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MDF or Plywood, which has the best resonance characteristics for use in speaker construction? ...

post #1 of 11
1/11/13 at 6:43am
Thread Starter 
Background:

For many years I have used MDF for construction of speaker enclosures. A long time ago I accepted this as gold standard and best practice. The argument was made(by someone else and I accepted this info) that the density of the material was the asset that made it most desirable for speaker enclosure construction. From memory I recall that the higher density disposed MDF to a higher resonance frequency. I took this info and really never questioned it.....

In discussing this with another member It appears an important part of the this behavior may have been overlooked by myself and whoever suggested this to me. The Elastic modulus does in fact play a part in most equations that I find determining panel resonance. Normally depending on the application it is some derivation that includes but not limited to the following:

E E= the elastic modulus of the material
M M= the mass of the material

By this relationship one would conclude that as you increase (E) so would the resonant frequency. Also, as mass increases the resonant frequency decreases. This document shows that the modulus of elasticity of regular plywood is at least 2X MDF's.

Is there a formula to calculate a panel resonance of say a speaker enclosure panel? This should be out there somewthere. We should be able to plug in the material's properties for a given panel size and calculate its resonance right? I'm still assuming the goal would be to push the panel resonance high enough to be outside of the bandwidth of the speaker.

Another aspect which I havent heard discussed much is the Damping Ratio of the material or how long it continues to oscillate after the excitation is removed.

So which Is it? MDF or Plywood?
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post #2 of 11
1/11/13 at 7:07am
Quote:
Originally Posted by NicksHitachi View Post

Background:

For many years I have used MDF for construction of speaker enclosures. A long time ago I accepted this as gold standard and best practice. The argument was made(by someone else and I accepted this info) that the density of the material was the asset that made it most desirable for speaker enclosure construction. From memory I recall that the higher density disposed MDF to a higher resonance frequency. I took this info and really never questioned it.....

In discussing this with another member It appears an important part of the this behavior may have been overlooked by myself and whoever suggested this to me. The Elastic modulus does in fact play a part in most equations that I find determining panel resonance. Normally depending on the application it is some derivation that includes but not limited to the following:

E E= the elastic modulus of the material
M M= the mass of the material

By this relationship one would conclude that as you increase (E) so would the resonant frequency. Also, as mass increases the resonant frequency decreases. This document shows that the modulus of elasticity of regular plywood is at least 2X MDF's.

Is there a formula to calculate a panel resonance of say a speaker enclosure panel? This should be out there somewthere. We should be able to plug in the material's properties for a given panel size and calculate its resonance right? I'm still assuming the goal would be to push the panel resonance high enough to be outside of the bandwidth of the speaker.

Another aspect which I havent heard discussed much is the Damping Ratio of the material or how long it continues to oscillate after the excitation is removed.

So which Is it? MDF or Plywood?



I used both MDF and Birch and laminated the materials to each other.

The cabinets are so dense and heavy along with the opposed drivers, you cannot feel any shake or vibration at full tilt. The cabs weigh about 1000 lbs each assembled, so no rocking or anything. I like ply but I also like the combo.



Keep cranking,


Robert
Edited by robertcharles - 1/11/13 at 7:22am
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post #3 of 11
1/11/13 at 7:15am
^ Half ton cabs?

Is this a Chevy pick up or a loudspeaker?

100lbs? wink.gifsmile.gif


James
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post #4 of 11
1/11/13 at 7:19am
In general Plywood is Stronger but less dense, and easier to work with. MDF has a higher density but again is a pain to work with, is a little more brittle (prone to breaking), and not quite as stiff. The surface of MDF is quite smooth but the edges are like a sponge.

I think it depends what you desire most, but I'm starting to think that good quality plywood would just be easier to build with. And with plywood there are huge differences in quality. At Lowes / HD, their plywood is all voided out. They used to carry some really good void-free 13-ply but not anymore.

Local Suppliers:
4 x 8 x 0.75" MDF: $42/sheet (lowes or HD)
5 x 5 x 0.75" Baltic Birch: $72 / sheet (and it's a 20+ minute drive for me).

The BB plywood is pretty dense, so really the only drawback is cost.
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post #5 of 11
1/11/13 at 7:26am
Quote:
Originally Posted by NicksHitachi View Post

For many years I have used MDF for construction of speaker enclosures. A long time ago I accepted this as gold standard and best practice. The argument was made(by someone else and I accepted this info) that the density of the material was the asset that made it most desirable for speaker enclosure construction.
What matters is whether the enclosure walls vibrate to the extent that they audibly color the speaker output. The two most commonly used methods to ensure that this does not occur is via mass and via stiffness. Thick MDF is the usual high mass route, thin well braced plywood is the usual high stiffness route. From a manufacturing standpoint thick unbraced MDF makes the most sense, as being non-labor intensive it's the far less expensive method. MDF also takes veneer with minimal prep, also reducing build costs. Thin plywood with adequate bracing works just as well, but it's highly labor intensive. That's not much of a concern for DIY, but a major concern for a manufacturer, so you tend to see it used only in the high end of manufactured cabs. In between the two extremes of high mass with no bracing and low mass with lots of bracing you will see both MDF and plywood of various thickness and level of bracing used, pretty much depending on where the designer's priorities lie, in lighter weight or lower cost. The DIYer can decide for himself where to set those priorities, a designer of commercial cabs pretty much has to toe the line drawn by the bean counters.
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post #6 of 11
1/11/13 at 7:35am
I recently used .75 BB and .75 MDF for my project (the MDF was strictly for the inner baffle to reduce cost). Here are my quick thoughts for what they are worth:
- MDF is noticeably more heavy. I suppose this could be a pro or a con.
- BB is much easier to work with, especially if you are dealing with larger sheets and a table saw.
- MDF dust makes a huge mess. No matter what, I recommend using some sort of mask or respirator, but even the cleanup of MDF takes more time. I doubt this is a huge factor for most people, but I am not a fan of MDF dust at all.
- MDF is definitely more brittle than BB. I am not sure what you plan on finishing your cabinets with, but if you have little kids or pets running around, I tend to think that BB might hold up better.
- MDF is definitely cheaper.
- MDF cuts easier. My blade went through it like butter...

