better to under or overpower cabs?

[ash2008]

ive got a hartke 7000 which is 2x350@4 ohms and 2x240@8ohms.
im currently using a carlsbro 15" which is 400w @ 8ohms therefore only getting 240w.
im also about to add a ashdown abm 410t which is 600 @ 8ohms again only using 240w.
so just wondering is that bad for either my head or the cabs?i always thought it would be worse to overpower a cab but now ive heard underpowering is also risky?
should this set up be a problem?

[johnnylager]

Try these links...

[url="http://basschat.co.uk/index.php?showtopic=21348&hl=power"]http://basschat.co.uk/index.php?showtopic=21348&hl=power[/url]

[url="http://wiki.basschat.co.uk/info:amps:impedance_and_wattage"]http://wiki.basschat.co.uk/info:amps:impedance_and_wattage[/url]

Edited July 30, 2008 by johnnylager

[bass_ferret]

You beat me to it - the first law according to Alex Claber: [size=3][b]You can use any power ouput amp with any power handling cab. If any of these combinations makes bad sounds then turn down and/or stop cranking the bass EQ excessively or damage may occur[/b][/size]

[ash2008]

[b]You can use any power ouput amp with any power handling cab. If any of these combinations makes bad sounds then turn down and/or stop cranking the bass EQ excessively or damage may occur[/b]

and theres my answer, thanks.

edit: ^didnt notice that post

Edited July 30, 2008 by ash2008

[Bilbo]

I had heard that you can use any power ouput amp with any power handling cab. If any of these combinations makes bad sounds then turn down and/or stop cranking the bass EQ excessively or damage may occur.

At least, that was the gist of it.

[Mr. Foxen]

I get the impression that the recomendation to have more amp power that cab power is so you hear the speakers farting out (which is bad but not too fatal, and quickly remedied) before your run your amp into clipping and put a square wave dc current into your speakers which will just make them die right away without necessarilly making a prolonged nasty noise. The explanation of the 'run your amp into clipping and put a square wave dc current ' bit you may want is the reason why people just say 'have more power in your amp'. Course, that might not be the reason at all.

[alexclaber]

[quote name='Mr. Foxen' post='251309' date='Jul 30 2008, 01:28 PM']I get the impression that the recomendation to have more amp power that cab power is so you hear the speakers farting out (which is bad but not too fatal, and quickly remedied) before your run your amp into clipping and put a square wave dc current into your speakers which will just make them die right away without necessarilly making a prolonged nasty noise. The explanation of the 'run your amp into clipping and put a square wave dc current ' bit you may want is the reason why people just say 'have more power in your amp'. Course, that might not be the reason at all.[/quote]

I'm just writing an FAQ for my website, and here's what I've just typed out on this subject:

Q: "What about clipping, does't that damage speakers through putting DC into them?"

To clear up the DC issue, a correctly functioning amp, however badly it is clipping, should never generate DC. However clipping does have two risks - firstly that a fully clipped amp can produce almost double its rated power. This is only a problem if you keep the amp running fully clipped for a length of time and your speaker's thermal power handling is less than twice the amp's rated power output. Fortunately in the real world this will never happen - we play bass, which by its nature has loud moments and quiet moments, thus power output is never constant. If you use an amp within the recommended power range for our speakers then you will not have a problem unless you are seriously abusive.

The second risk with clipping is that most of the extra power is actually in the high frequencies. This means that if the cab has a tweeter it is likely to receive more power than it can handle. However if you have a tweeter then you should be able to hear the clipping and react by turning the amp down. The plus side for our designs is that the rising impedance of any woofer with frequency actually protects the woofers from having to handle extra power (amplifiers are voltage amplifiers and the power that comes out is simply the voltage squared divided by the impedance at that frequency). So to recap, although your amp can produce more power when it is clipping, the majority of that potential extra power won't actually flow through your speaker unless you have a tweeter, in which case it will make a really ugly noise before the tweeter dies (which is why a well designed speaker should incorporate tweeter protection circuitry).

Alex

[johnnylager]

[quote name='bass_ferret' post='251236' date='Jul 30 2008, 12:34 PM']You beat me to it - the first law according to Alex Claber: [size=3][b]You can use any power ouput amp with any power handling cab. If any of these combinations makes bad sounds then turn down and/or stop cranking the bass EQ excessively or damage may occur[/b][/size][/quote]
I wanted to nip it in the bud before it got out of hand. Yet again.

[BOD2]

[quote name='johnnylager' post='251333' date='Jul 30 2008, 01:56 PM']I wanted to nip it in the bud before it got out of hand. Yet again. [/quote]

I'm just encouraged that several different people have remembered this and posted it in answer to this OP.

There's a long way to go but we're winning....

[Bill Fitzmaurice]

[quote name='Mr. Foxen' post='251309' date='Jul 30 2008, 08:28 AM']run your amp into clipping and put a square wave dc current into your speakers[/quote]Said 'square wave DC current' falls into the same category as Medusa, Chimera, Unicorns, Hercules and Fiscal Responsibility in Government.

