How good / bad is MDF for use in speaker cabinets?

[Ken Tajalli]

Why is aluminum better? IDK if is or not, just need to know why? Some measurements or studies would help too , if you have access to these.

Peace.

Alu is much stronger. For front baffle at least, Alu works better, because it won't bend or warp under stress. Repeated measurements through the years has shown that. I believe Magico recently have done extensive measurements that are available on the net to show this.
So a tough and super stiff front baffle makes sense. But once the front baffle has gripped the drivers tight, rest of the speaker cabinet's material becomes less critical, hence why some companies limit the use of Alu to front baffle only.
The Genelec mentioned above is one of them.
I know top B&W speakers use Alu for their midrange and tweeter assembly, it is all Alu.
Linn used composites in late 70's for their baffles (IIRC).
I have a pair of Sonus Fabers from 90's. the front baffle is MDF, but it is 35mm thick! rest of it is about 22mm thick, apart from top and bottom.
Top is 35mm, bottom I believe is 50mm. It has extensive bracing inside.
It has two 6.5 inch bass drivers.

 

[kemmler3D]

Why is aluminum better? IDK if is or not, just need to know why? Some measurements or studies would help too , if you have access to these.

Peace.

I would join others in saying aluminum isn't better per se, but is stronger than MDF and it can be milled into shapes that MDF can't, and so can be used to exceed the performance of a standard MDF implementation. Magico is the example manufacturer that always comes up around aluminum, they really go to extremes.

MDF is sort of like DACs. A regular old bit of MDF, like a regular old DAC, is almost as good as you can get, if a rectangular cabinet is acceptable for the speaker. But (for DACs and MDF alike) it's disappointing to think that something relatively cheap and ugly could be the best option, so people keep looking for something more exotic.

I'm personally excited about the possibility of multi-layered composite construction based on 3D printing, but that will only ever be suitable for DIY and boutique construction because of the time it takes to produce one housing... well over 24h per 3-way cabinet.

 

[Pearljam5000]

The saddest thing is MDF reminds me of Ikea and thinking about speakers that cost tens of thousands of dollars that are made out of that stuff is a bit disappointing
But obviously SQ is above everything else
It's hard going back after seeing / touching the metal Genelecs

 

[krabapple]

neutronium or gtfo.

 

[sigbergaudio]

It's somewhat disappointing that even on the 8381 $60K Genelecs only the top faceplate is aluminum and the rest is MDF
But it is what it is

So in effect what you are saying is that you would like speakers to be even more expensive without audible benefits. I'm sure Magico and the likes are thrilled to hear that, but I'm not sure I understand why.

EDIT: I understand it for products that are expensive (and make expensive design choices) just for the sake of being able to sell in the luxury segment, but that's not what the 8381 is.

 

[dfuller]

MDF is totally fine. It's rigid, easily machined, and pretty nonresonant. Aluminum is by comparison crazy expensive, harder to machine, or needs to be cast in (expensive) molds. It also can ring like a bell if not done absolutely perfectly.

 

[jhaider]

I'm personally excited about the possibility of multi-layered composite construction based on 3D printing, but that will only ever be suitable for DIY and boutique construction because of the time it takes to produce one housing... well over 24h per 3-way cabinet.

There are multilayer composites made with MDF, too. David Smith era Snells used two layers of MDF with a damping later in between. Earl Geddes used that approach on Gedlee speakers as well. The newer damped bracing designs from e.g. KEF seem to be a more efficient means of doing the same thing.

Personally I don’t much care for MDF, though I won’t throw my Revel Gem2’s out for being made of the stuff, either. The corners get damaged easily and when I thought I could build cabinets I hated working with it. All of the wood speaker cabinets I’ve commissioned in the last decade or so have been Baltic Birch or a domestic hardwood ply called Appleply. Prices have risen since then so I don’t know what I would spec if I were to commission something now.

There are also other materials to consider. One is HDPE board (Starboard). I’ve had a couple subwoofer cabinets built from 1/2 Starboard (double thickness baffles) and they’re great. Geddes switched over from constrained MDF to a polyurethane board called Renshape. I’m not sure anyone currently uses that.

 

[kemmler3D]

There are multilayer composites made with MDF, too. David Smith era Snells used two layers of MDF with a damping later in between. Earl Geddes used that approach on Gedlee speakers as well. The newer damped bracing designs from e.g. KEF seem to be a more efficient means of doing the same thing.

Totally - but with 3D printing adding more layers or materials is easier... you can design the cabinet with as many voids as you like and fill them with concrete, sand, resin, or whatever else can be poured in. Of course, I say this like it's no problem, but I haven't done it nor have I seen anyone do it, so this is mainly theoretical at this point. But there's no reason I know of it can't be done.

With MDF, each layer will tend to be pretty thick, with 3D printing you can have arbitrary thicknesses of plastic vs. air vs. other materials. The strength of 3D printing is that there's a very low penalty for complexity of the cabinet design, the weakness is slow speed and the fact that 3D printer materials are very likely not as good as MDF unless you reinforce them in a post-printing step.

