HELP! Blown Sub

[Schnitzer318is]

Well, I just finished my sexy ported enclosure that Luke has been generous enough to help me with. Stuffed an Alpine Type R into it (swr-1242). Wired the dual 4ohm vc's to 2ohm load at the amp. All was fine and dandy. HIT AWESOME!.

Well, last night the wife and I are on a cruise and the sub cuts out... and there is the unmistakable smell of burnt voice coil. I check the amp and it is in protection mode... sh*t. Reset the deck and the amp comes back on in normal mode and sub works. As soon as you give it some volume though it goes back into protection. Sooooo... time to bust out the multimeter. When the amp goes into protection the ohm level at the terminals is about .5 ohms. Crap, that's not going to work. Disconnect the sub and wire a known good test sub. Everything works fine as it should. Soooooo the Alpine is definitely fried.

My question, and hopefully Luke will chime in here. My sub amp has a built in subsonic filter at 27hz. Since the box was port tuned at 36hz, would this cause the sub to exceed Xmax? I wasn't bumping it too hard when it went out at all. Being in the car I of course couldn't hear any distortion. Now that I type this out I am pretty sure it was exceeding Xmax (xcursion limits). What do you guys think? TIA for the help. And here are a few teaser pics of the setup. As soon as I get this problem straightened out I'll post a full thread on it.

[DaveSmed]

Well, I'm not gonna be any help at all with your question, but I must say, clean install. Good work.

[Erik j]

If your amp is going into protection mode, then the sub has too low of a impedance. Try to hook up the sub as a either a single 8 ohm load, or if your amp is 2 channel then do 2 4 ohm loads. See what happens then. I think your sub is just able to work alot harder with the new box and its overloading your amp.

[Schnitzer318is]

If your amp is going into protection mode, then the sub has too low of a impedance. Try to hook up the sub as a either a single 8 ohm load, or if your amp is 2 channel then do 2 4 ohm loads. See what happens then. I think your sub is just able to work alot harder with the new box and its overloading your amp.

I'll wire it in series and see if that helps the problem at all... like you suggest. I'm not sure that's going to do much though since the amp is definitely 2ohm stable and has worked fine at 2ohms for a couple of years now. It's a performance teknique ICBM-Digital which is more than adequate for this sub. Gain is at about 1/3. Plus that wouldn't account for the wonderful smell of burnt coil. I even pulled the sub today to give the back of it a smell... yep it's the sub. I hooked up another sub at 4ohm and played it and pounded the crap out of it so I know the amp is still good. This is why I used a $50 sub for my first attempt at a ported enclosure... no big loss to replace it.

... Luke where are you? :-)

[StereoInstaller1]

Yeah, but that "too low of impedance" is because the voice coil has a dead short.

OK, so understand this: Sealed boxes have a huge rise in impedance right at the resonant frequency. So, if that Alpine is typical with a Qts of .44, and Fs of about 25, putting that woofer in 1.2 to 1.6 cubic feet will likely cause an impedance bump of about 30 ohms at about 45Hz...in other words, at 50Hz or so, your amp that makes 1000 watts at 2 ohms makes like 50 watts (I don't want to do the math, the fucker is already blown).

So, now that it is in a ported box, the impedance curve is much flatter, so it likely sees more like 8 or maybe even 5 ohms at the resonant frequency, which is likely somewhere between 25Hz and 35Hz...so your 1000 watt amp now makes like 400 to 600 watts instead of the 50 it made before...see?

This is why salesfucks seem to think they need a 1000 watt amp to power a pair of 12's. this is also why idiots seem to think sealed boxes handle more power, it is because the fucking amp doesn't MAKE any power!

A type R has a 2" voice coil IIRC, and thus can really only handle about 300 watts, RMS.

Oh yeah, the subsonic filter only kept the thing alive longer. BTW, there is no such thing as a "subsonic" filter. that is actually an Infrasonic filter, subsonic refers to speed.

Luke

[Schnitzer318is]

Ya I was aware that the load seen at the amp depends on the frequency being played... lol but that is dramatic differences. Explains why I've never blown a sub in a sealed enclosure before.

So Luke... what is your suggestion? Different sub? Box? It sounded mad clean and awesome while it was playing, but I don't want to be replacing subs all the time either. LOL especially not every 15 mins. :) I typically build a system for a car and leave it for years.

