Designing a cabinet for Mark Audio Alpair 7.3

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
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.
 
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:

An externally hosted image should be here but it was not working when we last tested it.
 
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!
 
Member
Joined 2010
Paid Member
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.
 
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:

An externally hosted image should be here but it was not working when we last tested it.
 
Last edited:
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
 
Last edited:
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 not 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



errata: should read as above - operate word being "NOT"
 
frugal-phile™
Joined 2001
Paid Member
Is the brace needed in such a rigid and strong cabinet?

To be as stiff as the sheet material used in a convential manner, wall thickness will need to be higher, and all bets are off if you use MDF.

When you cut up the ply like this, you are reducing its strength and the curved shape is not increasing its stiffness. The way to do that is like B&W do in their 800-series.

The brace's prime purpose is to draw energy away from the driver so that it is shared with the back of the box and not all dissipated by the baffle.

dave
 
Cutting so much material with a CNC machine, with all the associated wastage seems an incredibly brutal approach, surely flexi ply or mdf would form the basis of a more elegant solution, it would certainly be cheaper and I suspect stronger. Unless one was getting the material and facilities gratis of course.
 
frugal-phile™
Joined 2001
Paid Member
Cutting so much material with a CNC machine, with all the associated wastage seems an incredibly brutal approach, surely flexi ply or mdf would form the basis of a more elegant solution, it would certainly be cheaper and I suspect stronger. Unless one was getting the material and facilities gratis of course.

This is true... it may well not be as easy thou to get a pretty box.

dave
 
Facilities are free, material is not........did a rough cost, came in at more than i hoped. Using 18mm Birch Ply.

Perhaps a design utilising single ribs, as opposed to a complete hemisphere would allow for a lot less wastage....cost.

The miniOnken Sketchup picture has this as it was easier to flip one half than make both sides the same, perhaps this is the way to go? Insert a piece of solid wood matching the baffle to hide the seam?
 
Nice design but it would be a shame to use this construction method with birch ply - too much waste and you wouldn't be getting the best performance out of the material. It makes more sense with MDF, which is cheaper and could do with some stiffening.

Otherwise go for the laminated, thin ply approach or bendy / kerfed MDF. Best of all, make 'em out of metal.
 
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? ......[/IMG]

Hi there SAu: Have you considered cast concrete? Someone else on this forum recently cast boxes, his thread might be able to give you some ideas. You would build one reusable form and make several enclosures for your system, making your hardwood front plate removable for internal dampening changes. ....regards, Michael
 
SAu just to revisit the question, and with a little context. I've worked in a commercial millwork shop for 18yrs - we build a lot of curved reception walls, bulkheads, cabinet doors, etc. A few years back I built something very much along the lines of your design, but with the ribbed skeleton/ multiple layers of rubber ply approach. Not a huge success, and ultimately binned.


For the average DIYer, I'd concur with Colin's earlier suggestion of Kerf-core / Timber-flex etc. You can still use the CNC to route the top, bottom and one or two intermediate braces. Fabrication of the external shell for a Pensil style would be relatively straightforward, but curving of side mounted slot ports shown on the smaller enlcosure would be a bit trickier. It might be easier to build in two sections and join at the back with a full length spine. This would allow you to work on the inside of the curved panels before final assembly. .
 
Update...

The original aim was to try and achieve a teardrop shape, I started designing some speakers to replicate great design products, this one using the same materials as the Eames Lounge chair, with plywood and some solid rosewood.

I have recently been sketching out a version based on Ron Arads 'Well tempered Chair'

An externally hosted image should be here but it was not working when we last tested it.


This was the very quick sketch up model. Utilising a plywood, or possibly hardwood skeleton with bent aluminium or stainless steel wrapped around.

Im hoping it will form a organic and rigid shape simply by bending metal, riveted to hold it all taught.

Any thoughts?


An externally hosted image should be here but it was not working when we last tested it.
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.