Double Tops

bertie · May 2023

no not darts silly, acoustic tops - anyone experienced/played one ? Thoughts ?

Mellish · May 2023

Nope, never tried one.

ToneControl · May 2023

you mean ones with nomex in them?
I have a classical with one, and lattice bracing

ToneControl · May 2023

or do you mean the ones with 2 backs?

BillDL · May 2023

Is this the next big thing to annoy "solid top purists"? Thin kevlar sandwiched between two layers of "tonewood", i.e. composite and organic laminate? I can't see that the wood would impart much if any wooden flavouring to the sound produced by the man-made sandwich filling. I've played one of those carbon graphite acoustics (I think it was a "Lava" or something) and I have to admit that I was quite surprised that it sounded very much like a very resonant regular wooden acoustic rather than a brittle treble-laden artificial / man-made tone, so I can see no reason why a guitar with a thin layer of rigid kevlar between thin wood wouldn't sound as good. I would imagine that the layers of wood either side of the thin composite would help to add some physical weight and a slight dampening of what would probably be a very zingy and "fast" sound of a very thin composite centre. I would like to try one.

Sporky · May 2023

It sounds a bit akin to a flitch beam - thinnish steel bar between wooden beams. Lighter than steel, stiffer than wood, for almost any desired properties.

DavidR · May 2023

I know about double tops from the classical world @bertie ;. As far as I am aware, Eastman are the only big acoustic maker to have explored this, apart from boutique acoustic luthiers. Might be wrong but I've never seen any other big brand dabbling with double tops.

Review: Eastman Double Top Series DT30D (guitar.com)

I've never played one classical, acoustic or otherwise. Possibly a bit of an interesting blind alley in the evolution of the acoustic?? Full marks to Eastman though. Very pretty guitar too.

thomasross20 · May 2023

Is this a pre-war thing?
Vintage?
Lol

Soupman · May 2023

No, it's £2200 and made in china.
I think there are some good traditional guitars for that money, so I'll pass on the laminate top.....

Kittyfrisk · May 2023

ToneControl said:

or do you mean the ones with 2 backs?

That would be quite a beast...

earwighoney · May 2023

BillDL said:

Is this the next big thing to annoy "solid top purists"? Thin kevlar sandwiched between two layers of "tonewood", i.e. composite and organic laminate? I can't see that the wood would impart much if any wooden flavouring to the sound produced by the man-made sandwich filling. I've played one of those carbon graphite acoustics (I think it was a "Lava" or something) and I have to admit that I was quite surprised that it sounded very much like a very resonant regular wooden acoustic rather than a brittle treble-laden artificial / man-made tone, so I can see no reason why a guitar with a thin layer of rigid kevlar between thin wood wouldn't sound as good. I would imagine that the layers of wood either side of the thin composite would help to add some physical weight and a slight dampening of what would probably be a very zingy and "fast" sound of a very thin composite centre. I would like to try one.

I think it's something that has drifted from the realm of classical guitars.

Here is as much as I know about them. It's two very thin (1mm) soundboards of spruce (or cedar) with a printed layer of nomex in between them to add strength. I presume the thinner soundboard is to produce a louder guitar? I've gathered that this is something that occurs for some lattice braced guitars like Smallman, they have incredibly thin soundboards but are supposed to be louder than a lot of fan braced classical guitars.

I came across some good info in this thread

sev112 · May 2023

Kittyfrisk said:

ToneControl said:

or do you mean the ones with 2 backs?

That would be quite a beast...

I beleive classical luthiers tried this many decades ago, whereby the inside back vibrates more without being damped by the player’s body

thomasross20 · May 2023

That's interesting actually!!

ToneControl · May 2023

sev112 said:

Kittyfrisk said:

ToneControl said:

or do you mean the ones with 2 backs?

That would be quite a beast...

I beleive classical luthiers tried this many decades ago, whereby the inside back vibrates more without being damped by the player’s body

that's it

ToneControl · May 2023

I have one of these
https://goyetteguitarcenter.com/product/yulong-guo-koa-concert-classical-guitar-with-spruce-double-top

definitely a different sound

Tannin · May 2023

BillDL said:

Is this the next big thing to annoy "solid top purists"?

No. Classical guitars have done it for decades, and it is sometimes done for steel strings.

