Head more powerful than cab

[TechFoo]

Hey guys (and gals),
Apologies for what may be an obvious and/or stupid question (I had a flick through the Wiki and the other pages but I couldn't find an answer) but here goes:

Atm I've got a head rated at ~500W and a cab at ~250W (looking to get a second to add to it but funds are low). If I were to (hypothetically) crank the volume and input on the head to maximum would it try and send 500W into the cab and blow the speaker or would it be limited to the cabinets power handling (if that's the correct term)

Cheers,
Alex

[Mr. Foxen]

Theoretically yes. In practice you could break the cab without cranking, if you do it wrong, and ignore the fact the cab is making protest noises.

[chris_b]

Presumably the cab is 8 ohm, so your amp will only be putting out approx 300 watts. You can damage the speaker but it should sound pretty bad way before the amp gets to flat out.

[dannybuoy]

Unless it's a tube amp or an Orange Terror, which will put out the full 500w into an 8 ohm cab. Just start with the volume low and increase it gradually - you'll hear when the cab is approaching it's limit. Just watch out if you have any distortion or filter pedals that could push it over the edge!

[JTUK]

I must admit this sort of thing always concerns me...and that may be a legacy of breaking crap speakers years ago

A typical 500w amp would put that output out at 4ohms. If your cab is 4 ohms, this is a risk. As said above, the amp at 8ohms will be around 300watts which is still too much for the cab. Depending how good the cab/speaker is, I wouldn't even be putting 250w into your cab..legacy, again.. and how do you know how much power it produces on the master..???

For sure, you should hear it breaking up, but it may not be as simple as that, especially in very loud situations or using effects etc.

If you aren't confident about this..and your question probably assumes you aren't.. you need to be very careful, IMO

I'd aim to get that second cab pretty soonish and not take on any loud gigs in the meantime.

FWIW..I always try to run an amp maybe at around 60% of the cab power... ie, 400w into 600w cab power.

[270degrees]

You're more likely to blow a cone using an underpowered amp. Just use common sense when operating the volume control. Also note that the speaker can probably handle more power than stated and the figure quoted includes a safety buffer of some sort.

[waynepunkdude]

I was wondering this I have a back up cab cab that is 200W @ 8OHMS my head is 245W @ 8OHMS with a built in limiter, am I OK?

[Nostromo]

Yes . . your amp can put out more power than your single cab can cope with.

IMHO . . I think it pays to have headroom both in bass cabs and bass heads.

But when you havent got much head room, my thoughts are that I'd rather put 250 watts into a 250watt cab from a 500watt head at half power than from a 250watt head running flat out into that same cab . . . I'm thinking that with an amp running flat out you're more likely to get into clipping and unwanted distortion teritory so far as your output signal is concerned which might easily damage a cab, and possibly cause dasmage at below its rated power handling ?

If I was going to run a rig that needed 250 watts output to achieve a particular volume/tone/sound, then I'd like to be using a head that had pleanty of headroom (a 500w head at least probably) and cab wise, I'd like even more headroom again ? . . . then, you'd have no problem with transients etc . . . . My experiance with different bass rigs is that they generally sound sweeter when they are not being pushed to the limit particularly with solid state gear. Valve heads are a bit different and a bit more forgiving and, as an aside, do always seem to me to sound a hell of a lot louder and more powerfull for a given wattage rating ?

In your case, I suspect , like some of the previous posts have said, that if your amp is rated at 500watts, then that is probably 500w at 4ohms ? . . . and being as you are only using one cab, then, so long as that cab is 8ohms ? . . then you would have to be running very loud, around 6/10 or 7/10 or above, on your vol control for long periods to mechanically or thermally overlaod that cab. On thre other hand, if your cab is 4ohms take care, you could quite easily overdrive it with your amp.

The answer here is to use your ears and listen to what's going on . . . . your speaker will tell you when it doesnt like the signal you're putting into it - and hopefully you will hear the warning before things are too late ! ! ! . . . . . .

Must say that all my above experiance is based on the sound I'm trying to achieve which is always clear and distortion free. If you're into heavy distorted bass then thats a differtent ball park altogether and I wouldn't know how to advise you as you probably cant use your ears to warn you of whats going on as you drive a cab close and then beyond its power rating with a highly distorted bass signal ? ? ?

