Bracing a straight (unfolded) ML-TQWT?

[joensd]

Hi there,
I´ve been reading quite a few times that TL´s especially have to be quite rigid.
My design would have an inner height of 41,73in and SO=SL=7,09in*7,09in.

Would some bracing help to improve the cabinets rigidity?
I like the idea of having some cross-bracing but am not sure if it´s good to "change the area" in the line that way.

I´ll probably go with MDF as these will probably end up as prototypes anyway.
I´m thinking of using either 0.75in or 0.87in thick boards.
Would you rather take the thicker material?

Thanks for any directions!
Jens

[planet10]

with a dimension of only 7" there isn't a whole lot of need to brace it ... except that it is harder to work with, i'd go with 1/2" plywood.

dave

[leadbelly]

I agree with Dave. I am making my ML-TQWT's out of 3/4" MDF and they are both heavy and plenty rigid without bracing. Cutting down the weight with 1/2" ply would make them much more convenient to move around.

[planet10]

Originally posted by leadbelly
Cutting down the weight with 1/2" ply would make them much more convenient to move around.

And they would probably sound better.

dave

[joensd]

thanks a heap!
that´s all i needed to know.
the ware-house around the corner offers 0.6in plywood which is a birch-"multiplex" plywood, seen quite often recently in german speaker-diy magazines and probably anywhere else.

they also stock 0.7in and 0.83in thick material.
is it generally worth to go with the thicker stuff?

[planet10]

is it generally worth to go with the thicker stuff?[/QUOTE]

With short sides like yours, the thinner stuff is probably better... just a little harder to work with.

dave

[Bob Brines]

I put either a 1" dowel front-to-back or a window brace at the top and bottom of the driver and then another the golden ratio farther down the pipe. When using dowels, I put a companion dowel side-to side as close to the front-to back dowel as possible. This holds the driver rigidly in space.

The effect of bracing in a TL is pure resistance, i.e., stuffing. Don't worry about it if you are reducing the area by less than 25%.

Bob

[joensd]

thanks again,
I really appreciate the cool advices as some of the "wood vs. MDF" threads seem quite controversial and confusing to me.

I like the look of the multiplex anyway, it´s just a little more expensive. actually I´ll end up paying more for the wood than the drivers.

Just curious: What do you mean harder to work with? Are you talking about finishing or things like working with milling-machine?
The latter would probably have to work quite a bit harder but finishing should be easier if you leave the raw birch and just round the corners and put some primer, oil, lacquer or whatever on.

[joensd]

I put either a 1" dowel front-to-back or a window brace at the top and bottom of the driver and then another the golden ratio farther down the pipe. When using dowels, I put a companion dowel side-to side as close to the front-to back dowel as possible. This holds the driver rigidly in space.

The effect of bracing in a TL is pure resistance, i.e., stuffing. Don't worry about it if you are reducing the area by less than 25%.

Bob

Nice to know that bracing in general wouldnt´be a problem with a straight pipe or the like.
Wouldn´t brace panels not even be advantageous in that they divide the resonance frequencies if you distribute the panels not too evenly?

[Bob Brines]

joensd,

You very quickly get into personal preference and technique. You are correct that unevenly spaced braces break up panel resonances. In a TL you have the added problem that there is high internal pressure at the top of the pipe and low pressure at the bottom. That means the panels are going to be more prone to resonance at the top than at the bottom. By putting braces on the top and bottom of the driver, the upper part of the pipe DOES have unevenly spaced braces.

The important point in my bracing scheme is that the greatest source of panel resonance on the front of a speaker is due to the mechanical vibration of the driver. By making the front, back and sides around the driver one solid mass, this scource of vibration is greatly reduced. Remember that the structural integrety of the baffle is severly reduced by the huge hole cut into it for the driver.

Bob