Saturday, April 4, 2015

The Second Bass Horn For The Sound Transformer

Throughout the winter, I have been building the ribs for a second Sound Transformer bass horn.  At first, I thought about constructing a pair of redesigned bass horns based on what I learned building the first one.  However, after trying several different bass drivers on the original Sound Transformer, I settled on building another one identical to the first.  There are some minor differences in the way the second one is constructed, however.

A couple of days ago, I made three more ribs for a total of eight for the largest portion of the bass horn, the mouth flare.  Then I purchased a new sheet of AC plywood, 19/32" thick.  When I built the first one, I was not sure how it would work out so I used old pieces of plywood and paneling found at the dump.  The recycled plywood pieces were warped.  I had to reinforce the plywood flanges with pine cleats to try to correct the warping.  Parts of the plywood were damaged and could not be used. The second time around, I decided to use new plywood for the flanges.  The first two flanges I cut for the mouth flare are perfectly flat so I don't think I'll need the pine cleats.  As a result of having no cleats, I was able to use shorter sheetrock screws to fasten the ribs to the flanges.  Here is the mouth flare assembled.

Second Sound Transformer Bass Horn Mouth Flare Flanges And Ribs
Second Sound Transformer Bass Horn Mouth Flare Flanges And Ribs
Here is another view of the mouth flare that shows the curve of the ribs.


Sound Transformer Mouth Flare Showing Rib Curves
Sound Transformer Mouth Flare Showing Rib Curves
I have moved the ribs a little closer together to provide more room for the edges of the paneling at the smaller end.  The following picture illustrates why that will help.


More Clearance Between Rib Ends To Secure The Trapezoidal Side Edges
More Clearance Between Rib Ends To Secure The Trapezoidal Side Edges
The yard stick is about the same thickness as the paneling.  On the first Sound Transformer, I had the rib ends of adjacent sides in contact with each other so there was no overlap for the joint between the trapezoids and the curved sides.  The overlap provides a landing for glue applied later on.

For paneling, I selected a Masonite board with hard finish on one side.  The thickness is about 5/32".  Here is the panel with a yard stick as a straight edge clamped for marking out the trapezoid.


Marking The Trapezoid On The Masonite Panel With A Yard Stick
Marking The Trapezoid On The Masonite Panel With A Yard Stick
Tomorrow, weather permitting, I plan to cut out a couple of trapezoids for the first two sides of the Sound Transformer.


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