amp watts vs gain

[madball24]

the board i usually go alittle higher than 0db and on the amp its at 2 oclock. my amp doesnt have numbers just markings thats why i use the clock term

[madball24]

i figured out where i have my amp it is at 6db on both channels. The guy told me that he sets his limiter at 6db but to be safe u can set it at 0 is this correct?

[agedhorse]

I have my limiter set at 0 db is that okay

 

 

No way to know. Maybe, but maybe not.

 

You are officially in over your head. This is why powered speakers are a better choice for most folks if you plan on pushing your gear hard.

[Dogoth]

Professionals do NOT leave their amps wide open!

 

 

Agreed.

 

I set it up where the amp limiter comes on about 6 to 12db before the board output metering clips (there is sometimes another 6-10db usable gain above that, depending on the board). OK sometimes as much as 20db more usable gain (above the top of the meters (this is less true of digital boards, where -12 metering = 0 db out)).

 

I really try not to come anywhere near the max output of a mixer (If I do I'm doing something seriously wrong). Just remember make all of the meters red and it'll sound better (joke of course).

[dboomer]

Agreed. I set it up where the amp limiter comes on about 6 to 12db before the board output metering clips

 

 

Why? You SHOULD be setting your limiter where it protects your speakers and not to prevent your board or amp from clipping. Your mixing should do that.

[agedhorse]

Why? You SHOULD be setting your limiter where it protects your speakers and not to prevent your board or amp from clipping. Your mixing should do that.

 

 

If your board clips at the same time as your amps limit, it's exactly the same as operating thesystem without limiters. Exactly the same.

 

How many folks do you know that never run out of PA, never have an accident, and unplanned or unexpected hit input, a lapse of good judgement, etc.

 

The real world does not consist of a perfectly controlled mix. Of all people, I know that you know this.

[lifeloverwg]

If your board clips at the same time as your amps limit, it's exactly the same as operating thesystem without limiters. Exactly the same. How many folks do you know that never run out of PA, never have an accident, and unplanned or unexpected hit input, a lapse of good judgement, etc. The real world does not consist of a perfectly controlled mix. Of all people, I know that you know this .

 

 

Isn't that Dboomers point? If you limit to protect your speakers, you may hear nasty sound if/when your board clips due to poor mixing or attention, but you have a harder time destroying your speakers if they are voltage limited.

 

 

Why? You SHOULD be setting your limiter where it protects your speakers and not to prevent your board or amp from clipping. Your mixing should do that.

 

 

Maybe I'm missing something here, wouldn't be the first time. Winston

[agedhorse]

Isn't that Dboomers point? If you limit to protect your speakers, you may hear nasty sound if/when your board clips due to poor mixing or attention, but you have a harder time destroying your speakers if they are voltage limited.

 

 

No, I don't think so.

 

Voltage limiting doesn't protect the speaker in the case of hard clipping because two things happen...

 

1. the waveform changes shape and the thermal power increases up to 2x the unclipped value for the same voltage.

 

2. The duty cycle increases which decreases the peak to average ratio and the average power delivered goes up. this means more power to the speaker also.

[Dogoth]

Why? You SHOULD be setting your limiter where it protects your speakers and not to prevent your board or amp from clipping. Your mixing should do that.

 

 

Sorry, I guess I didn't explain enough. I was refering to the internal limiters in the amp that are of course preset to just under the amps voltage rails (no "clip" lights for me). Except for an occasional kick drum I rarely hit the limiters in real world use (FWIW the amps are rated at about 60% of what the speaker is rated at). In this part of the system I haven't lost a driver in years. If I know I'm going to have a hard hitting rock band, I'll rent a drum sub.

[Dogoth]

No, I don't think so. Voltage limiting doesn't protect the speaker in the case of hard clipping because two things happen... 1. the waveform changes shape and the thermal power increases up to 2x the unclipped value for the same voltage. 2. The duty cycle increases which decreases the peak to average ratio and the average power delivered goes up. this means more power to the speaker also.

