Mid Bass Horn Design 80-800 Hz

[Steve Mac]

In keeping this design process as "real time" as can be I'll discuss the next problem which is building curved side walls.

This is the "lowest hassle with the tools I have" solution I currently have so I thought I'd run it by you guys to see what ya think.

1) drill and bolt the wedges to the rear chamber
2) fergit scoring plywood, find the right bendy board material that will take on any shape easily.
3) cut to size, mark up where the screw/bolt holes go and drill small diameter holes and screw the sidewalls using sheetrock screws
4) find a filler for the walls...this I haven't figured out yet, but I'm gonna need a lot of it. Fill the grooves and let set until it's cured
5) Unscrew the sidewalls and get a very thin poplar veneer to make finishing clean and contact cement it to the outside of the sidewalls
6) create 4 fairly thick, long straight boards slightly angled on one edge and attach to the edge of the sidewalls that contact the rear chamber...should maybe do this before the veneer process
7) coat the wedge sides or whatever else with the neoprene and screw/bolt the whole thing dam thing together using the same holes used to clamp the sides in place

I like not needing clamps at all...that's kinda clever if I can get away with it.

I haven't figured out the right fill cement that is not too expensive and will be heavy and will be easy to work with and will hold the shape properly when dry and will not crud up a veneer coat afterwards. open to suggestions

[bfish]

You'll like this one...

F'getaboutit. You've got plenty of contact area on the edges alone.

[Steve Mac]

Originally posted by bfish:
You'll like this one...

F'getaboutit. You've got plenty of contact area on the edges alone.

<font size="2" face="Verdana, Helvetica, sans-serif">Yeah, encouraging.

I was really talking about filling the plywood after it's attached. Anyway, I've got 4 pieces kerf cut like this:
Pic
I can bend it enough to make the shape and still have the kerf cuts open plenty for filling.
...but it's still stiffer than I'd like(no comments please). I just want it to be pliable when it's screwed in...then I'll make it hard like a rock(now comments are welcome).

I wonder if a wall paper steamer hovered over a side for 10 minutes wouldn't soften it up enough as it's only an 1/8" of material to bend. This one man operation stinks. I suppose I could get a thin router bit and snake it back and forth thru the cuts a wee bit at a time until it got "just" pliable enough...the slice could be very thin as the material is cleared out basically...hmmmm.

[bfish]

Sorry, I had "fergit scoring plywood" fresh in mind and was thinking wedge sides instead. My bad.

Having to veneer the backsides kills all my rather idustrial ideas in their tracks. I have trouble trading off mechanical properties for aesthetic ones, just the farmer/plumber in me I s'pose.

I saw a steaming chart awhile back but can't seem to find it again. From memory, the item is enclosed to achieve saturation levels for 30 minutes or more for 1/8".

Don't s'pose you have access to a butfohr (sp?) by any chance? Might be an Amish thing.

<font color="#FFFFFF" size="1">[ January 01, 2008 08:12 AM: Message edited by: bfish ]</font>

[bfish]

You might find something of use in the Google preview of the Wood Bending Handbook.

[Steve Mac]

Originally posted by bfish:
Sorry, I had "fergit scoring plywood" fresh in mind and was thinking wedge sides instead. My bad.

Having to veneer the backsides kills all my rather idustrial ideas in their tracks. I have trouble trading off mechanical properties for aesthetic ones, just the farmer/plumber in me I s'pose.

I saw a steaming chart awhile back but can't seem to find it again. From memory, the item is enclosed to achieve saturation levels for 30 minutes or more for 1/8".

Don't s'pose you have access to a butfohr (sp?) by any chance? Might be an Amish thing.

<font color="#FFFFFF"><font size="1">[ January 01, 2008 08:12 AM: Message edited by: bfish ]</font></font>

<font size="2" face="Verdana, Helvetica, sans-serif">If you think you are going to get me to ask you "What's a butfohr?"...fergit it.

As far as industrial is concerned, if the kerf is filled with cement...well that's pretty industrial I guess. I'm hoping to find a dense fill material. Covering it up with veneer is an aesthetic choice not functional but I don't want the horn to look like a!s!s when it's done either. Who knows, maybe my gas tank will be empty when I reach that point.

[bfish]

Originally posted by Steve Mac:
If you think you are going to get me to ask you "What's a butfohr?"...fergit it.

Party pooper!

I've had the privelege of answering that question for 3 other engineers, always on the lookout for #4.

One might wonder about the quality of life someone has that lives for little moments like that...

[jnorv]

I have lost track of your original drawings but if I remember you are planing on not enclosing the backsides of the horn flares. Altec, on much shorter horns, used stiffeners on the backsides. If you added stiffeners and then put a flat plate of plywood from the throat to the mouth it would give great stiffness. You could also foam fill the cavity or if you don't plan of moving them much, sand filling. I sand filled the horn flares on my 828's and it really deadened the cabinets. Of course it added about 100 pounds to the cabinet weight.

Jim N

[Steve Mac]

Originally posted by Jim Norvell:
I have lost track of your original drawings but if I remember you are planing on not enclosing the backsides of the horn flares. Altec, on much shorter horns, used stiffeners on the backsides. If you added stiffeners and then put a flat plate of plywood from the throat to the mouth it would give great stiffness. You could also foam fill the cavity or if you don't plan of moving them much, sand filling. I sand filled the horn flares on my 828's and it really deadened the cabinets. Of course it added about 100 pounds to the cabinet weight.

Jim N

<font size="2" face="Verdana, Helvetica, sans-serif">I guess after I've figured out how to bend the pieces and attached them I can consider bracing but I THINK if I were careful...AFTER the walls were in place I could mix a fine grade portland cement and fill in the kerf cuts. That would certainly add a good deal of weight. If I keep the surface clean afterwards it could be covered with a real thin veneer just to get a smooth surface back for finishing. Like some of the previous design issues who knows where it'll end up because some of these decisions are being forced into a solution that I can pull off alone.

[Steve Mac]

Originally posted by bfish:

One might wonder about the quality of life someone has that lives for little moments like that...

<font size="2" face="Verdana, Helvetica, sans-serif">Well, to be honest I remember my brother sticking m&m's in his wife's nose one day while she was sleeping thinking it was the funniest thing ever so what do I know?