Octave Mandolin deflection tunning

[GaryTimmons]

I'm beginning my next build, a guitar body octave. I've been using deflection tunning for my A and F models but I'm not sure what I should expect or shoot for building an octave. Any help or suggestions are greatly appreciated. Scaled down L5 to 80 percent. 14" lower bout. Thanks

[Marty Jacobson]

Deflection tuning is all about repeating a known good configuration. Unless someone else has a known good deflection number for a specific force at a specific location on an octave mandolin top of a specific design, then it's all just experimentation.

That being said, isn't the string tension of an octave mandolin very similar to that of a normal mandolin? And isn't the break angle similar? So... shouldn't the deflection be similar?

[GaryTimmons]

I expect there will be a bit of experimentation. I got my spec's for deflection tunning for the mandolins from the Cafe and American Lutherier mag. Thought someone else may have explored some on the octaves. I take notes on my builds and compare them. Before I start carving the top and back I'll know the string tension and follow a method and keep notes. I've been wanting to build these for the last year or so. Hopefully the moulds will be made within the week. And I'll have a pair of rims soon. Thanks Marty

[j. condino]

The specs for a LLoar era F5 are close to the same era mandola and those in turn are close to a Stradivarious cello. It is often amazing to me that on a well made double bass the optimal rib thickness is approx. 2.4-2.7mm. Lots of mandolin builders go thicker than that.

Most builders I know use the specs for a nice 1920s / 1930s 16" L5 as their starting point fior an octave mandoln. DON'T use an old Gibson mandocello as your reference (unless you want that overbuilt wet cardboard dull thump...). Then drop the fairy dust & unicorns pseudo science by non-scientists, string the instrument up and listen to it as you play music on it and make minor carving and scraping adjustments. Everything you need is in your hands and ears.

Use good materials, don't overbuild it, don't waste time on unnecessary bling, and you'll have a nice sounding octave mandolin.

[GaryTimmons]

I've been studying the early 16" L5's this last year. I've built about 20 F5's and A5's combined and started gathering materials over the last year. I've got big leaf maple and Sitka spruce on hand and live a short drive from LMI if need be. I've been using deflection tunning for the mandos with good success. It's given me one more reference point to gauge my work or maybe rather a methodology to help me with consistency. In the same light I wanted to know if someone was using deflection tunning for these little beasts.

[Wrnchbndr]

I gotta say that I've never encountered the term "deflection tuning" before I read this post. I googled it. I'm going to guess that this is something best described and taught first hand by demonstration. I'll certainly do more reading up on this. I'm not an acoustic instrument builder but I'd certainly like to understand the concept. I build solid body mandolin family instruments but the more you know the better.

Is this something related to the way a violin subtly changes its geometry when first strung up? That is something I'm familiar with -- string tension and its effect on the sound board and to a lesser extent the neck and the entire structure?

[Marty Jacobson]

I gotta say that I've never encountered the term "deflection tuning" before I read this post. I googled it. I'm going to guess that this is something best described and taught first hand by demonstration. I'll certainly do more reading up on this. I'm not an acoustic instrument builder but I'd certainly like to understand the concept. I build solid body mandolin family instruments but the more you know the better.

Is this something related to the way a violin subtly changes its geometry when first strung up? That is something I'm familiar with -- string tension and its effect on the sound board and to a lesser extent the neck and the entire structure?

The concept is pretty simple - an instrument is a machine.
If I can get one machine to work the same way as a previously-built, known good machine, then it will do the same job (i.e. sound identical).

It gets complicated quickly because wood varies from piece to piece. So a 2mm thick piece of spruce might be quite a bit stiffer than another piece from the same tree. It might also have different internal damping characteristics, which are not easy or intuitive things to gauge.
Deflection tuning gives us a way to see if the structure is behaving the way we expect it to (at least in one regard) pretty objectively.

[Rob Roy]

Collings uses deflection tuning on probably a larger scale than anyone else in the business to great success. They're known for their consistency and loudness.