Birch Ply vs MDF

[lsiberian]

I've been look around trying to get varying opinions on which is better from a sound standpoint. People seem to have a lot of varying opinions with little actual scientific data. I've been looking for a good FR graph that might demonstrate the differences between MDF and Birch Ply to give some measurable differences, but haven't found anything yet.

So far I've come up with Birch being about twice as stiff as MDF. Which in my mind would result in the greater ability of a driver to vibrate accurately. This is due to the fact that a less stiff material would vibrate more with the driver as it is being pushed and thus resulting in smaller difference between the vibration of the driver and it's holding box. I would think that would yield less SPL, but could be mistaken

Birch is also more durable. MDF can break, chip, and scratch more easily than birch.

MDF can also be harder to work with. I know that routing it results in dust cloud sometimes.

Any other thoughts would be appreciated. I would love to formulate a very accurate comparison maybe even a chart for future reference. Obviously I would share a chart with the community here.

Thanks in advance

 

[jliedeka]

I'm currently building speakers out of MDF and I've worked with Baltic birch ply for other applications.

MDF is actually easy to work. It machines beautifully but the dust is a pain. If I had to do this again, I'd make this a summer project so I could do all my cutting and routing outdoors.

I can't help you with anything objective. Baltic ply is more rugged than MDF so more suitable for speakers that will be moved a lot like PA speakers. I think MDF will soak up more acoustic energy but lacks stiffness so needs more bracing. It would be interesting to build identical speakers out of both materials and measure them with an accelerometer.

Jim

 

[lsiberian]

I'm currently building speakers out of MDF and I've worked with Baltic birch ply for other applications.

MDF is actually easy to work. It machines beautifully but the dust is a pain. If I had to do this again, I'd make this a summer project so I could do all my cutting and routing outdoors.

I can't help you with anything objective. Baltic ply is more rugged than MDF so more suitable for speakers that will be moved a lot like PA speakers. I think MDF will soak up more acoustic energy but lacks stiffness so needs more bracing. It would be interesting to build identical speakers out of both materials and measure them with an accelerometer.

Jim

Good to know it never gets too cold out here so I can always work outdoors, but in the summer it gets very hot so I have to pick my time carefully. I know MDF is also cheaper in my area and I find the pieces to be very smooth for applying laminate and other applications.

 

[alexwakelin]

I know that routing it results in dust cloud sometimes.

I haven't noticed that in my Madisound project, but the holes I was routing were small enought that the router base completely covered the hole keeping the dust contained. Might be a different story with larger holes. Routered edges are nearly perfectly smooth too.

 

[sploo]

I'd love to see some good data on this too.

I usually use MDF, as it's easy to machine (mainly using bandsaws, router table and CNC).

Cheap ply in the UK is pretty nasty (lots of voids) but is still comparable in price to (or more expensive than) MDF. The only no void plys I've seen are very expensive, and pretty tough to cut - I certainly have to be much more careful with them on the CNC machine.

I'd like to know of a good source of birch ply in the UK, if the price were reasonable.

 

[highfigh]

I've been look around trying to get varying opinions on which is better from a sound standpoint. People seem to have a lot of varying opinions with little actual scientific data. I've been looking for a good FR graph that might demonstrate the differences between MDF and Birch Ply to give some measurable differences, but haven't found anything yet.

So far I've come up with Birch being about twice as stiff as MDF. Which in my mind would result in the greater ability of a driver to vibrate accurately. This is due to the fact that a less stiff material would vibrate more with the driver as it is being pushed and thus resulting in smaller difference between the vibration of the driver and it's holding box. I would think that would yield less SPL, but could be mistaken

Birch is also more durable. MDF can break, chip, and scratch more easily than birch.

MDF can also be harder to work with. I know that routing it results in dust cloud sometimes.

Any other thoughts would be appreciated. I would love to formulate a very accurate comparison maybe even a chart for future reference. Obviously I would share a chart with the community here.

