On a small body archtop, koa and walnut live closer together tonally than something like spruce versus maple, but they still feel different under the hands and to the ear, especially in how quickly the note speaks and how it decays.
Koa
Koa tends to be quick and articulate right out of the gate. On a small archtop, that usually shows up as a fast attack with a slightly sweet, rounded top end. The mids are focused and musical rather than wide and boomy, which works really well for single note lines and chord melody. There is often a gentle compression to the sound, so hard picking does not get harsh. Sustain is moderate, and the note bloom feels smooth rather than dramatic. Koa also has a way of warming up over time, so a guitar can sound a little tight at first and then open into a more complex midrange as it gets played.
Walnut
Walnut sits a bit closer to maple in clarity, but with more warmth and less glassiness. On a small body archtop, walnut often gives you a strong fundamental with excellent note separation. The low end stays controlled, the mids are clear and honest, and the highs are clean without being brittle. Compared to koa, walnut usually feels more immediate and linear, with less natural compression. Notes tend to decay a bit faster, which can be great for swing, Freddie Green style comping, or any context where you want definition and rhythmic clarity.
Side by side on a small archtop
- Koa leans toward warmth, sweetness, and a slightly forgiving response.
- Walnut leans toward clarity, balance, and a drier, more transparent voice.
- Koa often feels more lyrical for solo work.
- Walnut often feels more precise and rhythm focused.
Neither wood overwhelms a small body, which is important. Both keep the instrument focused and responsive rather than tubby. The real choice usually comes down to whether you wants a touch more color and bloom, or a touch more truth and definition. Either can make a small archtop feel alive and expressive, just in different ways.