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Weekly Thought


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It may take me a week to actually build up to having a thought, but here we go:

In my last thread, I had a thought about an arm rest to stop our fat hairy arms from deadening the vibrations of the soundboard. Last night however, I turned my attention to the bracing. Bracing obviously strengthens the soundboard however; I wanted to think about removing as much bracing as possible. The route that I'm going down is to try and get the purest vibration through the soundboard, with as little changes as possible. Bracing obviously works against that so I was thinking of the best way getting rid of as much of it as possible.

Well, I think that the primary problem here is the fact that the strings anchor to the soundboard. This will put a considerable amount of force on the soundboard as you can see from old acoustics where the soundboard can be bent in front of the bridge. I think that the best way of doing this is to secure the strings to what is essentially a tail piece that you would see on a jazz guitar. I was actually thinking of having it internally though to keep the looks right (although it might look rather nice). This would be attached to the tail block.

There would be a typical acoustic bridge and saddle that the strings would pass over in order to apply downward pressure on the soundboard.

So that's the majority of the forces off the soundboard and I'm sure that there would now need to be less bracing. I was then thinking about the using the arm rest idea with this, so that's another deadening source out of the top.

Also, a passing thought which I haven't had chance to think about properly yet. What if the above was combined with the soundboard mounted like a speaker, then it could flex relatively freely with the joint between it and the sides. Obviously the sides would need to be braced to take the place of the top making the box strong. This would also take any stresses off he top that we add by resting our arm on the top and having it pressed against out leg creating a bending moment. All the force would be in the sides and back leaving to soundboard to be able to wobble at its hearts content.

All I need now is someone to put these ideas into practice as I don't have the time and money to do it myself. Like with the metal resonators that I'm building with a luthier, as long as I get one of the guitars at the end of it, I'm happy. Or a job would be nice. :D

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The Monkey Man is at it again :D

I have put a lot of thought into the bridge function, and possible ways to improve upon it. It is hard to fully understand how a bridge moves(I should say what movements are most important). It is my understanding that a bridge moves up and down, side to side, wobbles, and twists. A major component of efficiency is how well the string is locked into the saddle(as slipping is going to amount to energy loss). My focus in "experimental" design has been on balance of forces in a "neutral state"(strings not being played), and applying tension at a straight angle to the soundboard(again at rest).

I have thought about anchoring the strings off the soundboard. I don't know if it is the real issue. In so much as the soundboard doesn't usually distort from linear tension as much as from twisting or torsion in conjuntion with the tension. Keep in mind a sound boards is very strong when you pull on it parallel to the surface, but when you pull perpendicular to its surface it is no where near as strong(it is less than 1/8" thick).The lever action of the bridge is an important one though as we can percieve by using a tall saddle and the big increase in volume(of course too much height and torque will deform the board).

I am working a concept now that takes a different approach to "balancing" as well as getting a better bite on the saddle. The only way I will know if all my theory actually makes things work better is to hear it in action.

I love the thought of the week! You rock ToneMonkey :D .

Peace,Rich

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A few thoughts:

1) If you want to remove mass, build with a much, much, much lighter bridge. It weighs more than all the other bracing put together, usually. Also, remember the top is much heavier than all the bracing - that's where the mass is. Then there's the issue of why a 'pure' unbraced soundboard is something to strive for; the bracing is there for strategic strengthening of specific areas. Look at Breedlove's implementation of the JLD bridge doctor into their tops; it takes some of the torque out of the picture, lets them brace very lightly, and cut down on top weight. I don't think they sound any better than any other guitar, but they are good guitars.

2) A tailpiece above the guitar will redistribute forces quite a bit; a pinned or pinless 'regular' bridge torques the top; bracing reflects this by being stronger and stiffer above the bridge/soundhole, and more flexible below. Add a tailpiece (inside the guitar, outside the guitar, matters a little but not hugely I'd think) and you're converting the pressure into almost purely downward pressure. A lot more tension coming down behind the bridge, so you'd need to beef up that area. Whether the energy transfer/conversion of vibration into sound is as effective in a flattop design (archtops are entirely different instruments that way) is very much up for grabs.

3) The soundboard already IS mounted like a speaker; very little connection on the edges, many folks thin out the edges to make them even more flexible, and many folks build with very stiff sides already. I can't think of a feasible, durable approach that will actually be able to withstand string tension (of whatever type) and really be an improvement.

