Acacia (Also look under "Black Acacia" and "Koa")

Keep in mind that there are 1300 species of Acacias, spread all over the world, and that even experts may have difficulty in telling them apart. Many do not grow large enough to be used for guitars. But for our purposes, their similarities are far greater than their differences. That does not mean they are all identical, but it may be hard to differentiate between them and make generalities that transcend the inherent differences caused by a luthier's particular build methods and the individual differences in a piece of wood of the same species.

From the Pono Website - As for tonal comparisons to Mahogany, the Acacia family (including Acacia Koa) is different in weight and density. Mahogany is lighter and less dense, and thus produces not only a warm tone, but a unique tonal clarity and open brilliance. And in time, Mahogany changes in color and tone more than any other wood we have experienced. For those who own vintage mahogany guitars and ‘ukuleles, the aged tone is unsurpassable.

Acacia is heavier and more dense than Mahogany, and thus has it’s own unique tonal projection. And of course a beauty all it’s own. Most people are familiar with the sound of Acacia woods, having owned or played instruments made of Hawaiian Koa. All Acacia woods are similar. The Acacia that we use for our Pono instruments is similar in appearance to what was known to old timers in Hawaii as “black Koa".

For lack of a better description, Acacia wood produces what could be called a deep woody tone. ... Acacia Preta does lack the rich red color tones of Acacia Koa, but still has beautiful black and brown figured grain patterns.