What Wood Type?

[Matthew J Poes]

I also wanted to comment on HDF, since, you know, when do I not have a comment I need to make!

I think the term is misused in the speaker business. HDF is Hardboard. When is the last time you saw 3/4" HDF? I myself was really confused. I had heard that HDF was hardboard and then saw the term thrown around with speaker enclosures. I went to a local specialty shop and asked for HDF in a 3/4" size. The guy told me he would have to see if he could order that, as it wasn't stocked. Not only is it not stocked, I had to order an entire lot because it needs to be made up in sizes greater than 1/2". I asked what HDF was, thought maybe I was confused. Turns out, HDF is hardboard and is rarely if ever used in thicknesses of 3/4" or more.

A lot of speaker manufacturers claim to be using HDF instead of MDF, but when you look at the raw enclosure, it sure looks like MDF. My understanding is that, as expected, MDF and HDF are basically defined by their density and as such, there is an accepted range between the particle board, MDF, and HDF. The primary differentiator is particle size of the wood byproduct used to produce a panel. I sat on the phone with the manufacturer (who actually makes the boards in Canada, and ships to here) and sent him emails of what I was reading, and what I wanted it for. He came back and told me that he thinks that the manufacturers probably are buying a high-grade MDF that is on the denser end of the scale and calling it HDF because it probably falls onto the low end of the HDF scale. This high-grade MDF is not only plentiful but even in stock locally. He told me that 3/4" HDF, as defined by the industry, is usually only made on an as needed basis for specialty purposes, often like CNC carving or furniture. He told me that it nearly doubles the weight of the board. He also told me that while the primary differentiator of MDF and HDF is the density, it does impact how they are made, with MDF having more fillers, like wax.

In other words, HDF is masonite and masonite is really hard to find in 3/4" sizes. If anyone knows differently, I'd love to know where you got your info and how I can obtain HDF in such a thickness. From the week I wasted investigating it, I left concluding the term is used wrong by speaker companies.

 

[Matthew J Poes]

LOL tell me about how well bamboo grows, I have a stand of bamboo in my yard (as well as pine trees).

Yup! My wife was growing one in our kitchen. In like 2 years it was touching the ceiling. We cut it, it forked, twice as much touched the ceiling. We were terrible about watering it, it still grew, it didn't die!

 

[everettT]

Got plenty of bamboo around me. That's a lot of work to get boards.

 

[speakerman39]

We were terrible about watering it, it still grew, it didn't die!

That's funny. I have experienced the same exact thing w/both of my ex-wives..........LOL!!!!! Sorry Matthew, I am on a roll here!


Cheers,

Phil

 

[2channel lover]

LOL tell me about how well bamboo grows, I have a stand of bamboo in my yard (as well as pine trees).

In a prior job, I had a little experience with wood mostly in a construction environment and bamboo is expensive,. but at that time was deemed to be the most eco friendly, sustainable wood. In flooring (our purpose) it wasn't anywhere near the most expensive wood. Granted we're talking about speakers cabinets and not flooring, but it makes you wonder why a 4'x8' sheet would be as high as $350-$500 a sheet.

 

[highfigh]

If it is for a full range speaker, the best enclosures are usually massive and well damped. This makes MDF with CLD walls an idea solution. It helps stop sound from transmitting out of the box panels or adding distortion. MDF is better damped than plywood, so in general, is a better material for that kind of speaker.

Subwoofers or boxes primarily used for low frequencies will find mass and damping a detriment, not an aid. Instead, you want rigid. This makes plywood a far better material as it is much more rigid than MDF. Damping is of little to no value at very low frequencies, though I would argue that Damping could have benefit in some special circumstances.

That box looks like a subwoofer box? If so, I would use void free plywood like Birch.

But, as long as the mass and stiffness of the box are sufficient to prevent movement due to the the internal pressure from the driver(s), the HP crossover for the low frequency driver(s) is low enough AND the resonance frequency of the box's panels is out of the LP range, it shouldn't produce much, if any, sound.