I paid about 1/3rd more for BB where I live (I agree that Home Depot and Lowes had some poor quality), but Menards near me had some good BB with little void and it was on sale. If I had to do it all over again I would buy BB again vs MDF for the project. It was just so much easier to work with and less messy.
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post #7 of 11
1/11/13 at 7:37am
Quote:
Originally Posted by Bill Fitzmaurice View Post

What matters is whether the enclosure walls vibrate to the extent that they audibly color the speaker output. The two most commonly used methods to ensure that this does not occur is via mass and via stiffness. Thick MDF is the usual high mass route, thin well braced plywood is the usual high stiffness route. From a manufacturing standpoint thick unbraced MDF makes the most sense, as being non-labor intensive it's the far less expensive method. MDF also takes veneer with minimal prep, also reducing build costs. Thin plywood with adequate bracing works just as well, but it's highly labor intensive. That's not much of a concern for DIY, but a major concern for a manufacturer, so you tend to see it used only in the high end of manufactured cabs. In between the two extremes of high mass with no bracing and low mass with lots of bracing you will see both MDF and plywood of various thickness and level of bracing used, pretty much depending on where the designer's priorities lie, in lighter weight or lower cost. The DIYer can decide for himself where to set those priorities, a designer of commercial cabs pretty much has to toe the line drawn by the bean counters.

Bill, what if you are using MDF and plywood of the same thickness? .75" vs .75"?
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post #8 of 11
1/11/13 at 8:00am
Thread Starter 
Quote:
Originally Posted by ack_bk View Post

Quote:
Originally Posted by Bill Fitzmaurice View Post

What matters is whether the enclosure walls vibrate to the extent that they audibly color the speaker output. The two most commonly used methods to ensure that this does not occur is via mass and via stiffness. Thick MDF is the usual high mass route, thin well braced plywood is the usual high stiffness route. From a manufacturing standpoint thick unbraced MDF makes the most sense, as being non-labor intensive it's the far less expensive method. MDF also takes veneer with minimal prep, also reducing build costs. Thin plywood with adequate bracing works just as well, but it's highly labor intensive. That's not much of a concern for DIY, but a major concern for a manufacturer, so you tend to see it used only in the high end of manufactured cabs. In between the two extremes of high mass with no bracing and low mass with lots of bracing you will see both MDF and plywood of various thickness and level of bracing used, pretty much depending on where the designer's priorities lie, in lighter weight or lower cost. The DIYer can decide for himself where to set those priorities, a designer of commercial cabs pretty much has to toe the line drawn by the bean counters.

Bill, what if you are using MDF and plywood of the same thickness? .75" vs .75"?

Yes, Apples to Apples. Assuming same thickness. Which has the best anti-resonance characteristics?

Equally sized, braced, glued, etc.

Something I didn't mention or make distinction, is the type of speaker. I'm assuming subwoofers and conventional loudspeakers are in the same "classification" but they don't need to be. Does that make a difference? Is one better suited for subs but not conventional speakers or vice versa?
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post #9 of 11
1/11/13 at 9:22am
Quote:
Originally Posted by ack_bk View Post

Bill, what if you are using MDF and plywood of the same thickness? .75" vs .75"?
The MDF box will be heavier. smile.gif
I don't use MDF. For that matter I don't use 3/4" plywood either. Properly braced 1/2" plywood will handle any application. FWIW my personal electric bass cab is made of 1/8" and 1/4" BB. It doesn't vibrate. cool.gif
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post #10 of 11
1/11/13 at 10:20am
Quote:
Originally Posted by Bill Fitzmaurice View Post

The MDF box will be heavier. smile.gif
I don't use MDF. For that matter I don't use 3/4" plywood either. Properly braced 1/2" plywood will handle any application. FWIW my personal electric bass cab is made of 1/8" and 1/4" BB. It doesn't vibrate. cool.gif

Ironically enough I stumbled across some threads from you on using well braced 1/2" ply vs more expensive 3/4" ply/MDF but it was after I already purchased the 3/4" smile.gif

It is something I will keep in mind for future builds

Especially with using the circle jig to cut both baffles. It would have gone much faster using 1/2" where I could probably make one pass.

I am actually surprised more commercial/ID sub companies do not leverage thinner plywood that is well braced. I get that MDF is probably cheaper but the shipping costs alone would be reduced substantially, and shipping 70-100+ lbs subwoofers is not cheap...
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post #11 of 11
1/11/13 at 10:24am
Quote:
Originally Posted by ack_bk View Post

Ironically enough I stumbled across some threads from you on using well braced 1/2" ply vs more expensive 3/4" ply/MDF but it was after I already purchased the 3/4" smile.gif

It is something I will keep in mind for future builds

I am actually surprised more commercial/ID sub companies do not leverage thinner plywood that is well braced. I get that MDF is probably cheaper but the shipping costs alone would be reduced substantially, and shipping 70-100+ lbs subwoofers is not cheap...

After building two large cabs I can attest to the substantial weight difference between ply and MDF. I thought my PB12/2 Ultra weighed a bunch. It's going to be a featherweight compared to this bad boy.
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