Coulomb said:
I'm not sure about American brand names but if it's indication of origin, then no. They certainly aren't the same. The last samples of plywood I recieved from several Russian manufacturers is far inferior to the Finnish (Baltic) supplier we normally use.
A good rule of thumb is that each ply should be less than 2mm, and that each layer including the outer (sanded) layers should not vary more than 0.25mm. Futhermore the board should not vary more than 0.1mm in thickness per meter in any direction.
Here's a link to my preferred plywood type for speaker building.
http://w3.upm-kymmene.com/upm/inter...chPremiumEN.pdf/$file/WISA_BirchPremiumEN.pdf
Coulomb said:
Well sometimes, Russian Birch and Baltic Birch are both used as I've seen on several wood suppliers. I don't know if Russian Birch is really from Russia, or used interchangeably with Baltic Birch...
As Saturnus said, the quality can vary depending on the country of origin, or the supplier...
Well, for the number of ply, a "standard" grade you can often find is 13 ply for 3/4".
You can often find some extremes, like this Aircraft Birch Plywood... 20 ply for 10 mm... http://www.thomescanada.com/html/acplywood.html
I always think of speaker cabinet as musical instruments. It is easy to compare a cabinet to a classical guitar, an electric guitar, a violin or a double bass.
What happens when you make a guitar with MDF and lacker ? It sounds really bad. Acrylic violins ? Bad too.
When building a speaker, the material used, the mounting technique, the joints and the lacker will form the instrument.
We have 2 choices:
- make the cabinet dead
- make the cabinet participate/work with the driver
If choosing the first option, the effort is on making the cabinet disappear.
If working with the second option, you have to give a voice to the cabinet. I am not an expert ... but my next step is trying to find a old luthier that is willing to share his secrets
http://en.wikipedia.org/wiki/Antonio_Stradivari
What happens when you make a guitar with MDF and lacker ? It sounds really bad. Acrylic violins ? Bad too.
When building a speaker, the material used, the mounting technique, the joints and the lacker will form the instrument.
We have 2 choices:
- make the cabinet dead
- make the cabinet participate/work with the driver
If choosing the first option, the effort is on making the cabinet disappear.
If working with the second option, you have to give a voice to the cabinet. I am not an expert ... but my next step is trying to find a old luthier that is willing to share his secrets
http://en.wikipedia.org/wiki/Antonio_Stradivari
What I don't like about the title of this thread is that it presumes a speaker cabinet should be made out of one material exclusively. That seems silly. Different panels probably have different requirements, and braces have other needs entirely. Moreover, it makes logical sense that combining materials (e.g. a baffle made using two panels of MDF or ply, with a layer of viscous glue between) may offer superior performance to a single material.
The least-sounding rectangular cabinets I've heard have been Tannoy's, based on their DMT principles. Basically, take a hardwood "spaceframe" and glue flat MDF panels to it.
FWIW, my current main system LCR cabinets are made from some sort of plywood (don't know what; I commissioned them and trusted their builder to make good decisions; they're painted but he shot me a picture before painting), cardboard (half-cylinder), plastic, glue, and MDF. The internal bracing is MDF (the shelf brace) and oak (dowel connecting the top and bottom endcaps. They definitely make for great-sounding speakers, though I tend to put most of that on the crossover design and low diffraction due to the large roundovers on all surfaces.
The least-sounding rectangular cabinets I've heard have been Tannoy's, based on their DMT principles. Basically, take a hardwood "spaceframe" and glue flat MDF panels to it.
FWIW, my current main system LCR cabinets are made from some sort of plywood (don't know what; I commissioned them and trusted their builder to make good decisions; they're painted but he shot me a picture before painting), cardboard (half-cylinder), plastic, glue, and MDF. The internal bracing is MDF (the shelf brace) and oak (dowel connecting the top and bottom endcaps. They definitely make for great-sounding speakers, though I tend to put most of that on the crossover design and low diffraction due to the large roundovers on all surfaces.
Old Philips "hi-Q" full range speakers used exactly this technique. A single 8" fullrange driver did duty, and the stuffing was a pillow of natural cotton (seeds and all).
They sounded pretty amazing back in the day, but I was about ten years old, so I don't remember what they sounded like, only that I felt like dancing when they came on
My pennyworth, borne from 20 years of experience trying to get it right is:
Baffle: Stiff and dense as possible. By the time you've made the driver cutouts the baffle can be suprisingly weak. I don't go overboard on thickness either. Cones are pretty transparent. If you clog the basket window with material you can definately hear the coloured backwave. My favorite material is 15mm paper grade Tufnol. Stiff as hell, relatively non-resonant and workable with woodworking tools.
Shell: Constrained damped layers- I go for a core of quality dado joined 15mm Birch ply, then clad the large area panels with two layers of 8mm MDF, just bonded with a lossy flexible glue, no fixings. Cork tile adhesive or silicone is good. You have to plan what to do with the edges cosmetically, dont make it up as you go along!
This will give you a cabinet that contributes almost nothing in terms of panel resonance and smearing due to poor mechanical stifness.
The contribution from the driver backwave coming through the cone is another matter though! Thats very hard to control. I just avoid similar dimensions and use the golden mean or Phi whenever I can.
Simon
Baffle: Stiff and dense as possible. By the time you've made the driver cutouts the baffle can be suprisingly weak. I don't go overboard on thickness either. Cones are pretty transparent. If you clog the basket window with material you can definately hear the coloured backwave. My favorite material is 15mm paper grade Tufnol. Stiff as hell, relatively non-resonant and workable with woodworking tools.