There's a guy in some audio/musician forums (fora?) who has been designing and building boxes using Birch plywood for years- one of the goals is to decrease the weight because initially, he was only making them for bass guitar players and there's no point in making it so heavy it needs a 40 mule team to get it into the venue. He uses fairly thin plywood with strategically placed bracing and people like these boxes quite a bit. He has since gotten into some work with subwoofers.

 

[highfigh]

I think what was meant is that it's a reed or type of grass, so it grows substantially faster and with less resources than does a pine tree. MDF is made from sawdust, basically, of uniform size. Any tree takes more to grow than Bamboo, but MDF remains far cheaper (and in some ways, is a better product for the environment) than Bamboo because its made from a byproduct of the existing lumber industry that would otherwise go to waste, or in some case, burned. Utilizing a new material to make a product that already could be made from the byproduct of an existing material that isn't going anywhere is never going to be better for the environment. Today, a lot of MDF uses binders that are green in nature and not as harmful as they once were, and Bamboo needs the exact same kinds of binders for its production.

What we need is Bamboo studs. Once they start making Bamboo engineered studs, maybe we could see a shift in the lumber industry that is actually better for the environment (though I'm sure our lust for building would lead to mass deforestation and replacement with bamboo genetically engineered to grow in a variety of climates).

The hard part of using Bamboo for studs is that the shoots always taper as it goes from the trunk to the tip. AFAIK, Bamboo will grow in all but the coldest climates but even there, the warm season is still fair game because it grows so fast.

The guy who sharpens blades and cutting tools for me (and others) described particle board and MDF as "the hot dog of building materials".

 

[highfigh]

In a prior job, I had a little experience with wood mostly in a construction environment and bamboo is expensive,. but at that time was deemed to be the most eco friendly, sustainable wood. In flooring (our purpose) it wasn't anywhere near the most expensive wood. Granted we're talking about speakers cabinets and not flooring, but it makes you wonder why a 4'x8' sheet would be as high as $350-$500 a sheet.

Tiny strips- lots of tiny strips, which have to be cut with some degree of accuracy, laid out, glued to a substrate and made flat. Particle board and MDF are just some kind of mixture that's dropped onto a flat conveyor, pressed & cured before cutting, but even that's becoming expensive. It's not terribly expensive at Menard's, but I stopped buying their lumber and sheet goods a long time ago.

 

[2channel lover]

Tiny strips- lots of tiny strips, which have to be cut with some degree of accuracy, laid out, glued to a substrate and made flat. Particle board and MDF are just some kind of mixture that's dropped onto a flat conveyor, pressed & cured before cutting, but even that's becoming expensive. It's not terribly expensive at Menard's, but I stopped buying their lumber and sheet goods a long time ago.

Thanks...I do understand the process of making a large sheet is expensive...with bamboo being much smaller strips would add to the cost. Still...the margin tells me there has to be more reason for such a price disparity.

Many of the highend residential trim guys use MDF in non moisture indoor situations now and claim it's more stable than real wood.

 

[lovinthehd]

So @montanhasan have you decided which way to go?

 

[Matthew J Poes]

Thanks...I do understand the process of making a large sheet is expensive...with bamboo being much smaller strips would add to the cost. Still...the margin tells me there has to be more reason for such a price disparity.

Many of the highend residential trim guys use MDF in non moisture indoor situations now and claim it's more stable than real wood.

Mdf and all engineered woods are more dimensionally stable than solid wood. Glue doesn’t expand and contract like wood, and wood can be oriented such that the grain goes in different directions to counter the expansion across the grain.

 

[Verdinut]

Probably, the only wood which is really stable is the expensive teak because of natural oils and rubber locked right into the tight grain of the wood.

All woods contain oils that protect the tree, but teak can retain these oils and its rubber even after being felled and processed. Because of this, teak has greater naturally weather-resistant properties than just about any other type of wood. When dried to a proper moisture level, the oils and rubber weatherproof the wood. The oils also protect the wood from dry rot, which is a common problem in older wooden furniture. What's more, the oils and rubber protect the heart of the wood from invaders like fungi and parasites that can destroy other woods.

 

[Matthew J Poes]

Probably, the only wood which is really stable is the expensive teak because of natural oils and rubber locked right into the tight grain of the wood.