I like brainstorming as much as the next guy, but I'm one for incrimental changes. I also like questioning the basic assumptions, and trying to figure out exactly what the goal of radical redesigns is. There's got to be a reason for acoustics, IMO. So, yeah, go ahead, rebutt me, let's got some heated discussion goin' on :D

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When reading about stuff like this I'm a little dubious as to such ideas.

Modifications such of this will change the sound of the instrument, I'm sure, and it will make the top vibrate more "perfectly", but it's the jangly imperfections in the guitar's sound that makes it what it is!

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Some interesting thoughts guys. Unfortuntely, I've got to get right into the middle of Birmingham via the M6 (got to be seen, going to spend the next hour and a half sitting still in traffic). So now I've got something interesting to think about rather than the meeting.

Should hopefully make it back to the office today, so I'll try to reply later.

Happy Monday guys :D

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"So, yeah, go ahead, rebutt me, let's got some heated discussion goin' on "

:D If you want a heated discussion. Then you have to give me something to argue about. :D

How light do you try to get with your bridges?(30,25,20gr??) I know that is going to vary a bit with wood, but what is your target. I know my last African Blackwood bridge is going no lower than 32gr.( it is a heavy wood).

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A lot of what I was thinking, wasn't to do with saving weight as such. It was more to do with decreasing the stiffness of the soundboard by reducing the bracing.

Anyway back from meeting, got to go and let the landlord in now. The door fell off my fridge last night.

Hopefully I'll have 5 minutes to myself tomorrow. I'll do a proper reply then.

Kaj :D

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I think that the best way of doing this is to secure the strings to what is essentially a tail piece that you would see on a jazz guitar....there would be a typical acoustic bridge and saddle that the strings would pass over in order to apply downward pressure on the soundboard...what if the above was combined with the soundboard mounted like a speaker, then it could flex relatively freely with the joint between it and the sides.

You're describing an archtop! This setup reduces the torque on the bridge, and carving the recurve basically gives you your "speaker" effect (for both top and back).

As I understand it, the pull/twist you get at the bridge contributes a considerable amount of energy to drive the soundboard. In this regard, one comment I've heard about the Bridge Doctor is that it tends to knock down some of the attack. I've been meaning to test drive some Breedloves to check this out, but havent' gotten around to it yet.

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If you want to route the strings internally so that they are exclusively in tension between the nut and the tailblock, by way of whatever means you like, but so that the strings still pass over a nut and through a bridge like a "normal" acoustic would, I think you will have some issues.

1. How on earth do you plan to get the ball ends into the tailpeice if it's all way inside the body? Do you want to reach into the sound hole and set them in carefully? Make 6 holes in the tailblock like an electric to make it a string-through designthat feeds up to the bridge? Is the tailpeice going to be fixed in place? Physcially connected by tubes to the bridge to facilitate stringing?

2. What about the length of stringds as they are currently sold? Adding an extra foot os so of length to reach the tailblock will probably not allow you to use off-the-shelf strings in your new guitar since they wont be long enouth to take up the full length from tailblock to tuning machines.

There's probably more to deal with, but as far as internal routing I think these two probably kill the reasonable feasibility of the design.

-Dave

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davee - ha ha, I thought of that/them.

Erik - Not heard of the bridge doctor. I'll have a look around for that.

Unfortuanetly guys, I just got back to office and straight into another (rather dull) meeting. But that was better than crawling around under a building, dodging used needles and playing with rats that I was doing yesterday (to be honest, I enjoyed the rat dodging more than the meeting). Who the hell builds a 17 story building over the top of a canal anyway?

I've been on the phone four times now since trying to write this and I've got someone blathering in my ear at the minute. Hopefully I can get a bit of a lunch break tomorrow and I can try to reply properly then. :D

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Can i just say Tonemonkey....

You poor bugger having to endure the M6 on a monday morning.

Thank god i live within 5 minutes walk of where i 'work'.

Oh.. and Cardiff rules.

S

Are you sure that you're not my borther :D ? Don't you work at heath hospital? He does, and lives a couple of minutes walk away on Clodian Avenue. Freaky.

Now that I've actually decided to have a lunch break, I'll reply (bet my phone rings at least 3 times while I'm writing this though.)

