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Thread: Building new sub/mid box

  1. #31
    backbeat2000
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    Looking for plans for Altec A-7 (Voice of the theatre)

    Hello all,

    I've enjoyed reading the postings here and following the progress of the sub/mid JBL cabs. Really nice boxes.

    We've built single 18 Jbl boxes ( in 2 sizes), and single & double 12 boxes - we 'stack' them with Altec 511 horns w/ 808 drivers. Crossover w/ Rane (24 Db - usually ~100-150h/1000-1500). In really small rooms we'll use JBL 15's w/ the Altec horns crossed over at 800 (really 'sweet').

    We are moving this stuff around always so we like the 'modular' concept for travel and flexibility.

    ~1970-71 we built Altec A-7 Voice of the Theatres. Plans were obtained by writing to Altec.

    We lost those plans long ago, but would like to get a copy again - we've 'got the bug' to build another pair. Anyone have a set of these plans?

    Thanks


    Bill & Chris - Here in 'arctic' central NJ, USA

  2. #32
    Senior Member maxwedge's Avatar
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    A7 plans

    Looks like they may be here. There's a lot of cool old stuff there and If I had the room I would build a few. Belive it or not , these 18's are going in my house, but if I were to do live sound then I'd much prefer to seperate the 12's. I wanted to keep the cabinets as low as I could and with the horn on top it should be about 4 to 4 1/2 feet high.

  3. #33
    backbeat2000
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    Thanks for the Altec plans link

    Max,

    I totally understand putting 18's in the house!! All our newer 18's are 2242's..........and, well, you know.

    I've had the 2226 15"s inside (2way w/ the 511B's and 3 way with the JBL 8" cone mid) and they are pretty impressive.

    But the 18 ,12, 511B combo is my favorite.

    Thanks again for the quick reply!

    PS - what music are you listening to w/ these?
    Last edited by backbeat2000; 01-17-2004 at 10:28 PM.

  4. #34
    Senior Member maxwedge's Avatar
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    Re: what music are you listening to w/ these?

    Hi backbeat,
    I grew up the 70's playing in bands in the SF bay area. In high school was into heavy metal and really wanted to be like Tony Iommi of Black Sabbath. When I heard the Ramones and Sex Pistols I cut my long hair off and never looked back! It was an awesome time for a musican during the punk scene of the '70s and '80s.

    So the short answer is I like hard rock, but I've mellowed a lot since then.

    Really though the main use of these 18's are for subs in my surround sound system with my big screen in the center.
    http://audioheritage.csdco.com/vbull...&threadid=1421

    Hey what do you tune your 18's to? I'm torn between 25hz to go really deep for movies or about 30hz as a compromise for rock and movies. I have 31 band eq's so I could flatten the responce if needed.

    Scott

  5. #35
    backbeat2000
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    18 tuning etc.

    Scott,

    Our smaller 18 boxes were actually built for E-155's and are tuned to 40hz. We upgraded to 2242's (and added some extra support to the cabs).

    The larger boxes are 8 cu.ft. tuned to 30hz. Designed so one person can carry them if necessary and to stack under JBL SR 4735's. The subs are 43" tall and ~18" deep (we wanted to make them tall so we could get the mid's and highs above the dance floor and audience. They are modeled somewhat after the older JBL SR single 18" boxes (but are not trapezoids). They can also be stacked horizontally when necessary.

    We use them for live sound and DJ work. Amps are Crown Macro tech 600 & 1200’s, and a number of older BGW's. We will often roll off the 25hz & down w/ eq. - for music that really low stuff just sucks up power and we compromise those really low lows for better amplifier performance.

    It seems like you've got plenty of power. I'd say to tune the cabs to 25 for theatre stuff ("to 'feel' the earth move"), and eq out the 25hz and down when listening to music. Tune the 25hz eq 'by ear' to the recording and type of music your listening to.


    Bill

  6. #36
    Senior Member maxwedge's Avatar
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    Thanks Bill,

    I think I'll just tune for 25hz as the slope in BB6P is nice and smooth at that tunning. I can always shorten the vents to go higher if I don't like it.
    Yeah, I think I have enough power....2 Hafler 500's for the 18's and 12's.

