[CordinaTe]

I'm going to be putting 300wattx2 RMS into 2 500watt RMS subs, until i can get a new amp. what exactly hurts the subs? i blew my old subs with this same amp. i'm guessing my friend turned the gain all the way up, and because i am a novice, i thought nothing of it.

any advice?

 

[Neil]

No, "underpowering" a driver does not hurt it. Match your input sensitivity (gain) to the preout voltage on your HU and you'll be just fine.

 

[CordinaTe]

No, "underpowering" a driver does not hurt it. Match your input sensitivity (gain) to the preout voltage on your HU and you'll be just fine.

my HU puts out at 2v

so, like 1/2 way?

 

[Oliver]

A by-product of using too small of an amplifier kills speakers [If the output is not enough the user turns up the gains {15% distortion is hard to hear, at subbass frequencies} which leads to more average power over time ].

Manville quote:

The only thing that thermally damages speakers is power... more specifically: average power over time.

I'll explain...

If you take a given amplifier, let's say 100 watts and operate it just below clipping with music material, the "Crest Factor" of the amplifier's output is equivalent to the "Crest Factor" of the program material.

"Crest Factor" is the difference between the average level of the signal and its peak level. For example, a pure sine wave has a "crest factor" of 3dB, meaning that it's peak level is 3dB higher than its average level. We all know that 3dB represents a power factor of 2, so another way to look at it is that the peak power of the signal is twice that of its average level. So, if we play a sine wave on our 100 watt amplifier, just below its clipping level, the average power (over time) the speaker is needing to dissipate is 50 watts.

A true square wave, by comparison, has a crest factor of 0db, so it has equal average and peak power. Our 100 watt amplifier, playing a square wave, unclipped, into our speaker requires that the speaker dissipates 100 watts of power (twice the heat as a sine wave).

Music has a significantly higher crest factor than sine waves or square waves. A highly dynamic recording (Sheffield Lab, Chesky, etc.) typically has a crest factor of 20dB or more, meaning that its average power is 100 times lower than its peak power. So, if we play our 100 watt amplifier just below clipping with the typical audiophile recording our speaker is only needing to dissipate 1 watt of average power over time.

Modern commercial recordings typically exhibit crest factors of around 10dB, meaning that the average power is 10 times lower than the peak power. So, our 100 watt amp just below clipping would deliver an average power over time of 10 watts that the speaker has to dissipate.

Okay, so what happens when we clip the amplifier (which we all do at times). When the amplifier enters into clipping, the peak power no longer increases, but here's the KEY... THE AVERAGE POWER CONTINUES TO INCREASE. We can often tolerate a fair amount of clipping... as much as 10 dB or more above clipping with a reasonably dynamic recording... a bit less with a compressed commercial recording.

So, if we turn the volume up 10dB higher than the clipping level with our Sheffield Lab recording, we have now reduced the crest factor of the signal reaching the speakers by 10dB... so instead of needing to dissipate 1 watt average, we are asking the speaker to dissipate 10 watts average, and we're probably ok.

If we turn up the volume 6dB past clipping on a compressed commercial recording (or bass music recording), we have taken the crest factor of the signal from a starting point of 10dB to only 4dB, asking the speaker to dissipate an average power of 40 watts instead of 10 watts... that's FOUR TIMES the average power, which generates four times the heat.

SO, in most cases, the reason clipping can damage a speaker really has nothing to do with anything other than an increase in average power over time. It's really not the shape of the wave or distortion... it's simply more power over time.

When someone plays Bass Mekanik clean (unclipped) on a 1000 watt amplifier the average power is 100 watts (10dB crest factor). You can also make 100 watts average with Bass Mekanik by heavily clipping a 200 watt amplifier.

If someone is blowing a woofer with 200 watts of power due to a lack of restraint with the volume control... they will blow it even faster with a 1000 watt amplifier because they will probably turn it up even more and now they have more power to play with... this is the recipe for aroma of voice coil.

When woofers are rated for power, an unclipped signal is assumed. We use test signal with a crest factor of 6dB for power testing and can run a speaker at its rated power for hours and hours on end without thermal or mechanical failure. For example, a W1v2 can dissipate 150 watts average power for eight hours or more with signal peaks of 600 watts. So, we rate the speaker for 150W continuous power. This way, when a customer needs to choose an amp for it, they will hopefully choose one that can make about 150 W clean power... Even if they clip the bejeezus out of that amplifier, it is unlikely that the speaker will fail thermally. This is a conservative method, but it needs to account for the high cabin temperatures in a car (think Arizona in the summer) which significantly impacts heat dissipation in the speaker. A top plate that starts at 150 degrees F is not as effective at removing heat as one that starts at 72 degrees F in the lab... and this affects the ramp up of heat in the coil.

