what causes a blown woofer?

I've been into deep bass for awhile, building some craptastic wal mart systems from peices and parts my buddies had laying around when i was younger, moving up to more quality stuff. At present i have an alpine m350 amp, pushing 350 watts @ 2 ohms with a peak of i beleive 700 watts, i had that coupled to a memphis audio pr15d4 15" sub with an rms of 200 watts...obviously i was treading in bad water, that sub blew the voice coil as i heard a loud pop and thats all she wrote no noise, no vibration nothing at all just dead silence...i could see 150watts to much power being a problem but the box was within spec for the sub at 2.46 cubic feet before the sub was dropped in and my rough guess was arond 2.3 with the sub in place and no fill.

With that sub done, i purchased a 15" cerwin vega hed with a rating of 300 watts rms and a dvc 4 ohm setup so again 2 ohm at the amp... i bought the sub tuesday, built the box by thursday with was 2.2 cubic feet with a nice stuffing of poly fill, i played it for awhile but it sounded kind of loose and boomy so i took some fill out and it tightened up nicely and had better punch and bottom end, last night after 5 mins of playing my sub at a decent level it slowly faded away and blew the fuses on my amp, when i replaced those the sub had a deffinate rattle to it like something was loose in the basket, this morning it wont play at all...now on my alpine amp for my gain settings i have a nuetral point that says 0v  to the left it turns the gain down to pretty much off and to the right it has .5v then at the bottom 1v with my gain set at 0v for both subs the amp gets alittle above in car tempeture maybe 80 degrees or so, warm to the touch but not hot by any means....how can it be i've blown 2 subs on a weak mono amp?  any help would be appreciated as this is driving me nuts and killing my wallet.

J~

There are two ways to break a sub; thermally and mechanically.  The first sub sounds like it broke thermally and the second one sounds like it broke mechanically.  My guess is that you have your gains set improperly on your amplifier.  Your gain should be set to match the output voltage of the head unit.  Turning it up too high will clip the input signal and can produce a great deal more power than what the amplifier is rated at.  Now mechanical power handling of a subwoofer is based on the enclosure.  A larger sealed enclosure will allow the sub to reach it's mechanical limits with less power than a smaller enclosure.  It sounds like that Cerwin Vega sub needed a smaller enclosure than what you were using for the amount of power you had going to it.  Especially if you had extra power from a clipped signal.  BTW, did you have a bass boost turned on in the amplifier as well?

Steven Kephart

Adire Audio

nope, bass boost set to zero, the recommended size for a sealed encloser on the vega is 1.9 to 3.0 if i recall correctly my box was 2.1 or 2.2 and i had it full of polyfill and it sounded alittle loose so i took some fill out and it tightened up nicely, i have a hard time beleiving that the sub mechanically failed, it never bottomed out, or seemed to reach its limits, as far as the way i tuned it, i turned up my stereo till it distorted then backed it down a couple clicks until it was clean and turned my gain up, as i said it was set at zero on my amp,  which was roughly half way up and wasnt that much louder than the rest of my stereo, it was pretty well even with everything else in the car...besides my memphis lasted almost a month, the vega blew after 2 days and doesnt seem to show any signs of damage, i mean nothings stretched or pulled, nothings out of shape, and i know it didnt get hot...so i'm very curious whats up with this amp.

J~

Unforutnately Cerwin Vega doesn't provide any helpful information on that sub on their website.  You mentioned that at first it sounded boomy which indicates that you were probably on the large size for that sub.  Larger enclosures will emphasize the lower frequencies making the sub sound more boomy.  Also, not all subs will bottom out before reaching their Xmech.  You said that you heard a rattle which indicates something broke.  Based on the information you provided, it sure sounds like you broke the sub by pushing it too far.  I do find it odd that it wouldn't play the next morning.  I'd almost suspect the tinsel leads broke, but you probably would have seen it on your inspection.  Plus for the sub not to play when wired in parallel, each voice coil would have to have a broken lead.

