Need advice for DIY sealed sub (long)

Discussion in 'Archived Threads 2001-2004' started by JohnOwens, Mar 3, 2003.

  1. JohnOwens

    JohnOwens Agent

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    OK all you DIY pros, I need your input and advice for a sealed sub project I would like to undertake. I apologize in advance for such a long and rambling question, but I don't want to leave any info that might be needed.

    I am attempting to build a sub in the $400 - $500 range for dual music/ HT duty. Basically I want a tight, articulate sub that will also sound pretty good for movies, while obviously not able to plumb the depths quite like a big vented sub.

    The room is around 5000 ft^3 - a large open space. The sub will be using the 100Hz fixed crossover from my Marantz sr7200. (wish it were more like 80). Mains and center are B&W CDM-1s. I usually listen to stuff like Dave Matthews, Lyle Lovett, Holly Cole, Norah Jones, Sarah McClaughlan (what is it about these female vocalists???).

    Because size of the box is a factor, I would like to use a 2 ft.^3 enclosure. I also think sealed would be easier to build and get right (for a newbie like me).

    The question is which driver to use. Using Win ISD, I have narrowed it down to Adire Shiva III or DPL 12.

    Shiva: F3 - 40Hz
    Qtc - 7.45

    DPL 12: F3 - 30Hz
    Qtc- .755

    group delay numbers for both are about the same and pretty low. I plan on using the 350W Rhythmicaudio amp.

    Does the added extension of the DPL 12 make it the obvious choice or am I missing something?

    Will adding in room gain make the Shiva play plenty low, and cause the DPL 12 to have too much extension
     
  2. Pete Mazz

    Pete Mazz Supporting Actor

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    If you're going to push the SPLs, the DPL12 will fall short of the Shiva and frankly either may not be enough in that sized room. Probably fine for music but questionable output for movies. You may want to add a Stryke AV12 or 15 into the decision, but may have to do a larger box for the AV15. How much power are you going to feed the sub? That will affect the decision also.

    Pete
     
  3. JohnOwens

    JohnOwens Agent

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    Pete, I looked at the AV12, but the -3db point is more like 42Hz, and the SPL is almost identical to the DPL12 (at least in this application). The Qtc, however is quite a bit lower.

    I was planning on using the ryhtmic amp that supposedly puts out 380w into 4 ohms.

    Max spl is really not too much of a factor. I usually listen to movies at about -30 to -25 compared to reference (calibrated to 75db.) Music at around the same levels.
     
  4. ThomasW

    ThomasW Cinematographer

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    The Shivas and the DPL12 are good drivers I have both. But you're not going to get any significant output with one of those in a small box in a room that big.

    I suggest going with a larger driver and a bigger box. Or use one of the high output 12"s such as the BluePrint 1203 available at closeout pricing from Audio Liquidators
     
  5. TimForman

    TimForman Supporting Actor

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    John,
    Take a look at the sealed Tempest I built. It is a 2x2 ft cube that handles music and HT very well. This is the MidQ plan available from Adire Audio. Timn8ter's Home Theater Page
     
  6. JohnOwens

    JohnOwens Agent

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    Thanks for the replies everyone.

    John, very nice looking sub!!! I wish I had the woodworking skills to pull that off!I am sure that would do the trick, but due to space constraints on where the sub can go and of course the dreaded WAF I am really limited to about 18 x 18 footprint max.

    Question to Pete and Thomas, what kind of SPL numbers should I look for? Keep in mind that overall volume levels will be in the "sane" range.

    I am getting the following numbers from WIN ISD w/ 350W @ 1m:

    DPL12 Shiva
    20Hz 100.9 99.9
    30Hz 106.2 106.3
    40Hz 108.3 109.6
    50Hz 109.0 111.3

    These are using the SPL function in the software, should I be using Max SPL instead?

    When I run the same test on a ported box I do get more like 112- 115db, but is this really a huge difference?
     
  7. Mark Leitch

    Mark Leitch Stunt Coordinator

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    I am in a similar situation... and picked the DPL12 over the Shiva (just starting construction). If footprint is all that matters, you could go to a bit bigger box (say, 18x18x24.. the dimensions I have chosen) and run it downfiring (I have been told the DPL12 is borderline for downfiring, but you would only lose on the order of something like .25db).

    M.
     
  8. ThomasW

    ThomasW Cinematographer

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  9. TimForman

    TimForman Supporting Actor

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    Would an IB application be possible for you? I think ThomasW could give you some pointers on a great "invisible" sub.
     
  10. Pete Mazz

    Pete Mazz Supporting Actor

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    Based on the sims:

    Freq DPL12 Shiva
    20 100 101
    30 104 106
    40 105 109
    50 106 110


    These are based on full excursion in a 3 ft^3 enclosure (18" cube, stuffed) for each driver at 1 meter distance. At 2 meters, deduct 6 dB from the chart. At 4 meters, 12 dB less.

