The three tenors - an experiment

jupiteruke

jupiteruke

Well-known member
Joined
Apr 15, 2015
Messages
265
Reaction score
251
Location
Eastern Pennsylvania / Jupiter Florida
I have a bit of a break from commissions, so I decided to conduct an experiment. I am building three tenors, with very similar top woods but different bracing/construction details. I am interested in comparing the resultant sound side-by-side. The top wood is some very fine grained redwood. Two tops are from the same board, and the third is very similar. I counted (under a microscope) 351 growth rings across the 5" board used to make the top. Picture is of a .5mm pencil point.

The three experiments from right to left:
An X braced top - a design which is my standard, and has yielded very good results. Note, no lower transverse brace, allows more of the top to vibrate I think.
Kasha braced top - I have built some Kasha instruments, and the results have been good, but I am interested in hearing this side-by-side with the X braced top. This uses wood from the same board as the X braced top.
Double-back - I read recently about having an inner back so that the instrument back does not get damped by being against the player. There are a few builders who seem to have built double-back instruments. I have a friend with a double-back Appalachian dulcimer which is quite loud. An intriguing concept, and an opportunity to figure out build issues and do something rather different. Spruce inner back (shellac on inside of top).
 

Attachments

  • WIN_20210222_09_20_41_Pro.jpg
    WIN_20210222_09_20_41_Pro.jpg
    98.6 KB · Views: 93
  • PXL_20210314_161555816.jpg
    PXL_20210314_161555816.jpg
    97.6 KB · Views: 154
Following. I was recently talking to Brian Griffin who I think is "all in" on the Kasha style now. I'm curious too though I have no budget at the moment
 
Interesting experiment although it would be nice to see a standard 3-fan braced uke as a sort of "standard control"... I am not a fan of the Kasha system, but will be interesting to hear a side by side comparison to an X-brace.
 
The thing that strikes me about Kasha is that the bracing is very strongly oriented lengthwise with the grain of the wood. I have to imagine that the top is much more flexible across the grain than along it, as a result. I feel like that would make it hard to do a comparison based purely on "amount" of bracing, in terms of deciding if it's over-braced or not.
 
three tenors - boxed up

The three tenors are boxed up. I have a rubber xylophone mallet that I use for consistent 'tapping'. The tone of the X braced tenor and the X braced/inner back are similar, with the inner-back maybe being a bit louder. The Kasha tenor is very different. Taps much lower in tone, much more base. Since the Kasha system is inherently low-G this may suit the instrument. Time will tell. (I have never been much of a believer in tapping' being a very good predictor of what an instrument will actually sound like when strung up.)
 

Attachments

  • PXL_20210316_135539284.jpg
    PXL_20210316_135539284.jpg
    95.5 KB · Views: 66
Excellent thread and great experiment. I’m curious to hear results of ukuleles actually played. I have read a few luthiers web sites about the double back. It makes sense. I can’t name them, I’d have to do a search. Very interesting. Thanks for posting.
 
dwizum said:
I've never heard of a double back but it makes sense. How is the double back itself braced?
Click to expand...

Here is a double top that I am currently building. (you can call it a double back if you wish). Although mine is a mandolin, the concept is the same. The inner top is not braced. It is free to vibrate. Some players say the inner top acts to "filter out" harsh overtones.
DSCF0001 (1).jpg
DSCF0002 (1).jpg
 
We are getting a bit off topic here... But, when I looked at the pictures posted by Tukanu what came to my mind was, "I sure would not want that false back to start buzzing or rattling around in there". I would think that you would want it well away from the sides and blocks by a generous margin to cover for expansion and contraction to avoid this potential disaster. I've never built one of these double backed ukuleles but I find the idea intriguing and the data seem to indicate it can make a real difference. Now back to our regular channel...
 
sequoia said:
We are getting a bit off topic here... But, when I looked at the pictures posted by Tukanu what came to my mind was, "I sure would not want that false back to start buzzing or rattling around in there". I would think that you would want it well away from the sides and blocks by a generous margin to cover for expansion and contraction to avoid this potential disaster. I've never built one of these double backed ukuleles but I find the idea intriguing and the data seem to indicate it can make a real difference. Now back to our regular channel...
Click to expand...

There are two schools of thought here: some build with the all the edges of the inner back secured to the sides with standard glue linings; others build with the inner back secured about half way around leaving the rest free to flex, but held back from the sides by about an 1/8" to avoid buzzing.
 
Last edited:
Tukanu said:
There are two schools of thought here: some build with the all the edges of the inner back secured to the sides with standard glue linings; others build with the inner back secured about half way around leaving the rest free to flex, but held back from the sides by about an 1/8" to avoid buzzing.
Click to expand...

I would never have thought to leave part of the inner back unattached to the sides, but rather kind of hanging there like a diving board. That would make me nervous, but it is interesting. My double-back is supported all the way around. I made some square edged kerfing. One side has the regular back glued to it, the other side has the inner back glued to the square kerfing.
 

Attachments

  • b.JPG
    b.JPG
    28.5 KB · Views: 43
jupiteruke said:
I would never have thought to leave part of the inner back unattached to the sides, but rather kind of hanging there like a diving board. That would make me nervous, but it is interesting. My double-back is supported all the way around. I made some square edged kerfing. One side has the regular back glued to it, the other side has the inner back glued to the square kerfing.
Click to expand...

Makes sense. You are trying to counter the dampened back...so you create an inner back, which needs no bracing because it's "inner". I am making an "inner top" and I want lots of flex like a top should have. Most of the double top mandolins are built this way, but it would be interesting with a ukulele.
 
Tukanu said:
There are two schools of thought here: some build with the all the edges of the inner back secured to the sides with standard glue linings; others build with the inner back secured about half way around leaving the rest free to flex, but held back from the sides by about an 1/8" to avoid buzzing.
Click to expand...

I would think that by securing the false back to the sides you have only created another "back" which would defeat the purpose of having a free vibrating body within the box. But then again, by having a sound hole in the false back, you are creating a sort of echo chamber which might make the piece of wood vibrate. Anyway, I find this idea fascinating. But does it actually work? And how much void do you have between the two plates?

Again, we are way off the thread topic. Let's see what the OP has to tell us about how that Kasha bracing works (skeptical).
 
Last edited:
Tukanu said:
There are two schools of thought here: some build with the all the edges of the inner back secured to the sides with standard glue linings; others build with the inner back secured about half way around leaving the rest free to flex, but held back from the sides by about an 1/8" to avoid buzzing.
Click to expand...

What sort of difference in the sound do you ear with the 'double top'?
 
jupiteruke said:
What sort of difference in the sound do you ear with the 'double top'?
Click to expand...

It is still under construction...a couple of weeks away. Another builder told me that there is a significant increase in volume and a bit more sustain in the one he built. I suspect the double back will have the same effect.
I placed the inner top about in the middle of the sound chamber. It looks like you have put it much closer to the back?
 
Last edited:
Tukanu said:
It is still under construction...a couple of weeks away. Another builder told me that there is a significant increase in volume and a bit more sustain in the one he built. I suspect the double back will have the same effect.
I placed the inner top about in the middle of the sound chamber. It looks like you have put it much closer to the back?
Click to expand...

Yes, mine is about 1/2 inch from the back
 
A bit more redwood info.

I have been in contact with a dendrochronology lab where they can date wood by comparing tree ring widths against a reference sample database. They dated the fine grained redwood sample. It is from a plank that is 11.5 inches wide. The results are that the sample had 755 rings, and are from 979-1734 AD. The head of the lab says "these dates are solid". So I have instruments on the bench with tops that grew some time between 979 and 1734 AD, depending on which side of the plank they came from. Old wood!
 
You must log in or register to reply here.

Similar threads

Tom Karol
A Tale of Three Unusual Tenors
Replies
6
Views
998
Tom Karol
Tom Karol
rappsy
  • Locked
Three Different Pono Pro Classic Tenors w/Hard Shell Case. I want these sold. NOW.
Replies
17
Views
2K
rappsy
rappsy
Doc_J
Three sinker redwood tenors
Replies
15
Views
1K
Tigeralum2001
Tigeralum2001
D
Three Tenors
Replies
0
Views
397
dwf1967
D
P
Watching three tenors grow
Replies
1
Views
278
mm stan
mm stan
Top Bottom