Will someone explain headroom to me?

[BassGen]

That's all perfectly logical and what I'd assumed, but in threads stemming from the FAQ Sticky, having more power in your amp than your cab is rated for is talked about as desirable for some reason beyond the cab of course being cheaper that way. And those posters relate this to headroom. I would quote one, but I'm really supposed to be doing something else right now

From my discussions with guys in the business you don't absolutely want more power in your head than the speakers can handle, you want balance. Too much speaker handling power will strain an amp and too much amp power can blow the cones out of the speakers.

i.e. You don't want a 200W RMS head trying to drive a cab rated for 1000W. You'll burn out the amp circuitry because you'll need to run the amp at high power all the time.

Likewise you don't want an 800W amp driving a 100W speaker cab. It probably won't end well because you'll turn it to 2 or 3 and the speaker cones will land across the room.

 

[Richard Lindsey]

That's all perfectly logical and what I'd assumed, but in threads stemming from the FAQ Sticky, having more power in your amp than your cab is rated for is talked about as desirable for some reason beyond the cab of course being cheaper that way. And those posters relate this to headroom. I would quote one, but I'm really supposed to be doing something else right now

That's because those particular posters you mention are mistaken. That's not what headroom is. The amp:cab ratio has no specific connection with headroom. The explanations above about headroom are correct.

To the extent that you have headroom with the amp > cab scenario, it's because the amp may put out more power than what you need to get the volume and tone you want, NOT because it is able to put out more power than the cab can handle.

 

[billfitzmaurice]

Headroom is simply how much louder your rig can go compared to how loud you usually play. For most players it's a negative figure.

 

[Son of Bovril]

Take this example for instance. I used to play with a rig that would only just supply enough volume for my gigging requirements. It served me well and did it's job. What I found to be happening though was that subconsciously because I was always only just able to hear myself I would play harder on the strings to get a little more volume from the rig.

Once I moved to a bigger rig I realized that I could actually play softer on the strings and get better tone from my fingers because I had more useable volume available from my rig, which IMO improved my dynamics and the sound of the band as a whole.

So in this situation the extra headroom allowed me to focus more on my playing from a tonal point of view rather than being distracted by the fact that I couldn't hear myself properly. I bet many bassists have a similar dilema and don't realize it

 

[jazzgeek79]

In my opinion when looking at all of these issues the idea of headroom applies to both the amp and the cab separately and together. The amp has an upper limit to how much power it can put out, and the speaker has a limit to how much power it can receive and convert into sound. So imagine that you are playing a blues bass line and mostly playing in the middle of the basses range (from around an open D to the D an octave above it). Now imagine in this scenario that your amp is pushing as much power as its capable of sending but not as much as your speaker cabinet is capable of receiving. Now you get to the turn around at the end of the changes and suddenly you drop to the low open a string and dig in. The lower note (which requires more energy to produce) and the harder attack are going to push the preamp section of your amp and cause the power section to try and push more power than the circuitry of your amp is capable of producing. This will cause a loss of low end and change the tone of your bass and not usually in a good way. This is why you may want an amp capable of producing more power then your cab can handle. You now have the "headroom" to play that blues. You may also want it because speakers sound and behave differently when they are moving. A speaker designed to handle 100 watts rms will be moving forward and backwards with 100 watts being sent to it. If only 50 are sent (everything else being equal) It won't exert itself nearly as much and may (or may not) sound as "good".

At the other side of the signal, Your speaker can only handle so much power. If you have an amp that is turned up to load for the cab and you imagine the same scenario of the blues and the turn around, then when you over exert your cab it will distort, possibly overheat the voice coil, and/or tear the cone of the speaker. All of which is bad.

The other aspect of this that some have metioned is that if you want your sound to be real clean then you only want your equipment working so hard. The less load you are putting on your amp especially the less distortion in your sound. On the other side of tone many bassists and guitarists like the sound of tubes distorting! Both preamp tubes and power tubes. Each can achieve a different kind of distortion. But cab distortion is NEVER desirable and will lead to speaker failure eventually.

By the way there is also the headroom of your preamp to consider. The more clean signal the preamp sends the power amp the easier it is for the power amp to be loud.

I realize some of these terms like "easy" are somewhat imprecise but I am trying to explain this in an as easy to understand way as possible.

 

[Richard Lindsey]

In my opinion when looking at all of these issues the idea of headroom applies to both the amp and the cab separately and together. The amp has an upper limit to how much power it can put out, and the speaker has a limit to how much power it can receive and convert into sound. So imagine that you are playing a blues bass line and mostly playing in the middle of the basses range (from around an open D to the D an octave above it). Now imagine in this scenario that your amp is pushing as much power as its capable of sending but not as much as your speaker cabinet is capable of receiving. Now you get to the turn around at the end of the changes and suddenly you drop to the low open a string and dig in. The lower note (which requires more energy to produce) and the harder attack are going to push the preamp section of your amp and cause the power section to try and push more power than the circuitry of your amp is capable of producing. This will cause a loss of low end and change the tone of your bass and not usually in a good way. This is why you may want an amp capable of producing more power then your cab can handle.

