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Thread: Fan-cooled sub

  1. #1
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    Fan-cooled sub

    Hi you car audio freaks!

    First of all, I need to get one thing straight. I have a subwoofer rated 400W RMS/800W peak and a 240WRMS/480W peak rated amp. The Xmech on the sub is 48 mm. From what I've heard before, it is possible for me to pump up the gain om my amp too much, causing the amp to clip and overheat my subwoofer thermally. But I've also read on this forum that it it almost impossible to overheat the sub that way (man, all the different opinions is really confusing ). What is the real answer to all this?

    From what I've heard, clipping an amp gives a DC voltage to the sub, making the cone movement different and the air-cooling work unproperly.

    I've been thinking of installing a fan inside the sub box, blowing air into the coil. Then I should never have to worry about getting my subwoofer coil burned from amp-clipping (I know the fan will give a buzzing sound, but hey- it's not a THX-system anyway). What do you guys think about that idea?

  2. #2
    Low Bitrate Blackrazor's Avatar
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    Quote Originally Posted by Matteman
    First of all, I need to get one thing straight. I have a subwoofer rated 400W RMS/800W peak and a 240WRMS/480W peak rated amp. The Xmech on the sub is 48 mm.
    You have a 400wRMS sub with a 48mm Xmech? Thats 4" total throw before you *** out... Damn, hook a brother up, i'll take 500 right now

    Quote Originally Posted by Matteman
    From what I've heard before, it is possible for me to pump up the gain om my amp too much, causing the amp to clip and overheat my subwoofer thermally. But I've also read on this forum that it it almost impossible to overheat the sub that way (man, all the different opinions is really confusing ). What is the real answer to all this?
    Its possible to fry that coil with that amp. But its NOT possible to do it without you overdriving the sub, which you'll hear. Amps dont fry subs, the hands on the volume knobs do.

    Quote Originally Posted by Matteman
    I've been thinking of installing a fan inside the sub box, blowing air into the coil. Then I should never have to worry about getting my subwoofer coil burned from amp-clipping (I know the fan will give a buzzing sound, but hey- it's not a THX-system anyway). What do you guys think about that idea?
    It wouldnt make hardly any difference, since most decent subs use vent cooling anyway. All the fan would do is muck up the airflow, and could actually have a detrimental effect...

    I've seen a guy attach a Peltier kit to a sub, that worked great, but why he didnt just spend the money on a better sub in the first place was beyond me

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    You have a 400wRMS sub with a 48mm Xmech? Thats 4" total throw before you *** out... Damn, hook a brother up, i'll take 500 right now
    Oops, i meant the total throw is 48mm, that means the Xmech is 24mm. Sorry if I gave you false expectations! Sounded good though

    It wouldnt make hardly any difference, since most decent subs use vent cooling anyway. All the fan would do is muck up the airflow, and could actually have a detrimental effect...
    Hmm, that's not what I had expected. Well, I guess I have to abandon that idea.

    Its possible to fry that coil with that amp. But its NOT possible to do it without you overdriving the sub, which you'll hear. Amps dont fry subs, the hands on the volume knobs do.
    I'm not sure how that sounds like, but I guess I have to try overriding it and figure it out. Is there no chance of burning it when it dosn't sound bad? I've heard that it is very hard to overheat it, that only extreme overrides for like 10 minutes will fry it. Is that true in my case?

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    The amp is supposed to be sending AC current to the sub. Thats what makes it move back and forth. If it clips, it starts sending DC voltage through the lines and that'll just freeze the sub in one position, overheat and melt the voice coil glue. Thats a really simple explanation of it, but basically true. You can break any speaker with any amp, pretty much.
    you have to be careful when you use it. If the amp is turned all the way up it might start clipping, you'll hear this pretty well, it'll sound like crap. You can blow a sub in a millisecond if you try hard enough, so be careful. Turn your headunit up to the point right before the other speakers start sounding like crap, then start turning up your amp. Stop when its loud but still clean bass.

