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500 Watt Head & 800 Watt Cab?

J

john_martin_sai

Dec 29, 2009
695
27
Dalian, Liaoning
#1
My head is spinning after reading countless threads on mismatched heads and cabs.

I know it's not a simple answer but what would I have to avoid doing with a 500 Watt Head into an 800 Watt Cab?

Here's a quote I just spotted on another site.


LittleWoodenBoy

04-10-2003, 01:16 PM

"Cab ratings are in RMS, that's Root mean Square. Meaning that the power handling rating is a value measured as an average along the waveform instead of at the crests or troughs. Meaning you can power a cab with an amp rated much higher and still be fine. Conversely, UNDERpowering a cab can be bad, so make sure your amp is at LEAST 800 watts for powering cabs rated for 800."


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I've read so many different opinions on this matter,...I don't know what to believe anymore.
 
#2
john_martin_sai said:
My head is spinning after reading countless threads on mismatched heads and cabs.

I know it's not a simple answer but what would I have to avoid doing with a 500 Watt Head into an 800 Watt Cab?

Here's a quote I just spotted on another site.


LittleWoodenBoy

04-10-2003, 01:16 PM

"Cab ratings are in RMS, that's Root mean Square. Meaning that the power handling rating is a value measured as an average along the waveform instead of at the crests or troughs. Meaning you can power a cab with an amp rated much higher and still be fine. Conversely, UNDERpowering a cab can be bad, so make sure your amp is at LEAST 800 watts for powering cabs rated for 800."


Link Removed

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I've read so many different opinions on this matter,...I don't know what to believe anymore.
Click to expand...

LittleWoodenBoy's nose is growing. He is wrong on every count. This is not a matter of opinion, and has been discussed endlessly here. Briefly: cab ratings are almost without exception thermal, not RMS. It is impossible to "underpower" a cab. That doesn't even make sense. You turn your amp off, right?
 
#4
john_martin_sai said:
I've seen so many varying opinions on this - I knew someone had to be wrong.

So, with my 500W head and 800W Cab - Danger occurs if I push the head beyond it's limits, which I will sense when the Cab starts to 'distort' or 'clip'?
Click to expand...

In a way -- it's not the limits of the head that are at issue, but the cabinet. In a nutshell, lots of low end and high volumes (i.e. overpowering) are what kill speakers. If your speakers are complaining ("farting", distorting) then back off one or the other or both. If you need to be louder and can't add more speakers, boost the mids and point the speaker at your head.
 
#6
GrowlerBox said:
LittleWoodenBoy's nose is growing. He is wrong on every count. This is not a matter of opinion, and has been discussed endlessly here.
Click to expand...

Gents,

I realise that I'm under extreme risk of scratching an old scab, however I don't really think anybody has ever suggested that underpowering a cab is bad. Not in that way anyway.

The whole idea of not underpowering your cab comes from that fact that using too little amp to drive a big cab in an effort to get more volume can lead to the amp distorting. And that can damage your cab unless it has enough rating to accept distorted signal. So you can put as little power as you want as long as your amp doesn't clip.

That was all. For some reason this is being interpreted sometimes in a most ridiculous way.

GrowlerBox said:
Briefly: cab ratings are almost without exception thermal, not RMS. It is impossible to "underpower" a cab. That doesn't even make sense. You turn your amp off, right?
Click to expand...
Now that doesn't make sense either. Thermal vs. RMS? That's comparing apples to oranges. Actually RMS and thermal are the quite closely related (same thing for DC for example). Perhaps you meant thermal vs cone travel.

Cheers

MP
 
#10
magic papa said:
The whole idea of not underpowering your cab comes from that fact that using too little amp to drive a big cab in an effort to get more volume can lead to the amp distorting. And that can damage your cab unless it has enough rating to accept distorted signal. So you can put as little power as you want as long as your amp doesn't clip
Click to expand...
This needs a caveat and some salt. DISTORTION DOES NOT INHERENTLY HURT SPEAKERS. I know you said "unless it has enough rating to accept distorted signal", and that is the twist that makes your statement "true", but the precise reason the bogus "underpowering" myth won't die is because of people saying distortion can damage cabs.

When a person is asking about whether their cab, rated for a high amount of wattage, will be damaged by a significantly lower-wattage amp, the answer is NO IT WILL NOT.
 