[ash2008]

[quote name='BOD2' post='251341' date='Jul 30 2008, 02:09 PM']I'm just encouraged that several different people have remembered this and posted it in answer to this OP.

There's a long way to go but we're winning....[/quote]
i dont think ill forget in a hurry...

[Fraktal]

A few years ago I connected the power output of a 3000w+ top of the line QSC power amplifier feeded with a 1k signal at full power and bridged to a... cheap sennheiser headphones!!! I was expecting it to blow up and throw the little speaker inside the headphones a few meters away, but to our surprise the headphones kept working for 2 hours approximately. The following day the headphones worked flawlessly with my walkman. I have heard QSC power amps have some circuitry to control the excursion/movement of the speakers and avoid damage to them and distortion, so this might not be a good thing to try with other brands of power amps... A sound engineer told me that as long as you dont feed a speaker with square signal, the chances of burning it are banishing low, and that the opposite experiment was also true, feeding a high power speaker with a low power amp distorting like crazy would possibly screw the speaker relatively fast.

Dont take my word for it though cos this is all speculation and the only experiment we did was with a top of the line QSC, although I trust this guy's word up to a certain point since he was a very experienced and skilled PA sound engineer.

[Protium]

In which case how do you amplify a square wave synthesizer? And how can you use distortion pedals?

[Fraktal]

Thats the reason I said dont take my word for it ^^

[bass_ferret]

[quote name='Fraktal' post='251517' date='Jul 30 2008, 06:17 PM'](snip) feeding a high power speaker with a low power amp distorting like crazy would possibly screw the speaker relatively fast.(snip)[/quote]
Alex Clabbers first rule applies to any amplifier driving any speaker.

[Catalin]

What about all tube amplifiers? I know they don't clip or if they clip is not dangerous for speakers.

Edited July 31, 2008 by Catalin

[Stewart]

Any decent amp will amplify a square wave fairly well (though never perfectly)
No loudspeaker will come close

[bass_ferret]

[quote name='Catalin' post='251812' date='Jul 31 2008, 07:32 AM']What about all tube amplifiers? I know they don't clip or if they clip is not dangerous for speakers.[/quote]
What part of
[quote name='bass_ferret' post='251742' date='Jul 30 2008, 11:28 PM']Alex Clabbers first rule applies to any amplifier driving any speaker.[/quote]
did you not understand?

[Catalin]

[quote name='bass_ferret' date='Jul 31 2008, 11:15 AM' post='251914']
What part of


Tube power amp.

Edited July 31, 2008 by Catalin

[cheddatom]

[quote name='Catalin' post='251944' date='Jul 31 2008, 11:43 AM']Tube power amp.[/quote]

A tube amp is still an amp, so if the rule applies to any amp.....

lulz.

[Catalin]

So a distorting tube power amp can damage speakers just like a clipping solid-state power amp ?

[Fraktal]

This is pure speculation cos Im no sound engineer, but I suppose the hardest work you can ask a speaker for would be a "perfect" square wave at full power (very unlikely to happen) since it will probably force the speaker to violent movements, shifting the cone between the limits of its excursion violently and fast... Though the physical limitations of a speaker are likely to "round the edges".

If that assumption is true, then I would also imagine that a distorting valve amplifier would be less dangerous than a solid state one, since valves "round the edges" the closer they are to their maximum headroom. Thats one of the reasons we find valve distortion much more pleasant and musical than solid state distortion, valves boost even harmonics while solid state boost uneven ones.

Duh, I should really try to find an english technical dictionary, LOL!

[alexclaber]

[quote name='Fraktal' post='252000' date='Jul 31 2008, 12:57 PM']This is pure speculation cos Im no sound engineer, but I suppose the hardest work you can ask a speaker for would be a "perfect" square wave at full power (very unlikely to happen) since it will probably force the speaker to violent movements, shifting the cone between the limits of its excursion violently and fast... Though the physical limitations of a speaker are likely to "round the edges".[/quote]

This is the common misconception about a square wave. In reality the cone position is the double integral of the current (which is proportional to voltage though the relationship varies with frequency) over time. Furthermore the rising impedance of the voice coil with frequency will filter out higher harmonics and thus make the square wave look more like a sine wave.

Alex

[Fraktal]

Thanks a lot for your insight, Alex, always good to learn new things. Unfortunately I think Im having a hard time to understand your response, do you have any graphics? Maybe it would be easier with a picture or 2...

[Bill Fitzmaurice]

[quote name='Fraktal' post='252047' date='Jul 31 2008, 09:06 AM']Thanks a lot for your insight, Alex, always good to learn new things. Unfortunately I think Im having a hard time to understand your response, do you have any graphics? Maybe it would be easier with a picture or 2...[/quote]
Graphics in this case is a culprit. The 'underpowering' nuts show a picture of a square wave as it appears on an oscilloscope to bolster their case. Musical waveforms of that sort do not exist. A clipped musical waveform consists of a normal sine wave at the fundamental to which has been added an abnormally high level of harmonics. Those harmonics can result in overpowering of tweeters, and in extreme cases midranges. They have absolutely no effect upon woofers.