Things that affect the sound of a bow

[GMM22]

Violinists often express how important the bow is. In fact, I have read more than once the suggestion that tone production is the first quality to be sought after when choosing a bow.

Obviously, the playing dynamics of a given bow can be altered drastically by changing the taper, camber, balance point, mass, etc. My question is: Has anyone directly observed a change of these or other criteria (excluding hair quantity or quality), as having a direct effect strictly on tone production? In other words, has anyone ever changed a grip from silver to silk for example, and precisely noted a change in tone production?

Similarly, has anyone been able to improve the sonority of an average sounding bow?

[Jacob]

The two elements which in my experience have a big influence on tone are the hair (more the amount than the quality) and most certainly the camber - the amount of the latter, as well as how amount of camber is distributed along the length of the stick.

[GMM22]

I must confess that it initially seems counter intuitive to me that the camber could have any effect on tone. I would have imagined that the camber would relate strictly to dynamics. Given that bows are often re-cambered, perhaps others will confirm or contest this. I would add that I hope that your suggestion that camber can directly affect tone is correct.

[Andres Sender]

Camber effects the elastic behavior of the bow, which in turn affects tone.

One of the best baroque bows I've made started out having a very lush full tone but was a bit too bouncy. I made some slight modifications to the way the stick worked by adding a slight camber. The operating characteristics of the bow improved drastically but the inherent lushness of tone faded slightly.

I think one needs to be clear on what is meant by "tone production". I take it to mean a bow's ability to translate the violinist's actions into the various tonal qualities a violin is capable of. It's not necessarily about one inherent tonal quality of the bow. The latter may be in bows much what it is in violins--something highly valued more by amateurs than by pros.

[Guy_Gallo]

A Bow On the Couch

An interesting online book by a bowmaker that might answer some of your questions.

[JasperSnavely]

The density of wood, quality of the hair, rosin used, and balance of the bow have most to do with the sound.

[Jimbow]

falstaff,

Thanks for introducing us to this excellent resource "A Bow On the Couch ".

Section 6 'Distribution of Strength' certainly confirms Jacobs opinion and elaborates on camber to those who would minimize the effects.

[jimbo]

Falstaff

I also am impressed with your ability to come up with these books ,etc,in answer to "in depth " questions. How do you do it? I peruse the web in several areas of endeaver but never seem to find the same info.

[GMM22]

I can see what you are saying about camber affecting tone production as you have described it, but I did mean it in a much stricter sense, e.g. the inherent tone as might be produced by long bow strokes on a single string or double stops, outside of any coloration induced by playing dynamics.

Do you think the differences in tone production are still present if hair tension is compensated for, i.e. tightening the bow hair to the same tension pre and post re-cambering? In other words, could the tone production have to do more with the hair tension in operation, than the actual camber? I am not sure if I have phrased this question adequately.

I did not quite understand your last two sentences. I thought it was the other way around, but I think you may be referring to something more subtle, which I am not yet aware of.

[GMM22]

Falstaff, I first read this some time ago. The author makes many interesting observations not to be found elsewhere. In fact, part of my early skepticism that camber could affect tone, is based on this author's own observations. He describes damping of specific frequencies as having great effect on tone. I cannot yet visualize any possible change in the damping characteristic as a result of changing camber, in the way that say changing the frog to one with a more massive ferrule might. I hope that this issue will become clearer to me.

[Guy_Gallo]

If I am understanding various sources correctly, including Gutter and my own experience trying out bows, then one aspect that directly effects tone is not the extent of the tension, but how precisely that tension is achieved.

Making a bow tighter to achieve greater tension is not the same a a strong bow with a good camber (even if the measurable tension is the same). The reason is that when you increase the tension using ONLY the hair, you are also changing the elasticity and the strength.

There is a aggregation of forces, in a different mix with every bow: weight, elasticity, camber.

Weight and elasticity are a function of Mass and Density. Less dense, more elastic. More density more weight. Less dense but more mass. The permutations are limitless.

I would describe camber as the distribution of strength along the bow.

Given a specific combination of Mass and Density, the nature of the camber will determine nature and distribution of the stength and tension along the length of the bow.

You will often hear a archetier speak of a "weak spot" behind the head or in the middle. Playing a long slow soft note you can detect this weakness a very slight modulation in tone or a slight diminishing of volume requiring adjustment by the right hand to achieve consistency along the length of the bow.

The change from the heavy frog end to the lighter tip end should be consistent.

And I believe how camber distributes the inherent strength of the stick is what achieves this consistent distribution of string tension.

That is why a good recamber can rescue a bow and a bad re-camber can completely alter its sound.

TIP: a seasoned bow person can tell much about the camber/strength simply by pressing the tip into the palm of his hand. I was taught another way of examining the strength/camber of a bow. With hair loosened point the bow to a blank wall (as you would to examine the straightness), turn it on it's side (hair to the left, stick to the right), loop a finger beneath the hair about three inches in front of the frog and pull. This should immediately display any humps and bumps and crooks created by weak spots. An evenly strong bow will straighten evenly from frog to tip.

[Fellow]

When you (people) talk about bow, you use the word "camber".

I don't know what it is referred to. Is it the abstract curve formed by the stick of the bow ? If you tighten it real hard, it will be flatened (the curve changes , in geometry) ?

Ot you mean the tension of the screw? Thank you in advance. /yuen/

[Guy_Gallo]

There is nothing abstract about the curve of a bow. It is achieved by a combination of carving and heating/bending the stick.

And yes, that is the camber. It varies from stick to stick.

[Fellow]

Another question : I often see a bow crooked (ie. go side way if you tighten it) can it be easily fixed ? I don't want to know how. Is it expensive to fix? I hear comments that they (most players) suggested throw the bows away. I am confused because I have to take into the account that people dislike something they say throw it away. Thank you. /yuen/

[Regis]

QUOTE: "I was taught another way of examining the strength/camber of a bow. With hair loosened point the bow to a blank wall (as you would to examine the straightness), turn it on it's side (hair to the left, stick to the right), loop a finger beneath the hair about three inches in front of the frog and pull. This should immediately display any humps and bumps and crooks created by weak spots. An evenly strong bow will straighten evenly from frog to tip."

Falstaff,

Thank you for the excellent tip. When a "hump" is present, in the middle for example, how do you approach correcting that? Using that method, I'm looking at one I'm working on that exhibits a slight hump covering about 6" long and centered slightly behind of middle when the tip is pulled straight with the butt (using this method). This bow's camber is very evenly distributed, frog to tip as is its taper. The deviation is only a couple mm but, enough to easily notice. When fully tightened with the screw, there is no evidence of hump (but the tip does not come fully straight).

Great discussion!

[Guy_Gallo]

I do not know how to correct for such a hump/point of weakness.

If I understand the process of cambering a bow, the application of heat to create the camber itself is a source of weakening. So recambering a bow with such a weak spot may further weaken the stick.

Perhaps others, who make and repair bows, will speak up here.

Perhaps by moving the point of the camber's start (more to the middle for instance) you can even out the weakness. But that is an uninformed guess.

[Guy_Gallo]

Fixing a bow that has a lateral bend (left or right) requires the same process of re-heating as recambering. Therefore doing so can weaken (or even break) the bow.

Some slight deviations laterally can be caused (and compensated for) by how the bow is haired.

I've also been told that a slight bend to the left is less of a problem than a bend to the right (in terms of tone production and tracking, I believe).

[GMM22]

"If I am understanding various sources correctly, including Gutter and my own experience trying out bows, then one aspect that directly effects tone is not the extent of the tension, but how precisely that tension is achieved."

"Making a bow tighter to achieve greater tension is not the same as a strong bow with a good camber (even if the measurable tension is the same). The reason is that when you increase the tension using ONLY the hair, you are also changing the elasticity and the strength."

............................

A small window of understanding is opening but it is slow in doing so. I believed that the elasticity and strength (and thus tone as well) are fixed by the bow's dimensions and not the camber, at least within the relatively minute variations found in bow camber. However, this can be experimentally determined with any piece of wood by making a simple cantilever, loading the end with a reference weight, measuring the drop, cambering the cantilever slightly, loading similarly, and noting any deviations. It is not necessary to perform the experiment since it is well known that the shift in the neutral axis would cause there to be some change in measured strength, but it is still hard to see it being significant at all at the degree of change observed in various bow cambers. This is the first glimmer of insight I have in accepting the camber's influence on tone.

Imagine that we have in front of us an excellent sounding Peccatte. We quantify the sound quality by mapping response with a spectrum analyzer on very simple bow strokes. Now we take a heat gun and alter the camber somewhat erroneously, and then re-analyze. That the mapping could be radically altered still appears miraculous. It seems likely that someone has already performed this experiment (not with a Peccatte of course!)

I have never observed the so-called weak spot you describe, but it is likely my ear is simply not yet refined enough to sense it. Back to Grutter's theories, perhaps this flat spot corresponds to the point at which the longitudinal waves meet and interfere as they travel in opposite directions. As well, if flat spots have any correspondence to camber, then it stands to reason that the flat spot will move depending on the given camber of a particular bow. I wonder if someone has ever noted the movement of the flat spot merely by changing camber.

I do not fully understand how to perform your tip about checking for humps. Where do you hold the bow? How is this different from merely tensioning and similarly sighting up? I realize this may be hard to express.

There seems to be another way to correct so-called weak spots at least when a bow is being made. If I understood my original source of information correctly, French bow makers tended to plane away wood in order to equalize strength distribution. It was suggested that they roughly taper, bend the bow, hair it, bring it to tension and then plane away until it yields ideal camber. Can anyone comment on this?

[Guy_Gallo]

"I believed that the elasticity and strength (and thus tone as well) are fixed by the bow's dimensions."

I do not think the equation is so simple. The "machine" part of a bow -- the thing that acts UPON the rest of the stick, is the camber in combination with the tightening of the bow hair. It should be obvious that a variation in camber -- its placement, its severity, its delicacy in creation (that is, how little damage was done to the wood in its making) -- would impact the overall strength and elasticity of the stick.

The strength and elasticity are NOT fixed. Perhaps a range of strength and elasticity is defined by the dimensions of the stick. But what will be their precise nature is determined by camber and the obviously related tightening of the hair.

As for checking for week spots. You are holding the bow at the frog end. Start holding it as if your are about the play, point the bow straight ahead, twist your hand so your thumb knuckle is pointing at the ceiling. The frog should now be parallel rather than perpendicular to the floor.

Take the thumb of the left hand and place it against the slide of the frog. Take the index finger and place it between the stick and the hair about two inches up from the ferrule. Using leverage against the left thumb, pull the hair until the stick straightens. Carefully. If there is a weak spot it should be visible even before the stick is completely straight.

As for why this method shows weak spots when simple over-tightening the bow hair -- I would guess it has to do with the even distribution of "pull" when tightening, and the ever so slight leverage of having the point of energy/force perpendicular to the stick rather than parallel. But that's a guess. I just know I've seen it.

[Guy_Gallo]

It occurs to me that those reading this may run off and immediately yank at their bows to check for weak spots.

Please be careful.

Like over tightening a bow, this test could do damage.

Be forewarned.

[Guy_Gallo]

"Making a bow tighter to achieve greater tension is not the same as a strong bow with a good camber (even if the measurable tension is the same). The reason is that when you increase the tension using ONLY the hair, you are also changing the elasticity and the strength."

Another thought on this aspect of tension as product of stick+camber versus stick+camber+greater tightening...

It has been my experience that a stick that requires greater hair tension in order to create a good contact with the strings loses something in stability. That is, such a over-tightened stick does not track as well (and thereforew produces a more erratic tone).

[Guy_Gallo]

Quote:

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I often see a bow crooked (ie. go side way if you tighten it) can it be easily fixed ?

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If a bow is straight when loose and curved laterally when tightened, it's likely a rehair problem -- not a problem with the stick. That is, the hair is tighter on one side or the other.

So, yes, it can be easily fixed -- by getting a better re-hair guy.

[Claire Curtis]

Falstaff said

"the application of heat to create the camber itself is a source of weakening. So recambering a bow with such a weak spot may further weaken the stick"

Not exactly. You heat the wood until it reaches a point of plasticity, and will both go where you bend it and take that new bend as a natural state. If you don't heat it thoroughly (probably the most common error) and bend the bow to shape, it may resist and crack. It will also have a tendency to eventually return to its original shape. For a properly heated bow, the new cambered shape IS pretty much the 'original' shape.

However, anytime you heat a bow in this fashion there is a chance that the relaxing wood stucture will unveil a hidden cellular stress, and the bow will quite literally explode. This is not necessarily anyone's fault; it is a fault in the wood itself and the break was inevitable (though perhaps may not have been so spectacular without intervention). Thus any recambering should be accompanied by warnings to the owner, and approached gingerly.

After the bow has cooled and solidified into its new shape, the wood is actually harder and stiffer than before the cambering. This is the same 'flame hardening' that primitive hunters used to harden wooden spear heads. (And is also one reason why recambering is, in my opinion, more difficult than the original cambering).

GMM22 said

"...French bow makers tended to plane away wood in order to equalize strength distribution. It was suggested that they roughly taper, bend the bow, hair it, bring it to tension and then plane away until it yields ideal camber. Can anyone comment on this? "

I learned to make bows in the French tradition, and that is indeed the sequence of events. I blinked a little at the description of planing to "equalize strength distribution", but then decided that while it's an odd way of putting it, it's probably correct. To me, the process is almost identical to the process of graduating a plate (at least in the way I was taught; that is, to remove wood in those places that seem insufficently flexible or springy). For a violin plate, you constantly stop and flex the plate in different directions, feeling for stiff spots; when graduating a bow, you stop and flex it all along its length, you tighten the hair and observe the bow's reaction, you play the unfinished bow and feel how it springs back at the tip, in the middle, near the handle. In both cases, you remove wood from where it seems stiff, so I guess that is to 'equalize strength distribution'.

The advantage of the French method is you listen to the wood at all times. It is the difference between graduating a plate "to the numbers" and graduating a plate according to what that particular piece of wood needs. And that, to me, is the essential difference between a handmade and a factory violin or bow. Skill at listening to the wood and determining what action to take then determines whether the violin or bow qualifies as a master-made item.

Just my 2 cents --

( I think I'm one of the few makers I know who thoroughly enjoys both violin and bow making.)

-Claire

[Guy_Gallo]

Thanks for the clarification (and elucidation), Claire.

Interesting to learn that the common error is not heating enough. (Scorching is a different issue, I assume.)

And to think of the "new bend as a natural state."

[GMM22]

"The strength and elasticity are NOT fixed. Perhaps a range of strength and elasticity is defined by the dimensions of the stick. But what will be their precise nature is determined by camber and the obviously related tightening of the hair."

...............................

I think the key is your suggestion of "range of strength". However, they are fixed in large part, and that the tone of a bow could be largely governed by this small range is still mysterious to me. It is an interesting starting point of new investigation.