Please help with Tempest Sonotube sub

Discussion in 'Archived Threads 2001-2004' started by Scott Page, Oct 12, 2001.

  1. Scott Page

    Scott Page Stunt Coordinator

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    Hi all, sorry but many questions before building my first sub.
    Ok, I've purchased 10' of 24" Sonotube, and 10' of 8" Sonotube for the port. I've got two Tempests on order for monday delivery.
    I plan to have two subs of about 340 liters or 12 cubic feet in volume, tuned to approximately 15.8 Hz as per Adire EBS application. Tempest on bottom, port on top. Do those parameters sound about right?
    I want to have the tuning low to avoid any sub bottoming with Toy Story 2, U-571 and the like at THX reference levels. Subs will be driven with an Adcom 545 amp I have laying around; 150 watts into 4 ohms per sub.
    What length should I use of the 8" tube for the port at that tuning? I thought 36" with fill or 39" without would be about right.
    The Tempest EBS application suggests using 64 ounces of polyfill for this. Will use of this much fill effect the correct port length?
    Should I use this fill with the port length that you recommend, or use no fill initially with about a 36" port, only adding fill to adjust final tune?
    Will the EBS tuning rolloff compensate for room gain or will I need to adjust final tuning to achieve a flater response if the room causes a peak? If so, how is this best accomplished (adding to port length or adding fill?)?
    If I should use fill, what's the best way to attach it to the sonotube?
    I will be using 3/4 inch MDF for caps, two inside and one outside. Should I laminate the 2 inside layers first prior to cutting them to the inside diameter, then laminate them to the larger pre-cutout outside layer, then cut out driver holes from the 3 layers? Is another way better? How much more in diameter do you recommend the outside layer be to compensate for the two sides of the sonotube and for a covering such as black automotive carpet.
    Do you recommend substituting Baltic Birch ply for the innermost MDF layer in order to provide a better connection with T-nuts? Or should they hold OK with glue added? I want to keep the cost down so I don't want to use too much Baltic or none at all if it will work well without.
    Any final suggestions? Should I be able to achieve THX reference levels with that tuning in a moderate size room (I think approximately 2900 cubic feet)?
    Thank you so much for your help. Please feel free to email respose as well as posting.
    Scott Page
    [email protected]
     
  2. Brian Fellmeth

    Brian Fellmeth Supporting Actor

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    "I will be using 3/4 inch MDF for caps, two inside and one outside. Should I laminate the 2 inside layers first prior to cutting them to the inside diameter, then laminate them to the larger pre-cutout outside layer, then cut out driver holes from the 3 layers? Is another way better?"
    Routering MDF thicker than 3/4 is tough. I would definitely cut all circles and driver holes first, then laminate. To get the driver and port holes perfectly lined up, stack them and male the pivot holes with one drill pass. Or, if your driver and port holes are going to end up in teh exact center of the end cap layers, just reuse the pivot holes used to rout the endcaps and the holes will end up perfectly centered and lined up.
    "How much more in diameter do you recommend the outside layer be to compensate for the two sides of the sonotube and for a covering such as black automotive carpet."
    Just depends on how much overhang you want.
    "Do you recommend substituting Baltic Birch ply for the innermost MDF layer in order to provide a better connection with T-nuts? Or should they hold OK with glue added? I want to keep the cost down so I don't want to use too much Baltic or none at all if it will work well without."
    I highly recommend this- but you can use cheap plywood. Also, with the plywood inner layer you can skip the second MDF inner layer.
     
  3. Patrick Sun

    Patrick Sun Moderator
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    Your amp may not get you to "THX reference" levels with only 150W/ch. But I'm not sure what "THX reference" refers to? 115dB @1m?
    You're free to peruse my Sunosub construction pages in my signature below, though none quite match what you are going to build.
    ------------------
    PatCave; HT Pix; Gear; DIY Mains; DIY CC; Sunosub I + II + III; DVDs; LDs
     
  4. Andrew Pratt

    Andrew Pratt Producer

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    Those sound very much like the ones I helpped Jeremy build for his basement. In a word they are phenominal [​IMG]
    http://www.hometheaterforum.com/bbs/equipment/28538.html
     
  5. Scott Page

    Scott Page Stunt Coordinator

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    Pat, I think the THX Reference Level is 105 db at the listeners position (same as the movie studio designed level). Calibrating with AVIA is done at 85 as it is set 20 db's below reference level. With Video Essentials, it is calibrated at 75 as it is set 30 db's below reference level. That is the tones are set on the DVD's 20 and 30 db's below DVD output, respectively so that you don't kill your ears during calibration.
    Correct me if I'm wrong, but that is what I understand.
    Scott
     
  6. Scott Page

    Scott Page Stunt Coordinator

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    Brian suggested that you can have the port and woofer in the exact center of the subs. Is this OK from a standing wave aspect, or like placing your subs in your room, for best sound should the drivers be different distances from the adjoining sonotube walls, or in other words, off-center?
    Anyone else have an opinion regarding the ability of two of these subs to reach 105 db's at the listener with 150 watts each? Or should I change volume and tuning for more output? Keep in mind the preventing bottoming is more important to me than high output. I hate it everytime I have to reduce the volume because of some low bass heavy scene. I want to watch at the AVIA calibrated level of 80 or 85 db's (100-105 db's peak output)without worry that I'm going to damage the drivers.
    Pat, I will diffently be using your website for construction help; it is great. I know this design is not exactly what you built; but what do you think of it? You seem to be one of the resident sonotube experts so I value your advice. What would you change in my intended design?
    Scott
     
  7. Patrick Sun

    Patrick Sun Moderator
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    I have a full day tomorrow at DIY 2001 Atlanta, so I can't respond until tomorrow night. Sorry for the delay.
     
  8. Patrick Sun

    Patrick Sun Moderator
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    I think you'll need more amp for your levels if you intend on powering 2 subs with 150W for each sub, unless you actually put the subs relatively close to you. If you get 105dB @1m for each sub, you may put each sub further away from you, then as the distance increases, your power requirement increases (plus having the headroom with more power will lessen the chances of clipping the amp, but you shouldn't be bottoming out your driver with this amount of power). But you'll have to decide when you step up to more power. [​IMG]
    Going with a 12 ft^3 sub, tuned to around 16Hz with a 8" port, and 24" wide tube, you'll need 51" of internal height on the 24" tube. Just add the thickness of the endcaps that will sit inside the tube to get the overall height. For example, if you have 1.5" of endcap thickness (a layer of 3/4" endcap for each end) plus 1/4" of plywood for the t-nuts on the inside of bottom endcap, you'd need 52.75" of total tube length.
    The 8" port should be 37.5" long (but if you take into consideration the 1.5" thickness of the top endcap, the port itself should be 36" long).
    The Adire LspCAD for this design looks pretty good.
    This will be a SVS-like sub in looks, but just bigger. The overall enclosure volume and tuning should be sufficient for it to survive those tough LFE passages.
    My preference is to keep the port on the bottom endcap, but I don't think you'll notice any significant differences porting from the top endcap.
    ------------------
    PatCave; HT Pix; Gear; DIY Mains; DIY CC; Sunosub I + II + III; DVDs; LDs
     

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