Purpose of bridge pins?

[Peter Wilcox]

In my readings I've gotten the impression that the pins are just there to plug the holes for sonic purposes, and have no part in keeping the strings in. I'm building an acoustic bass, and am thinking of just drilling holes through the bridge and bridge plate large enough to accommodate the ball ends, and seating the strings in the bridge slots, which I will make slightly deeper to preclude the strings slipping out. Does this sound reasonable? This way I wont have to make pins for it.

[Mark Swanson]

They are not there for any sonic reason such as plugging those holes. They are there to keep the strings in the slots. Of course there are other ways of doing it, and I have seen guitars made just as you describe. The bass holes and slots will need to be bigger, but it will work if you take care and get it right. However, tradition plays a big part in what people will like and buy, so that's why most guitars today have pins. There are plenty of string-through bridges too but the great majority of builders and manufacturers use the pins.
For an acoustic bass, you can use end pins for bridge pins.

[Alan Carruth]

The pins act as toggles, so that the strings don't pop out when the edges of the bridge slots get worn and rounded off. Not gonna happen to you? Don't be too sure...

I'm sure plugging the holes also does change the sound, although I don't have measurements to back that up.

Alan Carruth / Luthier

[Chuck Morrison]

The pins certainly do NOT provide an air tight seal in the holes. I haven't tested with and without bridge pins either, and I can see how it might affect the sound, but I'm not sure anyone could actually tell in a blind test.

Also, If you haven't had a bridge pin fly out as you tune up a string you're pretty lucky. The string doesn't usually move as much as they do when they break, but I still cringe a bit when I tune steel strings.

[Rodger Knox]

I could be wrong about this, but if a pin comes out when you're tuning, the string wasn't installed correctly. The ball end should be snug up against the bridge plate. If it's not, the string is held in by being wedged between the pin and the edge of the hole. This transfers the tension in the string to an upward force on the pin, which is resisted by the friction of the fit of the pin in the hole. When the tension force exceeds the friction force, the pin slips upward. Slotted bridge pins have made this a pretty common problem.
With the ball end against the bridge plate, the tension in the string is transfered to the bridge plate. There could still be some load on the pin, but it will be primarily horizontal, not vertical.
I believe that if the pin holes/slots are properly cut and the strings are correctly installed, the guitar can be tuned to pitch before the pins are installed.

[Don Parker]

I won't get into the debate of whether bridge pins (or the lack thereof) affect the sound. Smarter people than me have some opinions on that.

For me as a builder and a player, I want the ball end of each string to rest its force on the bridge plate, not the bridge pin. By having it sit right up against the bridge plate with a deep and wide enough notch, I know that the energy of the string is being transmitted to the bridge plate, the bridge, and the top. If the string ball is being held in by any significant pressure from the bridge pin (and by that I mean anything beyond just plugging the hole out of which the string might slip with loose tension), there is a sponginess to the string's response, and tuning just doesn't stay put. It is a very precarious situation, having that string only being held in by the presence of a round wedge. I have played guitars that had that problem, and it is not good.

One could draw from what I said above that I think it is OK to just have the holes there with no bridge pins. Well, that's not completely true. Without the bridge pins, it can be difficult to make sure that the string stays where it is supposed to while it is being tightened up. Keep in mind that the string has a couple of bends right there between the ball end and the playing side of the saddle. If the wire is thick enough (and with bass strings, they are pretty thick), I can see you having a tough time getting the strings to tension without some of them wanting to pop out. I guess you could prebend the strings right there in the last inch before the ball end. You wouldn't want to kink the strings in a bad spot, though.

A final consideration is aesthetic: Would the guitar look OK without bridge pins? My answer to that is no, but opinions are going to vary there.

Bottom line: I want the strings to be able to work perfectly fine without bridge pins once the guitar is strung and tuned, but I like having the bridge pins in order to get there. Plus, they look "normal" to me, while holes without bridge pins don't.

[Freeman Keller]

I also do not want to get in a big discussion/debate about whether bridge pins affect the sound of a guitar, but several years ago while pondering that question I did a series of recordings using my old D18 with four different kinds of pins (stock plastic, bone, ebony and brass) and NO pins. I used the same set of strings, same mic and record, same pic and same chords/notes - in other words I held everything as constant as I could with the exception of the pins. All four sets of pins were fitted to the taper of my holes and because the bridge is slotted they were turned around. Because the bridge is slotted I was able to pull the pins with the strings under tension (a bit scary) and do a recording with only the balls pulled up tight against the plate.

