Four-piece tops, stiffness, and tone

[PeteyPower16]

I recently purchased a guitar with a four piece koa soundboard top.

Most of the guitars of this particular model have a two-piece top, but there are a handful with four. The four piece tops have a book-matched wedge design that mostly covers the width of the bridge, with larger book-matched wings on the outside.

Most traditionalists would run away from a four-piece top, even if they might consider four piece for a guitar back. At this point, I am committed to this particular instrument.

The manufacturer says that they brace the four piece tops differently than the two piece, which results in additional stiffness, which could limit dynamic range and make the guitar better for strummers. This leads to four questions I’ve been thinking about:

1. All other factors being equal (and they never are), how would a four piece top (compared to a two-piece top) affect tone, resonance, and volume?

2. Why would different bracing be needed? Is the top with additional glue joints stiffer, or less stiff than its two-piece equivalent?

3. All other factors being equal (and they never are), how does bracing thickness affect tone, resonance, and volume?

4. Why would a strummer prefer a stiffer top with heavier bracing?

By the way, this guitar plays well, sounds great, and also (in my opinion) is the nicest looking specimen of the entire line. I’m just trying to understand the theoretical differences due to construction.

[runamuck]

I don't understand why the manufacturer would brace a 4 piece top differently than a 2 piece unless all the wood they'd amassed for 4 piece tops were less stiff than they would usually use. There's nothing inherently weak about a glue joint.

[PeteyPower16]

Originally Posted by runamuck

I don't understand why the manufacturer would brace a 4 piece top differently than a 2 piece unless all the wood they'd amassed for 4 piece tops were less stiff than they would usually use. There's nothing inherently weak about a glue joint.

Could it be that the possibility of slightly different grain directions on a four-piece too ADDS stiffness, which would thereby require LIGHTER bracing? I am just speculating…it could be the opposite.

[redir]

1. All other factors being equal (and they never are), how would a four piece top (compared to a two-piece top) affect tone, resonance, and volume?

In no way.

2. Why would different bracing be needed? Is the top with additional glue joints stiffer, or less stiff than its two-piece equivalent?

It would not require different bracing. The top stiffness given all things identical would be equal.

3. All other factors being equal (and they never are), how does bracing thickness affect tone, resonance, and volume?

Thickness has much less affect on tone then height does. So not much really within reason of course.

4. Why would a strummer prefer a stiffer top with heavier bracing?

There is a concept called 'head room' which is analgous to a high versus low watt amp for an electric guitar. the low watt amp would break up and distort as you increase the volume while the high watt amp would stay clean. Strummers tend to hit the strings hard. Stiff braces would give you less responsiveness but more head room.

-

It's possible one could argue that three glue joints on a top might make it stiffer than a top with just one but it would be negligible. None the less even if that was the case a small shop luthier would use methods like deflection testing or even old school touch and feel to make it so that the top had the proper stiffness for the standard bracing.

[Alan Carruth]

redir wrote:
"Stiff braces would give you less responsiveness but more head room."

A heavier top also tends to increase 'headroom'. The limiting factor in how light you can make a top is stiffness; ant piece of wood that is stiff enough should be strong enough. Stiffness is a function of the Young's modulus of the wood along the grain (E-long), and the cube of the thickness of the top. In softwoods E-long pretty closely tracks density, in a linear manner. Making a low-density top a little thicker gets the stiffness up without adding much weight, and ends up making a top that is lighter, more 'responsive', and with less 'head room', all else equal. Hardwoods, like koa, don't follow the same rule because they're structurally a bit different: they tend to be denser but not to have higher E-long values. You need to leave a hardwood top almost as thick as a softwood one, usually, to get the same overall stiffness, but since it can be as much as twice as dense the top weighs more. It will tend to have less treble response, and more headroom.

We've been spoiled for a long time by the availability of large trees. We're so used to seeing two piece tops we think they're required. They aren't. I suspect that will be one of the many things that our children won't have the luxury of getting used to. They will still be able to buy good guitars, though.

[John Arnold]

Without seeing what was done to stiffen the bracing, it would only be speculation. I can only conceive of one scenario, and that would be adding cleats or a continuous reinforcement strip (like on back joints). IMHO, that is totally unnecessary.
I have built guitars with multi-piece tops, and have never felt any need to compensate in any way. One of those is ten-piece, and it is now over 40 years old, having been built in 1981.

[PeteyPower16]

Looking closely at the two GS mini koa guitars in the video, the plus model appears to have the four-piece wedge top. The tone is slightly different, and I think I appreciate the warmth of the four piece top better. Hard to say if there are not other factors here that would affect the slight difference as well.

