ean611

I didn't say it becomes an 800w amp, as it is not an 800w amp in effective music power, or any realistic rating. However, understanding the max theoretical power output (square wave to the voltage rails) will produce significantly more power than the amp is rated for, but not in a way that will sound anything like the music you're trying to reproduce. I think we're debating semantics here, as we've all destroyed woofers at one point or another, typically proceeded by speaker distortion.

Biz77, looking over how I went through that, I think we're saying the same thing. The point of bringing up the voltage rail was exactly that point, which is simply pointing out how a small "underpowered" amp can still damage a speaker. The reason is still overheating/overpowering the voice coil, but the point is that you can blow up a 75w speaker with a "50w" amp.

Example for above: http://legacygt.com/forums/images/editor/separator.gif Amp has voltage rails at +42V and -42V (This is Class A, rather than class AB) Amp could be rated at 400w RMS at 4Ohms. (leaving small margin over rating). Peak power of amp while distorted would be significantly higher, approaching a theoretical limit 882w at 100% duty cycle. If one were to add more margin, bringing the voltage bias significantly higher for the same rating, let's say +60V/-60V, the RMS power rating could be unchanged, but the max distorted output of the amp has increased significantly. Bottom line, power output can increase beyond rating, and will only stop at electrical limits.

mwiener2, I've got melted voice coils to show for it Biz77, the ripple is often too small to matter in this case. An average sub woofer will have virtually no response above 200-300Hz. Also, when you're running distorted power through a speaker, you're turning your theoretical sine wave into a square wave. (not fully, but the power calculation becomes more complex). This will output more power than the amp is rated for, assuming the transistor and power supply can support the voltage. The amp is rated at a power and THD level, for instance 50 w @ .1%THD. That does not mean that the amp cannot output more power at an unacceptable level of distortion (85w @ 20%THD). In a good number of cases, you're seeing this, and it will melt the voice coil. Amps typically do not publish how much power they can truly output if you're not concerned about harmonic distortion.

biz77, I'm simplifying, but let's take a 60Hz sine wave. If you clip off the top and bottom 25%, take a look at the waveform. For a short period of real time, you're effectively providing DC voltage (around .21ms) to the voice coil. (.42ms total distorted time) If you measure the voltage provided from when the clipping starts at t=0, between t=0 and t=.21ms, you're going to see the voltage rail, and this static voltage will appear to be DC. This type of action will melt many voice coils. (Excluding seriously overbuilt drivers, but almost everything today isn't manufactured with that kind of margin). This can melt voice coils, as heat buildup during that time frame will compound, and since the woofer is now not moving for periods of it's oscillation, there is less airflow than design spec over the voice coil.

well, I have two 200w subs, and an 800w amp Trick is as long as I don't turn up the gain to the point of getting the subs to their xMax, I'm good.

roosien092, to be clear, you are not describing "underpowering" a sub, you're describing running DC voltage through the voice coil (distortion). Running less power than a sub is rated for will not damage it. Overheating the voice coil due to short term DC voltages can.

no worries, JaeGT, thought I'd seen the car before though, but guess the owner isn't reading this thread.

Never said I heard it, just saw it. Where'd you see my car? Couldn't have been Monday, as I had a stupid rental Charger.

I saw a DGM LGT in the center of Framingham on Monday around 5:35 (rt126 just north of the traffic circle there). Had what might have either been Invidia or some other exhaust. Tinted too.

To bump this thread, check this out. http://i96.photobucket.com/albums/l177/ean611/DSCN1106.jpg I don't think I need to add anything

finse, I think the bigger issue is that Village Subaru is more interested in selling Outbacks and non-turbos (their volume sellers). If they really wanted to unload the Spec B, they could register as a vendor here, and get rid of it relatively quickly. I also think that it may be sitting because only people who know what it is would want it, as if you randomly test drove it, and didn't realize that those are snows, it would be an issue. Also, the newer Spec Bs have 6MT, and I believe that one is 5MT. Good luck.

finse. The engine bay was sparkling clean. I mean dealer off the truck clean. I found that odd for a car with 58k miles Also, it has aftermarket rims on it, (I forget if 17 or 18) with snow tires. Good luck and let me know if you check it out!

Saw a black Leggy with a "18" on the rear left window on prospect st in Waltham.

Biz77, Clipping and distortion can damage speakers, as both can cause voice coil overheating with under designed voice coils. Some speakers can handle pure distortion, but most drivers cannot sustain certain distortion effects. I've melted the voice coil of an old Phoenix Gold XS130 woofer in this method. (Amp was nowhere near powerful enough to cause effects based on rating alone).

I'm familiar with Elemental Designs. They're a small outfit, and they would be the exception, not the rule. CEA2006 attempts to address this, but I still see many amps rated at 14.4V.

hutru01, the input voltage has little to do with meaning the amp is underrated. In fact, most amps are rated at 14.4V to give them the highest number. For average car use, you're going to see around 13-13.6V typically while the car is running, and that is a safe range to use for power assumptions. Also, I'll be adding some charts to demonstrate clipping to my long post when I get some time.

I agree CCSubaru, Hence the long post about amp power. I'm going to add more to it as I think it's good info for people who are asking these questions

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.

CCSubaru, What amp is it? There are many amps that make wattage claims that they can't deliver. Bottom line, what mwiener2 said, just don't turn it up too much on the amp, and it'll be fine.

I saw an OBP Wagon yesterday at Kimball Farms in Westboro. It had Saab wheels wrapped in Bridgestone RE050s

It's crystal clear and LOUD

BigInALegacy, coulda used an install meet, just did this: http://i96.photobucket.com/albums/l177/ean611/DSCN0905.jpg It's freaking sweet

I always have something that I need to work on. Plus, I have new reference monitoring gear, be glad to test it out on people's cars

Saw an OBP LGT definitely with a modified exhaust. You were sitting at the light on westbound RT 30 at the intersection of 126.