Nose bleed time

[Puff]

Why is a banjo bridge normally set close on 2/3 back on the resonating surface (from neck side of pot to tail) but resophonics are all in the centre be they spider or biscuit.
Have some notions here but would appreciate a think tank.
Cheers

[matthew]

perhaps because the tonal response is better?

here's my favourite banjo

[kiwigeo]

Here we go again......

[kiwigeo]

Might as well start the ball rolling

[Puff]

Hi Martin - was actually a genuine enquiry. Perhaps if I add that the classicals i'm eyeballing have their bridges pretty much in the middle of the resonating area of the top and the acoustics tend to be the reverse of banjos in being around 2/3 of the way between tail block and the neck end of the resonating surface.
I guess for the sake of this we could propose that all could be fretless and the bridge placed purely for best tone or top activation. Are we purely talking bracing here?
An imagined scenario of building the instrument to a comfortable size and effective shape and strength. Stringing it up and moving, and perhaps skewing, the bridge to get the sound and then going back and fretting (either straight or fanned).

[kiwigeo]

Hi Martin - was actually a genuine enquiry. Perhaps if I add that the classicals i'm eyeballing have their bridges pretty much in the middle of the resonating area of the top and the acoustics tend to be the reverse of banjos in being around 2/3 of the way between tail block and the neck end of the resonating surface.
I guess for the sake of this we could propose that all could be fretless and the bridge placed purely for best tone or top activation. Are we purely talking bracing here?
An imagined scenario of building the instrument to a comfortable size and effective shape and strength. Stringing it up and moving, and perhaps skewing, the bridge to get the sound and then going back and fretting (either straight or fanned).

Hi Puff,

Sorry for the banjo jibes...unfortunately it's bit of a tradition in this forum.

I don't actually know a huge amount about banjos but I'm thinking that the fact that the instruments vibrating surface is perfectly round may mean that placement of the bridge isn't as critical as for a guitar. The only reason I can think of for the bridge being as far back as it is is to keep the neck of the instrument as short as possible. An interesting question.

Cheers Martin

[Puff]

My thought on the banjo was that with the older skins it required less overall tension to get a specific tension under the bridge. With newer/stronger materials I would have thought that less of an issue and the bridge could be placed for optimum resonance/response/tone but it doesn't appear to have changed bridge placement.
Hence the "nose bleed".

In part where I am coming from here is to do with the lattice bracing question and especially the fine lattice of nomex.
The banjo thing really only came in as it is a relatively pure and free resonating surface but bridge placement was pretty much the reverse of the other tops mentioned. That is 2/3 of the resonating surface ahead of instead of behind the bridge.

Your point is taken Martin but I am not convinced that aesthetics/ergonomics of the instrument or 'wingspan' required to play the instrument was an original fundamental in banjo design

With the shape change (banjo round to female torso with sound hole or lute shape) we have gone from round to tear-drop shaped effective areas? But why the reversal in bridge placement?
I do not mean the above to be interpreted as a chronological argument.

[Nick]

I'm wondering if it's what gives the Banja it's timbre? Closer to the edge I'm seeing an area of less resonation (in my minds eye....no scientific evidence) so the sound would be 'tighter' and maybe a little more focused toward the higher register, maybe in the centre of the head it's just not focused enough for what was intended for the instrument? We need Ron or Phil to chime in being knowledgeable Banja people. Anyway, just my idea to throw into the great melting pot.

[Puff]

Nick they don't use timbre in banjos - they use lumbre
I think both you and Martin are on good tracks but why is the same sort of soundboard formula applied in reverse for guitars - or is this just a blip?

[kiwigeo]

Perhaps a snare drum would be a fair analogy....a much tighter sound on the edge of the skin than in the centre.

[Puff]

Certainly I see the cord length and the placement of 'excitement' in longer or shorter cords as relative to tension and hence tightness but why the front to back reversal (neck to tail). Other than Martin's suggestion? Or are we now doing tightness on the other axis as well?
Think tank

[matthew]

Also the skin deflection under string pressure is going to be much greater in the middle of the skin. Perhaps this has ramifications for tuning stability.

I'm inclined to think that keeping the neck short as Martin says is a likely factor too. Instruments tend to evolve towards the playable.

[Puff]

[quote/]Perhaps if I add that the classicals i'm eyeballing have their bridges pretty much in the middle of the resonating area of the top and the acoustics tend to be the reverse of banjos in being around 2/3 of the way between tail block and the neck end of the resonating surface.[quote/]
Sorry guys finally got my brain back into gear (sort of) and pinged that the bridges on the classicals and acoustics are actually very close to central on the vibrating surface they just appear differently disposed because of the different bracing which, by virtue of the X bracing extending further 'north' in the acoustics than the fan in the classicals. So poof goes my whimsey on the 1/3 v 2/3 being inspired by anything more than ergonomics or tension. Classic case of not seeing the wood for the soundhole
Still rather like the idea of optimum placement of the bridge on the top for tone as being paramount above any pre-determined scale though; still thinking lattice bracing
Thanks for the input.

[DarwinStrings]

I you see that the whole front on a Torres braced guitar is the sound board then the bridge is 2/3 of the way down, a steel string moves the bridge forward cause the neck is 14 rather than 12 fret to body. This man has a view on that difference...http://www.danielbrauchli.com/Acoustic_Concepts.htm

Jim

Edit...the first word should be If not I

[Puff]

Thanks for the time and the links Jim. All grist to this slowly turning mill.
Erwin shone the light on the primary 'resonating surface' with its extents being determined by the perimeter of the top up to the UTB. In a fan typically below the sound hole but in an X typically above. Leaves room for "where do I go with fine lattice bracing" and something is whispering tear-drop or reversed heart. Maybe a play with some sacred geometry along the lines of Stradivari could prove fruitful. More thought required.
Cheers

[Nick]

This man has a view on that difference...http://www.danielbrauchli.com/Acoustic_Concepts.htm

Interesting site, thanks Jim for the link.

I think Martins analogy probably sums it up for me after hitting the skins myself for a while. The rimshot hit (close to the rim & also hitting the hoop at the same time) always has more of a focussed 'crack' than hitting it in the centre of the head, maybe this positioning not only gives it it's voice but increases this voice also ?

[Puff]

No argument Nick. There is some excellent stuff on what makes banjo bridges work and the differences obtainable with different woods, combinations of woods and size of footprint; and I dare say that crosses over to floating bridges on guitars to a certain extent. More rather than less as the construct of the top moves closer to that of a banjo head as I see a fine lattice doing.
There will always be conundrums. A cherry bridge on calf skin, a cherry bridge on kevlar, an ebony bridge on....., a maple bridge on.... a maple bridge with ebony saddle on etc.... Tune the skin to what...

[Nick]

No argument Nick. There is some excellent stuff on what makes banjo bridges work and the differences obtainable with different woods, combinations of woods and size of footprint; and I dare say that crosses over to floating bridges on guitars to a certain extent. More rather than less as the construct of the top moves closer to that of a banjo head as I see a fine lattice doing.

Again, no proof or evidence of what I've just 'thought up', but maybe the lattice bracing 'assists' the top in moving more as a monopole (as with 'arched top' instruments)? With X bracing I can see the bracing driving most of the top but there will be nodes that aren't where the other two dipoles cross. Whereas a lattice, if done right, would tend to spread the movement across the whole top more evenly (if it tended to move more as a singular unit) thus reducing the 'dead nodes? Just a thought off the top of my head, probably look at it tomorrow & think "what a dipshit!".

[Puff]

Also interesting would be setting up the lattice as a 'square' lay (with longitudinals and laterals) and as diamond (X-type) lay. Oh shit - more nosebleed.

[Nick]

Also interesting would be setting up the lattice as a 'square' lay (with longitudinals and laterals) and as diamond (X-type) lay. Oh shit - more nosebleed.

I'm just wondering how the 'square' one would go with one lot of bracing traveling along the line of, or parallel to, the grain? Whereas I'm thinking the 'diamond' would tend to spread the loads more evenly across the plate. Could be a worthwhile experiment though.

[DarwinStrings]

Do you mean "square" as in the way I did it?

Jim

[Puff]

That is what I meant Jim if you are referring to the tele bracing - effectively a ladder style. The 'diamond' would be it turned 45 degrees to an approximation of X-bracing.