The Tonewood Project

[Mark Kelly]

Will

The note regarding the time was only to say that the information above is also two years old and I've learnt a lot in that time, so things have changed.

The boundary thing is simply that there's a reflection coefficient at any boundary between two materials which is given by (Z1-Z2)^2/(Z1 +Z2)^2. This drops to zero if the two impedances are the same and increases as the impedance mismatch increases. An interesting aside is that because of the square law relationship interposing an intermediate impedance reduces the total reflection*.This is one of the reasons for incorporating boron fibre: the acoustic impedance of a boron composite is between those of carbon and stainless.

I basically used stainless because I like it acoustically and I couldn't bond Ti reliably. I think I've worked out a method of bonding Ti so the next prototype will incorporate that.

The loss tangent I'm using is different from, but analogous to, the RF loss tangent: they're both ratios between an energy loss component and an energy storage component, it's just that the components are different in each case.


* Aside for those interested in TT design: I spent a bit of time and effort developing a platter material based on this concept and the use of high modulus and high density fillers in a polymer matrix. The intention was to achieve gradual impedance change through the platter from the impedance of PVC at the top to that of stainless at the bottom. The fun part was getting the particles to settle at the right velocity, eventually solved using the "Reverse Brazil Nut Effect". I'm not joking, that's actually a thing.

[hmbatrail]

We're still talking about building a bicycle, right? Not trying to launch a satellite or anything? Just a bicycle?

[spopepro]

We're still talking about building a bicycle, right? Not trying to launch a satellite or anything? Just a bicycle?

Without stepping on Mark's toes here, it's say it's not about building a bicycle--it's an engineering exercise which might result in an outstanding bicycle. But it's more about the engineering than the transportation.

Mark is somewhat legendary in DIY audio circles (to me at least...) as one of the few to really put the maths and science behind design choices, which is rare in audio. Granted, I'd personally rather have a 301 plinth made with these principles than a bicycle... but it's enjoyable for what it is in any case.

-Jared

[Mike Mcdermid]

Without stepping on Mark's toes here, it's say it's not about building a bicycle--it's an engineering exercise which might result in an outstanding bicycle. But it's more about the engineering than the transportation.

Mark is somewhat legendary in DIY audio circles (to me at least...) as one of the few to really put the maths and science behind design choices, which is rare in audio. Granted, I'd personally rather have a 301 plinth made with these principles than a bicycle... but it's enjoyable for what it is in any case.

-Jared

I used to do these cabinet things for an audio company and it was full of people who said blah blah blah.....eventually it came down to a guy in a room who went .....that one and pointed with his very experinced finger.....who knew stuff

[Mark Kelly]

We're still talking about building a bicycle, right? Not trying to launch a satellite or anything? Just a bicycle?

Yep, just a bicycle.

I like bicycles.

[Mark Kelly]

For those interested, I found a nice explanation of the Reverse Brazil Nut Effect

[summilux]

Mark, have you thought about making a tonearm this way?

[Mark Kelly]

You really don't want to get me started about tonearms.

Angling for 90° - tangential pivot tonearms - Page 22 - diyAudio

[summilux]

I was hoping that you would be the next Sheu.

[ru-tang]

sooo I have no idea about the tonal mathematics you guys are discussing, but I think this project is really cool.

I would like to point out a product that may help you make your tubes in a faster and cleaner method. You can buy treated heat shrink tubing from Soller Composites. Its like the heat shrink for electronics but it comes in really large diameters and is treated on the inside to not bond with epoxy. I make wood whitewater kayak paddles, and I use it to bond woven composite sleeves to paddle shafts. You wet out the material over the wood, slip this stuff over, and hit it with a heat gun. It compresses and squeezes out any excess resin. When it cures, you slice it off, and you have an almost perfect surface. For secondary layers, you can scuff it up with sandpaper, or hit it with steel wool for topcoats.

http://composites.sollerpaddles.com,carbon-fiber,carbon,fiber,sleeve,fabric

[Mark Kelly]

Thank you for the tip, I will look into it.

The problem you are addressing is, however, one I had two and a half years ago. I'm now using a filament winder and a spiral wrap of woven poly ribbon with a compressive overwrap. Works a treat.