It's Infinitely Baffling...

Discussion in 'Archived Threads 2001-2004' started by Robert George, Mar 28, 2002.

  1. Robert George

    Robert George Screenwriter

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    ...or otherwise titled, "Look Mom, No Box".

    I posted several days ago that I was considering trying an infinite baffle subwoofer design to replace my dual SVS 25-31s. After struggling with design issues, and at the prodding of my wife, of all people, I decided to go forward with a dual-driver, front-firing design. The drivers used are 12" SVS Ultra drivers.

    In order to overcome some design problems related to isolating the back wave from the front wave (the basis of the infinite baffle principle), I had to begin the project with constructing an interior wall to divide a 15' wide area on the oposite side of the front wall of my living room. There was no architectural concerns as this area is only a large closet anyway. This and other structural modifications were to prove to be the most difficult part of the project.

    I began making sawdust yesterday morning and as of noon today, after a lenghty "break" to go to work, I have reached the point that the physical construction of the closet and driver installation are acoustically complete. Still some trim work, painting, and other odds and ends to finish up, but I am very pleased to report that damn thing really works.

    I was pressed for time when I was able to hook up the drivers (having a real job is a bitch, isn't it) and I have yet to even touch the eq, but with a quick level calibration, I was greeted with some surprisingly deep, tight, quick bass without a single SVS tube in sight. I'm looking forward to some serious tweaking and listening over the next few days, but my initial impression is this is one hell of cool way to get serious bass and score huge WAF points.

    I'll be posting pics of the project in the DIY section this weekend (if anyone is interested) and I'll probably have some more thoughts on the performance of this design that I'll be discussing here as well.

    Thanks to ThomasW, Rich Kraus, Jack Gilvey, Mike Knapp, and everyone that was quick to offer advice and encouragement. Obi is very pleased with himself right now.
     
  2. Cam S

    Cam S Screenwriter

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    Hey that's great to hear Robert, I hope you took alot of pics in the buildup so you can show us exactly what you did and how you did it.
     
  3. Robert George

    Robert George Screenwriter

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    Cam:

    I didn't stop for pics while I was constructing, but it will be obvious from the pics of the front and back sides of the install what was done and how I made this work. I do have a "before" pic of the front of the living room with the SV Subs in place and I'll post that along with an "after" shot from the same place.
     
  4. Jack Gilvey

    Jack Gilvey Producer

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    Great to hear...that was quick! I'd be planning my first cut for weeks. [​IMG] Once everything's "tuned-up", settle in for some bass-realism. Even though those drivers are likely optimised for reflex loading, they'll give you a nice taste
    of boxlessness, and what a driver sounds like when allowed to operate as if in free-air. Keep us updated.
     
  5. ThomasW

    ThomasW Cinematographer

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  6. Rich Kraus

    Rich Kraus Stunt Coordinator

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    its a good thing. [​IMG]
    obi, your aware that theres no turning back now.....
     
  7. rodneyH

    rodneyH Supporting Actor

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    obi, what are you planning on doing with you old SVS enclosure(s)???
     
  8. Robert George

    Robert George Screenwriter

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    Rodney,
    I still had the original drivers so I basically returned the two subs to the same configuratyion as when they were new. They now have a new home with another forum member [​IMG].
    I did have two custom SVS Ultra enclosures ordered for use with some Ultra drivers I have before I decided to try the IB. They were delivered today so I have two "one of a kind" SVS Ultra enclosures based on 25-31CS size specs. Don't know yet what I'll do with them.
     
  9. rodneyH

    rodneyH Supporting Actor

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    Robert, let me know if you ever think about selling one. I am looking to build 1 of my own (since I got the upgraded driver and have a spare, and happen to have a spare amp sitting around), but I would rather just buy one, if I could find one. let me know
     
  10. Robert George

    Robert George Screenwriter

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    Rodney:

    I don't think I'd sell just one, even if I were to decide to sell at all. I'll keep you in mind, though, in case I do.
     
  11. Jim A. Banville

    Jim A. Banville Supporting Actor

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  12. Robert George

    Robert George Screenwriter

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    Jim:
    That looks very interesting. I'd be curious to see how it actually sounds, but the theory looks solid.
    Not as interesting a a sub without a box, however [​IMG].
     
  13. Parker Clack

    Parker Clack Schizophrenic Man
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    Obi:

    Isn't this similar to what Mike Knapp did with the closet that he has in his house? Great idea! I look forward to the pictures.

    Parker
     
  14. Jack Gilvey

    Jack Gilvey Producer

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    The dipole woofer concept intrigues me as well. It appears largely free of the room interactions that can effect even the best monopole woofers, even IB. My experience with dipole bass in the form of Magnepans hints at this this, and was one of the first things that struck me about them.