 

 

So true. Limiters (like the ones in most modern amps) really only takes the transient edge off of the wave form (possibly saving high end drivers). If you're into limit all night long you are causing a lot of excess heat in the VC and pushing your amp beyond it's thermal design limits as well (like agedhorse said, actual power is predicted by amplitude and duty cycle).

[lifeloverwg]

No, I don't think so. Voltage limiting doesn't protect the speaker in the case of hard clipping because two things happen... 1. the waveform changes shape and the thermal power increases up to 2x the unclipped value for the same voltage. 2. The duty cycle increases which decreases the peak to average ratio and the average power delivered goes up. this means more power to the speaker also.

 

 

 

JRBLE wrote; So true. Limiters (like the ones in most modern amps) really only takes the transient edge off of the wave form (possibly saving high end drivers). If you're into limit all night long you are causing a lot of excess heat in the VC and pushing your amp beyond it's thermal design limits as well (like agedhorse said, actual power is predicted by amplitude and duty cycle).

 

 

Right! Two times.

Which is why I understand Dboomer to be saying that in the end it's your mixing that is the final limiter.

 

Maybe I'm just reading it that way because that's how I operate. My sub amp is rated for just a bit under 1.5X the RMS rating of my sub drivers and the only real limiter in use is the internal amplifier clip limiter. When the clip limit lights starts to flicker on the kick hits, I know that's all I've got availible in my system and "I" limit my mixing to that level. My DRPA limiter is set to start limiting right after the amp clip limits for some further protection, but I don't rely on it.

 

My tops are actually running off an amplifier rated at 3X the RMS handling of the drivers. (Don't try this at home kids!) On them I have the DRPA set to limit just before the internal speaker protection kicks in, but "I'm" still the real limiter, because the tops start to sound like crap just before they go into limiting. And, by chance, with the style of mix I like, I run out of sub level just before the tops start to sound like crap.

 

As other threads have demonstrated, bad operators can destroy even well protected and limited systems despite the engineers best efforts when driven to the ragged edge. The recent JBL PRX threads come to mind.

 

Size amps reasonably, limit for further protection, but in the end understand that it's still going to be up to the driver to operate the system within it's "limits" no matter where you add the gain.

 

Winston

[dboomer]

You guys are missing my point.

What does "0" relate to in terms of the speaker's power handling ability. It's completely different if we are talking about 10w than if we are talking about 10,000W.

Andy's point about voltage limiting not protecting assumes facts not in evidence. Power handling (thermal) limits are power limits. It doesn't matter how you get there. It doesn't matter if you have 1/2X 1.5X or 150X power available ... it only matters what power you actually deliver and for how long.

The other thing is that you can repeatedly overpower a speaker by a large amount without harming it ... because ... you are still probably nowhere near continuous at this point. Now before you run off and start overpowering speakers you need to really understand what I mean here.

Clipping does not cause a problem to speakers. Repeat this 3 times out loud. The wave shape doesn't matter at all ... only the power. I fully understand that different shapes have different duty cycles and that a square wave has twice the power of a sine wave. I think a lot of users do not understand that it's not the Watts that causes the problem ... it's the power.

Second point ... the dB numbers on all of your gear only mean something in relation to something else. Usually they are referenced to some standard in which case the could be a voltage value (or similar) ... but if your systems is not calibrated (gain structure) then they don't mean anything in terms of your system (which is what I think most of these questions are really asking)

[SteinbergerHack]

I think a lot of users do not understand that it's not the Watts that causes the problem ... it's the power.

 

 

Great post. However, Watts ARE power, by definition.

 

I think that what you meant to say was that instantaneous or rated Watts aren't what cause the problem, it's total power integrated over time - which is ENERGY.

 

A speaker can only get rid of heat energy at a certain rate. If the rate of heat input (i.e. power input / speaker efficiency) exceeds the rate at which the speaker can dissipate the heat, the speaker will eventually fail when the voice coil overheats.

 

That said, it IS possible to fail a speaker mechanically with an instantaneous over-power event - but it generally takes a REALLY big power peak to do so.

 

 

Second point ... the dB numbers on all of your gear only mean something in relation to something else.

