help with D-123

[Vinnie]

Hello Folks
My first post as a newly registered member. I just acquired a pair of D-123's and I am looking for information on the best enclosure to build for them. I did a few searches here and checked the FAQ's, but I did not find much. I would appreciate hearing from anyone with information on a good enclosure to build (diy) for this speaker. A site with plans would be most welcome.
Thanks
Vince

[pos]

Hello and welcome,

Please learn how to use the search function

here you go:
http://audioheritage.org/vbulletin/showthread.php?t=12791
http://audioheritage.org/vbulletin/showthread.php?t=2214
http://audioheritage.org/vbulletin/showthread.php?t=21616

[clmrt]

Are you going to use it as a mid-woof or a woof?

[Vinnie]

I have been very impressed with the midrange of this speaker and I saw a post that said it should make a very good midrange in a 3-way system, but I was hoping to stay uncomplicated. I was thinking last night that a two way speaker and a sub-woofer might be the way to go. Got any good ideas for using it as a woofer?

[clmrt]

I'm not sure if I was the last person here to try the 2-way thing with a D123, but my limited attempts failed in that it wouldn't play bass.

I'm using 123A-1's in place of the D123 and it's a whole new ballgame. Better, I mean. Perfect, actually, for now.

I think 4 cubic feet tuned to 50Hz is the best you can get on paper. Closed Q=.707 would be 3.35 feet but would be bass shy and would need to be high-passed at about 100 to avoid damage.

Play with WinISD Pro to get a feel for it.

Maybe read up on the "Econowave" threads and consider a sealed, actively hi-passed 2-way 3.3 cu ft box with a horn top end.

If you find it a wasted effort, the woofers could be swapped with nearly any decent 12".

[Vinnie]

Sounds like you have been there and it didn't work. What would be the best enclosure to use if I just wanted the 123 for it's midrange magic and had a subwoofer for the low end?

[pos]

download WinISD and try experimenting with this driver (it is included) in sealed and vented boxes.
You will also find many exemples and curves in the links I posted above

[Zilch]

You will also find many examples and curves in the links I posted aboveIt's a wonder we don't have a bad attitude.

[Can't click the links for 'em, alas.... :banghead: ]

[Vinnie]

I know diddly squat about designing speaker boxes. I would not know what to do with the design program if it walked up and bit me in the arse. What I am looking for are some plans from someone who has already been there and done that. I sent an email to the dude in South America who built something like what I want to do, but I have not heard back from him yet.

[speakerdave]

I know diddly squat about designing speaker boxes. I would not know what to do with the design program if it walked up and bit me in the arse. What I am looking for are some plans from someone who has already been there and done that. I sent an email to the dude in South America who built something like what I want to do, but I have not heard back from him yet.

Back in the days when JBL was in the business of selling drivers like the D123 to retail customers such as yourself they published construction guides. You can find what you need on these pages in our library:

http://www.lansingheritage.org/html/jbl/plans/1970s-kit.htm

http://www.lansingheritage.org/html/jbl/plans/c35-c39.htm

http://www.lansingheritage.org/html/jbl/plans/jbl-plans.htm

[Vinnie]

It looks like there is general agreement that 4-5 feet cubed is the way to go, and the 5 cubic foot enclosure plans from JBL ought to do the trick. Just one last question...
I have a spiffy pair of Klipsch Cornwalls that I like pretty well. I am wondering if there is any way to use a separate enclosure for the 123 and set it on top of the cornwalls and tie them in as midrange speakers. I know I would have to figure out some sort of cross over, but do you folks think the 123's would fight with the mid horns of the klipsches if I did that? The cornwalls have 15" woofers and plenty of bass, so it would take care of that problem. Or do you all think I would be better off building a new enclosure for the 123's?.
Thanks for all the help!
Vince

[GordonW]

You know... it'd be interesting to LIGHTLY aquaplas a D123... not as much as the 123A, of course... but a light coat. Maybe like 10 grams or so, tops.

I'm guessing that you could get bass down into the high-30s, probably... without losing much sensitivity or too adversely affecting the high-frequency response...

[pos]

Gordon, I am most interested by these aquaplass experiments.
I have a 2123H that has a broken frame here (my fault... :banghead:) and would be the ideal condidate for such an experiment!
That is what JBL did to turn the 2251J (http://www.audioheritage.org/vbulletin/showthread.php?t=17040) (mms 32g) into 251J (http://www.audioheritage.org/vbulletin/showthread.php?t=11985) (mms 58g, with aquaplass + mass ring) for their Hercule center channel.

The 2123H mms is 25g. I would like to be able to go down to 150 or 200Hz without too much equalisation, and also calm down the rising in frequency above 600Hz. 95db/1w/1m would also be a target.
The 251J is only 91.6dB/1w/1m so I guess adding 26g is a bit to much for my purpose.

Is there a way to simulate how would 10g of aquaplass affect T/S parameters (I know that was done in a recent "heavy 2226h" thread, but I don't know the formula used)

[grumpy]

FWIW, on the low-end, in WinISD you can add mass to the transducer without
modifying the T/S model parameters themselves. I wouldn't believe the high-end
business of the model though. I left the box vol/tuning the same (didn't re-optimize)
for comparison at 1w input.

[pos]

great!
thanks grumpy.

I am not used to WinISD pro, I mostly use WinISD 0.4 all the time because its JBL database is more consistant.
(Anyone have driver files to share? I have some for winisd 0.4 that I will try to convert with a little script)

I will plays with that. I will try to simulate the 2251J to 251J conversion to see if simulation match reality.

[pos]

here it is:
yellow is 2251J
Oragne is 2251J plus added mass
Red is 251J
all in the same 11L box (14L minus driver displacement, as in the 434X serie)

Pretty accurate indeed :D
The only strange thing is that in the simulation the 2251J plus added mass has more input under 100Hz than the normal 2251J and 251J.

[Vinnie]

Hi folks
Wanted to report back on how it all turned out as I learned quite a bit and it may be helpful to someone else. I read through all the advice in the posts below, and then I looked at several of jbl's recommendations for different size enclosures for the 123, and I also found a handy site for calculating port size at http://www.carstereo.com/help/Articles.cfm?id=31.
Armed with all this info I decided that the easiest approach was to first try tweaking the existing enclosure (2.5 cf with two 2.25x6.5 ports in the baffle). The jbl info said tune the enclosure to 45hz, so I plugged that and the cf into the port program and put in the size of one port and it said make it 4.6 inches deep. The baffle is 5/8" so I figured an additional 4" would be about right.Made up two of them 2.25 x 6.5 on the inside from 1/2" plywood and glued them to one port in each cabinet. Glued another piece of 1/2" ply over the remaining port in each one. Just for good measure I stuffed each cabinet loosely with poly fiber batting and ran a bead of string caulk under the back cover.
The difference is nothing less than amazing. The bass is very acceptable now, and nice and clean. All the mid range magic is still there too. Not too sure about the high end though, it's tolerable but I wonder if it could be better. Anyone familiar with the University T-202 super tweeter? How good is it supposed to be? Anyone got any recommendations for a replacement tweeter that would match up better with the 123?
Thanks to all who helped earlier, I really appreciate it. It's been fun and educational as well.