Anyone used the 328ct?

[badman]

I'm looking at getting a quad of these to use as switchable bipole/dipole surrounds, a task they should be excellently suited to. Has anyone used them in such a capacity? I'd have to source the 12" faceplates ('cause they're cool) or build them out which would be a pain, but I think it'd be pretty hard to beat these, 2 per cab, in an application like that. I'd run them sealed since as surrounds I don't need <80hz out of 'em.

[badman]

Bought a quad for my bipole/dipole surround project. Should be sweet, they're in pretty good shape, got the quad for $200. Would love to hear any feedback on these- I suppose the phragms are cheap enough I could always risk coating them (on the compression drivers) to smooth the highs a bit, but doubt it's necessary since they'll be pointed away from the listener.

[badman]

Not a high-end driver to be sure, but there's some things to like- more extension than most 1" CDs, thanks to the small phragm, less sensitive (a function of what is presumably a wider gap, weaker motor, and smaller phragm) which means less padding needed in the XO, and inexpensive embossed diaphragm replacements (that could potentially be tweaked with coatings, which I found useful on the embossed selenium d2500ti).

The JRX systems used it, and asked 1.6kHz XO with a 1st order notched crossover- but, that was first order incorporating constant directivity EQ so it was a small cap. The 328CT gives it a higher, steeper filter (1.9k @ 3rd order) but has a wider horn angle (120 deg approx.)

I guess I'll find out what makes this driver tick and see if I can tickle out some better performance. . One easy tweak will be to put a reticulated foam plug into the throat, which helps harshness in other drivers by suppressing throat reflections (and adds a very slight low pass characteristic). With the steeper, higher XO utilized in the 328CT, maybe this driver will not be so bad as in the JRX systems (also, only trying to keep up with an 8" for SPL, not a 12"/15" as in some of the other systems).

Enclosures will be 24"x18"x8" with incorporated horn extension on the front baffle to approximate a 12" horn. Sealed for starters, and utilizing the stock XO.

[JuniorJBL]

I have 4 Control 226C/T's that seem pretty nice. They will go overhead for my Atmos conversion in my theater. I am not sure what compression driver is in them but they sound pretty good. :)

[badman]

I have 4 Control 226C/T's that seem pretty nice. They will go overhead for my Atmos conversion in my theater. I am not sure what compression driver is in them but they sound pretty good. :)

From looking it sure seems like the 2412h/2412h-1 under question. I've not been able to find anyone who's used this driver outside of the bog-standard jrx systems or other completed setups, so it'll be interesting to see how they play outside of those under-performing systems. Generally a waveguided 1" dome is plenty to keep up with an 8", particularly with a highish crossover of 1.9khz, so we shall see I suppose. I'll do some real testing and tweaking once the enclosures are at least partially together.

[badman]

I've cut the main panels (24"x18") for the front and rear, laminated the front to 1.5", using Baltic Birch ply, and will cut a 120 degree waveguide into the baffle using that depth. It'll wind up around 14" wide once I've smoothed out the flare for transition to the baffle. I've cut rings to use behind the drivers for mounting, probably unnecessary but it allows me to damp the mechanical interface to the cab. I haven't decided on thickness yet, but will keep the enclosure/rear panel removeable (screwed from the front panel into corner structures)

So far so good, I'll be using a coping saw to do the main waveguide cuts then clean up with hand and drum sanding.

[JuniorJBL]

Make sure to take pictures. Sounds like a cool project! :)

[badman]

So far just a quad of 1.5" baffles and the rear-mount rings for the drivers. Have my coping saw (Olson) and a router bit on order to create the baffle profile. 69567

[JuniorJBL]

Looking like progress.

I think I have decided to sell the 226's and go with the 321c's. I have enough room in the ceiling to create 2.5 cu ft for each of them. 12's in my ceiling should be cool!! :D


BTW that 8" driver looks to be a decent sized driver with a cast basket. the 300 series look to be well made.

[jlyons]

This control ceiling install group is very impressive. They are coaxial with a continuous curve from the HF to the surround and baffle. The 328 and 321 each use a 2412, the 322 uses a 2407 through a 3" voicecoil woofer, which is a worthwhile improvement. The 227 uses a steel backcan with drivers similar to the plastic 226, including a very impressive smaller compression driver. I have tried the 328s as main speakers in their BB cylindrical one cubic foot backcans sitting atop bass boxes-neat industrial look without grill screens- (and 227's in their half foot cans... the "waveguide" baffle is 120 degree-so really designed for ceiling use, and the crossovers are sophisticated. Any of these would be useful, but I chose to leave them stock with venting and enclosures. The 3 cubic foot boxes for the 12" models(heavy) are designed for easy installation of the driver/ baffle assembly after the box is secured (and room finished) I only have one each of the 321 and 322c, (and no example of the 312c sub bass unit for the same backcan) and was thinking of kitchen receiver setup with 227c units... I want to hear about your surround developments, please. I had thought these were underappreciated. Thank you, John Lyons

[badman]

Thanks, appreciate the feedback! I'm working on these a bit today and will keep the "crew" here posted. Mine are an older version, so it's an earlier crossover and the baffle plates aren't shaped as much (which is why I'm making the waveguides as part of the baffle).