DISCLAIMER: The frequency components of clipping can affect tweeters due to their low inductance and lack of low-pass filtering. Clipping essentially raises the average power of high frequencies to a point that can damage tweeters... Woofers and midranges couldn't care less about these high frequency components because their filtering and/or inherent inductance knocks that stuff out of the picture.

Best regards,

Manville Smith


ok... from a non-audio professional, (but a big enthusiast, and car audio geek) I see one word here being misused a lot, and that word it.. dum dah dah dummmmm

Watt

We are not talking about watts here, we're talking about volt-amperes, and that makes the whole issue come together really. When we talk about watts, we are talking about the actual output of the speaker, the amount of electricity running through the coil that is actually doing work. In an inductive motor (such as oh, I don't know, a speaker) you have a massive amount of power lost due to the inductance of the coil, as well as moving the speaker cone, there is capacitance as well, in the windings of the coil, but generally that is by far overshadowed by the inductance generated by the moving coil. Lets look at inductance first, the inductance of the coil puts the voltage delivered by the amplifier, and the current drawn by the coil at that voltage out of phase, which causes a large reduction in wattage, this power is lost as reactive power, or VAR (volt-amperes, reactive) I have seen (calculated acutally) speakers that are being fed 600 volt-amperes from an amplifier, but put out less than 60 watts of power, at some frequencies, the rest is lost to inductance, as well as frequency and box related issues.

All this said, when a small amount of DC is a componant in the amplifier output, the voltage and current are in phase for that amount of time, causing a HUGE surge in the wattage that the speaker actually sees, imagine going from a 60 watt output, to a 600 watt output in a split second. As Mr manville Smith said, speakers are rated with an assumption of clean power coming from an amplifier, any DC output changes not only the amount of output, but the carachteristics of that output dramatically. in industry we call it "Power Factor" but it gets overlooked in car audio completely.

anyways, that's my view, take it or leave it.

"So if you run it with less power and even though you are not getting enough bass out of it, no harm will befall your driver."

 

[CamCrazy42]

Distorted and clipped signal from the amp will cause a subwoofer to break. There is also the over powering factor which could include overextension or thermal limits be exceeded. Find someone knowledgable that can help you set your gains on the amp if your unsure. You should never have the amps gain on full tho.

 

[Oliver]

If you push something too hard, eventually it breaks...[the only question here is, do you realize you're doing something wrong ].

 

[Candisa]

As long as you don't drive the amplifier into clipping, it won't hurt, but it's not very easy to hear a small (but big enough to kill a driver) distortion on a subwoofer, so many people kill their subs by underpowering them and pushing the amp too far without knowing it.

Best way to get the maximum out of an amplifier is by playing test-tones (frequency's) and using a scope to adjust the gains.

greetz,
Isabelle

 

[kyheng]

Well, with amp power less than sub's power, you won't damage it if you don't push till it clips(most of us agree with this).
Normal mistakes people make when using such combination : they cannot feel the tight bass and start increasing amp's gain(such group of people have limited knowledge) all the way up till 100%

 

[Rudeboy]

Yup, just remember that you will be under powering those subs, so they won't give you the volume you want. You will only damage them if you try to compensate for two small an amp by cranking the gains.

 

[~thematt~]

Wanna test to see if feeding less power damages them?

Turn the volume down......they're receiving less power now....

 

[reindeers]

Here's a nice link on underpowering your drivers.

http://www.audiojunkies.com/blog/1306/overpowering-underpowering-distortion-clipping-and-everything-in-between

 

[jp88]

ok... from a non-audio professional, (but a big enthusiast, and car audio geek) I see one word here being misused a lot, and that word it.. dum dah dah dummmmm

Watt

We are not talking about watts here, we're talking about volt-amperes, and that makes the whole issue come together really. When we talk about watts, we are talking about the actual output of the speaker.

."

I feel it necessary to point out that a Watt is a measurement of power equal to voltage times current, Basically "volt amperes" and watts are interchangeable terms.

Also if under powering your speakers in and of itself would hurt your speakers You could never turn them down

 

[BEAVER]

I was recently involved in an interesting discussion regarding clipping and it's effects.

What I took away from it is clipping will not harm your sub... the excess power produced by clipping may (if clipped hard enough to surpass the subs thermal or mechanical failure rate).

Basically, if you're grossly underpowered you can clip the shit out of it with no ill effects. If you're borderline underpowered you'd better pay close attention to your gains setting so you don't clip hard enough to surpass the subs capabilities.

It was an interesting discussion that went against everything I had been told in the past.

 

[sqshoestring]

I've read up on this and the answer is usually no. What happens is an amp can produce up to twice its rated power when clipping, providing you clip it hard and play it that way. It will sound very bad with tons of distortion. Lets say you have a 100wrms amp and a 150wrms sub, it could possibly burn it up that way if the amp does 200wrms in heavy clipping. If you had a 500wrms sub then no, there is virtually no way you could hurt that sub with the 100wrms amp no matter what you did. Now are amp and sub ratings all perfect? No but in general this will be the case. Also in clipping you will get more DC into the sub due to clipping, this could heat the VC more than a proper unclipped signal but it is debatable how much. The sub would be moving a lot then anyway and thus cooling itself, but it could add some heat. Other than that, the sub could care less what quality sound comes out of it.

What you should do is pick a spot on your HU that is below any distortion the HU may make. You can turn the amps way down and play it to try to hear how clean it is, then go well below where you hear any distortion. An expensive HU you might be able to run at full volume but most you do not want to. (This assuming you are using RCA, if not then you might have to go much lower) Then you set the amp gain up until it distorts some and back it off a little, so it sounds pretty clear. That is the most you can get for that setup, for an initial setting it should be pretty close. Then set your high side amps to match it in music unless they distort too then ease them below that point.

The other problem with underpowering subs is that high power subs tend to be less efficient, so you really need more power just to get them to work the way they are intended. But they should work if you have say half the sub's rated wattage amp amp because you need 10x the wattage to go twice as loud. That means it takes a 1000w amp to go twice as loud as a 100w. So there is more difference between 100 to 200w and hardly any difference between 800 and 1000w. So at low power a small amp will seem smaller and at higher wattages there is less difference. That means if you have half the power you are not that far from the full volume the sub can make.

One last issue is ratings, you need to use RMS ratings. I looked at a cheap amp the other day that was 1000 watts and 500x2. After some searching I found it to be 115rms x2.

 

[machinehead]

I've been giving my avalanche 15 well under its rating for years. Then again, I'm a more responsible listener...

 

[sqshoestring]

A large amp can sound better on a sub. It may have more headroom, meaning it can play a loud hit loud like it is supposed to be where an amp near max output may not have the reserve to do so. A quality amp will tend to have more headroom. A quality clean signal is less likely to damage a sub so you can go over ratings a little with clean power depending on what the sub can actually take and how it is installed.

But sometimes it does not work as well if you have maybe a ported or IB setup as opposed to a smaller sealed box. What can happen is the amp will bottom the sub on hard hits with that extra power where a smaller amp will play louder without doing that. If you want loud music, bottoming will destroy the sub shortly.

Playing distortion is kind of a kids thing, anyone listening will think it sounds like... well you know. Amps are so cheap now there is little point. I bought a 600rms that was new in the box for <$40 shipped. Yeah insignia so not the best but better than a 100w. I've sold a few brand name 850-1000wrms class d amps for around 100.

 

[ViperVin]

I was recently involved in an interesting discussion regarding clipping and it's effects.

What I took away from it is clipping will not harm your sub... the excess power produced by clipping may (if clipped hard enough to surpass the subs thermal or mechanical failure rate).

Basically, if you're grossly underpowered you can clip the shit out of it with no ill effects. If you're borderline underpowered you'd better pay close attention to your gains setting so you don't clip hard enough to surpass the subs capabilities.

It was an interesting discussion that went against everything I had been told in the past.

Did this discussion happen to be on CA.com?

 

[sqshoestring]

Did this discussion happen to be on CA.com?

I don't go there but that about sums it up.

 

[BEAVER]

Yes, it was ca.com. Are you guys saying you disagree with the idea?

There were some pretty compelling arguments made to debunk the notion of clipping being harmful, as long as it was kept below the point of mechanical or thermal failure of the driver.

It was rather interesting once you waded through all of the b.s.

 

[gijoe]

Yes, it was ca.com. Are you guys saying you disagree with the idea?

There were some pretty compelling arguments made to debunk the notion of clipping being harmful, as long as it was kept below the point of mechanical or thermal failure of the driver.

It was rather interesting once you waded through all of the b.s.

I'm going to have to say that makes sense to me. I'm not very knowledgeable yet, but I would imagine that even a severely clipped signal wouldn't hurt much if it's still below the drivers limits. I always understood that clipping kills subs because it the amp is already putting out close to the subs limits, then clipping sends it over the edge. So my hypothesis is that given and amp that maxes far below the subs max, you could clip the hell out of it and never push the sub hard enough the really damage it. It would sound like crap, but wouldn't kill the sub the way a high wattage clipped signal would.

What do you think?