The XBush Mark 2. A synergy/Unity horn of spherical proportions

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So I am sure some of you will remember the crazy month earlier this year where I spent a mad few weeks knocking out a really nice 'little' synergy horn using a full range driver (the SB65WBAC25), two 8 inch woofers (SB23NRXS45) and a SOTA CD horn (XT1464) under the expert guidance of Xrk - master of computer simulations!

It ended up having rather good measurements and sound (It is my favorite speaker and I have some rather good ones).

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536587d1457613073-bookshelf-multi-way-point-source-horn-polar.jpg]diyAudio


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The one problem with it was the way it looked...........

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So, I have spent the last 6 months thinking and planning how I can make this thing look half decent......

This won't be everyone's cup of tea I am sure, and my progress pictures are likely to look fairly poor before it looks better, so bare with me.:D

CLICK ON IMAGE TO VIEW CORRECT ASPECT RATIO

So take one spherical planter:

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Usually a sphere shaped enclosure is not great for internal modes. This is due to the overwhelming single internal dimension - the diameter - causing a large resonance. Fortunately, due to the design of a synergy horn - the horn sits right inside the enclosure - subdividing the space up and breaking up any resonances:

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Try horn for size with a bit of cutting:

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Strengthen further - just because I can......with two layers of fiberglass, then a 2cm thick layer of structural two part car body filler......

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make a 3mm aluminium/6mm MDF/3mm aluminium CLD baffle ring:

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take one heavy gauge peony plant support, turn it upsidedown, angle grind off the legs, and spray it black....

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Getting there - nearly finished with the Mark 1 - white box for comparison......
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The polystone sphere is about 6kg. It appears to have a hard polystone outer layer, with a 4mm fiberglass inner which is orange. It is fairly light for it's size but very strong - I can sit on the side of it without any deformation.

Cut away rim in two areas to allow 8 inch woofers to slot in....
 

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Next. Strengthen further - just because I can......with two layers of fiberglass, then a 2cm thick layer of structural two part epoxy.......

Sphere now weighs about 15kg and is utterly 'dead' to a knuckle wrap test......
 

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Obviously the horn will need some gentle modification. I will cut back the corners and round them. I will also need a new baffle.

So I have made a cardboard template and plan to cut a 5mm aluminium baffle with sorbothane gasket..
 

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Founder of XSA-Labs
Joined 2012
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Try a circle jig and a carbide router blade. Wesayso cut holes in thick aluminum plates with a wood router until the cows came home. Carbide should cut Al nicely - just don't take too much off at a time.

Jasper Circle Jig Model 200

There are other brands of course...

Rockler Circle Cutting Jig - Rockler Woodworking Tools

There is always a hand held jig saw and then files or rotary sander (large Dremel type drum).
 
are you looking for a single flat disc with no center hole, or a torus for mounting flange?

compass jigs need a pivot point - usually a screw hole, but a temporary block could be hot glued to the metal if you're wanting to avoid the penetration

if cutting aluminum that thick with a router, I'd certainly recommend a variable speed motor set to well below the standard speed (e.g. Porter Cable 690 = 27,500 RPM)

and take precautions - full face shield - not just glasses, work gloves, and hearing protection

a small shard of metal can do a lot more damage than a splinter of plywood or MDF dust
 
Don't panic - aluminum is a perfectly valid choice - but with any material, there are considerations in machining, and safety should always come first. What is the exact intended function and size / shape of the piece you have in mind here?

I'm not a huge fan of it for an entire speaker enclosure, but any particular reason why not MDF in this instance? It's dirt cheap, and far more easily machined with standard wood working tools and bits than any of the high density plastics / thermoset resin materials.
 
Thanks Charlie and Chris,
I did consider MDF - but the baffle needs to be quite thin - no more than 6-8mm to ensure the synergy horn sits down in the sphere and the woofers don't hit the rim - if that makes sense.

So I thought aluminum would be perfect.
I have hit upon serendipity just now on a certain auction site - the baffle circle needs to be exactly 400mm diameter to fit the top - and a chap is selling two laser cut aluminum 400mm diameter discs which are 3mm thick for about £25....

So I am thinking I could make the baffle with some CLD techniques - 3mm aluminium/constrained layer ~1mm (?epoxy) /3mm aluminium = total thickness of 7mm.

From some CLD work and research I have done for previous projects - I am pretty sure there are some good epoxy products that work well in CLD with aluminium - it needs some thing stiffer than the usual stuff you would CLD with wood if I remember right.
 
Founder of XSA-Labs
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I think 1mm sorbothane sheets that you have should work nicely with aluminum. Use contact cement to bond it all together. The rim should have some screws to keep form coming apart but driver mounts naturally do that.

Water activated Loctite PL Premium adhesive could work too. Spritz it with water mist prior to clamping down.
 
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Thanks X!
Will have to look back through my research - for some reason I thought sorbothane was more likely to work as an isolating layer rather than a constraining one due to the aluminium being so stiff.

But you are right - given I was going to use sorbothane as an isolating gasket, I could also use it for the constraining layer - not tried using contact cement with it....
I will start experimenting. ;)
 
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