Two blown MB Quart subs... ideas?

Hi all,
I recently completed my installation of Nik's Uberstealth box, MB quart RLP254 10" shallow subwoofer, JL audio XD300/1, and LC2i. I followed the thread on this forum by Veedoubleme's very closely (which was excellent btw ty very much for that) for my install and I was very happy with it... for about a week. After about 30 min of driving one day with fairly loud music playing, the bass cut out. All fuses were in place and amp and LC2i were still on. I later pulled the sub, put a DMM on it, infinity ohms, and a scratchy sound when I pushed the driver. Text book blown speaker. Being impatient, I purchased another sub on Amazon prime figuring I may have had a defective speaker. Then I double, triple, quadruple checked every connection and tried it again. It sounded absolutely amazing... for about two days now its dead again. A little different this time. The sub reads 2 ohms (DVC wired in paralell) but its barely audible, scratchy, and sounds horrible. Only was playing for about 20 min of heavy bass when it died this time.

I am by no means a professional car audio guy, but I have installed systems in almost every car I have ever owned. I am also an electrical engineer by trade so I am fairly confident with my wiring. Nik's box was lightly packed with 8 oz of poly fil, just on the sides, not behind the woofer. The sub was tightened down and not leaking air, there were no stray or crossing wires. The MB quart was wired in parallel to the JL XD300/1 which should put out 250W RMS at 2 ohms. The specs on the MB quart claim 300W RMS power handling. It doesnt sense that even my amp could blow this speaker

The fact that it happened twice definetely points to an error on my part but I can't imagine what that was. I thought maybe the first time I damaged it from using the 50 hz test tone and messing with the gain and crossover settings, but the settings were all tuned the second time. It was sounding great right before it died both times. I suppose it is possible that I got two lemon speakers? Maybe the MB quart power handling is overrated? Either way I need a new speaker and I think I need to try something different. I would love to hear from some one with this setup that is working properly. Also, any suggestions on another speaker or thoughts on what I could have done wrong would be greatly appreciated.

It could also be that since you are underpowering the sub you are clipping the signal when listening to loud bass.

i have seen this with the ED SQ10. some shallow mount subsdo not have a shorting ring to make them shallower. this allows the sub to over extend, damaging the voice coil.

The only sub i have never seen this happen to is the pioneer sw-2501

BostonMKVI said:

I would love to hear from some one with this setup that is working properly. Also, any suggestions on another speaker or thoughts on what I could have done wrong would be greatly appreciated.

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That seems very unlikely to me. The chances of blowing two drivers that close together, yet others aren’t having the same problem? You have the identical system to Veedoubleme, and I’m assuming several others on here. I have the same amp with a LC2i that's been running my old sub for awhile now without issue. I have a MB Quart RLP254 sitting in my closet for weeks now waiting for my Uberstealth that just showed up last night. I’ll let you know in a week if mine pops :-{

I dunno though, perhaps an issue with the XD300?

Simply, turn the gain level all the way down on LC2i.
And only use the LC2i bass boost to match the bass roll off frequency on RCD510

ughhhhhhhhhhhhhhhhhhhhh

take the sub out, did you unwind the voicecoil to a point where the cone wont move??

if the cone moves, did it seperate internally from the voice coil???

without knowing what actually happened to it, it will be hard to diagnose why.

I have some background in speaker building and repairing, so videos of the blown driver or photos of the failure point would be awesome!!! hint hint

Thanks everyone for the input, much appreciated. I am really want to get to the bottom of this so hopefully others can avoid what happened to me.

nikbrewer said:

i have seen this with the ED SQ10. some shallow mount subsdo not have a shorting ring to make them shallower. this allows the sub to over extend, damaging the voice coil.

The only sub i have never seen this happen to is the pioneer sw-2501

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First off, great work on these stealth boxes Nik. Everyone I show it to is very impressed with craftsmanship and I was loving the sound and convenience before my issues. I figured this may be an problem with some shallow subs.

I wanted to try a different sub so I ordered a sw-2501. It just arrived today. This thing looks like a tank compared to the MB-quart and is much heavier. They both are speced for 300W rms but I find this hard to believe as the pioneer is so much beefier and also almost double the price.

The sw-2501 fits my the box, but should I be concerned with anything else? The mounting depth is very close to the same. The spec sheet says .35 cuft min, .7 cuft max, .45 cuft recommended for the pioneer. As the mbquart was 6.5 recommended, my box may not be optimum volume but its within the range. Also, nowhere on the pioneer sheet did I see anything about polyfill. Should I be pulling it out?

Hinhin said:

Simply, turn the gain level all the way down on LC2i.
And only use the LC2i bass boost to match the bass roll off frequency on RCD510

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I tried to set up the LC2i very carefully. Bass was in the stock straight up position, accubass a little past 1/4. I verified the roll off point of the RCD-512 with my spl meter and the 50 hz test tone and set the threshold accordingly. I checked the voltage with the speaker unhooked at 3/4 volume like the XD300 manual suggested. 60hz, 24db crossover, with the gain a little below 12 o clock on the amp. I had the music very loud both times, perhaps I was clipping the speaker, but I like to think I had the amp/LC2i settings correct.

phd-12v said:

ughhhhhhhhhhhhhhhhhhhhh

take the sub out, did you unwind the voicecoil to a point where the cone wont move??

if the cone moves, did it seperate internally from the voice coil???

without knowing what actually happened to it, it will be hard to diagnose why.

I have some background in speaker building and repairing, so videos of the blown driver or photos of the failure point would be awesome!!! hint hint

Click to expand...

phd, I cant comment on the second sub as I returned it, but I know the cone did still move and it did still show 4 ohms on each coil even though it sounded horrible. On the first one, the cone moves but it makes the scratchy sound when you push it and it reads like an open circuit on the DMM on both voice coils. Since I threw away the box for this one I will try to dissect it tonight and post up some pictures for you to take a look.

