Will someone explain headroom to me?

[Korladis]

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.

I send a clipped signal to my speakers pretty much all the time. Every rehearsal, every gig. They're fine. Woofers don't care if the waveform is clipped or not. Otherwise lots of guitarists would be blowing a speaker every time they played.

Clipping does increase the amount of high frequency content going to a cab, and so it can damage tweeters by overpowering them, as the ones in bass cabs aren't intended to take very much power.

Thankfully, there are no tweeters in my bass rig.

 

[BassGen]

Well we did pretty much cover that. Any distortion is clipping the normal natural sine wave whether it by by design of a stomp box, overdriven signal at the amp stage or a signal that is too strong for the speaker to handle. It's the sharp edges that causes the distortion anyway. Speakers like nice smooth waves. It would take a significantly clipped signal to cause damage or a very clipped signal for a period of time.

 

[Korladis]

The only way you can damage speakers is by causing over-excursion, or by melting the voice coil.

For woofers, a clipped signal won't do either of these unless it has enough power to damage the voice coil, or enough power or low end to cause the speakers to exceed the mechanical limits of the cones. The fact that it's clipped makes no difference, as a clean signal of the same strength would also damage the speaker.

 

[billfitzmaurice]

Speakers like nice smooth waves. It would take a significantly clipped signal to cause damage or a very clipped signal for a period of time.

Speakers can't tell the difference and no amount of clipping bothers a woofer. You're perpetrating the myth of under-powering. Please stop. It's confusing enough for newbies when they're only given facts, not to mention fantasies.

 

[jazzgeek79]

I should have specified in my post that I am assuming that most of us by as much Cab as we need for the gig. Which is why it is often good to have a power amp capable of handling more power than what the speaker is rated for. Not to be able to send the cab more power then it can take but to send a clean signal that isn't pushing the amp to its limit.

 

[Korladis]

I use an amp that doesn't put out as much wattage as the cab is probably rated for. All the time.

My signal is rarely clean. So far, no damaged anything.

 

[Thylacine Dream]

I should have specified in my post that I am assuming that most of us by as much Cab as we need for the gig. Which is why it is often good to have a power amp capable of handling more power than what the speaker is rated for. Not to be able to send the cab more power then it can take but to send a clean signal that isn't pushing the amp to its limit.

But isn't the amp putting out the same amount of watts regardless, and wouldn't that mean the size of the cab wouldn't matter so long as it's not being overpowered?

 

[GrowlerBox]

But isn't the amp putting out the same amount of watts regardless

Capable of the same power output, yes, but that's why we have volume knobs.

and wouldn't that mean the size of the cab wouldn't matter so long as it's not being overpowered?

Exactly. There's a lot of overthinking of stuff that doesn't matter, and not enough attention being given to what actually makes a difference.

 

[billfitzmaurice]

But isn't the amp putting out the same amount of watts regardless, and wouldn't that mean the size of the cab wouldn't matter so long as it's not being overpowered?

Pushed to clipping any amp will put out more than its rated power, sometimes considerably more, so you can't assume that a 100 watt amp can't toast a 200 watt cab, as a for instance. If you want to be sure that you can run pristine clean to the cab's displacement limit have the amp power rating equal to or higher than the cab. If you prefer to be able to get more crunch from the amp size it at half the cab's capacity or less. If you size the amp from half the cab rating to equal the cab rating you'll get a mix of both amp and speaker sourced crunch. If all this is too much to worry about size the amp anywhere between half and twice the cab rating and just play already.

 

[BassGen]

Capable of the same power output, yes, but that's why we have volume knobs.

Exactly. There's a lot of overthinking of stuff that doesn't matter, and not enough attention being given to what actually makes a difference.

Thank-you!

 

[BassGen]

Pushed to clipping any amp will put out more than its rated power, sometimes considerably more, so you can't assume that a 100 watt amp can't toast a 200 watt cab

That is what I've been trying to say.

 

[BassGen]

For woofers, a clipped signal won't do either of these unless it has enough power to damage the voice coil, or enough power or low end to cause the speakers to exceed the mechanical limits of the cones. The fact that it's clipped makes no difference, as a clean signal of the same strength would also damage the speaker.

