MDF v Plywood construction

[greenie512]

I thought I’d move this topic out of the (Fullrange) Fostex 166ES-R thread.

Fostex FE166 ES-R; reviews, cabinets, & notch filters

I mentioned MDF as part of the construction of the BLH cabinet and got politely flamed for not using plywood which these guys though was more “musical” and had more “soul”.

My heart like this idea but my head says otherwise?

Surely, if we consider a CD recording of a single violin piece and the audio engineer does a good job and captures all the nausea and tonality of the session. If we have a speaker driver (that could) play back this perfect recording a cabinet resonating at any pitch would add to the reproduction and we would not hear the true original sound.

Even if the cabinet did? add complementary sound for this recording. How could it do so for a electric guitar, organ, double bass etc any mixture of instruments/voices etc – without “mudding” the sound.

Now I know there are a hundred other factors and all this is compromise which I’d like to avoid here?

So what is the best cabinet building material!

[Bill Fitzpatrick]

I know there are a few people here that think an enclosure should have the appropriate tone.

IMHO, In a sealed enclosure, the appropriate tone is none. The only sound you want is coming from the front of the speaker - nothing from the back and nothing from the cabinet.

[tiroth]

There are a bunch of threads that deal at least tangentially with this issue. I believe it comes down to

Plywood (high ply count/void free)
+higher stiffness
+lower mass
+more durable
-more expensive
-not as uniform substrate (harder to machine)

MDF
+cheap
+higher damping (?)
+higher mass
+uniform substrate
-less resistant to gouging
-extremely heavy
-not as stiff

Note that both higher and lower mass are listed as benefits! Mass relates to simple portability, resonance, and damping; higher mass may or may not be desirable in the context of other design decisions.

I think MDF vs. plywood is not really a big issue. Plywood is probably better but I don't think it is better for the money--I'd rather use MDF than low-quality ply, and high-quality ply costs a mint, at least where I live. What is more important is other aspects of construction, such as bracing, damping, constrained layer damping, different materials construction techniques.

[greenie512]

Originally posted by tiroth



I think MDF vs. plywood is not really a big issue. Plywood is probably better but I don't think it is better for the money--I'd rather use MDF than low-quality ply, and high-quality ply costs a mint, at least where I live. What is more important is other aspects of construction, such as bracing, damping, constrained layer damping, different materials construction techniques.

I've added the same question to the Loudspeaker forum here just to get a wider view - I was woundering if this might be specific to horm design.

I also dropped this into Madisound for the same reason.

http://www.madisound.com/cgi-bin/dis...gi?read=335371

And got very similar response to your reply.

I've got same cost problem in Brisbane Australia, and as this is only a hobby and I don't expect these to out perform my Thors I''m going to use MDF!

[SirPoonga]

I made my home theater sub with a dayton titanic 10" and MDF. Me (and my friends) thinks is sounds awesome. However I don't have a plywood version of it to compare too.

I only have a 80W amp. But for a small apartment I can feel my movie explosions and pick out the bass guitar from music in clarity.

[RHosch]

When the first mode of an enclosure panel resonance is outside the passband of the drivers in that enclosure, you don't need damping... only stiffness. This is the case with sub enclosures, where panels (should) resonate well above the operating range of the drivers and the goal should be to increase stiffness by any and all means necessary to minimize the amplitude of forced excitation vibrations. Here both MDF and ply can be used, with the first resulting in a heavier enclosure for the same performance. The final cost will likely be fairly similar between the two, with ply perhaps having a slightly smaller finished enclosure for a bit higher cost.

When the first mode of an enclosure panel resonance is within the passband of the drivers in that enclosure, you need both damping and stiffness. This is the case with full-range (or satellite) enclosures, where panels almost unavoidably resonate somewhere within the operating range of one of the drivers. Here the goal should be to increase stiffness as much as possible to minimize the amplitude of forced excitation vibrations, and to maximize damping so that the amplitude at resonance is kept in check as well. This can be accomplished with either MDF or plywood, with the first requiring more bracing or thicker walls for the same result, and the latter requiring more applied damping material liners for the same result. Relatively speaking, since MDF is usually cheaper than both good plywood and good damping materials, and since bracing techniques contribute way more to the overall panel stiffness than either panel thickness or material modulus, it would seem obvious that MDF is the more economic choice. And, with any experience with proven engineering methods, an equally or better performing choice as well.

Since forced excitations are relatively low in amplitude compared to sub enclosures, one should focus most of his efforts on proper damping. Hence, use MDF as a good starting point and spend the extra money (saved vs. ply) on additional damping.

Don't forget that stuffing is also important when the enclosure dimensions become large wrt the lowest wavelength in the passband of the drivers used (i.e., when the enclosure is 1/4 wavelength or larger, as a rule of thumb). This leads to the conclusion that subs don't require stuffing for backwave damping (but might otherwise benefit from the apparent increase in enclosure volume when a lot is used), but fullrange enclosures do require stuffing to dampen internal standing wave resonances.

In my observations, you'll find that the people who think plywood sounds better for fullrange enclosures are the same people who think some resistors sound better, some cables have a preferred direction, some volume knobs (the knobs, not the pots) sound better, etc. Take that for what you will... perhaps they are self deluded about practically everything "golden ear" related, or perhaps they are the ones who really do have good ears and can give the most consistent advice. Depending on which side of the greater subjectivist/objectivist argument you fall, you will either take their endorsement of plywood as an endorsement, or a warning.

[REDSKIN]

Thank you RHosch for the most eliquent and unbiassed (IMO) view of the MDF v PLY debate I have read. No silly theories or imaginative reasons for either just some good facts, excellent. Obviously with this post the question of which is better has been answered but I fear others will not let it die so easily.

[chipco3434]

Depending on which side of the greater subjectivist/objectivist argument you fall, you will either take their endorsement of plywood as an endorsement, or a warning.

Very, very funny. I'm choosing "warning".

[planet10]

Originally posted by RHosch
This can be accomplished with either MDF or plywood, with the first requiring more bracing or thicker walls for the same result, and the latter requiring more applied damping material liners for the same result.

Don't you have that backwards... plywood walls can be thinner for the same stiffness, and MDF has greater damping?

MDF also has greater energy storage, which comes back to haunt you.

I've been in the stiff, well-braced, get the panel resonances out of the way by moving them up where they won't get excited camp for a long long time. I used to use HDF (medite) exclusively. Lately thou i've been using plywood by preference (except for subs, where box material is less critical and the extra weight is offset by the availability of no cost MDF scraps). Why. We built a number of speakers from both MDF & birch plywood and the BB was a clear winner....

And i do know that there are differences between the sound of caps & resistors... anyone who says there isn't is deluding themselves & can use recycled bipolar electrolytics in all their crossovers....

dave

[tiroth]

Originally posted by planet10
Don't you have that backwards... plywood walls can be thinner for the same stiffness, and MDF has greater damping?

I believe that is exactly what he said...