MDF...

[Gruvula]

So I have been doing my homework on "dye sublimation" to make my traps more attractive. As a seasoned woodworker I have access to a full shop, and a lot of friends. So I have been playing with veneers, milk paint, and some cute joinery techniques.

For a "Deep Bass" trap with a plywood face is there any reason I should not use MDF for the face? Or other sheet goods.

MDF paints easier (especially if I am doing a custom milk paint job), and it's easier to lay exotic veneers on (with the veneering techniques I use). The frame, of course would be plywood (for many many reasons).

This is my first post. I looked around, and didn't find anyone asking about MDF in this way. So any ideas? I have already considered the weight, but at 1/4" thickness I am not concerned.

[SAC]

Please describe the proposed construction of this MDF faced bass trap.
Are you talking about a tuned resonant trap or a faced porous absorber?

[tINY]

MDF is probably a good material to use for such things - if you don't mind the weight.

It's much more consistent than plywood and has more mass.



-tINY

[Washington]

I made some membrane bass traps a few years ago with an MDF front. It works very well, but whatever you intend to use, you'll need to calculate the area/thickness ratio given the mass (lb/cubic ft) of the material, and the result shall differ between MDF and plywood (normally, you'd have a thinner membrane in MDF due to greater mass). I remember I had found a calculator online for that.

Good luck!

[Gruvula]

Not familiar with that equation. Think you could point me towards the web site?

Other than the weight, MDF seems the natural choice. It's a more stable product, paints and veneers quite easily, and they do offer a lightweight version now. Course it is a bit spendy. Thanks for the feed back guys.

Anyone else?

[vincentvangogo]

Weren't they the ones that did 'You're Unbelievable'?

[Washington]

Originally Posted by Gruvula

Not familiar with that equation. Think you could point me towards the web site?

I don't remember the adress, sorry. I stumbled on it years ago while searching for a QRD calculator, which you can google easily... I recall it took a while before I found a site with membrane resonance calculator it was a period when I was trying to read about every paper published on the subject.

The basic idea of membrane bass traps is that every rigid surface does "ring" at a certain frequency or "note" when excited, just like a tom rings when you hit it with a stick. What you want to achieve with a membrane bass trap is for it to sympathetically resonate when a certain frequency is emitted. By then damping the membrane, the energy is absorbed and transformed into heat by friction.

In a very empirical but effective way, you could take any large panel of MDF, suspend it in the air, hit it gently with a mallet and measure (with a mic and an analyzer) its ringing frequency. Then adjust it (that is, cut it by small increments) to as close to one of your room's modes as you can manage (room mode calculators are very easy to find). Repeat for each of the three modes, build your traps with that and then build some more a little higher and a little lower tuned for good measure. It's quite some work, but it can be a much more effective procedure than a math calculator, because it is simply based on the real physical property of the room and the MDF panels.

Hope this helps! Good luck.

[Gruvula]

Originally Posted by Washington

I don't remember the adress, sorry. I stumbled on it years ago while searching for a QRD calculator, which you can google easily... I recall it took a while before I found a site with membrane resonance calculator it was a period when I was trying to read about every paper published on the subject.

The basic idea of membrane bass traps is that every rigid surface does "ring" at a certain frequency or "note" when excited, just like a tom rings when you hit it with a stick. What you want to achieve with a membrane bass trap is for it to sympathetically resonate when a certain frequency is emitted. By then damping the membrane, the energy is absorbed and transformed into heat by friction.

In a very empirical but effective way, you could take any large panel of MDF, suspend it in the air, hit it gently with a mallet and measure (with a mic and an analyzer) its ringing frequency. Then adjust it (that is, cut it by small increments) to as close to one of your room's modes as you can manage (room mode calculators are very easy to find). Repeat for each of the three modes, build your traps with that and then build some more a little higher and a little lower tuned for good measure. It's quite some work, but it can be a much more effective procedure than a math calculator, because it is simply based on the real physical property of the room and the MDF panels.

Hope this helps! Good luck.

I see where you are going with this. Thanks you so much for the advice, and for increasing my reading list for the week. Like you, I have been reading as much as possible. I am more the designer/woodworker, my partner on this venture is the science guy. Still I am trying to perfect my design concepts, which has lead to more research on my part.

Any other words of wisdom you want to through my way, are always appreciated.