Thanks very much guys

Just so you know, I listen to a little over an hour of loud music each day on my 70 mile round trip commute. I have a wide variety of music, but a lot of it is bass heavy. It continues to preform flawlessly. I'll give you the main specific configuration points that pertain to my sub:

Main Source: iPod through MDI
MDI Input level set to minimum
Bass on RNS-315 set to -2

My JL Audio remote amp level control is centered perfectly so that if I point the level indicator toward the front of the car, that is 50%. I generally leave it pointed directly to the passenger side of the car in the 3 o'clock position. There is a little room to turn it up, but not much. It's an attenuator knob, and is supposed to be configured in this manner. I never listen to it above "21" on the RNS-315, but most listening is between 19 and 21.

Here are my LC2i settings:



Here are my JL amp settings:



Good luck with the new sub, and I'm glad my thread helped you out! Sorry the MB-Quart sub sucks for you. It's not very beefy, and I was worried about that when I got it, but so far so good. Sounds great and it's been problem free. Regarding your polyfill, it won't hurt to take it out and try it that way, and then to add it back in and see if it sounds better. I'm guessing you'll need it, but it's always good to test.

veedoubleme said:

Just so you know, I listen to a little over an hour of loud music each day on my 70 mile round trip commute. I have a wide variety of music, but a lot of it is bass heavy. It continues to preform flawlessly. I'll give you the main specific configuration points that pertain to my sub:

Main Source: iPod through MDI
MDI Input level set to minimum
Bass on RNS-315 set to -2

My JL Audio remote amp level control is centered perfectly so that if I point the level indicator toward the front of the car, that is 50%. I generally leave it pointed directly to the passenger side of the car in the 3 o'clock position. There is a little room to turn it up, but not much. It's an attenuator knob, and is supposed to be configured in this manner. I never listen to it above "21" on the RNS-315, but most listening is between 19 and 21.

Here are my LC2i settings:

Here are my JL amp settings:

Good luck with the new sub, and I'm glad my thread helped you out! Sorry the MB-Quart sub sucks for you. It's not very beefy, and I was worried about that when I got it, but so far so good. Sounds great and it's been problem free. Regarding your polyfill, it won't hurt to take it out and try it that way, and then to add it back in and see if it sounds better. I'm guessing you'll need it, but it's always good to test.

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Thank you for the response and the great DIY. I was hoping you would chime in I followed your setup very closely and my settings are almost identical to yours on both the amp and LC2i. My gain on the amp is actually a little lower. I have the attenuator knob as well but I had it up full volume both times, also the bass on the HU was 0. Perhaps that little extra on full blast was enough to do it? I also was probably past 21 but its hard to say because I use the SD card and a USB stick in the MDI rather than the ipod so the input volumes may be different. We also have different HUs. I think I will be a little more conservative next time with the volume knobs.

Its unfortunate because it sounded great right off the bat. That is why I was so quick to try the same sub again. I will keep you posted on the new sub.

Unfortunately, a 10" shallow mount sub is never going to hit like a full 10" sub. They fill in nicely and have good low end, and they do hit nicely, but they will never hit that same level of performance. I think it's easy to try and push it to hit like a normal 10" sub, but you can't push them too hard. When I was setting all of my levels, it wasn't hard to get it to clip. That's why I never go over 21. I know for a fact that a lot of my music will make the sub clip at 22.

It sounds like if you over push the MB Quart it might not be too tough to blow one. Hopefully the new one is more durable, and if I ever blow mine I'll switch over.

Here's me dissecting the blown MB quart RLP 254. Sorry about the links, I am sort of a forum noob.

http://i1052.photobucket.com/albums/s460/LeeJBrandenburg/ab837ab2.jpg
http://i1052.photobucket.com/albums/s460/LeeJBrandenburg/935e4762.jpg
http://i1052.photobucket.com/albums/s460/LeeJBrandenburg/f5eb8c26.jpg
http://i1052.photobucket.com/albums/s460/LeeJBrandenburg/e954d6db.jpg
http://i1052.photobucket.com/albums/s460/LeeJBrandenburg/23012497.jpg

Clearly the voice was shot. There actually was some soot that rubbed onto my fingers when handling it.

veedoubleme said:

Unfortunately, a 10" shallow mount sub is never going to hit like a full 10" sub. They fill in nicely and have good low end, and they do hit nicely, but they will never hit that same level of performance. I think it's easy to try and push it to hit like a normal 10" sub, but you can't push them too hard. When I was setting all of my levels, it wasn't hard to get it to clip. That's why I never go over 21. I know for a fact that a lot of my music will make the sub clip at 22.

It sounds like if you over push the MB Quart it might not be too tough to blow one. Hopefully the new one is more durable, and if I ever blow mine I'll switch over.

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Agreed. I think I got greedy and wanted it to sound like 2x 15"s

didnt read all the long replies. but first instinct is your gains were too high, especially on the amp. and any bass boosts could have done it too.

BostonMKVI said:

60hz, 24db crossover, with the gain a little below 12 o clock on the amp.

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a sub likes a smooth 12db slope. or 18db slope at most. 24db is un-neccessary on a sub and causes gaps in your sound.

By the way, will the TS-SW2501S2 fit in the hole on your sub box? It has a larger cutout of 9-3/8" vs. 9.06 on the MB Quart. You may have to enlarge the hole a little.

plac said:

a sub likes a smooth 12db slope. or 18db slope at most. 24db is un-neccessary on a sub and causes gaps in your sound.

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You'd think, but I tried both settings and felt the 24db slope blended better in my car. :iono: