smart51
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| posted on 31/7/09 at 09:04 AM |
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Speaker cabinet material
I'm going to be making some under seat speaker cabinets for my other car. The problem is there's only 60mm of space below the seat.
I've been told the best stuff for making speaker cabinets is MDF as it is an acoustically dead material. Because of the lack of height I want
to use a thin sheet of the stuff. Is 6mm too thin?
The bottom panel will be against the carpet so won't resonate as if it were in free air. The baffle will be braced internally some how too. Do
I need to sacrifice some internal volume to make the baffle plate thicker?
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tegwin
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| posted on 31/7/09 at 09:20 AM |
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Assuming you have a small space you wont be able to fit a powerful driver in there... so I wouldnt worry too much...
IMHO 6mm would be ok, assuming you have some form of internal bracing....
I built a BIG sub years ago using 1.5" MDF... it weighs the same as the moon!
Dont forget that most car speakers dont really have an enclosure as such....
So if you are clever with your design you could use GRP....
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Triggerhappy
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| posted on 31/7/09 at 09:33 AM |
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Bracing is the name of the game then...make some inner bracing between the bottom and top faces of the box (the biggest walls) and that will stiffen
the box considerably.
Im from Sweden, so im escused...The Muppet drummer for president!!
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nick205
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| posted on 31/7/09 at 09:34 AM |
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What sort of driver are you intending to use and how are you mounting it?
(I'm assuming a small sub facing up under the seat?)
Personally I'd use a min. of 12mm MDF - IMHO 6mm is too thin and will resonate too much. The drop in internal volume is not worth worrying
about, the enclosure stiffness is.
That said 60mm is very little space to start with so you're not going to move much air either side of the driver and probably need to think
about designing in a reflex port of some kind.
Another option might be a bass tube mounted on the behind or just in front of the seat. These can produce quite good bass detail when driven properly
and mounted securely. And you could probably fit one either side of the car to bolster the overall sound level.
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Steve Hignett
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| posted on 31/7/09 at 09:46 AM |
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I would make the base of the enclosure in Fglass, that woay, you would be using as much as possible of the room available by following the contours of
the floor, then use the MDF for the sides and top, and use ribs to strengthen...
Search youtube for custom sub enclosures...
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smart51
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| posted on 31/7/09 at 10:11 AM |
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quote:
Originally posted by nick205
What sort of driver are you intending to use and how are you mounting it?
(I'm assuming a small sub facing up under the seat?)
Personally I'd use a min. of 12mm MDF - IMHO 6mm is too thin and will resonate too much. The drop in internal volume is not worth worrying
about, the enclosure stiffness is.
That said 60mm is very little space to start with so you're not going to move much air either side of the driver and probably need to think
about designing in a reflex port of some kind.
Another option might be a bass tube mounted on the behind or just in front of the seat. These can produce quite good bass detail when driven properly
and mounted securely. And you could probably fit one either side of the car to bolster the overall sound level.
Yes that's it, though not so much a sub-woofer as just a woofer. The main speakers in the car are mounted in the sides of the foot wells and
the bass response seems to roll off from about 150Hz. Good for speech.
There's space under the seats for a 4 litre enclosure but only for small drivers. I've got some old kenwoods that I'll try for now
to see how it goes. My head unit has 4 outputs so I'll drive these from the rear outputs.
I'd planned to mount the drivers facing up to the inside of the baffle plate and have large (25mm or more) holes drilled in the baffle to let
the sound out. That way if I have a heavy passenger, they're not going to push the seat foam and springs into the driver cone.
One idea I had was to have 2 6mm baffle plates glued to each other to make a 12mm thickness. The inner one would have a larger diameter cut out so
the speaker would mount only to the top piece, a bit like a rebate in a single thicker panel. That will give more stiffness and still allow the
driver to fit in the box.
It will be a reflex cabinet. Helmholz equations are simple enough.
My ambition is not to make it sound great, just to sound better. How much will the seat bases absorb middle frequencies? Do I need a low pass filter
to cut them out?
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nick205
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| posted on 31/7/09 at 10:41 AM |
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Dedicated bass drivers would be much beter, but if you have the Kenwoods to hand then worth a try. Again a low pass filter would help seperate the
sound, bu TBH the seat will cancel a lot of the upper frequencies out by itself.
Shame you can't buy MDF tube as the bass tube approach seems idela for the vehicle. You could always cut and glue a lot of MDF rings together
to make one  
Seeing as you have the materials and skills an GRP cabinet could work well, certainly would maximise the cabinet volume in the space available - i
guess it depends how much time, effort and money you want to throw in.
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suparuss
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| posted on 31/7/09 at 12:08 PM |
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quote:
Originally posted by nick205
You could always cut and glue a lot of MDF rings together to make one
dont laugh too hard, ive made a few pieces of furniture like that, but with wisa birch ply. includeing some hifi speakers-
 
layered ply speakers
if you look for some drivers that have a low compliance (ie, quite stiff) then the volume matters much less and you can even get away with an open
baffle design.
for thckness of material it sounds like it isnt going to matter in this situation, everything in a car resonates anyway so i think a bit of 6mm mdf is
the least of the problem.
[Edited on 31/7/09 by suparuss]
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nick205
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| posted on 3/8/09 at 09:23 AM |
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Cracking speaker cabs 
I've made a few speaker door pods this way too - can be labourious, but it's worth the effort.
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