Study of the acoustic effects of wood types

Roland

This has been sitting in my "read later" pile since January 2019. It's a study by the University of Lancaster into wood types used for acoustic guitars: https://pubs.aip.org/asa/jasa/article/144/6/3533/994108/Effect-of-back-wood-choice-on-the-perceived. I'm putting it here, not so much for general interest, but so that I don't forget where I put it.

Kittyfrisk

TLDR 
https://newatlas.com/guitar-wood-types/58139/

VimFuego

Kittyfrisk said:

TLDR 
https://newatlas.com/guitar-wood-types/58139/

they didn't say where the welding googles were made, nor from what material. 

rossi

I can attest that the  sides make no difference from my observations .In the 60's a discerning fan at a party kicked  in the side of my 64 Harmony Sovereign rendering a very large hole and splits .After the Police raid had finally ended and the house occupants all arrested  my mate and I crept back through the window  we had scarpered from and retrieved the guitar and many little bits of wood  before leaving with dignity by the front door avoiding the blood glass and an idignant  cat .It was one hell of a party .

After a few weeks I began glueing it all back using cascamite . First i clamped the top and bottom using a spacer  to stop it all flapping about  restrung and tensioned up .it played OK and sounded fine .I then stuck all the little bits in to fill  the hole up  .it looks dreadful but sounds the same as ever .i removed the spacer .

WezV

6 guitars build by Fylde all sound like Fylde's.  You could say the same about Martin, Taylor, or any other well established builder.  With acoustics the way it is built is just as important as what it is built from.

The top is more important than back and sides on acoustics, and where most of the tonal character comes from... We have some very old examples to demonstrate that
https://www.cumpiano.com/torres-cardboard-guitar

drofluf

I think it was the guys at Brook who said to me that the wood for back and sides doesn’t matter as it’s just a box as WezV said it’s the way it’s built and the soundboard that make the difference. 

DavidR

Interesting that the only person who is documented as having heard the ‘papier mache Torres’ found it ‘muted, bland and low’. 

This story is usually brought up to show that the back and sides aren’t as important as the top  of a classical for tone and volume!

See ‘Antonio de Torres. Guitar maker. His life and work’ by Jose Ramanillos. I asked our local library to source me a copy a few years back. Fascinating book. 

stickyfiddle

drofluf said:

I think it was the guys at Brook who said to me that the wood for back and sides doesn’t matter as it’s just a box as WezV said it’s the way it’s built and the soundboard that make the difference. 

The top is def a bigger contributor, but the back/sides just have some impact, otherwise a D18 and D28 would sound the same

menamestom

Personally I think the wood density and hardness are more of a factor than the actual species.

Rosewood is heavier and denser than Mahogany and definitely does make a difference on the back and sides.

But woods of different species of similar stiffness and density are probably harder to tell apart.

WezV

DavidR said:

Interesting that the only person who is documented as having heard the ‘papier mache Torres’ found it ‘muted, bland and low’. 

This story is usually brought up to show that the back and sides aren’t as important as the top  of a classical for tone and volume!

See ‘Antonio de Torres. Guitar maker. His life and work’ by Jose Ramanillos. I asked our local library to source me a copy a few years back. Fascinating book. 

there is a recording of his cardboard one on the link I posted, as well as an explanation that it needed some restoration and didn't sound inferior to other Torres once this was done

"Until recent times, the only record of the sound of this instrument was a description by Domingo Prat: “This guitar has an extraordinary sound, if perhaps a little muted, bland, and low, as the author of this dictionary was able to confirm when he played it in the house of Tarrega. Since then, no one has said anything more about the quality of its sound, generally adducing the instrument's poor condition as the reason: for a while it could not be played, being seriously damaged by a crack in the soundboard. Strangely, this attitude of renunciation has survived the recent extensive restoration of the instrument by the Yagüebrothers of Barcelona, guitar makers of rare sensitivity and experience in the restoration of instruments by Torres. As a result of the restoration we were able to try the instrument, not without some excitement. It was truly astonishing to discover that it has a cantabile quality that is in no sense inferior to that of the other Torres instruments we are familiar with. Only when one comes to terms with this fundamental aspect is it possible to give thought to matters of detail, and perhaps attribute to the cardboard a certain acoustic affinity with guitars made of lighter wood, such as cypress; but it should be remembered that, especially in the case of Torres, such differences in material (and in the resulting sound) are secondary to the instrument's predominant musical identity. "

Tannin

Essentially, there are two ways to make a back. A live back plays a significant part in the sound production. A dead back plays pretty much none at all. 

drofluf said:

I think it was the guys at Brook who said to me that the wood for back and sides doesn’t matter as it’s just a box as WezV said it’s the way it’s built and the soundboard that make the difference. 

Andy (or was it Simon) said to me "We don't think it makes much difference" - note the distinction between "much difference" and "no difference". 