[badman]

You can see the router work in the baffle with the "lip" which then was cleared off less than perfectly (but actually, pretty darned consistent on the angle) with a coping saw. Sanding will smooth that and let me transition the waveguide smoothly into the baffle.

6962369624

[JuniorJBL]

You can see the router work in the baffle with the "lip" which then was cleared off less than perfectly (but actually, pretty darned consistent on the angle) with a coping saw. Sanding will smooth that and let me transition the waveguide smoothly into the baffle.

6962369624

That is a pretty tough angle no matter how you slice it! Pun intended!! :D

Nice job.

[badman]

That is a pretty tough angle no matter how you slice it! Pun intended!! :D

Nice job.

Thanks! The inner section is near perfect except for a few coping saw scrapes- so I'm hoping that with sanding, the outer section can be smoothed out to look more consistent. I cut the through-hole, then removed the bulk of remaining material with a large-format 45 degree chamfer bit, then used a 60 degree chamfer bit to set the start of the profile. I then cut the remaining "lip" off with the coping saw by hand- not fast or easy, trying to keep the angle right. 2 are done, needing sanding, the other two will need a good-weather day to complete, raining all day tomorrow and my workspace is outside.

The sanding will reduce overall thickness somewhat, which will allow even better tracking to the cone profile. I have to decide how I'm going to do the mounting ring setup internally, but that's an easy problem, as is the rest of the enclosure assembly, the waveguides are by far the hardest part of this job and they're 75% done.

[badman]

Spent some serious coping saw and file time yesterday so now all four are cut and mostly shaped/smoothed out from the less-than-perfect coping saw work. I could've used finer teeth and gone slower but now I'm past that part and stumbling forward. If I had it to re-do, I'd do it all with the 60 degree bit and templates, which would require careful alignment of the workpieces but would ultimately be easier and better.

My next decision to make is regarding the mouth flare- do I do it now, or use felt on the baffle to terminate the waveguide? If I use felt, I could extend the profile out later if I so desired, letting me bolt on a horn continuation if I want lower directivity control. If I were to flare the mouth, I'd then have to fill that discontinuity.

[badman]

6979269793

An awful lot of sanding and they're smoothed into the baffle nicely. Overall diameter of the waveguide is about 12.5" A fair amount of finishing work remains but the guides are nice and smooth with a good transition to the baffle.

[JuniorJBL]

Very nice! I look forward to your impressions. I ended up getting the 328's as well. The 321's turned out to be the 312 subs.

[badman]

69809

Still plugging away. Crossovers are mounted, with rubber grommets for standoffs. For the drivers I used the ply rings and threaded inserts into the baffle with 10/24 bolts and washers. This layout let me get a good amount of mounting strength, centering, without having to try to fasten into the thin wood near the "mouth" of the baffle waveguide. I still had to be careful not to break the wall of the waveguide, as the fasteners are about halfway along the profile.

[badman]

A lot more router and sandpaper equity 69898 and the sawmarks are completely gone from the waveguides. The profiles aren't cast-metal perfect, but they're good enough for gov't work. I also flush-trimmed the bonded panels and put a 1.25" chamfer on, as well as relieving the back of the waveguide a smidge so that it's a little closer to a perfect cone profile continuation. Lot of sandpaper action too (not all reflected in this pic but you get the idea). If I can get the top veneer layers sanded well enough, I'll probably go ahead and finish these first with clear shellac as a pore fill then maybe wax/oil.

[JuniorJBL]

A lot more router and sandpaper equity 69898 and the sawmarks are completely gone from the waveguides. The profiles aren't cast-metal perfect, but they're good enough for gov't work. I also flush-trimmed the bonded panels and put a 1.25" chamfer on, as well as relieving the back of the waveguide a smidge so that it's a little closer to a perfect cone profile continuation. Lot of sandpaper action too (not all reflected in this pic but you get the idea). If I can get the top veneer layers sanded well enough, I'll probably go ahead and finish these first with clear shellac as a pore fill then maybe wax/oil.


