The new baffle test jig was developed after it became clear that the older
construct was limited in flexibilty. The need to be able to test both one-
and two-sided baffles which have maximum triangular shapes and/or minimum
width at the top was a design focus.
Initially a design was created that was to have been fabricated from steel, and would have been even more flexible than this design due to it's smaller bulk. Unfortunately that design would not be implemented with the time/resource s available prior to the first gymnasium testing session. A crash program was instituted to get something working, and the construct at the left is the result. Unfortuately, it was not ready until after the first gym testing session, and was first used during the March 1, 1998 gym testing.
Wood is easier to work than metal, but as always there are/were compromises
in the design. The concept of having the driver's base rest directly on the
floor is retained. A major new feature, the ability to 'dial-in' a precision
tilt-back of the baffle has been added. Photos of the jig in use can be seen
in the Gym Testing section.
The primary material used in the jig was 1.5" x 1.5" clear Douglas Fir. Lumber
of that dimension was choosen to match with the width of the RD75 driver. A
3/4" x 3/4" x 75.6" section of cabinet moulding was attached to the side of the
upright 1.5" x 1.5" using glue and drywall screws.
The 1.5" x 1.5" upright is approximately 72" long, and was cut on an angle
over about 14" of it's length as shown in the photographs. The angled cut was
made to allow triangular baffle sections to butt directly against the RD75's
mounting flange - that is, to obtain the maximum triangularly shaped baffle
possible with the driver. A small filler section must be usually be fabricated
to fill the void between the baffle and the upright. Filler sections can be seen
in the baffle photographs in the Gym Testing section.
The 'T' section base was cut at a 7 degree angle where it meets the upright
piece. It was determined that this angle would provide sufficent tolerance to
investigate up to 5 degree tilt-backs of baffles under investigation. Assembly
of the 'T' section was completed with glue and 4 - 3" drywall screws per
junction.
A 3/4" hardwood dowel was used as a bracing piece for the construct. It was
inserted into pre-drilled holes in the 'T' section and the upright, and affixed
with glue and screws.
The tilt-back adjustment mechanism was created from two 1.5" x 5/16" hexagon threaded sleeves. The sleeves were pounded into holes drilled into the ends of the 'T' section. Six inch long x 5/16" 'stovebolts' with 3/4" felt pads glued to the bolt head are the adjusters. Two inch diameter wooden door knobs were screwed onto the ends of the bolts to facilitate adjustment.
Self-adhesive, closed-cell rubber weather stripping 3/16" x 3/4" was affixed
to the inner side of the 3/4" x 3/4" moulding as a spacing gasket. As
previously noted in the construction notes for the original baffle prototyping
system, this gasket allows the RD75 driver to be 'pulled-in' to be exactly
flush with the front face of the assembly.
The assembly was then finished with multiple coats of water-based polyurethane, which special attention being paid to the left side (facing front) of the upright. That side it the attactment point for one-sided baffles.
Fabricated baffles are affixed to the left side of the 1.5" x 1.5" upright
(viewing front) using 1.5" wide double-sided carpet tape. Ususally the front
and rear side 'seams' are further taped with 'artist's tape' to reduce any
diffraction points at the interface.
The Original Test Baffle.
Outdoor Measurements.
The RD75 Dipole Baffle Study - Table of Contents.
Acoustic Line Source Research - Table of Contents.