[Gruvula]

Washington...
I almost forgot. Any thoughts on how paint might effect the MDF trap? Specifically milk paint. If your not familiar with the product I can send you a link. It's paint, but it's not as dense, and has a great distressed look to it when treated and finished correctly.

[Glenn Kuras]

So I have been doing my homework on "dye sublimation" to make my traps more attractive. As a seasoned woodworker I have access to a full shop, and a lot of friends. So I have been playing with veneers, milk paint, and some cute joinery techniques.

Dye sublimation is a process of dying the fabric which will not clog up the cells. We do it ourselves so let me know if you have any questions.

Here is one.



And one more for good measure.

[tINY]

Originally Posted by Gruvula

Washington...
I almost forgot. Any thoughts on how paint might effect the MDF trap? Specifically milk paint. If your not familiar with the product I can send you a link. It's paint, but it's not as dense, and has a great distressed look to it when treated and finished correctly.

Anything you apply to the surface will change it a little bit. However, any paint that is less than 1/8 thick will not likely change it enough to matter.



-tINY

[Washington]

Originally Posted by Gruvula

Washington...
I almost forgot. Any thoughts on how paint might effect the MDF trap? Specifically milk paint. If your not familiar with the product I can send you a link. It's paint, but it's not as dense, and has a great distressed look to it when treated and finished correctly.

First, listen to those who are scientifically more qualified than I (as in the post above). But I'll add that in the real world, paint applied normally on a BT will change just nada.


Glenn : OOOOooooooH... that new pic !

[Gruvula]

Glen,
I have done the research on sublimation, and ran across your company. I love the pics. I have been contacting local businesses to find a supplier. That's what lead here as well. Do you know if the Milk Paint will have an effect on the "Deep Bass Traps"? As a design choice I think it opens up a lot of interesting avenues.


Thanks again to everyone. Keep 'em comin'. I am finalizing the new designs, and will start construction in the next two weeks. I will post pics as I go.

[SAC]

Anything applied to a surface may affect its compliancy and mass.

I know of no databases where various substances are categorized as the variables are infinite!

To beg the issue, if one examines the formula for the calculation of membrane/panel tuned enclosures, the variables are already defined in terms not of material or color or other amorphous characteristics, but in terms of the mass/density, spring compliancy, etc.

Might I suggest you refer to and focus upon the various fundamental design formula variables rather than attempting to focus on minutia which merely modify the primary variables, the extent of which must ultimately be measured. Simply asking how a very general type of material may effect the characteristics is an open ended question that one cannot answer with more than a 'it may modify the characteristics'.

Additionally, panel/membrane absorbers are divided into two primary designs.

1. Panel absorbers with the entire surface of the panel glued to a dissipative/absorptive layer.

2. Panel absorbers featuring a laterally clamped panel.

Panel absorbers are just another form of a resonant oscillating mass-spring system. A panel absorber consists of a flat panel made of a material such as wood, metal, drywall, or plastic that is positioned in front of an enclosed air volume. The air volume is partly or completely filled with an absorbent open cell energy dissipative material such as Fiberglass or mineral wool. Such a system has several resonance frequencies that can be excited by airborne sound.

If the panel is glued over its entire surface area to a dissipative layer located in front of a rigid wall, the panel as a whole is allowed to oscillate on the spring formed by the absorbent layer. The resonance frequency of the panel absorber can be calculated from the mass of the panel and the stiffness of the spring (k) formed by the dissipative layer. The heavier the panel and the less dense the dissipative layer, the lower the resonance frequency.

If, however, the panel is clamped in any way, it will no longer be able to move as a whole but will only be able to perform flexure or 'bending' oscillations. Generally, calculation of the associated eigen-frequencies requires a lot of effort since they depend on the method of clamping, the dimensions, thickness, and material of the panel as well as on the air volume and its filling.

The oscillations of the panel are slowed down by the friction between the molecules of the panel material. So the sound energy is first converted into oscillation energy and only then into heat. Typically, the air space behind the panel requires additional damping by means of Fiberglass, mineral wool or an open cell foam.

This resource offers a few example solutions: Ford, R; McGormick, M: Panel Sound Absorber, J. Sound Vib. (1969), No.3, p.411-423.

Also here, and in the D'Antonio & Cox AA&D, p 166 1st ed..