Thoughts about the bridge

Henning · Mar 24, 2018

Hello, I have some questions concerning the design of the bridge.
If you make the bridge lighter and smaller it will asumably have effect on the sound of the instrument.
It is easy to make the assumption that a small and light bridge will give a stronger tone and shorter sustain. Is that right?
How do you design your bridge?
Do you make it smooth (i.e. sand it out) or accept straight and sharp edges, please?
It might have some influence on the tone as well as aesthetics too.

Kind regards

stevepetergal · Mar 24, 2018

I'll be interested in responses to this question. I would have thought a light bridge would have less effect on tone and allow more sustain than would a heavier one.

Beau Hannam Ukuleles · Mar 24, 2018

The bridge is two things:

1- The most important brace that the top possesses.
2- A "heat sink", but for vibration.

So the heaver the bridge, the most is sucks up vibration...like a heat sink sucks up heat (not a technically correct term but i think it illustrate it well)

A light bridge promotes a fast attack, longer sustain, and allows the top to vibrate more.
My usual uke bridges are about 9-10-11 grams, depending on if i use ebony, brazilian or african blackwood. Classical guitar bridges aim for about 15 grams, steel string about 25-30 grams.

The lightest uke bridge i've made was this one at 5.2 grams which was a uke i built in 1 day ( yes 1 day)- bridge is tassy blackwood. the body is all spruce.

printer2 · Mar 24, 2018

The lighter the bridge the quicker the top responds to the string. The more mass in the bridge the more it looks like a fixed unmovable point. This has the effect of leaving more energy in the string for a given period of time. This lengthens the length of time the string vibrates. Since more energy remains in the string and less energy is being taken out of it the volume of sound is lower. The heavier the bridge the lower the top's resonant frequency. The aspect ratio of the bridge will change the sound as short wide bridge compared to a thinner longer bridge should effect the sound, I have not played around with this on ukuleles so I can not speak to the effect. You can trade off size and stiffness using the same material or keeping the size the same but using a denser or lighter wood.

jhnmdahl · Mar 24, 2018

I think Printer makes a good point in that you want both light and stiff - two properties that aren't always easy to find at the same time. This helps dictate what woods work best for a bridge as well.

Beau Hannam Ukuleles · Mar 24, 2018

Indeed stiff- I forgot to mention that.

A bridge needs to retain its structure, being a brace.

sequoia · Mar 25, 2018

Beau Hannam Ukuleles said:
Indeed stiff is better- I forgot to mention that. .

My wife keeps mentioning that to me but I just don't understand.... I think we are getting into some deep waters here on bridges and energy transmission. Black box stuff if you ask me. Again, there is probably that mystical, mythical "sweet spot" or the dreaded Goldilocks Effect where everything is in perfect balance but who knows where the hell that actually is? I will say I think a bridge could be too small and light and that a heavier bridge could transmit energy in a stored energy sort of way...... That this is an important subject is an understatement but who the hell has the data? I've never found it. It all seems to be a lot of "well that seems about right" if you ask me. Actually I think a lot of bridge data is just scaled down Spanish guitar dimensions extrapolated to the 4 stringed ukulele and as we all know, the ukulele is just not a friggin "little guitar". Somebody should do some research on this. It ain't gonna be me. Where are you Lloyd Allayre Loar when we need you? Dying is no excuse!!!

Henning · Mar 25, 2018

The bridge being a brace is something the ukulele has in common with the guitar. Though the guitar (usually) has a more advanced bracing under the top then an ukulele has. But what seems to be the thread of Ariadnes here is that a lighter bridge gives a stronger bass. How well that now might be transformed to an ukulele?
http://www.acousticguitarforum.com/forums/showthread.php?t=168294

printer2 · Mar 25, 2018

sequoia said:
My wife keeps mentioning that to me but I just don't understand.... I think we are getting into some deep waters here on bridges and energy transmission. Black box stuff if you ask me. Again, there is probably that mystical, mythical "sweet spot" or the dreaded Goldilocks Effect where everything is in perfect balance but who knows where the hell that actually is? I will say I think a bridge could be too small and light and that a heavier bridge could transmit energy in a stored energy sort of way...... That this is an important subject is an understatement but who the hell has the data? I've never found it. It all seems to be a lot of "well that seems about right" if you ask me. Actually I think a lot of bridge data is just scaled down Spanish guitar dimensions extrapolated to the 4 stringed ukulele and as we all know, the ukulele is just not a friggin "little guitar". Somebody should do some research on this. It ain't gonna be me. Where are you Lloyd Allayre Loar when we need you? Dying is no excuse!!!

I didn't get into how much is good as I have not built many ukes, Still need to get a handle on the guitar end of it but in that case and probably with ukes it is the sum of the top bridge and braces. If you have more of one you can have less of the other within reason. If you go real light you have a drum skin for a top, a little bridge and you have yourself a banjo uke. Go the opposite direction and you have a solid body platform to build an electric. One is real loud and has a short time envelope while the other hardly makes a sound but has lot of sustain. It depends where you want your instrument to fall in between these two ends. As far as data on ukuleles there is a book that I have come across and I think the author has done a lot of work in that regard. If I did not spend $300 on the two guitar books on design and building I would pick it up. I have read a few preview pages and I think it would be well worth the money for anyone doing their own thing rather than troding the well worn path.

http://ukuleles.com/?page_id=56

Beau Hannam Ukuleles · Mar 25, 2018

sequoia said:
... Again, there is probably that mystical, mythical "sweet spot" or the dreaded Goldilocks Effect where everything is in perfect balance but who knows where the hell that actually is? I will say I think a bridge could be too small and light and that a heavier bridge could transmit energy in a stored energy sort of way......

I would argue that a bridge isn't a battery that can store and transmit energy at a later time than it receives it.

It simply receives the vibration from the string and wobbles it out (that's technical speak

)

On the size of bridges, take a look at this Lute bridge- from what i can make out, this lute has 15 strings, and a tiny (in width) bridge (its length is a necessity of the string span). Think of how small this bridge would be if it only had 4 strings!!

On paper, the best thing would be a super light and stiff/stable bridge. However, the instrument would sound different if the bridge had (magically) no mass- perhaps not what people generally like to hear.
Just aim for a small, light bridge and you will be ok

sequoia · Mar 26, 2018

Beau Hannam Ukuleles said:
I would argue that a bridge isn't a battery that can store and transmit energy at a later time than it receives it.)

I'm going to go out on even thinner ice and say that yes the bridge does store energy and release it. Not unlike a capacitor in an electrical circuit that modulates and stores energy releasing it in a controlled, filtered way to the components down stream like the braces and the top. Your thought that a thinner bridge like on the thing shown would transmit energy quicker and more efficiently is totally correct. The attack would be quicker and there would be less absorption of string energy. However I think the sound would be be thinner and there would be less sustain because there is no modulating effect of a more massive bridge. You are absolutely right Beau, but how would the uke sound?... I'm not totally convinced of my arguments however. The Macaferri guitar is a good example. Note how small the bridge is and note the sound. Pretty damn good.

Sorry to beat this thread to death, but I think herein lies some important thoughts to ponder on how the thangs sound in the end. I'm still trying to sort it out.

printer2 · Mar 26, 2018

The bridge works with the other braces and you have to factor them in when thinking of the sound being produced.

gerardg · Mar 29, 2018

Soprano African mahogany bridge and ebony saddle.

50 x 19 x h. 7 mm. bridge.
2 mm. saddle thickness.

3.5 g. the whole

printer2 · Mar 29, 2018

Waiting for a doctor's appointment I was scrolling though my tablet, I came across a pdf that has some relevance. Chapter 2, 5, 6 are recommended reading, the violin chapters if you got through the rest and want more. Just scratching the surface but not a bad introduction.

http://www.speech.kth.se/music/acviguit4/index.html

Index of chapters
Preface/Chapter I
Sound and hearing
Chapter II
Resonance and resonators
Chapter III
Sound and the room
Chapter IV
Properties of the violin and guitar string
Chapter V
Vibration properties of the wood and tuning of violin plates
Chapter VI
The function, tone, and tonal quality of the guitar
Chapter VII
The function of the violin
Chapter VIII
The tone and tonal quality of the violin
Chapter IX
Sound examples and simple experimental material – under preparation

Matt Clara · Mar 29, 2018

Beau Hannam Ukuleles said:
I would argue that a bridge isn't a battery that can store and transmit energy at a later time than it receives it.

Well, not later, like hours later, but if you've ever split wood on a stump, as opposed to on a concrete block/pad, you'd know exactly what he means. The concrete block absorbs the energy from your swing and gives none of it back. It's a poor choice to cut wood on because of that, among other reasons. The stump receives the energy of the blow and pushes it right back, like a spring, making it ideal for cutting wood. Also, cutting wood on a concrete block is a good way to ruin your ax head! (Don't ask me how I know...)

BlackBearUkes · Mar 30, 2018

The bridge stores energy and release it.? I think not. If that were the case, wouldn't you pluck a string, stop it immediately and still hear the note from the stored energy? You can sometimes here the echo, but that is not stored energy. The bridge/ saddle merely transmit the energy from the plucked string to the top plate. You can hear sound from the vibrating string (sustain), but nothing is stored unless electronics are involved.

sequoia said:
I'm going to go out on even thinner ice and say that yes the bridge does store energy and release it. Not unlike a capacitor in an electrical circuit that modulates and stores energy releasing it in a controlled, filtered way to the components down stream like the braces and the top. Your thought that a thinner bridge like on the thing shown would transmit energy quicker and more efficiently is totally correct. The attack would be quicker and there would be less absorption of string energy. However I think the sound would be be thinner and there would be less sustain because there is no modulating effect of a more massive bridge. You are absolutely right Beau, but how would the uke sound?... I'm not totally convinced of my arguments however. The Macaferri guitar is a good example. Note how small the bridge is and note the sound. Pretty damn good.

Sorry to beat this thread to death, but I think herein lies some important thoughts to ponder on how the thangs sound in the end. I'm still trying to sort it out.

printer2 · Mar 30, 2018

More like if you have a heavy bridge it takes a while to get it moving rather than it storing energy in the bridge. The top acts as your spring, the bridge the mass and the string the driving force. A lighter bridge is easier to move so should have a more immediate sound. A heavy bridge may not store the energy but rather traps it in the string and only sucks more out of the string after the first cycle or two. Think of pushing a child on a swing. The first push does not get the swing to its highest point.

sequoia · Mar 30, 2018

Yeah, yeah, perhaps "storing" energy was the wrong word. But the transmission of energy from the saddle to the top could certainly be "transmogrified" by the bridge. I love the word transmogrified. Look it up. I think what a person wants is pretty much a quick transfer and thus these dense woods that don't "store" (absorb?) string energy like rosewood or ebony are going to have little absorption. Theoretically you would want a pure transmitter of energy to the top like glass or ceramic or... However I think my point is that a bridge does "color" the transmission of energy by slowing it down and there is a certain amount of energy that is "stored" and thus perhaps lost as heat which is a pity because we can't afford to lose much energy from that pitifully small energy that comes from plucking those pitifully small strings on the small top area. However, the one thing I'm pretty sure of is that the bridge material does "color" the sound that goes into the top and that makes a difference. And what the hell does "color" mean? I'll shut up now. ;

DPO · Mar 30, 2018

sequoia said:
Yeah, yeah, perhaps "storing" energy was the wrong word. But the transmission of energy from the saddle to the top could certainly be "transmogrified" by the bridge. I love the word transmogrified. Look it up. I think what a person wants is pretty much a quick transfer and thus these dense woods that don't "store" (absorb?) string energy like rosewood or ebony are going to have little absorption. Theoretically you would want a pure transmitter of energy to the top like glass or ceramic or... However I think my point is that a bridge does "color" the transmission of energy by slowing it down and there is a certain amount of energy that is "stored" and thus perhaps lost as heat which is a pity because we can't afford to lose much energy from that pitifully small energy that comes from plucking those pitifully small strings on the small top area. However, the one thing I'm pretty sure of is that the bridge material does "color" the sound that goes into the top and that makes a difference. And what the hell does "color" mean? I'll shut up now. ;

Colour? OK!

Uke Don · Mar 30, 2018

The bridge has a massive impact on how the top responds to sound. The size of the bridge -- width, height, and thickness, changes the dynamics greatly. If you really want to geek out on this stuff, I'd suggest "Left Brain Lutherie" by David Heard, Ph.D. He shows via deflection graphs what a top looks like before and after you add the bridge. You can still order the book from him at Ukuleles by Kawika.

Thoughts about the bridge

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