Pages: 1 2 [3]   Go Down
  Print  
Author Topic: Question about Sustain  (Read 6201 times)
Danny
Donuts?
*****
Offline Offline

Posts: 13250




Ignore
« Reply #40 on: December 01, 2008, 03:01:46 AM »


Yo Tad,

I'm totally unable to post stuff like pictures, but there is an interesting thread on a luthiers' forum I just hope to have finished up recently.  It starts out with a question about mid range, and morphs into a near battle over scalloped vs.  parabolic bracing.  Lots of pictures from other luthiers, and one of a top I built with my comments. 

Here's the link:  http://www.luthiercom.org/phpBB3/viewtopic.php?f=32&t=482&st=0&sk=t&sd=a&sid=d241e4eabe7b759a1464081ada843467

It goes on for five pages.



Deadpan Danny,

I like it!!

Scoot
  Two more posts and you can post pics
Logged

O,OO,OOO,LS,D02
Zohn
Gold Member
****
Offline Offline

Posts: 2463




Ignore
« Reply #41 on: December 01, 2008, 10:55:59 AM »

Greetings, Larriveets!  Or, is it Larrivites?

I hope you will forgive the shameless self-promotion on my website. 

Since increased sustain is one of the things my re-voicing work provides, I would like to comment on this question.  While it is true that sustain can be increased slightly by changing strings, nuts and saddles, bridge pins, the main cause of string die out is the shaping of braces--both internal, top and back, and on the bridge. 

It is my observation, if not discovery, that corners and ridges, even tiny irregularities of brace shapes absorb energy, contributing to dampening and die out.  I think this is because the strings' vibrational energy travels on the surface of all the braces.  Even if braces are shaped into an arched cross section along most of their length, I have yet to see a guitar whose brace ends are curved and flowing with the rest of the brace into the kerfing at the sides.  You can see on the back braces that the ends are just sanded down by sticking the brace end under a drum sander.  This leaves square corners on at least all the brace ends in the guitar, which I believe suck up energy.

In addition to balancing the brace strength to be no more than necessary to equal that of the string tension at any place along a brace, I shape the ends into a curved cross section and flow the lengthwise contour into each brace.  This makes an amazing improvement in sustain by eliminating energy absorbing/dampening corners and other irregularities in shaping.

I have developed a model for how I think each string, or even note finds resonance in a guitar which is that it finds resonance in a circular, or ring pattern.  Much the same way a stereo speaker works.  With its sides cut out.  The lower the frequency, the larger the ring, and vice versa.  On this guitar, my suspicion is that the D string ring has a brace or brace junction in it that has corners or is just too heavy.  More so than for the A string or its harmonic rings, which were noted to last a little longer.

Happy pickin',

Scott

  Hi Scott!
I'm the guy who took the liberty of adding your article on this forum, and I'm delighted to see your voluntary and spontaneous reaction to joining the discussion - thank you for that  . I'm in the mechanical engineering profession, and was involved in Finite Element Measurement (FEM) years ago on the structure of an artillery gun's turret. a Turret of that nature and a guitar's body have a lot in common namely: how stresses are generated, absorbed and or dissipated by means of vibration. As you rightly pointed out, stresses emanating into vibration, tend to be concentrated mostly at sharp corners, and the ideal is to direct the flow of vibration evenly over the whole structure to prevent cracking. This is where forums play an important part in all walks of life, and it is with most interest that I follow some posts on this thread. Thank you for sharing your more detailed views and experience. I wish I could get my Larrivees out to you. Perhaps you could visit South Africa, and I'll take you on a tour??? 
Logged

"To me...music exists to elevate us as far as possible above everyday life." ~ Gabriel Faure
Zohn
Gold Member
****
Offline Offline

Posts: 2463




Ignore
« Reply #42 on: December 01, 2008, 11:05:34 AM »

Tom Thumb lives there.


And his brother use to live here...




Great Pics indeed Jeremy, thanx!!! 
Logged

"To me...music exists to elevate us as far as possible above everyday life." ~ Gabriel Faure
Zohn
Gold Member
****
Offline Offline

Posts: 2463




Ignore
« Reply #43 on: December 01, 2008, 11:22:21 AM »

Tom Thumb lives there.


Hi Jeremy
Would you be so kind to explain the "happenings" in that end-block please? - could it be some compound-design, and why would that be? I notice there is no end-pin installed, so it couldn't possibly be for "added strength at the end-pin", or could it? (another excellent photo  - thanks!!)
Logged

"To me...music exists to elevate us as far as possible above everyday life." ~ Gabriel Faure
jeremy3220
Gold Member
****
Offline Offline

Posts: 4598




Ignore
« Reply #44 on: December 01, 2008, 03:58:31 PM »

Hi Jeremy
Would you be so kind to explain the "happenings" in that end-block please? - could it be some compound-design, and why would that be? I notice there is no end-pin installed, so it couldn't possibly be for "added strength at the end-pin", or could it? (another excellent photo  - thanks!!)

I'm not sure but it looks like a strip of spruce with the grain running perpendicular to the grain in the endblock so maybe it's to prevent cracking, but it would take a lot to crack that big end block and that thin strip of spruce probably wouldn't do a whole lot.