[JTUK]

[quote name='waynepunkdude' post='897333' date='Jul 17 2010, 03:06 PM']I was wondering this I have a back up cab cab that is 200W @ 8OHMS my head is 245W @ 8OHMS with a built in limiter, am I OK?[/quote]


My personal experience would not feel comfortable with this in anything but gentle conditions.

If the signal you send into the amp is overdriven or very attack orientated, ie a pick playd hard, then this tends to muddy the water for me.
And as my rule is to have more in hand with the cab, then I think you would be able to overpower this cab quite easily if you have the volume
anyway around half on the Master.

As I said, this is because notches on a dial seem to mean not much conclusively. Some amps seem as loud at 5 as they would as 10 and our ears are not really able to tell the diiference between 200w and 250w.

In short, I don't trust it and use my ears, but the failsafe is to build in the output difference with a high rating on the cab.

I do concede this thinking is based on overpowering cabs years ago and speaker chassis are much better today...but the feeling remains that chassis' are still a pretty basic piece of engineering, IME.

[bigjohn]

I wouldn't think twice about putting 500W into a 250W cab if it sounds ok. If it sounds ok you're not doing it any harm. The worst that could happen anyway is you'd need to replace the speaker cones

You could use a compressor / limiter to reduce the work the cones have to do. Or play quieter

If you are really worried about it or is sounds like it's still crapping out, you could rewire the cab to increase it's impedance. A 4ohm cab could be rewired to be 16ohm.

You'll get more usable "power" out of it then without any worries.

Edited July 17, 2010 by bigjohn

[TechFoo]

Thanks for the info guys. It is an 8 ohm cab and also I prefer to use a clean tone so I'll be able to keep an ear out for any disgruntled cab noises. Thankfully I'm only doing small gigs atm (think coffee shop sort of thing). Just need to save up and get that second cab now

[Mr. Foxen]

[quote name='270degrees' post='897331' date='Jul 17 2010, 03:03 PM']You're more likely to blow a cone using an underpowered amp.[/quote]

If you can explain how, without making up physics that isn't true, you win a prize.

[bigjohn]

[quote][/quote][quote name='TechFoo' post='897384' date='Jul 17 2010, 04:38 PM']
Thanks for the info guys. It is an 8 ohm cab and also I prefer to use a clean tone so I'll be able to keep an ear out for any disgruntled cab noises. Thankfully I'm only doing small gigs atm (think coffee shop sort of thing). Just need to save up and get that second cab now [/quote]

If it's 8ohm I reckon you'll be fine. Don't come to me if you blow it smithereens like, but seriously, I wouldn't give it a second thought unless it sounded bad.

I put 500W @ 4ohm into 400W @ 8ohm all the time without any problem. Admittedly 400W isn't 250W but my speaker gets nowhere near distorting. And the 500W I put in is from a real heavy duty power amp.

To be honest, with your set up I'd be more worried about overheating your amp than blowing the speaker.

[mart]

[quote name='Mr. Foxen' post='897393' date='Jul 17 2010, 04:47 PM']If you can explain how, without making up physics that isn't true, you win a prize.[/quote]

I was going to ask the same question, but there is an answer in Nostromo's reply:

[quote name='Nostromo' post='897346' date='Jul 17 2010, 03:30 PM']....
But when you havent got much head room, my thoughts are that I'd rather put 250 watts into a 250watt cab from a 500watt head at half power than from a 250watt head running flat out into that same cab . . . I'm thinking that [b]with an amp running flat out you're more likely to get into clipping and unwanted distortion teritory so far as your output signal is concerned which might easily damage a cab, and possibly cause dasmage at below its rated power handling ? [/b]

...[/quote]

[Merton]

[quote name='mart' post='897446' date='Jul 17 2010, 05:35 PM']I was going to ask the same question, but there is an answer in Nostromo's reply:[/quote]
But that's a *bit* of a misconceptionespecially regarding bass drivers. Read the wiki

[algmusic]

I was selling an Ampeg 2x12 a about 6months ago it could handle 400@ 4ohms.. a guys turns up with a 1200@2ohms (valve as well).. you can imagine my comments...

