I have a really big room. I need lots of Bass. Help?

Discussion in 'Archived Threads 2001-2004' started by Daniel J, Aug 12, 2002.

  1. Daniel J

    Daniel J Stunt Coordinator

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    [DanielJ crawls into a room high atop some mountain somewhere, seeking the secret of the 'sub-bass']
    I've got 4 JBL MS115s, and I'd like to know what my options are, DIY wise, to fill a 80'*20'*20' room (It's an old movie theater, 211 seated capacity) with balanced bass? (hopefully sub-25Hz)
    (I'm currently using a pair of Mackie srs1500s, which are okay for performances, but lacking in the sub-40Hz area. they were the best I could get within my budget at the time we put the system together)
    What kind of prices am I looking at for drivers/amplifiers? (I can do almost any carpentry myself)
    I'd just like to get an idea if it could be done for significantly less than buying PA equipment that's not really designed for sub-bass, or THX-certified subs that I'll never find money for.
    I humbly offer my thanks in advance, wise and powerful keepers of sub-bass.
    [DanielJ bows to floor, chants 'suuub baaass' a few times, and slides backward out of room]
     
  2. Pete Mazz

    Pete Mazz Supporting Actor

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    Try a search for "labhorn". Lots of bass if you can build and live with the enclosures.

    Pete
     
  3. Kyle Richardson

    Kyle Richardson Screenwriter

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    Personally I think Maelstroms are a good candidate for this type of project. Flat to the low 20's, great efficiency, not extremely expensive, etc.
    If you want to go for premanufactured subs then I would get a hold of Mark Seaton of Servodrive
     
  4. Mark Seaton

    Mark Seaton Supporting Actor

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    Hi Daniel,
    Indeed, the depth and size of the space you have dictate a very different solution than what would achieve 16-20Hz extension in a home theater. Especially due to the very long dimension of 80', and your interest in keeping the price down while using your woodworking skills, I would strongly recommend the LAB bass horn (Live Audio Board). Our designer, Tom Danley, voulanteered his time and knowledge to design the subwoofer, and in the end, the desires of the forum led to a subwoofer with quite similar characteristics of our servomotor driven, BassTech7. Basically Tom was able to have a 12" driver made publicly which is suitable to drive this horn. The driver is basically a very beefed up evolution of the Adire Shiva, which is also assembled by Eminence. Builders have posted prices of ~$150 per driver.
    Do not think of this as a dual 12" subwoofer. It is a properly sized bass horn with quite astounding power. Within its passband, the subwoofer effectively has the full radiating area of the mouth of the horn. This 22.5" x 45" dimension makes for a volume displacment capability equivalent to 12-16 sealed 18" subwoofers. See the thread here at HTF on the bass horn:ProSoundWeb LAB Subwoofer thread - HTF
    There I have gone into some detail about corner loading the subwoofer to extend the flare. I would think you could very easily achieve this in your theater. With 2-6 LAB subwoofers in this theater, you will have very intense bass power, and possibly useable output to 25Hz or even 20Hz if you extend the flare. The efficiency will be very high keeping your power demands reasonable.
    Keep us posted with what you decide.
     
  5. Mark Fitzsimmons

    Mark Fitzsimmons Supporting Actor

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    I'm curious, do you have any pics of the room?
     
  6. Daniel J

    Daniel J Stunt Coordinator

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    -overhead picture-
    It's a pretty basic movie theater, built in the 50's (I need to get some pics of the original carbon-arc projector we have upstairs!) the roof was burned off and re-built in the 70's, and the place has been going downhill since.
    We bought it last year, sold the 'newer' 35mm projector, installed an LCD light cannon and a decent 16 in/6 out PA system (two stage monitors are currently doubling as a centre channel; yeah, I know...) and completely renovated the lobby/concession area.
    I'm not sure that we'd be able to spend anything over $800 CA anytime soon, not without additional fundraising anyway. The 40Hz output of the Mackie's is 'good enough' for what we spent on them, but I'm alays thinking ahead to the next upgrade...
    mmmm... basshorns... Let me finish reading all that info and I'll post my thoughts.
     
  7. Daniel J

    Daniel J Stunt Coordinator

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  8. Mark Fitzsimmons

    Mark Fitzsimmons Supporting Actor

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    So it's just a theater in town somewhere? Not actually your home right?

    I was going to suggest twin Tumalts in a huge enclosure with big ports. But the bass horns may be better. There's lots of room behind the screen right?
     
