How to Build Sub into Wall Unit?

Discussion in 'Home Theater Projects' started by GaryJ, Feb 18, 2004.

  1. GaryJ

    GaryJ Stunt Coordinator

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    Hi:

    I have built a rather large wall unit for my family room. The unit is 8’ tall 12’ wide and 28” deep. I have left the bottom area open from 18” down and covered the front with speaker fabric. My original plan was to put a couple of retail box subs in there but am thinking I could build in a couple of neat subs in that space. The spaces in-between the supports are approx 18”HX24”WX28”D. I have never built a sub before but I did build the unit so I have some woodworking skills. I am planning on using a 15” Tempest driver and a 250W plate amp. Here are my questions.

    Do I just close in the area and use all the space as a box and mount the sub in the front and the amp in the back.

    Are there particular volumes I should be looking to create?

    Am I better off building a box that fits in the space to avoid coupling of the sub to the wall unit?

    Any other advice would be greatly appreciated.

    The sub(s) will be working with Acoustic Energy Aegis One speakers. The room is 3200^3.

    Thanks,

    Gary
     
  2. Baldemar Garcia

    Baldemar Garcia Stunt Coordinator

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    My quick experience recap:I decided to simply fill my space with a standalone DIY sub, which is good idea in case you ever want a change. I could never isolate the sub from the cabinet, loud volumes would eventually lead to skipping dvds or cds.

    Whatever you decide, you need to decide the appropriate enclosure size for your sub design.
     
  3. Dave Poehlman

    Dave Poehlman Producer

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    Well, you've got 7 cubic feet of space in each section which translates to about 198L each. You're right in the ballpark for a couple of ported subs.

    The things I might be concerned about would be bracing (which will detract from your total volume) and the possibility of magnetic interference with your TV since the Tempests aren't shielded.


    [​IMG] Dual ported Tempests would be a big first project. Not in difficulty, but in volume. You might be standing there when you first plug 'em in thinking "did I really need this much bass?"

    And the DVD/CD skipping mentioned above is another good point to consider.
     
  4. GaryJ

    GaryJ Stunt Coordinator

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    OK so it seems the best is to build a stand alone box and put it into the space. There is not a single piece across the bottom so I could make the sub not physically touch the wall unit.

    How do I determine the correct size for the sub?

    The bass volume will probably be at modest levels in the family room. I have a 5700^3 dedicated theater where I let reffernce levels rip.

    I was thinking of a sealed box, with my limited experience a sealed box just seems to be tighter.

    I am using a Pioneer 55" RPTV in the wall unit there will be two inches of MDF between the subs and the RPTV.

    Probably for my first project building one with existing plans would be best but since I am short on height but long on length I wanted to take advantage of the space I have available.

    Thanks again for your help.
     
  5. Baldemar Garcia

    Baldemar Garcia Stunt Coordinator

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    Wood thickness doesn't relate to magnetic shielding. I'd suggest placing the woofer to be used in its approximate position (to be installed) and checking for convergence errors on the tv screen.
     
  6. GaryJ

    GaryJ Stunt Coordinator

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    Thanks Beldemar:

    How do I determine the correct size to make the enclosure or does it matter.

    How do I determine how much cross bracing will be required?

    And how do I know if I need to put any filler in the box?

    Thanks for your help, I think this will be a fun project.
     
  7. Baldemar Garcia

    Baldemar Garcia Stunt Coordinator

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    There are many answers to your questions. But I always start by asking how much space is available for the enclosure. You already have that answer. So, I'd follow by first looking at Adire's site and downloading the plans for their recommended enclosures. IMO, if you can fit a vented design in your space, and movies will be the majority of material played through the sub, I'd go with one of the vented designs. I guarantee a much bigger smile on your face [​IMG] Since you're tied to certain dimensions, you may have to alter the design, but as long as you maintain the same internal net volume of the box, you're doing fine. Have a look at them to get an idea of how bracing and stuffing are used. They are located in the 'white papers' section on their site, iirc.
     
  8. GaryJ

    GaryJ Stunt Coordinator

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    Thanks again Baldemar:

    That was my original thought to just copy one of the Adire designs and just squash it so it fits in my space. Unfortunately it looks like I am just a little shy of room for a vented design. Do you think I could make up for the difference by making two of the Q 0.707 sealed designs. These I can get to fit in there.
     