"if you want to blow the cab... give me the cash first, but you need to change the head or by a cab"

[Mr. Foxen]

[quote name='algmusic' post='899042' date='Jul 19 2010, 03:24 PM']I was selling an Ampeg 2x12 a about 6months ago it could handle 400@ 4ohms.. a guys turns up with a 1200@2ohms (valve as well).. you can imagine my comments...

"if you want to blow the cab... give me the cash first, but you need to change the head or by a cab"[/quote]

Fender/sunn 1200s?

Anyway, cab would be fine if you don't crank the amp.

[Phil Starr]

[quote name='270degrees' post='897331' date='Jul 17 2010, 03:03 PM']You're more likely to blow a cone using an underpowered amp. Just use common sense when operating the volume control. Also note that the speaker can probably handle more power than stated and the figure quoted includes a safety buffer of some sort.[/quote]
This is one of the old chestnuts and like most it has a grain of truth in it.

Assuming we are talking RMS or EIA watts or something similar the amp is rated on the undistorted sine wave it can produce for a few hours continuously into a stated load. usually nowadays it is rated on sine waves in the form of filtered noise called pink noise which is meant to be like music in its energy content.

When an amp distorts the sound waves rise to a peak much more quickly, clip at the amps full power and then drop quickly. This means that on every wave there is more time at full power and the amp has more energy to handle and so does the speaker. The absolute maximum is a Square wave which contains 1.414 (root 2) times the power of a sine wave with the same voltage peak. So a 100W amp with total distortion will give 14oW in the speaker. It won't outpower a 200Wamp though.

Speakers are rated differently. What destroys speakers is heat, 100W through a speaker means the coil gets as hot as an old fashioned light bulb. in the old days this melted the glue and the coil unwound, sometimes you even saw charring and smoke from a paper former. The EIA rating of a speaker is the heat it can dissipate for a few hours. It even assumes that the air can circulate freely in the test room and is at 20degrees. There is usually a peak or music figure 2-4 times the EIA rating, if this is done properly this should be the figure where the distortion reaches 10% and becomes audible.

If you are playing normally then you have loud bits and quiet bits. The quiet bits let the coil cool down so the speaker can handle a lot more than its rating so long as it isn't distorting. If you play with a 40dB range (no compression) your 500w amp is only putting an average of 5W into the speakers. If you use lots of compression and bass boost/distortion you probably still have a 20dB dynamic range and are only putting an average 50W into the speakers so don't worry about a minor mismatch unless you get lots of distortion. The physics is on your side.

[algmusic]

[quote name='Phil Starr' post='899825' date='Jul 20 2010, 11:11 AM']This is one of the old chestnuts and like most it has a grain of truth in it.

Assuming we are talking RMS or EIA watts or something similar the amp is rated on the undistorted sine wave it can produce for a few hours continuously into a stated load. usually nowadays it is rated on sine waves in the form of filtered noise called pink noise which is meant to be like music in its energy content.

When an amp distorts the sound waves rise to a peak much more quickly, clip at the amps full power and then drop quickly. This means that on every wave there is more time at full power and the amp has more energy to handle and so does the speaker. The absolute maximum is a Square wave which contains 1.414 (root 2) times the power of a sine wave with the same voltage peak. So a 100W amp with total distortion will give 14oW in the speaker. It won't outpower a 200Wamp though.

Speakers are rated differently. What destroys speakers is heat, 100W through a speaker means the coil gets as hot as an old fashioned light bulb. in the old days this melted the glue and the coil unwound, sometimes you even saw charring and smoke from a paper former. The EIA rating of a speaker is the heat it can dissipate for a few hours. It even assumes that the air can circulate freely in the test room and is at 20degrees. There is usually a peak or music figure 2-4 times the EIA rating, if this is done properly this should be the figure where the distortion reaches 10% and becomes audible.

If you are playing normally then you have loud bits and quiet bits. The quiet bits let the coil cool down so the speaker can handle a lot more than its rating so long as it isn't distorting. If you play with a 40dB range (no compression) your 500w amp is only putting an average of 5W into the speakers. If you use lots of compression and bass boost/distortion you probably still have a 20dB dynamic range and are only putting an average 50W into the speakers so don't worry about a minor mismatch unless you get lots of distortion. The physics is on your side.[/quote]


I love this kind of bravery.. I just can't afford the risk of blowing my amp.. I've only done this once at rehearsal an played very quietly, but I always have the rule of getting a cab that can handle at least about 20% more than the amp, then you can drive the beast how you want... I'm sure you get a better sound.. well IMHP

[Mr. Foxen]

[quote name='algmusic' post='899855' date='Jul 20 2010, 11:48 AM']I love this kind of bravery.. I just can't afford the risk of blowing my amp.. I've only done this once at rehearsal an played very quietly, but I always have the rule of getting a cab that can handle at least about 20% more than the amp, then you can drive the beast how you want... I'm sure you get a better sound.. well IMHP[/quote]

Depends on what you mean by 'handle', and at what rating. Plenty of cabs won't handle 80% of their rated RMS power due to excursion limit at the frequency where cone excursion is at maximum. Exceeding the excursion limit is the bit that will break most bass guitar speakers, because you don't need to do it for a length of time, push the speaker past that limit and its gone.

[peted]

I've run a Hartke HA3500 350 Watt head into a Hartke PRO 2200 2x12" 300 Watt 4 Ohm cab for many years without any issues. I don't turn the volume on the head past 4/10 and when I EQ I cut rather than boost. I'm also loathe to let anyone else use my gear in that setup as I know they would only have to crank the volume all the way up or put silly amounts of bass boost on and it could break the cab.

[Alec]

Well, I happily use my TC RH450 head with my Genz Benz STL-10T cab for my home/practice rig.

That's a 450W head into a 200W speaker.

Obviously, the head won't be kicking out it's full load, as it's only driving 8 ohm. I have no problems with this, but obviously play with a listening ear to any problems and would drop down before they happen. Actually, I've never taken it up to its full load as I've never needed to. And, rather nicely with the RH450, you can throttle the amp back with the "preset volume", which I've done, so I can use more than the first 10% of the master volume control. My, how I love this amp!

[algmusic]

[quote name='Alec' post='899991' date='Jul 20 2010, 01:37 PM']Well, I happily use my TC RH450 head with my Genz Benz STL-10T cab for my home/practice rig.

That's a 450W head into a 200W speaker.

Obviously, the head won't be kicking out it's full load, as it's only driving 8 ohm. I have no problems with this, but obviously play with a listening ear to any problems and would drop down before they happen. Actually, I've never taken it up to its full load as I've never needed to. And, rather nicely with the RH450, you can throttle the amp back with the "preset volume", which I've done, so I can use more than the first 10% of the master volume control. My, how I love this amp![/quote]


Exactly.. if the environment is quite enough.. you're safe, I guess

[algmusic]

[quote name='Mr. Foxen' post='899903' date='Jul 20 2010, 12:37 PM']Depends on what you mean by 'handle', and at what rating. Plenty of cabs won't handle 80% of their rated RMS power due to excursion limit at the frequency where cone excursion is at maximum. Exceeding the excursion limit is the bit that will break most bass guitar speakers, because you don't need to do it for a length of time, push the speaker past that limit and its gone.[/quote]


Ooow.. Do you mean the whole handling over the RMS.. That's when the cab can handle short burst of power but not continuous, right???

[Mr. Foxen]

[quote name='algmusic' post='900123' date='Jul 20 2010, 03:04 PM']Ooow.. Do you mean the whole handling over the RMS.. That's when the cab can handle short burst of power but not continuous, right???[/quote]

No. I mean excursion limited power handling rather than the RMS rating which is thermal. It depends on the cab as much as the speaker, as it is the amount of power needed to push the speaker physiclally far enough it breaks, and the cab controls its movement. RMS is mostly useful for PA subs running constant loads of compressed bass signal where a melting is a possibility, rather than the much more dynamic requirements of instrument amplification, where a signal peak at a wrong frequency is the killer, since there is lots of cooling time. So a short burst of enough power will break it, since the cone tearing loose of the surround or the coil squashing against the backplate isn't something that will be forgiven shortly after.