fury

An Oblate Spheroidal Journey... AKA Project Overkill! :)

70 posts in this topic

It all started with a few seeds planted by Dr. Geddes on Oblate Spheroidal waveguides, and what might be the ideal profile for reducing the horn colouration from horns (HOMs), while maintaining controlled directivitiy...

Based around a 12" OSWG from Poland married to a BMS 4550 compression driver, this design also uses a 12" JBL 2206H mid.

Plans as follows:
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A seperate cabinet also houses a JBL W15GTI 15" subwoofer. Yes, a car audio sub, with JBL's patented Dual Differential Drive system. I chose this driver as it will play relatlively low, without requiring a huge enclosure volume like some of JBL's counterparts, while still being ~92db efficient.

Cabinets are 50mm thick MDF, with an internal 25mm brace and all drivers rear mounted as to see no screws. This meant that the backs had to be removable which presented a few problems in itself, of which these are documented later on.
Edges are also feature a 25mm roundover (would have liked bigger but finding a router bit was proving difficult).

My next task was finding some (un)lucky sucker to do the hard work for me :P
He conveniently had access to a CNC, which made life much easier!

Wow, lots of wood! I think we used about 4 or 5 sheets of 2400 x 1800 x 25mm MDF.
Getting it back to his place sure was fun!
 

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Next thing we did was a test fit, to make sure things were cut correctly and all lined up and what not...

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Looking good so far... And what a lovely 15" sub we have here :)

The next step was laminating pieces together. After all we used 25mm thick material, but I wanted 50mm thick walls (yes, i am a little crazy).

Some lovely ~30kg/ea batteries used as dead weight.

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Some more test fitting once panels have been laminated (back panel hasn't been done yet).

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Now came a thought - how would we join these without using screws....?

Hmmm... dowel you say? Sure why not!

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Maybe a little overkill, you tell me :)

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[ATTACH=CONFIG]39351[/ATTACH]

And eventually...

We end up with this!

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Next task was routing the edges to have a nice smooth round over.

Enter 1" roundover bit (actually 2" wide):

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Which sadly was too wide to fit in the router, so an adaptor plate needed to be made:

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And then we could round over the edges!

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And then... the boxes multiplied!!!

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The inside corners were also treated with some quad and liberal amounts of glue.

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After a little bit of filler and sanding, the edges came up a treat!

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And so on to the internal bracing...

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Now how will we secure these?

Some fancy flip and twist method with dowel:

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Now onto the top cabinets....

Yummmmmmyyyyy test fit!!!

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And rounder over:

Even yummier!!!

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Back side view:

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And then a similar process constructing them..

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And then there were 2... And some happy fool sticking his head through :)

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These were magically rounded over as well...

Oh, and can you say Tower Of Power!?!?! :)

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Multiplication!!!

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Someone got happy with some undercoat:

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And forgot to blend the waveguide in :)

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Much better...

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And some undercoat:

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The backs of the waveguides were filled in with polyester resin:

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Great carpentry there Fury. Looking forward to reading about how they sound.

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Mounting the drivers was fun... Not!!

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A brace behind to sandwich them into place:

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The inside of the sub boxes also got a layer of paint on sound deadener (also helps seal the insides):

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And somewhere along the line they also got a coat of paint (note: it is actually matt black).

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Mounting the back panels was a headache.

In the end we used some insert nuts which are freaking awesome!

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Some foam was also placed inbetween as a gasket.

Mounting the terminals through 50mm mdf also proved challenging:

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The inside of the top cabinets was lined with 25mm foam:

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And I ended up with this...

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Please note that the finish is not the final finish these speakers will get.

They will be professionally painted when time and funds persist.

We used undercoat to seal the MDF so it will not absorb moisture, and we painted them matt black with $2 spray cans.

We also needed to finish these in a bit of a rush, so there are still a few spots that require a bit of fill and/or sanding back.

The next drama was how to hell do I get them to my house?

Well thankfully these 70+kg/ea speakers aren't so bad with 2 ppl and a trailer involved:

[ATTACH=CONFIG]39391[/ATTACH]

[ATTACH=CONFIG]39392[/ATTACH]

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And this is how they currently sit in my living room...

Very imposing speakers indeed :)

(Apologies for the phone camera pic, more to come!)