 

 

This is probably the single most important message anyone could take from this thread.

[Dogoth]

Second point ... the dB numbers on all of your gear only mean something in relation to something else. Usually they are referenced to some standard in which case the could be a voltage value (or similar) ... but if your systems is not calibrated (gain structure) then they don't mean anything in terms of your system (which is what I think most of these questions are really asking)

 

 

You are absolutly correct and this IS something that many don't grasp. The decibel scale is purely a relative thing. It's based on a log square scale but where you place 0 can be anywhere. Over the years there have been some standards for 0db set forth, but they are by no means set in stone. Examples would be dbv, dbu, dbm, and the most elusive of all db spl (which weighting scale would you prefer today?).

 

It's like the log square number line on a slide rule (anyone remember those). You can slide it to make 0 begin anywhere you want, relative to the linear number line.

[dboomer]

 

Great post. However, Watts ARE power, by definition.

 

 

Ah -ha! Watts actually are a derived unit of power which is not exactly the same thing. That's the rub

 

Duty cycle is the missing component, which is commonly not considered when stating amplified power in Watts.

 

Watts in the context of power amp measurement is most commonly derived from voltage amplitude usually figured at RMS value. Music is rarely (or never;)) sine wave only.

 

I'll give you energy though:thu:

[Shaster]

Just when I thought I knew what I was doing, a thread like this comes along. Ouch my head hurts.

Wanted to comment on running amps wide open. There are times I run my amps wide open because of the sticky finger factor. I've had people (I actually call them worse) mess with the amp's attenuator mid production... and have found it hard to return to the original position (bad memory, no markers). Wide open just eliminates a varable in the "music in the trenches" gigs. I'm talking only of amps that are "underpowering" my speakers. I realize this is not necessarily the "proper way" but neither is putting drinks on my subs!

Off to find a slide ruler now.

[agedhorse]

Watts is a unit of power. Not derived, but a unit of power.

Watt-seconds (or minutes or hours) is the time integrated measurement of energy

Duty cycle is directly related to energy, in that as the duty cycle increases, the energy increases. This can be due to number of cycles or duration of cycles. For example if you have a signal that is 5 cycles at 100% power and 20 cycles at 0% power, you have a waveform with 25% duty cycle and the energy will be 25% of the full power energy integrated or available over a given time period. Frequency plays into this as duration, and power handling can vary in part because the time slice of 5Hz at 20Hz is 1/4 second whereas 5 cycles of 1kHz is only 5 mSec. So 2 x 5 cycle bursts per second of 20Hz is 1/2 second at rated power and 2 x 5 cycle bursts per second of 1kHz is only 10mSec per second. Which has the greatest energy (heating effects)? Even though the number of cycles is the same, the duty cycle of the 20Hz signal is much higher and the 20Hz signal contains 50x the thermal energy for the specified test signal.

All of this stuff goes into how we develop power handling specifications and some of us choose to be more conservative because clearly it's a confusing subject and lots of abuse occurs out in the field. The marketing folks like big numbers because it makes them feel more manly and sells product to the less educated better. In the big picture, it makes the industry look bad, when folks blow up speakers even though they think they are powering ok because of the marketing crapola.

[agedhorse]

That said, it IS possible to fail a speaker mechanically with an instantaneous over-power event - but it generally takes a REALLY big power peak to do so. This is probably the single most important message anyone could take from this thread.

 

 

Or a bunch of events.

 

This is probably the most common failure I see these days with people buying into the bigger amp is better syndrome. The speaker is a spring and as long as you remain in the linear region, everything is good, As soon as you go beyond the elastic limits, the fibers begin to distort and tear in the suspension components. Alignment suffers, the spring becomes stretched, the TS parameters shift and the driver is no longer loaded properly by the box. That's the usual order of failure.

[dboomer]

Wide open just eliminates a varable in the "music in the trenches" gigs. I'm talking only of amps that are "underpowering" my speakers. I realize this is not necessarily the "proper way" but neither is putting drinks on my subs!