The traditional wisdom is that back timbers make 10% of the sound quality, the top is responsible for 90%. I reckon that's about right. (And this is holding equal all the many, many differences to do with body shape and construction.)

Sides practically never make any difference, and if they do it's for the worse. Top-end makers go to a good deal of trouble to make the sides as dead as possible, adding weights to deaden them, and using multiple layers of timber for the same reason. 

Having said all that, sticking to the same top (Sitka Spruce, let's say) the difference between guitars made from Indian Rosewood, from Blackwood, from Sugar Maple, and from Queensland Maple is significant. And yes, as per @menamestom, it's not about the species, it's all about density, hardness, and one or two other physical properties complicated enough to make my brain hurt. For a first approximation though, density and hardness give a pretty fair idea. 

ICBM

If the back and sides don't make a difference, why does a Martin D-28 sound different from a D-18?

Yes, the fingerboard and bridge are also different woods, but the 'wood doesn't matter' brigade will say that's even less important.

The binding?



Yes, it's certainly correct that there are other more important factors, but saying the back and sides make no difference is clearly not true.

DavidR

Yes. Anything you change in a guitar makes a difference. It’s just a question of extent. 

In acoustics, the difference between Rosewood and Mahogany for the back and sides is something that most people would spot. 

If you want to hear this, listen to a few videos of the new Yamaha FG9 and AB test the FG9M and the FG9R. Identical guitars apart from different wood for the back and sides. 

Also a very nice (but too expensive) guitar!

MartinB

ICBM said:

If the back and sides don't make a difference, why does a Martin D-28 sound different from a D-18?

Yes, the fingerboard and bridge are also different woods, but the 'wood doesn't matter' brigade will say that's even less important.

The binding?



Yes, it's certainly correct that there are other more important factors, but saying the back and sides make no difference is clearly not true.

I dunno, I would think the bridge would be fairly high up there in significance, it's where the energy applied to the strings meets the top, and in a location where even small changes of mass can make an audible difference. 

ICBM

MartinB said:

I dunno, I would think the bridge would be fairly high up there in significance, it's where the energy applied to the strings meets the top, and in a location where even small changes of mass can make an audible difference. 

I doubt there’s much mass difference between a rosewood and an ebony bridge. If there’s any tonal difference - as with the fingerboard - I think it’s down to the hardness, not the mass.

It’s often said that a heavy bridge kills tone and volume, but the Gibson Dove has a much larger bridge than any Martin - I would guess at least 50% heavier - and doesn’t lack either…

Tannin

Further to @ICBM's remarks about bridges and weight and hardness, we should also remember that there is a great deal else happening in that area, from the composition and thickness of the top, through the size, shape, design, and placement of the bracing, to the forgotten (fairly) large and heavy out-of-sight component underneath - the bridge plate. 

Guitar makers calculate all these things into their builds - be that consciously and scientifically, or simply with years of skill and experience.

matt3man

The wood in question can have more or less impact, in my opinion.  The difference between mahogany and rosewood for the back and sides is subtly different but if you've ever played a guitar with a maple back and sides they sound notably different - and not desirable to my ears - I couldn't put it down quickly enough.

The age changes the wood too in my experience.  I bought a new Taylor 410 (spruce top, mahogany back & sides) back in the 90's and it was pretty bright sounding initially but over the 20 years I had it, it mellowed and improved notably.

Paul_C

The back wood (and its construction/braces) could make a noticable difference if the guitar is played without it being damped by the player's body, as it would work a little like a drum with top and bottom heads both moving and contributing to the sound. 

There was a lady jazz guitarist on That Pedal Show who made a point of holding the guitar so she didn't touch the back while playing for that reason. 

drofluf

There’s a mandolin device, which some players swear by, that is effectively a cage to separate the back of the instrument from the player’s body. 

Soupman

Paul_C said:

There was a lady jazz guitarist on That Pedal Show who made a point of holding the guitar so she didn't touch the back while playing for that reason. 

She wasn't a yoga teacher by sny chance...?
 
 

ICBM

matt3man said:

The wood in question can have more or less impact, in my opinion.  The difference between mahogany and rosewood for the back and sides is subtly different but if you've ever played a guitar with a maple back and sides they sound notably different - and not desirable to my ears - I couldn't put it down quickly enough.

I would say that was probably that particular guitar. I’ve played many maple guitars and owned two - both Gibsons - and to me they sound in the same ballpark as rosewood, on an equivalent design - definitely more different from mahogany. It’s often described as a bright wood, or neutral - I would say a bit of both, but also deep and punchy. The one I’ve still got is my Dove, which to me is the best-sounding dreadnought I’ve heard, it’s like a great D-28. The other was a CJ-165 mini-jumbo, which was much more midrangy... very diffferent despite all the same woods.