You can blow a sub by underpowering? I know you can blow speakers out by overpowering (for obvious reasons!) but how do you blow them by underpowering? Is there like a minimum volume or something?

Obviously I'm not completely on top of things audio-wise

 

No you can't blow a driver by underpowering it. You can however set your gains wrong, clip the amp and blow your driver.

 

Actually, you can blow a sub by underpowering it. The reason most speakers blow is not due to too much power, but too much distortion. So if you don't have enough power going to a speaker/sub and you try to compensate by turning the volume past optimal it can blow the speaker... because of the distortion it creates. That's why alot of the Monsoon stuff blows. The stock CD player is a big source of distortion. When the volume is turned up too far it sounds like garbage but also is damaging the speaker.

 

I'm sold on the stealth enclosure, I just sent a payment to Ian to make one for me. Top notch lookin'.

 

not quite.

for example, a low powered signal thats fully distorted will not hurt your speakers at all.

However, distorted (clipped) material has a higher average power level over a period of time then the same signal unclipped. The driver blows because of the higher then rated power, it has nothing to do with the music being distorted or not.

You can just as easily blow a sub with a 1000 watts of 'clean signal', and not blow it with 300 watts of clipped signal.

OEM monsoon speakers blow because they are cheap speakers that can't handle any power for a prolonged period of time.
mike

 

So you are saying by keeping the volume at low/moderate levels will blow your speakers?

Clipping is a form of waveform distortion that occurs when an amplifier is overdriven (setting your gains unproperly). Which then attempts to increase the voltage or current beyond its threshold of power.

"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
JL Audio, Inc."

 

Ok, I stand corrected!! Thank you for the education from both Papa Smurf and Mike!! I was going by what i was told in the past. I have never actually blown a speaker in my car before. I've had them deteriorate to the point of not operating properly (long time ago), but not "blow" as far as voice coil damage or anything.
"So you are saying by keeping the volume at low/moderate levels will blow your speakers?"
That is not what I meant at all. I simply meant ie: trying to run a 10" sub with a 100watt amp and turning the gains up so much that it creates a distorted signal can do more damage to the sub than if you had a 500watt signal running to it cleanly. That's what I meant by underpowering. Not keeping low to moderate volume levels. Apparently I was mistaken by this and I appreciate you pointing out that I was wrong.

 

you're example of running a 100 watt amp with the gains cranked blowing a sub is a correct example. But you blow the sub because of the increase in power delievered by the clipped signal, not the fact that it's distorted to begin with. And if you were to measure it , the RMS power would be substantially higher then 100 watts.

 

Ok, I understand!! I was being sincere by the way about the education!! I am always willing to admit when I am wrong for the sake of learning something useful. I actually have this page saved now so I can refer to it...lol!! Thanks guys!!