  9. Mark gas

    Mark gas Second Unit

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    With a RPTV I don't think you have to worry about magnetic shielding.
     
  10. Baldemar Garcia

    Baldemar Garcia Stunt Coordinator

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    Gary,

    I think you'd be very happy with twin sealed Tempests. But, there is the possibility that their summed response in your room would be detrimental. What would be their distance apart? I'm assuming each would occupy the bottom space adjacent to both sides of your tv.

    Mark,

    It's true that CRT-based RPTVs are less sensitive to magnetic interference due to the additional distance (created by the cabinet) to the crts, but I think it's a good idea to do a test fit of the woofer to be used. Different sized woofer magnets will obviously create different fields. In my situation, I had to place by 12 woofer away from the rptv cabinet, as placing it right next to it (to the side) caused convergence problems.
     
  11. GaryJ

    GaryJ Stunt Coordinator

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    Thanks Mark and Baldemar:

    I am planning on putting the woofers on either side of the RPTV, approx 5' apart for each other. The RPTV is elevated 20 inches off the ground the subs will be on the ground. I currently have one 12" KLH in there (don't laugh, I needed something quick to hold me over)and it isn't causing any problem.

    BUT, if the bigger magnets of the Tempest do cause a problem is there something I can line the box with or something that will negate the effects on the RPTV?
     
  12. Dennis Gardner

    Dennis Gardner Stunt Coordinator

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    You shouldn't have to worry about your RPTV and magnets.

    Put them downfiring at the bottom of the box.

    A sealed box design found here can be adjusted to the dimensions you need. The mid Q should work great.
    brace the heck out of the box to avoid unwanted vibration and keep it away from direct contact with your wall unit and you should love the results.Tempest Designs

    Dennis
     
  13. GaryJ

    GaryJ Stunt Coordinator

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    Thanks Dennis:

    I was planning on modifying the 0.707 model sealed which would give me a 16x20X25 box. However I was planning on having it be a front firing design, do you see a problem with that?
     
  14. Dennis Gardner

    Dennis Gardner Stunt Coordinator

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    Front firing is probably prefferable since you are considering the sealed design. I was thinking back to
    my own ported dual Shiva design that I adjusted from
    the EBS alignment design to fit my needs. Being ported,
    many use the downfiring setup as I did to get a shorter
    box. My dual Shiva is only 10 inches deep under my 3 cushion couch.

    Good luck and good sound,

    Dennis
     
  15. GaryJ

    GaryJ Stunt Coordinator

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    Thanks Dennis:

    It looks like I have a plan.

    If I do have a problem with the RPTV what could I do to shield the subs?

    Thanks,
     
  16. Dennis Gardner

    Dennis Gardner Stunt Coordinator

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    Bucking magnets work for some. These are large magnets that are fitted to the back of the magnet that helps to reduce the magnetic field. I have heard that using them on drivers with humps on the back (like the Tempests have)of the magnet system is a little harder to accomplish since there isn't a flat surface to mount to.

    You really don't have nearly as much to worry about with your RPTV since the light is being directed to the back side of the screen as light instead of charged phosphor particles as a direct tube type TV.

    You can test the TV quickly by holding the raw driver close to the cabinet. I emphasize quickly, since I really put a dark spot on the monitor I am typing this with when I walked in front of my computer holding my Shiva within a foot of the screen. I have had to degauss it daily for a couple of months to completely get rid of the spot. If no difference in color is noticed when checking this quickly, then you have no reason to worry.
     
  17. GaryJ

    GaryJ Stunt Coordinator

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    Thanks again Dennis.
     
  18. Pete Mazz

    Pete Mazz Supporting Actor

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    I would build the enclosures as big as you can fit in the spaces and make the front baffle removeable with screws for possible future considerations. Leave ~1" around the enclosure for stuffing with foam or fiberglass to remove resonances and keep it isolated from the ent ctr. Building the boxes large, you can always adjust internal volume (down) with bricks or whatnot. Sealed is my preference also. If loud volume levels is not the priority, sealed is much easier to build and tinker with later on.

    Pete
     
  19. GaryJ

    GaryJ Stunt Coordinator

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    Thanks Peter:

    Those are some very interesting and very good ideas. I will be incorporating them into my project.

    Thanks again.
     
  20. GaryJ

    GaryJ Stunt Coordinator

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    double post.
     

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