Ken Ellis Luthier
© Whippoorwill Acoustics LLC, 2015-2018

Wood Choices and Sound

In this article we will look at the various wood choices, how they affect the sound of an instrument, and how they relate to different styles of music and playing techniques. Information for this article was gleaned from various sources, primarily guitar-related. They include wood suppliers, manufacturers, luthiers, and my own experience. Keep in mind as you read this that while we can identify trends for a given species of wood, every piece of wood is different and there are exceptions to every rule. In addition, not everyone will agree on what a particular species does to the sound. Nevertheless, it does seem to me that we can have some general idea of how the sound of a walnut harp will compare to that of a maple harp, etc. Of course, there is no substitute for actually playing the instrument. You may be pleasantly surprised at what you hear.   There are no standard definitions of words for describing the sound of an instrument. The terms we use are often vague, like “bright”, or “warm”. Not being able to relate the terminology to measurable quantities, we may each mean something different when using the same word. This is not going to stop me from using them and it's a problem I'm not even going to try to solve here.   There are a few terms that seem to keep popping up when people discuss tonewoods: Sustain, Projection, Balance, Harmonic Content, and Note Separation. Sadly, not all terms are used to describe all species in the references I have found. But I'm over it.   Sustain indicates how long a string will ring after being plucked. Projection is the ability to sound loud not just  up close but also at some distance from the instrument. Balance is how the bass, mid-range, and treble note loudnesses relate to each other. Note separation is how well one can distinguish the separate notes in a chord. Do you hear a munge of sound (how's that for a musical term?), or can you pick out the individual notes when a chord is played?   Harmonic Content deserves some additional explanation, to contrast it with Balance. While Balance can be thought of as a passive filter, reducing loudness of some frequencies or notes relative to others, Harmonic Content is an indicator of new frequencies that are added to the sound by the wood. A discussion of the physical mechanism behind this phenomena will be left for another time.   Harmonic Content can be described as follows. Recall that when a string vibrates, it vibrates simultaneously at many frequencies (modes) that are approximate multiples of the fundamental (lowest) frequency. When these frequencies are exact multiples of the fundamental, they are called harmonics. When they aren't exact multiples, they are called partials or overtones. Now vibrational energy from the strings can be transferred to wood vibrational modes that have totally different frequencies from those of the string modes. Thus the wood can add new overtones to the sound. Different species of wood add different amounts of overtones at different frequencies. This is what we mean when we say that a tonewood adds Harmonic Content.   There is another effect that is in contrast with Harmonic Content. Some woods can suppress the string partials so that the fundamental note frequency is emphasized. When this happens, the wood is said to have a “strong fundamental”.   Hardwoods Cherry We will start with cherry, since of all the hardwoods it seems to have the most neutral response. Cherry has a rich, projective midrange without favoring bass or treble. It adds little harmonic content and has good note separation.   Maple Maple has a bright bell-like tone, due to the strong fundamental and low harmonic content. It is loud and projects well. Maple has a weak bass response and less midrange than cherry. It has very good sustain and note separation, but not as good as cherry.   Black Walnut Black walnut has a sound that is described as woody and warmer than cherry or maple. The warmth is probably due to a better bass response than cherry and maple, and a treble that is somewhat muted. Black walnut adds some harmonic content, but not as much as exotics like rosewood. It is loud and projects well. Mahogany Mahogany is similar to walnut in that it has a warm tone with full bass, a strong midrange, and soft treble. It has a strong fundamental and adds harmonic content primarily in the midrange, giving it a fatter midrange than walnut. Sapele Sapele looks a lot like mahogany, but is significantly denser and so needs to be cut thinner than Mahogany. It has a warm, enhanced midrange with a nice bright treble. It has a bit stronger treble and a bit more harmonic overtones than Mahogany. Koa Koa has a bright sound, blending the midrange of mahogany with the top end of maple. Unlike these woods, however, it can add a lot of overtones across this range. Oak Oak has a clear, even sound from bass through treble. It has strong fundamentals, and a rapid note decay. The bass is similar to that of cherry while the midrange and treble project even better than cherry. Sycamore Sycamore has a clear punchy sound that is bright like cherry but develops more bass than cherry as it is played in. Goncalo Alves Also known as Brazilian Tigerwood, it produces a resonant, balanced sound throughout the range. It has a quick response with clear and crisp bass, lush trebles, and a superior midrange. Choosing Materials When choosing a new autoharp, keep in mind that its sound will improve as it is played. It may take several months, a year, or more of frequent playing for it to reach its full potential. But if you like the sound now, you will really like it after it gets “played in”. It's one of the advantages of owning a solid-wood instrument.   Your choice of materials may be influenced by your playing style, the type of music you play, and who you play music with.   If you play lyrical solo pieces, a hardwood top with lots of sustain and harmonic content may be a good choice. If your musical style is more up-tempo, fingers flying, you may want less sustain and better note separation. If you play both types of pieces, you might consider having different kinds of autoharps for the different kinds of music.   If you play in an ensemble, consider the concept of musical space. Each instrument in the ensemble can be said to have its own space that allows it to be distinguished from the other instruments even while all instruments are playing.  You may get best results from an autoharp having a balance that fills in gaps left by the other instruments in the ensemble. More clarity and less harmonic content might also help you to find your own space in the sound of the band.   These are all suggestions to get you started. Ultimately, they are generalizations that might not apply to a particular autoharp or situation. The final choice should always come down to what sounds best to you.