Sub without a box?

mach189
mach189 Posts: 12
edited September 2011 in Car Subwoofer Talk
I know I may be crossing the line with this post but does a sub always need a box? Depending on how my speakers sound with an amp I may buy an 8" sub like the Polk MM2084. There is an area about 12"x12" that's cut out of the frame in the trunk behind the rear seats and I was wondering if I could treat a sub like a coax and install it there? Space is at a premium in my trunk so this idea appeals to me. I look forward to any input. Thanks.
Post edited by mach189 on

Comments

  • michael_w
    michael_w Posts: 2,813
    edited April 2006
    I'm not sure if it's what you're describing here but yes you can run a sub without a box. All you have to do is have something seperate the backwave that is produced, so basically some kind of barrier that you mount the sub into.

    Maybe this will help explain things.
    Infinite baffle link
  • mach189
    mach189 Posts: 12
    edited April 2006
    Yeah that's exactly what I was talking about. The "rear deck" installation is how I was planning on it if I got a sub. Could I use the Polk MM2084 in this situation or would I need a sub designed specifically for this?

    Thanks for the info.
  • neomagus00
    neomagus00 Posts: 3,899
    edited April 2006
    mach189 wrote:
    I know I may be crossing the line with this post but does a sub always need a box? Depending on how my speakers sound with an amp I may buy an 8" sub like the Polk MM2084. There is an area about 12"x12" that's cut out of the frame in the trunk behind the rear seats and I was wondering if I could treat a sub like a coax and install it there? Space is at a premium in my trunk so this idea appeals to me. I look forward to any input. Thanks.
    what line could you possibly be crossing? :confused::)

    infinite baffle is great in theory, very difficult to pull off accurately in practice. it means that, once you mount your sub into its hole in the rear deck, you have to seal the cabin of the car from the trunk, and make it completely airtight - in effect making the whole trunk your box. this is, as you may imagine, rather difficult.

    an 8" sub generally requires very little airspace, and you could potentially build a sealed box to spec, then simply bolt that sealed box to the rear deck (where there's an existing hole). that gives you the sealed box on the sub, but keeps the whole assembly out of the way.
    It's not good, very fundamentally simply not good. - geolemon

    "Its not good enough until we have real-time fearmongering. I want my fear mongered as it happens." - Shizelbs
  • 98thumpin
    98thumpin Posts: 649
    edited April 2006
    sounds good but hard to pull off
    John Tyler Birch

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  • mach189
    mach189 Posts: 12
    edited April 2006
    neomagus00 wrote:

    an 8" sub generally requires very little airspace, and you could potentially build a sealed box to spec, then simply bolt that sealed box to the rear deck (where there's an existing hole

    That's actually a really great idea. I don't know why I hadn't thought of that already. Basically I want my car to look stock.

    When I said "crossing the line" I was referring to the idea that subs must have a large box and take up alot of space. I was just kidding of course.
  • iworkfortweeter
    iworkfortweeter Posts: 53
    edited April 2006
    theoretically possible, yet not the best idea ever...you will need a sub specifically designed for this application, and do some serious reading pertaining to the "infinite baffle" theory described earlier. i would just build a box, but that's a personal matter.
    in any event, good luck!
    currently in car:
    '00 Honda Accord LX V6
    AEM V2 cold air induction
    c400.4 amp powering a pair of momo 6500's
    and a pair of momo 6x9's
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    custom fab work for tweeters
    jl rca's, dist block and power/grounds
    alpine cda 9857 head
    three ground loop isolators
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  • MacLeod
    MacLeod Posts: 14,358
    edited April 2006
    Nothing wrong with using a sub IB as long as its designed for it. Scott Buwalda ran his 3 12's in his old Altima free air and never seemed to have any trouble cleaning up at competitions.

    The 300M that I keep raving about also runs 3 10's free air and has no trouble hitting that 25 Hz thump on the test disc. But these subs are designed for free air.
    polkaudio sound quality competitor since 2005
    MECA SQ Rookie of the Year 06 ~ MECA State Champ 06,07,08,11 ~ MECA World Finals 2nd place 06,07,08,09
    08 Car Audio Nationals 1st ~ 07 N Georgia Nationals 1st ~ 06 Carl Casper Nationals 1st ~ USACi 05 Southeast AutumnFest 1st

    polkaudio SR6500 --- polkaudio MM1040 x2 -- Pioneer P99 -- Rockford Fosgate P1000X5D
  • neomagus00
    neomagus00 Posts: 3,899
    edited April 2006
    in the 300M's context, however, 'free-air' is just a misleading euphimism for 'really really big box' aka 'the trunk'...
    It's not good, very fundamentally simply not good. - geolemon