    The drawback, of course, is the rolloff/cancellation induced by allowing the back wave to mingle with the front, the specifics of which are determined by the baffle size (and the counteraction of which is the purpose of the eq intrinsic to the Linkwitz design). It's really even closer to a "boxless sub" than an IB in my view, at least from an acoustic standpoint. On my list of things to do is a dipole sub using four Adire DPL12 woofers, OEM units expressly designed for such use and made available to the basslist a for a very short while. These would make stellar IB units as well, the qualifying specs of each type being largely the same.
     
  15. ColinM

    ColinM Cinematographer

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    Pardon the intrusion, but are there pics somewhere?

    (As I suspiciously eye my SVS)

    - Thx
     
  16. Jack Gilvey

    Jack Gilvey Producer

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    Check out this page for some IB project photos/descriptions.
     
  17. Robert George

    Robert George Screenwriter

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    Parker:

    Mike was considering using that closet adjoining his HT/music room as a built-in type of sub design. He has not done it yet, though I know it is still something he is considering.

    Colin:

    I just finished painting, final wiring, and other trim and finish jobs on the install. I'm working this afternoon/evening, but I'll get a quick web page put together tomorrow (Sunday) with some pics and will post a link here and in the "speaker/subwoofer" section.
     
  18. Robert George

    Robert George Screenwriter

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    Jack:
    RE: the conversation in the other thread about the Tempest driver..
    I don't have actual specs on the drivers I'm using as this is a modified version of what looks like the Audiomobile Mass 2012. I don't know what SVS' mod'd specs are, but here are the specs on the Audiomobile...
    Big-Ass Woofer
    I'm not an expert on speaker drivers, but this one looks like a pretty okay one, huh? [​IMG]
     
  19. Jack Gilvey

    Jack Gilvey Producer

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    "Pretty okay", indeed, very good. [​IMG] Based on the Dumax (third-party verified) specs from the Audiomobile site, 2 of the 2012's have approx. ~3.7L of displacement, vs. ~5.1L for a pair of Tempests. The SVS drivers are obviously working well for you, so I don't know if the added bit of headroom with the Tempests would be worth it.
    http://www.audiomobileinc.com/images...ass2012s24.gif
     
  20. Mark Seaton

    Mark Seaton Supporting Actor

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    Hi Richard and all,
    Indeed the Tempests are somewhat better suited to IB use, and would have some additional headroom. That said, if you really want to upgrade, wait for the new 15" XBL^2 driver Adire is working on for home use. They would be a few dB less sensitive, but not by much, and I'd be pretty suprised if you were able to bottom them out before the N804's cry mercy. Of course the preffered choice would be 4 Tempests mounted like Rich Kraus's. This would give about the same output, cost similar, and be more efficient.
    In the other thread you asked some questions about the percieved sound quality you are experiencing... I wouldn't so much equate what you hear to the IB design itself, but rather the performance advantages it affords. VERY similar response CAN be had from a sealed box. It is only a matter of getting the same response, maintaining low distortion, and keeping power compression low. The power required to make most sealed boxes achieve the same response as an IB in a small box typically makes up for most of the differences in distortion, which is indeed audible.
    Would you believe I have here a 3.5 cu.ft. sealed box with almost 4 times the clean displacement (which ~=12dB more headroom), probably lower distortion at most levels, and actually deeper flat response without EQ? It indeed sounds just as you have described in the other thread. What I am curious about is your room size. The real advantage to such an alignment and response is that it typically compliments the gain function of a room very nicely. When dropped into a moderately sized room, the sub I mention measured flat to 5Hz!
    Beyond just the ability to produce such frequencies, by achieving ~flat in room response to such low frequencies, by definition you correct the phase response and group delay of the system. So not only do you now properly reproduce very low frequencies, which even at lower relative levels still make up the waveform, but the rest of the subwoofer range is produced more accurately. What we also find is that the more you limit the low frequency reproduction, the more we will want to boost the region above cutoff to enhance the harmonics of those attenuated frequencies to achieve a percieved "balance." Small mini-monitors are the extreme example of this phenomenon, where a speaker with minimal output below 70-80Hz can "sound" like it has some bass. This is achieved by boosting some frequencies in the 80-200Hz range. The real confounding issue here then becomes in selection of speakers to go with a sub. Examining the situation, it stands to reason that a bass limited speaker which sounds good on its own, will tend to have excessive upper bass response when a capable subwoofer is added...
    Now there's one to mess with the reviewers. [​IMG]
    Regards,
     

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