Subwoofer

Discussion in 'Speakers' started by -, Jan 8, 2010.

  1. Guest

    Ok so I am wanting to get a better sub for my theater system. I want to build a box for my 8" sub. I want to know what is the best way to build the box. I know that the boxes to the subs are designed different to produce more bass from a small sub. Any one suggest a box design or something to get alot of bass from my sub. Ported, Sealed, Bandpass, and help would be appriciated.
     
  2. Robert_J

    Robert_J Lead Actor

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    Without knowing the Thiele/Small parameters of your sub we can't help. Post those and we can get started with a design.
     
  3. Guest

    • Blue Injection-Molded P.P. Cone
    • Black Rubber Surround
    • Chrome Finished Basket with Vent for High Performance
    • Bumped & Vented Yoke Plate for Extended Excursion
    • Silver Plated Terminal
    • Rubber Magnet Boot for Better Protection
    • 1.5'' High Temperature Kapton Polyamide Voice Coil
    • 4 Ohm Impedance
    • 200 Watts RMS/400 Watts Peak
    • SPL @ 1W/1M: 89dB
    • Overall Diameter: 7.76''
    • Mounting Depth: 3.54''
    • Magnet Weight: 60 oz.
    • Here are all of the specs. Not sure if this is what u was wanting. Might upgrade the sub to a kicker or something later on.
     
  4. Peanut123

    Peanut123 Agent

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    What 8 inch sub are the specs for?
     
  5. Robert_J

    Robert_J Lead Actor

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    Those are the descriptions of the speaker, not the Theile/Small parameters. Without the parameters we have no idea how to properly design an enclosure for that driver. Any recommendation would be nothing more than a guess.

    http://www.eminence.com/resources/data.asp
     
  6. Peanut123

    Peanut123 Agent

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    This is true. I was only asking so I could see if I could find that info for him if he couldnt find it.
     
  7. Guest

    It is a American Legacy sub. Not a name brand or anything but I have 2 of them laying around so was wanting to do something with them.
     
  8. Guest

  9. Cees Alons

    Cees Alons Moderator
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    David,

    "Thiele/Small parameters" may sound like impressive nerdish bullshit, but they really are information about the weight of the cone of that driver, its stiffness, the strength of the magnet and how much it moves. That info is necessary to design a proper box. The box has to counteract some wild movements of the cone at certain frequencies and help it move correctly in general. It even uses some of the sound (-energy) of the backside of the cone to reflect it back into your room (ears). This is why you are absolutely right about a box being able to produce more bass from a sub of a given size.

    That's also why people asked this, and that's why you cannot build a really good subwoofer box if those figures aren't known. Fortunately, that manual has all the info necessary to build a proper sub! Do you happen to have a program called WinISD? If you have, you're all set. If not, you can either try to download it, or else we may be able to help you if you tell us how big the box can be maximally, etc.


    Cees
     
  10. Robert_J

    Robert_J Lead Actor

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    Actually, my favorite modelling program is Unibox. It is an Excel spreadsheet with built-in macro. In fact, Dan Wiggins posted years ago that is was almost as accurate as the software he used and he is a professional transducer engineer.

    If you want to mail me one of your subs, I can determine the T/S parameters using Woofer Tester 3.
     
  11. Cees Alons

    Cees Alons Moderator
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    Robert,

    The T/S parameters of David's woofer are in the above mentioned manual. No need to get them mailed.


    Cees

    PS: I edited your link out. It's against our rules (link in my signature) to promote commercial websites and you've done it enough now.
    C.
     
  12. Robert_J

    Robert_J Lead Actor

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    I didn't have time to check the link earlier. As for the PS, my mistake.

    David,

    In Unibox, I came up with a sealed one cubic foot box. Unfortunately the F3 is 42hz. You won't get much low bass from this. A two cubic foot enclosure tuned to 20hz isn't bad. I tried tuning higher but the limited xmax (I guessed at 8mm) limits that. Both designs were done using a standard 50w Parts Express plate amp with no boost and the SSF set around 18hz to 20hz.

    -Robert
     
  13. Guest

    Ok, thank you, srry about the links
     
  14. Cees Alons

    Cees Alons Moderator
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    David,

    That weren't your links I was referring to!
    No need to apologize, therefore.


    Cees
     
  15. Guest

    well is there anyone that can help?
     
  16. Robert_J

    Robert_J Lead Actor

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    Can you explain what was lacking in my post with two different designs?
     
  17. Peanut123

    Peanut123 Agent

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    I think he wants the dimensions and such for it. But I might be wrong.
     
  18. Cees Alons

    Cees Alons Moderator
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    We need some additional info if you're not going to design it yourself!


    Cees
     
  19. Guest

    well the box size doesnt matter to me. I will build it as big or as small as needed to make it sound good. A design would be nice but im looking for some info on what type of box and stuff like that.
     
  20. Cees Alons

    Cees Alons Moderator
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    OK, yours is the LW89X, I assume?

    Also, I'll assume you only need one speaker in your box. Using the second speaker as well, would give you twice the possible max power (+ 3 dB), but you'd also need two amplifiers in stead of one - and a bigger box. That's because if you want to use both, it's advisable to go for a bigger box, not use two subs in the same room (it's quite possible to do that, but one box is better).

    Your speaker(s) has (have) a resonance frequency of 38 Hz. Therefore, I wouldn't go for a sealed box, nor would I try to design a vented box tuned lower than approx. 27 Hz. The sealed box will not give you that extra bass you wrote about, a vented box will.

    The "optimum" box would be 3.2 cubic feet and be tuned at 32 Hz. That box will also keep the frequency curve pretty straight, keep something called the phase plot within reason and the "group delay" not too ugly. But it's possible to get a bit more lower bass, within a reasonable range, if you a bigger box (4.5 cubic feet) tuned to 27 Hz. There will be a little bit more distortion of the lowest frequencies, though.

    Here are the measures:

    I'll give you dimensions of a box for 1 speaker. Use 1" thick chip-plate, or similar material. No need to "stuff" the boxes heavily: all inside dimensions are much smaller than the wavelength of the highest frequency it will reproduce (100-125Hz).

    Optimized box (tuned at 31.81Hz): volume = 3.18 cf
    Outside dimensions: h x w x d = 30.6" x 19.9" x 12.7"
    vent: 3.2" x 3.2" and 6.2" deep

    More lower bass, but less straight curve (and more group delay, tuned at 27.15Hz): volume = 4.53 cf
    Outside dimensions: h x w x d = 34.2" x 22.0" x 14.0"
    vent: 4.0" x 3.2" and 6.6" deep

    Your choice!

    Cees
     

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