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Thread: JBL D123 Cabinet Ports?

  1. #1
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    JBL D123 Cabinet Ports?

    I have a pair of walnut veneered cabinets with JBL D123 woofers, some tweeter I can't identify with a large vintage 4mfd capacitor for each tweeter. There is a square cut out in the top of the front for the tweeter. I believe it to be a cone tweeter. There is a port measuring 13.25" wide by 2.25" tall for @30 sq.in. and no duct or tunnel. The interior space measures 2.292 cu.ft. Using the port charts on this website I should have a 13 sq.in. port with a 2" duct by one chart and 20sqin with a 5" tunnel.

    Should I modify the port to be smaller and add a tunnel? If so, what length and sq.in.? I probably should replace the wiring and capacitors. They are a Mallory and Aerovox. I do have a pair of Magnavox horn tweeters I could replace the smaller tweeters with. Any ideas?

    I did take some photos earlier, but can't find them. Maybe on my other computer. Thanks for any help.

    Bo

  2. #2
    RIP 2011 Zilch's Avatar
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    You make a manifold that installs over the rectangular port from the inside.

    Tune D123 in 2.3 cuft to 40 Hz using three 2" vents 5" long.

    Install heavy fill for F10 = 36 Hz and an actual tuning of 37.5 Hz, but don't block the ducts doing it:
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    Thank you for the response. Since the large port is at the bottom, I will have to stuff the top and middle of the cabinet. I assume you mean to entirely load the space with insulation but leave a small cavity behind and around the ports?

    Bo

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    RIP 2011 Zilch's Avatar
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    Heavy fill is more like 2/3 full.

    You taper it a couple of inches back from the ends of the ducts at the bottom, is all. Restrain it with some open plastic mesh, if you have to....

  5. #5
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    The manifold out of plywood?

    The ports out of ?????

    Thank you.

    Bo

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    Senior Member Baron030's Avatar
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    Hi Wedweb

    I think what Zilch was suggesting was making a small panel out of plywood or MDF that is slightly larger then the existing hole in your enclosure and then installing the 2" ducted ports to this panel. The thickness of this panel should be about the same as enclosure's existing front panel. (3/4" maybe?) You could purchase some ports from www.partsexpress.com or you can make your own out of PVC plumbing pipe or even cardboard tubing. The material that the ports are made out of is not really that important. It’s the inside diameter and length that are important. If you go with plumbing pipe, you can use epoxy glue or J-B Weld epoxy filler to attach them to the wood.

    And here is a link for some useful tips on cutting the holes for the ducts:
    http://audioheritage.org/vbulletin/s...ad.php?t=10047

    Baron030

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    Thank you. I figured the flanged right, it was just the material of the port and attachment to the flange. I think I am going to give it a try. The ports I may use heavy cardboard/fiberboard roll first. Then if that doesn't work so well I may try the PVC.

    Bo

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    RIP 2011 Zilch's Avatar
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    I use the black ABS pipe from Home Depot, and imagine its "Cell-Core" construction has less resonance.

    Hole saw gets me the right OD in the baffle, and masking tape wrap allows me to try different lengths with a decent seal to test the tuning before final installation.

    There IS no final here, typically, so I never get to that part....

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    Zilch,

    I miss calculated my cu. ft. for the speaker. I had a number in my head of what to divide the cu. in. by and that was incorrect. My recalculated cu. ft. is 3.27 cu. ft. Thank you for all your help.

    Here are the dimensions on the inside: 22.375" tall x 17.125" wide x 14.75" deep.

    Bo

  10. #10
    RIP 2011 Zilch's Avatar
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    3.3 cuft, 40 Hz, heavy fill, maybe 20W max.

    3 x 2" vents, 2" long.
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    Ok, I've got the flanges made with the help from my father-in-law. I used 1" thick osb that I had laying around. Since this flange is to be larger than the original opening I will have to move the braces on the sides up and the one on the bottom completely. These are the small triangular braces screwed into the corners between the front panel and sides. Is there any consideration I need to take before doing so?

    Bo

    P.S. If someone needs a photo of what I am talking about I could post one.

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    Ok, I am just now getting around to have some time to put towards these. I will be completing the ports soon. I have a few questions regarding the tweeters, woofers, crossovers? and connectors.

    1. Lets start with the tweeters. I don't know the brand of tweeters or their range.

    2. The capacitors for them are old. Should I replace them? If so, then with what?

    3. The tweeters are not open back and thus help keep the cabinet sealed. However, they are mounted on a board and the board is mounted on the inside of the cabinet. Does the thickness of the board cause less tweeter sound dispersal? Should I remount them through hole and to the front of the board?



    4. Should I leave the woofers full range or add something to cut the highs out?

    5. I am going to replace the connectors on the back of the cabinets, should I consider a JBL crossover with connectors instead of capacitors and such for the tweeters and woofers? What would you suggest?

    6. The backer board isn't very thick. Should I move the braces inside the cabinet to allow for an mdf backer board? 1/2" thick?

    As you can see I have been thinking about all kinds of options for these. Let me know any information. Thank you.

    Bo

  13. #13
    RIP 2011 Zilch's Avatar
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    Yes, I would remount the tweeter onto the front black face of that subpanel. You may have to make a new one with the proper diameter hole.

    Use foam gasket tape (closed-cell weatherstrip) to make good seals between the tweeter and the subpanel, the subpanel and the main baffle, between your port flange and the main baffle and between your new rear panel and the cabinet.

    I would make a new rear panel out of 3/4" stock.

    I would not change the crossover or components at this point. Get them running and see how they sound. You are expanding the scope here to a comprehensive system redesign.

    That can be done, of course, but requires more detailed consideration.

  14. #14
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    Thank you Zilch for your response. That is what I expected would be most folks answer. Fix what needs fixin' and then lets see.

    I am guessing you agree with the connector upgrade when I redo the back panel?

    Bo

  15. #15
    RIP 2011 Zilch's Avatar
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    Yes, of course. It only requires two small holes to do it with some binding posts.

    Some members like to get fancy, tho....

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