The principle has been known and used in other applications for a very long time. It is the standard and best way to make the lightest possible structure of a given strength. Buildings and bridges and structural members of aeroplane wings all use the same basic idea, which starts from the knowledge that nearly all the stress on a beam is concentrated on the outer layers. Structures of various other shapes work the same way. If you have, for example, a 6 x 2 flooring beam and put a piano above it, the top few millimetres of the beam are heavily loaded in compression (which is some help but not much because wood is fairly weak in compression) and the bottom few millimetres are heavily loaded in tension. The wood in the 150-odd mm area in between the top and the bottom doesn't do anything much other than hold the two working sections apart.

This is why skyscrapers are made using I beams: an I beam has lots of material at the top and the bottom where it is effective, and as little as possible between. But the same principle applies to other forms too, including flat sheets.

Racing dingies (small, very fast yachts) are routinely made using sandwich construction. When I was a growing up (many years ago now!) they were made from the lightest possible woods, mostly Western Red Cedar (the same cedar we use for guitar tops). Ply was preferred for most tasks. It can be stronger for a given weight because you can use thin layers of a strong timber on the outside and a thicker middle layer of something softer and usually cheaper, and also because it's much better on the cross-grain. Everyday yachts were often made from fibreglass but fibreglass of the required strength is heavier than timber, so racing yachts always used wood. About this time the smart builders figured out that they could make something lighter and stronger by having a thin layer of wood coated with two very thin layers of fibreglass. The timber filler is loaded vertically in compression (the top and the bottom "want" to squeeze closer together; the task of the filler is to resist that) and timber is stronger when compressed end-on rather than sideways, so the next step was to use end-grain timber. What was the lightest possible timber strong enough to hold the outer sheets apart when used in end-grain? It turned out to be Balsa, and fibreglass over end-grain Balsa became the standard racing yacht construction material. As time went by refinements were made: carbon fibre and Kevlar replaced glass fibre; the end-grain Balsa was replaced by expanded polystyrene foam.

To guitars. If a light top is desired, wouldn't it make sense to do the same sort of thing? Couldn't we make a top just as strong but lighter and more responsive by using a sandwich? Yes indeed. It gets more complicated than a yacht because we don't just want strength and light weight, we also care about the vibrational qualities of the top. So the top and bottom layers are made of a suitable tonewood such as spruce, while the filler is carefully chosen to have good acoustic properties. Oh, and it is important to use as little glue as possible while still getting a good bond.

Tannin · May 2023

On to practicalities. I have only played one double top guitar, an Eastman dreadnought. It sounded fine and was very responsive. I didn't especially care for it, but it was a perfectly playable instrument.

(Not being a classical player I've never played a double top classical. I do see them advertised from time to time, mostly very expensive single luthier ones but I've not paid much attention.)

I however own a falcate braced guitar and have another one under construction. The top is orthodox timber (Englemann Spruce in the example illustrated) but the braces are curved and made from a carbon fibre-timber sandwich. There is no necessary connection between falcate bracing and sandwich brace construction but they tend to go together.

The curves are designed to spread the loads better than an X brace does (whether that makes any practical difference I could not say), the sandwich construction allows the use of a much smaller, lighter brace with equal strength. The end result is a lighter, stronger top - i.e., the same sort of thing that double top construction aims at.

Does it sound better? Does it play better?

I think there is such a thing as a top that is too light. This guitar - it has long since been completed and now I play it every day - approaches that limit, in my opinion. There are certainly things that I don't normally play on it because they are a bit much for it. Cheaper, more solidly built (some would say "over-built") guitars do better in those styles.

Equally, there are things that it does far better than any of my other instruments.

Personally, I wouldn't choose it as an only guitar* - but then I have rock 'n roll roots and like to thrash a bit from time to time. Someone who plays more delicate "fingerstyle-style fingerstyle" (so to speak) would have a different view.

In short, I reckon this guitar is close to the limit of how light a top should be - not from a strength perspective, modern engineering of things like falcate bracing and double tops makes low-weight strength a bit of a non-issue - but from a playability perspective. I think a top needs a certain amount of weight to play well. (Or can stiffness substitute? Imagine, as a thought experiment, a top with zero mass but given stiffness qualities. Any reason that couldn't sound good? I think my head just exploded.)

One last thing. For most players, volume is not terribly important. For many players, it really doesn't matter much at all. But for a couple of very large sub-groups, volume is all-important. The obvious example is classical players, who to this day attempt to fill an entire hall with an unamplified instrument. Doubtless this is why double tops are more of a thing in classical circles (despite the almost legendary conservatism of classical players!). I have not heard of a flamenco double top (how would it cope with all that tapping?) nor does the idea seem to have taken off with bluegrass players (who seem to be, if anything, even more conservative than the classical crowd).

