highs as well. Biamping solves this, as each section has its own power supply. This is why we biamp subs instead of passive crossovers (in addition to the expense of the crossovers). I find it quite audible in the tops also... and so do many commercial loudspeaker manufacturers. In fact, most powered cabs are biamped, as are nearly all touring cabs. Passive crossovers are generally the domain of entry to mid level cabs.

I'll state that, from what I've observed, the piezo arrays aren't really subject to this phenomenon, probably because they draw so little current.