You definitely followed the right procedure in setting your gains.  But it still doesn't rule out amplifier clipping.  If you set your gains with source material that doesn't have very high peaks in the response, then music with sine waves recored at 0 dB could still clip the signal.  This could also be what you heard as a "rattle" as clipping can sound very mechanical like that.  Here's a video I recorded of one of our subwoofers playing full range and me intentionally clipping the amplifier.  It will give you an idea of what it sounds like: http://www.woofervids.com/displayimage.php?album=7&pos=35

I'm trying to give my best guess at what happened based on what information your provided.  Unfortunately there is no way for me to tell exactly what went wrong without being able to test the sub myself.

Steven Kephart

Adire Audio

the leads were all intact, they werent even showings signs of being pulled, i double checked all my wiring but nothing was wrong or crossed up or even loose, the box i built i had filled with poly fill, the boom wasnt that bad, it was just slightly loose sounding on deeper bass notes, wasnt excessive at all i had just decided to take out some polyfill to tighten up the bass alittle, i watched that video but my sub wasnt making any noise like that, it was hitting nice and clean and hard, when i setup my stereo i used a couple different tracks, snoop doggs 3rd track on his paid da cost to be da boss cd...i think its called stoplight, 36 mafias late nite tip and usually something techno, i had actually changed cds from snoop dog to crystal method when the sub blew, so it actually blew while the stereo was loading up the cd, because as soon as the first bass line hit my sub barely had any output at all and it faded out from there. when i replaced the fuses the sub hit and rattled really bad like it was distorting or something was loose and hitting the basket, then it slowly cleaned up but only hit at about half the power it usually does, it was like someone turned my gain all the way down on the amp.....now one thing i did different from the memphis to the vega is i was using 14ga power wire on the memphis, on my vega i was using 12ga power wire...could this be part of the problem?

i told the guy at the shop i got my vega at my exact setup, the amp, the box size everything and he said this sub should be just fine, as far as setting up my gain, when i was using my test tracks which cover a wide range i turned the gain all the way down and slowly brought it up until the sub hit nice and hard but still sounded clear, the overall sound of my sub never changed from around a 1/4 turn from fully off till a 1/4 turn past half way at which point it became distorted and muddy so i backed it back down until it hit nice and clean and hard around the half way mark.....this is how i set up my little 10" sub and that things still playing great even after being on a different amp for months, then switching to the current amp it played beautifully for around a month or more and is currently pulling back up duty while my 15 is away....on a side note i really want a diamond audio d315 i think this sub will handle whatever is going on far better than the vega did...on a side note my mother happened to throw the box/white paper and template to my vega away the day after i bought it so i'm having to use vegas website specs which arent very helpful at all, luckily i got my box specs from the white paper before it was thrown away. i mean even if the amp was clipping alittle bit it woudl of had to be horrible to destroy a sub in 2 days wouldnt it?

J~

i cut apart my first blown sub today, the memphis i had, the voice coil was pretty much toasted on it, so ya it thermally blew, the vega i took back to the dealer who looked at my amp, looked at the box it was in and the sub itself and said that my amp was set up pretty much perfect for the sub, and put another vega in my box and tested, i had a slight air leak but its a very small leak and he said it shouldnt cause a problem, i hooked everything back up and started listening alot closer, i wouldnt call it clipping exactly but just to be safe i turned my gain down alittle bit, i figure till it breaks in a bit more i'll leave the gain low, better to be safe than sorry i always say :).  oh and if anyone was wondering my vega was locked up, if you push on the cone it made this grinding scratching noise all the way in and out and was extremely stiff so something went wrong...dunnoif it was my setup or the sub.

J~

Hey, steven kephart  that tone generator works great as i have an input on my head unit and can run a set of leads from my lap top to the head unit, i've found that around 50 hz my sub seems to hit hardest its a toss up between 51 and 52hz and that at 60hz i have what i thought was clipping but it turns out my rear deck speakers are bottoming out at 60hz which creates this sound kinda like your video with the amp clipping, i did find however that backing my gain down 1 line which is about an 1/8th of a turn creates more bass inside and outside the car, so i'm guessing my levels were just alittle high, thanks for the link to the tone generator as its already helped massivly in finding little problems that have been bugging me all along....one thing i'm curious about, do you know any online dealers that have the new line of adire audio subs in stock? i'm really interested in the 15" tempests.

J~