D123 In wall mounting

[honist_bob]

I plan to mount two D123 between actual wall studs for use as the rear channels in my home theater system. Does anyone have any insights, or experience, or links to JBL information about this?

[boputnam]

Hey, Honest Robert...

Presuming you've read this: http://www.lansingheritage.org/images/jbl/specs/home-comp/d123/page1.jpg - there may not be much to add.

Dood, you are very old school with this approach! It may be acceptible for rears, but intrinsically you have so little control over the behavior of any transducer mounted into a wall: You don't know the effective volume. Then again, it may not be so critical because they are "rears", and you've made an interesting selection of transducer.

It may be a smart solution for it's non 5.1 appearance...

[speakerdave]

A stud space in an eight foot wall will yield about 2.6 cu. ft. with this speaker in it. As an infinite baffle it would probably start rolling off at or above 100 Hz (a guess). In their old (70's) charts JBL recommended a 13 sq. in. duct 2 inches long for cabinets in that size range for this driver. Mounted flush at the front such a duct would end too close to the rear inside surface in a 3.5 in. stud space, although there are so many other problems with this idea that I probably wouldn't worry about that one. You would also want to put a layer of fiber glass on the surface behind the driver to dampen reflections back through the cone.

I would definitely first build a test box of the same size to see if liked it. It wouldn't sound exactly the same, but it would give you the general idea. I'm guessing that would give you a cut off in the mid 40's or higher. I think FAR on this speaker is about 35. This can all be checked online. Flush mounting in the wall would tend to reinforce the bass by at least 3 dB, but I don't know what frequencies would be affected.

Also, I would not try to use this driver full range. Even folks who are into that seem to suggest this driver should be crossed over no higher than 3500 to avoid the spike the metal dome makes at about 7000 Hz. The old Lx2 crossovers and the LE20 tweeters both show up on eBay fairly regularly, if you want to stay in-era. Or you could use something else, but remember, drivers and crossovers selected at random seldom work as coherently together as engineered systems.

Sheetrock transmits sound, so I would expect poor-cabinet type anomalies from this kind of installation. I always assumed JBL's 50's-60's mention of wall installation for this speaker was meant for pa and musak systems where the degree of fidelity expected is not as high as for hi fi. Part of the sound would also be heard in the other room behind the wall.

If your priority is to use some drivers you happen to have, and you already have the wall apart, with the above considerations in mind, it might be worth a try.

Good luck,

David

P.S. Are you the Honest Bob from the old Honest Bob's Used Stereo on Shattuck in Berkeley?

[boputnam]

Originally posted by speakerdave
A stud space in an eight foot wall will yield about 2.6 cu. ft. with this speaker in it. I thought that too, but, we don't (yet...) know if this is an interior wall, or exterior. :confused: If interior, there will be no fiberglass batting and the unintended consequences you refer to will certainly be an issue.

If exterior, since this is northern CA, there could be cross-bracing that reduces the expected volume. I know running cabling down behind finished walls is almost impossible in Code homes around here.

And, if these are aluminum "studs", well then you're hosed... :(

[speakerdave]

Bo--

Right you are. And in an interior wall there will likely be fire blocking. He would need to have the wall apart to prepare the space. Just cutting a hole and mounting the driver will not work.

David

[boputnam]

Yea, David, good point.

I liked your thinking about the crossover and HF - I had similar thought too, since the D123 "can" do full range, or at least brochure full range... :rotfl: Even wondered about the LE8T's - they were similarly "perfect" for this application (again needing an LE20 up top), but Honest Robert has the D123's I guess.

I personally think sinking a pair of 4406's into the wall between the studs would give a superb result! :yes: So what if they stick-out into the room behind - makes wiring eee-asy!

[speakerdave]

Bo: "brochure full range..."

To be fair, JBL distinguished between "extended range" (D208, D216, D123, D131 and D130) and "full range" (LE8 and the coaxials, LE12C and LE14C)

David

[honist_bob]

Thanks for your replies and the link.
Yes, I am rather old school. Maybe I can work that into a new user name.

No, I'm not the honist bob of Shattuck Ave. in Berkeley, but I did steal his name for old time's sake. I bought several dynaco amps and some jbl drivers off of him in the early seventies.
I lost track of him after he moved to Marin County. And I'm not at all sure that he was all that honest!!!!

You're right, Bo, the rear channels of my Home Theater set-up are non-critical for me: I'm sure a pair of D123s will sound better than some of the plastic Cr##p that my friends have back there in their living rooms.
Most of that track on a dvd is treble, though: maybe I'll miss the high end and add a pair of tweeters. I'll let you know. . . .

Finally, your'e all missing a very important point about in-the-wall speakers: If they are built in, the wife can't pick up the boxes and move them to the garage when I'm not looking!

[honist_bob]

I forgot to add that the D123s are not in my hands yet. I noticed today that I did win the auction. The pair for $90, plus shipping. I hope I didn't get conned: you know how it is with ebay. . .

One wall is interior, and one wall is exterior, with fiberglass batting 3-1/2" thick.

Didn't I read somewhere in the JBL enclosure literature that a box stuffed full of insulation has more effective volume? I'm trying to think of where I read that.

[boputnam]

Originally posted by honist_bob
Didn't I read somewhere in the JBL enclosure literature that a box stuffed full of insulation has more effective volume? I'm trying to think of where I read that. Ha!, about the wifey!!

I think if you Search using various strings incorporating "effective volume, "batting", etc., you might find some very interesting contributions on that. In particular, I believe Ian just added some comments attributed to Greg Timbers wrt the 4345 Studio Monitor plans that address just that!