Using plywood for building cabs

[Dubs]

Just wondering, is 12mm ply thick/ridgid enough to build a square cab with an internal volume of about 1.3 cu.ft without any bracing? ...or will I have to use 18mm?

Just trying to keep the weight down as much as possible for a small 10" practise cab that I'm about to start building.

[alexclaber]

You'll need to brace 12mm. Decent 18mm on a box that small will be fine unbraced but I'd still consider bracing it.

[Dubs]

Cheers for that I'm just being lazy and don't want to have to spend a lot of time with the jigsaw

[exup1000]

[quote name='Dubs' post='857363' date='Jun 4 2010, 03:25 PM']Just wondering, is 12mm ply thick/ridgid enough to build a square cab with an internal volume of about 1.3 cu.ft without any bracing? ...or will I have to use 18mm?

Just trying to keep the weight down as much as possible for a small 10" practise cab that I'm about to start building.[/quote]
hello mate

its always 18mm although i dont use it anymore in my trade for health and safety reasons mdf is good for making boxes.but which ever material you use make sure you glue every joint until it seeps out and once you've built it go round all the internal joins with more glue and wipe your finger over it to get it right in there (a bit messy but its washes off) and then your have a really tight and strong box.i'm a carpenter and i make stuff like this all the time so i dont think your need a brace to be honest.not sure if your handy with a router if so you can run round all the external corners and the sub hole with one to finish it off and give it that neat rounded look through the material

[Mr. Foxen]

MDF isn't used for the higher end stuff cause it isn't very durable when dropped.

A sort of check for needing bracing is rap on the panels with your knuckles, if it thuds, producing a low note, that note is being absorbed by the cab flexing and wasting energy in use. Better cabs give a higher and quieter note as they don't flex much producing little sound.

[Guest johnzgerman]

[quote name='Mr. Foxen' post='862775' date='Jun 9 2010, 11:44 PM']MDF isn't used for the higher end stuff cause it isn't very durable when dropped.

A sort of check for needing bracing is rap on the panels with your knuckles, if it thuds, producing a low note, that note is being absorbed by the cab flexing and wasting energy in use. Better cabs give a higher and quieter note as they don't flex much producing little sound.[/quote]

surely a cab is going to produce different sounds depending on where you rap upon it, ie. if you hit it where one of the braces is attached to the side of the cab internally then it will be very dead, if however you hit it on a surface that is in between the bracings and a corner of the cab it will be more responsive. i think

[Guest johnzgerman]

[quote name='Mr. Foxen' post='862775' date='Jun 9 2010, 11:44 PM']MDF isn't used for the higher end stuff cause it isn't very durable when dropped.

A sort of check for needing bracing is rap on the panels with your knuckles, if it thuds, producing a low note, that note is being absorbed by the cab flexing and wasting energy in use. Better cabs give a higher and quieter note as they don't flex much producing little sound.[/quote]

and MDF does not like to get wet

[Mr. Foxen]

[quote name='johnzgerman' post='862782' date='Jun 9 2010, 11:55 PM']surely a cab is going to produce different sounds depending on where you rap upon it, ie. if you hit it where one of the braces is attached to the side of the cab internally then it will be very dead, if however you hit it on a surface that is in between the bracings and a corner of the cab it will be more responsive. i think[/quote]

It will make more noise in the more flexible bits. Those bits will flex when the cab is being used, cause pressure inside is in all directions. Any flexible bit is a bit that is losing energy. When I first heard about this I went over my cabs giving them a good tapping, the ABM is so heavy no-where stood out as a loud bit, and the Tech was also dead all over, even though it is light, there is all sorts of funny bracing going on.

[Pentode]

I like these!

12mm ply with a bit of bracing.

[url="http://www.billfitzmaurice.com/Jack.html"]http://www.billfitzmaurice.com/Jack.html[/url]

Edited June 10, 2010 by Pentode

[bumnote]

[quote name='exup1000' post='862768' date='Jun 9 2010, 11:37 PM']hello mate

its always 18mm although i dont use it anymore in my trade for health and safety reasons[/quote]


What are the Health and Safety reasons? is it the material or where you use it

[Mr. Foxen]

[quote name='bumnote' post='862939' date='Jun 10 2010, 09:19 AM']What are the Health and Safety reasons? is it the material or where you use it[/quote]

The dust is pretty bad for you if you breath it in, think it is the resin that bonds it all.

[ShergoldSnickers]

Got me wondering as well....

Rather than using wooden battens and bracing, would it be possible to use a threaded metal rod to stress opposing panels by pulling them inward toward each other? I guess this rules out lots of designs due to the driver(s) getting in the way of the rod. You'd want the panels joined by the rod at the point where they flex most - slap bang in their centre I would presume. Might mean narrow front, deep cabs!

Use an aluminium rod for weight saving and.... well like I said, jus' wondering. Hang on... that's it - geodesic bass cabs as per Barnes Wallis!

