Fun with FST - Build Thread

[mattp]

I've finally been able to break ground on my big three way build and I'll try to take you all along for the ride.

Driver Compliment

Tweeter: Transducer Labs N26CR2-A
Mid: B&W Continuum LF27170
Bass: Dayton RSS210HO-8 x2

Originally I was going to use the four NOS ScanSpeak M22WSR-46 woofers I have in my stash but I discovered one of them has debris in the gap and they are NLA, so I had to make a change. The RSS210HO-8 works very well in the same volume and has a lower F3 but at a loss of efficiency. A pair in parallel should help a little but I am ok with this sacrifice.

Cabinets

Dims: 40-3/8"H x 10-1/2"W x 15"D externally

1.5" thick baffles, 18mm Baltic Birch exteriors, solid walnut accents and MDF for inner baffle and bracing. 3/4" round-overs down the front edges and 1/4" around the top front/sides. Woofer chamber is ~1.8 cubic feet gross with a single down firing 4" port tuned to 28 Hz. Mid chamber is my simplified version of a Helmholtz resonator. The two panels with holes come together at the back and there will be densely packed damping material behind them. The cavity in front will be lined with foam and lightly filled. I have no idea how well this will work to absorb the back-wave of the driver but it seems reasonable to me. It's a bit of an experiment.

Cabs will sit on spiked outriggers (as pictured), finish will be semi-gloss poly.




Crossover

TBD. These will be crated and shipped for Klippel NFS and I can go into more detail at that point. I am hoping for XO points around 450 and 2k. Why not use OmniMic? If you had the chance to have something near field scanned for free... wouldn't you take it?

Baffles are underway now.





They still need to be cut to length and once they are glued to the cabs they will be trimmed a further ~1/4" around the sides and top. Driver cutouts are next, then onto the rest of the cabs.

[a4eaudio]

If you had the chance to have something near field scanned for free... wouldn't you take it?

Yes.

Looking forward to the build as it comes together, this should be pretty impressive.

[Wolf]

Matt, I like the look and direction!
As to your midrange chamber, some thoughts if I may-
I would use spray adhesive on the holey partitions, and line them with open-cell foam to where there are no gaps fore to aft. Lining both sides is also an option. Lightly stuffing the front is good to complement the foam lining, however, lining the rear chamber is likely the better path than dense fill. Essentially, this creates a double-chambered aperiodic sealed alignment. It can reduce Fs magnitude of the midrange mechanically, and better damp the driver and its operation. The fill in front still remains in the right place for standing wave or column resonance suppression.

Just my 2c,
Wolf

[mattp]

Matt, I like the look and direction!
As to your midrange chamber, some thoughts if I may-
I would use spray adhesive on the holey partitions, and line them with open-cell foam to where there are no gaps fore to aft. Lining both sides is also an option. Lightly stuffing the front is good to complement the foam lining, however, lining the rear chamber is likely the better path than dense fill. Essentially, this creates a double-chambered aperiodic sealed alignment. It can reduce Fs magnitude of the midrange mechanically, and better damp the driver and its operation. The fill in front still remains in the right place for standing wave or column resonance suppression.

Just my 2c,
Wolf

Thanks, Wolf!

I am open to suggestions with how to best damp this enclosure so I will certainly try this out as it does make sense. What type of open-cell foam do you recommend? I will probably line both sides of the holed partitions.

[Wolf]

I think last I did it was the foam seat cushions you can get from Joanne's. Open-cell 0.75-1" thick, white flat foam. You may be able to find it in the packing materials aisle at Walmart too with the bubble wrap. You don't want the rigid flower foam, the green stuff ($), or the nufoam products. I recently tried Gorilla spray adhesive, and it was awesome for this kind of purpose.

I know the holey boards are also structural, so im working on that suggestive path. It would actually be better to sandwich the foam between 2 panels, so you can squish it slightly, rather than sandwich the brace between 2 foam sheets. Pegboard actually works quite well, and you don't have to cut holes.

Wolf

[mattp]

Finally had a chance to cut the driver holes last night. A lot of trepidation with this one but everything turned out nice. Hopefully I can get started on the rest of the cabs soon.





The tweeter recesses ended up about 1/16 too large but they will be fine once I shim the tweeters for mounting. The mids are interesting, they require a two-step recess which is tricky to measure. I'm very glad I didn't screw these up but test holes helped a lot. The woofers were pretty straight forward and ended up with the best fit of the three, oddly. Woofer and mid holes are chamfered in the rear.

I must say, this is turning out to be one sexy looking thing if I do say so myself. I'm very pleased with the look so far.

[Wolf]

Top quality components for sure....

(Did you keep the prior Epique design?)

[mattp]

Top quality components for sure....

(Did you keep the prior Epique design?)

Ben,

I ended up selling the cabs, woofers and stands to a close friend of mine (Chris Frechette, another PE tech you may remember) who put Aurum Cantus ribbons in them and is bi-amping them for studio monitors. They did not go to waste.

The two dual opposed reference subs I had with that system are in storage and will eventually augment these towers once I have them in a dedicated room.

Side note: I know you used a variant of the Ref 8" subs as a woofer in a 3 way years ago but I don't remember the outcome and your thoughts on it. Do you remember where you had them crossed and any details regarding that?

[Wolf]

I used the original RSS210HF-4, and the others weren't out yet at the time. I was able to xover at 850Hz to a 2" dome mid, so you should be golden with the mid you have. I think DanP used the RSS210HO4 or 8 in the Boxers, and xoverd up at 1kHz to a waveguided tweeter, so even in a 2way you would be fine. They are remarkable drivers.

Im glad the former are still being enjoyed. Those were pretty!
Wolf

[tktran]

I went through multiple iterations of on and off axis measurements at 1x diameter of driver distance and careful inspection of zoomed impedance traces and higher order harmonic distortion to detect cabinet issues.

In the end I used a mixture of trio of cabinet deadening and rear damping materials for my fibreglass spherical cabinet.

I have a newfound respect for over-engineered cabinets like those of B&W.

[mattp]

A few more pics.









Cab shell Forum is underway. Bracing and inner panels are next, all out of MDF. Things are going together really nicely so far.

[mattp]

Bracing is underway and ports are glued in. I made more progress than I expected to last night.

[DeZZar]

Really nice build! Looking forward to seeing these finished.

[tomzarbo]

Thats a MAN VENT there!
Those things are beautiful!

TomZ

[mattp]

Thats a MAN VENT there!
Those things are beautiful!

TomZ

Thanks, Tom!!

I added the mid/tweeter partitions and started on the damping material. Mostly 3/4" Sonic Barrier with the mass added in all chambers. There is a 48" long 8" wide chunk of R6 fiberglass stuffed in the bottom cavity on each. I still need to cut the mid baffling and add more damping there, but this is the majority. I'm pretty happy with the amount. I weighed the Sonic Barrier before I took the cut pieces out of the box and it weighed 13.4 lbs, so minus the box weight, there is roughly 6 lbs of Sonic Barrier in each of these.