    The technical way to do it is with an oscilloscope and watching the AC waveform and turning it up till it starts to send out nasty hard square waveforms and dc voltage.

    Dave

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    Low Bitrate Mcnovy's Avatar
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    hmm.!
    first of all, as the other says.!
    you wont be in any doubt that the amp is clipping, you'll hear it straight away..!

    second, most subs cool themseelves, of course more cooling is never bad, but i would'nt recommend it, you could unbalance the airflow i would think (though iv'e never heard of anyone fan cool there subs )

    third. are you turning you sub all up, cause 240 watt i laud in a small car, i got a 150 watt sub in my tv room, and that is more than enough, and im pretty sure that my room is bigger than you're car

    but if you're afraid of dc on the sub, then im sure you can find a anti DC short cirquit (i dont know what's it called) in the nearest car audio shop, or if you're familiar with electronic's, then make one you own..!
    like this one http://sound.westhost.com/project23.htm
    i have not tested it, just a quick and that was what i've got..!
    insteed of the diode, i would put in a relay (contact) så when dc i detected, the relay opens, and the sound want get trough
    Sorry for the english

    CarPC Specs.

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    Thanks both Dave2 and Mcnovy for their great answers!

    I have a separate amplifier for my sub, so it'll be harder for me to hear any distortion (from what I've heard, it's harder to detect distortion in the sub than the tweeters). But are you saying that I will still hear the distortion, even though I have a separate amp for my sub?

  7. #7
    Low Bitrate Mcnovy's Avatar
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    I have a separate amplifier for my sub, so it'll be harder for me to hear any distortion (from what I've heard, it's harder to detect distortion in the sub than the tweeters).
    hmm, i would turn it around and say that the midrange at the sub is the easier area of hearing clipping (distortion)

    But are you saying that I will still hear the distortion, even though I have a separate amp for my sub?
    -- YES..!!! --

    you will only hear the clipping from the sub, (if that's the only speaker that clips)
    Sorry for the english

    CarPC Specs.

    Via Epia MII 12000 \\ 512 Mb Ram \\ 200 GB Western Digital \\ PCmcia asus wi-fi
    Xenarc 7" Touchscreen \\ Usb Bluetooth \\ Carnetix P-1280

  8. #8
    Low Bitrate Blackrazor's Avatar
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    Quote Originally Posted by Matteman
    I've heard that it is very hard to overheat it, that only extreme overrides for like 10 minutes will fry it. Is that true in my case?
    You'd have to have some pretty horrendous distortion to kill that sub with that amp, but how long it takes depends on how well built the sub is, and how effective it is at dissipating extra heat

    Quote Originally Posted by dave2
    If it clips, it starts sending DC voltage through the lines and that'll just freeze the sub in one position, overheat and melt the voice coil glue.
    It does start sending a DC component to the speaker (along with many harmonics and a subsonic complimentary signal which is actually one of the things that can do the most damage), but it doesnt stand still, it still moves in and out according to the frequency, it doesnt do it smoothly is all... so long as a sub (or speaker) can dissipate at least ~3x as much power as the amp can output, you'll have a very, very difficult time killing it. When i say very, very difficult, read 'impossible, unless you deliberately operate it outside its normal frequency range in a poorly designed enclosure in a deliberate attempt to kill it'

    Quote Originally Posted by dave2
    You can break any speaker with any amp, pretty much.
    ... except for amps with output transformers (including tube amps) since by definition a transformer cannot pass DC, and therefore cannot feed a DC component to the speakers Ever heard of people blowing speakers with a tube amp?

  9. #9
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    k, but yeah.. he's not gonna be buying tube amps.. :P

  10. #10
    Constant Bitrate LeoTheHamster's Avatar
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    Heres an idea

    GET THE DAMN SYSTEM SCOPED PROPERLY SO YOU DON'T HAVE TO WORRY ABOUT IT
    Leo

    http://www.talkaudio.co.uk

    A million people can't be wrong, right?

    Well... unless they're all from the red states...

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