As you rightly pointed out, stresses emanating into vibration, tend to be concentrated mostly at sharp corners, and the ideal is to direct the flow of vibration evenly over the whole structure to prevent cracking.

Sounds like stress risers. It seems to be important to eliminate them from occuring over the longitudinal profile but I don't think it matters much if the cross section profile has corners as crack prevention is concerned. However making the cross section profile triangular seems to have the highest strength to weight ratio. The mass on the corners at the top of the cross sectional profile don't add much stiffness whether squared or rounded. Obviously you don't want to make the braces too thin at the top and risk someone cracking it by reaching around in there.
Logged

Zohn
Gold Member
****
Offline Offline

Posts: 2463




Ignore
« Reply #45 on: December 01, 2008, 04:21:50 PM »

However making the cross section profile triangular seems to have the highest strength to weight ratio. The mass on the corners at the top of the cross sectional profile don't add much stiffness whether squared or rounded. Obviously you don't want to make the braces too thin at the top and risk someone cracking it by reaching around in there.
Good (and valid) point.
I must just add that when I refer to cracking, I specifically mean welded steel structures. The stress concentration nodes are where cracks are most likely to appear. Conversely, in the guitar's case, stress concentration(sharp  points and/or edges) are the likely ones where you'll expect to find "dead" points. (with reference to Scott's theory on scalloped braces and sharp edges)
Logged

"To me...music exists to elevate us as far as possible above everyday life." ~ Gabriel Faure
Scott van Linge
Member
**
Offline Offline

Posts: 22




Ignore
« Reply #46 on: December 01, 2008, 11:51:22 PM »

Hi Scott!
I'm the guy who took the liberty of adding your article on this forum, and I'm delighted to see your voluntary and spontaneous reaction to joining the discussion - thank you for that  . I'm in the mechanical engineering profession, and was involved in Finite Element Measurement (FEM) years ago on the structure of an artillery gun's turret. a Turret of that nature and a guitar's body have a lot in common namely: how stresses are generated, absorbed and or dissipated by means of vibration. As you rightly pointed out, stresses emanating into vibration, tend to be concentrated mostly at sharp corners, and the ideal is to direct the flow of vibration evenly over the whole structure to prevent cracking. This is where forums play an important part in all walks of life, and it is with most interest that I follow some posts on this thread. Thank you for sharing your more detailed views and experience. I wish I could get my Larrivees out to you. Perhaps you could visit South Africa, and I'll take you on a tour??? 


Yo Zohn,

Interesting analogy, for sure.  If I understand correctly, then, a re-voiced guitar would  have a better chance of surviving a thermo-nuclear explosion!  ??

And, just send enough money, and I'd love to take a turret of South Africa...

Scott
Logged
Zohn
Gold Member
****
Offline Offline

Posts: 2463




Ignore
« Reply #47 on: December 02, 2008, 06:12:56 AM »

Tom Thumb lives there.


And his brother use to live here...


ohmy  This picture got me thinking of something else. Is there a significant measure of adjusting a top's voice or tone or sustain by varying the length of bridge pins? Some people claim differences in using different materials like Iveroid, Tusk, Ebony, Ivory, bone etc. Logic suggests that one could reduce mass by reducing pin length?
Logged

"To me...music exists to elevate us as far as possible above everyday life." ~ Gabriel Faure
jeremy3220
Gold Member
****
Offline Offline

Posts: 4598




Ignore
« Reply #48 on: December 02, 2008, 01:59:38 PM »

ohmy  This picture got me thinking of something else. Is there a significant measure of adjusting a top's voice or tone or sustain by varying the length of bridge pins? Some people claim differences in using different materials like Iveroid, Tusk, Ebony, Ivory, bone etc. Logic suggests that one could reduce mass by reducing pin length?


I don't like to think of changing bridge pins as changing the 'voice'. Yeh, you can reduce mass by reducing pin length, I don't know if it will make any noticable difference or not.
Logged

Danny
Donuts?
*****
Offline Offline

Posts: 13250




Ignore
« Reply #49 on: December 02, 2008, 04:37:38 PM »

   Something I noticed was that the pins are not slotted at all. Is that a good thing? I've heard that to slot each pin to it's string width was best.        Danny
Logged

O,OO,OOO,LS,D02
jeremy3220
Gold Member
****
Offline Offline

Posts: 4598




Ignore
« Reply #50 on: December 02, 2008, 04:58:22 PM »

   Something I noticed was that the pins are not slotted at all. Is that a good thing? I've heard that to slot each pin to it's string width was best.        Danny

The bridge is slotted instead of the pins, this moves the string forward and increases the break angle and contact with the bridge. This is generally thought to be better than slotting the pins.
Logged

Danny
Donuts?
*****
Offline Offline

Posts: 13250




Ignore
« Reply #51 on: December 02, 2008, 05:09:21 PM »

The bridge is slotted instead of the pins, this moves the string forward and increases the break angle and contact with the bridge. This is generally thought to be better than slotting the pins.
                   I knew of doing the slot to stop buzz. That does make sense, but I guess you could cut through the bridge faster that way.
Logged

O,OO,OOO,LS,D02
Pages: 1 2 [3]   Go Up
  Print  
 
Jump to: