Wattage question: continuous rms vs. program

[Hey Im Matt]

So what's the difference between continous and program watts? I have noticed that a cabinet will be rated at X amount of watts rms continous and then it will say that it is rated at X amount program (which is usually twice the amount of the rms). What does this all mean and how would it relate to how much power your amp should put out to the cabinet?

 

Thanks,

Matt

[Raven]

Power ratings on speakers are just that: Ratings. Power ratings don't determine how loud it will be, how good it will sound, or even how it will stand up to physical abuse. The power rating tells you one thing: how much heat the speaker's voice coil can dissipate (in Watts) before it burns up. Make sure the power rating you go by is RMS, not peak power or acoustic power which doesn't really mean squat. (The same applies to power amps.)

The RMS rating of your power amp or head should be at least 1-1/2 times the RMS rating of your cab. That way you will have enough power to drive your speakers to the volume needed without driving the amp into clipping (bad distortion). Clipping generates spikes of DC voltage which will wind up killing your speakers if you keep it up.

[alexclaber]

Originally posted by Raven:

The RMS rating of your power amp or head should be at least 1-1/2 times the RMS rating of your cab. That way you will have enough power to drive your speakers to the volume needed without driving the amp into clipping (bad distortion).

That's assuming you need to get every ounce of volume out of the speakers. If your amp isn't clipping at the volume you need, then you have enough power, even if it's much less than the speaker's rating. But yes.

 

Originally posted by Raven:

Clipping generates spikes of DC voltage which will wind up killing your speakers if you keep it up.

How many more times? No DC. Clipping is bad because it allows the amp to put out more than its rated power (voice coil over-heating), with less cone control (speaker over-excursion) and more HF content (unhappy tweeters).

 

Alex

 

P.S. From talkbass right now, our own LizzyD also labouring under the same misconception: "Has anyone blown up a Bergantino? I suppose clipping an amp would do it, no matter the watts." Hmmm...

[Rick Hoffman]

I play an SVT3-Pro through a 4x10 HLF. The amp is 450 watts rms and the cab is rated at 500 watts rms. I rarely turn the gain past 5, when the tube gain and master are maxed. I never experienced clipping.

 

If I'm ever playing a really big venue and I need to turn up, I'll let you guys know what happens. Chances are, I'll probably plug in my old Morley wah pedal with the gain switch, turn it up, turn down the tube gain and shut off the graphic EQ on my amp...just an idea to get max volume without clipping...hmm I will have to try that at home...

[LizzyD]

Originally posted by C. Alexander Claber:

P.S. From talkbass right now, our own LizzyD also labouring under the same misconception: "Has anyone blown up a Bergantino? I suppose clipping an amp would do it, no matter the watts." Hmmm...

I always heard clipping = really bad for your speakers.

 

What exactly am I not getting? Am I perpetuating a myth here? Please clarify, for my own good at the very least!

 

I was thinking of the possible ways to have a fry-up with a cab, such as over- or under-powering. And specifically, wondering how much abuse (of any kind) a Bergantino might take before bursting into flames. Not that I'm worried about ruining mine.

 

And sorry Matt, I can't answer your question about program and continuous watts.

[_Sweet Willie_]

Try a search for "clipping" and maybe also for "matching" (as in matching head and cab). Also try "peak" and "continuous". We've had lots of discussion about these issues before, and it's through this forum that I came to understand them.

 

If your amp allows you to be loud enough for the gigs and rehearsals you play without clipping (rough layman's term = "overly straining itself"), you should be fine. Raven's "rule of thumb" is a reasonable one, although there will certainly be variation in circumstances as well as variation in the ways in which amp and cab companies report their specs. This means using your ears is always important.

 

"Continuous" power is what your cab can take as a norm throughout a performance. "Peak" gives you an idea of the max power a cab can take. Assuming you play dynamically, there will be some variation in what you send to your cab throughout a performance.

 

So, a cab might be rated for 500W continuous and 750W peak. That means it will happily take 500W continuously throughout the gig, rehearsal, jam, whatever and will also happily manage short bursts of power up to 750W (probably even more). Again, these are generalizations and some manufacturers are more or less conservative in their ratings.

 

I think it's nice to have more power than you need -- you don't always have to use it. It sucks to find yourself in a situation where you really don't have enough power and now you're at risk of clipping and doing damage to your speakers.

 

Peace.

--SW

[getz out]

Originally posted by John William Hofmann:

If I'm ever playing a really big venue and I need to turn up, I'll let you guys know what happens. Chances are, I'll probably plug in my old Morley wah pedal with the gain switch, turn it up, turn down the tube gain and shut off the graphic EQ on my amp...just an idea to get max volume without clipping...hmm I will have to try that at home...

The poweramp section of your amp doesn't care where the gain is coming from; whether it is the integrated preamp, the bass, or something inbetween the two, it can still cause your poweramp to clip. Gain is gain. Think about it; when you put a really hot signal into a mixing board (line level, like a keyboard), what do you do to the gain trim on the board versus a low output device (like a passive guitar)?

 

So no, you cannot defy the laws of physics with a wah pedal.

[bruiser_dup2]

Originally posted by C. Alexander Claber:

How many more times? No DC. Clipping is bad because it allows the amp to put out more than its rated power (voice coil over-heating), with less cone control (speaker over-excursion) and more HF content (unhappy tweeters).

