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Enclosure Design Help

Discussion in 'Archived Threads 2001-2004' started by Chris Eriksen, Jul 15, 2001.

  1. Chris Eriksen

    Chris Eriksen Stunt Coordinator

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    Hello Everyone,
    I am hoping you can help me with a DIY sub enclosure for my home theater. I have a lot of experience designing and building exotic sub enclosures for car audio, so the fabrication will not be a problem. However, car audio applications rely heavily on cabin gain, so my design plans may be a bit suspect. [​IMG] Any recommendations will be greatly appreciated.
    I already have the driver and the amp, as well as a Behringer Feedback Destroyer. The sub amp is a Hafler 9290, which produces approximately 500 watts rms into a single 4 ohm load. The sub is a Cerwin Vega XL-18S, a high-efficiency lightweight paper-cone driver that was originally aimed at the car audio market. Here are the T-S parameters on this 18" sub:
    Imp. 3.5l
    Fs 28
    Qes 0.173
    Qms 5.249
    Qts 0.167
    Vas 7.31 cu ft
    Xmax 0.33"
    PE 500 watts rms
    SPL 96 dB @ 1w/1m

    My oddly-shaped HT room is on the large size, with a length of 27', a ceiling height of 11', and a width of 10-15', depending on the location. A drawing of the room is located HERE . Please ignore the speaker locations, as these have changed. The primary seating area has now been moved back to a line that extends between the green blocks.
    My design goals are as follows: Deep bass extension and good transient response (for an 18" sub) in an enclosure of less than 6 cubic feet. This sub will be used for HT only, as my mains have a useable in-room response to below 40 Hz.
    Here is where I become uncertian. From my preliminary calculations, I am considering a 5.3 cubic foot vented enclosure, tuned to 18 Hz. Should this enclosure yield my desired results? Or am I barking up the wrong tree? Please let me know if I am overlooking something, or if anyone has suggestions for a better design.
    Thank you in advance,
    Chris Eriksen
     
  2. James W. Johnson

    James W. Johnson Screenwriter

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    That driver is pretty much best for car use, but if you have the driver already I guess it could'nt hurt to try it out.(I would)
    I would drop it in something like 8cuft and tune it to 18Hz if it were me.
    However if you don't already have the driver then look at purchasing a Tempest driver ($140ea) it is much better suited for home use.
    ------------------
    James' DIY speakers
    [Edited last by James W. Johnson on July 15, 2001 at 10:39 PM]
     
  3. Chris Eriksen

    Chris Eriksen Stunt Coordinator

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    Hi James,
    Thank you for the quick reply. Unless this driver is a bad candidate, I will give it a try. (I already own it.) Out of curiousity, what makes this driver better-suited for car audio use? Is it the higher resonant frequency, or are there other factors?
    Thanks,
    Chris
     
  4. Patrick Sun

    Patrick Sun Moderator
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    The high Fs=28Hz (resonant frequency) is the main drawback to this driver IF you want the sub to maintain high SPL down to 20Hz. The driver is highly reliant on cabin gain inside a car to produce the low end output, but in a home theater environment, it may not produce as much sub-25Hz output as desired, and might sound boomy/one-note if the box volume and tuning isn't done correctly.
    Have you modelled this in WinISD to get an idea of the roll-off around 20-25Hz?
    ------------------
    PatCave; HT Pix; Gear; DIY Mains; DIY CC; Sunosub I + II + III; DVDs; LDs
     
  5. Chris Eriksen

    Chris Eriksen Stunt Coordinator

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    Hi Patrick,
    Thank you for the reply. I have modeled this sub using several programs (including WinISD), and I am having trouble finding fault with its performance. Maybe I am overlooking something? In a 5 cubic foot enclosure tuned to 18 Hz, it appears to slope gradually to 20 Hz, rolling off below that point. It is about 5 dB more efficient at 70 Hz than at 20 Hz, but I am assuming my Behringer FBD should take care of that. Please let me know if I am missing something?
    Thank you,
    Chris
     
  6. ThomasW

    ThomasW Cinematographer

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    Can you sell the driver?
    It's really not at all suited for your desired performance. As noted the Fs is too high, also the Qts is way too low, the Xmax is low, and the Vas while not big, is just a little inappropriate for a 6 cu ft box. Trying to tune this driver to play at 18Hz is probably impossible in the real world, regardless of what the software model predicts
    As a result unfortunately you will not be able to obtain you stated goal of "Deep bass extension and good transient response in a box of less than 6 cu ft".
    The driver is most likely designed to have good output in the 35-40Hz area. So if you try to EQ the driver to perform per your desire, 20Hz or so, you'll melt the voice coil with any attempt at reasonable output.
    [Edited last by ThomasW on July 16, 2001 at 11:06 PM]
     
  7. Chris Eriksen

    Chris Eriksen Stunt Coordinator

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    Hi Thomas,
    Thank you very much for your honest opinion. I will sell the sub and try something else - maybe a Tempest. [​IMG]
    Thanks again,
    Chris
     
  8. Gregg Loewen

    Gregg Loewen Video Standards Instructor, THX Ltd.
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