Mid Bass Horn Design 80-800 Hz

[bfish]

She packed up her bags and she took off down the road
Left me here stranded with the bills she owed
She gave me a false address
Took off with my american express
Sunspot baby
She sure had me way outguessed


http://pds5.egloos.com/pds/200706/11...9_02065333.jpg

<font color="#FFFFFF" size="1">[ December 09, 2007 03:50 PM: Message edited by: bfish ]</font>

[Steve Mac]

OMG, that's what I'm talking about bFish...

Back to reality, got a lot of work done today:
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[Steve Mac]

Originally posted by Jim Norvell:
Question on cutting the horn end pieces on an angle. Calculating the shape is fairly simple but how did you compensate for the angle when you did your router cuts. It looks like it might be setting in there at about a 15 degree angle and short of a 5 axis router table I am at a loss on how to do that cut. In the end it might not make that much difference to the final fit.

Jim N

<font size="2" face="Verdana, Helvetica, sans-serif">Hi Jim, thanks for responding.
There's major thing left to "engineer" in the wedge and let's see if we're talking about the same thing:
This is the wedge:
side view of the wedge

Now I've color coded the top wedge piece's upper edge and lower edge on its curved side...with yellow being the exact dimension of the face of the wedge(in effect this dimension is spot on)...and blue being the edge that sticks out because it is not 90 degrees with the floor or base wedge piece:
side view of the wedge color coded

I'm up for suggestions but the only way I know how to do it fairly cleanly is to get a swivel base router set to the angle of the wedge, place another wedge piece on top as a guide...overlapped slightly to catch the edge of the ball bearing on the bit, and then hold it it one plane throughout the slice.

[bfish]

It doesn't look to me like anything a single fixed-angle trim would correct. The "wedge" edge at the throat end should need little if any correction, while the overhang will get progreassively worse as you move towards the mouth end and the flare angle widens.

Looks to me like a good place for some skillfull freehand work with a jigsaw in "float" mode (base angle screw loose).

[jnorv]

It would be informative to know how the altec guys did it 50 years ago. My 828 cabs have somewhat the same construction.

Jim N

[bfish]

They cut the flare ends to fit the flat "wedges", instead of vice-versa. The flare curve is established and held rigid by the backside braces, not the top and bottom panels (which extend full width of the cab).

<font color="#FFFFFF" size="1">[ December 10, 2007 07:49 PM: Message edited by: bfish ]</font>

[jnorv]

I think my first attempt would be to assemble both ends and then screw a flat plate across the mouth. This would hold the ends in position . You might have to throw in a diagonal brace to keep it rigid. Then you could take a round clothes pole (~1.5" dia). Wrap some sand paper around it and , then using guides on the parallel end plates sand in some guides on maybe 1-2" centers. This would be guides to freehand in the correct shape. And use lots of Gorilla glue.

Jim N

[bfish]

Or have a helper drag a carpenters square on the floor (in the pictured position) in front of the saw for a visual guide.

Or hire my fishin' buddy...a carpenter who can do things with a shieldless skillsaw that I couldn't replicate with the best equipped woodshop.

[jnorv]

Trying to do a project of this type illustrates the problems we DIY'er have with what tools we have. I don't know how I would cut an "perfect" angle on the bottom of the flares either.

Jim N

[bfish]

Right, when the conical panel angles away from 90 degrees, the match cut on the curved panel is no longer a straight line when the panel is cut from flat stock.

To clone one, just make a pattern with large foil or paper. From scratch, trial and error till you get one right, maybe using alternate materials to prototype with. When you finally get it right, you keep that baby for a pattern and guard it with your wife.