Anyone know the weight difference between a sheet of 3/4 Birch and 3/4 MDF??

[VWBobby 10+ year member]

The reason for the MDF is because it tends to absorb sound. Its "sonically dead", so to speak. A plywood box can reverberate and the sound can resonate inside the box more. If you're concerned with this, you can line the box with sound deadener or poly batting. The trend these days for SPL is to coat the inside of the box with fiberglass resin or anything smooth to make the box "slippery" to the air. This flies in the face of box building a few years ago. :-s

 

[FIMPALASS 10+ year member]

Baltic birch is way stronger than MDF And lighter.

Got the below info from-

http://www.talkaudio.co.uk/index.php...d=91&itemid=26

Mechanical properties:-

In laymen’s terms, strength is an indication of how much load a material will withstand before failure and stiffness is how much the material will flex, or deform, when subjected to a given load.

We are not really interested in the ultimate strength of our sub boxes as they seldom fail, so the material strength is of little use. However, we are interested in how much a box will flex. Therefore, we will concentrate on the stiffness of sub box materials.

Eb = Modulus of elasticity in bending.

Eb describes how stiff a material is under bending. The higher the number, the stiffer the material is and the less it will flex. It allows us to easily compare the stiffness of different materials.

The following properties are all based on 18mm sheet materials:

Birch faced ply:-

Eb = 2700 N/mm^2 perpendicular to grain

4600 N/mm^2 parallel to grain

Density = 11.6 kg/m^2

Birch ply:-

Eb = 3400 N/mm^2 perpendicular to grain

4600 N/mm^2 parallel to grain

Density = 12.4 kg/m^2

MDF:-

Eb = 2200 N/mm^2

Density = 10.8 kg/m^2

It can be seen from the above, that the plywood properties are directional depending on the orientation of the grain. For the purposes of this analysis, we can assume the stiffest properties as sub box panels are generally supported on all four edges. MDF is a homgeneous material and the mechanical properties are identical in any direction.

Comparing the Eb values given above it can be seen that the birch based plywood is over twice as stiff as the MDF. Therefore, if two identically sized sub boxes were fabricated, one from 18mm MDF and the other from 18mm birch ply, the MDF box would flex twice as much as the birch ply box.

That’s quite an improvement from simply using a different material for your enclosure.

 

[helotaxi 5,000+ posts]

If weight isn't an issue, properly bracing the MDF enclosure will reduce flexing to a negligible amount. Twice as stiff only matters if the flexing is excessive with the less stiff material. Once you have "good enough" any more is simply a waste, especially if it costs more.

 

[FIMPALASS 10+ year member]

If weight isn't an issue, properly bracing the MDF enclosure will reduce flexing to a negligible amount. Twice as stiff only matters if the flexing is excessive with the less stiff material. Once you have "good enough" any more is simply a waste, especially if it costs more.

I definetly agree. There is no need for a super rigid box for a low power setup.

 

[SpeedEuphoria 10+ year member]

right but the main point of this thread is Weight, not super rigid

I'm going to Go to Lowes and see what I can find as they had no idea what i was talking about. Asked a guy about Baltic Birch and he had no clue and said he had been building for 35 yrs. I called Menards and a young kid found baltic Birch for $70 a 4x8 sheet.

 

[Ineed$ 10+ year member]

I'm just curious what is so great about baltic birch? I'm going with arauco i checked it out at home depot today and it's way lighter than the mdf and only $39.97 for a 4x8 sheet.

 

[Alex K 10+ year member]

that's one big *** dowel..

rofl!!!!!

 

[SPLAudioHz 10+ year member]

Quick question, would solid birch be preferred over ply birch? I have been working with many variations of lumber over the years and understand the density and resonance that birch achieves. Thus why home audio enclosures use birch. Just asking. Really dont know how it would work in car audio

 

[VWBobby 10+ year member]

The reason the weight savings is important for some people is: no wasted horsepower, better MPG, no sagging suspension, etc,

One of the other big reasons for using BB or Aruco, etc is because you can build a box that is just as rigid as a MDF box, but use less layers. It is also a lighter material so if just doing a single 3/4" box, it'll be stronger while still being lighter. //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif

Baltic Birch comes from forests in Russia. That's why its so expensive. Even at $70 for a 4x8 sheet, that's not too bad.

SPLAudioHz, Good question. There's no reason you couldn't use solid birch. Some people in home audio/theater guys prefer the sound or "coloring" a solid wood box can do to the sound. I don't know if this would be any benefit in car audio though. Most people try to go for a sonically dead box so 100% of the sound is coming from the speaker and environment instead of the box as a whole. Guitar players and other musicians are very picky over the box because it affects the tone to a great extent.

 

[helotaxi 5,000+ posts]

The reason that you go with ply is that it is rigid in two directions as opposed to only with the grain. The reason that birch ply is preferred is that it is one of the only plywoods of reliable quality that lacks voids in the plys. Additionally birch wood is much lees dense than other woods used to make plywood. As a result a sheet of 3/4" is much lighter than other woods.