Hardwood vs. MDF for a DXT-MON build.

[BostonJack]

Well, I'm getting my act together to build a pair of DXT-MONs. Purchased the plans a year ago! I will have to join a maker space to access a proper table saw, thickness planer. My plan is to build to the spec. *but* substitute Dark Walnut hardwood for the specified 19mm and 38mm MDF.

I'm doing this for aesthetics and satisfaction. I've seen plenty of builds (mainly European) with a hardwood front baffle and nobody blinks at that. Here is my table of density estimates for Black Walnut, MDF, and Baltic Birch plywood:


black walnut is 660 kg/m cubed or 41.2 lb/ft cubed
MDF is 31 to 62 lb/ft cubed
baltic birch is 580 - 620 Kg/m cubed

So black walnut is below the median of MDF density, but not out of range. its somewhat denser than baltic birch. MDF is essentially isotropic and (I assume) relatively invariant across a given panel. Black walnut will have different properties depending upon axis and some variation.

I've convinced myself that in this compact (12"" x 8"" x 9.5") little box, the effects will most likely be inaudible. What do you think? Please point to objective data if you can. Thanks!!

 

[digitalfrost]

Do you want to build the whole enclosure out of hardwood? One reason people choose MDF - besides the cost - is that MDF doesn't "work" much. Unless your hardwood is aged, you run the risk of getting a leaky enclosure because the wood will change depending on temperature and humidity.

I would be a better idea to apply veener to an MDF box or only build the baffle out of wood.

 

[BostonJack]

Do you want to build the whole enclosure out of hardwood? One reason people choose MDF - besides the cost - is that MDF doesn't "work" much. Unless your hardwood is aged, you run the risk of getting a leaky enclosure because the wood will change depending on temperature and humidity.

I would be a better idea to apply veener to an MDF box or only build the baffle out of wood.

Thank you. Yes, changes in humidity/water content are a factor. I've seen some DIY blogs that show small cracks after moving from a very humid environment to a desert home. That builder fixed the cracks using resin and touch up (this was on a set of towers, so much larger enclosure).
I'm more concerned about resonances, but will research the humidity issue more.

 

[ppataki]

I had used MDF for my speaker projects but for the last 2 projects (both are published here on ASR) I have chosen Baltic Birch plywood (I live in Europe)
The reason being: you can have almost double the thickness vs MDF for the same weight or same thickness and almost half the weight - whichever you prefer (this is the objective part)
I also fancy the 'knock on wood' test of the plywood vs that of the MDF (this is the totally subjective part)
I will personally keep on using plywood

 

[ppataki]

Thank you. Yes, changes in humidity/water content are a factor. I've seen some DIY blogs that show small cracks after moving from a very humid environment to a desert home. That builder fixed the cracks using resin and touch up (this was on a set of towers, so much larger enclosure).
I'm more concerned about resonances, but will research the humidity issue more.

Forgot to add to my previous post: if you are worried about the resonances you can try either Decidamp or Green Glue between two layers of plywood or MDF or whichever you decide on
More about the whole subject here:

(in my next line array project I will be using Green Glue between two layers of 12mm plywood since Decidamp is "unobtanium" in Europe - btw that project is also followed in a post here on ASR)

 

[BostonJack]

Cool. DXT-MON design calls for two layers of butyl/bismuth damping material (used as automobile sound damping) with a constraining layer of XXX between it. (I have to find out what XXX is, it might just be a thin plywood ply). The translations from the German I've used haven't been super clear on this point.

 

[BostonJack]

Here is an article on measuring cabinet resonances on a test cabinet. Interestingly, the author discovered plywood to have lower resonance than MDF.

Measuring the sound radiation of speaker cabinet walls

Measuring the sound insulation of different types of woods used in speaker cabinets: MDF, plywood, OSB.

www.tonestack.net

His conclusion is that differences in cabinet material are less than those in absorption material and are less significant than commonly believed.

 

[BostonJack]

One of the techniques he mentioned is a sort of doppler image which can be translated to SPL through software.

Yikes! Very geeky, probably expensive. Would be great for real speakers.

 

[BostonJack]

One of the techniques he mentioned is a sort of doppler image which can be translated to SPL through software.

