Cabinet Plans for D123

[elcamino]

I have a pair of D123 in "Acousti Craft" cabinets. About 2 cubic feet with a retangular port running along the bottom. I love the sound, first JBL's I have owned. Mids and highs jump out into the room, wonderful sound stage, deepest I have had in my home. I think if I could get a bit more bass out them I would make an everyday speaker out of them. Ideas on modifing exsisting cabinet?

Or... Plans for the ideal cabinet for these as a single driver system. Exact plans with dimentions, port size etc. The cabinet disscusion have found here with all the techical talk are beyond my understanding, lol. :blink:

Thanks!

[Harvey Gerst]

Bill Burton, the designer of the JBL D123, always felt they sounded best in a four cubic foot box, with a port down around 30 cycles or so. (I'm guessing 30 cycles, since they would have dropped that low by now.) When they were new, I would have ported them around 40 cycles or so.

Ed May's home system consisted of two handmade 123A's per side (for woofers), in 8 cubic foot boxes, with a port tuning of around 27 Hz.

I always felt that the D123 and the LE14 were the two best speakers JBL made during that period.

[elcamino]

What size port is that ? I understand cutting back the tube til it sounds right, but I need a starting point. Diameter and lenght. Again I am not a tech. just a music fan.

[Earl K]

CLICK HERE & FIND some useful porting info ! (http://www.lansingheritage.org/html/jbl/plans/1970s-kit.htm)

"LANSING LIBRARY" (http://www.lansingheritage.org/)

:)

[Zilch]

D123 in 4.5 cuft tuned to 37.5 Hz (2 x 3" ports, 2.75" long,) has usable bass down to ~30 Hz.

In 6.5 cuft tuned to 34.5 Hz (2 x 3" ports, 1.5" long,) it'll play a little lower, ~27 Hz.

In both cases, cone excursion is the limiting factor; can't put huge power in without the cone bottoming out at low frequency.

Even so, in these alignments, D123s will produce respectable SPL levels of 110 and 105 dB overall.

Those are the BB6P "suggested" tunings for "high fidelity" and "extended bass." With more effort, a designer might be able to come up with something more optimum....

[Zilch]

Is there some depth to that port?

'Cause, if it's just the 0.75" panel thickness for a 2" x 12" rectangular port, the alignment is, uhmmm, well, "terrible," and you can achieve much better tuning with those cabinets.

Look for an internal baffle, maybe? If there's something inside, a pic of it would be helpful....

[elcamino]

Zilch if you can offer a better port size great ! I will not bulid cabinets if decide to until spring. I re-sealed the back on with flexable chaulk so I can remove and change port. Here is a picture of insides :

[Zilch]

Your present tuning, ~90 Hz, red.

BB6P suggested tuning, ~50 Hz, blue, extending your present port to 11" deep.

Zilch's try at improving it more, ~40 Hz, orchid, 2" x 6" port, 8.25" deep.

You can make that to screw on from the inside over the existing opening.... :thmbsup:

[elcamino]

Excellent info, formulating a way to accomplish your port size Zilch !

[Zilch]

Well, if it sounds like poo, at least we didn't disfigure anything.

[I jus' click buttons here.... :p ]

[wedweb]

elcamino,

Your inside of cabs look similar to mine. Do you have any outside cab photos?

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 Westinghouse 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