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What range do you like your bridge mass to come in at. I am work on an OM at the moment. What weight do you suggest.

Thanks,

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EddieLee

It really depends on what sort of sound you're after, and, of course, the bridge and top bracing/bridge plate have to be considered as a unit in some ways. Remember that the main function of the bridge is to tell the string how long it is, so that it will know what note to make. To define the string length you need to have enough mass and stiffness at the bridge, but more than 'enough' costs sound. Too much stiffness cuts down on bass, and too much mass reduces treble more.

I make primarily 'fingerstyle' guitars, and use 'tapered' bracing. This makes the bridge area pretty stiff, so I don't need to use a heavy bridge. Anything in the range of 25-30 grams seems to work well. I had a student who got a bit carried away when she was carving her bridge, and ended up with one that weighed 22 grams, and a 'brighter' sound than she liked. We had to add a few grams of mass to the top to dial that back.

Guitars with scalloped bracing lack stiffness in the center, and tend to need a heavier bridge to keep from having 'wolf' issues. 35 grams is a sort of nominal weight there. Between the lower stiffness, the added mass, and the way the stiffness is distributed in those tops you tend to get plenty of bass and 'punch' on the attack.

It's fairly easy to add some mass to the bridge within limits. A set of plastic pins can be as light as 3 grams all up, wood more like 5, bone around 8-9 grams/set. The set of brass pins I weighed a few years ago was 26 grams, and 'Power Pins' with all the bolts and washers was 31 grams. Titanium should be somewhere in between, and tungsten even heavier: the weight of a set of Depleted Uranium pins is, of course, classified....

Thanks Al Great info!!!!!

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EddieLee

Don't worry about it.

Bridge weight is VERY important to outcomes and can make a huge, noticeable difference in how an instrument sounds.

It's also the primary reason why some folks insist that they can hear a difference between different materials for bridge pins. It's not the materials but the weight of the different pins that they may indeed be hearing.

The bridge location is the single most sensitive spot on an entire acoustic guitar where changing mass can make a very big difference.

Speaking of bridge pins weight, is it practical to make the bridge marginally light and then use metal pins to adjust the tone?

I am sure others will weigh in -- but I believe one consideration that is often over looked is the overall string set tension. One may find that the extra weight of say, metal pins could be over come by using strings with a little higher overall tension. I've heard quite noticeable changes in sound quality by merely changing one or two strings making a custom set that suits the ear and the guitar. This was pointed out to me years ago by Bob Taylor -- I bought a used 814 that was just pitiful, Bob suggested that I use the strings that were factory recommended (can't recall what they were) sure enough huge improvement. I had just re-stung with my favorites at the time, but it just does not work that way.

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Ken Cierp

http://www.kennethmichaelguitars.com/

String gauge and tension are variables in calculating the 'impedance' of the strings. This is a measure of how hard it is to move the strings aside at any given frequency, and also, in a sense, of how hard the strings push on the top at different frequencies. The top also has it's own impedance, related to the stiffness and mass, with the bridge mass being a big factor. Impedance varies depending on frequency: it's always lowest at resonances. When you hook two things together, like a string and a top, the relative impedance determines how well energy is passed between them. When the impedance matches exactly it's like there was no difference; all the energy can pass through the joint. The greater the mismatch the less energy gets passed across the junction.

The main job of the bridge is to tell the string how long it is, so that it will know what pitch to make. It does this by providing a pretty large impedance mismatch: the bridge is generally harder to move than the string because it's heavier and the top is stiffer. The bigger the mismatch the better the string works, in terms of making harmonious sounds. However, you can't have too great a mismatch or the guitar would not make any sound acoustically. Thus, as usual, we're looking for some sort of balance here.

Keep in mind that impedance is frequency dependent. The impedance of the top at any given frequency is more or less fixed by the structure and bridge mass, but different strings will have somewhat different impedance. That's why some strings match up better that others with a given guitar. In general, lighter strings, with lower impedance, will 'see' a bigger mismatch at the bridge. It's harder for the energy to get out of the string and into the top, so there's more sustain, and less power. Also, the frequency response is usually different.

Adding mass at the bridge raises the overall impedance of the top, and also shifts the resonant pitches downward. In general you'll get less sound out of a given set of strings, and much less at higher frequencies, so the sound tends to become 'bassier' and more sustained.

This is a great thread. It confirms many of my intuitive thoughts about bridges.

Thanks to Alan, Ken, and Hesh for zeroing in on things here. I can clearly see some answers in these posts.

-j

Although you're not wrong, as mass plays an integral part of the sound of an instrument, i would argue that unless you're weighing every single part, and grain counting every piece of wood, you're swimming upstream. Guitars are a stew. Every little thing impacts the sound in some way, and unless you have a point of reference, you're really just guessing anyway. You're putting so much energy in figuring out the weight of a bridge when something else could have as much of an impact. As long as the bridge is the right dimensions and place, and the neck is set correctly, you'll have a very nice sounding guitar.

I use ~20gm for my medium sized falcate SS (about OM sized, different shape)

Seriously worry about it if you're looking for a responsive guitar, like a 000/OM you'd use for fingerpicking. The responsiveness of a guitar (monopole mobility) is proportional to the 1/SQRT(effective mass of top) and the bridge forms a good chunk of the effective mass

Yes, but you likely won't need more than one brass bridge pin. Al gave the range of pin masses. If you're tuning the top main resonance, adding side mass is usually a better first step.

I think both would be steps in the same direction. More bridge mass > more bass, less treble; increased string gauge, same thing (see below)

Generally there is a pretty large impedance mismatch between strings and guitar top, or the thing would never play in tune. The string wouldn't know where its end was. The impedance of a string is proportional to its diameter; the bending stiffness of a string is proportional to the fourth power of diameter. Changing the string gauge over the normal range will affect the impedance mismatch marginally. Changing the string bending stiffness, which happens much faster (4th power), affects how many and how long the high harmonics exist on a string, very evident to those who mess with classical guitar strings and swap between nylon and fluorocarbon*, but also evident with steel strings. I'd contend that any heard difference is more to do with the change in harmonic content due to stiffness/diameter change. Those wanting practical examples, try using the same gauge wound strings, with different core diameters (and therefore bending stiffness). The sound difference is significant, the impedance mismatch is the same.

This came in whilst I was typing:

But the builder is the chef and can can control the ingredients.
I think there might be a little more to it than that, but it depends on where you set your sights...


* Fluorocarbon or "carbon" is getting on for twice the density of nylon. So nylon strings are ~1.4 x the diameter for the same mass per unit length (same tension at pitch), same impedance mismatch. "Carbon" strings are a lot "brighter", mainly because they are used at a smaller diameter.

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Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.

http://www.goreguitars.com.au

Certainly agree to disagree. Just seems like an awful lot of planning for such an organic and naturally imperfect instrument.

If a chef just follows a recipe, is he/she really a chef? Just food for thought (no pun intended).

What an odd thing to post -- I get the sense that most members are seeking knowledge in persuit of excellence not mediocrity.

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Ken Cierp

http://www.kennethmichaelguitars.com/

Doesn't have to be a recipe but I'm sure any good chef has some pretty stringent guidelines he follows. I guess if your making beef stew or building a heavy hand flat pick dreadnought throw in whatever you like.

Perhaps some of us focused more on build and less on repair look for more than just being able to get a good neck angle for decent string action.

I know I do. Though I don't weigh my bridges. I make them the same size mostly every time, but I'm sure the weight/mass varies from piece to piece.

But I account for that in other steps.

Hey Claw - hope you don't mind that I resurrected this thread AND a big, warm welcome to the OLF to ya too my friend!

In your post above that I am quoting there is actually a lot of agreement between you and I in what you said. Guitars are a stew, nice way of putting it as well, and it's very possible to put a bag of parts together and have a GREAT sounding instrument!

For some of us though we are wanting to push the envelope so-to-speak and have more control over our resulting tone. That's when things such as bridge weight get more important. Mind you I have never been a grain line counter but now that you brought it up there is still time.... But.... I am keen to weigh every single component part of my own guitars including estimating finish weight.... Wrapped too tight - you bet!

Last summer one of our clients (we have a busy repair shop, Martin authorized, Taylor too) brought us a 30's Martin that is not an all that valuable instrument, maybe $5K in current condition, and not all that rare either. But it's his and as such priceless to our friend and client. Somewhere back in time some Yahoo repair person replaced the original BRW bridge with an ebony one. The current steward of the instrument had only known his ax in the time that he has had it with the ebony bridge.

This was his idea mind you and we only enabled his dysfunction as we love to do at times but he was wondering about replacing the non-stock ebony bridge with a BRW bridge that we would craft from scratch. I was all for it. My business partner was not all that keen that it would make any difference. At the end of the day the client's wishes prevailed and we ripped off the rasta imposta ebony bridge (carefully removed it...) and replaced it with a BRW bridge that was 5 grams less in weight.

What resulted was the guitar was a VERY different instrument. Open, lots of sustain, and seemingly better definition as well. I heard it but I'm nuts.... and the client heard it big time too and was thrilled. Anyway happy camper, end of story, everyone got to where they had hoped to be. Next.

Moving back to the thread Al and Trevor (just occurred to me that if I got their names confused we might have Al Gore.... no offense intended... besides you can claim that you invented the Internet and get massages from.... well I won't go there...) Al and Trevor have done the math and heavy lifting applying physics to what we do.

Something that they can do far better than folks who assemble a bag of parts is approach or achieve to some degree "repeatability" with their creations. Being able to manipulate the response of a guitar is huge AND likely a life long study with some surprises I suspect along the way.

When one is a builder and selling their wares repeatability is HUGE and very desirable.

OTOH as you say guitars are stew I'm also keen to agree with this idea and also offer that in my experience it's pretty difficult to make a bad stew in respect to guitars. All or most of them are going to sound fine and even great I suspect at times too. But the ability to predict the outcomes and target specific models for specific playing styles won't be there to the degree that it is for the guys who do the math.

That's my take on things and it's not a matter of agreeing to disagree with me because I actually agree with much of what you said. In your model guitars are much more likely to be individuals just like we human bags of mostly water (on a Star Trek kick, sorry). And there is something to be said for guitars that are individuals as well in that some are going to be exceptional individuals more than likely.

Again welcome aboard.

Trevor and Al these are some of the very best posts ever IMHO on the OLF that you guys made - Thank You!

I plan on taking the more scientific approach in my version 2.0 building of guitars as I finally open up my new shop in the next month. I've retooled a lot having said that...

My approach was always that of the stew so to speak. After all when I started building I was study Geology at a prestigious university So I had my head in science all day. The guitars I thought of as an artistic outlook. But anyway I digress.

First, I know ebony bridges on classical guitars are commonly referred to as a no no but two of the best classical guitars I've ever built have ebony bridges. The first one I built for me before I knew what I was doing (not that I now really know what I am doing), the second was for a guy who played mine and wanted it so bad that I built him a direct copy, it sounded great too.

Second, I hate carbon strings. Does anyone really like those? Brash ugly sound imho of course.

Here comes the odd man out again...
Never bothered to weigh my bridges. They are all pyramid anyway and African Blackwood to boot. Of course, I never weigh the top or anything else either. Pretty hard to get into light when your tops are thick and braces are half hardwood...

Count me in as another builder who thinks the bridge mass is easily one of the most important variables in determining how a guitar will sound.

For the record, for myself I usually build pretty light and like my bridges very light too, in the 20g range. It helps me make a super responsive instrument for my particular style. I figure I can always add weight later if need be, but it's pretty tough to take it away on a finished instrument.

OK: the guitar is a stew. So, when you're making a stew, which ingredient will have the greater effect on the flavor, the beef or the potatoes? In our case, the bridge is more like the beef than the potatoes. Of course, all of the ingredients count, especially when you're trying to make gourmet dish, which is what we're after.

A few years ago another local builder came over with a guitar that was giving him trouble. It was a Dread, and he'd tried a rosewood bridge instead of his usual ebony. It wasn't working right, and we spent a good part of a day trying to figure out why. In the end, he took it home, swapped the bridge for an ebony one , and was happy. One of my students just finished a Dread with an eboby bridge, and loves it. He used scalloped bracing on that one, and we felt that the added mass would help to avoid 'wolf' notes. OTOH, I've made one ebony bridge for a Classical guitar, and the best thing I did for that instrument was to swap it out for a rosewood one. Different strokes...

Trevor is, of course, right, that most of the change in timbre from using heavier strings has to do with stiffness. However, the change in impedance is particularly apposite in terms of wolf notes and pitch change.

The fact is that in many cases you can clearly hear the change in sound from adding or taking off a couple of grams at the bridge. Sometimes you can even measure it!

You guys have made me hungry for a good beef stew.
As far as bridges go, all of mine have been EIR with one exception. I weigh them mostly because I can, and the EIR bridges come in around 20-22 grams. The lone exception thus far is an ebony bridge that I couldn't get below 25 gm. Went with ebony on this classical (classicals are all I've made thus far) because the fret board was ebony. Ebony just looked better on this maple guitar to me. Don't know how it sounds in comparison to the others I've made, don't have strings on it yet (waiting for tuning machines). I'll report back in a few days.
What cut of beef do you use for your stew?

You know sometimes all it takes is a suggestion, the power of suggestion that is. It's a nasty cold and rainy day here in the mountains of Virginia and I think I'm gonna have to make some nice hot beef stew tonight.

Speaking of power of suggestion, #1, eir sitka om cutaway, ebony bridge, a Martin kit, still my go to steel string. It has a good balanced sound, nice in bluegrass/celtic jams, but I'm a finger picker. I've always thought it wasn't as responsive as I would like albeit versatile. The idea of swapping bridges has been brewing, um can I say simmering?, for a few years. This thread has pushed me over the edge, picked out a nice eir blank from my stash and started shaping. My son just invested in a nice mike for recording Ill have him do a preswap and postswap recording. I'll weigh the ebony after removal and note the weight of the new bridge, should be an interesting project.

Good to know.

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George :-)

So easy a caveman could make one!

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Ken Cierp

http://www.kennethmichaelguitars.com/