( * As a matter of interest, that thought prompted me to run an eye over my little collection of seven and conclude that there is really only one that would make a first-class only guitar. That might be worth a new thread.)

ToneControl · May 2023

Tannin said:

BillDL said:

Is this the next big thing to annoy "solid top purists"?

No. Classical guitars have done it for decades, and it is sometimes done for steel strings.

The principle has been known and used in other applications for a very long time. It is the standard and best way to make the lightest possible structure of a given strength. Buildings and bridges and structural members of aeroplane wings all use the same basic idea, which starts from the knowledge that nearly all the stress on a beam is concentrated on the outer layers. Structures of various other shapes work the same way. If you have, for example, a 6 x 2 flooring beam and put a piano above it, the top few millimetres of the beam are heavily loaded in compression (which is some help but not much because wood is fairly weak in compression) and the bottom few millimetres are heavily loaded in tension. The wood in the 150-odd mm area in between the top and the bottom doesn't do anything much other than hold the two working sections apart.

This is why skyscrapers are made using I beams: an I beam has lots of material at the top and the bottom where it is effective, and as little as possible between. But the same principle applies to other forms too, including flat sheets.

Racing dingies (small, very fast yachts) are routinely made using sandwich construction. When I was a growing up (many years ago now!) they were made from the lightest possible woods, mostly Western Red Cedar (the same cedar we use for guitar tops). Ply was preferred for most tasks. It can be stronger for a given weight because you can use thin layers of a strong timber on the outside and a thicker middle layer of something softer and usually cheaper, and also because it's much better on the cross-grain. Everyday yachts were often made from fibreglass but fibreglass of the required strength is heavier than timber, so racing yachts always used wood. About this time the smart builders figured out that they could make something lighter and stronger by having a thin layer of wood coated with two very thin layers of fibreglass. The timber filler is loaded vertically in compression (the top and the bottom "want" to squeeze closer together; the task of the filler is to resist that) and timber is stronger when compressed end-on rather than sideways, so the next step was to use end-grain timber. What was the lightest possible timber strong enough to hold the outer sheets apart when used in end-grain? It turned out to be Balsa, and fibreglass over end-grain Balsa became the standard racing yacht construction material. As time went by refinements were made: carbon fibre and Kevlar replaced glass fibre; the end-grain Balsa was replaced by expanded polystyrene foam.

To guitars. If a light top is desired, wouldn't it make sense to do the same sort of thing? Couldn't we make a top just as strong but lighter and more responsive by using a sandwich? Yes indeed. It gets more complicated than a yacht because we don't just want strength and light weight, we also care about the vibrational qualities of the top. So the top and bottom layers are made of a suitable tonewood such as spruce, while the filler is carefully chosen to have good acoustic properties. Oh, and it is important to use as little glue as possible while still getting a good bond.

One of my best friends is a Professor of mechanical engineering. His team have been testing beams (intended to replace I beams) made from lightweight solid foam with fibre type layers on opposite faces, it works extremely well, I have a sample he gave me when I visited his office.

When they test the samples with compressive load to failure, it's always the top face that fails (I assume the bottom layer is under tension, and can cope easily)

ToneControl · May 2023

I tried a few Yulong Guo double-top classicals, all very good

For those who don't know, because classicals use nylon strings at very low tension, they need much lighter bracing to be able to move the top and make an adequate sound. Hence why using steel strings on a classical will damage the guitar.

(Aussie-made) Smallman classical guitars are typically well over £25k, and have lattice bracing, John Williams has several, and I think plays them as his main instruments
Greg Smallman - Wikipedia

Stephen Hill in Spain also makes these, I have a 1A, it is amazing, and I bought it in preference to the Ramirez 1A I went to see at the shop:
Stephen Hill Concert guitars (stephenhillguitars.com)

The Yulong Guo ones are also lattice braced. I tried a double-top steel strung one once, it was good, but not as good as Lowden/Avalon/Goodall/Santa Cruz. I assume steel strung guitars don't benefit as much from the design

HerbieTheRadDorklift · May 2023

https://www.gear4music.com/Acoustic_Guitars/Hartwood/Libretto?page=1

These are both Nomex double tops.

LastMantra · May 2023

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