Also what I've been trying to say.

 

[1958Bassman]

I've tried looking through the FAQ, but nowhere seems to really start at the beginning, and you must admit it's a counterintuitive idea (what I know of it) to a newbie. Thanks!

The power supply determines the max power output, along with the output devices and how it's biased (set up to maintain undistorted power). The power supply can only provide so much voltage and current- once it reaches its limit, the waveform of the signal clips off and that's the limit of anything that resembles the input signal, assuming it hasn't been altered by a pedal that adds gain.

The speaker load has a lot to do with how much power the amp develops- if the speaker impedance drops, the current increases. If the power supply isn't very robust, the supply voltage will sag unless the amp has been designed to minimize this. A tube rectifier vs solid state rectifier with a lot of capacitance in the supply. As the supply voltage drops, the headroom decreases. If the amp is run too hard for too long, components will fail because high current conduction produces more heat and heat is what kills just about everything.

If you want a good example, put a trampoline in a room with a 15' ceiling and jump on it slightly. Your head won't hit the ceiling at first but it will if you jump harder. The difference between the average head height and the ceiling is your headroom, literally and figuratively.

 

[Korladis]

Yes, but you seemed to be saying that a clipped signal was more dangerous to woofers than a clean signal of the same power.

 

[BassGen]

I can admit when I'm wrong. I may have been confused myself a little but in the context of an amp pushed to clipping as Bill described in detail. The clipping may not be the direct cause but in that case at least is an indirect cause that delivers too much power and possibly damages the speaker.

New guys appreciate getting info from guys who know their stuff but sometimes the answers provided are not "dumbed down" enough for the beginner to understand. You don't need to understand how an internal combustion engine works to drive a car but it can help you understand the operation of the car better.

Likewise you don't need to know every detail of how amps work and the electrical theory to play bass and make good sound. Back to the OP I was really just trying to steer him down an easy path. Sorry if that perpetuated some myths.

 

[Korladis]

Right, that is true, newer guys are often unaware that the amp is capable of putting out much more power than normal when it's driven into overdrive.

 

[billfitzmaurice]

I can admit when I'm wrong. I may have been confused myself a little but in the context of an amp pushed to clipping as Bill described in detail. The clipping may not be the direct cause but in that case at least is an indirect cause that delivers too much power and possibly damages the speaker..

What kills the driver is overpowering. If that's over 100% of the driver rating of clean signal or over 100% of the driver rating of pure square wave it's still over 100% of the driver rating either way. The under-powering believers think that a clipped signal of less than 100% of the driver rating will hurt it, and that's not the case. A 100 watt amp can toast a 200 driver when it puts out over 200 watts. The fact that the signal would be heavily clipped is irrelevant. All that matters is that it's over 200 watts.

 

[BassGen]

What kills the driver is overpowering. If that's over 100% of the driver rating of clean signal or over 100% of the driver rating of pure square wave it's still over 100% of the driver rating either way. The under-powering believers think that a clipped signal of less than 100% of the driver rating will hurt it, and that's not the case. A 100 watt amp can toast a 200 driver when it puts out over 200 watts. The fact that the signal would be heavily clipped is irrelevant. All that matters is that it's over 200 watts.

I appreciate that info Bill. I will remember it. All I was (finally) trying to say was that it was over-complicating the answer for the OP. For you as an owner of a loud speaker company it's easy to understand. For many others here it just confuses the real heart of the matter that they are trying to understand.

 

[GrowlerBox]

I appreciate that info Bill. I will remember it. All I was (finally) trying to say was that it was over-complicating the answer for the OP. For you as an owner of a loud speaker company it's easy to understand. For many others here it just confuses the real heart of the matter that they are trying to understand.

I dunno -- to me it seems much simpler to say too much power = damaged driver, and your amp may put out more than you think for short bursts. As always, listen to your cab and turn down volume and/or bass level if it complains, even if you you have a 50 W head.

 

[BassGen]

I dunno -- to me it seems much simpler to say too much power = damaged driver, and your amp may put out more than you think for short bursts. As always, listen to your cab and turn down volume and/or bass level if it complains, even if you you have a 50 W head.

+1

So you and I agree on this then.