Headroom is one of those terms you hear a lot in the amp world.
For our purposes, it has nothing to do with how high the stage is in relation to how low the ceiling is (although that is occasionally cause for concern). We’re talking about the concept of headroom in the context of available amplifier power. You hear the term all the time—guitarists are always talking about how this amp has tons of clean headroom, or about how that other amp distorts in such-and-such a way because it doesn’t have much headroom.
So what is headroom?
While it would be very easy to delve into a sea of scientific jargon and technical terminology from the complex worlds of acoustics and physics and electricity, headroom is more simply a term used to denote and describe how much power your amp can provide before the sound starts to break up and distort.
A car analogy illustrates the concept nicely. If you have a car that can go up to 100 miles per hour and you always drive the car at 100 miles per hour, you’re constantly pushing that vehicle to the upper limit of its abilities and specifications. You can’t make it do any more than it’s already doing; there is no spare “headroom” to go faster or to get more power out of it.
But if you usually drive the car no faster than, say, 65 miles per hour, you’re not constantly pushing the vehicle to its performance extremes. You’ve got some more speed in reserve there and extra room to go faster. In other words, you’ve got some headroom—another 35 mph, to be exact, if you need it. Headroom is like power to spare.
Similarly, how hard you drive your amp vs. how hard it can be driven factor into its headroom. In the guitar world, headroom usually refers to how hard you can push an amp before it starts to distort. Some tube guitar amps are designed to be very loud and clean (the venerable Fender Twin Reverb® being a great example). Such amps are said to provide plenty of “clean headroom”—you can turn them up halfway or so, where the amp isn’t working too hard, and produce a good clean sound that’s strong enough to hang with a loud drummer.
In another example, if your gig would just barely be covered by, say, a 50-watt guitar amp driven hard, a 100-watt amp would give you plenty of headroom to turn up as loud as necessary without introducing unwanted amp distortion and without pushing the amp as hard. You’d have more than enough power at your disposal to compete with the drummer and the PA system and you wouldn’t be pushing your amp to the peak of its limits.
On the other hand, plenty of amps are designed specifically so that their sound will start to break up and distort in a specific way at a specific point before you even crank them past four or five (the equally venerable Fender Bassman® being a great example here). These amps, tube and solid-state alike, are designed to offer less headroom because the kind of distortion they provide is perceived by the human ear as a good thing—say, the deliciously raunchy tone of authentic Texas blues (think Stevie Ray Vaughan) or the electrifying excitement of buzzsaw garage rock (think early Kinks).
Therein lies the rub: Rock, pop and blues guitarists are just about the only musicians who don’t necessarily want a great deal of headroom built into their amps, because they crave the kind of distortion that results from “pushing” their amps. It’s good distortion (there’s bad distortion too, but that’s a whole other Tech Talk column).
The same is not true of most other musicians. If you’re a jazz guitarist, bass player, keyboard player, drummer or singer, you want amplification with plenty of headroom, because you want to be as loud as the occasion requires and still have a clean sound with little or no distortion. Also, you may require an amp with significant headroom if you’re a loud guitarist who wants distortion but prefers it to come from a source other than the amp (i.e., from effects units and stomp boxes instead).