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A cabinet will be made to fit the length of the wall, and house all equipment and speakers.... But this will be a project for another year :)

Equipment consists of the following:

The drivers in use:

Highs: BMS 4550 1" exit compression driver in 12" Oblate Spheroidal waveguides, filled with 30ppi reticulated foam.

Mids: JBL 2206H 12" midrange/midbass

Lows: JBL W15GTI

Top cab is approx ~1cu.ft, while the bass cab is approx 3cu.ft.

CD Player is Tascam CD-01U Pro

Which feeds into a Behringer SRC2496 sample rate convertor.

Crossover/EQ/TA will be handled via a Behringer DCX2496.

Volume control is still an Altronics volume control kit, awaiting on a mate to finish the custom volume control wink.png

Power is delivered by 3 Yamaha P7000s amplifiers

and filtered through a PS Audio IPC 9000

TV is a Panasonic 55" Plasma

Thanks for viewing ;)

Edited by fury
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Very impressive they look great, along with the pictures showing the progress.

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I've only had very limited time to tune this setup (only got them to my house sunday evening) but first impressions are fantastic.

Imaging is great, and dynamics are impressive. The speakers ability to play loud and clean is incredible!

I had measurements however my silly computer decided it wanted to crash instead of let me show you them, so i'll take more at some stage.

The room they're in is bare. There is only a couch in there, so I added 2 large beanbags to help. RT is about 500ms, so definately some room treatment coming. There are also windows next to each speaker, and curtains still need to be put up.

My only negative so far is the midrange... I feel that the 20+ yr old JBL 2206's might not be up to the task. May look at some AE TD12M's when funds persist :)

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Nice work Danny! So you have moved to DIY central? I think another GTG is on the cards soon!

What kind of finish are you looking at? The tricky one with MDF is the cracks at butt joins. Do you have a strategy in mind for that? I'm trying out two part filler applied to a groove over the join cut with the router. I'm also getting set up to spray automotive paint.

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I'm thinking a 2 pack finish. Something metallic.

Although there is the posibility these will be hiding behind a projector screen at some stage, which would mean they would not need to be finished...

In hindsight, all edges should have been cut on 45's and biscuit joined. This would hopefully stop any signs of joins showing through.

There was also a little bit of damage done in transit. Nothing major, just a bit of paint rubbed off, and certain spots will need a bit of filler.

Yeah, between building these speakers, I have moved to DIY central, not far from you and Andi :)

Still lots of work to do on the house too though.

More then happy to organise an impromptu GTG at some stage over the holiday break. You guys can help me position and tune these things :)

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Looks great Fury. A nice piano black finish maybe?

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Metallic finish sounds nice. You could try what I'm doing. It is a bit of a hassle but you cut a groove at the join, then fill with 2 part filler. Given all the effort you've put into this, I'd say it's worth it. All the joins on mine will be hidden, but I'm trying it out so that I'll know with the other jobs where it's critical.

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Cut a groove at the join on the outside of the speaker?

Would the filler not be at risk of moving and causing lines to be seen?

If your boxes are flat (and not rounded like mine), I would suggest vinyling your speakers, and then painting over the vinyl.

The vinyl should hide any joins.

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Looks great Fury. A nice piano black finish maybe?

Thanks!

I did my last speakers in piano black.

It's a bit too mundane for me.

I'm thinking either a metallic dark blue, or metallic dark grey.

If however they end up behind a projector screen, i'll leave them as is.

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Metallic finish sounds nice. You could try what I'm doing. It is a bit of a hassle but you cut a groove at the join, then fill with 2 part filler. Given all the effort you've put into this, I'd say it's worth it. All the joins on mine will be hidden, but I'm trying it out so that I'll know with the other jobs where it's critical.

Paul the 'Technical' name for what you are doing is called "Purfling" Luthiers use decorative materials like shell, wood and metals to hide the join and make it stronger. Using body filler is obviously less time consuming, but the results are the same. A stronger invisable joint with a high resistance to hairline cracks. Certainly well worth the effort if you plan on a high gloss finish.

FANTASTIC!! speaker build Fury, thanks for taking the time and effort to document your build.

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Danny,

If you leave MDF butt joins you are certain to get hairline cracks. The filler has a much better chance. Veneer is not an option for me because all edges will have a roundover

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Fury, great to see you are up and running :) The roundover and integration of the waveguide is excellent. I'm thinking I will be able to hear these speakers from my place :)

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Awesome work!! Very nice indeed. I bet they sound rather dynamic!!

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