Building a DIY sub...many questions...

Discussion in 'Archived Threads 2001-2004' started by dave shreve, Dec 16, 2001.

  1. dave shreve

    dave shreve Extra

    Joined:
    Dec 13, 2001
    Messages:
    18
    Likes Received:
    0
    Trophy Points:
    0
    I'm starting to plan the construction of a sub for a 70/30 movies/music mix. I've got lots of questions, and feel free to comment on anything else as you see appropriate.

    Here's where I am so far:

    85L net enclosure volume from 18" sonotube, ported and tuned to 20Hz with 50% stuff for 23 Hz F3 and projected in-room F3 of 19Hz

    Shiva 12" driver

    250W plate amp

    Plug to close port for detailed music

    Questions:

    How will a plate amp fare being mounted horizontally on one of the end caps instead of vertically as on a normal box? I realize this will decrease the effectiveness of the natural convective cooling. Will it survive on the bottom plate(preferred)? Or the top plate(rather not run the wires up the side, though...)? Or do I need to go to a class D amp?

    I've noticed that most of the sonotube designs point the driver at the floor. In order to get the amp on the bottom(if it will live there), I need to put the driver on the top. Is there any reason not to do this? Well, other than SPL? I'm not that concerned about the ultimate output--the 250W amp is mainly for generous headroom.

    Some place the ports on the same end as the sub and some put them on the opposite end. Are there inherent advantages to either? My initial leaning is to port opposite the driver on the end with the amp. How close can the ports be to the wall of the enclosure? The driver?

    How many/what size ports do I really need? LspCAD predicts some ugly compression with just one 3" or 4" port, and minor compression with two 3" ports. Is it really as bad as it looks?

    I've noticed most use 2 layers of 3/4" MDF at each end. How would one layer of MDF and one layer of hardwood(for appearances and hence spouse approval) fare?

    I was planning on assembling this thing with all-thread rod and weatherstripping instead of glueing/caulking the caps to the tube. I want the flexibility of being able to tear it apart to make adjustments to the enclosure volume and/or porting if I want to down the road.

    That's all I can think of right now. I'll probably have more in a while, though...

    Thanks!

    -dave
     
  2. dave shreve

    dave shreve Extra

    Joined:
    Dec 13, 2001
    Messages:
    18
    Likes Received:
    0
    Trophy Points:
    0
    One more thing--where can I get 18" Sonotube without having to buy a whole 12' long piece? I am near Indianapolis, IN...
     
  3. Dustin B

    Dustin B Producer

    Joined:
    Mar 10, 2001
    Messages:
    3,126
    Likes Received:
    0
    Trophy Points:
    0
    The main reason we don't put the driver at the top end is balance. That put the center or gravity pretty high. So unless you plan on making a really heavy base plate for it I'd stick the driver on the bottom.

    Have you considered mounting the amp to the side of the tube like Hank Frankenberg and I did? Follow my sig to see some pictures.

    A 4" port shouldn't be a problem with a Shiva. If you are a little worried use a flared one. People have had excellent results with a 4" flared port and a Tempest. The Tempest displaces a litre more air then a Shiva, so if it can work for a Tempest it will surely work for a Shiva.

    The 3/4" MDF and 3/4" hard wood should be fine. And there was one guy on the sonotube links page that did what you are suggestioning with the threaded rod. Check his page out and send him some questions to find out how that worked.

    There are some people that have managed to buy scrap from a concrete supply place. I wasn't, I still have 6' of 18" sonotube sitting in my garage (to bad it would cost an arm and a leg to ship it to you).

    As for the horizontal plate amp bit. I remember Dan saying it would bo okay for the AVA250, but if you were going to do it he figured the fins should be sticking up, and air should be free to rise off them.
     
  4. Brian Fellmeth

    Brian Fellmeth Supporting Actor

    Joined:
    Jul 30, 2000
    Messages:
    789
    Likes Received:
    0
    Trophy Points:
    0
    Fireing up is sonically fine, but it creates the problem of protecting and hiding the driver.

    Since you need to mount three things on your endcaps, that means that one side will have 2. Why not go to a 20-22 inch diameter to create more endcap space.
     
  5. Hank Frankenberg

    Hank Frankenberg Cinematographer

    Joined:
    Oct 13, 1998
    Messages:
    2,573
    Likes Received:
    0
    Trophy Points:
    0
    Dave, he meant to say Hank, not Frank. My side-mounted amp encolsure (for the Adire 250-watt amp)is visible in a couple of the photos on my low-res web site:
    http://www.geocities.com/hankbond1/My_page.html
    I tuned to 17.5 Hz and used a dual-flared end 4" port tube which is plenty of porting.
     
  6. Dustin B

    Dustin B Producer

    Joined:
    Mar 10, 2001
    Messages:
    3,126
    Likes Received:
    0
    Trophy Points:
    0
    Oops, sorry Frank :p) I'll go fix that.
     
  7. dave shreve

    dave shreve Extra

    Joined:
    Dec 13, 2001
    Messages:
    18
    Likes Received:
    0
    Trophy Points:
    0
    On amp mounting:

    Those side-mounts look nice. How hard was it to get the geometry right for the mount? I'm more worried about actually cutting the right shape than designing it(I'm an engineer..) Did you do anything to ensure no leaks around the screws mounting it to the tube? What about the wire pass-thru?

    On tube size:

    I have very little available space in my living room. 18" diameter by 30" overall height is the limit. If I weren't so limited on space, I'd be going with a 15 for sure.

    How do I adjust the port length for flares? LspCAD had an option regarding flares, but I can't say I really understand how it works--it wants a huge radius. Also, with just a 12" driver, will I be sacrificing anything(efficiency, etc.) by going to a 4" port? That just seems like a big hole...

    -dave
     
  8. Dustin B

    Dustin B Producer

    Joined:
    Mar 10, 2001
    Messages:
    3,126
    Likes Received:
    0
    Trophy Points:
    0
    Follow the link in my sig. Once there go DIY/Contruction/Plate Amp Mount. I have a couple rough scetches and a description of what I did and how I did it.

    As for the wire, I drilled a hole through the tube inside the plate amp mount barely big enough for the wire to fit through. After I had the driver in place with the wire hooked up to it, I pulled it snug through the hole, and then put some caulk in the hole around the wire. Let it dry and done, hasn't given me any problems.
     

Share This Page