Pics Altec VOTT A7 using CAD and CNC

**atilsley** · March 4th, 2014, 10:47 PM

Whilst I'm developing a smaller Altec bass horn for my own system, I'm using part of that experience to do a CAD/CNC Altec VOTT A7 cabinet.

Attached are the initial drawing from my engineer CAD mate.

This will be built in Euro Birch Ply, 19mm.

A significant change over the original is the central baffle which is rebated into the sides, top and bottom of the cabinet.

The horn sections will be bent by CNC'ing the multiple grooves into the back of the ply. This creates an easy bend. CNC'd brace supports are used as the template for the 31 inch radius curve.

The back 2/3 of the cabinet will be fixed, while the top 1/3 will be removable.

As a decorative feature, we'll create an oval shape port at the front, which will sit in a removable panel, per the original design. This way we can add different size ports to suit the tuning of the cabinet. The initial sizing is smaller than the original A7?and the current pic shows the oval cut out too large. We?ll target a size of approx 30cm x 7cm (12 inches x 2.75 inches).

And yes, I've purposely gone to town on the cut-outs for the inner baffle/support, including CNC'ing the letters VOTT into the panel.

Altec 515's will be used in this version.

I suspect the cabinet will be heavy, with as little cabinet resonance as possible.

What extra things should I be looking for in the design...?

Photobucket links here also -

Front
Top
Back

Kind regards.
Andrew

**endeeinn** · March 5th, 2014, 12:12 AM

You attachment says 4 views but only 1 came through

**atilsley** · March 5th, 2014, 12:56 AM

Originally Posted by endeeinn

You attachment says 4 views but only 1 came through

Only the one attachment (PDF)...but the other three are URL links to Photobucket. Please click on the words, Front, Top, Back per above.

Kindly

**endeeinn** · March 5th, 2014, 10:18 AM

I was only looking at the pdf and completely missed the front, back and top. Great cad drawing. Thanks.

**VolvoHeretic** · March 5th, 2014, 01:38 PM

How do you calculate the bottom cut for the curved side horn flare so that after cutting a flat piece of plywood and bending it, it has a straight bottom face where it meets the angled bottom flare of the horn? I assume the cut is some kind of curve, maybe some kind of ellipse segment?

Edit; maybe it's just a straight line and I am trying to think too hard.

**atilsley** · March 5th, 2014, 08:36 PM

Originally Posted by VolvoHeretic

How do you calculate the bottom cut for the curved side horn flare so that after cutting a flat piece of plywood and bending it, it has a straight bottom face where it meets the angled bottom flare of the horn? I assume the cut is some kind of curve, maybe some kind of ellipse segment?

Edit; maybe it's just a straight line and I am trying to think too hard.

It is straight...see pic HERE.

What I need to work out is wehther or not I need to add a chamfer/mitre to this edge. If I don't, there'll be a small gap behind the face of the curved panel...which is OK...just need to fill it with putty/bog later.

Andrew

- - - Updated - - -

My CAD man says -

No mitre. The vertical piece intersects the sloping piece at 90 degrees. The width of the curved panel is given by the length of the arc, but on the bottom of the panel the length increases because of the intersection with the slope. Front edge height is fixed, back edge height (at the baffle) is fixed and width is fixed by arc length. Attached shows 2 rectangles intersecting on slope ... no curve required.

**VolvoHeretic** · March 5th, 2014, 10:27 PM

Thanks Atilsley, I new I was overly thinking it. Remember that the top and bottom panels where rabbited over the side panels and the angled bottom horn panel is dadoed into the side panels in my A7's. Don't know about the top and bottom of the curved side flared horn panels, but I think that they should be also. Good luck.

**atilsley** · March 6th, 2014, 05:28 AM

Originally Posted by VolvoHeretic

Thanks Atilsley, I new I was overly thinking it. Remember that the top and bottom panels where rabbited over the side panels and the angled bottom horn panel is dadoed into the side panels in my A7's. Don't know about the top and bottom of the curved side flared horn panels, but I think that they should be also. Good luck.

Thanks Volvo....I've CAD'd a channel into the underside of the top panel to secure the curved panel....just for further anchoring.

**bowtie427ss** · March 6th, 2014, 08:31 AM

I suspect the cabinet will be heavy, with as little cabinet resonance as possible.

Resonance will be dependent on what methods of bracing and damping you choose for the particular material you build with. Undamped, and unbraced, Birch ply has as much "ring" as solid hardwood................... because it IS solid hardwood, just with biased layers of grain to control warping and checking.

Birch ply has a very high tensile strength that fairly negates the ability of it's mass alone to damp resonance, it in fact can be very "alive" at certain frequencies and requires a different approach to damping than softwood ply or MDF. Some folks will still only hear what they believe, YMMV.

**atilsley** · March 7th, 2014, 02:04 AM

Thanks...I've used quality ply and mdf for my various altec, tannoy, GOTO and lowther projects.

For this new project, check the drawings to see very substantial bracing.

Originally Posted by bowtie427ss

Resonance will be dependent on what methods of bracing and damping you choose for the particular material you build with. Undamped, and unbraced, Birch ply has as much "ring" as solid hardwood................... because it IS solid hardwood, just with biased layers of grain to control warping and checking.

Birch ply has a very high tensile strength that fairly negates the ability of it's mass alone to damp resonance, it in fact can be very "alive" at certain frequencies and requires a different approach to damping than softwood ply or MDF. Some folks will still only hear what they believe, YMMV.