Page 1 of 2 12 LastLast
Results 1 to 15 of 23

Thread: Acoustic isolation chamber for LE5-series

  1. #1
    Senior Seņor boputnam's Avatar
    Join Date
    Apr 2003
    Location
    northern california
    Posts
    7,007

    Acoustic isolation chamber for LE5-series

    Anybody have some clever solutions to isolating the LE5-series MF from the cabinet?

    The JBL cabinets used a dense cardboard tube end, stuffed with batting, with the MF leads caulked through the tube wall.

    There's four problems in trying to approximate this, near as I can tell:
    - must acoustically isolate the MF
    - must be firmly attached to the baffle
    - must be minimally sized to minimize the impact on cabinet volume
    - must be mounted so as to not interfere with the T-nuts.

    How have you'se guys beat this? What have you used?

    A 5-inch PVC end-cap would be divine, but I haven't seem any.

    Thanks!
    bo

    "Indeed, not!!"

  2. #2
    Administrator Mr. Widget's Avatar
    Join Date
    Apr 2003
    Location
    San Francisco
    Posts
    9,928
    Back in the 70's there was a company called Speakerlab out of Seattle. They solved the problem with house plant pots. They used smoked acrylic pots that didn't have any drain holes that were available in a variety of sizes, 4",5",6" etc.

    They drilled a hole in the end and siliconed some color coded leads through it. after the baffle was made you simply siliconed the "chamber" to the inside of your baffle.

  3. #3
    Senior Seņor boputnam's Avatar
    Join Date
    Apr 2003
    Location
    northern california
    Posts
    7,007
    Hell, Widget - I shoulda just phoned! LOL

    I've got "a" workaround like that - I'm using a dense plastic cup (some sorta paint mixing container) that I can trim off the edge of, and since it's tapered I can almost precisely get the ending diameter I want.

    So, I've routered the baffle to 4-5/16 in, slip-in the cup, and then slip-in the LE5. It seems like it will work good. Having 3/4-in of the cup lip within the baffle will give me a good bite on mounting (maybe tack the cup lip into the baffle cutout...?).

    I just have to believe that I dno't need to invent this, and there's some "Doh!" solution right before my eyes...

    Thanks, man.
    bo

    "Indeed, not!!"

  4. #4
    Senior Member GordonW's Avatar
    Join Date
    May 2003
    Location
    Marietta/Moultrie GA USA
    Posts
    1,457
    Funny you should mention this...

    A guy I work with occasionally, was reminiscing on some of the more unusual speaker midrange sub-enclosures he'd seen.

    I think the one that took the cake was someone who had used a STYROFOAM HOTEL ICE BUCKET, as a sub-enclosure behind a 5 or 6" (can't remember which) midrange/midbass driver in a multi-way system.

    Bo, I'd take a look-see, and see if you can locate some 5 or 6" diameter "sono-tube" cardboard tubing, commonly used as concrete forms. Take such a piece, cut out a billet of MDF to plug the back end, and bond to the backside of the panel. Take said enclosure, damp the back end thoroughly (I like either carpet padding foam or thick felt, or both, on the back wall, with thickly-packed fiberglass/dacron polyfill mix layered between that and the back of the driver), and let it rip!

    Regards,
    Gordon.

  5. #5
    Senior Seņor boputnam's Avatar
    Join Date
    Apr 2003
    Location
    northern california
    Posts
    7,007
    Hey, thanks, Gordon! I've "heard" of sono-tube, but hadn't thought they came in small diam. I've known the larger of them to be used for acoustic absorption devices. I might be able to find some smaller? It "sounds" very similar to what JBL used, hey?


    Sorry for the lame metaphors - life in real life, seems to revolve around sound...

    Lookie what I found: Sono tube Link
    Attached Images Attached Images  
    bo

    "Indeed, not!!"

  6. #6
    Obsolete
    Join Date
    Apr 2003
    Location
    NLA
    Posts
    14,548

    Re: Acoustic isolation chamber for LE5-series

    JBL has always specified a subenclosure volume of ~ 80 cubic inches for the LE5.
    The ratio of the inside diameter of the subenclosure and it's depth is usually roughly equivalent to the "Golden" ratio:
    (SQRT(5)+1)/2 or ~ 1.62 : 1 : 0.62

    The inside diameter of the tube is often 5.3125"
    On some models they purposely tilted the closed end of the subenclosure so it wasn't parallel with the baffle.

    The 3.5 mH inductor having 7.5 ohms of DCR is set to smooth out the impedance peak of the LE5x in this sealed volume.

