Speaker to amp power matching
Dra
Posts: 3,777
Hey guys. Lets give this one more go around.
This topic goes around and around and around. Pro Sound Web, Harmony Central, DJ Chat, etc.
Here is my 2 cents. Assuming proper gain structure ....
\"Not enough power kills speakers\" - I think that this is true IF running the amp at or near its capacity. As Gadget has often said, the power supply drops in and out (sags / exhausts) as it approaches it limits. If a amp has 100 watts available and let's say for the sake of discussion that the power supply is 100% stable up to 75 watts. If the amp is producing 75 watts, all is well, whether driving a 75w speaker or a 1000w speaker. If your needs are met (output), fine. But if you need more and push the masters up then first the power supply starts acting up and/or clipping begins. Seems as though I read that a clipped output can actually be double the wattage or the amp rating. The 75w speaker dies a pretty rapid death while the 1000w slowly goes the way of all good dogs. If the amp is only allowed to out put 75w, then the 75w speaker would live a long and fruitful life and the 1000W speaker should last until the cone rots. Granted, there are tonal issues, but that is not not considered here.
\"2 to 4 times rated (continuous) power\" - Well that obviously is 1 to 2 times Program power and not more than Peak power. The key here is reserve power. This extra power, if used, can melt a coil or make the cone fly apart. Here's an example. Put a 60,000 mile street tire on a Nascar car. Will it work? Sure, for 60,000 miles (assuming that it doesn't have to go beyond the rated speed parameters of the tire). If the max recommended speed is 85mph, they may do well at 100, maybe 125 for a short period of time. But they will not last long at all at 180 - 200mph. Can you enter the race with all that power and only street tires? Yes. Can you win against other drivers with racing tires? Obviously, No. Can you finish the race? Yes. Can you reach a goal of 85 mph? Most likely, Yes. However, the moter still has a lot of extra horses under the hood. If at some point in the race you decide to try to run with the rest of the boys and run to the potential of the engine, trouble lies ahead. You could take out the big engine and put in a 78 chevette motor to protect the tires, but now you lose passing power. The obvious solution is to keep the big motor and limit its speed by some means, but not necessarily it horsepower. In the same way, I think, amp potential is more important than amp output when matching to speakers. But amp output should be limited to somewhere between program and peak ratings, but in the lower section. I would suggest for a 400/800/1600 speaker, that actual output from the amp be limited to 1000 - 1100 wats. Limiters on amps can't provide this kind of limiting. They only keep the amp from clipping and will allow full power output. The limiting needed here is like that in the 260 or others with brick wall limiting prior to the input of the amp. The DRPA helps, but limiting has to start much earlier and in reality can't stop a stubborn soundman.
Too much power will kill. The coil is rated to a certain wattage, which basically determines how much heat it can produce before it fails. The amp is a heat producer, with it's own heat rating. The movement of the cone helps remove the heat but if the heat can't be removed as fast as the amp is producing it. (I am not saying that the more the cone moves the cooler it gets.) Bottom line - A 200w (cont) coil can dissipate 200 continual watts of energy, 400 grogram watts of energy (averaged on and off) and 800 peak watts (very occasional).
Sooo...
Too much power IS never enough, IF limited to the capacity of the speaker. The problem in every system is supply & demand, and knowing when to say, \"That's all there is! She only built for warp factor 8. If we try warp 9, she'll break up!\"
Let me have it!
DRA
This topic goes around and around and around. Pro Sound Web, Harmony Central, DJ Chat, etc.
Here is my 2 cents. Assuming proper gain structure ....
\"Not enough power kills speakers\" - I think that this is true IF running the amp at or near its capacity. As Gadget has often said, the power supply drops in and out (sags / exhausts) as it approaches it limits. If a amp has 100 watts available and let's say for the sake of discussion that the power supply is 100% stable up to 75 watts. If the amp is producing 75 watts, all is well, whether driving a 75w speaker or a 1000w speaker. If your needs are met (output), fine. But if you need more and push the masters up then first the power supply starts acting up and/or clipping begins. Seems as though I read that a clipped output can actually be double the wattage or the amp rating. The 75w speaker dies a pretty rapid death while the 1000w slowly goes the way of all good dogs. If the amp is only allowed to out put 75w, then the 75w speaker would live a long and fruitful life and the 1000W speaker should last until the cone rots. Granted, there are tonal issues, but that is not not considered here.
