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Overpowered/Underpowered Sub Woofers


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it's safe so long as you don't turn up the volume too loud. If it sounds like it's distorting (which is about the level most honda civics listen at) it's too loud, back it down or you're gonna blow something.

(Updated 8/22/17)

2005 Outback FMT

Running on Electrons

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You need to match RMS power for both the amp and the sub. I highly doubt, unless you spent a lot of $$$ that you have an amp capable of 1200 rms. Most cheaper amps advertise with ridiculous claims about their power ratings. Some of the cheaper amps will advertise 800W but really only put out ~120W rms.

 

I remember friends in school that bragged about blowing up subs with their 1200W Legacy amp. What actually happened is they underpowered the subwoofers and damaged them that way.

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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.

Edited by ean611
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You need to match RMS power for both the amp and the sub. I highly doubt, unless you spent a lot of $$$ that you have an amp capable of 1200 rms. Most cheaper amps advertise with ridiculous claims about their power ratings. Some of the cheaper amps will advertise 800W but really only put out ~120W rms.

 

I remember friends in school that bragged about blowing up subs with their 1200W Legacy amp. What actually happened is they underpowered the subwoofers and damaged them that way.

 

 

It is an expensive amp and the amps you speak of are what most people get just because its cheap. But you get what you pay for

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As long as you tune it right (assuming the amp is within the range of the subwoofers RMS at a specific ohm level) you shouldn't have any issues with blowing a subwoofer.

 

RMS(continuous) power is the most important thing to pay attention to. Amp's RMS ratings are rated at (12.5v, 13.8v, 14.4v etc.) so therefore a lot of amps are underrated.

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In regards to underpowering, its better to have an overpowered amp rather than underpowered because you can always turn down the amp. Underpowering a subwoofer is just as bad as overpowering with the gain set too high. This causes clipping and can kill your speaker.
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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.

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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.

 

Well I can tell you that I just bought a Elemental Design nine2x amplifier and its rated at 200Wx2 RMS at 4 ohms (input voltage 12.5v).

 

http://www.edaudio.com/store/product_info.php?cPath=22_31&products_id=54

 

That would make that amp underrated and its worth noting with certain amps that are rated lower like this one.

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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.
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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.

 

I think the new JL HD amps can run lower as well and still retain the same output. There's a switch for low/high voltage.

 

Either way, why does this thread have a sticky?

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In regards to underpowering, its better to have an overpowered amp rather than underpowered because you can always turn down the amp. Underpowering a subwoofer is just as bad as overpowering with the gain set too high. This causes clipping and can kill your speaker.

 

Clipping will not kill a speaker. There is only two things that can kill a speaker. Too much instantaneous power, which = mechanical failure or too much average (long-term power), which = thermal failure.

 

Things that DO NOT kill speakers:

clipping

distortion

underpowering them

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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).

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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).

 

Not possible. Speakers can only fail via the two modes I mentioned above. A speaker does not care, nor can it discern if a signal is clipped or clean, it only reproduces what is fed into it. If you had a speaker with a melted voice coil, then you simply overcame the thermal limitations of the speaker.

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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.

 

 

 

If your car is running properly, it should be at about 14.4v all the time for almost all cars. Only when the battery is FULLY charged will it drop to 13.6ish. Only after about an hour or so on the highway will it drop to 13.6ish.

 

For most people, they should never see it lower than 14.4v. Outside temp will change the voltage quite a bit as well, but once warmed up, the car should come back to 14.4v.

 

 

 

RMS @ voltage is entirely dependent on the manufacturer of the amp. You have to look at each one individually and can't make a general assumption that it's rated at 14.4v because it gives a better number. Usually cheaper amps are rated at 14.4v but alot of the higher end ones are rated at 12.5v

(Updated 8/22/17)

2005 Outback FMT

Running on Electrons

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RMS @ voltage is entirely dependent on the manufacturer of the amp. You have to look at each one individually and can't make a general assumption that it's rated at 14.4v because it gives a better number. Usually cheaper amps are rated at 14.4v but alot of the higher end ones are rated at 12.5v

 

Hence my comment about Elemental Design amps being rated at 12.5v. :rolleyes:

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  • 2 months later...
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).

 

agreed. Why do you think stock speakers blow? Stock head units do not have the ability to overpower a speaker, therefore its the distortion that kills the speaker in most situations. You will be fine running an amp that is slightly more powerful than the sub, just make sure that your gain is low (more gain, more distortion) and set your bass EQ lower (higher EQ also causes distortion). Underpowering can damage a sub, but its most often caused by people turning the gain way up on their amps to try and compensate for the lack of power. As a general rule never turn your gain past half way on most amplifiers. I would suggest starting at 1/4 and working your way up slowly until you are happy with the output as this is what I do on all my installs

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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.

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