Different timbers for violin bridges.

November 9, 2020, 7:38 PM · A number of discussions have been about different timbers for violin construction but this question is specifically about the bridge. It does not take much material to make a bridge so have different timbers been used to make a violin bridge and did it make any difference to the sound at all ?

I was thinking about the ebony insert used under the E string on some bridges and I wondered what a whole bridge made of ebony would sound like.

Replies (21)

Edited: November 12, 2020, 4:55 AM · Indeed, the weight and stiffness of a bridge, and their distribution via the design, have a notable effect on tone and response.

Maple is strong and stiff, but transmits vibrations well.
I improved the sound of several Skylark VSOs by replacing their crude and soft bridges with Aubert ones.

The bridge design is such that the vibrations from each string do not descend directly to the violin but work round the various cut-outs. Starting with an Aubert "blank", after fitting the feet and trimming the top edge, I tried lightening it in two ways: thinning the whole bridge, or enlarging the cut-outs. The effects are noticeably different, and in fact one combines both methods.

"Miracle" bridges appear from time to time, using new shapes and materials, but have never dethroned the classic designs which have evolved over the centuries.

November 12, 2020, 6:04 AM · That's 3 more ways of tweaking violin sound to add to the daunting number we have already. But does anybody except the tweaker and (maybe) the player notice? The problems, of course, are that these methods are all to some degree interdependent and we're unable to make side-by-side comparisons.
Edited: November 12, 2020, 7:02 AM · There are common misconceptions about how the energy of the vibrating strings are transmitted through the bridge to the violin body. One of the more prominent is that a "sound wave" takes a path around the various cutouts of the bridge and this is the major factor for energy transmission.

Some simple physics counters this notion. Most violins have a response roll-off at around 4000 cycles per second. The sound speed of maple is around 4000 meters/second. So the "worst case" length of a sound wave as it travels through the bridge is:

Length = soundspeed/frequency = 4000/4000 = 1 meter.

The height of a bridge is about 0.03 meters. When the length of travel is so much smaller than the wavelength, the bridge acts like a rigid body to the strings instead of a transmitter of sound waves.

This means the most critical parameters for energy transmission are related to inertia: the overall mass of the bridge, as well as the distribution of the mass (rotational moments of inertia). Vibrational modes that are close to rigid body movements will dominate the bridge response.

The bridge material must be strong enough to hold up the strings in a stable position. If you use a material with a different stiffness than maple, you will need to adjust the thicknesses of the bridge to make sure it will not bend or crack under the string loads.

The total mass must strike a balance between the vibrating energy the strings pump into the bridge, and the flexibility of the violin body for efficient energy transfer, a concept known as impedance matching. Experienced luthiers trim bridges to achieve a certain overall mass.

Over the centuries, the range of mass needed for maple bridges to impedance match the violin has been deduced by trial and error. If your new material has a different density, this will affect how you thin the bridge.

Finally, the mass distribution must be such that the simpler modes of vibration do not cause the bridge to over emphasize some notes over others. Some theoretical work has been on this, but as a matter of practice, the way a maple bridge is tapered from foot to lip distributes the mass so that one of the primary vibrational modes is around 3000hz. Some prefer it lower, others higher.

The density and sound speed/stiffness of the new material will affect this so you might have quite a challenge trying to match the vibrational mode while also achieving the other requirements outlined above.

Hopefully this wasn't too technical. But it might explain why people use high quality maple and do not bother to consider other materials. It is quite a juggling act to get all the performance requirements to match up and the challenge has been "solved" over the centuries by the use of maple bridges.

Also, a well cut maple bridge looks cool, so if you cannot sound good, you can at least look good!

Edited: November 12, 2020, 7:44 AM · Carmen, thank you. Not too technical; just right.
November 12, 2020, 8:12 AM · The bottom line is that maple works and delivers the expected sound. There's no reason to try something else, but probably everything has been tried by someone, somewhere. Still, everyone comes back to maple.

Within maple, there's plenty of variation and good or bad things can happen. Likewise with the style of cut. In most sound matters, everything you do has some effect, usually. I agree more with Carmen, above, than with what most violin makers suggest happens, though: the various ways of weight distribution is a huge factor.

Edited: November 12, 2020, 10:52 AM · My "vibration path" was just an image. But the cutouts and thickness reduction provide flexibility as well as reducing mass and modifying the moment of inertia. I have (somewhere) a text where the writer starts with a solid bridge and cuts away first between the feet, then the "heart", then the "ears" until reaching our present design.

I have only take Long Term Average Spectra with slightly different bridges and mutes on the same viola: I find some correlation between ear and eye. The overall character of the instrument remains, but one can accentuate or reduce certain resonances.

Edit: the covid lock-down is providing me with too many "moments of inertia"...

November 12, 2020, 12:52 PM · I recall reading that ebony inserts on bridges were used on cheap bridges. It makes sense that using a harder wood insert would avoid having the E string cutting into the softer wood.
Edited: November 12, 2020, 4:13 PM · Nowadays, a small piece of parchment is often used to protect the bridge from the E string. This is far better in all respects than the ubiquitous and ugly plastic tube thingy that usually comes with many strings - except gut of course!

If I find such a thingy on a new string I invariably move it up the string out of the way into the pegbox zone during string installation because it cannot always be slid off over the thick winding at the string's pegbox end. And I never attempt to remove it with a sharp blade - there's too much risk of damaging the string.

If you need a piece of parchment for the bridge in a hurry, and you haven't got any to hand, then a piece of chamois leather cut to size makes a useful temporary expedient.

November 12, 2020, 3:49 PM · ..and the same at the other end can cure the whistling open E when slurring from the A-string.
I use a fragment cut from an old leather glove.
November 12, 2020, 4:00 PM · Adrian, I'll bear that tip in mind to pass on to anyone I know who suffers the whistling E problem. I can't advise from personal experience because for some unknown reason I've never had a whistling open E.
Edited: November 12, 2020, 5:24 PM · I don't know if this is an "old wife's tale" but I heard that twisting the E string at least 1/2 turn when mounting it can help prevent the whistle. I have been doing that ever since I heard about it. It would appear to be the principle of the Warchal E strings and their metal A strings.
Edited: November 12, 2020, 5:12 PM · Andrew, possibly not an "old wife's tale" if the whistling is due to a torsional or twisting vibration of the string about its longitudinal axis, which could be nullified by applying a "pre-twist" to the string, as you described. If this is so, then maybe someone will have done the math and we're now seeing the result in Warchal's Amber E, and one of their high-end metal A's (Timbre?).
November 16, 2020, 8:02 PM · I had a friend named Charles Herbaut who compared materials for bridges for his project when studying violin making at the London College of Furniture with Pat Naismith (He later studied physics at Grahamstown). There were only two materials used for bridges that conducted sound at all well. One was, of course, maple. The other, boxwood I think, performed about the same. Metal didn't conduct it at all (I was his tester).
November 16, 2020, 9:29 PM · I wonder Why only boxwood and maple performed well ? Do they have similar densities ?
Edited: November 17, 2020, 7:22 AM · I think, Brian, it wouldn't just be densities - There are tensile and even shear coefficients to consider as well.

I'm very rusty on Physics, I may not even be using the right terms, but if I were still in touch with Charles, he might have more to say on this.

November 17, 2020, 9:40 AM · Boxwood is about 20% denser than hard maple, but it is also over 30% stiffer and crush/rupture resistant. So one might be able to carve a boxwood bridge a bit thinner than maple to get an equivalent mass distribution as maple and still have the bridge be a stable platform to support the strings.
November 17, 2020, 7:05 PM · I know it would be too much trouble and probably pointless but it would be interesting to hear the same violin/strings played with different timber bridges to hear how they sound in comparison to each other.
November 17, 2020, 10:55 PM · As long as you can get the mass, distribution, and mode frequencies in the range of good maple bridges, other woods should work as well acoustically.

Someone went to the trouble to carve up a pernambuco bridge blank, and sent it to me to try out. Pernambuco is far more dense and hard than maple, so it was a pain in the ... fingers ... to carve away enough material wherever possible to get the mass down and maintain normal bending frequencies. It looks rather spindly, but the sound on the violin was pretty good, but likely no better than a well-cut maple bridge. And maple is MUCH easier to carve. It's part of this thread on Maestronet if you scroll down the page: https://maestronet.com/forum/index.php?/topic/341622-alternative-bridge-materials/

November 18, 2020, 2:07 AM · Some luthiers use sycamore (acacia) bridges.
Edited: November 18, 2020, 3:04 AM · In Britain I think (from Wiki) the sycamore is a species of maple (genus acer).
I wasn't distrusting you, Herman- a friend had asserted that koa was an acacia, which it does seem to be, so I looked them up.
Woods are interesting because their properties have been known about for thousands of years. In Homer (700BC) there are descriptions of wagons and ploughs employing 5 types of wood, and modern carpenters agree that one is light and used for yokes, for example, another is heavy and used for plough beams. So, what luthiers have been using for four hundred years is probably the best thing to use.

(Plough is English for plow.)

However, I'm an ignoramus when it comes to woods and woodwork, so feel free to criticise me.

Also, taxonomy has subtleties that I might miss - I don't want to make the equivalent error of saying "a dog is a mammal and a cat is a mammal therefore a dog is a cat"!

Edited: November 20, 2020, 12:18 PM · "same violin/strings played with different timber bridges" - Brian, that's exactly what Charles and I did. But I think the bridges all had the same dimensions. Don has introduced another parameter that we should really have looked at. I suspect a balsa bridge would have to be impossibly thick to get the performance.

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