    "Its not good enough until we have real-time fearmongering. I want my fear mongered as it happens." - Shizelbs
  • mach189
    mach189 Posts: 12
    edited April 2006
    I kinda found out the answer to my question yesterday. My family went to eat with my grandmother and I looked in her trunk for something and saw a 10" "free-air" sub. It's a '98 lexus gs300 and the sub is setup pretty much the way I was thinking about doing it except the hole in the trunk fits a 10" sub perfectly in hers whereas I would have to fabricate something to make it fit in mine. Thanks for feedback guys.
  • ward91
    ward91 Posts: 338
    edited June 2006
    do you mean using the boot as a giant subwoofer enclosure like 6x9's ect
    ELECTRONICS
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  • PaintballFREAK
    PaintballFREAK Posts: 28
    edited August 2006
    ive tired that actually
  • cult4d5
    cult4d5 Posts: 7
    edited September 2011
    how about a piston sub?

    edit: wow this is an old thread lol. didnt catch that til just now
  • 20hz
    20hz Posts: 636
    edited September 2011
    how about building a clamshell isoberic (2 speakers with the cones facing each other) with that the driver only needs 1/2 of the needed cabinet size .
    But if thats still to big a freeair designed speaker using the trunk as a cabinet is probebly best , just be sure the the sound from the back of the speaker is isolated from the front .
    You will probebly need a large equalizer to smooth out the sound .
  • digidave
    digidave Posts: 1
    Hi everyone. I just installed two 10’s dvc ultramarine subs on my boat. But the space behind the sub is very tight to fit a sealed box. Any idea how I can still manage to seal the space to give the sub a better performance. I see the cone moving like crazy but not hearing the sound on that level of movement.
  • Hansvelton
    Hansvelton Posts: 59
    edited May 3
    You absolutely NEED a box. The lack of bass is due to cancellations from the back wave reaching the front sound wave and cancelling it out.
    That is the very reason for a box, to separate the out of phase front and back sound waves.
    Not sure what to advise, without seeing the space you have, but you must somehow separate the front/back sound if you expect to have any bass at all.

    Perhaps an automotive box, as there are many that fit odd sized spaces in cars.
  • Jammin06Ion
    Jammin06Ion Posts: 16
    I've only ran one free-air setup in a car ever, and it worked pretty awesome! It was a pair of Pioneer 4-ohm 12" free-airs in a 1975 Dodge Dart. I did my research on infinite baffle, so I got my plan in order. I removed the back seat, then cut out the bracing that goes across the trunk opening. I then used cardboard to draw out a template for my 1/2" MDF. I cut it out, cut the two 12" holes, then mounted it to the back of the seat. YES, I did seal the trunk from the cabin! I ran a thick bead of silicone around the entire piece of MDF and it worked great! To protect my Phase Linear Graphite 6x9's I put them in foam speaker baffles and added silicone to those also to keep the sound waves from the subs from getting to my 6x9's. I paid more for the 6x9's than I paid for both subs, the MDF, and the caulk so I didn't want to damage them! Everything sounded awesome! I ran the subs in parallel to a 1200-watt Profile amp. It all worked out amazing! That was in 1995.

    As for today's cars with fold-down rear seats, I personally would not suggest free-air subs because of the fact that you'll not be able to seal off the trunk from the interior due to the fabric. I'd only do free-air in a car without fold-down rear seats.

    I can tell you from personal experience that a decent pair of free-air subs will sound great, they won't pound as hard as subs in a box, and the response is not as tight. When I sold that car and bought a Nissan Sentra wagon, I sold the Pioneer free-airs and bought a pair of Kenwood 4-ohm SVC subs and a ported Q-Logic box and it was like night and day! Crutchfield told me the exact length to cut my ports to for the box size and subs, which really helped.

    That's MY two cents worth on free-air (infinite baffle) subs. I'm assuming the original poster wasn't talking about just ANY sub with no enclosure.
    Kenwood eXcelon KDC-X704 head unit, McLaren MDSP-15 sound processor, Eclipse PA5422 4-ch to full range, Cadence Q75T tweeters in parallel with Pioneer TS-A1686R up front, Image Dynamics XS28 tweeters in parallel with Pioneer TS-A6990F in back, Polk Audio PA-D1000.1 driving a single Alpine S-W10D4 sub in Belva box, all in 2006 Saturn Ion.
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