Tap Tones of Brazilian Rosewood, Bubinga, Sitka Spruce and More!

[Portland Guitar]

A question we're often asked is what wood will produce the right tone for a guitar.
Every piece of wood has a different sound and once it is used for the guitar it colors the tone heavily.
It’s common to hear the rosewoods are warm and maple is bright.
We wanted to figure out exactly what this means and provide a way to be objective and compare them.

To do this I recorded a few common tonewoods and took pictures of the frequency graphs to provide a comparison.
Some are "woodier" and some have more delicate overtones and brightness.
A few things to keep in mind are that the thickness of the wood plays a major effect. The goal for a guitar top is to make it as thin as possible while retaining structural support.
The thinner pieces of wood “open up” and the higher resonances come out.
This can be seen between the two pieces of sitka spruce. Another effect on the sound is where the piece is tapped and how it is held.
It doesn’t change the fundamental resonances, but it does bring out different ones.
The last note is that once the bracing is applied and the body is put together the outcome will change.

When I played this on my laptop and computer speakers everything sounded woody, it’s hard to pick up on the subtle differences.
On higher quality desktop PC speakers and certainly with a small sub-woofer it’s possible to hear that they are all unique pitches.
Here are the recordings followed by a graph of the frequency response.
Where the peaks are shows the characteristics of the wood.
The thickness, bracing and note played will affect which of those peaks are excited most.

I hope that these are helpful in some way!
Let me know if you have and questions or woods you'd like to see tested out.

Backs:

Bubinga at 0.12in





Caro Walnut at 0.12 in





Brazilian Rosewood at 0.12in





Tops:

Adirondack Spruce at 0.12in





Sitka spruce at 0.11 in





Sitka spruce at 0.17 in





Western red cedar at 0.16 in





Spanish cedar at 0.17in

[justonwo]

I think this is one of those cases where hearing it in person and working with it is much more valuable than analyzing in the frequency domain. I think the guitar is a difficult place to use the engineering approach.

[mercy]

The walnut and the cedar had the strongest "drum" sound. Interesting because I dont like either of them in a guitar. Well not, not like but I think that other woods sound more like what I like in a guitar.

[iim7V7IM7]

Originally Posted by justonwo

I think this is one of those cases where hearing it in person and working with it is much more valuable than analyzing in the frequency domain. I think the guitar is a difficult place to use the engineering approach.

Science with too many variables is known as art...

[runamuck]

The thicknesses and sizes of all the test pieces were different I would guess.

[Portland Guitar]

It definitely is easier to work with and hear it in person. The graphs aren't that helpful because it's hard to relate what we hear to the graphs. I agree, there is a lot of art involved in making a guitar.

Here is a picture of some of the woods used. Most of the thicknesses were around 0.12 or 0.17 inches.

[Bruce Sexauer]

I listened to several of those samples, and I have to say they do not resemble what I hear when I tap on my various pieces of wood. I am tempted to try to record and see if I can get something closer to what I hear.

EDITTED TO SAY I TRIED TO GET WHAT I HEAR USING PERNAMBUCO AND IT SOUND MUCH LIKE THE OP'S SAMPLES. OH WELL.

[Portland Guitar]

Oh very intersting, I'd like to hear a sample as well.
There's a lot of coloring that happens in the mics and that might be enough to make the tone only possible to hear in person.

[justonwo]

Originally Posted by iim7V7IM7

Science with too many variables is known as art...

Indeed, and we’re both science nerds!

[Iain1231]

Brazillian and spanish cedar have a similar curve structure, with brazillian giving more depth.
Western red cedar has a mid scoop
Sika seems to muffle and seems to resemble Caro Walnut.
Adronack and Brazillian seems to have an echo.

Perhaps Spanish Cedar and braZillian will make a great guitar with lots of overtones

[j. Kinnaird]

I think you would get a more characteristic tap tone comparison if each sample was exactly the same thickness and size. The percentage difference between .12 and .17 is large enough to skew the results. In my experience thicker plates vibrate with a higher frequency. I thin my plates when trying to enhance the bass respobse

[redir]

The thickness has everything to do with it.

[Alan Carruth]

Any piece of wood will potentially have a large number of resonant frequencies; possible ways that it can vibrate. These will depend on the material properties and the size and shape of the piece. Depending on the details some of these resonances will 'couple'; work together to produce vibration 'modes' that are a combination of things.

What you hear when you tap on the piece is a mix of all of the resonant modes that are moving at the spot where you tapped, and are not moving at the spot where you are holding it. A microphone will, of course, be most sensitive to those resonant modes that are sending sound out toward it. On top of everything there are resonances in the air of the room that can boost or cut the power of the sound at particular locations.

There are ways to more or less isolate individual resonant modes, and analyze them to determine useful things about the wood. In particular, when its done right, you can use this information to determine the 'Young's modulus' of the wood along and across the grain, and the associated 'damping factors'. Young's modulus tells you how stiff the piece will be at a given thickness, so it's particularly useful to know when thinking about the top thickness. Damping is a measure of the rate at which the wood dissipates sound energy. When the damping is high the vibrations die out fast, and you get a short 'thump' when you tap, while low damping allows the wood to 'ring' for along time, and has a more musical pitch, all else equal.

As with everything related to the guitar, all of this gets complicated, and there are ongoing 'disCUSSions' about how useful any or all of this information is. Determining the Young's modulus of the wood can help you make a top as light as it can be and still hold up,so that's probably not too controversial. It's hard to say just what effect damping has on the sound of the guitar; most of us think it ought to be important, bit it's hard demonstrate that in any definitive way. IMO material damping by itself probably sets a limit, but is not in itself determinative. It is, sadly, very easy to screw up a good set of wood: factories do it all the time.

So, yes, it can be a rabbit hole, but understanding what those tap tones are telling you, and what they're not telling you, can also be very helpful.