Wood thickness for 4 - 12" cabinet

[bluesbear]

I'm ready to build a 4 - 12" cabinet for my son. I know the dimensions for it but I'm not sure what thickness wood to use. I also am unsure what's best to build it out of. This is for a 50 watt plexi (sorta) head. I've never done anything but combos before. He wants to get a sheet of 1/2" plywood for everything. I would use 7/16" clear baltic birch ply for the baffle, 1" pine for the cabinet, and 1/2" ply for the back. Any words of wisdom to inject into our disagreement before we make an expensive mistake?
Thanks!
Dave

[Frankenamp]

1. Is this furniture or is it goin' on the road?
2. What level woodwerkin skills- GP, cabinetry, or luthier?
3. Oh yeah, how old is the kiddo?

There's a lot of ways to skin this particular cat- I want to find out what's right fer you.


*my feline just gave me a rather aggrieved and reproachful look at my choice of words... some aminals just have no sense of humor.

[bluesbear]

Hi. I guess I could have been more specific. He's 29. The amp is to be used in bars. I build my own cabinets. I used to use double rabbet joints, glued and screwed. Due to popular demand, I do box joints now. Since this isn't a "for sale" amp, I'll go for strength, depending on the material used and, as always, tone comes first. It will be covered in tolex. The only cabs I've ever owned were Bassman cabs. I never use any amp over 20 watts myself, so I've never dealt with a 4 - 12" before. I'll be using 1/2" clear baltic birch for the baffle. I just don't know which wood choice (ply, pine, etc) and the thickness that would be best for the sides.
I'll attach a pic of the head I made for him. That should give you an idea of my cabinet making skills, such as they are.
Thanks,
Dave

[rafe]

I would use 1x------ (3/4"actual)white pine if you have it or can get it....I hoard the stuff !!
Well, my girlfriend hoard some for me .....ba-dump-bump.... Knotts and all. I can get what they call slash pine around here too, but it's dense and resin saturated. I've used that for small cabinets...it's heavy...The white pine is lighter than plywood and if constructed properly holds up well and adds to the sound IMO. 3/4" plywood would be OK . Birch, but I really prefer solid pine, the older the better ....   

[PRR]

By structural geometry, 1/10th is very strong, 1/50 is very weak.

2x2x12" is at least 25" wide. So 2.5" thick is very strong, 1/2" stuff is very weak.

> use 7/16" clear baltic birch

Then run "joists" to cut the span to just the 12"-14" of one speaker. IMHO 7/16" is too thin to span 25" with decent strength and stiffness. A simple 1x3 down the middle will help a lot. The critical detail is getting the "joist hanger" connection (to the sides) VERY strong. (Not like they did in my ceiling....)

> 1/2" ply for the back.

Stuff that WON'T buzz/rattle. Not CDX sheathing, which is like 10% void and a toothpick size splinter in every other void. And again: 25" is too far a span for 1/2" stuff. But since this panel will be half the total weight, you don't want to do 1.25" stuff (oof!). So go to joist bracing, then good 1/2" ply will be acceptable.

> tone comes first

Bah. A four-12 is not about tone, it is about POWER. It is the biggest array which will fit in the Econoline. Even then, it only fits if the front is "all cones". This isn't a Ten in a 18" box, where you can use the panel for acoustic support and woody resonance. The function of a four-12 box is to limit the front-back air slosh, and to connect the four speakers to a handle. As long as it doesn't rattle or wheeze (which can be hard to achieve), there's no "tone" in the box.

Since it will be heavy and loaded in the dark by a tired musician, hopefully distracted by band-chicks, it needs to be drop-proof.

> white pine if you have it

Come on over. I have a slab of pine 29 inches wide and 5 inches thick, 7 feet long. Been curing in the chicken-shed for 15 years, and several years in a good wood shed before that (there's a story). Plane it, bevel it, dowel it with broomsticks, it could be an acoustically sound four-12 baffle. But you better own your own bar.... this would not be portable.

[rafe]

noooooo that's 15 1x10 x7' you could get 15 champs out of that easy

[imaradiostar]

Short answer: 5/8 or 15mm, whichever you come upon.

Long answer:

If you have a decent plywood distributor in your area I'll recommend two different things. The first would be Russian made "baltic birch" plywood- it's about 5/8" (:more like 15mm) and completely void-free. The only catch is that it seems to only be available in 60" by 60" sheets. This would explain the dimensions of a 4x12 better than Jim Marshall's explaination because the average 4x12 seems to be closer to 30", not the 26" required to stuff 4 speakers in a square box. I'm pretty certain this is what most of the decent early Marshall cabs were made of. Hopefully someone else can chime in and set me straight if that's not the case.

The second wood I would recommend (if you can find it) is Appleply. It's a top quality US made version of the aforementioned birch ply and it's available in 4'x8' sheets.

I cut finger joints for all 4 pieces of a given cabinet at once; one end then the other with all four pieces clamped together in the jig. I only use a line of scotch tape to prevent the wood form tearing out on the backside and it works perfectly with no tearing of the plywood. My jig uses a metal template from some site in the internet and a dado blade and produces nice accurate finger joints up to 14" wide. If you want any pics or details I'd be happy to share.

Good luck, I'd love to see pics!

jamie

[Frankenamp]

OK, now that I'm home from work (gag), I can put my brain cells to what I like....  PRR has it pretty well nailed. A 4 by12 is the absolute worst speaker design for tone that can possibly be achieved. Jim Marshall designed them with his eyes, not his ears. They are comb filter hell. A stack or half stack is all about having a wall of speakers as a backdrop to the guitar player's ego and antics. If you want a box that was designed for an electric guitar to sound good, check out Bill Fitzmaurice's site. Otherwise, what you want is a box that is lightweight, and wont break. A four-by anything is not designed for that at all but there are some things that you can do. 1, reenforce the corners 2,tie the front and back panels together with a front to back brace at least 2X2 minimum- a couple of plywood pieces cut to make an X brace in the center of the speakers is better, size it so that it gives as much support around the speaker frames as possible. 3, 12mm or 14mm baltic birch is stronger than any of that 3/4" crap at Home Repo or any other box store. Most of the white wood ply comes from the ROC and has water soluble glue which delaminates as fast as particle board falls apart. It is utter crap. Plywood's strength is in the plys- 9 ply baltic birch is stronger than 5 ply wood even if it is half again thicker. Buy once- cry once. 4, use PL plus polyurethane glue (the stuff in the caulking gun size tubes) those large hairy ape glues are more expensive and not as good. Hide glue is for fine instruments, PL is for things that will be repeatedly dropped at 3am by drunken roadies. Finger joints and rabbets are fine- anything that provides a large surface area for the glue to grab on to. Solid wood looks beautiful on a bootique box, and finger joints look fabulous and turn me green with envy- but are too heavy and inappropriate for gigging. And the unfortunate bloke that dings my clear-coated stained work of art would be stuck in the top 5 of my 'special' list for life. A couple dozen dings in the tolex- who cares!
And the amp pic looks great, especilly on top of one of these: http://billfitzmaurice.net/XFCabs.html

[bluesbear]

Frankenamp, how does it look on top of one of these ?

Thanks to all for the help. I just happen to have a 30" x 30" peice of baltic birch baffle board left over. That oughta work!
Dave

[HotBluePlates]

tie the front and back panels together with a front to back brace at least 2X2 minimum...

Detail, but the Marshall 4x12 (with "100" logo in the corner) I used to have had ~2x2 brace from front baffleboard to back panel. If I remember right, the side on my cabinet looked to be ~3/4" ply, and high on the ply-count. I'm no woodworker, but 11-ply birch seemed like the common side material. And my dimension guess is only that.

Gee, I'm a lotta help, huh? 

[imaradiostar]

FWIW- A friend let me take apart his late 60's angled 4x12 and measure stuff- pretty sure the entire thing was 15mm birch with lots of plies- I have some scraps from cabinet builds out in the shop and I can count if you like but I'm pretty sure it's 11 ply. Internal brace front to back was a 2x4 with a rubber material at the top that looked like the rubber foot tread area on a fuzz face. His rattled a little bit until we put a screw into the center support from the back. It tightened up the sound quite a bit.

jamie

[Frankenamp]

If yer a 'Stang man, it looks pretty cool!
Get your sawdust goin on, man! One other thing that might be helpful is the depth of the cabinet. Deeper cabinet = lower bass response... to a point- which is not much lower than 100Hz, which is fine for guitar. Just be careful where you point that thang- you have massive beaming. Bright as hell straight in front, but not much at all to the sides. If that's what you want tho' have at it!

[bluesbear]

"If that's what you want tho' have at it!"

It's not what I want, it's what a 29 year old wants. I'll take 1 - 12' with about 20 watts pushing it. personally, I see no reason for more.
Thanks to all,
Dave