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rms vs. peak vs. program

#21
onlyclave said:
You know that you're never going to overpower a cabinet, right? What is the wattage coming out of your amp 99.99% of the time? It's a fraction of rated power. What WILL blow your speakers is underpowering them. In order to get the volume that you want you'll keep turning up the volume on your amp until it runs out of headroom and pushes into clipping (distortion). That DC at the top and bottom of the wave is what melts your voicecoil.
Click to expand...

Uh, no.

Disregarding this post can be in its entirety will raise your IQ. ;)
 
#22
jpark369 said:
ok so i get rms is steady amount of watts pumping, and peak is a loud burst, but program?

so, what does it mean when the description of a bass cab says:

1600 watts program power handling?
3200 watts peak?
nothing about rms?

does that mean the cab can do 1600 rms? or what? damn manufacturers and their confusing jargon!
Click to expand...

"Program" power is a loudspeaker manufacturer's roundabout way of specifying a maximum recommended amp power point for a particular loudspeaker. (So if the manufacturer assigns a program power rating of 1600 watts to a loudspeaker, then you could match it up with an amp of up to about 1600 watts--of course, you would have to know the impedance--and then avoid driving the amp into any significant clipping or using a large amount of bass boost.)

It's usually about 1.5× to 2× the loudspeaker's continuous average (commonly known by the misnomer "RMS") power rating, which is really a thermal rating.
 
#24
I have a question Bob.

You can take a smaller amp than the cab is rated for that lets say does not clip very friendly and blow drivers by trying to squeeze more out of less correct?
 
#25
Red Planet said:
I have a question Bob.

You can take a smaller amp than the cab is rated for that lets say does not clip very friendly and blow drivers by trying to squeeze more out of less correct?
Click to expand...

Check the stickies for threads about "underpowering." To the best of my knowledge, using an amp with a lower power rating than the speakers is not a primary cause of speaker failure.
 
#26
No need to check stickies to have a conversation.

Let me give an example.

I have separated a cone from the former in a speaker cab with less power than the cab can handle according to the amps specs.

Amp was a QSC RMX 850 running one side into an 8 ohm Mesa Boogie Powerhouse 4x10.

No need for stickies.

How did I pop the speaker then?

200 watts into a 600 watt cab and I over ex cursed a speaker. So how did it happen?


And let me say I was pushing pretty hard.:D
 
#27
Well, harmonic distortion products certainly wouldn't have done it because those are at higher frequencies that contribute to coil heating but not significantly to excursion.

But the 600-Watt rating of the cab is only the thermal rating of the voice coils. It doesn't tell you how much power will drive the cones to the excursion limit.

Still, what you experienced does sound pretty extreme. I would not expect 50 W per driver to frappe a driver. Maybe a driver was defective, or already damaged from some other cause.
 
#28
The driver was good with no issues. Had been using it with another higher powered head for some time. Hooked it up to the QSC RMX 850 with a Preamp and pop.

So, what got it?
 
#29
Red Planet said:
How did I pop the speaker then?

200 watts into a 600 watt cab and I over ex cursed a speaker. So how did it happen?
Click to expand...

Because the cabinet was excursion limited to 175 watts. ;) Or something less than 200, at any rate.

It's surprising how may commercially available woofers will reach X-lim with around 1/3rd the power of the thermal ratings. Take a look at some of the Eminence drivers in the Parts Express project ideas PDFs, for example.
 
#31
Jaco who? said:
Because the cabinet was excursion limited to 175 watts. ;) Or something less than 200, at any rate.

It's surprising how may commercially available woofers will reach X-lim with around 1/3rd the power of the thermal ratings. Take a look at some of the Eminence drivers in the Parts Express project ideas PDFs, for example.
Click to expand...

But I had been using the cab with a 450 watt head for a good while prior to using it in this manner.

And the cab was rated at 600 watts. So I popped a driver at 200 watts but had no issues at 450 watts. :eyebrow:
 
#33
As a contrast to that situation I ran a QSC RMX 2450 bridged mono into an 4 ohm SWR GIV 4x10 rated at 800 watts without any issue, occasinally lighting up the peak indicators on the power amp.