I posted these clips on another forum and there was strong opinion (1) that materials (or mass or whatever) did make a difference, and (2) no pins was the worst sounding. There are many possible explainations - less mass, the ball is not as tightly coupled to the plate since it is not also pushing sideways on the pin, etc. The clips were posted "blind" - ie. not identified, so people where just commenting on "Test 1" vs "Test 2". There was no one who liked the no pin test.

The hosting site is no longer available but I still have the clips and would be happy to e-mail them to you if you want to take a listen.

[Arnt Rian]

If your main concern is that you'd rather not use pins, why not just make a more common style pinless bridge? Here's one I did a while back.

[Peter Wilcox]

If your main concern is that you'd rather not use pins, why not just make a more common style pinless bridge? Here's one I did a while back.

I've always felt that this is a mechanically unsound configuration - it seems to me the strings are trying to pull the bridge off the soundboard, tail side first. With a pinned bridge, (or the ball ends locked against the bridge plate,) it seems the forces are actually clamping the bridge onto the soundboard, although somewhat toward the neck/headstock. In fact, maybe I'll try to not even glue the bridge down, but just glue a small strip of wood onto the soundboard just in front of the bridge to keep it from sliding forward. Of course, this may decouple some of the bridge energy from the soundboard, as in a floating bridge with a tailpiece.

Thanks for all your responses - food for thought. I agree that aesthetically the pins are probably superior, at least to most people - that's the way it's done, and it would look funny without them. Interesting that sonically, people apparently were able to identify the pinless bridge, and disliked the sound.

[Chuck Tweedy]

I'm surprised people couldn't tell the difference between plastic pins and brass. That is a huge difference in mass.

[Clay Schaeffer]

Chuck Tweedy wrote
"I'm surprised people couldn't tell the difference between plastic pins and brass. That is a huge difference in mass."

Who said they couldn't? Freeman said it was a "blind" test, and that no one liked the pinless recording.
Was that the test where most people preferred the sound of plastic pins?

[Mark Swanson]

Interesting that sonically, people apparently were able to identify the pinless bridge, and disliked the sound.

Ahh, but that is not what Freeman's test showed. There is a big difference in a pinless bridge such as the one in Arnt's photo, and a pin bridge that has the holes open, which is what Freeman was talking about. Pinless bridges usually sound just fine.

[Barry Daniels]

I've always felt that this is a mechanically unsound configuration - it seems to me the strings are trying to pull the bridge off the soundboard, tail side first. With a pinned bridge, (or the ball ends locked against the bridge plate,) it seems the forces are actually clamping the bridge onto the soundboard, although somewhat toward the neck/headstock. In fact, maybe I'll try to not even glue the bridge down, but just glue a small strip of wood onto the soundboard just in front of the bridge to keep it from sliding forward.

I predict that the experiment would not be successful. Most pinned bridges that come loose start at the back of the bridge. There is definitely an upward force on the back. Anyone doing repairs would confirm this.

[Peter Wilcox]

Interesting that sonically, people apparently were able to identify the pinless bridge, and disliked the sound.

Ahh, but that is not what Freeman's test showed. There is a big difference in a pinless bridge such as the one in Arnt's photo, and a pin bridge that has the holes open, which is what Freeman was talking about. Pinless bridges usually sound just fine.

I meant, of course, the pinned bridge used in the test, without any pins in it. Sorry if my nomenclature was in error.

[Arnt Rian]

I've always felt that this is a mechanically unsound configuration - it seems to me the strings are trying to pull the bridge off the soundboard, tail side first. With a pinned bridge, (or the ball ends locked against the bridge plate,) it seems the forces are actually clamping the bridge onto the soundboard, although somewhat toward the neck/headstock. In fact, maybe I'll try to not even glue the bridge down, but just glue a small strip of wood onto the soundboard just in front of the bridge to keep it from sliding forward. Of course, this may decouple some of the bridge energy from the soundboard, as in a floating bridge with a tailpiece.

Trigonometry certainly isn't one of my areas of expertise, so I may be all wet here, but... The rotational force on the bridge is a function of the string's break angle over the saddle and their height above the soundboard (or the theoretical plane between the string's anchor, or fulcrum points). The way the strings are attached doesn't affect this, and these factors may or may not be identical on pinned or pinless bridges. If you attach the strings as on a normal pinned bridge (with or without pins) and don't glue it down, with only a stop in front to keep it in place, I'm pretty sure it will not stay put. Even glued pin bridges peel up from time to time.

I also generally prefer pinned bridges over "stringthrough" pinless ones though, for one thing the finish behind pinless bridges usually gets dinged up pretty quickly after repeated string changes. I also like the idea of having the string ball anchored solidly under the bridge plate, and I believe it contributes 'something' to the sound.

