OBL-11
 Baffle construction
Copyright 2011 © Troels Gravesen

Construction pics     Panel dimension      

The Baffle
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From outer appearance my baffles may resemble the SFBs, but rather than making a sandwich from thin plywood filled with sand, I'll laminate two sheets of 25 mm Baltic birch and there will be some heavy bracing between the 15" and JA8008 drivers.
The original SFBs came with a stretched metal grille, probably not bad from an acoustic perspective, but hard to realise in a diy context, thus a frame with fabric will replace the metal grille.


The OBL-11 baffle. As close as possible to the Wharfedale SFB.
 

The main panels: Sub-panel and front side panels
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Do not cut front side panels to size before last.


The front side panels will be veneered with tiger striped anigree like seen above. Anigree wood comes from West Africa.
Baffle fillets and front vertical fillets will be from solid elm, which goes well with anigree.

Placement of drivers


Bass driver is only partly countersunk.

8008/TW034 additional baffle and rear support panels


The 8008/TW034 drivers are placed on additional 12 mm Baltic birch baffle as shown on drawing.
The width of the additional baffle is 360 mm. The width is smaller than the gap between front side panels to allow
fillets framing the drivers as on the original SFB baffle.

Front grille, front fillets, rear support panels and rear bracing


Panel seen from top. The green line is 10 mm felt material surrounding JA8008 driver and TW034 waveguide.
280 mm brace is placed at bottom. 200 and 120 mm braces are placed between drivers.
Upper 120 mm bracing has a cut-out, r = 80-85 mm. Remember to offset 50 mm! I didn't and had to rework the panels.

Panels dimensions:

- Basic panel: 850 x 850 x 25 mm Baltic birch (or MDF). MDF or similar may do well too.
- Front side panels: 215 x 825 mm Baltic birch.
- Additional 12 mm panel for 8008/TW034: approx 360 mm x 500 mm, don't cut before side panels and front fillets have been added.

- Rear support panels: 2 pcs 500 x 850 mm will make four support panels.
- Bracing between 8008 and TW034: 650 x 120 mm, chamfer 6 deg.
- Bracing between Eminence and 8008: 650 x 200 mm, chamfer 6 deg.
- Bracing at bottom: 650 x 280 mm, chamfer 6 deg.
- Panel for terminals: 80 x 650 mm placed vertical from bottom bracing - or to your liking.

The two additional front panels (215 mm x 825 mm) are cut to final dimensions last.

Step by step:

- Cut all panels listed above except for the 2 (4 in total) additional front panels. These I cut 240 x 850 mm for pre-veneering before cutting to final size. Final size may depend in total width of front grille and vertical fillets.
- Start making the front grille frame.
- Make the 2 (4 in total) front vertical fillets.
- Add additional 12 mm panels for 8008/TW034 drivers so that this fits into the front grille frame.
- Route holes for all drivers, remember none of the drivers are flush mounted.

Construction pics:
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Test set-up from newly cut panels. Front side panels cut too wide for pre-veneering.


Rear bracing: Width = 650 mm, depth 280, 200 and 120 mm respectively. All chamfered 6 deg towards main panel.
The rear will be covered by cloth - quite a challenge to make a curved frame for holding the cloth.


Gluing the rear support to front panel. More clamps were used than seen here.
Use biscuits at bottom panel to keep rear support in place during tightening of clamps.
I rarely use screws for cabs, but here a added four screws to keep front panel in place (not seen on photo).


Tiger striped anigree veneered side panels, ready for cutting to size.


Panels finally shaping up.


Left: Note gasket for lifting 8008 driver. Made from 2.8 mm plywood. Right: Felt padding around mid and tweeter, this was temporary.

 
Extended listening made me try out a second option: No felt on front panel and in the end this is what I prefer. Slightly more midrange presence.
Consequently I added a 10 mm sheet of plywood in replacement of the felt and painted it black.

Mounting of 8008/TW034 drivers:

Depending on front panel damping material, being either 10 mm polyester foam, 8 mm felt material or a 9-10 mm sheet of plywood, mount drivers to be flush with foam/felt/plywood material as seen above. If you use plywood, glue this first and route for drivers last.
The ~10 mm green felt material seen above fits nicely with the 8 mm height of waveguide flange. To align the 8008 driver with the waveguide a thin gasket was made from 2.8 mm plywood.
To make the cut-out in the waveguide flush mount the waveguide on a piece of spare MDF. Secure the waveguide with screws and route for the 8008 driver as usual (view TQWT and DTQWT constructions. View more detailed pics TQWTcabs). Route to depth of 5.5 mm.


Only thing missing is front grille and top fillet.


- and maybe some nicer wiring for mid and tweeter....


First front grille in place.

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