anyone know about cabinet building?

justinhedrick · November 21, 2011, 12:14:39 PM

what is the advantage of 13 ply over say, 7? i'm assuming it has to do with the resonance?

James1214 · November 21, 2011, 02:40:15 PM

Well, from a construction standpoint (which is my knowledge base) the more plys, the stronger the plywood is. The more plys there are the less flexible the wood is. It is my understanding that in speaker cabinet design your goal is to make something solid enough to (as much as possible) only have the speakers vibrate, therefore the stiffer and heavier the wood (and cabinet) is the better. This is also why finger joints are good, providing 3-4 times the gluing area of a standard butt joint increases rigidity greatly.

thats my 2 cents

Mr. Foxen · November 21, 2011, 03:02:28 PM

Resonance is the thing you want to avoid in cabinet building. So stiffness is the name of the game. If you want to move it about, there are better ways to achieve stiffness than lots of plies, such as bracing, and pre-tensioning, because they add less weight. Manufacturers generally go for the more plies because it is less labour. Joint style doesn't really figure, because a corner is stiff because its a corner, it is the panels that flex. The jointing part is a concern if you drop it and its heavy, cause that cab bust seams, but the magnet will probably fall off your speaker with less force. In fact, probably better if the joint bursts, because it will take the impact out of the drop an save the speaker, and speakers are more expensive than wood, like a crumple zone.

inductorguitars · November 23, 2011, 02:24:42 AM

I;m going to disagree with senor vulpine.

Unless the cab is open backed you can't get away from resonances/laws of physics. It depends on the volume/port...

I'd rather replace a speaker that busted than repair a cab joint that broke. Way more man hours.

To answer your question - more ply = Stiffy.

In my experience biscuit joints are the best. Way higher point of failure. Plus they are easy and less time consuming to build.

I'll have to dig up an article on points of failure of various joints later if anyone is interested.

Mr. Foxen · November 23, 2011, 06:28:59 AM

Air resonance is a separate thing to the actual cabinet resonating. Panel resonance is always a bad thing, the idea of stiffening it is to move the resonant frequency too high to be relevant. Internal resonance aside from the port tuning is something a properly designed cabinet aims to eliminate as far as possible with stuffing/lining depending on alignment. Aside from notching the frequency response, panel resonance is what makes your head move about on the cab and causes mechanical wear on it.

Complex joints are hard to fix, simple joint is scrape out, glue and clamp, faster than waiting for a new speaker to arrive, way cheaper.

Edit: In addition to raising the resonant frequency you can also do stuff to dampen resonance, but because it is stuff like 'use MDF' and double walls filled with sand, its pretty much for hifi and installation only. MDF isn't good for MI use becaue it is heavy and tends to burst in an unfixable way if dropped, but it is acoustically dead which is idea for the purpose.

justinhedrick · November 23, 2011, 09:10:28 AM

thanks for the replies.

i'm going to copy the electrical amp companies 2x12 using 3/4 inch 7 ply and use butt joints and re-inforce everything. then slather it all in bed liner.

thoughts?

Mr. Foxen · November 23, 2011, 10:34:54 AM

This a guitar cab? Lots of things don't matter as much for guitar cabs, cause proper low frequencies aren't happening. If you are happy with reinforcing and panel bracing, can totally use thinner ply, and have less to carry. Bed liner is a good call, it will act to dampen panel vibration as well as being super tough and easy to repair.

If you want a bit more sophistication that a crude box with speakers in, check this: http://billfitzmaurice.net/XFCabs.html

justinhedrick · November 23, 2011, 10:51:02 AM

Quote from: Mr. Foxen on November 23, 2011, 10:34:54 AM
This a guitar cab? Lots of things don't matter as much for guitar cabs, cause proper low frequencies aren't happening. If you are happy with reinforcing and panel bracing, can totally use thinner ply, and have less to carry. Bed liner is a good call, it will act to dampen panel vibration as well as being super tough and easy to repair.

If you want a bit more sophistication that a crude box with speakers in, check this: http://billfitzmaurice.net/XFCabs.html

yes, it is a guitar cabinet. thanks for the link, i will check it out.

inductorguitars · November 23, 2011, 01:20:14 PM

So much "common wisdom"... that is wrong.

Cab resonance as opposed to air resonance is a function of mass and bracing. everything has natural resonance frequency. The trick is to have the freq's outside of the guitar's spectrum. You can knock down a building if you can find it's resonant freq. Don't believe me look up the Tacoma Narrows bridge. http://www.youtube.com/watch?v=3mclp9QmCGs

In a sealed cab you'll have horizontal, vertical, and tangential standing waves. But for all intents if the waves hit more than 4 or 5 IIRC planes they tend to die out.
The internal insulation is only going to dampen the higher freq's depending on material and thickness. Bed liner will probably have the opposite effect. Take a look at the sound absorption/reflective properties of fiberglass insulation and the plastic used in bed liners.

Why repair when you can build to last? If there is some sort of abuse it's going to break no matter what.

justinhedrick · November 23, 2011, 01:22:38 PM

Quote from: inductorguitars on November 23, 2011, 01:20:14 PM

So much "common wisdom"... that is wrong.

