Tonewoods and ukulele sound
Terms like warm, bright, mellow, cool and even muddy are often used in describing tones that result from ukuleles. Most of that comes from the wood used in construction. The woods that influence the sound are called tonewoods. Woods used for acoustic instruments are often quite different from those used for electric, solid-body instruments (these are also called bodywoods, a term also used for the back and side woods on a ukulele).
The sound from a uke is generated by plucking a string. Strings themselves generate almost no audible sound, but their vibration is translated through the saddle, to the bridge and from there to the top, which creates the audible sound.
The top vibrates forward, creating a sound wave that rushes forward to the listener. How well the top vibrates creates the quality of the note.
The top also vibrates inward. This sound bounces around inside the uke and is shaped by the inside space as well as how it reflects off or is absorbed by the back and side woods. This second wave is released through the sound hole as a changed and more complex pattern. The listener hears both, very close together, as a rich, complex tone full of harmonics. See the section on saddles for more information.
Because of the smaller body size and high pitch of the strings (compared with a guitar), ukuleles produce tones in the upper range - commonly called bright. You don't get the kind of tonal resonance and depth you get with larger-bodied instruments. Many luthiers try to balance this by using woods that dampen the higher range a bit and offer more mid- to low-end tones.
Wood is a major factor in sound quality, but not the only one. Body size, volume and shape are important, so are the size and position of sound holes, the saddle and bridge material, internal bracing, back and side material, and string type and tension.
Ukuleles all sound like ukuleles, but not all ukes sound alike. That's because of the differences in body shape and size, the sound hole size and the kind of woods used in construction. But no matter how it's made, no one will ever think you're playing a cello, or a harp or a flute - it will always sound like a uke!
Ukes are traditionally made from Hawaiian koa and some aficionados still swear it's the best of all the tonewoods to use. It's certainly one of the most attractive (especially the curly koa). The sound is often described as "woody" which roughly translates to warm and full. Acacia is a cousin to koa and shares its properties.
However, many ukes are also made with mahogany, and it has its supporters as the prime tonewood.
Both are similar in sound reproduction: warm, bright and loud without too much emphasis on either end of the tonal spectrum. Koa is generally somewhat brighter than mahogany, while mahogany has richer mid-range tones.
You can find solid ukes made entirely from these two woods (top, back and sides). It's easier to find soli tops with laminate backs and sides or with different side and back woods (i.e. rosewood).
There are several related tonewoods that look like koa and are similar in sound but are generally less expensive, such as acacia, such as Australian blackwood. Mahogany also has related species, some of which are called mahogany but are actually a different wood.
Mahogany itself varies quite a bit depending on where it was grown and mahogany from different countries will have different tonal qualities.
Ukulele makers also use spruce and western (or red) cedar, both popular as tonewoods for acoustic guitars. Sitka spruce is the common choice, although custom builders may select Engelmann, European or the rare Adirondack spruce. Spruce is considered by many luthiers as having the optimum elasticity for sound reproduction.
Spruce gives a bright, loud sound, while cedar is less bright but with more sustain and mid-to-lower-end tones. These two are used for the top (soundboard) but not the back or sides. Spruce may, however, make a uke overly bright.
Other tonewoods and bodywoods include rosewood (a dense wood also used for fretboards that also comes from many countries), walnut, pine, Douglas fir, redwood, bloodwood, cypress, ovangkol, myrtle, walnut, sapele, bamboo and recently mango. Each has its own distinct tonal qualities.
Mango intrigues me because every ukulele I see made with that wood looks different. I don't know if the various types or cuts of mango have different tonal qualities, but I suspect they vary considerably. My Pono and Mainland mango ukes sound radically different.
You will also see maple (often spalted maple) listed as a tonewood, but it is probably a laminate. Spalted maple is too soft on its own so it's always a laminate (spalting is a discolouration caused by fungus). Maple itself is sometimes considered "acoustically transparent" as a tonewood but as a hardwood it is generally used to create bright tones. Spalted mango has recently become available, too.
Custom builders have experimented with a wide variety of other woods including uncommon regional woods such as myrtle, and you may be able to get something quite exotic, but at a higher price. Tonal qualities of these woods are probably unknown, however. Using exotic woods for the back and sides alone is probably better than for the top, which is most important for sound transmission.
