This is a bit rough, and from memory, but Benade in "Fundamentals of Musical Acoustics" talks about what he calls the "impedance" of strings and soundboards and bridges. He likens it to light going through a glass window - some of the light goes through and some is reflected, depending on the relative characteristics of the glass and air. In the same way, the sound wave that is traveling down a string can be reflected back to the string causing the sound to sustain, or can go the bridge and top of the instrument and make a sound. Just how much is reflected versus transmitted to the top depends on the relationship in "impedance" between the string and bridge. A light bridge and top, like in a banjo, means more of the sound goes from the string to the top, in a quick loud burst. A heavier bridge and top, like the brass bridge that people used to put on electric guitars, causes the more of the sound wave to reflect back to the string, and causes more sustain and less volume. Presumable on the banjo the pressure from the tailpiece also changes the relative impedance ratio. The same impedance match takes place between the top of the instrument and the air.
Wayne Begin forwarded message: > From: Martyn Hodgson <[email protected]> > Subject: [LUTE] Re: Lute Bridge vs Guitar Bridge Functioning > Date: August 1, 2014 at 2:29:35 AM EDT > To: "lute-cs.dartmouth.edu" <[email protected]>, Bruno Correia > <[email protected]> > Reply-To: Martyn Hodgson <[email protected]> > > In fact both lute and guitar bridges function in the same way. In > short, a horizontal force (imposed by the string) is momentarily > increased when the string is displaced (plucked); this in turn > increases the turning moment of the bridge (ie force x height of string > above belly at take-off point) which in turn causes the belly to > vibrate with mostly a wave action (tho' some vertical pumping action > too) and thus amplifying the sound by varying the air pressure within > the soundbox. Whether the vibrating string leads from a loop (lute) or > from over a saddle (later guitars) is immaterial - it is the height of > the string at take-off which is relevant. Vibration patterns have, in > fact, been studied: eg the Galpin Society Journal (Hellwig I recall) > which contains relevant papers. > Differences in timbre between instruments may well be due to many other > factors rather than the way the physics of the bridge works, including: > mass of bridge (size and density), surface area of base of bridge, > stiffness of bridge, barring, internal shape of soundbox and its > volume, etc. > An illustrative example: many years ago I made a 5 course guitar after > Sellas and fitted an ebony bridge (thinking the original had one). The > sound was quiet and muffled (tho' with considerable sustain). I had a > rethink and after further investigation decided to remove it and fit a > fruitwood (actually pear) black stained bridge to precisely the same > design: the resulting sound was considerably freer and increased the > output ie volume. In fact the much greater mass of the ebony bridge was > acting as a considerable dampener requiring more of the vibrational > energy of the string to set it in motion than that of the fruitwood > bridge which had a mass less than half that of the ebony. On the other > hand, the ebony bridge's greater mass meant that it had more inertia > and thus continued to oscillate for longer than the fruitwood bridge - > thus giving the greater (if much quieter) sustain. > MH > PS Incidentally, drilling the string holes low down on a modern guitar > bridge does not increase the string tension/force and hence the turning > moment of the string at the bridge (and it could not be otherwise, > since for a given string the pitch is simply a function of transverse > force/string tension) but does increase the resultant vector > downbearing on the saddle which avoids excessive frictional string > slide (and hence loss of energy ie output) across the saddle. The > discrete loop take-off point used on lutes and early guitars avoids > this problem. > __________________________________________________________________ > > From: "[email protected]" <[email protected]> > To: lute-cs.dartmouth.edu <[email protected]>; Bruno Correia > <[email protected]> > Sent: Friday, 1 August 2014, 1:18 > Subject: [LUTE] Re: Lute Bridge vs Guitar Bridge Functioning > Thanks Bruno! So far, yours is the only response. > I hope to hear some more also : ) > Tom > Date sent: Sat, 26 Jul 2014 18:57:28 -0300 > To: "lute-cs.dartmouth.edu" <[1][email protected]> > From: Bruno Correia <[2][email protected]> > Subject: [LUTE] Re: Lute Bridge vs Guitar Bridge Functioning > Very nice question! Hope to hear some responses on this topic. > 2014-07-26 11:20 GMT-03:00 <[1][3][email protected]>: > Dear List, > A I have always assumed that a lute bridge moves / vibrates in a > different manner than a guitar bridge, and that this, plus the > bracing, etc. mainly account for the difference in timbre between > the two different instruments - that the strings of a lute exert > force in a plane parallel to the belly, while the saddle of a > guitar bridge creates "downbearing" or force perpendicular to the > belly, causing more of a rocking motion. A Following this line of > reasoning anything on top of a lute bridge would be primarily > decorative. A But - could a luthier angle the string holes in a > lute bridge at about 30 degrees to create a downbearing-like > function? A Would that have any positive or negative impact on > lute tone or projection? A Am I correct in this assumption, or > way out in left field? BTW, has anybody done vibration pattern > imaging on lute bellies similar to the what has been done in > violin research? A Looking forward to your responses, A A > Thanks, Tom Draughon Heartistry Music > [2][4]http://www.heartistry.com Date sent: A A A A A A A Sat, > 26 Jul 2014 15:27:26 +0200 To: A A A A A A A A A A > "[3]lute-cs.dartmouth.edu" <[4][5][email protected]> From: A A > A A A A A A A Anthony Hind > <[5][6][email protected]> Subject: A A A A A A A A > [LUTE] Re: Lute bridge Dear Bruno Looking at the instruments of > the CitA(c) de la Musique seems to show that ivory or bone on the > bridge goes together with the same decorations on the fingerboard > and elsewhere, [6][7]http://tinyurl.com/nlvpy32 Thus unlikely to be > acoustic in intention. Regards Anthony Sent from my iPhone > On > 26 juil. 2014, at 00:32, Bruno Correia <[7][8][email protected]> >> wrote: > > Dear Daniel, > This thin slice of bone is precisely > what I was referring to. I'm > sure you have seen many lutes with > these cap. All the best. > 2014-07-25 18:44 GMT-03:00 Dan Winheld > <[1][8][9][email protected]>: > > A Never had a bone on any of my > lute bridges (except the guitar > A saddle bone on my first > guitary-semi-lute). I have never seen a > A bone on any lute > bridge either. A thin slice of bone, ivory, or > A hard wood > seems like a good idea to limit string wear on the top > A edges > of a bridge, so long as it does not increase mass to the > A > extent of degrading the sound. Of course, as a player & not a > A > luthier I'm sure I haven't all the lutes out there. Maybe some > > A Tielke extravaganza has bone or ivory bridge decoration. What >> A particular lutes have you seen with this feature? Any > pictures? > A Dan > > -- > Bruno Figueiredo > A > Pesquisador > autA'nomo da prA!tica e interpretaAS:A-L-o > historicamente > informada no alaA-ode e teorba. > Doutor em PrA!ticas > InterpretativasA pela > Universidade Federal do Estado do Rio de > Janeiro. > > -- > > References > > 1. > mailto:[9][10][email protected] >>>> To get on or off this list see list information at > > [10][11]http://www.cs.dartmouth.edu/~wbc/lute-admin/index.html Tom > Draughon Heartistry Music > [11][12]http://www.heartistrymusic.com/artists_tom.html 714 A 9th > Avenue West Ashland, WI A 54806 [12]715-682-9362 > -- > Bruno Figueiredo > A > Pesquisador autA'nomo da prA!tica e interpretaAS:A-L-o > historicamente informada no alaA-ode e teorba. > Doutor em PrA!ticas InterpretativasA pela > Universidade Federal do Estado do Rio de Janeiro. > -- > References > 1. mailto:[13][email protected] > 2. [14]http://www.heartistry.com/ > 3. [15]http://lute-cs.dartmouth.edu/ > 4. mailto:[16][email protected] > 5. mailto:[17][email protected] > 6. [18]http://tinyurl.com/nlvpy32 > 7. mailto:[19][email protected] > 8. mailto:[20][email protected] > 9. mailto:[21][email protected] > 10. [22]http://www.cs.dartmouth.edu/~wbc/lute-admin/index.html > 11. [23]http://www.heartistrymusic.com/artists_tom.html > 12. tel:715-682-9362 > Tom Draughon > Heartistry Music > [24]http://www.heartistrymusic.com/artists_tom.html > 714 9th Avenue West > Ashland, WI 54806 > 715-682-9362 > > -- > > References > > 1. mailto:[email protected] > 2. mailto:[email protected] > 3. mailto:[email protected] > 4. http://www.heartistry.com/ > 5. mailto:[email protected] > 6. mailto:[email protected] > 7. http://tinyurl.com/nlvpy32 > 8. mailto:[email protected] > 9. mailto:[email protected] > 10. mailto:[email protected] > 11. http://www.cs.dartmouth.edu/~wbc/lute-admin/index.html > 12. http://www.heartistrymusic.com/artists_tom.html > 13. mailto:[email protected] > 14. http://www.heartistry.com/ > 15. http://lute-cs.dartmouth.edu/ > 16. mailto:[email protected] > 17. mailto:[email protected] > 18. http://tinyurl.com/nlvpy32 > 19. mailto:[email protected] > 20. mailto:[email protected] > 21. mailto:[email protected] > 22. http://www.cs.dartmouth.edu/~wbc/lute-admin/index.html > 23. http://www.heartistrymusic.com/artists_tom.html > 24. http://www.heartistrymusic.com/artists_tom.html >