Shell: Constrained damped layers- I go for a core of quality dado joined 15mm Birch ply, then clad the large area panels with two layers of 8mm MDF, just bonded with a lossy flexible glue, no fixings. Cork tile adhesive or silicone is good. You have to plan what to do with the edges cosmetically, dont make it up as you go along!
This will give you a cabinet that contributes almost nothing in terms of panel resonance and smearing due to poor mechanical stifness.
The contribution from the driver backwave coming through the cone is another matter though! Thats very hard to control. I just avoid similar dimensions and use the golden mean or Phi whenever I can.
Simon
simon5:
Young's modulus is the focus of the O.M. ( Opposite Moduli ) I mentioned earlier:
Re: Speaker Builder 5/96 ( Hajo Prodan ). The author explored creating amalgams of substances with dramatically differing Young's Modulus and acoustic properties.
From my limited experience, it helps when applied to panel layering as well
One untested material I have considered in an OM sandwich is the commercial tile backer boards.
These are approx .25 thick and a mixture of cement utilizing polystyrene(?) beads as the "aggregate" instead of pebbles.
Perhaps this could offer some OM benefits.
Young's modulus is the focus of the O.M. ( Opposite Moduli ) I mentioned earlier:
Re: Speaker Builder 5/96 ( Hajo Prodan ). The author explored creating amalgams of substances with dramatically differing Young's Modulus and acoustic properties.
From my limited experience, it helps when applied to panel layering as well
One untested material I have considered in an OM sandwich is the commercial tile backer boards.
These are approx .25 thick and a mixture of cement utilizing polystyrene(?) beads as the "aggregate" instead of pebbles.
Perhaps this could offer some OM benefits.
I believe you can get back issues from:
http://www.audioxpress.com/magsdirx/backissues/BISSBM.htm
http://www.audioxpress.com/magsdirx/backissues/BISSBM.htm
I saw that article, I remember there were granules of rubber and metal in a resin matrix to scatter travelling waves in the material.
There would have been difficulties stopping the granules separating under gravity as you cast the panel I should imagine. A nightmare for DIY!
I also remeber the author was going into commercial production at the time of writing. Wasn't he german? I wonder what became of the idea.
Simon
There would have been difficulties stopping the granules separating under gravity as you cast the panel I should imagine. A nightmare for DIY!
I also remeber the author was going into commercial production at the time of writing. Wasn't he german? I wonder what became of the idea.
Simon
Advice Needed
I want to make a double-TQWT, this one:
http://www.troelsgravesen.dk/JA8008_DTQWT_cabs.htm
What would you think of Douglas fir / oregon pine for the cabinet?
Would it alter the sound, and in what way?
Oregon pine is a very hard and dense solid wood, occasionally used in musical instruments.
I want to make a double-TQWT, this one:
http://www.troelsgravesen.dk/JA8008_DTQWT_cabs.htm
What would you think of Douglas fir / oregon pine for the cabinet?
Would it alter the sound, and in what way?
Oregon pine is a very hard and dense solid wood, occasionally used in musical instruments.
Speaker Builder also had a reader who built his cabs from a mix
of recycled tire rubber granuales,sand and epoxy. I would be a
little scared of this the more exposure to epoxy you have the more likely you are to get an allergic reaction.
I believe Planet10 pointed out solid wood can split or warp on
you. I personaly saw a lovely DIY enclosure out of solid oak too
bad this 60" tall enclosure had a split right down the front baffel!
Darn seems like baltic burch is the way to go.
of recycled tire rubber granuales,sand and epoxy. I would be a
little scared of this the more exposure to epoxy you have the more likely you are to get an allergic reaction.
I believe Planet10 pointed out solid wood can split or warp on
you. I personaly saw a lovely DIY enclosure out of solid oak too
bad this 60" tall enclosure had a split right down the front baffel!
Darn seems like baltic burch is the way to go.
The point about damping is that you simply broadband a resonance with it.
Doing this just increases the probability that the resonance will be excited, and research shows that a single high q resonance is far less audible than the series of low q resonances that are the result of damping.
As I pointed out previously the lowest panel vibration amplitude is given by the stiffest material and of all homogeneous materials steel is by far the stiffest common one, (Beryllium is stiffer than steel but getting and paying for 3/4 inch Beryllium plate is a problem).
Another point about panels is that the stiffness increases as the cube of the thickness.
This results in 4.3mm. steel being equally as stiff as 20mm. plywood or mdf.
It is true that the steel panel will have a higher q resonance, but the probability of it being excited on music signals is very low and in practice the other materials have more colouration.
rcw.
Doing this just increases the probability that the resonance will be excited, and research shows that a single high q resonance is far less audible than the series of low q resonances that are the result of damping.
As I pointed out previously the lowest panel vibration amplitude is given by the stiffest material and of all homogeneous materials steel is by far the stiffest common one, (Beryllium is stiffer than steel but getting and paying for 3/4 inch Beryllium plate is a problem).
Another point about panels is that the stiffness increases as the cube of the thickness.
This results in 4.3mm. steel being equally as stiff as 20mm. plywood or mdf.
It is true that the steel panel will have a higher q resonance, but the probability of it being excited on music signals is very low and in practice the other materials have more colouration.
rcw.
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