Re: Am I going to blow a speaker cab?

JimmyM wrote:
On Sat, 24 Dec 2011 22:20:33 -0800, Jim<ask@first> wrote:

On 12/24/2011 4:25 PM, Les Cargill wrote:
BW wrote:

Quick question. It seems to me that I can plug a high output head
(like a Markbass Tube 800) into a cabinet rated for substantially
lower power (like an SWR 2x10 rated at 350 watts) and won't do any
damage to the cab as long as I am gentle with the volume output on the
head. Am I right?

Happy holidays and a grand new year to all.

if. That's a big if.

Okay - speakers fail from:

1) getting stuck at Xmax ( full extension ) and burning up the voice
coil. If the cone cannot move, all 800 watts go into heat. The voice
coil will fry, and you get to replace or recone the speaker.

2) From clipping from an underpowered amp throwing too much
high frequencies in square waves that are expressed as heat.
This is cause by an *under*powered amp.

Both true,

No they're not.

1. Speakers have what is called Xmech, which is the point between
Xmax and voice coil burnout. Exceeding Xmech will blow speakers, not
Xmax. However, the heat buildup in speakers exceeding Xmax will cause
them to weaken over time.

Interesting. I had never run into that measure before. This explanation works for me. Xmech was not part of the traditional Theile-Small parameters... the term also has a strong "car stereo" aroma,
based on a Google search.

2. The underpowering business is bullshit. Pure and total bullshit.

I am afraid not.

If it were true, I couldn't take my 25w B-15 head and crank it all the
way up in a cab rig that takes 500w. But I've done it more times than
I can count with absolutely no ill effects. Clipping can blow
tweeters, but again, that's not "underpowering" them, that's
OVERpowering them.

So if you send square waves to a speaker that rolls off at frequency f,
then all the Fourier components of that square wave above frequency f
will be expressed purely as heat. All the heat adds up, and you
can - emphasis *can* - roast a driver that way.

Sounds like your 25w amp doesn't do that. A ... 125w amp *might*,
if you run it clipped for a while.

The point is that using an underpowered amp can be just as dangerous as
an overpowered one.

Les Cargill