Yikes! Very geeky, probably expensive. Would be great for real speakers.

here is a commercial vendor of doppler vibration test systems:

Vibrometry

go.polytec.com

Looks beyond the DIY budget. (hahaha).

 

[headshake]

Check out https://www.diyaudio.com/forums/multi-way/356130-monster-construction-methods-shootout-thread.html

Do you plan on measuring the speaker? If yes, then you can fix things later with some bracing, or melamine, or whatever.

 

[antennaguru]

I have built speaker cabinets out of solid hardwood boards from Lowe's, using only my chopsaw, biscuit joiner, and my router to round all of the corners. I used lots of glue and every clamp I own, and never had a problem with the cabinets down the road.

 

[somebodyelse]

Cool. DXT-MON design calls for two layers of butyl/bismuth damping material (used as automobile sound damping) with a constraining layer of XXX between it. (I have to find out what XXX is, it might just be a thin plywood ply). The translations from the German I've used haven't been super clear on this point.

In the DXT-MON 182 it's two layers of butyl/aluminium topped with a layer of HDF. The butyl/aluminium combination uses the aluminium as a constraining layer and the butyl as the lossy shear component.

 

[BostonJack]

Check out https://www.diyaudio.com/forums/multi-way/356130-monster-construction-methods-shootout-thread.html

Do you plan on measuring the speaker? If yes, then you can fix things later with some bracing, or melamine, or whatever.

Thanks. I may (repeat may) ask Amir to test them, if he is interested. Your monster thread above was interesting, also frustrating as there was little to no discussion of acoustic modes vs. vibrational modes of the cabinet itself. Data seemed to show stuffing materials with strong effect on former. Not much clear data on vibrational modes vs. construction material.

 

[BostonJack]

In the DXT-MON 182 it's two layers of butyl/aluminium topped with a layer of HDF. The butyl/aluminium combination uses the aluminium as a constraining layer and the butyl as the lossy shear component.

Thanks! I can resolve this, certainly. Just need a more careful view of the pictures, maybe a query to the designer.

 

[BostonJack]

I have built speaker cabinets out of solid hardwood boards from Lowe's, using only my chopsaw, biscuit joiner, and my router to round all of the corners. I used lots of glue and every clamp I own, and never had a problem with the cabinets down the road.

I'll be biscuit joining side panels, as 10" black walnut is pretty rare. a small cabinet should have relatively low expansion/shrink, especially if I stabilize water content for a couple of months.

 

[ZolaIII]

Mentioning hardwood I don't know can you get Sorbus torminalis (for cabinets enclosure) nor how much would that cost you.

 

[BostonJack]

Good for colic. Hardwood suppliers in the Northeast US don't have it. Maybe good for threads that go on too long or degenerate on ASR?
Black walnut is ~$200 for the quantity I need.

 

[ZolaIII]

It's great both acoustic (very tight) and almost doesn't breed at all (dry/wet and in time). That's why it's used in so many musical instruments.

 

[BostonJack]

It's great both acoustic (very tight) and almost doesn't breed at all (dry/wet and in time). That's why it's used in so many musical instruments.

Oh, interesting. I'll keep my search open.

 

[Morpheus]

Thank you. Yes, changes in humidity/water content are a factor. I've seen some DIY blogs that show small cracks after moving from a very humid environment to a desert home. That builder fixed the cracks using resin and touch up (this was on a set of towers, so much larger enclosure).
I'm more concerned about resonances, but will research the humidity issue more.

20 years or thereabouts ago I built a small bookshelf loudspeaker from Visaton units in an passive radiator config ( AL130 midwoofer) in solid birch. They were drop dead gorgeous, with heavy radius all around 25 or 30 mm thick walls, professionally made by a small kitchen and wc cabinet maker to furniture grade standard. He assured me the wood would be perfectly dry and wouldn't budge, got it treated/lackered inside and out for ease of mind, plus bituminous sheets lining the inside.You know where this is going...they were always in my living room, subjected to little temperature and moist variation, but after some 7 or 8 years the humitidy that somehow had crept in and out, caused too much of different expansion rates along the wood grain (unavoidable) and too much stress accumulated and the whole thing begun to disjoint...Don't do it, or get Sonus Faber to do it for you if you must, I tried to be as carefull as I could and got burned...( then again, I didn't build them myself...)