Assuming that all other factors are the same (e.g., same bracing type, size, and strategy as I confirmed when comparing bracing in my spruce mini with a two piece top and my koa mini with a four piece top), how would you say the tone differs between these two koa models, and what would you say might be the physical reasons that a four piece would result in that difference?

https://m.youtube.com/watch?v=KJgbaw612gc

[Alan Carruth]

Basically, I don't think anybody can say for certain what the difference would be simply due to the number of pieces in the top. Even using matched wood it's probably impossible to make guitars that sound 'identical' (and I've tried!), so there's no good way to do a definitive test. You will get lots of opinions on what people think the difference should be, but that's all they are; opinions. At least, that's my opinion...

[GCWaters]

Originally Posted by PeteyPower16

Looking closely at the two GS mini koa guitars in the video, the plus model appears to have the four-piece wedge top. The tone is slightly different, and I think I appreciate the warmth of the four piece top better. Hard to say if there are not other factors here that would affect the slight difference as well.

Assuming that all other factors are the same (e.g., same bracing type, size, and strategy as I confirmed when comparing bracing in my spruce mini with a two piece top and my koa mini with a four piece top), how would you say the tone differs between these two koa models, and what would you say might be the physical reasons that a four piece would result in that difference?

https://m.youtube.com/watch?v=KJgbaw612gc

Haven’t watched this, but does Taylor say they’re using four piece tops?

[PeteyPower16]

Originally Posted by GCWaters

Haven’t watched this, but does Taylor say they’re using four piece tops?

There is a spot on a podcast where Bob says they will start doing it soon. Some of the GS mini Koas definitely have four piece wedge tops—on recent models it is as frequent as 1/3 of them. I would expect others in the Taylor line to follow soon.

Check this out at 1 hour 2 mins in:

https://www.youtube.com/watch?v=usAM7BO9DoA

[GCWaters]

Originally Posted by PeteyPower16

There is a spot on a podcast where Bob says they will start doing it soon. Some of the GS mini Koas definitely have four piece wedge tops—on recent models it is as frequent as 1/3 of them. I would expect others in the Taylor line to follow soon.

That’s interesting…Taylor never does anything this big without a major announcement …

[GCWaters]

Originally Posted by PeteyPower16

There is a spot on a podcast where Bob says they will start doing it soon. Some of the GS mini Koas definitely have four piece wedge tops—on recent models it is as frequent as 1/3 of them. I would expect others in the Taylor line to follow soon.

And where does your 1/3 figure come from?

[PeteyPower16]

Originally Posted by GCWaters

And where does your 1/3 figure come from?

This is a VERY rough estimate based on a review of peoples’ posts on the Facebook GS mini appreciation group, Sweetwater “buy this exact model” photos, and my local guitar store. I wouldn’t call that a statistical sample size, but I could post 5-10 photos of these as I’ve saved and photographed the examples. You can tell if there is a slight diagonal wedge right below the bridge.

[PeteyPower16]

Originally Posted by GCWaters

That’s interesting…Taylor never does anything this big without a major announcement …

I’m pretty sure that it isn’t getting much attention from customers yet because it is primarily on Koa minis. Maybe Taylor’s strategy on this one is to avoid the “splash risk” and phase it in much more quietly than…V bracing.

In either case, I would be curious to hear Taylor’s formal published opinion on the impacts of a four piece top. If they move them into other parts of the line, I’m sure they will explain it to customers and help us understand how it affects tone, longevity, and/or value. I’m guessing it will be “different, but not inferior.”

My experience supports that perspective. I have one of these Koas with four pieces and I am quite happy with it. It seems a bit warmer and louder than the two piece equivalents of the same model when I have played twos and fours side by side, which I also hear in the Alamo Music video. This warmth perhaps comes at the cost of some glassier and sometimes sharper trebles, which on a mini is a good thing. It still sounds like a Taylor guitar but shifted more toward Martin’s tone. Still trying to understand why and how that works. Rumor is that the extra glue joints make it slightly stiffer:
https://www.classicalguitardelcamp.c...ic.php?t=22668

Anyway, I would look for it on the K series and/or the Tecate-made or AD series, as I’d expect this to show up on either affordable models or else those with extremely rare wood species.

[PeteyPower16]

Here is another video where I see a book-matched four piece wedge top on a plus model compared to a two piece top on a standard Koa model. I hear less difference here, but that could be due to the playing style being much heavier.
https://youtu.be/Mbd3xYKN7X8

It could be my ear, but again I hear warmth and bass from the four piece, but more brightness and glassy high end resonance from the two piece. It sounds like the four piece can be driven just a little harder. Both top constructions sound fairly similar with a classic koa tone though.

Maybe I am biased because I’m a strummer and because I have a four piece, but I prefer the four over the two in both of these videos (Casino and Alamo) and also when I have A/B’d these in person.

In terms of construction-only tone impacts (not considering string type, gauge, or playing style), the top piece count (two vs. four) might be third or fourth behind top wood, guitar size, and possibly bracing, so not a primary but definitely a secondary consideration if one had a choice.