How to build extension cabs...

Kalimna · May 8

Greetings folks,
I'd like to have a go at building an extension cab or two and wondered if anyone could point me in the direction of useful info/tutorials? Really looking for internal dimensions/structure, wall thickness to aim for (will be using hardwood), how to cut the speaker 'hole'. Tolexing not so important as will prob be oiled finish, but still handy to know.
Any suggestions much appreciated,
Adam

paulnb57 · May 8

Following this with interest as its something I am planning too....

victorludorum · May 8

I did mine with some off the shelf pine. I cut the box joints manually with a little hand saw and a chisel and glued with epoxy. Baffle is made of 1/2 inch ply (again, the basic stuff). Closed back Marshall 1912 dimensions. Sounds good to me ;-)

Speaker hole cut slowly with a jigsaw.

Winny_Pooh · May 8

How many speakers? Depends how much cab vibration you want. I specifically used pine ply for mine. I had the square cuts done by the lumber yard and used the router's included attachment for the speaker holes and a round over bit for the edges. It will make Alot of dust. Then contact adhesive and tolex/vinyl. Lots of info online about diyers.

Kalimna · May 8

Thanks for the info so far. Initially it would be a 2x12" cab, but if I feel luike experimenting further, so be it.

I will do the joinery myself, and am quite familiar with the dust a router produces, having built a couple of guitars amongst other items.

Regarding cab vibration - I don't currently have any ply (well, not strictly true, but I'm not sure 4mm would be any good), but have a good stock of afromosia, rippled ash and laburnum I could use.

I am sure that there is a lot of info online, but the reason I didn't go straight to google is I find it difficult to assess the 'quality' of random internet wisdom. Whereas asking on a forum, that wisdom can be prodded a little

Cheers,

Adam

Winny_Pooh · May 8

12 -15mm ply recommended and it depends on the density and whether you will reinforce the edges and centre of the baffle. Solid pine cabs need a bit more thickness. Most guitar cabs are pretty unscientific so you can just take measurements and specs of a cab you like and duplicate them. You should also consider if you want a front or rear mount baffle. Grille cloth is a pain but doable.

Kalimna · May 8

That's actually very useful, thanks Winny_Pooh. I think I was perhaps getting a little caught up in whether specific sizes (for instance, say, a guitars' scale length, but for cabs) and dimensions are important or not.

Cheers,

Adam

Winny_Pooh · May 8

Dimensions matter more if closed back, but famously Marshall sized their cab to fit a superlead head with no consideration for internal volume. More of a deal with ported bass cabs etc.

hywelg · May 8

The 2x12's I built are as good as a Marshall 4x12 for sound. Oversize, oval rear port can stand vertical or horizontal but are much better vertical. If you want the plans I can send you them.

http://www.thefretboard.co.uk/discussion/69186/2x12-vertical-dumble-style-speaker-cab-project-bare-shell-for-sale

I'd use 15mm for the baffle , preferably birch ply, and definitely drill all 8 holes for the speaker mounts even though you only need 4, you never know if you might chew up a tee-nut. 12mm for the rear, can be ordinary ply. If you have a router and are intent on having a lacquered wood finish definitely consider getting yourself a dovetail jig. Dovetails look the dogs bollocks when stained and lacquered and are very strong, no need for internal bracing.

Kalimna · May 8

Again, thanks for the advice chaps - I shall check out the link you mention hywelg. The two corner joints I am considering are indeed the dovetail (but by hand, eek) or a splined long-mitre, which with a little more practice and improvement to my shooting board should work well.
My Thornton amp has a nearly-dovetail joint which does indeed look the whippets wedding tackle -

https://i.imgur.com/xlGwtEm.jpg?1

Not sure I could match that though!

Cheers,
Adam

hywelg · May 8

A lock mitre would also look nice and tidy but not as impressive as dovetails.

Kalimna · May 8

And having just googled it, I'd need a new cutter and probably a router table..... But yes, they do look neat.

prowla · May 9

There's a project on BC.

https://www.basschat.co.uk/topic/324014-easy-12-cab-build/?tab=comments#comment-3517363

paulnb57 · May 9

You Tube link for the above Bass Cab, showing easy jointing method....

Col_Decker · May 9

I was gonna do this too with a spare speaker thats lying about. Then I thought no wait, make a Leslie-esq rotating cab. What a great idea. Though to be honest I've got no further than thinking about it.

Kalimna · May 9

All fabulous information, chaps. Thanks very much

Adam

SexualChocolate · May 15

Celestion did a pamplet on speaker cab design which contains some useful information. It is available for free on their website.

https://celestion.com/speakerworld/downloads/patech/109.pdf

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