 

 

Agreed ... of course you could do it the way we did in the good old days and insert a pad in the line, keeping the knob wide open and reducing the drive at the same time.

 

I don't know why you think it makes a difference whether the amp is big or small however.

[dboomer]

people buying into the bigger amp is better syndrome. .

 

 

Depends on how you define "better" and how you operate the system. Bigger amps most certainly have advantages ... if you are willing to accept the risks.

 

Again I'll say that simply driving your speaker over their rated limits isn't usually the problem ... it's driving them grossly over their limits and even then mechanical issues outweigh thermal issues by 1 number like 10:1 or better (IMHO). It's all the other things in a poorly setup and poorly run system that are much bigger culprits that simple power.

[agedhorse]

I will say that bigger is not better for the majority of users. I am not talking about the top 5% of users but the masses.

The average user just does not (and does not care to) grasp all the technical details that are necessary in order to safely run speaker powered above say 1.5x the "RMS" power. So, for them, an amp that's smaller may indeed be better in the big picture. If it improves their reliability, that's generally a very important factor.

Same thing applies to the kid who buys a car with 500HP because bigger is better. Without really understanding the limits (which takes knowledge as well as practice/experience), the kid is likely to end up in a ditch hurt. Put the same car in the hands of a real pro driver and it will be plenty safe because he understands all the tradeoffs and limitations. It's one thing to have 500HP available all the time and another thing to use the 500HP only when it's really necessary AND safe.

[dboomer]

We don't disagree ... well except that "Watts" are indeed "derived" because they are not one of the "base" units:thu:

[SteinbergerHack]

We don't disagree ... well except that "Watts" are indeed "derived" because they are not one of the "base" units:thu:

 

 

Sure but since there isn't a "base unit" for power, it is safe to say that Watts are a legitimate unit of power - which was what I posted. (Should we convert everything to ergs/second just to confuse the guy looking for an attenuator setting for his amp?)

[agedhorse]

Sure but since there isn't a "base unit" for power, it is safe to say that Watts are a legitimate unit of power - which was what I posted. (Should we convert everything to ergs/second just to confuse the guy looking for an attenuator setting for his amp?)

 

 

Oh, this just brought back some basic physics memories... yikes.

 

So going back further, that would be dyn-cm/sec? Now why I would remember this is even more scary.

 

A Watt is defined as 1 volt x 1 amp. It's pretty basic, even whey you get into reactive power, a Watt is still the voltage x the real + imaginary current P=V(x+jy) where I=x+jy

 

Now for (more) practical terms, we use the term power factor which is the ratio of real vs. apparent power so if for example we are driving a reactive load with a phase angle of say 45 degrees (somewhat typical of a really inductive LF driver), the power factor is I x cos 45 deg = I x .71 This means that the real power is the voltage x the current x .71.

 

So for those of you who are reading between the lines, the whole power thing has a twist... an amp can not ever deliver full rated power into a real world speaker (which is why more speakers do not blow up) due to the reactive part of the load. In this case the amp delivers 71% of rated power but the currents and voltages are as high as if it were trying to deliver 100%. This is something that we as amp designers must take into consideration when designing output stages. Fortunately it affects all amp manufacturers alike, so even though your amps are rated in resistive power, the deratings apply to everybody equally (provided their protection circuits are aware ofthis.)

[Dogoth]

an amp can not ever deliver full rated power into a real world speaker (which is why more speakers do not blow up) due to the reactive part of the load. In this case the amp delivers 71% of rated power but the currents and voltages are as high as if it were trying to deliver 100%. This is something that we as amp designers must take into consideration when designing output stages. Fortunately it affects all amp manufacturers alike, so even though your amps are rated in resistive power, the deratings apply to everybody equally (provided their protection circuits are aware ofthis.)

 

 

Are you speaking of the back EMF that must be absorbed by the output stage due to the inertial (overshoot) of the cone. Is this called damping factor?

 

I've always wondered how those super small, high powered amps like Powersoft can absorb this (doesn't it have to be dissapated as heat?). Where are the heatsinks? To me it's just FM.