Single 12" bass Cab

[Phil Starr]

Every time you ask a simple question it opens up a can of worms

I'd copy Stevie's design in your position. I recommended 18mm in the Mk1 for simplicity in the build. Even then I built an 18mm and 12mm cab with more extensive bracing and tried the cabs before deciding which I'd recommend. I preferred the sound of the 18mm cab. Stevie went for thinner material and more extensive bracing in the Mk2. again a lot of testing took place to get a good compromise.

Cabinet resonances are complex, you have a lower frequency resonance of the box itself but each panel has it's own series of resonances and I'm looking at an equation which shows a whole series of resonances for a square panel. The factors that determine the frequencies of these resonances are the dimension, mass, Young's Modulus and the speed of sound of the panel. On top of that the volume of the resonances and their decay time are affected by the internal damping or Q of the panel and also the way the edges of the panel are treated. Even a minor change in the glue can affect the volume of some resonances by 10dB.

I've also got some practical measurements in front of me and some of these resonances mean the output from the cab matches the output from the speaker meaning the cab is virtually transparent at those frequencies. Cross bracing will kill some of the cab resonance but will usually simply shift the panel resonances to higher frequencies where they may be less or more troublesome.

That's not there to put you off though, I suspect few commercial cab designers spend a lot of effort on bracing yet still come up with much loved products. My gut feeling is that unless you want to spend some time fiddling around with bracing a thicker panel is likely to give a better sound.

[Bill Fitzmaurice]

[quote name='DIYjapan' timestamp='1497001664' post='3315182']
12mm or 15mm? [/quote]Properly braced 12mm is all you need.

[quote]bagends look rugged as heck and they are thicker 18mm not 15mm.
[/quote]Commercial cabs tend to use 18mm, because lower labor costs make it less expensive to build barely braced or unbraced 18mm than well braced 12mm. Besides, they don't have to haul the cab but once to the loading dock for shipping. The sweat equity invested in building a lightweight cab is repaid every time you lift it.

[DIYjapan]

Wiring question: which gauge of wire does everyone use inside of your cabinets? 16? 18?

Question 2 is it better to solder the wires directly to the input connectors and the speaker-or- use those push on clips?

[Phil Starr]

I don't think you need to agonise over the solder/connector thing. I always used to solder because it was what i had to hand and I preferred a permanent fixing. However I've some Yamaha speakers that are well over 20 years old with push on connectors that are still working faultlessly. You can simply decide on the basis of what is convenient.

Again you don't need to worry too much about speaker wires in the box. The runs are very short so the resistance is going to be low compared with the resistance in longer external cables. Although the currents in speaker cables are remarkably high the duty cycle is low and they are unlikely to burn out, just think how thick they are compared with the wire in the voice coil. I tend to go for something about 1.5mm. More than enough to handle the power but flexible enough to be convenient. Make sure it is fixed in a way that won't allow any rattling.

[DIYjapan]

Got this 12mm plywood to make a bookshelf for my kids. Never seen anything like it. It's plywood on the outermost layers but the core is regular boards glued up together. We will see how it works before I consider it for an amp cab but I'm curious if anyone has seen/ used anything similar?

[Bill Fitzmaurice]

That's called lumber core plywood. It's not as stiff or stable as regular plywood.

[Phil Starr]

I'm not clear from your description what you have but in the UK we have something called blockboard, it's strips of wood about 2-5cm glued together with the grain reversed in alternate strips, then laminated either side with one or two plies. generally it is made for furniture manufacture and is stiffer in the longitudinal direction than ply so you use it for load bearing structures like shelves. I've used it for my kitchen cupboard carcasses as they are supporting a granite surface and were available with high quality veneers. you can also come across laminboard with much thinner plies which is also stiffer and more stable but finishes better than blockboard. http://www.design-technology.org/Blockboard.htm The stuff I have has a hardwood core.

Edited June 25, 2017 by Phil Starr

[DIYjapan]

I've been away for awhile but I'm back now and just starting summer holidays. I'm hoping to finish my cab in the coming weeks. I ordered 12mm Latvian birch ply and they'll cut it for me, parts express hooked me up with fast international delivery on small parts, and my beta 12a-2 came in the mail two days ago. Yippee!!