I was told this would absolutely not work. It worked extremly well. :bassist:
 
#37
Hi.

Will digging up older under-powering threads make the said action more real?
Or more acceptable?

If a reputable, good speaker blows without even giving a hint about reaching its thermal or mechanical excursion limit, the first I'd check would be the DC offset in the output of the amp.

But since DC offset is quite audible, really the first sensible thing would be to check the hearing of the user.

Regards
Sam
 
#38
I had a Yamaha stereo head (about 200 watts per side) running into cabs that were rated 400 watts and all the speakers in the cabinet blew up within a couple of minutes, the first time I used it. Smoke came pouring out of the cab. I didn't even have it anywhere near practice volume, much less gig volume. So I was under-powering the cabs, right?

Turns out that something went very wrong in the amp and it fed some high voltage into the speakers, but still..... :p

The funny part is that when I called the store, the salesman told me to switch the speakers around. I told him I thought that would be a bad idea, but he insisted, so I did and ... Boom! Took the amp (and speakers) back in and he plugged it into some store speakers and Boom! + the lights went out. They fixed everything under warranty, but as I was leaving, I could hear the tech yelling at the salesman.
 
#39
A couple of questions for Bill Fitzmaurice, or Bob Lee (QSC), or hasbeen, or agedhorse (if he happens by), or anyone else: My understanding is that two mechanisms are at play when an amplifier is driven into clipping. The first is a rise in the average power level, increasing the heat (wattage) that the voice coil(s) must deal with. The second is an upward shift, in the frequency domain, of the power envelope, due to the addition of higher harmonics from the flattened waveforms. In theory this upward frequency shift in the power envelope would result in a disproportionate amount of the additional power going to the tweeter.

My first question is, in practice is this upward frequency shift in the power envolope due to clipping a significant issue for a tweetered bass cab; and if so, any general guidelines on how much of a shift to expect? Like 1/2 octave, 1 octave, etc? Probably the answer starts out with "it depends...", but my grasp here is rudimetary enough that anything would be appreciated.

My second question is, as far the thermal effect on the speaker goes, what's the difference between distortion from amplifier clipping and distortion from a cranked fuzzbox? In an attempt to compare apples-to-apples here, let's assume the we have the fuzzbox on a bigger amp so we can compare similar average power levels without the addition of power amp clipping to the fuzzbox.

I have heard that guitar cabs don't have tweeters because the distortion will blow a tweeter, and yet I see PA systems seemingly reproducing that distortion with no problem. Is there some significant difference in the signal that a guitar cab is asked to reproduce vs what comes out of the PA system, or is it a matter of the PA system having big, beefy compression drives with ultrahigh efficiency and enormous thermal capacity?

Thanks!

Duke
 
#40
DukeLeJeune said:
My second question is, as far the thermal effect on the speaker goes, what's the difference between distortion from amplifier clipping and distortion from a cranked fuzzbox? In an attempt to compare apples-to-apples here, let's assume the we have the fuzzbox on a bigger amp so we can compare similar average power levels without the addition of power amp clipping to the fuzzbox.
Click to expand...

Should be no difference. Waveform is waveform.

I have heard that guitar cabs don't have tweeters because the distortion will blow a tweeter, and yet I see PA systems seemingly reproducing that distortion with no problem. Is there some significant difference in the signal that a guitar cab is asked to reproduce vs what comes out of the PA system, or is it a matter of the PA system having big, beefy compression drives with ultrahigh efficiency and enormous thermal capacity?
Click to expand...

Guitar cabs don't have tweeters because any bassist or drummer with a sense of self preservation would poke a stick through the tweeter, before allowing the guitarist to plug in. :D

My guess is simply that the designer or setter-upper of the PA system has taken into account what sort of signals will be reproduced, and has sized the components accordingly. This, and I would also guess that a contemporary active x-over could easily incorporate some driver protection measures that might even be transparent to the listener.
 

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