    You'd need more power to outdo these numbers with an AV12.

    As TW said, running these full tilt won't even put a dent in that room.

    Pete
     
  11. JohnOwens

    JohnOwens Agent

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    Ok, the consensus here seems to be to go ported with a 12" or use a much bigger driver and box. Thomas makes a good point that you can always run a capable sub at less than full tilt, but there is no way to really compensate for a design that won't cut it.

    Looking at T/S parameters, is VAS the displacement of the driver?

    Here are the specs on the 85L ported Shiva tuned to 21Hz w/ 350w:

    20Hz - 105db
    30Hz - 111
    40Hz - 112.5
    50 and up about 113db

    I guess keeping in mind that decibels are logarithmic, that is a pretty fair increase.

    I think the max box size I can do is about 3 ft.^3.

    Anyone else using an 85L enclosure, ported or sealed in a large (>4000 ft.^3) space? Any feedback?
     
  12. George W

    George W Stunt Coordinator

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    Jim,

    I'm running an Adire alignment 85L ported Shiva in an ~2500 ft^3 room. I'm finding that it has enough output for music but there are times when it doesn't quite keep up with home theater. If your room is as big as you say I'd definately heed the advise of those who advocate a larger driver. Like they said you can always turn a sub down but don't be like me wishing you had built something bigger. By the way take a look at my sub, it's easy to design them taller if you want to reduce the footprint.
    [​IMG]



    George
     
  13. Ryan Schnacke

    Ryan Schnacke Supporting Actor

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    If you really do listen at -30 to -25dB then any of these drivers would have plenty of overhead in a ported sub ... even with a 5000 cu ft. My living room is open to basically the whole house. The main room is 6000 cu ft but openings into another living room, dining room and hallway effectively double that space. I've got one of the original SVS 25-31PC subs that'll get to about -8dB and I've never bottomed it.

    My suggestion for a "smallish" sub like this is to tune somewhere around 22 - 25Hz and use a rumble filter to prevent unloading below tuning. This will keep port lengths reasonable give you higher SPLs and keep you from bottoming the driver.

    Here's an idea: I'm thinking a 10 inch Titanic Mk2 in 2 cu ft tuned to 24Hz could hit -20dB no problem ... maybe even -15dB. But once you're hooked, that might not be enough.
     
  14. JohnOwens

    JohnOwens Agent

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    Thanks to all for the advice so far.

    Mark, are you planning to go with a sealed or ported box for the DPL 12? Is this mainly for HT or music, and how big is your room?

    I am interested to see how your sub turns out!
     
  15. Mark Leitch

    Mark Leitch Stunt Coordinator

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    John... my room comes in a little under 3000 cu.ft. I am going sealed with the DPL12 and my first priority is music, though I will use them for HT too. I am going with two subs though and to be honest, I do not think two are that much more expensive than one if you use an external amp (I think plate amp prices get pretty high when you see all the nice two channel amps out there).

    I have been looking at the numbers a fair bit (and forum members like Dustin and Jack have been a great help) and while it is obvious what I am giving up by going sealed, I really do not want to compromise two channel. I also do not listen at reference levels, so I think I will get adequate output for my needs.

    I think it will be weeks before mine are finished... though I will be sure to report my results back here.

    M.
     
  16. JohnOwens

    JohnOwens Agent

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    George, what are the dimensions of your sub? It looks great - maybe I could get Brian or Kyle to build me something along those lines.

    You said it started to run out of steam for movies sometimes - do you listen near reference levels?

    How much power are you running into your sub?

    Thanks in advance.
     
  17. JohnOwens

    JohnOwens Agent

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    After evaluating all the good info I got from you guys, I decided to go with a ported 12" design.

    I know that DIY is the way to go to get the absolute best sub for the $$$, but with no tools, patience, ability, or garage to use, I decided to go the "let somebody else do it for you" route.

    Brian @ Rutledge Audio is going to build it for me using the following:

    Stryke SAE1204 12" driver
    Rhythmik 350w amp
    approx 80L (net) cabinet internally braced and tuned to around 25Hz w/ 2 3" flared ports.

    I expect that it will be a pretty good combo for me for music and HT - roughly equivalent to SVS PB1 or even HSU VTF-3. It may not go quite as low as some, but output from 25 Hz up should satisfy.

    I have to say that Brian has been extremely responsive, helpful and knowledgable throughout the process. I am sure that is not a surprise to anyone here!


    Anybody tried a similar setup, or have thoughts on how this will compare to commercial offerings in the $600 range?
     
  18. JohnOwens

    JohnOwens Agent

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    bump for edit to add question...
     

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