Again, this has nothing at all to do with the amp being able to put out more power than the cab can handle. It has to do with having more amp power available than you actually need to use, which is not determined by your cab's power handling (though it may be affected by its sensitivity, which is something else).

The situation would be exactly the same, in terms of running out of power, if you were using a higher rated cab with equivalent sensitivity and frequency response. If you run out of power in your amp, you lack headroom; if you have power in reserve, you have headroom.

 

[Muttleybass]

THIS^^^

It's really simple. Also applies to PA, with regards to both power and feedback. "How much headroom in my monitor before it starts to feedback?"

Simply, the amount of volume you have available to you that you don't neccessarily need.

 

[NoiseNinja]

What is maxing out the amp then?

 

[Son of Bovril]

Maxing out an amp is the point at where it is clipping (creating distortion) - tube amps have a sort of soft cap for where they max out, allowing you to get usable overdrive/distortion after the point where they begin clipping. for a solid state amp it is usually a hard limit of where they go from clean to where they are clipping, creating unusable distortion.

 

[JHAz]

From my discussions with guys in the business you don't absolutely want more power in your head than the speakers can handle, you want balance. Too much speaker handling power will strain an amp and too much amp power can blow the cones out of the speakers.

Likewise you don't want an 800W amp driving a 100W speaker cab. It probably won't end well because you'll turn it to 2 or 3 and the speaker cones will land across the room.

AFAIK this is incorrect. We all play our speakers at less power than they are rated to handle essentially all the time. The rating is how much the speaker can take before it burns up/melts (ie thermal) not how much it can take before it starts to sound like crap. Most of the knowledgeable seeming folks around here suggest 50% of rated power as the typical fart-out onset power.

The speakers do not sit there and demand power, in the sense that a 200 watt speaker "wants" 200 watts. You cannot feed a speaker more power without it getting louder. Essentially, what controls how much power the speaker gets is your volume control(s). If you play your gig rig in your house, you're probably not using 10 watts ever (well, except during those "testing" periods where you're seeing what the rig's got). The speakers will require however much power it takes to respond to the output voltage of the amp. Lower speaker impedance calls for more amperes (at the same voltage) and thus takes more power. Ohm's law.

The power rating of the speakers has zero to do with how much power an amp will put into them. That is controlled by the amp, and influenced (in the sense that it is mathematically controlled) by the speaker's impedance.

Where speakers can wreck amps is if you connect too low a total impedance to a transistor amp, or too high a total impedance to a tube amp. But that's only about impedance, not power rating.

 

[BassGen]

I may have "dumbed" that right down without going into heavy detail but I don't think we're really saying anything dramatically different.

 

[gnjpowell]

Technically speaking, headroom is how much additional power (or voltage) you have available Vs how much you are using at any instant in time. So, headroom is dynamic and will vary. If you are at maximum power capability or clipping you have zero headroom, not good at all. If you are at 50% power you have 50% headroom, nice. You should shoot to have 3 - 6 db headroom for nice, clean sound and capability to handle large transients.

 

[Richard Lindsey]

I may have "dumbed" that right down without going into heavy detail but I don't think we're really saying anything dramatically different.

I imagine he was objecting mainly to the apparent suggestion that running, say, a 200 W amp into a 1000 W cab somehow automatically imposes a strain on the amp. It doesn't.

 

[BassGen]

Also applies to PA, with regards to both power and feedback. "How much headroom in my monitor before it starts to feedback?"

Volume is not the actual cause of feedback. Feedback is a resonant frequency that the Mic pics up and since the mic is sending that signal to the PA the PA turns around and pumps it out the speaker which the mic pics up even more and so on and so on.

Sound crews don't turn volume down on feedback, they figure out which frequency is causing it and eliminate that frequency from the mix.

Rush carries something like a 140,000 watt PA on tour. I know that's not going to the monitors but if you are playing in an arena there's a heck of a lot of volume and no feedback.

Yes if you all wore earphone monitors instead there would not be any feedback because the resonant sound from the earphones can't get to the mic. But the PA could still cause feedback if the right frequency is present.

 

[gnjpowell]

Feedback is both volume (gain really) and frequency related. Too much gain at various frequencies for the overall system will result in feedback at various resonant frequencies. Monitors and FOH can both feedback but the usual problem is with monitors. You can reduce the overall gain buy reducing the "volume" or you can reduce the gain at specific frequencies that are problematic given the existing venue and system via the judicious use of EQ - what good sound engineers do. There is some "art" involved in doing this well and with EQ in general.

 

[BassGen]

I imagine he was objecting mainly to the apparent suggestion that running, say, a 200 W amp into a 1000 W cab somehow automatically imposes a strain on the amp. It doesn't.