That's a lot of elbow grease right there! Nice work. :)

[badman]

That's a lot of elbow grease right there! Nice work. :)

Thanks again! Definitely some work, but I really love the layered look of well-done exposed Baltic birch that I'm emphasizing it for this build- between the gigantic chamfers and the waveguide, there will be many concentric circles and rectangles to ogle :)

[badman]

The initial intent was to do these sectionally, 4 units. The challenge with that is the lack of knowledge about the thiele-small parameters for these, I'll have to measure the woofers with a mocked-up box to see if I can sim an enclosure decently, but for now, I think I'm going to do an open-sided dipole with drivers front and back. There will be some midbass to midrange bloom but since >1khz should be well controlled by the waveguide, it's only really the mids/midbass that will be an issue, and that's the balance between needing to EQ them and maintaining dipole dispersion. To start with I think I'll fasten baffles back to back, wired out of phase, so there will be no net pressure in the gap and the cancellation will have to traverse the waveguides, baffle width, and gap size (12" tentative).

I do own a pair of heil AMTs, which might be a nice option to use if I roll off the top end where the CD is at it's worst and swap those in instead.

[JuniorJBL]

If I remember correctly the back box for those is 1 cu ft. Insulated.

From the 328 spec sheet,

"The optional MTC-300BB8 one cubic foot backcan is made of extra-thick 16 gauge steel and the top is lined with ½” medium density fiberboard."

https://www.jblpro.com/ProductAttachments/JBL_MTC300BB8v2[1].pdf

[badman]

If I remember correctly the back box for those is 1 cu ft. Insulated.

From the 328 spec sheet,

"The optional MTC-300BB8 one cubic foot backcan is made of extra-thick 16 gauge steel and the top is lined with ½” medium density fiberboard."

https://www.jblpro.com/ProductAttachments/JBL_MTC300BB8v2[1].pdf

Thanks- knew that but I'm approaching this a bit differently, it looks from the FR curve that it's a lumpy alignment, I suspect it might be a poor match for home hifi. We'll see- it'll be a deep project!

[JuniorJBL]

Thanks- knew that but I'm approaching this a bit differently, it looks from the FR curve that it's a lumpy alignment, I suspect it might be a poor match for home hifi. We'll see- it'll be a deep project!


Sorry, I should have known that you were on top of the situation, More so than I might have been. Carry on!! :D

I did however end up getting the 321's as well for my ceiling Atmos upgrade. Probably be a couple of months before I get to install them. :(

[badman]

70211

Not a great picture (though it does have LSR305s in it if you look closely) but these are the frames. They're designed to allow me to mount everything in the enclosure with only one panel (bottom) having exposed fasteners. The idea will be to fasten blind on each set of corners and use gasketing on all coupling from the panels to the frame. Constrained layer damping, though not the entire surface will be damped (it'll be reasonably well-coupled to the damped sections though).

The next steps are:

Align and pre-drill the mounting bolt holes on all 4 baffles/both frames, mount the drivers and crossovers to all baffles, and assemble them (without top/bottom/sides) as dipoles for testing.

[badman]

704537045470455 Some precision hole drilling so that the frames/etc all line up (a better planning with a master template would've helped that process substantially) and they're rollin'. The wiring took two swings- I realized after I wired them up the first time that I'd done parallel (default) rather than series wiring- they're low-ohm woofers (5) so rather than have a sub-3 ohm load through the midbass, I went series and have a nice easy 10- most manus would call this a 16 ohm system but they're fulla horse hockey.

Sounding pretty fine- nice and open and airy, detailed, and good dynamics, though as dipoles, bass "impact" isn't really there.

[badman]

I was expecting much worse performance from the compression drivers- they actually are sounding quite nice! The fairly high 3rd order crossover seems to be keeping them out of any problematic range, and the soundstage/imaging I'm getting is superb. Beethoven's 6th right now, sounding delicate and lovely. They're still sitting on the floor, but seem to be fairly good about dispersion within the 120 degree pattern, so I get a nice big lobe. Really fun "little" system (rather bigger than L100s). Bass resolution is superb thus far, probably due to the dipole directivity.

[JuniorJBL]

Very cool! Glad that they sound better than you first thought they would!! Those should be great surrounds. :)

[badman]

Very cool! Glad that they sound better than you first thought they would!! Those should be great surrounds. :)

I think they'll be fantastic surrounds- the only issue is that they're 18Wx24Hx15D- I mismeasured the location where one was to go when planning the build, and they won't fit in my room!

[JuniorJBL]

I think they'll be fantastic surrounds- the only issue is that they're 18Wx24Hx15D- I mismeasured the location where one was to go when planning the build, and they won't fit in my room!


Houston, We have a problem...

I have NEVER made a mistake like that before!! :rotfl:

( I lie a lot as well) :D

[badman]

I think I'll have quite a bit of fun playing with them as mains first, anyway. I just HAPPEN to have some dual 123a/2213 M-frame dipoles I've built and never implemented...... Might not be too terrible to passive those into the rig :) The coaxes from 300hz up ought to really reduce the cone motion and keep the mid and tweet nice n clean