  7. #7
    Senior Seņor boputnam's Avatar
    Join Date
    Apr 2003
    Location
    northern california
    Posts
    7,007
    Fantastic.

    Interesting tid-bit about the non-parallel end of the subenclosure - not intuitive, but then again...

    As well, I surmised there might be something to the "aspect" ratio (my layman's term) to the chamber, but thought maybe being stuffed with batting would moot any concern on this. Smarter, once again.

    Thanks, man.
    bo

    "Indeed, not!!"

  8. #8
    Obsolete
    Join Date
    Apr 2003
    Location
    NLA
    Posts
    14,548

    Re: Acoustic isolation chamber for LE5-series

    "The 3.5 mH inductor having 7.5 ohms of DCR is set to smooth out the impedance peak of the LE5x in this sealed volume."
    Attached Images Attached Images  

  9. #9
    Senior Seņor boputnam's Avatar
    Join Date
    Apr 2003
    Location
    northern california
    Posts
    7,007
    The 3.5 mH inductor having 7.5 ohms of DCR is set to smooth out the impedance peak of the LE5x in this sealed volume.
    Well now there's a problem: I hoped to employ the N65 network - there's not a 3.5mH inductor in the MF circuit. Got a suggestion?
    Attached Images Attached Images  
    bo

    "Indeed, not!!"

  10. #10
    Obsolete
    Join Date
    Apr 2003
    Location
    NLA
    Posts
    14,548
    "Well now there's a problem:"

    Not really, the N65 was fine for the time. True, some people hated it from the get-go, but some people thought it was too cool.

    "I hoped to employ the N65 network"

    If you happen to like that sound then stick with it.

    "there's not a 3.5mH inductor in the MF circuit. Got a suggestion?"

    Don't worry about it? It's an old circuit... times change... pop the inductor in there and see if you like the result.

  11. #11
    Senior Seņor boputnam's Avatar
    Join Date
    Apr 2003
    Location
    northern california
    Posts
    7,007
    ...pop the inductor in there and see if you like the result.
    in the place of the 13221? And, got a specific one/source you're happy with?

    Maybe this one: Jantzen 3.50mH - PartsExpress Link Recommended DCR is too low...?
    bo

    "Indeed, not!!"

  12. #12
    Obsolete
    Join Date
    Apr 2003
    Location
    NLA
    Posts
    14,548
    There are two versions of the 3.5 mH (7.5 ohm) air core inductor that I know of.

    56138 is the original version with the copper lead wires.
    60677 is the PC-board mounted version.

    You should be able to order either from JBL Pro Parts.

    For the N65 you would mount it across the blue and white wires coming from the MF L-Pad. (#1 and #2 taps) Look at your 3113B schematic for reference if needed.

    *****
    Don't put it directly across the terminals of the LE5x because the magnetic field of the LE5x will interfere with it.
    Last edited by 4313B; 08-24-2003 at 04:55 PM.

  13. #13
    Obsolete
    Join Date
    Apr 2003
    Location
    NLA
    Posts
    14,548
    Which drivers are you planning on using with the N65 again?
    Do you already have a pair of N65's?
    Did you look at my posting of the LX30 schematic?

  14. #14
    Senior Seņor boputnam's Avatar
    Join Date
    Apr 2003
    Location
    northern california
    Posts
    7,007
    Sorry, was merrily routing away...

    Which drivers are you planning on using with the N65 again? LE14A / LE5-9 / 075 or 2405 (leaning toward 075 'cause the lads think they look "cool", plus, I can hoard the 2405's for a bit longer...)

    Do you already have a pair of N65's? Yes - great visual condition, clean unbent face-plate, too

    Did you look at my posting of the LX30 schematic? No, but I will right now...
    bo

    "Indeed, not!!"

  15. #15
    Senior Seņor boputnam's Avatar
    Join Date
    Apr 2003
    Location
    northern california
    Posts
    7,007

    Sono tube, 6-in...

    Hey, GordonW...

    Cool, man.

    After much BOGUS excuse from the builders supply, I found a resource for the 6-in version of these badboys. I think I'll have a 12-ft length of this, by tomorrow.

    If successful, I only need about 2, 3.08-in length pieces for two 80 cubic inches subenclosures (to allow for a 0.25 in end-cap, and after careful thought, I'm ignoring the baffle thickness... ). Regrettably, this Sono Tube won't conform to the Golden Ratio but it's very dang close, and I've found no other suitable alternative.

    Anyone interested in chunks of this, pm me. My cost, plus shipping (I'll cut if for free, but you're on your own for end caps... ). I'll post same-same on "Marketplace", as well.
    bo

    "Indeed, not!!"

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •