IME I have found that particle board laminated both sides (ie. the stuff they use for kitchens) is pretty good for enclosures. Lacks the stiffness of ply, but better than MDF (again IME).
Cheers,
Alex
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Radiation resistance is another point which I didn't mention in my previous reply. See below.
I still disagree. Read on:
You're missing the energy term. E=MC^2. You have to transfer energy from the enclosed air into the box in order to transfer it from the box into the surrounding air. Doubling the mass will halve the acceleration, but the amount of energy transferred per time unit is unchanged.
So a heavier box will vibrate at a lower amplitude and frequency, but it will vibrate for longer. Radiation resistance...
(All of this assumes no change in compliance with the change in mass.)
On the 3 cabinets I have seen this in:
Two used a plastic terminal cup recess. One had the crossover mounted on the inner side.
The other box used a thin piece of hardboard to mount the terminals inside a cutout in the back panel.
No. Most terminals are too short to mount through the thickness of a back panel, let alone through the thickness of a (usually thicker) piece of baffle material.
I recommend flooring grade particle board. It is dense, stiff, and water resistant (designed to withstand rain until you get the roof on.) And I have a good stock of aged and finished solid oak sheets waiting for a deserving design. Remember when beds had wire bases, and solid oak head and tailboards? The thrift shops and junkyards here were full of the boards some years back. They could hardly give them away. I bought a couple of dozen for a buck or two each. How much would you pay now for a dead flat sheet of solid oak, about 3/4" to 7/8" thick, and about 3 by 5 feet? (Usually made from 2 or 3 planks, joined so well the joints can only be seen by the grain change.)
I like brick boxes and baffles. They rock out. Unfortunately all baffles sound like garbage. That's why everyone isn't running out to buy those little bolt or stick on voice coils and just pasting them to any old thing that ain't actually a speaker cone. Arguing the right "tonal balance" from a baffle by choosing various materials and and construction is a bit humorous. The fact is, unless you are dealing with insanely high mass, strength, and damping, you're talking about tradeoffs in terms of sound quality. Anything you do to make a speaker box dainty is going to make it sound worse, with exception to controlling the thicknesses and contours around the drivers and edges for various reasons.
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I've used that trick before... a lot of work, fiberglassing both sides is even better, but i hate working with the stuff.
dave
Hi Don,
The entire reason I use undercoating on the interior walls of an enclosure is to disrupt energy transfer from the air to the box material (whatever it may be). Plus, this increases the damping and kills off surface waves too.
I'm sure both of us can select examples for either side of this argument. But I will say that a speaker manufacturer will do as much as they can to reduce shipping weight. They often take this concept to evil extremes, and it's also the reason why boxes are at less 1/2 the volume they should be.
Here in Canada, Particle board and MDF refer to the same thing. There is also Chipboard (nasty stuff) and other things. It's possible that what I refer to as MDF might actually be "Particle board" in your country, I'm not sure. It is very common for terms to be slightly different even across the same country, never mind different countries.
Hi AmadeusMozart,
Karlson enclosures are exactly wrong for particle board or MDF, just because of the way they are made. I'd say the same for some horn enclosures. Whenever you have a situation that doesn't allow for proper bracing, you are locked into a smaller set of possible materials to use.
The better the box is to start, and driver(s), the less messing around you need to do upstream. But then again, this applies to any material and box construction.
-Chris
Actually, the first part of your statement is exactly what I'm trying to get at there, and I agree with you 100% on that. Note that if you reduce the acceleration, you do reduce the amount of energy transfer - per unit time. Your next statement follows nicely though, the logic is fine.
As the box vibrates at a lower amplitude, it transfers a lower amplitude to the air resulting in a less audible sound. That's how a speaker cone works. So the unwanted contribution is less audible with a heavier box, even if we accept that the transferred energy is identical.
The entire reason I use undercoating on the interior walls of an enclosure is to disrupt energy transfer from the air to the box material (whatever it may be). Plus, this increases the damping and kills off surface waves too.
That's fair enough.
The cut out is simply used as another bit of material. The thickness doesn't matter since the plastic cup holes are normally cut clear through anyway. The plastic is the only thing separating inside from outside. I have seen long binding posts used through both thicknesses. Don't ask me why, but someone thought it was a good idea.
I'm sure both of us can select examples for either side of this argument. But I will say that a speaker manufacturer will do as much as they can to reduce shipping weight. They often take this concept to evil extremes, and it's also the reason why boxes are at less 1/2 the volume they should be.