First thing to remeber is that this was just a thought, it may be that I'm completetly wrong. I wasn't really thinking of how to build it, more the theory behind it. My initial thinking is that in order to get the air vibrating within the sound box, it is the motion of the soundboard working in a vertical motion (when the guitar is laying on it's back) that causes it. I started to think about how to maximise this movement and this led me to think about reducing the stiffness of the board as much as possible. In my head, looking at the very ends of the spectrum, if the soundbopard was absolutely stiff (i.e. no motion) then the air inside the air box will not be affected to any significant extent by strumming. If however, the soundboard was made of rubber (i.e. lots of motion) it will affect the air inside the soundbox to a much grater extent. So I followed this and thought QED the less stiff the soundboard the more of an effect it will have on the air inside the soundbox (rightly or wrongly).

So I was thinking about how to reducing the bracing to reduce the stiffness of the board. The weight issue that Mattia was refering to would alter the transient response of the soundboard, but not the amount of affect that it will have on the soundbox. If the soundboard was heavier, it would react slower, but the affect on the air would be much the same as for a lighter soundboard of the same stiffness.

My thought process took me down the route of: There is a massive lateral force acting here that appears to be detromantal to the movement of the soundboard. As someone mentioned, this lateral force (of the strings pulling along the same line as the soundboard) may be a good thing. I certainly wont argue against this fact, as to be honest I just don't know. However, I was thinking of reducing this as much as possible so that if you draw a force diagam of the soundboard, the only major force acting upon it would be the strings pushing in a vertical vector, directly down onto the soundboard (or as close as possible anyway). That way the affect that the strings have when plucked is turned into as much vertical motion of the soundboard as possible (therefore more movement of air).

The strings were to be solidly mounted to the heal so that it is this that would be taking the force which would usually be transfered through the soundboard. I have had a few thoughts on that, but once I realised that it was possible, I stopped. Not worked out the best way of doing it, but it's possible and that's good enough for me. I did once think of a bridge design that would even out the forces anyway, but for ease of understanding, I figured it was better to model the strings as being mounted off the soundboard. I thought that with this design it would be worth increasing the vertical force on the strings to compensate for some of the force that would be lost from mounting the strings.

3) The soundboard already IS mounted like a speaker; very little connection on the edges, many folks thin out the edges to make them even more flexible, and many folks build with very stiff sides already. I can't think of a feasible, durable approach that will actually be able to withstand string tension (of whatever type) and really be an improvement.

No neither can I, but I bet it's possible :D It was more of an asside thought while I was typing B) .

Davee - It's possible, that's all you need to know B) Kidding aside, I'm not worried about how to build it at the minute, it's just a theoretical discussion.

So any thoughts anyone. Would decreasing the stiffness of the sounboard increase the sound. Also like I said, or haven't said more to the point. I don't know if it would sound better even if it did work. But it's getting close to sounding like a resonator where the soundboard is the speaker.

I've got two very much deserved days off work tomorrow and the day after, so if I don't get chance to have a look later this afternoon, I'll probably see you all on Monday.

And the phone did go a couple of times, it's taken me nearly an hour to write this reply while wrestling with work, so if it's not too conherent, then I'm not to blame.

Kaj :D

Edited by ToneMonkey
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Larry Davis described it to me this way. Basically, when building an acoustic, you're trying to thin the wood just short of the point of collapse, but leave it thick enough that it will stay together for decades.

You're really in the archtop way of thinking; the tailpiece takes up the lateral tension that a saddle takes on a flattop. You could conceivably relieve more of the lateral forces by having your tailblock (where the tailpiece screws into) attached to the headblock....almost in a neck-thru sort of way, with the rest of the box sort of "suspended" around the neck-thru. This way, you don't transmit the string pull to the box.

Problem is, that bit of wood running down the center will impede airflow within the box. I have no idea what the tonal affect would be on a flattop; on an archtop (where the top also drives the back), I think it would be detrimental.

To maximize the downward driving forces on the top, you increase the break angle over the bridge (one reason why archtops are arched), but now you're also putting more stress on the top. Too much stress, and the top won't vibrate freely in response to the strings (or could collapse); too little stress, and the top won't move much air. Somewhere in there is that magic balance everyone strives for.

Edited by erikbojerik
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