What are the characteristics of a better material for enclosure?

[Saturnus]

It doesn't matter what type of plywood it is. Plywood by very design is dual axis stable meaning it's more rigid on two axii (the lenght and breadth of the board) than on the thickness. MDF on the other hand is triple axis stable.

[MJL21193]

Originally posted by thoriated
Well, you have not even started to address my points regarding MDF's uniformity and its effect on resonant Q and the resin's poor acoustic qualities, so I must assume you concede my points.

So, don't be offended if I regard rigidity as the end all and be all of a material's suitability for use in a speaker enclosure as a bit of a side issue here.

I have addressed all of this, 2 years ago nearly to the day in the thread posted by Dave. Read it, your answers are inside.

You have your ideas, that's fine. Don't expect to be able to say "whatever" you think or feel and not be challenged.

[thoriated]

I never stated that BB is not 'more rigid' than MDF (although there are some grades of MDF in existence that BB is not more rigid than, so it's sensible to shy away from a blanket assertion either way, IAC).

Once again, what I posted is that MDF has problems with its resonant characteristics that are more noticeable because of its high degree of uniformity (on three axes, thanks!), and the resins that give it most of its rigidity and mass have sonically poor characteristics.

This is what I posted and so far it has not been challenged in any way.

Hey, MDF is cheap and it is relatively rigid. I've used it myself (in a 1.5" thickness) for some subwoofer boxes where heavy is good.

[Saturnus]

Let's be clear about this. The main reason MDF is used in many commercial products is that it's cheap, easy to process and have reasonable sonic qualities. In builds where it matters a better suited material is usually used.

[nickmckinney]

Originally posted by Geek
You forgot one:

Oiled softwood (pine, spruce, hemlock, fir):
- Takes on some characteristics of hardwood
- Less resonance than hardwood
- Light weight
- Least wear on tools
- Good damping
- Used throughout the cab and not just the baffle, can become part of the LF driver system and increase LF output over hardwood/MDF (spruce is often used by luthiers for this)

Cons:
- Takes more router skills than hardwood
- Requires more bracing for a sonic-neutral cab

When I was at Lambda I had a customer from Japan order at least 50+ cabinets from me and they had to be made from soft pine ply with no voids as he was basing it on the older WE and Atlec designs. I found a marine grade that worked really good and decided to try it myself with a set of pro cabinets. I have never used another material again it was that dramatic. Just talking into the open cabinet without a driver mounted it was much better with the pine ply compared to baltic birch.

[BlueWizard]

I don't think the question of 'what is best' is ever a question of material.

I think it is a question of time, money, skill, and available tools. If you have unlimited resources of these four commodities, then you can choose any material you want.

But rarely to never does anyone have unlimited quantities of these four commodities.

Money being a critical factor. Using marble, ceramic, of having fiberglass laid up is never going to be cheap. And if you are spending thousands on material, you probably don't want to spend 10's or 100's on drivers. Likely you want to spend 1,000's on drivers. So, if your goal is to spend $10,000 on a pair of speakers, then you certainly can get into some exotic construction materials.

But, really, how many DIY speaker builders can afford $10,000 for a pair of speakers?

Just a few thoughts.

Steve/bluewizard

[Geek]

Hi,

Originally posted by nickmckinney
When I was at Lambda I had a customer from Japan order at least 50+ cabinets from me and they had to be made from soft pine ply with no voids as he was basing it on the older WE and Atlec designs. I found a marine grade that worked really good and decided to try it myself with a set of pro cabinets. I have never used another material again it was that dramatic. Just talking into the open cabinet without a driver mounted it was much better with the pine ply compared to baltic birch.

Pine is my choice of wood too

I'm trying to get my mitts on some of this colourful "Bettle Pine" from our infested forests, but it's easier to get one's mitts on endangered mahogany remnants with the demand for "Beetle Pine" for finish carpentry in Japan

Cheers!

[simon5]

Originally posted by thoriated
For that matter mdf is generally regarded as being more rigid than many plywoods, not less rigid. That is, until it cracks or crumbles (yeccch).

Originally posted by Saturnus
That is correct. MDF is "stiffer" as defined as being less flexible than plywood.

Hi guys, I don't know if you are familiar with Young's modulus.

In solid mechanics, Young's modulus (E) is a measure of the stiffness of an isotropic elastic material. It is also known as the Young modulus, modulus of elasticity, elastic modulus (though Young's modulus is actually one of several elastic moduli such as the bulk modulus and the shear modulus) or tensile modulus. It is defined as the ratio of the uniaxial stress over the uniaxial strain in the range of stress in which Hooke's Law holds. This can be experimentally determined from the slope of a stress-strain curve created during tensile tests conducted on a sample of the material.

Here we are talking about a very good grade of Baltic Birch Plywood, Void free and multi layered, of at least 3/4" or more. In that case, Baltic Birch Plywood has a much higher Young's modulus than MDF, which means it is stiffer.

Thanks !

[rcw]

The most important criterion for enclosure material is stiffness
by far the stiffest common material is steel, this being about 100 times stiffer than plywood mdf etc.

If you make an enclosure from three quarter inch boiler plate instead of mdf you can expect at least 40db. less panel output.

Optimally if you use carbon fiber honeycomb you can get steel like stiffness, but the lower mass pushes the panel resonances up to much higher frequencies and the internal pressure drops off at a rate that is approximately the reciprocal of frequency.
Carbon fiber honeycomb is then the best.
rcw.

[Saturnus]

Originally posted by simon5
Here we are talking about a very good grade of Baltic Birch Plywood, Void free and multi layered, of at least 3/4" or more. In that case, Baltic Birch Plywood has a much higher Young's modulus than MDF, which means it is stiffer.

I assure you that is not the case on all axii. Futhermore you're comparing appls to oranges. MDF is a group nominator in the fibreboard group just like plywood. Comparing a specific product to a product group is invalid.

Originally posted by rcw
The most important criterion for enclosure material is stiffness by far the stiffest common material is steel, this being about 100 times stiffer than plywood mdf etc.

Whatever makes you assume that stiffness is the most important criterium? There are two equally important criteria, stiffness and dampening, both work against eachother. In theory 2 perfect materials exist, one which has infinite dampening but zero stiffness, and one which has infinte stiffness but zero dampening. All real world materials is some sort of compromise between the two.