[Erik j]

^^^ What Luke said :D

[Schnitzer318is]

Another Type R on ebay for about the same price Luke... Should I pick that up, or you think of a better sub for the box? I'm an audiophile and am going nuts with no low frequencies. :)

Damned my noob-ness to ported designs. Was my math correct? Or did I just throw too much power at it? Gains at 1/3, used to have it 1/2 in my sealed designs (on 2 subs though). Head unit has 5.0v preouts so either of those should be fine as long as the sub can handle it right?

[StereoInstaller1]

Well, what the hell are you gonna do about finding a 2 ohm woofer with an XMAX over 4mm, a Fs under 27Hz or so and a Qts of under .4, with power handling of that magnitude?

Memphis M3 is the first thing that comes to mind, but I bet RE has something, as would DD.

If you could find a NOS Fosgate Power DVC, that woulf fill the bill nicely too, since those had a 4" voice coil. The old JBL 1200GTi did too, but good fucking luck on that one.

It is such a shame that the box fires into the trunk. You could sell that beast of an amp, make half a house payment and still buy enough power to do the job, if it fired through the back seat with an arm rest. I bet I get more SPL that yours using a puny little 600 RMS 2 channel Exile, on a $250 Exile woofer.

[Erik j]

Well, what the hell are you gonna do about finding a 2 ohm woofer with an XMAX over 4mm, a Fs under 27Hz or so and a Qts of under .4, with power handling of that magnitude?

Memphis M3 is the first thing that comes to mind, but I bet RE has something, as would DD.

If you could find a NOS Fosgate Power DVC, that woulf fill the bill nicely too, since those had a 4" voice coil. The old JBL 1200GTi did too, but good fucking luck on that one.

It is such a shame that the box fires into the trunk. You could sell that beast of an amp, make half a house payment and still buy enough power to do the job, if it fired through the back seat with an arm rest. I bet I get more SPL that yours using a puny little 600 RMS 2 channel Exile, on a $250 Exile woofer.

Ive been looking for some old GTi subs too, nothing, so I've settled with GTx subs instead. Little smaller but still a great low end driver.

[Schnitzer318is]

LOL... so what you're saying is... I need a tougher sub. :) I wasn't even pushing it hard though when it popped. Under 100db for sure. I didn't turn it up too loud cus the wifey was with me and I hadn't tuned it yet.

With the ported design... I thought it didn't matter which side the sub fired since all the energy goes into the cabin through the ports anyway?

Ok million dollar question. Do you think it's worth it to get the bigger sub? I was hitting 125db easy with my sealed designs in a BMW trunk. That was good. I thought this would as loud while maintaining decent spl, and only using 1 speaker? It was definitely hitting lower. I liked what I heard while it lasted. I'm leaning towards getting a bigger sub to handle the extra power, but again don't want to be blowing subs. Or... should I just get another sub like the Alpine Type R and run it at 4 or 8 ohms?

Hehe am I getting annoying yet with all the newb questions? I really know next to nothing about ported setups (as I'm sure you've noticed)... so I really appreciate all the guidance.

[Schnitzer318is]

Update: Wired the coils in series just for the F of it. And it's working fine. In fact better than fine. I don't know if only one coil is running or what but I don't care. After some tuning this thing hits both low and sharp. Exactly what I was looking for. Thanks for all the help Luke! You helped make my first foray into ported boxes a success.

I'll bust out my cheap Radio Shack meter tomorrow to see what it's hitting. I used to hit 125+ with the 2 s12d solo barics in a sealed enclosure. This 1 sub plays lower... and maybe louder.

[Erik j]

Dont I get any thanks? I was the one who said to wire it for 8 ohms :)

[Schnitzer318is]

Dont I get any thanks? I was the one who said to wire it for 8 ohms :)

Yes. Thanks for the suggestion, reason I tried it. I think it's about the same though as just running one of the coils... the other one is shot. I just ran it series to try it out. Hooking up the single 4ohm coil had the same result with the multimeter... so I'm guessing it's only running the one good coil. Oh wells, one coil is better than none. :)

[SamE30e]

Well, I'm not gonna be any help at all with your question, but I must say, clean install. Good work.

QFT to the max!