Designing a cabinet for Mark Audio Alpair 7.3 - diyAudio
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Old 18th October 2011, 10:40 AM   #1
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Default Designing a cabinet for Mark Audio Alpair 7.3

While in the states I purchased a pair of Gold Alpair 7.3's.

I have build a few speakers before (Ikea Salad bowl ones can be found on here) these have always been multi ways, sealed and altogether rather complex from source to sound.

I understand there are always compromises with speaker design but wish to create the best possible cabinet I can.

I have access to an old CNC router, and want to build the cabinet up in layers, sandwich construction utilising some hard wood for the baffle. Taking inspiration from the Eames lounge Chair, low cost curved plywood with walnut or rosewood veneers.

Here are my requirements:

1) Single driver design, covering as large a frequency range as practical
2) Made in layers of cnc cut plywood

If anyone wishes to collaborate, with permission, I am happy to give away the CNC plans to all, once finished.

Any help much appreciated.
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Old 18th October 2011, 10:47 AM   #2
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Here was the initial idea, using the Pensil design as a starting point for internal volume, port size, overall height and positioning. I am by no means set on this design, but do want to keep the aesthetic, curved walls, solid wooded baffle. And Ideally as small as practical or visually small.

Can anything more radical be done? Perhaps a bookshelf design with a larger internal volume? Curving design both vertically/horizontally (Kef Blade).

I can create quick mockups in Sketch Up, if anyone can describe their ideas in enough detail.

Here is the original starting point:

Click the image to open in full size.
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Old 18th October 2011, 04:39 PM   #3
chrisb is offline chrisb  Canada
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This is a cross posting with your thread on the Mark Audio commercial forum, so don't be surprised if you get similar responses here.

Firstly, big surprise, but the subject of stacked laminated construction is not new here- it's often been used to create folded labyrinth / horn designs that can otherwise be quite complicated. There are commercial loudspeaker products utilizing this method (Magico and others?) .

Secondly, some folks have objections to the idea, simply from a point of view of material yield - look at how much waste is involved - in many cases well over 60% of total surface area, particularly with the more irregular shapes . In the case of some designs, smaller parts can be recovered from nested offcuts, but mostly it's dumpster time.

Thirdly, while with the right machine virtually anything is possible, implementation of some of the more elaborate 3D curved shapes, such as the very cool KEF Blade concept you mentioned would require many hours of meticulous programming and machine time with a standard 2D (3-axis) and lot of post CNC hand profiling or access to 5 (or 8) axis routers.

5 axis CNC Machining - Biedermeier armchair prototype - YouTube


Finally, the Alpair7.3 is a delightful driver, and certainly deserves a well thought out and executed design - I can remember being this excited about a loudspeaker challenge - go for it!
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Old 18th October 2011, 09:07 PM   #4
Tom V is offline Tom V  United States
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It sure is pretty!!

Walnut or mahogany for the face plate will be really nice. (Mahogany is not that expensive, and it really sets off the gold or coppery Alpair drivers - my computer speakers are mahogany with CHR-70.2.)

An X brace near the bottom will help keep the stuffing in.
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Old 18th October 2011, 09:51 PM   #5
chrisb is offline chrisb  Canada
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Quote:
Originally Posted by Tom V View Post
It sure is pretty!!

Walnut or mahogany for the face plate will be really nice. (Mahogany is not that expensive, and it really sets off the gold or coppery Alpair drivers - my computer speakers are mahogany with CHR-70.2.)

An X brace near the bottom will help keep the stuffing in.

Cherry with ML Campbell Woodsong Stain Cinnamon & nitrocellulose lacquer makes for a very nice match to the copper. Alpair12s:

Click the image to open in full size.
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Last edited by chrisb; 18th October 2011 at 09:54 PM.
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Old 19th October 2011, 02:23 PM   #6
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Chrisb,

I would tell you that those are absolutely gorgeous but you know that already.

I wish I could get a finished enclosure even half as nice.
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Old 31st October 2011, 07:19 PM   #7
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Here is quick mock-up of a cnc curved Onken style cabinet.

Click the image to open in full size.

And side by side next to the Eames chair they are designed to emulate.

Click the image to open in full size.
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Old 31st October 2011, 07:41 PM   #8
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Don't forget the holey driver brace.

dave
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Old 31st October 2011, 08:29 PM   #9
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Is the brace needed in such a rigid and strong cabinet?
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Old 31st October 2011, 08:30 PM   #10
chrisb is offline chrisb  Canada
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Issues of material "waste" aside (or do the latest drawings imply a vertical "seam" that would allow for nested pattern layout that would substantially improve yield?), also keep in mind that the very high aspect ratio of the port slots is an important part of the overall tuning of bass performance of this archetype.


To my eye the width of slot in the central figure of the three looks to be wider than the 7mm spec on both rectangular and trapezoidal tapered versions of the "marken7" that I've built or currently have underway.

as to the requirement for bracing, since we've used the stacked lamination method ourselves, who knows for sure?- I have some vague ideas on the subject that would be and exercise in very wooly logic if I attempted to expressed them, and could be completely booooh-gus, so I'll refrain

BTW, these could look silly gorgeous
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Last edited by chrisb; 31st October 2011 at 08:37 PM.
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