\"2 to 4 times rated (continuous) power\" - Well that obviously is 1 to 2 times Program power and not more than Peak power. The key here is reserve power. This extra power, if used, can melt a coil or make the cone fly apart. Here's an example. Put a 60,000 mile street tire on a Nascar car. Will it work? Sure, for 60,000 miles (assuming that it doesn't have to go beyond the rated speed parameters of the tire). If the max recommended speed is 85mph, they may do well at 100, maybe 125 for a short period of time. But they will not last long at all at 180 - 200mph. Can you enter the race with all that power and only street tires? Yes. Can you win against other drivers with racing tires? Obviously, No. Can you finish the race? Yes. Can you reach a goal of 85 mph? Most likely, Yes. However, the moter still has a lot of extra horses under the hood. If at some point in the race you decide to try to run with the rest of the boys and run to the potential of the engine, trouble lies ahead. You could take out the big engine and put in a 78 chevette motor to protect the tires, but now you lose passing power. The obvious solution is to keep the big motor and limit its speed by some means, but not necessarily it horsepower. In the same way, I think, amp potential is more important than amp output when matching to speakers. But amp output should be limited to somewhere between program and peak ratings, but in the lower section. I would suggest for a 400/800/1600 speaker, that actual output from the amp be limited to 1000 - 1100 wats. Limiters on amps can't provide this kind of limiting. They only keep the amp from clipping and will allow full power output. The limiting needed here is like that in the 260 or others with brick wall limiting prior to the input of the amp. The DRPA helps, but limiting has to start much earlier and in reality can't stop a stubborn soundman.
Too much power will kill. The coil is rated to a certain wattage, which basically determines how much heat it can produce before it fails. The amp is a heat producer, with it's own heat rating. The movement of the cone helps remove the heat but if the heat can't be removed as fast as the amp is producing it. (I am not saying that the more the cone moves the cooler it gets.) Bottom line - A 200w (cont) coil can dissipate 200 continual watts of energy, 400 grogram watts of energy (averaged on and off) and 800 peak watts (very occasional).
Sooo...
Too much power IS never enough, IF limited to the capacity of the speaker. The problem in every system is supply & demand, and knowing when to say, \"That's all there is! She only built for warp factor 8. If we try warp 9, she'll break up!\"
Let me have it!
DRA
0
Comments
http://srforums.prosoundweb.com/index.php/t/36920/0/
and I am the one that started this whole thing here by PM'ing the principle posters here...
My opinion is tempered by guys like John Roberts (the designer of much of Peavey and Crest amps and such) and this was the statement that got me questioning myself:
\"The clipping didn't blow up the speaker. The fact that the fader was pushed up so far that the amp was heavily clipped, means the average power of the waveform (the part that makes heat in the voice coil) was also very high. It was the very high average power of the waveform that melted the voice coil.\"
He further stated:
\". Again the problem is not because the wave form is a square wave but because that sine wave is turned up so far the average power is 2x what a clean sine wave could make. If that same gain setting was applied to a bigger power amp, it would probably make even more power and blow up the speaker even faster.\"
Now, that makes sense...its the AVERAGE power here. Think of it in terms of an over compressed signal where the average power the amp is expected to put out is greater and greater. The power the amps put out is dissipated in the form of heat... pure and simple. The only mechanism the speaker has to dissipate said heat is in the motion of the voice coil as it moves through the air. Some speakers have vented gaps, heck Peavey now claims to have a ram air cooling system for it's new Neo woofers...one of the problems with speakers that use fixed magnets has always been that the more you heat up the magnets the less gauss (magnetic field) is present, but when the magnet cools, it's potential returns. This can also act to exacerbate the problem because as the magnetic field is reduced, the movement of the coil within the field is also reduced...further exacerbating the problem...
As for the flat top wave form, be it exhausted power supply, or synthesizer square wave/sawtooth... whatever output, the speaker doesn't see any difference, and that alone won't fry the speaker, loosen the glues so that the coils fly off and get sheared in the mechanism... or whatever. It's the heat not being dissipated sufficiently by the motion of the voice coil, or it's ability to withstand the heat it's subjected to.
An amps duty cycle, (the amount of power it is required to put out) is never a continuous thing. It's usually (in most music) off, or low, a whole lot more than on (if you will excuse the over simplification) but with some types of music, like extreme metal (Dragon force comes to mind... and if you haven't heard them or if you are a drummer you really should get your eyes opened by these insane freaks) that unleash such sonic fury that the amp is called upon to be on more than off.. well there were getting into high average power, and if we cannot cool those coils (which even under normal conditions can get in the 500 degree and more temperature range for rock concert volumes) guess what... The SMOKE GETS OUT... and once out, you cannot get it back in.:shock:
So I still think (as Dra pointed out.. you have the horsepower in most cars today to get up to well over 100 miles an hour in less than a mile... but you don't need to...do you? but none the less the power is there) more power is better than less... but there is a limit the speakers can handle and using a 10,000 watt amp on speakers that are rated @ 1000 watts is overkill, but meted out properly will have twofold benefits...
1. The sound will be much tighter, more controlled if you will (less power compression
2. The amps won't have to work as hard and will most likely last longer.
And of course, for those instantaneous bursts the power to NOT double the output that a clipped amp exhibits...is there, and MUCH less likely to fry the voice coils... :idea:
Well, that's my take on it...
G
So I guess, the next critical discussion will turn to truly limiting for speaker protection and away from speaker protection by limiting the amps ability to clip.
DRA
PS - I liked Gadget's top speed example better than mine.
http://srforums.prosoundweb.com/index.p ... msg_346584