 

Alex,

 

The textbook definition of clipping is that the signal has exceeded the linear range of the amplifier, and there are flat (DC) sections--

the limits of the amplifier are DC voltages. When you reach that level, the signal has DC components. The previously sinusoidal wave takes on the characteristic of a square wave, with the results you mention-- less cone control and more high frequency. But if there was no DC component, you would not call the signal "clipped."

 

Bruiser

[Raven]

Perhaps I oversimplified when I said clipping causes DC current.

First, it is important to understand how manufacturers actually determine the RMS power rating of an amp. Putting all the math and other stuff aside, the amp is driven at its rated output with a 1 Khz signal for at least 10 minutes and the maximum THD (total harmonic distortion) does not exceed 1%.

First, 1% is a lot, second, your bass doesn't generate a 1khz pink noise signal. If you ever have an opportunity to look at your bass' output on an oscilloscope, you'd see the signal is all over the place, with harmonics many times the fundamental frequency. If you push an amp too hard it creates spikes, which while not technically DC, the shape of the spike is such that it might as well be. It causes the speaker cones to exceed their maximum linear excursion, (x-max). This causes damage and if allowed to continue, the speaker will be ruined.

The 1 1/2 : 1 ratio of amp power to speaker power is my personal rule of thumb, cause I like the assurance of knowing the power is there and the amp will never have to bust its ass to get the sound I need. I don't mean to imply that you can pump 500 watts into a 100 watt cab and not let the smoke out of the speakers. If you really need to increase your volume, add more speakers and move more air. Just don't drop the total speaker impedence below the minimum impedence of the head. That will let the smoke out of the amp. It's like having a car with a 320HP engine as opposed to a car with a 110HP engine. When you're trying to get onto the interstate, and all the cars are going 75 MPH, its nice to be able to go from 0 - 75 now. (what are those flashing blue lights behind me???)

There ae a multitude of sources online which can explain all this and more, much better than I can. If you're interested, just do a Google search for "RMS vs. peak power", "power bandwidth", "Ohm's law and speaker impedence", or most anything else pertaining to electricity, physics and audio.

Its really worth the time to learn as much as you can about the fundamental principals that determine the sound of the music we are involved in making.

[Raven]

Oh...sorry... how rude of me.... Welcome to the forum Matt...

[Fred TBP]

Matt, to be really honest I've lost touch with all those adjectives like "program" and "continuous". My decision process is much simpler:

 

(a) find out what my lead guitarist is bringing in terms of power output, and double that;

 

(b) for two guitarists: sum their power output, and double that;

 

© if it's too loud, face one of the cabinets towards the drummer; if it's not loud enough, run a signal to the PA board and let the sound person fix it for you.

 

[g.]

Raven:Putting all the math and other stuff aside, the amp is driven at its rated output with a 1 Khz signal for at least 10 minutes and the maximum THD (total harmonic distortion) does not exceed 1%.

Probably should do a search for AES RMS certs - your info here is not correct. Just to start -

 

second, your bass doesn't generate a 1khz pink noise signal.

NOTHING generates a 1 KHz pink noise signal. The two terms are contradictory. PINK NOISE is a not a sine wave at a given frequency - nor is it a fundamental and the usual integer overtones. It is NOISE and like WHITE NOISE represents all useful audio freqencies simultaneously. But usually swept noise is used for testing - this is where an emphasis is swept up and down the bandwidth so that a certain portion of it is always 6 dB above the unswept portion. That stress tests more like a full-program musical signal would.

 

If you push an amp too hard it creates spikes, which while not technically DC, the shape of the spike is such that it might as well be. It causes the speaker cones to exceed their maximum linear excursion, (x-max). This causes damage and if allowed to continue, the speaker will be ruined.

It doesn't HAVE TO overexcurd to cause problems. One could easil send clipped signal to a speaker that NEVER reaches full excursion. All clipping has to do is force the speaker piston to try to switch directions too quickly over and over until the voice coil overheats and fuses/shorts and/or the gap gets bent.

 

* * *

 

Program power for most designs is usually 3 dB higher - TWICE as much when stated as wattage - as the actual RMS by the most stringent AES spec. This simulates the 3 dB of minimum headroom usually desired in a full-program (all the band) signal. Actually the amp hardly reaches even 10 % of its power for very long during a typical program whern peaks are driven to RMS unless tons of hard compression and limiting is used.

 

PROGRAM power rating is not a hard and fast spec to everyone in the industry and is well explained on a tech paper on the Yorkville site, among others.

[g.]

getz76: The poweramp section of your amp doesn't care where the gain is coming from; whether it is the integrated preamp, the bass, or something inbetween the two, it can still cause your poweramp to clip. Gain is gain.

Indeed. I hear this stupid talk about "My volume knob was only at 9 o'clock and my amp was louder than anyone's amp ever made!" BS all the time. All that means is

 

(1) the amp designer weighted the pregain or volume knob early in the scale to reach full gain at a low number so as to give the suckers a false impression

 

and/or

 

(2) somewhere else before that knob a lot of gain has already been applied.

 

* * *

 

The only ways to really get more apparent CLEAN amplitude/volume are to

 

(1) introduce very mild amounts of harmonic distortion so that more upoper partials are represented without seeming distorted - this can be achieved with exciters, tube circuitry, or non-linear subtle overdriving circuitry as is common in many cheaper amps.

 

(2) use compression or limiting so that the AVERAGE (but not PEAK!) gain is higher

 

(3) cascade several of the above, with a cumulative rise in THD.

[Hey Im Matt]

Thanks for all the replies. I understand the wattage thing a little more now.

 

Matt