 

[Tassin]

Ever heard of WBP?
It is a bit more expensive version of MDF that moisture proof.
It is very tough and hard, and can be precisely cut and shaped.
Lasts outdoors for couple of years.
Indoors, forever .

The term WBP refers to the glue between the veneers of a plywood panel. The glue can withstand 72 hours in boiling water without the veneers separating from each other. Hence the designation "Weather and Boil Proof", internationally the highest bonding class.

 

[Ken Tajalli]

The term WBP refers to the glue between the veneers of a plywood panel. The glue can withstand 72 hours in boiling water without the veneers separating from each other. Hence the designation "Weather and Boil Proof", internationally the highest bonding class.

In UK, I can buy WBP MDF from builders merchants.
Or at least that's what they call moisture proof MDF.

 

[Plcamp]

Concrete can take any shape and is stiff.

Why not concrete?

 

[sigbergaudio]

Concrete can take any shape and is stiff.

Why not concrete?

Crazy heavy?

 

[fpitas]

Concrete can take any shape and is stiff.

Why not concrete?

Go straight for neutronium, as previously suggested.

 

[Plcamp]

Crazy heavy?

But would it actually be crazy heavy for the same stiffness? I suspect not. For example I’d expect a 3/4” panel of MDF to have similar stiffness to a 1/4” thick dense concrete panel?

I don’t know…but the advantage of “any shape” is huge IMO.

 

[Pearljam5000]

Granite is the new thing

 

[Plcamp]

Granite is the new thing

I have been pondering quartz resin countertop material as well. But it doesn’t have the “any shape” quite as simply.

 

[Plcamp]

Here is a related question that maybe some experienced speaker designers might answer…

I noted in Linkwitz’ various papers a short discourse on mounting the mass of the driver independently from the enclosure that surrounds it. (The driver pokes through a tight toleranced hole in the baffle). Doing this both evades the resonance of the driver mass with its baffle, and eliminates the need for the baffle to support the driver mass.

Question is…could cabinet stiffness and material requirements be significantly reduced by doing this, leading to lighter boxes?

I like the idea for bass drivers on open baffle, an application where the compression of air inside an enclosure isn’t required.

 

[Tangband]

Obviously it's the most common material in speakers
Question is how good or bad is it
Do most speaker brands use it only Becaue it's cheap ?
Is real wood better for the same use but just costs more so they don't use it ?

It depends .
Its often a good solution to have different thickness front and back of the cabinet, spreading the resonances from each wall at different frequencies. A very stiff cabinet has its resonances at a higher frequency. A wooden baffle made of oak is stiffer than MDF with the same thickness, and will have its resonanses at higher frequencies .
MDF may offer better inherent damping of the resonances than hard wood.

So what matters for the sound ?

I have experimented with bitumen in two DIY mdf cabinets filled with rockwool , and having bitumen on all of the inside walls made the resonances lower in frequency , and the sound was clearly inferior to the none-bitumen mdf cabinet . I took away all bitumen on only the left inside of the cabinet and this trick made the music sound better than the cabinet without bitumen.

So…. In my experience - its better with a cabinet that has different resonance frequencies on different walls and the music will sound cleaner and better. This can be done using bitumen only on the left or right inside of the cabinett , or build a cabinet with different thickness of the walls.

This is probably more important for the sound than the material its made of.
In my experience, a very stiff cabinet will often sound better with its resonances at higher frequencies, with a higher Q .
Thats less disturbing to the ear compared to a lower resonance at 150 Hz, with a lower Q .

A very stiff cabinet can still have a ”tuning fork” effect If the walls are identical. One must pay attension to the way the drivers are mounted on the baffle , using wooden screws may trigger resonances.

A couple of years ago I was test listener for some people who had made an identical loudspeaker except for the material in the boxes. One was made of 0.75 inch mdf and the other of 0.75 inch chipboard . The mdf cabinet sounded better to all listeners .

The loudspeaker with less resonances ever tested in Stereophile is made by Genelec , the G3 model.
This cabinet is made of aluminium and the drivers are clamped to the cabinet from behind .

Genelec G Three active loudspeaker Measurements

Sidebar 3: Measurements I used DRA Labs' MLSSA system, a calibrated DPA 4006 microphone, and an Earthworks microphone preamplifier to measure the Genelec G Three's frequency response in the farfield. I used an Earthworks QTC-40 mike for the nearfield responses.

www.stereophile.com

I investigated the enclosure's vibrational behavior with a plastic-tape accelerometer. It was extremely inert. The only resonant mode I found was on the sidewall, at 637Hz (fig.1), but this is vanishingly low in level, even at SPLs >90dB.

 

[CrustyToad]

Comparison of mdf and plywood for generic woodwork use:

TL;DR
Mdf is cheap and easy to form in complex shapes. Not as bad with humity as expected
Structural rigidity is not that great

 

[Tassin]

In UK, I can buy WBP MDF from builders merchants.
Or at least that's what they call moisture proof MDF.

Some manufacturers have picked up the trend about WBP and are using is also to label lower bonding grades. These plywoods end up delaminating in humid conditions more rapidly. Anyway, do you expect advantages over regular MDF/HDF?