All woods contain oils that protect the tree, but teak can retain these oils and its rubber even after being felled and processed. Because of this, teak has greater naturally weather-resistant properties than just about any other type of wood. When dried to a proper moisture level, the oils and rubber weatherproof the wood. The oils also protect the wood from dry rot, which is a common problem in older wooden furniture. What's more, the oils and rubber protect the heart of the wood from invaders like fungi and parasites that can destroy other woods.

Could be. I’m by no means a wood expert. When I was studying sound proofing and transmission loss I had to pick a topic for a end of course paper and chose the transmission loss properties of common loudspeaker enclosure materials above and below the resonant frequency. The only reason I know much of anything about this is that paper. A while after finishing the paper I posted a bunch of my conclusions over on AVS and it created a bit of controversy too, oddly enough.

I didn’t have the ability to do much real world testing so most of what I did was theoretical, modeling, or very specific tests using a contact microphone accelerometer. Still, nothing I found was in any way different from what is accepted in the industry.

Plus, as @shadyJ likes to remind me, none of this was ever tested in listening tests or any reasonable kind. It’s not like we have any idea if any of this stuff matters.

For instance both models of and actual tests of enclosures show that they proruce non-linear distortion along with some linear distortion (can negatively impact the polar response, steady state response, and add group delay. Yet surely the driver is going to remain the dominant source of this for the most part. So does it matter? It’s easy to dismiss, but truth be told, we have no idea. Still, it’s super easy to get rid of using proper enclosure design steps like composite damped wall construction, appropriate bracing, internal damping, etc. most of this isn’t very expensive.

 

[highfigh]

Thanks...I do understand the process of making a large sheet is expensive...with bamboo being much smaller strips would add to the cost. Still...the margin tells me there has to be more reason for such a price disparity.

Many of the highend residential trim guys use MDF in non moisture indoor situations now and claim it's more stable than real wood.

It is more stable and it's flatter, more smooth, routs beautifully, doesn't have grain that may show through the paint and when it's pre-primed, it's ready for paint, unlike pre-primed real wood. That said, nailing or screwing into the edge of particle board or MDF is risky because either will split if the fastener is large diameter or particularly long. MDF is described as a paper product because the particles aggregate in layers. The edges definitely need to be sealed when painting, though.

Reason for the price difference? It's trendy.

 

[highfigh]

Probably, the only wood which is really stable is the expensive teak because of natural oils and rubber locked right into the tight grain of the wood.

All woods contain oils that protect the tree, but teak can retain these oils and its rubber even after being felled and processed. Because of this, teak has greater naturally weather-resistant properties than just about any other type of wood. When dried to a proper moisture level, the oils and rubber weatherproof the wood. The oils also protect the wood from dry rot, which is a common problem in older wooden furniture. What's more, the oils and rubber protect the heart of the wood from invaders like fungi and parasites that can destroy other woods.

I searched to find info about rubber in Teak and didn't find anything- the link mentions both, but they're different species and are native to different places.

http://www.differencebetween.info/difference-between-teak-wood-and-rubber-wood

Teak also has a high silica content, which makes life difficult for cutting tools. WRT the oils and wax in Teak make glue-up difficult and it needs to be wiped well with a strong solvent, like Acetone beforehand.

 

[highfigh]

Could be. I’m by no means a wood expert. When I was studying sound proofing and transmission loss I had to pick a topic for a end of course paper and chose the transmission loss properties of common loudspeaker enclosure materials above and below the resonant frequency. The only reason I know much of anything about this is that paper. A while after finishing the paper I posted a bunch of my conclusions over on AVS and it created a bit of controversy too, oddly enough.

I didn’t have the ability to do much real world testing so most of what I did was theoretical, modeling, or very specific tests using a contact microphone accelerometer. Still, nothing I found was in any way different from what is accepted in the industry.

Plus, as @shadyJ likes to remind me, none of this was ever tested in listening tests or any reasonable kind. It’s not like we have any idea if any of this stuff matters.

