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Old 5th March 2014, 01:21 AM   #1
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Default Altec VOTT A7 using CAD and CNC

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).

Altec 515's will be used in this version.

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

Andrew
Attached Files
File Type: pdf Baffle Panel.pdf (18.0 KB, 107 views)
File Type: pdf angled cone board.pdf (94.5 KB, 47 views)
File Type: pdf Back Panel.pdf (24.8 KB, 30 views)
File Type: pdf Base Panel.pdf (61.3 KB, 26 views)
File Type: pdf Curved & Top Panels.pdf (113.8 KB, 51 views)
File Type: pdf Front Panel.pdf (38.6 KB, 38 views)
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Old 7th June 2014, 08:53 AM   #2
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After some delay, got my cnc'd panels today...going to be one sturdy cabinet.
Attached Images
File Type: jpg top panel inside.jpg (90.9 KB, 608 views)
File Type: jpg baffle.jpg (100.1 KB, 599 views)
File Type: jpg loose panels 1.jpg (90.6 KB, 593 views)
File Type: jpg baffle 1.jpg (91.0 KB, 589 views)
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Old 7th June 2014, 09:39 AM   #3
naca5 is offline naca5  Belgium
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Gorgeous Andrew...
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Old 15th June 2014, 11:53 AM   #4
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started glup up today
Attached Images
File Type: jpg baffle glue in.jpg (81.3 KB, 523 views)
File Type: jpg baffle side glue in.jpg (83.3 KB, 168 views)
File Type: jpg baffle with roof underside.jpg (68.3 KB, 145 views)
File Type: jpg front vent glue on.jpg (124.6 KB, 125 views)
File Type: jpg inside glue up 1.jpg (95.6 KB, 197 views)
File Type: jpg middles shelf braces glue on.jpg (92.8 KB, 192 views)
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Old 15th June 2014, 02:04 PM   #5
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Gotta love CAD/CNC!

GM
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Old 15th June 2014, 03:35 PM   #6
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Old 15th June 2014, 03:53 PM   #7
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Interesting approach.

The holes through the braces might not act exactly like the open space in the original A7. I suspect they may behave like a "bandpass" type enclosure, in essence two volumes + the final port.

Also the holes that access the rear side of the horn flares likely ought to be sealed up as they too will act like some sort of tuned volume/space.

Fwiw, I converted an A7 for a client to 4 x 4" dia PVC ports (or was it 5 ports?). This improves the performance at LF and reduces substantially the rear lower mid radiation through the large open port of the original A7, and permits precise tuning.

I used a gypsum pour as a solid/stiff backer for the horn flares. The amount of energy impinging upon them should not be underestimated. The original flares, the way they were built, resonated badly - both from the front energy and the stuff inside the box going to the rear side.

The stiffer the mount/throat for the driver, the better the results too...
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Old 16th June 2014, 05:42 AM   #8
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Quote:
Originally Posted by bear View Post
Interesting approach.

The holes through the braces might not act exactly like the open space in the original A7. I suspect they may behave like a "bandpass" type enclosure, in essence two volumes + the final port.

Also the holes that access the rear side of the horn flares likely ought to be sealed up as they too will act like some sort of tuned volume/space.

Fwiw, I converted an A7 for a client to 4 x 4" dia PVC ports (or was it 5 ports?). This improves the performance at LF and reduces substantially the rear lower mid radiation through the large open port of the original A7, and permits precise tuning.

I used a gypsum pour as a solid/stiff backer for the horn flares. The amount of energy impinging upon them should not be underestimated. The original flares, the way they were built, resonated badly - both from the front energy and the stuff inside the box going to the rear side.

The stiffer the mount/throat for the driver, the better the results too...
Appreciate the insights.

I chose to open up the smaller chamber either side of the horn flare to maintain the overall cabinet volume (as I've added quite a lot more bracing). I can always close these off later.

With bracing, I guess there'll always be a potential trade-off with bandpass odd tuning, vs lower/better cabinet resonances. I'm purposely choosing the latter to focus on.

Given the stiffness of the cabinet, would do you recommend for deading? I use a 2.5inch thick wool/fibre house insulation product on my other projects...seems to work very well.

The attached pics show Tannoy GRF-R, Altec '620,' and my current large bass bins for EV 18's...all with the same wool fibre.
Attached Images
File Type: jpg walnut glued up 2.JPG (624.0 KB, 179 views)
File Type: jpg rear%20panel.jpg (169.5 KB, 183 views)
File Type: jpg wool for bass cab.jpg (90.5 KB, 149 views)
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Old 16th June 2014, 11:57 AM   #9
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More gluing tonight...
Attached Images
File Type: jpg glue in shelf.jpg (97.0 KB, 151 views)
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Old 16th June 2014, 12:23 PM   #10
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Everyone has their favorite methods and materials for internal wall damping.

For the A7 there is, imo, some yin/yang in the choice. On one hand absorbing the midbass and midrange reflections is a really good idea. The short rear wall distance behind the driver makes this important if you want to hear hi-fi. The problem, if there is one, is that too much "stuff" back there could reduce the effective air volume at LF... the density of that stuff vs. thickness of the stuff and how it behaves at LF will have *an* effect.

Think about making that front port removable - although I think you just glued it in place. Difficult to change or modify after it is glued in place.
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