Explained above. There is no need for the wood to be less thick as it's cut out straight through.
Sure, that will work as well.
Here in Canada, Particle board and MDF refer to the same thing. There is also Chipboard (nasty stuff) and other things. It's possible that what I refer to as MDF might actually be "Particle board" in your country, I'm not sure. It is very common for terms to be slightly different even across the same country, never mind different countries.
Hi AmadeusMozart,
Well, no kidding!
Karlson enclosures are exactly wrong for particle board or MDF, just because of the way they are made. I'd say the same for some horn enclosures. Whenever you have a situation that doesn't allow for proper bracing, you are locked into a smaller set of possible materials to use.
That can be don no matter what material you are using. Nulls out.
Wow.
The better the box is to start, and driver(s), the less messing around you need to do upstream. But then again, this applies to any material and box construction.
Okay, so you like Karlson's. A box made from concrete would be interesting.
-Chris
That is what you might expect, but the research (Toole) has shown that it is the opposite. The paper linked above covers the subject referring to the same work as Toole and adds some.
If you are talking about energy transfer from the air space inside the box, this is only a small part of the energy input, and if the panel resonances are sufficiently high, adequate air space damping will kill most of this energy. This leaves the predominant energy source for exciting resonances as that provided by the driver's direct connection to the box. (and no, compliant mounting is a cure worse than the problem, magnet mounting is a whole nouther thing, as exemplified by the Fujitsu TEN ellispsoids can work well, but moves us into a whole new world of complexity)
No they do not. I have a set of FH Mk3 protos here made of particle board and it is a distinctively different material. We used it as it is cheaper, and by all the research, better, than MDF, and we won't feel guilty when they go to the tip,
dave
heres what I could find showing particle board
in my youth, when I built backloaded horns, this was all we could get, MDF wasnt yet invented
YouTube - Cutting Particle Board
YouTube - table saw particle board 1200fps
btw, I just recently got a pair of Lowther horns returned from a friend
I built them maybe 30 years ago, using particle board
modified with curves in cast concrete
they have been stored for years in an old barn, and damaged from moist, but all joints are still intact, only in need of small repair job on a couple edges
I dont know, but would be a shame to scrap them, so I will try those WildBurro I got a while ago, might work, if my diy ribbon works too
in my youth, when I built backloaded horns, this was all we could get, MDF wasnt yet invented
YouTube - Cutting Particle Board
YouTube - table saw particle board 1200fps
btw, I just recently got a pair of Lowther horns returned from a friend
I built them maybe 30 years ago, using particle board
modified with curves in cast concrete
they have been stored for years in an old barn, and damaged from moist, but all joints are still intact, only in need of small repair job on a couple edges
I dont know, but would be a shame to scrap them, so I will try those WildBurro I got a while ago, might work, if my diy ribbon works too
Hi Chris, I'm afraid dave is correct. Particle board is what we used before MDF came along. Most speakers in the 70's and 80's used it. It was also known as K3. You could get it in varying densities according to the pressure used to manufacture it. IIRC there was low medium and high and 70 lbs was one of them you could buy at the local lumber yard, the other two you had to order. The particles in particle board are much larger than the sawdust used in MDF or HDF. Chipboard is often referred to as oriented strand board, aka OSB. I'm sure there are others here that are more aware of these things than I, but this is what I remember with the remaining brain cells.
I learned from my very first step with box building.....to take exstreme care when applying the glue
ends needs to be carefully soaked, several times
that was water proof white glue
Now I mostly use foaming polyurethane
But even with that, I still soak ends with glue, several times, spreading it carefully with a knife
And I even apply glue to both parts to be joined
btw, its important to remove excessive glue before it dries, or it will be a pain to remove
It seems like this last poly glue I got is more dense, and soft, kind of flexible
Less foamy than I have been used to, and gives the feeling of good strength
oh, I forgot, have some glue to remove, have to go, cheers
ends needs to be carefully soaked, several times
that was water proof white glue
Now I mostly use foaming polyurethane
But even with that, I still soak ends with glue, several times, spreading it carefully with a knife
And I even apply glue to both parts to be joined
btw, its important to remove excessive glue before it dries, or it will be a pain to remove
It seems like this last poly glue I got is more dense, and soft, kind of flexible
Less foamy than I have been used to, and gives the feeling of good strength
oh, I forgot, have some glue to remove, have to go, cheers
What sort of undercoating do you use? I would imagine it to be soft, thick compared with the wavelengths involved, and internally damped.