As explained to me by someone at the Long & McQuade Music Store here (They make Yorkville and Traynor) if you run a low power head into a cab too large you will need to run the amp at too high a power for too long and either cause strain on the amp or damage the speakers because the amp is constantly sending a clipped signal to them.

Balance.

 

[Richard Lindsey]

As explained to me by someone at the Long & McQuade Music Store here (They make Yorkville and Traynor) if you run a low power head into a cab too large you will need to run the amp at too high a power for too long and either cause strain on the amp or damage the speakers because the amp is constantly sending a clipped signal to them.

Balance.

This is obviously wrong. A cab that's "too large" doesn't force you to turn up your amp. I think you're confusing power handling with sensitivity, and even then the claim wouldn't be true, because whether you have to turn up your amp too high or not really depends on your playing situation (ie, your volume needs in context).

You could use a 200 W amp into a 1000 W cab for decades without harm, if in your own context that rig gave you more than enough for what you were trying to do. For instance, if you were backing up a cabaret singer at a coffeehouse (don't laugh, those gigs are real).

Look at it this way: Suppose you have an 8 ohm cab of sensitivity X and frequency response Y-Z, rated at 1000 W. What safety do you think you would gain by substituting a theoretically equivalent 8 ohm speaker, also of sensitivity X and frequency response Y-Z, but rated at only 500 W? Would you be louder? No. Would you be safer? Also no.

Here's another thing to think about. I usually use an Acme Low B-2 2-10, which has a relatively low sensitivity. That's not a problem, because I don't play loud. Now, I used to have a B-4, the 4-10 version, which has twice the speakers and twice the power handling (700 W versus 350, IIRC). By your theory, using the bigger speaker ought to have strained the amp more. But in fact, because the bigger speaker was also more sensitive, it was louder for the same amp setting. This meant that I could set the gain lower to get my desired volume, which in turn meant that with the bigger speaker there was actually LESS strain on the amp, not more. IOW, the opposite of what you were told.

 

[BassGen]

This is obviously wrong. A cab that's "too large" doesn't force you to turn up your amp. I think you're confusing power handling with sensitivity, and even then the claim wouldn't be true, because whether you have to turn up your amp too high or not depends on your playing situation, not on the rated power handling of the cab.

Overhead. Playing a 200W Amp might work good in a practice room but if you get into a venue where you need more power, despite having a 1000W cab attached if you crank the amp up (and the temptation will be there to do so if you can't hear yourself - nobody said anything about being forced to do so) and it's sending a clipped signal to the cabinet you risk damage to the speakers in the cab. Not because you are over-driving them with power but because the clipped signal is difficult for the speaker to handle.

To have overhead you need a sufficiently powerful amp and speakers with sufficient power handling capability. If you put strain on either of the components the sound will suffer.

Never mind the point of "why would you buy a 1000W cab if all you have is a 200W head.

 

[Richard Lindsey]

Overhead. Playing a 200W Amp might work good in a practice room but if you get into a venue where you need more power, despite having a 1000W cab attached if you crank the amp up (and the temptation will be there to do so if you can't hear yourself - nobody said anything about being forced to do so) and it's sending a clipped signal to the cabinet you risk damage to the speakers in the cab. Not because you are over-driving them with power but because the clipped signal is difficult for the speaker to handle.

To have overhead you need a sufficiently powerful amp and speakers with sufficient power handling capability. If you put strain on either of the components the sound will suffer.

Never mind the point of "why would you buy a 1000W cab if all you have is a 200W head.

You're mistaken about the clipped signal, as has been explained here countless times.

As for your scenario, how would the situation you described be any safer if you substituted a LOWER-powered speaker of the the same sensitivity and frequency response? Answer: it wouldn't. Your volume needs would be exactly the same, and you would have to push the amp just as hard. If anything, you'd be LESS safe, because of the reduced power handling.

Of course you don't want to strain your amp, but whether you strain it has NOTHING directly to do with the cab's power handling. That's where you're getting confused.

 

[BassGen]

I'm here to learn Richard. If I knew it all I wouldn't bother. Agreed that a smaller cab would not make a difference in that example. But the discussion was about overhead (as you described well in your reply to jazzgeek at 10:21). We got off track a bit. At the top of this page Thyaciline Dream related having more amp power than speaker handling = headroom which you also responded to. We were both trying to tell him that was incorrect. I added some "Reader's Digest" versions of what I've been told.

It was a long time ago I had that discussion with the Bass guy at L&M. If I think hard and recall correctly his reference was that some people think that if you buy a cab which significantly exceeds your amps power that you won't be able to blow a driver. That, he assured me, was not the case. I'm pretty sure he also suggested that if someone did have that kind of a mismatch they would be more inclined to run the amp at full power too often and potentially damage the amps circuitry. Whether that be from excess heat or something else I do not remember. Their recommendation was to have some balance in your rig and may well have even said that a bit more amp power than the cabs are rated is OK and probably a good thing because you should never run wide open anyway.