Other woods may be used for the neck or headstock and fretboard (often rosewood or ebony, but cherry is an option). These are usually chosen for strength and durability as well as aesthetics.
Denser woods can transmit tones as well as reflect them, but may be muted and not as loud as softwoods like spruce or cedar which are more flexible. These hardwoods are more often used for sides and back with other softer tonewoods on the top, to create complex tonal qualities that a single wood alone can't achieve. That has allowed ukulele makers to create a wide range of products with very different and richer sounds by mixing different woods together. For example, a spruce top with koa back and sides sounds different than a spruce top with rosewood back and sides.
Because wood varies considerably in density and grain, even pieces cut from within the same tree may have different tonal characteristics. Instruments made of the same wood may therefore not sound alike, although they should have some commonalities.
Also, the structure of the top - thickness, sculpting and bracing - have an effect on the sound. The sound waves bound around inside, taking shape before they exit.
As an instrument ages and is played, the wood will actually change its density and tonal effects. This is sometimes referred to as 'breaking in' or 'opening up.' Most often this will result in richer sounds, with more complex overtones in the mid range coming forward. In general, an instrument will benefit from being played and will improve its sound with use. So if you don't like its sound now, keep playing and you may like it in the future.
Laminates (plywood) are different again. A laminate may have more than one kind of wood in it, so you can't generalize on its tonal qualities.
A laminate is made of several thin sheets called "plies." Each ply is placed to the grain in the wood runs at 90 degrees from the previous ply. This strengthens the wood but also has significant effect on sound because the woods cannot move as well in response to the sound as a solid wood can. Laminates do not open and compress the same way solid woods do.
Some ukuleles have laminate backs and sides with their solid wood top because the role of the sides and back is more to reflect than transmit sound. In fact, laminate sides and backs may even be better than some solid woods in reflecting sound because the solid woods may absorb more of the energy.
Laminates may also be made with other materials. The guitar maker, Martin, uses a high-pressure laminate that has seven pieces of grey craft paper with a layer of Formica added for strength. The result, says Dick Boak, is "light and strong like guitar wood." That doesn't say anything about its tonal qualities, however. Like carbon fibre, it is a novel material for making instruments, but the long term acceptance remains to be seen.
There is considerable discussion online as to what sounds each wood produces. It's worth investigating and is a fascinating discussion. Here's a page of info on tonewoods to start your appreciation of the subject. Luthiers James Goodall, Dana Bourgeois, John Mayes, Ervin Somogyi all have has a Web page on tonewoods. Taylor Guitars publishes an excellent magazine, Wood and Steel, and the Fall 2008 issue includes an article on tonewoods. In 2012, a Martin luthier wrote this piece.
I also recommend reading the article, the Heretic's Guide to Tonewoods, in which the author notes, "Psychoacoustics plays such a large role in this matter that it's difficult to discuss tone objectively. (I think that it's called psychoacoustics because trying to figure out stringed instruments will make you psycho.) We hear what we expect to hear, what we have been taught to hear, what we want to hear, and often what we hope to hear. Many luthiers and musicians alike spend hundreds of hours and thousands of dollars collecting information and recordings and they have come to have a stake in the sanctity of its rightness. They need the vast body of instrument mythology to be correct, and strongly oppose the possibility that it may be bogus. This makes it extremely difficult for a daring luthier to sell instruments that aren't made of standard varieties of wood."
For tone comparisons of electric guitar bodywoods see this page.
Keep in mind that while you can generalize about a wood's tonal properties, the resulting sound is a combination of design, construction, size and strings, humidity - plus playing conditions and how often you actually play a particular instrument. Musical instruments benefit from playing and will change over the years in response to use.
Many woods used by environmentally-conscientious luthiers are certified by the Forestry Stewardship Council's sustainable wood program. FSC-certified woods include katalox (a Central American wood similar to rosewood). Machiche, also from Central America, is used for backs and sides. Tsalam and Solomon paduak are other choices. Some traditional woods, like Brazilian rosewood, are no longer available because the methods of harvesting don't meet international agreements on sustainable forestry practices.
