View Full Version : Acoustic isolation chamber for LE5-series
08-23-2003, 04:54 PM
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? :hmm:
A 5-inch PVC end-cap would be divine, but I haven't seem any.
08-23-2003, 05:07 PM
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.
08-23-2003, 05:14 PM
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...
08-23-2003, 10:46 PM
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. :nutz: :coolness:
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!
08-24-2003, 11:49 AM
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 (http://www.windsorplywood.net/lumbbld/concrete/sono.htm)
08-24-2003, 01:13 PM
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.
08-24-2003, 01:27 PM
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.
08-24-2003, 03:24 PM
"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."
08-24-2003, 03:48 PM
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?
08-24-2003, 04:02 PM
"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.
08-24-2003, 04:20 PM
...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 (http://www.partsexpress.com/pe/showdetl.cfm?&User_ID=13815640&St=8218&St2=53291267&St3=91349014&DS_ID=3&Product_ID=121375&DID=7) Recommended DCR is too low...?
08-24-2003, 05:51 PM
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.
08-24-2003, 05:59 PM
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?
08-24-2003, 07:51 PM
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...
08-25-2003, 08:45 PM
Cool, man. :coolness:
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... :duck: ). 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.
08-25-2003, 10:05 PM
Here's a link to the source I use for port and subenclosure material:
03-28-2005, 09:27 AM
Here's a very useful Thread where much of the design behind the acoustically isolated subenclosure for the LE-series was discussed.
See specifically Post #6 (labels are in upper-right of each Post).
03-28-2005, 10:58 AM
Mailing tubes are great, I've always used plastic tubes myself. It appears you can use virtually any material as long as it is stuffed with fiberglass.
JBL is using a thin walled aluminum cup for the LSR 6332.
03-28-2005, 02:19 PM
01-07-2006, 07:55 AM
The JBL component series instruction manual from 1980, posted elsewhere here, also recommends 80 cubic inches, typically 4.5 internal diameter by 5 inches deep. However, all the L100s and 4311s I have opened up have much smaller midrange chambers, about 4.090 ID by 3.25 deep, or about 42 cubic inches before stuffing. Can anyone shed light on the reason for this design decision, and could it be one of the reasons for some of the less than smooth response people hear with the LE5 midrange in those boxes?
Also, was there a preferred orientation for the woofer voice coil leads in the L100/4311? They stand out clearly on the white cones. A large majority appear to orient the leads toward the midrange, indicating this might have been a factory decision.
From a new member, many thanks to all of you for sharing your knowledge.
01-10-2006, 01:54 PM
Can anyone shed light on the reason for this design decision, and could it be one of the reasons for some of the less than smooth response people hear with the LE5 midrange in those boxes?Most of the best of what has been posted on the LE5 sub-enclosure, is just a few posts above.
Regarding the LE5 series, and perhaps the "splendiferous" LE5-2 of which you most likely refer to, you can Search for posts on that - it has, shall we say, a unique response characteristic, that is not related to the enclosure, per se. :hmm:
01-10-2006, 09:17 PM
Thank you. I searched as much as LE5 information as I could find herein before asking, and found a great deal of useful information, including the recommended subenclosure volume and this thread. I probably confused my question about JBLs design decision for those early subenclosures, by making conjecture about the response peaks.
More simply put, I am hoping a forum participant may know why JBL undersized (by a factor of 2) the isolation chamber on the L100/4311 (and other models?), versus their own recommendation. It seems odd!
(This all started innocently enough...a pair of abandoned loudspeakers by the dumpster, painted black...tags on the back said JBL 4311WXA...now there's a restoration going on, and JBL-fever...)
01-11-2006, 04:37 AM
I made my DIY 4313B's according Giskards recommendation and I have a smooth midrange section.
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