[DIYjapan]

Acoustic foam question: I can get acoustic felt relatively cheap a couple bucks per meter in Japan but acoustic felt is really expensive. I'm looking at 50$range for the one cab.

So, do I really need the thick foam or will acoustic felt be alright?

[Bill Fitzmaurice]

I use felt specifically with very small cabs, where a thicker material won't fit well, as a half inch of felt is as effective as an inch and a half of foam or polyester batting. I never pay for felt, I get free scraps from carpet stores. Since it costs them money to have their scraps disposed of they happily give it away.
There's no advantage to anything labeled as 'acoustic', other than to those who make and sell it, as that label enables them to charge more for it.

[Phil Starr]

Yep, another lover of carpet felt here.

[DIYjapan]

Is hot glue a feasible way of fastening the carpet felt?

I just ordered some and it came over night. I'm not at the point of cab building yet but hopefully in a week (ahem, or two) I will be putting it all together.
Getting excited!

[Bigwan]

[quote name='DIYjapan' timestamp='1501139227' post='3342710']
Is hot glue a feasible way of fastening the carpet felt?
[/quote]

I wouldn't have thought that was practical for a large surface area like a cab. I'd go with a roll on or spray adhesive.

[DIYjapan]

Which does everyone think will work better? This, let's call it A. Or...

[DIYjapan]

Or this. Let's call it B.

[DIYjapan]

A

[DIYjapan]

B.

[DIYjapan]

A seems to support the central area better. But both are braced side to side so maybe not much difference either way?

[Bill Fitzmaurice]

I wouldn't use either, both use too much material where it doesn't do anything useful. This picture compares typical 'window' bracing on the left with the better method on the right:


The method on the right is more effective while using less material. I see you also have battens on the corner joints. They serve no purpose, other than adding dead weight, as that's the strongest part of the cabinet, requiring no reinforcement.

[DIYjapan]

Wow, as always thank you for the prompt and very informative reply to my previous post.
The "better" version of window frame supports will definitely be used in my next build (if the wife doesn't explode before this one is finished).
Secondly I don't have any clamps larger than 65mm so I decided on battens as a way to secure the sides while the glue along the joints dries. Will see what I can do about removing them after that point in time. Unfortunately it will most likely be difficult at least because I glued them in place. Doh! I should have asked my question earlier.

[Bill Fitzmaurice]

Clamps aren't required. I use an external wood caul temporarily screwed to one panel to perfectly align the parts, isolated from the glue line with polyethylene sheet cut from a trash bag, with a few screws holding the joint secure until the adhesive sets. After the adhesive has cured all the screws are pulled, cauls removed, the screw holes filled with adhesive. Like so:

Edited August 9, 2017 by Bill Fitzmaurice

[DIYjapan]

Felt Question:
Do you you apply it to the back of the front panel?
I was planning on just the back, left/right sides, top, and on top of the port shelf. Will that be alright or Do I apply some to the front panel as well?

Second question: how far away should I stay from the opening of the shelf port?

[DIYjapan]

Is this felt deadening enough? It is 10mm thick. I was thinking to glue it in tomorrow morning. Should/can I double it up to 20mm or does it even make a difference?

Once I have it all in I plan on glueing the front baffle in place so I can't really go back and redo any of it after I glue the baffle on.

[Phil Starr]

I'd say you'll be fine, it looks a lot better than most commercial cabs. If you did have any troubling resonances the back of the cab is usually the critical face and you could add felt through the speaker hole. That felt is quite heavy so there's a compromise between practicality and optimum damping. If you had continued the 25mm battens along the top panel and the top of the port you could have had a removable baffle, always helpful when prototyping but this looks like a lovely job. Well done, I hope you love it.

[DIYjapan]

Phil, thanks for the kind words. Actually I had planned on continuing the 19mm battens but neglected to add them by accident. Thanks for pointing that out. Put them in tonight. Originally I wanted a screw free front baffle but I think I may use some light foam trimming around the battens and screw in the baffle. There will likely be something that needs a fixed in the future, hopefully not, but likely.