Thanks in advance

Neither is particularly hard but you can make them harder by coating the box with polyester resin. In addition to hardening the surface, it also seals the joints. MDF is one of teh easiest materials to work with, IMO. It is dusty but if you have a shop vac with the larger hose, you can collect the dust easily using just about any power tool. Go to a woodworking supply store like Rockler or Woodcraft and look at the dust collection attachments. I bought my 2HP double bag collector at Harbor Freight and it works great. I looked at all of the others that are the same and there was no reason to spend more money and get the same thing. For routing, I use my shop vac.

I would estimate that literally millions of speakers have been made commercially, using MDF. Add the millions that have been made in large and small car stereo shops, garages and with minimal tools and you'd have to conclude that there's a reason it has been so widely used. If you go to a lot of new home jobsites when the trim is being installed, you'll see a lot of it there, too, because it paints so well.

Scientific data? Don't hold your breath. All you really want is a very inert cabinet, with bracing on long surfaces to break up resonances by stiffening the panel. Yellow carpenter's glue will work with either plywood or MDF and as long as any leaks are sealed, it will be fine. I did car audio for 20+ years and never had a glue joint let go on a box I built. I never bothered to use birch plywood for them because of the fragile edges, although I used it when I made the drawers for my kitchen.

With any woodworking that generates dust, regardless of whether a dust collector is used, a NIOSH approved dust mask should be worn, as well as safety glasses and hearing protection. I can't estimate how many people I have talked to who claimed to be "really into the sound of a great system" but you wouldn't catch them dead with ear plugs.

 

[highfigh]

I'd love to see some good data on this too.

I usually use MDF, as it's easy to machine (mainly using bandsaws, router table and CNC).

Cheap ply in the UK is pretty nasty (lots of voids) but is still comparable in price to (or more expensive than) MDF. The only no void plys I've seen are very expensive, and pretty tough to cut - I certainly have to be much more careful with them on the CNC machine.

I'd like to know of a good source of birch ply in the UK, if the price were reasonable.

I would contact a cabinet shop to find out who they get theirs from. Remember to ask about cabinet grade birch plywood- the utility grade isn't even worth using to build the carcass for a set of drawers.

 

[avaserfi]

Here is a thread that has dealt with it before (on another forum). I always try to use ply unless I plan on painting the finished product. Why? Well cabinet grade ply is lighter and more stiff than MDF meaning less resonances and less weight. It is a little harder to work with, but big deal. With the amount of work I put in my builds the extra effort isn't a problem.

 

[highfigh]

One other thing about composite materials like MDF and particle board- they're more abrasive than other wood products, so a good carbide blade is definitely a necessity. The glue in plywood is harder than yellow glue, so that causes its own issues, like chipping carbide that's too hard, which is usually found on cheap blades. A Forrest WoodWorker II can be found for about $70 when it's on sale, or about $90 when it's not but it will outlast most other non-industrial brands when it comes to how long you can use it before it needs to be sharpened. Forrest also offers excellent services after the purchase, like sharpening, carbide replacement, flattening, etc.

The guy who does my sharpening refers to particle board as "The hot dog of the lumber industry". It has wood, dust, crap swept up from the floor and all kinds of other stuff that really shouldn't be in it.

 

[fredk]

Well cabinet grade ply is lighter and more stiff than MDF meaning less resonances and less weight.

You wouldn't have any physics related sources that explain the relationship between stiffness and resonance would you.

My current understanding is that stiffness affects resonant frequency and mass affects damping.

I am still quite confused on the whole matter.

 

[avaserfi]

I don't have any sources I can recommend. If all things were equal your mass/stiffness idea would work, but bracing takes a large effect. The end goal is to raise resonances beyond the passband between the stiff ply, a viscoelastic constraint layer and dense bracing it will be done. MDF will work, but it will be heavier and slightly less efficient.

Do note I recommend using mass and stiffness in conjunction with the constraint layer. 3/4" ply - viscoelastic constraint - hardibacker cement board. All grounded with dense bracing from a stiff material such as steel or oak.

 

[fredk]

I don't have any sources I can recommend.

That bit has me scratching my head as I have yet to find a good explanation overall. The relationship between mass and damping (mass spring) can be expressed as a simple formula. One would think that the same could be said about stiffness and damping. Its strait forward known physics.

The total effects of stiffness damping and bracing is something that one should be able to model just like using ts parameters to model a sub. Ah well...