[Mr. Foxen]

[quote name='ShergoldSnickers' post='862955' date='Jun 10 2010, 09:30 AM']Got me wondering as well....

Rather than using wooden battens and bracing, would it be possible to use a threaded metal rod to stress opposing panels by pulling them inward toward each other? I guess this rules out lots of designs due to the driver(s) getting in the way of the rod. You'd want the panels joined by the rod at the point where they flex most - slap bang in their centre I would presume. Might mean narrow front, deep cabs!

Use an aluminium rod for weight saving and.... well like I said, jus' wondering. Hang on... that's it - geodesic bass cabs as per Barnes Wallis! [/quote]

Putting it all under tension should work great. The other way would be to pre-tensioning the whole thing in assembly, then you have all the fun of it exploding when you drop it and a joint gives. Aircraft design is a fairly good place to look, pressurised and light, not a very practical shape though. The airflow stuff for jet intakes probably applies to ports too.

[alexclaber]

[quote name='ShergoldSnickers' post='862955' date='Jun 10 2010, 09:30 AM']... that's it - geodesic bass cabs as per Barnes Wallis! [/quote]

Buckminster Fuller I believe!

[Alien]

[quote name='ShergoldSnickers' post='862955' date='Jun 10 2010, 09:30 AM']Rather than using wooden battens and bracing, would it be possible to use a threaded metal rod to stress opposing panels by pulling them inward toward each other? I guess this rules out lots of designs due to the driver(s) getting in the way of the rod. You'd want the panels joined by the rod at the point where they flex most - slap bang in their centre I would presume. Might mean narrow front, deep cabs![/quote]

Bag End do something similar whereby they brace with wooden battens and wedges to push the panels outwards rather than inwards. The idea was to raise the resonant frequency by pre-stressing the panels in a similar way to the skin of an aircraft.

A

[Mr. Foxen]

[quote name='alexclaber' post='863065' date='Jun 10 2010, 11:07 AM']Buckminster Fuller I believe![/quote]

Pretty sure he is referencing the mainstay of early WW2 bomber command the Wellington:



Course, bouncing 2 ton metal explody things on water is cooler.

[exup1000]

[quote name='bumnote' post='862939' date='Jun 10 2010, 09:19 AM']What are the Health and Safety reasons? is it the material or where you use it[/quote]
hello mate
yes its the dust that can cause cancer. so if you ever use it make sure you use a good mask and you have to seal it as its give off gases but once sealed its fine. but they say you get cancer from any thing.i only suggested it as i thought for a practice amp it would be fine as you wouldnt be lugging around in and out of giggs.but by the sound of it its be a full on little cabinat!!!!
good luck mate

[bumnote]

thanks for that

much appreciated

[ShergoldSnickers]

[quote name='alexclaber' post='863065' date='Jun 10 2010, 11:07 AM']Buckminster Fuller I believe![/quote]
You are correct - geodetic was the term used by Barnes Wallis, a technique used in constructing the the R101, Wellington, Warwick and others.

Geodesic describes the archetypal Buckminster Fuller designs.

A relative of mine met Barnes Wallis during the war. Her father was tasked by Churchill with building dam defence towers near Sheffield, after the raids on the German dams. He built large towers with wires strung between, off which were hung large concrete blocks, all to a Barnes Wallis design. Her father had taken her and his wife up onto the moors above Sheffield, and spotted a lonely figure tramping the road back to the city. It was Barnes Wallis, so they gave him a lift.

"The only person I heard father address as 'Sir'".

I think someone used Aerolam for hi-fi speaker cabinet construction at one point - Celestion I think, tricky and expensive to construct. I also seem to remember Wharfedale used a hard plastic laminate and foam sandwich as a material for cabinets at one point.

[Dubs]

Cheers for the info guys, very interesting stuff. Ironically I've ended up going with the carcinogenic MDF over the ply, simply on cost. I've cheaped out, but the ply was going to cost me 3 times more than the MDF has cost me. Sacrifices have been made...

[Bloodaxe]

[quote name='Mr. Foxen' post='862943' date='Jun 10 2010, 09:24 AM']The dust is pretty bad for you if you breath it in, think it is the resin that bonds it all.[/quote]

Breathing any sawdust is a fairly bad idea, oily hardwoods even more so. I once got a lungful of [url="http://www.eoburton.com/Timbers/Keruing.htm"]Keruing[/url] dust on a job & 4 hours later I was the proud owner of raging 'flu. Not good.

Another thing to watch with any composite board (Ply, MDF, Chipboard etc) is the glue - it can give off some really dubious fumes when it gets hot, which is a given if you're routing at full speed with a blunt bit. A good face mask is compulsory for this kind of stuff & if you can hook a vacuum cleaner to the router so much the better - some jigsaws will do this too.

Alternatively, get the hand tools out if it's a one-off. Japanese Pullsaws and razor-sharp chisels & planes create a fraction of the mess!

Pete.