    Scott

  7. #37
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    You could whip up some "25 Hz" ducts and some "30 Hz" ducts and see which you preferred in your environment.

    Don't forget that for HT you can pop in a +6 dB bump filter set to the same tuning frequency as the enclosure to increase VLF. It might not sound quite "right" when playing back recordings of certain musical instruments but it can sound damn fine for DVD playback

    I often place a piece of 3/4" or 1" MDF on the inside of the baffle, cut to the outside diameter of the port, so I can swap out duct lengths until I "get it right" for a specific environment. Then I measure Fb to see what it really comes out to be.

  8. #38
    backbeat2000
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    I like Giskard's idea. We have 4" round duct's and we're thinking about creating some thin cardboard 'sleeves' to insert in the ducts and play around with changing the length. With a tone generator and Db meter we figure we can do rough measurements along with 'ear training' .

    What do you guys think?

  9. #39
    Senior Member maxwedge's Avatar
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    I've got the baffle glued on and the spk and port holes cut out and I've still got another to build, but at least all the pannels are already cut out.
    Anyway about the ports....after looking around all the local hardware stores and on line I gave up on a cheep solution and bought these 4" flaired units :http://www.psp-inc.com/images/4%20x%2017%20port.jpg . I couldn't find anything else that was long enough! I need to use at least 3 of these and because of the way I designed my box I can only mount 2, to the side of the dox box. I had to mount one on the rear....I've read that this isn't a problem. I'm stuck to using these as I've already cut the holes and the flair diameter is 7". They are fairly long so I should have enough length to play with.

    Good news is the 1st cabinet should be operational by saturday

  10. #40
    Senior Member maxwedge's Avatar
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    2202 vent size

    I'm having a bit of a conflict about what the JBL enclosure guide and BB6P says about the tuning for the 2202. BB6P wants much bigger ports than JBL for tuning to 80hz...what do you think? I havent cut any holes in the dog box yet.
    http://www.jblpro.com/pub/manuals/enclgde.pdf

    Heres the dog box dimensions
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  11. #41
    Senior Member maxwedge's Avatar
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    vents

    If I go with 1 vent then it's around 6".....seems kind of large to me. JBL says one 4.2" in a 3/4" baffle.

    Scott
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  12. #42
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    Yeah I noticed that...

    I guess you'll just have to try the easiest one first and measure the actual tuning frequency. I don't have any 1.5 cubic foot enclosures laying about or I'd just test it real quick for you.

  13. #43
    Senior Member maxwedge's Avatar
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    I just had a bright idea! I'll just make a test box of the same dimensions as my dog box and cut my ports after testing, lol. Won't be a problem fitting my router because I made the baffle with a flush face. I'm gonna get both box's built and then work on this aspect then.

    Thanks,
    Scott

  14. #44
    Senior Member maxwedge's Avatar
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    new pic

    This is my 1st day off from work and gitting off to a slow start. Got a full mockup picture here and I'm off to buy materials for the base, so I hope to get it useable by tomorrow.
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  15. #45
    Senior Member maxwedge's Avatar
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    Thumbs up Rattles to fix

    Well I got the left one in place and I tell you what...with a 25-40hz input from the RTA, at near my haflers max output, the whole house shakes! The doors, walls, windows and my TV's dust screen rattle big time. But the box is still. At normal loud volumes there arn't many rattles. I just set the ports to what BB6P said for 25hz and typical fill (weather or not I used typical fill???) and I'm just going to leave it for now because it really sounds great!

    Right now I've got the crossovers set to about 200/1200 but I'll fine tune latter with the RTA. I know the placement isn't the best but I'm thinking that maybe I'm getting a deep bass increase (+6db ?? guess?) being in the corner. Maybe this will go well with a 25hz tunning. Any ideas on this?

    Scott
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    Last edited by maxwedge; 01-26-2004 at 06:36 PM.

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