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billsburgundy
01-27-2013, 12:48 AM
I am upgrading my subs from two 10" alpine to two 15" subs, not sure what kind yet..however I cannot be persuaded to a certain brand so save your breath. The only advice I am asking you people maybe laughable to the versed car audio individual....but here goes. I drive a custom car. The trunk is almost completely fiberglass (major structures and mechanics aside) and I don't want to encourage my trunk walls to flex, bend, alter, warp, or MOVE. BUT, the trunk is not sealed...In the front seat of my car I can look and see the very back of the trunk. Would it make sense for me to buy a sealed box or a vented box? (keeping the request of having minimal flex in my trunk walls in mind) My dim witted logic tells me that a vented box pushes more air around and would encourage the fiberglass trunk structure to move around more. BUT, because the trunk isn't sealed would the air pressure dissipate to the rest of the chamber/cabin of my vehicle and not be an issue? Should I dynamat and get the subs in a sealed box? I need your 5 cents here, folks. I don't want my fiberglass trunk walls to move..sealed or vented?

UnderFire
01-27-2013, 12:51 AM
No matter what you do, even with an open trunk, it will still pressurize, your best answer would probably be a trunk wall, the subs would seal off into the cabin behind the rear seats and minimize pressure buildup in the trunk itself.

Ported or not depends mainly on space/design constrictions, most cars wouldn't be able to fit the ~8 Cubes a pair of ported 15's would need to breathe properly.

Tenacious
01-27-2013, 12:52 AM
2 15s is going to flex the **** out of it either way. I'd recommending using CLD tiles (dynamat or similar) on the back of the fiberglass if possible

audiobaun
01-27-2013, 12:56 AM
2 /12 in Daytons in a sealed enclosure, with min rms power might be alright

TeamProdigyMike
01-27-2013, 12:57 AM
Yea with 2 15" you are going to have flex. unless you only use about 300 watts. and you still will have some minor flexing.

billsburgundy
01-27-2013, 12:58 AM
I do have the abililty to seal the trunk area if I want, but wouldnt that make more pressure (smaller space)? So you are recommending a sealed box with a sealed trunk?

UnderFire
01-27-2013, 01:04 AM
I do have the abililty to seal the trunk area if I want, but wouldnt that make more pressure (smaller space)? So you are recommending a sealed box with a sealed trunk?

I'm assuming behind the back seats you have a large hole? if so, this is what I mean.

http://img.photobucket.com/albums/v287/byron2817/DSCN1381.jpg

The box is port and subs firing forward, into the cabin, completely sealed off from the trunk itself.

Beatin'
01-27-2013, 01:05 AM
I have two sealed 15 inch radio shack pieces of junk on 300 watts rms in the trunk of my car and there is FLEX.

Jes 42
01-27-2013, 01:05 AM
I'm assuming behind the back seats you have a large hole? if so, this is what I mean.

http://img.photobucket.com/albums/v287/byron2817/DSCN1381.jpg

The box is port and subs firing forward, into the cabin, completely sealed off from the trunk itself.

^^that^^

billsburgundy
01-27-2013, 01:12 AM
jes 42...that would be very similar to my setup...do you get more trunk flex when the backseat lid is up or down?

billsburgundy
01-27-2013, 01:14 AM
or, is the lid always down...kindve looks that way....

UnderFire
01-27-2013, 01:16 AM
or, is the lid always down...kindve looks that way....

Most of them will fold up just fine and work like stock, I would prefer to mount the amp in the trunk rather then on the seat directly in front of the port though.

av83
01-27-2013, 01:17 AM
seriously people?

op, fiberglass is used in the construction of subwoofer enclosures fairly often. It's very stiff stuff unless it's a large flat panel, but even then you can stand on a quarter inch thick piece, lol... If it's strong enough to be part of a vehicle, then it will hold up fine to a system.

UnderFire
01-27-2013, 01:19 AM
seriously people?

op, fiberglass is used in the construction of subwoofer enclosures fairly often. It's very stiff stuff unless it's a large flat panel, but even then you can stand on a quarter inch thick piece, lol... If it's strong enough to be part of a vehicle, then it will hold up fine to a system.

I wouldn't want constant flex on fiberglass, if it's anything like a boat hull, it may be very stiff, but fiberglass is very prone to stress cracks.

av83
01-27-2013, 01:26 AM
I wouldn't want constant flex on fiberglass, if it's anything like a boat hull, it may be very stiff, but fiberglass is very prone to stress cracks.

fiberglass car body panels are thicker than boat hulls. They are also smaller, which increases the resistance to vibration caused by sound.

billsburgundy
01-27-2013, 01:28 AM
AV83.....ok riddle me this then...lets says it IS a large flat panel...and lets say the fiberglass was a centimeter thick and YOU were trying your best not to mess the fiberglass up....would you choose a sealed box in a sealed trunk, sealed box in an open trunk, vented box in a sealed trunk or vented box in an open trunk?

av83
01-27-2013, 01:36 AM
AV83.....ok riddle me this then...lets says it IS a large flat panel...and lets say the fiberglass was a centimeter thick and YOU were trying your best not to mess the fiberglass up....would you choose a sealed box in a sealed trunk, sealed box in an open trunk, vented box in a sealed trunk or vented box in an open trunk?

It's dependent on what subs and how much power are you putting on them? Ive seen two twelve's sealed make metal panels go nuts. but I wouldn't feel safe even driving a car that couldn't handle a system out of fear of breaking/cracking it. If it can handle vibrations caused by everyday driving without cracking up , it can handle some bass.

billsburgundy
01-27-2013, 01:42 AM
ok. and now ill be honest with you...this is a purely cosmetic issue...I think it looks stupid when you see someones car trunk shaking and physically moving but I do love a lot of bass. it's about 1000 watts RMS per sub. the fiberglass is quite sound and the car is safe I just want to be able to crank it a bit and not have it look like trash from the outside while driving...I dont care about rattling i just dont want it to be seen.

akadj
01-27-2013, 01:49 AM
I'm assuming behind the back seats you have a large hole? if so, this is what I mean.

http://img.photobucket.com/albums/v287/byron2817/DSCN1381.jpg

The box is port and subs firing forward, into the cabin, completely sealed off from the trunk itself.

x2 or 3.. or what ever the score is.. but because the trunk isnt flexing anymore probably means now your doors and roof will flex and vibrate. . or as you say.. "trash look"

you need sound deadening as well

ThatChevyGuy
01-27-2013, 01:56 AM
pics of vehicle?

av83
01-27-2013, 02:00 AM
ok. and now ill be honest with you...this is a purely cosmetic issue...I think it looks stupid when you see someones car trunk shaking and physically moving but I do love a lot of bass. it's about 1000 watts RMS per sub. the fiberglass is quite sound and the car is safe I just want to be able to crank it a bit and not have it look like trash from the outside while driving...I dont care about rattling i just dont want it to be seen.

Then face the subs (and port If you have any) forward into the cab. you'll lose some of the low frequency response, but you shouldn't have much trunk flex. But, tbh, 2000 wrms is going to equal body flex somewhere. You are going to have to do some bracing and such to prevent the roof from having the same problem if you have them firing into the cabin. I'm pretty sure cld tiles, dynamat, etc won't help with fiberglass as much as they would with metal, either.

keep_hope_alive
01-27-2013, 02:24 AM
to get a serious answer you need to share pics of the vehicle and space available. a generic answer to a generic question is not going to be very useful. it would also be helpful to see what you currently have that you are not happy with. getting good bass out of a sub system is heavily dependent on execution.

high SPL will pressurize the cabin/trunk and something will give. if the vehicle is not air-tight, then that pressure release will alleviate some of your concerns, but can also tune the cabin as a bandpass enclosure.

custom vehicle or not, fiberglass is much more stiff and stronger than the sheet metal of modern cars. if you want to ensure stiffness, glass some ribs on the larger pieces to enhance strength. but a concern for vibration is independent of vehicle strength. vibration is caused by two pieces vibrating against each other - such as door/trunk latches and body seams. doesn't matter how strong a singular piece is, it can still move in it's entirety in lieu of flexing in a wave-like motion. strength at seams/joints is independent of individual piece strength.

just about any SPL can be attained with any combination of subs/sizes/quantity. how you integrate the sub(s) into the vehicle and how they are powered is key.

billsburgundy
01-27-2013, 02:39 AM
thanks to everyone! vehicle is unfortunately in storage. I believe i will just dynamat trunk and use vented box. i dunno.

mlstrass
01-27-2013, 06:41 AM
not many trunk cars will fit 2 15's, so why is that your choice? Single 15 ported or 2 12's off the power you have should be fine.

pickup1
01-27-2013, 09:17 AM
Any pic of said fiberglass trunk panels?