[Alan Carruth]

Arnt Rian wrote:
"The rotational force on the bridge is a function of the string's break angle over the saddle and their height above the soundboard (or the theoretical plane between the string's anchor, or fulcrum points). "

I made some measurements on a classical guitar (tied bridge) where I could alter both the string height above the top and the break angle. The actual torque, as measured by top displacement, seems to depend only on the height of the strings above the soundboard. Changing the break angle, without altering the string height, changes the 'centroid' of the rotation: as the back of the bridge pulls up, and the front pushes down, there's a computable stationary point, and the lower the break angle the further back from the saddle that point is.

I don't have similar measurements on a steel string bridge, but I rather suspect there would not be that much difference. OTOH, I've never done an experiment yet that didn't turn up something unexpected.

I sure would like to know what sound is being transmitted to the bridge plate by the ball ends of the strings. Sure, if those are not seated the string can shift under tension, and you'll get pitch shifts and a lack of tuning stability, but that's just because the string tension isn't being held constant because the end isn't properly fixed. That's not the same thing as losing signal.

Alan Carruth / Luthier

[Freeman Keller]

I went back in the archives and found the old pin test thread. I was wrong on one statement in my earlier post - I said that these clips were posted "blind" - actually, that was another similar test I did at the same time of a whole bunch of different strings. The pins were identified in the test - sorry (it was 5 years ago, my memory has trouble with 5 days).

I said earlier that I don't want to open the "what is the best bridge pin" arguement again - the very simple results of this very simple test were that people could tell a difference and no one liked the Martin without pins. Brass was easily identified, ebony a little less so, and many felt that there was little difference between plastic an cow bone. Because of my personal ethics, I will not use any kind of ivory, regardless of how long its been dead, so that was not included.

Here is the thread - when I tried to access the Putfile clips I got error messages. If someone wants to actually listen I can put them somewhere else or email them to you (PM me an addy).

http://acapella.harmony-central.com/sho ... 8-Pin-Test

If you notice in my post #14 I say that in Audacity you can get a rough idea of the sustain of a single note by comparing the little graphs. I realize this was very crudely done - I tried to use the same picking force but Alan's wiring breaking scheme would be much better. However I could see a difference. Another aspect of this that I did not follow up on is that Audacity will do a frequencey domain transform (FFT) which should show the components of each note. I think that would be very interesting on the single open strings - does one pin have more or less of certain components.

Last comment - this was never intended to be a study of pinless bridges. The fact that I could (carefully) pull the pins without the balls flying out of the holes gave me one more comparison. I think there are some very good pinless bridges (Lowden) and some maybe not so good (Ovation) - however the pinned bridge has worked well for so long and I'll personally stick with it.

[Chuck Tweedy]

Alan asked:

I sure would like to know what sound is being transmitted to the bridge plate by the ball ends of the strings.

I'm just thinking out-loud here - no data, just theory.

Steel string bridge...
Consider a plane through the bridge, just between the saddle and the top, parallel to the top.
What does that plane cut?

Pin bridge:
The wood under (and around) the saddle AND 6 steel wires.

Pinless:
Just the wood

I don't know if it makes a big difference, but those 6 steel wires are directly connected to the signal, and they have a much (MUCH) higher modulus than the wood. Even ebony

[Peter Wilcox]

Well, I built a model to test the forces on the bridge- it's not a guitar, but it should approximate one.

The bridge is about 5/16" thick, the wood under the bridge about 3/8", to approximate the thickness of the bridge plate and soundboard. The saddle is bone, about 3/16" high. The "pin holes" are 1/2" from the saddle at one end, and 5/8" at the other. I only did two strings - scale length 24.5" so I could tune them to pitch and have appropriate tension.

Initially, with just the strings holding the bridge, forces moved it forward to the point where the break angle tried to originate from the soundboard, remaining straight through the bridge holes, then forming the usual angle up to the saddle. I placed two screws in front of the bridge to keep it from moving forward (the screws are not holding the bridge down in any manner - merely acting as stops.) Now the bridge is just held on by the clamping force of the string between the ball end and its passage over the top of the bridge hole and the saddle. It seems quite stable.

I see no advantage to not gluing the bridge, or even not using pins, but I now feel much more comfortable about the stability of a pinned bridge. I don't know why one would pull up from the back, as there seems to be no rotational force from that (or any) direction.

the "guitar"

the top

the bottom

[Peter Wilcox]

More pics.

from the side

from the tail

through the holes