#11
john_martin_sai said:
what would I have to avoid doing with a 500 Watt Head into an 800 Watt Cab?
Click to expand...
Worrying about it.
The whole idea of not underpowering your cab comes from that fact that using too little amp to drive a big cab in an effort to get more volume can lead to the amp distorting. And that can damage your cab unless it has enough rating to accept distorted signal. So you can put as little power as you want as long as your amp doesn't clip.
Click to expand...
No. Clipping might hurt a tweeter. It never has nor ever will bother a woofer.
 
#13
bongomania said:
This needs a caveat and some salt. DISTORTION DOES NOT INHERENTLY HURT SPEAKERS. I know you said "unless it has enough rating to accept distorted signal", and that is the twist that makes your statement "true", but the precise reason the bogus "underpowering" myth won't die is because of people saying distortion can damage cabs.
Click to expand...

I think it's been established that it could blow the tweeter. And I know it could because I had done this myself in almost lab-like conditions (same volume, same gear, the only difference was distortion).

That still classifies the cab as damaged IMHO.

So I think for distorted signal you do need higher power rating to minimise the risk. Hence that myth isn't completely bogus if it's said in the right way ;)


I think this must go to Mythbusters, who's for it?
 
#14
magic papa said:
Now that doesn't make sense either. Thermal vs. RMS? That's comparing apples to oranges. Actually RMS and thermal are the quite closely related (same thing for DC for example). Perhaps you meant thermal vs cone travel.
Click to expand...

So are they apples and oranges or quite closely related? :)

I was trying to be brief, given that there must be in the order of 5000 threads on this topic. But, for the OP: the power rating stamped on the back of most commercially available cabinets represents the sum of the thermal limits of the drivers enclosed; i.e. expose them to that much or more power for long and the voice coils will be irreparably damaged by heat. "Useable" power is most often somewhere in the order of half that figure. That is all.
 
#15
SVT's @ 300 watts are matched with 8X10's rated 800 watts
I'm pretty sure they got that right.
The very early ampeg 810 were rated 240watts (but they were just underrated to get folks to buy two?)

then again I see people matching the SVT-4Pro @ 1600 watts with the 810
infer what you like.

is it a tube power vs solid state power consideration?
 
#16
oinkbanana said:
SVT's @ 300 watts are matched with 8X10's rated 800 watts
I'm pretty sure they got that right.
The very early ampeg 810 were rated 240watts (but they were just underrated to get folks to buy two?)

then again I see people matching the SVT-4Pro @ 1600 watts with the 810
infer what you like.

is it a tube power vs solid state power consideration?
Click to expand...

No it is a non issue, but the "1600 watts" will smoke the 810 cab if you are dumb enough to try it! We hardly ever use all the power available from our amp heads unless they are under 300 watts and used in the loudest conditions.
 
#17
oinkbanana said:
SVT's @ 300 watts are matched with 8X10's rated 800 watts
I'm pretty sure they got that right.
The very early ampeg 810 were rated 240watts (but they were just underrated to get folks to buy two?)

then again I see people matching the SVT-4Pro @ 1600 watts with the 810
infer what you like.

is it a tube power vs solid state power consideration?
Click to expand...

The Ampeg 8x10 has no tweeter AFAIK, so it'll be fine as far as distortion is concerned.

Tube power and solid state power are the same thing. That's another myth :)
 
#19
john_martin_sai said:
My head is spinning after reading countless threads on mismatched heads and cabs.

I know it's not a simple answer but what would I have to avoid doing with a 500 Watt Head into an 800 Watt Cab?

Here's a quote I just spotted on another site.
Click to expand...

What you need and how well this will work depends on A) how loud you will play through it, and B) how long you will run it that hard. The speaker's voice coil needs to dissipate heat well enough to not go into thermal compression- a conductor's resistance increases when its temperature rises and if it gets too hot, increases in signal (voltage) will go unnoticed unless they're large increases. If you don't need to run it hard, you'll be fine.
 
#20
IncX said:
i see this as something like a voltage issue:

-when you plug in a 110 volt tv on a 220v socket = you will see smoke.
-when you plug in a 220 volt tv on a 110v socket = you will not see smoke, but the picture sucks!

lol

something like that.
Click to expand...

Sorry no, while the output of an amplifier is measured in volts. With no signal to amplify, the voltage from the most powerful amp is still zero volts. So no cigar tonight :D ;)
 

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