lining boxes

[busterno1]

s friend gave me a sheet of 17 mm ply so i was thinking a set of speakers with it .
I was wondering is there a benefit in lining the wall of the boxes with mdf thanks

 

[AllenB]

Could be. Making the walls more stiff reduces vibration. It also changes the nature of the panel resonances. They can move higher in frequency and this may make them more of a problem. The glue you use to laminate the panels can go a long way to absorbing (damping) these vibrations.

 

[ewollowe]

Could be. Making the walls more stiff reduces vibration. It also changes the nature of the panel resonances. They can move higher in frequency and this may make them more of a problem. The glue you use to laminate the panels can go a long way to absorbing (damping) these vibrations.

What glue do you use? Is your standard PVA stuff ok?

Some would recommend bracing over wall thickening.

 

[4392Viper]

AllenB,
I guess what you referred to is more of "bracing" rather than "lining".
I'm not sure but I guess Busterno1 meant that, is it any beneficial to line an MDF box?
If so, lining with damping material is almost always beneficial if done properly, IMHO.

AllenB, Your point of view towards bracing impressed me. I thought that bracing can always correct weak box wall problems. I was never this skeptic to the subject. Thanks for the good idea!
Regards,
Ali

 

[system7]

s friend gave me a sheet of 17 mm ply so i was thinking a set of speakers with it .
I was wondering is there a benefit in lining the wall of the boxes with mdf thanks

Just as well you weren't working on the plywood construction De Havilland Mosquito aeroplane. It would never take off with the added weight of worthless MDF!

The whole idea of plywood construction is light and rigid.
http://www.diyaudio.com/forums/multi-way/223174-interesting-read-i-found-lossy-cabinet-designs-harbeth.html#post3234256

You then can add panel damping of some sort, sometimes bitumen, sometimes rubbery stuff, like in this Harbeth ply construction.

See, people have built speakers out of concrete, because they think heavy is good. It doesn't always work well. It's a subtle problem, and a good solution is cabinets that have no glaring resonances. And low stored energy.

 

[AllenB]

Is your standard PVA stuff ok?

PVA is a good choice. There are others. I have had success with polyurethane adhesive.

The result is that if you drop a hammer on a panel you get a dull thud instead of a higher pitched ringing.

It would be wise to search 'constrained layer damping'. This is an effective technique with a few good simple choices.

I guess what you referred to is more of "bracing" rather than "lining".

Why not do both. Not to oversimplify the issue but the bracing is effective in dealing with the lowest frequency box resonance where the panels all move together. The panel damping deals also with higher frequency issues. The stimulus for each is slightly different and each can be its own problem.

If so, lining with damping material is almost always beneficial if done properly, IMHO.

I agree. Lining the walls with mass, as system7 explains is the same goal as laminating the panels with lossy glue.

 

[busterno1]

I should have explained bit better .

i am going to build the boxes out of ply then glue mdf to the panels to give me a thicker panel as well i will be bracing the box .

i wanted to know is there any benefit to using mdf over using double thick layer of ply

 

[Lojzek]

I should have explained bit better .

i am going to build the boxes out of ply then glue mdf to the panels
to give me a thicker panel as well i will be bracing the box .

i wanted to know is there any benefit to using mdf over using double
thick layer of ply

I wouldn't glue mdf over ply, I'd use something like this to reduce the
wall vibrations and leave spots without it to glue ply braces.

Sound dampening material: Improve car acoustics with Teroson by Henkel - Loctite

Read this:
Factors in the design of loudspeaker cabinets. - BBC R&D

 

[andy19191]

I should have explained bit better .

i am going to build the boxes out of ply then glue mdf to the panels to give me a thicker panel as well i will be bracing the box .

i wanted to know is there any benefit to using mdf over using double thick layer of ply

In general no. Decent plywood is a lot stiffer in bending than MDF and so it will not help much in this respect. It will add a bit of mass but that is only beneficial at high frequencies. It will not add significant damping.

Stiffness is more effectively addressed by bracing, mass doesn't do much and the loudest noise from the cabinet is almost certain to come from the cabinet walls resonating. What reduces resonances is effective damping. Constrained layer damping is possibly the most effective DIYable damping and consists of gluing a layer of stiff rubbery material and then a constraining layer such as another layer of plywood half as thick as the load carrying layer.