  9. Daniel J

    Daniel J Stunt Coordinator

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    Yes, it's the "Princess Theater" in downtown Killam, AB (pop. 1200).
    A bunch of people from my church decided this would be a cool thing to do for the community; we've been showing saturday matinees for kids as well as the occasional concert, local talent show or music recital. We're calling it "The Living Room", hence it's 'almost a home theater'
    There's a space about 6' deep behind the screen, we're using it for storage right now [​IMG] Again, I wouldn't neccesarily want to use that space for anything other than a center channel speaker (which wouldn't be used for non-cinema performance), as it does bad things for musicians. I suppose it would work if it was a "sub-sub" component, which, again, wouldn't be used for live performance. I like the idea of the LAB horn, though, because of what people are saying about the quality of sound- I want kick drums that are 'there', not just some 50Hz buzz @120dBSPL.
    (BTW, anyone know of any websites with info on cleaning/tightening big screens? It's a bit lose in one corner, and it's a wee bit dirty in spots.)
    [edit: smacks head] Why couldn't I have the horns fire out the sides of the stage? would that give me the right diffusion and gain? Maybe if someone could point me toward material that would explain exactly what is accomplished by firing into the corner?
     
  10. Mark Seaton

    Mark Seaton Supporting Actor

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    Hi Daniel,

    You first posted:
     
  11. Daniel J

    Daniel J Stunt Coordinator

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    Mark,
    You've been too cool about this! Thanks once again!
     
  12. Daniel J

    Daniel J Stunt Coordinator

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    Stage dimension diagrams here
    I'd just like to say thank you to Mark once again, this thread has been very helpful.
    One more question about the horn-type subs: Will they transmit more or less vibation through the stage itself (or anything else touching the enclosure) than a ported sub?
     
  13. Daniel J

    Daniel J Stunt Coordinator

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    Mr Seaton, (if you're still reading this thread,) what are the recommended amplifiers for the Eminence LAB12 drivers? Any preferred dealers?
     
  14. Dennis XYZ

    Dennis XYZ Stunt Coordinator

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    Hi Daniel,

    Interesting project. Looks like your main problem is a low budget. $800 might be enough to get good bass in the average living room but I doubt it will be the best you've ever heard at 15 Hz in a theater. Here's what I would consider. Sell the gear you have to add to the budget. Seal up the area under the stage so it acts as an infinite baffle. Then mount drivers across the front face in a line array. The advantage of an infinite baffle is they are very efficient down low so you don't need thousands of watts for every driver. I'd start by looking for a good deal on a (used?) high-powered pro amp. You can find good deals on the QSC RMX series. Then spend the rest of your budget on Adire Tempest drivers - best bang for the buck. Space them equally across the stage. As more money becomes available, you can easily add more drivers. If you start with a decent amp, you probably won't have to add more amps because of the efficiency noted above. I'm not sure how much volume you have under the stage but about 40 cu.ft. per Tempest would be nice. Smaller would be okay but it will start requiring more amp power and EQ boost. In a true infinite baffle, it only takes something like 30-40 watts to drive a Tempest to Xmax at 15 Hz.
     
  15. Daniel J

    Daniel J Stunt Coordinator

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    Dennis, thanks for the suggestion.
    We probably won't be doing any upgrading for another couple of months, there's allot of renovations still going on in other areas, but it's nice to have a plan that I can rely on when the time comes.
    RE: stage as infinite baffle
    That's a great plan, but I'm really starting to like the idea of a bass horn; from what everyone has said, it's the best option for music, with enough power for movies (albeit not quite as extended).
    I suppose I could alays do both [​IMG]
    What impedance does the Tempest require (or: how many can I use with a stereo amp)? (I've got around 380 ft^3, no problem with space; unless it's too much volume)
    What's a "true" infinite baffle, BTW?
     
  16. Dustin B

    Dustin B Producer

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    I don't think 380ft^3 would be enough space for an infinite baffel with the number of drivers he'd need.

    You want at least 5 times preferrably 10 times the combined Vas of all the drivers used or more. The bigger the space behind the drivers the better.

    So 4 Tempests would require 225 ft^3. And you would need a lot more than 4 of them for that space, which would kill your budget pretty quick as well.

    Plus you'd have to beef up the stage and make it air tight. Where as with the horns you are sticking much smaller completed enclosures (in comparison to make the stage a proper sub box) into the stage.

    I'd stick with Mark's suggestion. Will be easier on the pocket book and easier to make.
     
  17. Daniel J

    Daniel J Stunt Coordinator

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    Are there any other options for -20Hz power? I'd rather use the stage as an infinite baffle than try to find 12' of Sonotube...

