Headroom is a concept that is applicable to numerous different aspects of pro audio, from PA systems to loudspeakers to guitar and bass amplifiers. Each of these devices are intended to operate within a range- one that does not put stress on components or risk damage by operating too far out of the product’s capabilities. Headroom is the room you have above what you normally need or will need from your gear. Headroom is needed for both signal levels and output levels, but here we will be looking at output level.
To take headroom to its simplest thinking, when you get into a car there is a little room from the top of your head to the ceiling. In the big hair eights metal days, we were lacking headroom in most cars, some of us actually stuck to the ceiling. This space above your head is actual “head” room. Most of the time when you drive on decent roads you should not be touching the ceiling of your car. If you have ever been caught by a large water channel dip in the road, you may have discovered the amount of headroom you were lacking with a bump on your head. To bring this to audio system thinking, the bump on your head is when you have driven the amplifiers or speakers beyond the available headroom. Hitting the ceiling is like clipping your amplifier, if you do it hard enough or over and over, you will get a sore spot or damage something permanently.
To illustrate this principle with controllable parameters, let’s look at a common example of driving the car. Most cars have a maximum limit, usually this is discussed in top RPM of the engine, but here, for simplicity, we will use driving speed in mph. Let’s say your car has a maximum speed of 140 mph. Your car can conceivably operate at this speed for a short burst, but it definitely can’t do it 100% of the time. If you tried, (we are not suggesting that you do this!) the car’s components will fail and/ or the engine will overheat. If you need to be driving at 140 mph consistently, you are probably a racecar driver and need to invest in a car that is designed to operate normally at 140mph.
When it comes to musical instrument amplifiers and pro audio, consider headroom as your safety zone or wiggle room. For the cleanest possible sound and to avoid clipping your amplifier, you ideally need to put together a setup that has plenty of headroom. This way you can be sure that you are operating your equipment within its nominal level, just like how you would drive a car safely around 20-70 mph on any average day.
Of course, many guitar players enjoy using low wattage tube amplifiers and cranking them to their limits to get a thick overdrive. While headroom is still applicable here, the way a tube clips and the application of distortion is less obvious, but you can still hear the dynamic loss when you turn up that amp a little further. Having enough headroom is essential for solid-state equipment like bass amplifiers and power amplifiers. If you have inadequate headroom, you can expect a harsh mid range tone, a lack of dynamics and possibly blown speakers, which can be a real show stopper. If you are put into a louder situation and find yourself turning up, watch for these signs and just back off before damage occurs. Better to realize you need a bigger amp or another cabinet next time, than to have to replace blown gear.
Remember, with pro audio equipment, you can always turn the volume down, but turning it up past its limits can have bad results. It is essential to select a system that has enough headroom for your application. If you are a bassist who needs a minimum of 250 watts to cut through your loud rock and roll band, it’s recommended that you go with a larger amp like the Carvin Audio BX700 over the 250 watt amp like the Carvin Audio BX250. With a 4 ohm load this will give you 3dB or twice the headroom you need for your application. Now headroom is not all about power amp wattage output. What you hear is the SPL (sound pressure level) of your system, and this includes the speaker’s efficiency and how many speakers you have. In the example, you could go with the 250 watt BX250 amp and have twice the speakers you had for a similar 3dB of head room. Just a simple rule of thumb is “double the speakers for double the output.” This of course only works with doubling the same speakers. You may also get more output from an amplifier when you add another speaker, because you are lowering the impedance on the amp. Always be sure your amp can handle the lower impedance before connecting more speakers.
Be sure to consider headroom when selecting your next rig or reevaluating your current one! This will give you extra wiggle room, extra dynamics in your tone, and ensure that you won’t have to push your equipment too hard to give you the proper level of audio output.
For more in depth reading on headroom in a larger PA system, read our article on “How to Provide Audio For Outdoor Events: What Do I Need to Know For a Successful Show?” in our Audio Info and Education blog.