Cab resonance as opposed to air resonance is a function of mass and bracing. everything has natural resonance frequency. The trick is to have the freq's outside of the guitar's spectrum. You can knock down a building if you can find it's resonant freq. Don't believe me look up the Tacoma Narrows bridge. http://www.youtube.com/watch?v=3mclp9QmCGs

In a sealed cab you'll have horizontal, vertical, and tangential standing waves. But for all intents if the waves hit more than 4 or 5 IIRC planes they tend to die out.
The internal insulation is only going to dampen the higher freq's depending on material and thickness. Bed liner will probably have the opposite effect. Take a look at the sound absorption/reflective properties of fiberglass insulation and the plastic used in bed liners.

Why repair when you can build to last? If there is some sort of abuse it's going to break no matter what.

the bed liner is going to be used on the outside of the cab, instead of tolex, it will be painted on.

inductorguitars · November 23, 2011, 01:25:25 PM

Quote from: justinhedrick on November 23, 2011, 01:22:38 PM

the bed liner is going to be used on the outside of the cab, instead of tolex, it will be painted on.

ah... a bit caffene deprieved. That will work good.

fallen · November 23, 2011, 04:18:08 PM

A nice thing about vintage cabs is that a thinner baffle board will move with the speakers a bit creating a sort of natural reverb. Basically trading off loudness for a livelier sound.

I wonder if it would be possible to build a cab with a thinner baffle board but with an adjustable brace running back to the back that could be on a bushing and tensioned with an allen bolt from the outside of the cab.

Adjustable cabinet resonance?

justinhedrick · November 23, 2011, 04:31:09 PM

Quote from: fallen on November 23, 2011, 04:18:08 PM
A nice thing about vintage cabs is that a thinner baffle board will move with the speakers a bit creating a sort of natural reverb. Basically trading off loudness for a livelier sound.

I wonder if it would be possible to build a cab with a thinner baffle board but with an adjustable brace running back to the back that could be on a bushing and tensioned with an allen bolt from the outside of the cab.

Adjustable cabinet resonance?

hmm. i don't think that sounds like a good idea.

MichaelZodiac · November 23, 2011, 05:14:47 PM

This is a great thread! I've been reading up on cabinet building, I was going to build one last summer (2000S clone) but lack of funds and knowledge put it on hold.

What kind of internal isolation would you use when building a 2x15 2000s clone? Would it even be necessary?

justinhedrick · November 23, 2011, 05:37:56 PM

Quote from: MichaelZodiac on November 23, 2011, 05:14:47 PM
This is a great thread! I've been reading up on cabinet building, I was going to build one last summer (2000S clone) but lack of funds and knowledge put it on hold.

What kind of internal isolation would you use when building a 2x15 2000s clone? Would it even be necessary?

you could seperate the 15s to give it a tighter sound. my randall cab has this and sounds awesome.

Hemisaurus · November 23, 2011, 05:49:48 PM

If your baffle board moves, you won't get a reverb effect, you'll get phase cancellation and smearing, and it will sound like crap, or you may like that sound, a lot of so-called crap is now what tube amp afficionado's seek, so pays yer money. I should define here that crap is a non-linear frequency response.

Justin, if you haven't already got it, I can email you the Eminence Loudspeaker cookbook, as well as plans it has basic theory and construction tips. There's also dancetech.com and speakerplans.com both have useful construction tips for general speaker building

justinhedrick · November 23, 2011, 05:57:13 PM

Quote from: Hemisaurus on November 23, 2011, 05:49:48 PM
If your baffle board moves, you won't get a reverb effect, you'll get phase cancellation and smearing, and it will sound like crap, or you may like that sound, a lot of so-called crap is now what tube amp afficionado's seek, so pays yer money. I should define here that crap is a non-linear frequency response.

Justin, if you haven't already got it, I can email you the Eminence Loudspeaker cookbook, as well as plans it has basic theory and construction tips. There's also dancetech.com and speakerplans.com both have useful construction tips for general speaker building

hemi, i don't have it. i got the deminsions for the cab off the electrical amp website, i got the idea for the butt joints/bracing from the matamp pictorial i posted earlier. the rest is a bit fuzzy . . .

Mr. Foxen · November 24, 2011, 06:39:05 AM

Has anyone ever lined a guitar cab with knobbly foam? I did it to my Acoustic cab and it sorted out some ugliness in the highs, but guitar cabs never have it, and I dunno if the mess it causes is part of their 'tone' and they'd sound wrong with it.

martha_KH · November 28, 2011, 11:35:50 AM

Quote from: Mr. Foxen on November 23, 2011, 10:34:54 AM
This a guitar cab? Lots of things don't matter as much for guitar cabs, cause proper low frequencies aren't happening. If you are happy with reinforcing and panel bracing, can totally use thinner ply, and have less to carry. Bed liner is a good call, it will act to dampen panel vibration as well as being super tough and easy to repair.

If you want a bit more sophistication that a crude box with speakers in, check this: http://billfitzmaurice.net/XFCabs.html

This post is dead on. BFM cabs are great and the XF cabs are an easy build.