As others have pointed out, MDF is the same the world over.
MDF / HDF:
Manufactured from very small wood fibres with dimensions similar to those used in paper making.
Particle board / Chipboard:
A generic name for boards made from relatively large wood chips, in some cases several inches long. Usually lighter than MDF because of the air space in the wood cells and lower binder (resin) content, and can be stronger because the length of the chips forms "plies".
OSB (Oriented Strand Board):
A variant of chipboard where the wood chips are lined up parallel to each other (oriented) and then arranged in multiple "plies" in alternating layers.
Flooring grade chipboard:
In NZ, it is a board made from fibres larger than MDF but smaller than "chipboard", up to 1 cm or so. If you imagine MDF to be "white bread", flooring board is "wholegrain bread". (And chipboard is "muesli".)
The binder is a melamine resin (water resistant) and high pressures are used to make a strong and dense board. It will withstand standing water for a reasonable time, the main effect being raising of the surface grain requiring sanding if the floor is to be painted / varnished. (Floors may be rained on several times before the building is "closed in".)
Dead it may be, but here in Mississauga at the lumber stores, the terminology was the same. How am I to know in a case like that.
So, I'll describe what we used, bought as MDF. Formed wood sheets using fine wood particles and glue in a matrix. It will absorb water and swell to about 50% size and fall apart. That's serious water damage though. The stuff had to sit in water for a while before that happened. This stuff was normally stocked in various lumber stores. High density was always special order and expensive. It worked well, so we used it for all high power speaker enclosures (200 watts and up - real power).
There seems to be a couple grades of chip board. Some known as OSB, and the lighter junk known as chip board. So whatever I used (tell me) worked very well, and we knew it as MDF. It held screws very well and was pretty dense stuff. I'll admit that I have no clue what the name really is at the moment. The last time I bought this stuff was over 12 years ago.
Hi Don,
The undercoat remained pliable and thick / heavy. I think it contains asphalt or something like it. We originally used the stuff that Ford used, but moved on to better things. I'm considering it's use on our metal duct work in the house. It damps that right completely out. I have seen it in spray cans, but we used the paint on stuff. No way are you going to spray this stuff out. As a side benefit, it will seal air leaks. You shouldn't have any if your cuts are done well and the glue was spread properly.
I think any pliable coating that remains "rubbery" should work for damping out panels. I know that when knocking on a box we made, it sounded high pitched and could ring. This coating changes the sound to more of a thump (knocking on the outside) and totally kills the ring off.
Anyway, it could be that the local lumber yard or my wood guy called these by the wrong terms. I just designed the box and put some together. The stuff I used was called MDF, so I just accepted that.
-Chris
I think any pliable coating that remains "rubbery" should work
-Chris
Here we paint bathrooms with rubber stuff, before mounting tiles or painting
Theres also another type, more glue like, and good for mounting isolating materials
And theres that black tar like stuff used for roofing work
But thats nasty toxic stuff
I suppose thats Cal´s department
btw, its very good fore coating driver diaphragms
Chris, a few years ago I also had the thought, that soft rubber paint on outer surfaces would change fore the better, mostly with regards to diffraction/reflection, but have not yet tried it
I agree it will do a good job of damping highly resonant panels (changes a "bong" to a "thud"). I'm a bit more doubtful that it would do what you wanted it to do:
I suspect the amount of energy transfer will be very similar with or without the coating. The only way it could reduce the energy transfer would be if it deformed significantly (compressed, like foam) and then internally dissipated the energy so stored.
As for damping materials in general, I've been there many years ago in places such as the rec.audio.car newsgroup. For example:
Dynamat- What's it made of? - rec.audio.car | Google Groups
As for the many different names for manufactured wood, it's no big deal. Stick to the definitions I gave in my previous post and you can't go far wrong.
OSB, or 'oriented strand board", is typically made of poplar, or similar soft-wood copmposites. The "chip sizes range in size from approx. 1/4" to about the size of a Loonie (!$ coin for you non-Canucks!)
So called because approx. 60% of it's fibers are oriented in a similar direction. Typically used for sheathing, it would belong nowhere around speaker enclosures, IMHO.
Don
So called because approx. 60% of it's fibers are oriented in a similar direction. Typically used for sheathing, it would belong nowhere around speaker enclosures, IMHO.
Don
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