For instance both models of and actual tests of enclosures show that they proruce non-linear distortion along with some linear distortion (can negatively impact the polar response, steady state response, and add group delay. Yet surely the driver is going to remain the dominant source of this for the most part. So does it matter? It’s easy to dismiss, but truth be told, we have no idea. Still, it’s super easy to get rid of using proper enclosure design steps like composite damped wall construction, appropriate bracing, internal damping, etc. most of this isn’t very expensive.

ASTM may have more useful info about the STC and NRC of wood products relating to this application. I'm sure some speaker manufacturers have used different materials and tested for the differences, but in more than 40 years in audio, I haven't seen or heard proof of this. Simple curiosity must have entered the process though, right?

FWIW, I built a box for a sub that needed to be low-profile because it was to be placed on top of a cabinet in a living room and I don't know why, but I bought some MDF from Menard's. That was the last time I bought it from that place. It was flexible, felt damp and it wasn't very hard. I cut the pieces and glued it up, then installed the driver after it had dried. It was also the only time I built a box without some kind of mechanical fastener- I had read so many comments from people making speaker boxes here and on other forums who said it didn't make any difference but it really does. I don't know how they came to that conclusion, but a butt joint is never as strong and groove/dado is even stronger. The box resonated badly, so I used drywall screws along the edges and across the brace- that made a huge difference.

 

[2channel lover]

It is more stable and it's flatter, more smooth, routs beautifully, doesn't have grain that may show through the paint and when it's pre-primed, it's ready for paint, unlike pre-primed real wood. That said, nailing or screwing into the edge of particle board or MDF is risky because either will split if the fastener is large diameter or particularly long. MDF is described as a paper product because the particles aggregate in layers. The edges definitely need to be sealed when painting, though.

Reason for the price difference? It's trendy.

I think the bottom line is they can get it.

 

[Verdinut]

I searched to find info about rubber in Teak and didn't find anything- the link mentions both, but they're different species and are native to different places.

http://www.differencebetween.info/difference-between-teak-wood-and-rubber-wood

Teak also has a high silica content, which makes life difficult for cutting tools. WRT the oils and wax in Teak make glue-up difficult and it needs to be wiped well with a strong solvent, like Acetone beforehand.

When I got married, we bought a Teak dining room table and chair set which was imported from Denmark. The table is still amazing after more than 40 years but with the chairs, the legs ended being unglued after twenty odd years and some broke. We finally replaced all the chairs.

 

[Verdinut]

I searched to find info about rubber in Teak and didn't find anything- the link mentions both, but they're different species and are native to different places..

The article relating to rubber in teak:

https://home.howstuffworks.com/home-decor/decorating-styles-techniques/teak-wood-furniture1.htm

 

[Matthew J Poes]

ASTM may have more useful info about the STC and NRC of wood products relating to this application. I'm sure some speaker manufacturers have used different materials and tested for the differences, but in more than 40 years in audio, I haven't seen or heard proof of this. Simple curiosity must have entered the process though, right?

FWIW, I built a box for a sub that needed to be low-profile because it was to be placed on top of a cabinet in a living room and I don't know why, but I bought some MDF from Menard's. That was the last time I bought it from that place. It was flexible, felt damp and it wasn't very hard. I cut the pieces and glued it up, then installed the driver after it had dried. It was also the only time I built a box without some kind of mechanical fastener- I had read so many comments from people making speaker boxes here and on other forums who said it didn't make any difference but it really does. I don't know how they came to that conclusion, but a butt joint is never as strong and groove/dado is even stronger. The box resonated badly, so I used drywall screws along the edges and across the brace- that made a huge difference.

The last box I built doesn’t use any screws, but i did use those little grooved wood posts that you drill a hole for and put in place. I did it in a. Goofy way but I think it’s a good approach for strength. I used a special viscoelastic high-strength glue. I glued and clamped the box. Then drilled a hole the length of the dowel plus 1/2”. I filled the hole with glue and inserted the dowel. I wiped off excess and let dry. I finished with a finishing putty before paint. I did this instead of screws.

Why would ASTM have anything on this? Maybe. I didn’t find anything in the journals other than some Harman papers. Some old stuff from Bell labs.