ibhknl

Still not getting the point?

 

For what its worth, I like more power and properly set gains.

This is the bottom line for this thread and it’s been said at least every 3rd post in one form or another.

Set your gains kiddies. Learn to listen to your drivers (speaker, woofer), learn to hear them reaching their mechanical limits then back off. If you do this your speakers will last a long time.

I still have my JL10w3 subwoofer from 12 years ago, bumping away, its been in 3 generations of Legacy's. "OVERPOWERED" by the same amp the ENTIRE time. Anecdotal? Yes. But if I go outside and push that woofer beyond its mechanical limits (by feeding it too much power: cranking the gains) I will be replacing it by the end of the month.

I'm only saying this again because beyond all the technical info and arguing, it's all you need to know. Set your gains.

yeah, too late. everyone here already knows that the best quality sounds REQUIRES a 2000w amp and dual bandpass 15's in a 3CuF enclousure

Add a Little Wayne CD and we are set.

Rage33 et al. You cannot "Underpower" a sub woofer and damage it that way, period. (he likely had a crappy sub and a crappy amp, see following)

 

What an amp does is amplify a semi-sinusoidal wave from a low voltage to a higher voltage. The way the amp works is that there are two limits to the amp. One is the voltage that the MOSFET operates at, which once you try to exceed it, you get distortion, which can sometimes but not usually damage a sub, but this is not "underpowering". The second limit is the power supply to the MOSFET. If the FET is biased at a certian voltage, but once the current draw is demanded to support the voltage, the voltage may drop on the rails, also causing distortion. This is how they can claim power greater than the amp can really produce, becauce theoretically, a FET biased at a certian voltage can produce power at a level proportional to the voltage. (Power = v^2/r = i^2*r).

 

For example, if the FET in the amp FET bias has 40v peak to peak, in ideal conditions it can produce 400w at 4ohms. However, most amps are between 50 and 65% efficent (class AB), and for subs, somtimes around 80% efficent (class D) This means that if you look at power consumption, you have to consume a minimum of 500w of power to produce 400w for the sub. (more typical would be 650-800w, or in a car, 50-60A current @ 13.6V). What this means is that if the fuses are not set with some margin over these values, the power supply cannot consume that much power, and the rating is bullsh*t. (Also, typically one of the rails will fail first in a Class AB setup, as if both rails are same distance from the signal, that's Class A, but class A isn't typically used in cars as it's ~25% efficient, but for the sake of this explination, that's just a detail.)

 

There are two types of power in a FET, static power and dynamic power. Static power is typically small, and is used to bias the FET, and the dynamic power is when the FET is changing state. This means it is possible to consume a small amount of static power, rate an amp at a high wattage, because it is biased with very high voltage rails, but not have a power supply to support it, therefore causing the design th "fail" under load, and not produce the power desired by the end user.

 

Where I was going with all of this is that like I said earlier, if you try to demand too much from the amp, the waveform will run into the voltage rails, and you will have a very horrible distortion, which can damage a sub, but is unlikely to, as you're at a low power, and should not be able to heat up the voice coil enough to melt it.

 

On the other hand, "overpowering" a sub would mean you're trying to push the cone further than the voice coil can allow, and this would mean that at the extremities, the voice coil is not moving, and may heat up and melt. Also, you would be at a higher voltage than the vendor spec'd the sub for, and can damage it. The solution here is don't turn it up too loud, and you'll be fine. My sub channel can push ~600w at 2 Ohms, and my pair of subs are rated at 250w each. However, unless I push the maximum power (read, VERY high volume), it will not be an issue. Keep in mind, a 10w sine wave @ 630Hz will be almost deafening on most speakers. (BA Z6/SPZ60s not withstanding, they're very inefficient).

 

Another note, the reason for overpowering is to get a bigger power supply and higher voltage bias rails. This means that when you run the amp under normal (read: not rock concert deafening or louder), you're running the amp at less of a percentage of it's maximum, which is generally desireable. Given the same amp vendor and model line (say JL Audio 250/1 and 500/1), the higher power amp will, in theory, be better on the same sub at the same volume, as it's operating at less of the amp's rated maximum. (It is often difficult to compare wattage numbers across different amp lines).

 

 

Just wanted to add, an example. There is a Kenwood Excelon amp in my room (belongs to a friend). It claims on the shell that it produces 1200w. (5 channel amp, KAC-X6500). This is impossible, as the math demonstrates. There are two fuses on it, 30A each. This means that the amp will draw a max of 60A (most likely a bit less as you don't want to tempt fate by getting too close to blow a fuse). This means at 13.6V, the Amp consumes 816w before the fuses will blow. In all likelyhood, the amp will consume around 600w at a typical max, as the fuses are there in case the power supply fails so it doesn't cause a fire. With 600w consumed, it has around 300-350w in real music power to distribute to all 5 channels. Sufficent to say, the amp, under no circumstance, can generate 1200w in music power.

 

For comparison, I have a Rockford Power1000 25 to life limited edition amp, 5 Channel. Fuse is 250A!!. This means it will consume 3400watts before the fuse blows, and again, it is likely to have margin. If we assume 2800w consumed under maximum nominal load, that means that at 50% efficiency (a conservative number, but safe to make assumptions with), the 1400W it's rated for is a very honest and expected number. Now, like the OP was asking, that amp I have can produce more power than most of the speakers in my car can handle, but I have to exceed the power limit of the speaker before I have a problem. Meaning, if I don't make myself deaf, I have no problem, and consume significantly less power.

 

If there are any questions on amp power, or anything on this topic, I'll update with information as I can.

...and learn to get your gains correctly, end thread.

ps. You ever haunt the12volt forums Biz?