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.
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.
Geek said:
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.
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
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
thoriated said:
Saturnus said:
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 !
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.
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.
simon5 said:
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.
rcw said:
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.
After I looked up some numbers I find I may have been giving MDF too much credit for rigidity. After all, the gook holding the compressed wood waste product together for typical MDF may actually be less rigid than many cheaper grades of plywood.
IAC, it occurs to me that plywood, with its orthogonal alternate layer grain orientation with their significantly different shear strengths (along the length of the grain vs cross grain), offers the possibility of significantly improved internal damping due to this mechanism alone.
IAC, it occurs to me that plywood, with its orthogonal alternate layer grain orientation with their significantly different shear strengths (along the length of the grain vs cross grain), offers the possibility of significantly improved internal damping due to this mechanism alone.
Saturnus said:
Well, there's 3 axii, since it's built with layers, alternating the side of the grain, then we could say two axii are similar, length and width. Those are the two interesting axii for loudspeaker enclosures. The edge axii isn't very interesting, since the loudspeaker enclosure will not "flex" in that axii. It's not similar to the two other axii, but who cares.
Since you assure me it's not the same in all axii, can you bring a technical document to add weight to your insurance ?
Well, in this thread, we only talk specifically about a specific material, which is multi-layered, void free, thick baltic birch plywood. Why would we need to include other types of plywoods ?
We could compare it to a specific member of the MDF group if you want to. You could try to find a member of that group with a Young Modulus similar to multi-layered, void free, thick baltic birch plywood since you seem familiar with members of that group.
Absolutely. I just object to the notion that a "perfect material" exist as it is physically impossible. The object is to seperate two different states of energy, in this case air pressure, and we all know that it is physically impossible two completely seperate two different states of energy. So the solution has to be some sort of viable compromise.
Some designs solve the problem with a very stiff material, or inherently rigid designs, others by controlled dampening. It's a choice of design but no one way is inherently better suited for audio than another.
Some designs solve the problem with a very stiff material, or inherently rigid designs, others by controlled dampening. It's a choice of design but no one way is inherently better suited for audio than another.
planet10 said:
MJL21193 said:Absolutely the most sensible way of building, no matter what the material is. Dave showed me the light.
Hi planet10 and MJL21193 ! Can you share the Eureka moment ? I just read a fair part of that interesting discussion and would like to follow it into that next thread where the light was seen...
thoriated said:
Seems like thoriated saw the light too ! Just kidding thoriated !
You better explained what I wanted to say, since you possess a better written english skill than me. You also added a few good points in that post.
"orthogonal alternate layer grain orientation" <-- Well said, thanks.
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