    Then again, the LAB sub may provide the extension I want. Perhaps I could EQ tune the system (If I'd get 125dB SPL at 30Hz, I should be getting at least 100dB @ 17Hz, right?)

    Has anyone else had experience with the LAB design? (Maybe I should start a thread there?)
     
  18. Mark Seaton

    Mark Seaton Supporting Actor

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    Hi Daniel,
    I've been busy, but paying following the thread. The simple answer is, yes, you get output below the predicted 28Hz cuttoff with the ideal size. Doing a quick search, I found an older post by Tom where the version 1 driver simulated to a -10dB point of 23Hz for 4 boxes. This is roughly what you will have if you double the mouth area for 2 boxes, but you will also have a longer path, which will allow for a little better low frequency performance. The final(v2) driver is supposed to also increase efficiency and low end. How much more below the low end cutoff is yet to be seen. I believe that with the front area of your stage we can expand the mouth by 2.5 to 3 times with maybe a ~30-36" setback from the front. I can only guess as to the effect of having a subwoofer move an 18 FOOT long x 2 FOOT tall slab of air moving back and forth. You almost have a line source of bass, and the levels projected at the back of the theater should be rather startling. A line of front loaded drivers would not achieve this anywhere near as well as the horn. You will not only have a large mouth for the horn, but also a longer path length, which will help low frequency production. I suspect 20Hz will be no problem and could easily be only 10-12dB down. The drivers are sealed, so there is no reason you cannot apply some boost to the bottom end. That said, I would not suggest doing this without measurements, and I would guess that you will be hugely suprised by the bass within the room without any EQ. With a quick simulation, I'm seeing that even 16 Tempests with 4000W won't even be close to the two LAB subs as described above 25-30Hz out in the room. At 1M they are getting close, but the LAB sub does this with 1/4 the power and much more output at distance.
    Maybe it should be noted that Dan Wiggins is building a pair of these using his DPL-12 drivers for his church where presently they have a pair of Tempests or Maelstroms in a large vented enclosure. When you have the space, and the horn is optomized, it will be hard to beat. The application you have is much more of a prosound situation than home theater. I have talked with a few who have completed their LAB subs and they are hugely pleased and suprised. They have described the sound as very "HiFi" with amazing headroom.
    Do note that Tom nor I nor our company are making any money off of this project. It is done freely. As for the IMAX theaters, I guarantee you they don't have anything close to the bass performance you will have in this theater. I'm still trying to find an opportunity to discuss that with the guys at IMAX.[​IMG]
    Here is the old post which Tom made when he first came to a design: http://www.prosoundweb.com/community...board=3&id=200
    I would say use the LAB forum for construction questions. This thread and the other LAB sub thread here at HTF have more relevant info for your application. I will talk to Tom about comparing a few options, but first you have some homework...
    I've looked at the dimension drawings and what you need to do is determine the space availble under the stage and at the front which can reasonably be made part of the mouth. One nice factor is that you do not NEED to put a grille over the opening, as there are no exposed drivers to protect. Vertical bracing is all that is really needed. Figure out how far back under the stage you can locate the subs. Ideal would be to have maybe 7' of depth. Next you need to determine more precisely how tall the opening can be at the front face of the stage. Next figure out how much of the 222.5" width can be made the horn's mouth. From this we can figure out how much we can extend the flare and mouth size.
    If you do go ahead with this, I will probably have to work out some time in my travels to stop by, or at minimum find one of our consultants to measure the sub's performance.
    Should be quite impressive...
     
  19. Daniel J

    Daniel J Stunt Coordinator

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    Mr. Seaton, I'd just like to give more thanks and praise for your assistance, this is too cool! I'm not sure when I'll be trying to install (lots of other things on the table) but when I do I'll be sure to give a shout and tell you about it.
    Is Dan Wiggins on the LAB? That project sounds very cool.
    I'm glad to hear that the low-end extension is adequate- But I imagine, from everything you've said, that the extension is nothing like what you hear in other subs; the description of "an 18 FOOT long x 2 FOOT tall slab of air moving back and forth" makes me shiver in anticipation... I can imagine that it would reproduce explosions quite well! [​IMG]
    There's a scene in A.I. (where David is getting cleaned) which has a slow buildup of very low bass; With the Mackie's 40Hz cutoff it sounds ominous, but with the LAB horn system I can see it pressurizing the room!
    And I can't wait to mix a kick drum through these subs... [saliva begins dripping from mouth]
    Thanks again, and tell Tom (and everyone else who has contributed) to keep up the good work!
     

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