Update: I started thinking about tonewoods and what I had assumed was the conventional wisdom about them when I got my Mainland cedar top. I was surprised by the sound - not what I had come to expect from cedar at all. It was brighter and louder than I had expected and certainly quite different from my other two cedar tops.
That's when I started looking for some alternate thinking about tonewoods and found the Heretic's Guide to Tonewoods. The author of that article writes:
"...discard the notion that some species of wood
make good instruments and that others don't. The concept of tonewood is
a hoax. Of the few things that we can do to a guitar and still call it a
guitar, changing the wood it is made of will have the least impact upon
the quality of the sound that it produces...
Guitars sound like guitars. No matter how poorly or bizarrely they are
made, you'll never confuse the natural sound of an acoustic guitar with
that of a banjo, a mandolin, a drum or a flute. Obviously, not all
guitars sound alike, but even when we think we can distinguish a
night-and-day difference, it won't be so extreme that one will sound
like a guitar and another won't...
The tone of a guitar lies more in the hands of the builder than in the
materials from which it is constructed."
I think the point was driven home to me when I got my cigar box uke from Tom Guy. It really sounds lovely, but very different, too. A good part of that difference, I realized, is in the size and shape of the sound-box. Perhaps tonewoods play a lesser role in the sound than I had previously believed - and build, size, and shape play more of a role.
It makes me wonder what - if anything - is lost in the cutaway design. Are there subtleties of tone and harmonics that go missing when a portion of the upper bout is removed? Or are they just transformed? And what about those designs with more than one sound hole?
Update: Some new woods are being used on ukes, including cocobolo, used on a new Samwill ukulele. This small Chinese manufacturer makes a limited line of interesting, handcrafted ukes, but doesn't have a distributor yet, although Ukulele World has a couple for sale.
The wood used in electric solid-body ukes is important, but not as critical to the tone as with acoustic ukes. Solid body instruments are usually made of a dense wood like maple to give the strings some additional sustain.
Laminates versus solid wood tops
Laminates are two or more very thin slices of wood glued with their grains at 90 degrees from the grain of the previous one. Depending on the type of laminate, it may have different woods on the top from what is underneath (i.e. the top ply is often a veneer for aesthetic effect).
Solid woods used for instruments have rather different physics. They expand and compress with play; the wood actually changes its structure over time. Solid woods also transmit sound better because they vibrate more freely. There are several good articles online about the physics of tonewoods.
Laminates are built for strength so they do not vibrate or expand-compress the same way. In fact, the alternating 90-degree grains tends to dampen vibration, so some tonal qualities will be lost.
Although laminates used for instruments may have a nice piece on top, in general wood chosen for plywood is not the prime selection: it's more often the less attractive, or 'seconds' selection because appearance or flaws aren't as important. Your laminate top may hide more than blemishes: it can contain knots or holes you can't see in other plies.
In a solid top, the grain has varying areas of wood density. Each density transmits sound a little differently. Because no two slices of wood are identical, and each of us plays music differently, over time the wood will change to match our style and volume as well as the particular piece of topwood. That gives your instrument a unique voice.
Each solid-topped instrument has a 'break in' period during which it will undergo the most of these changes. Sometimes this is called 'settling in'. If you play it a lot, your instrument will have a different sound in a year from what it had when it was new. The time and the amount of the change will depend on the construction, the wood, your style, your environment (humidity in particular) and the phase of the moon (just kidding - but each instrument ages differently).
Laminates by their nature tend to average out tonal and playing effects, so they will not change as much or as noticeably. This can be a positive if you don't want your sound to change much.
Woods used on sides and backs do not transmit sound as much as the top does - they are predominantly reflectors - so they can be laminates without compromising the overall instrument's sound. There's even an argument that back and sides may be better choices as laminates than some tonewoods because laminates reflect the sound waves better (less absorption) than some tonewoods.
Laminates may present extra problems if they get wet, too. If water causes only part of the wood to swell, it can separate the plies (layers) and cause bubbling or cracking. Small pieces of laminate may come away and break off.
After all that - what matters most is the sound you like from your instrument. If you like the sound of a laminate-topped uke, get it. If you like a solid-topped, keep in mind that it will eventually alter - perhaps insignificantly and so slowly you won't notice, but it will do so.
