Koa. Tonewood profile

Acacia Koa | Tonewood Profile | “Koa”

Koa

Tonewoods Database

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Quick Facts
Scientific name: Acacia Koa
Trade names: Koa
Janka: 1250
Uses: Tops, Veneer, Back and sides
RIYL: Walnut, Mahogany
Bling factor: Curl and colour variation is not uncommon
Availability: Uncommon
CITES status: Not listed. No restrictions

Note: (RIYL) Recommended If You Like

Natural History

Koa is endemic to the Hawaiian Islands attaining heights of 30 metres and 6 metres in diameter. It is found thriving in forest zones of 100–2,300 metres on all 6 major Hawaiian Islands. As a nitrogen fixing species, it is able to thrive in very young volcanic soils.

Status

koa was used by ancient Hawaiians for a variety of uses from to build dugout canoes to surfboards. During the Hawaiian music craze of the 20’s it’s similarity in strength and weight to that of black walnut led it to be extensively logged for use in wood carving and furniture. Today only 10% of the original Koa forests survive but due to conservation efforts and it’s hardy nature, Koa is not endangered.

Physical properties

The wood is fine-grained can display a number of figure: plain, straight, banded, fiddleback and in one instance quilted. Heartwood can vary from a rich crimson-brown to golden yellow and can vary greatly from log to log. The janka of Koa is around 12250 and it has a specific gravity of 0.55.

As a tonewood…


Claxton EMc Koa guitar courtesy of goodacoustics.com

Koa guitars can vary tonally, in accordance with density and weight. They are most often described as a warm sounding Mahogany to a brighter sounding Rosewood. A lower density koa guitar tends to produce a more mahogany tone, whereas denser sets tend towards the rosewood spectrum.

Subjective tone…

I would broadly characterise the tone of Koa as being similar to Australian Blackwood, with a woody, open tone somewhere between mahogany and rosewood

Availability

As a managed species, Koa stocks are still available and tonewood stocks look limited by healthy. Alternatives exist, namely close cousins Australian and Vanuatu Blackwood. Read more about Australian Blackwood here.









©Terence Tan.

Pictures copyright individual holders.
Claxton Emc and Shimo Kamaela Koa guitar courtesy of goodacoustics.com

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7 thoughts on “Koa. Tonewood profile

  1. Kevin Hall

    hi Terence;

    While koa is enjoying a resurgence among both builders and players these days, perhaps some consideration should be given to past experience with the material. Generally the old chaps at Martin who had been there when a lot of the species was being used there tended to dislike it as a building material.

    While it can be stunning in appearance, the general opinion among those old Martin hands was that the plainer wood tended to yield the better tone and was more reliable structurally.

    Koa does not have a great deal of stuctural integrity along the grain, in fact when thinned to guitar plate or rim thickness it may start to unravel like hemp rope if dampened during the bending process. In addition, the highly prized curly koa often tends to crack at the ‘curls’ when being bent.

    Curl or fiddleback figure is caused by end grain coming to the surface of the wood where you wouldn’t normally expect it. With more robust materials like maple, the wood is strong enough that this repeated pattern of end grain popping up in the main body of a plank doesn’t significantly weaken the plank, but with koa the effect can be disasterous.

    One builder with a lot of experience with koa has been quoted saying ‘Anyone bending curly koa rims will becomem familiar with the use of cyanoacrylate adhesives’, cyanoacrylates being the Super Glue types. He’s referring to the common practice of repairing bending cracks on the curls with Super Glue as you go. Effective, but less than an ideal way to expensive instruments.

    Another very well known builder whose fame largely comes from his highly figured koa ukes and classical guitars once told me privately that ‘Koa is Hawaiian for crap’. Strong opinion there, but he has a point.

    The outrageous prices often carried by highly figured koa instruments are not entirely due to the premium price of the material itself. The aggravation of having to bend the stuff and the fact that you may need to bend more than two rims for any given project come into play.

    While a well made curly koa instrument can be a visually spectacular piece and some have excellent tone, potential clients need to take the relative fragility of the material into consideration before plonking down a deposit.

    Many may well feel that the risk is worth it, others may not.

    As a builder, I strongly recommend against the use of curly koa for tops since the factors which make the best tops are virtually all missing from koa. The vast majority of koa-topped Martins from the early days that I’ve seen have had serious structural problems directly attributable to the use of that species in a function for which it is entirely unsuitable.

    Just one mans’ opinion, of course, but one formed through a fair bit of experience.

    All the best,
    KH
    Timberline Guitars and Ukes,
    Canada.

  2. Well, I’ve got a Takamine PT – 406 from the ’80es made out of rather plain koa, and it keeps getting better and better, beautiful tone, and people usually think it’s an old Martin- Maybe I’ve just been lucky…

  3. Frankly, I’ve disliked all-one-wood instruments without exception–until I found koa. In particular, I love the all-koa Tacoma PKK-40, a modern parlor model which I feel is one of the great guitars of our time. Unfortunately, it’s been discontinued. Maybe they had too many problems with it.

    Yes, koa is a terrifying wood to build with, so I always start with quartersawn sets. It helps to keep the sides thin for easier bending but caution dictates installing 10-12 vertical braces to reinforce the sides and prevents splits. Over time, I’ve come to depend on a contact thermometer when bending koa and I never heat past 265 degrees; better support the sides well when bending and go very slowly; don’t soak koa, especially if curly!

    It’s always in my mind that all figured wood is defective to some degree and the more highly figured it is the more defective it is—especially curly woods. The fact that it’s so pretty drives builders to use it, but the best instrument woods are quartersawn and straight grained. It’s no coincidence that so many old guitars (esp. Martins) were made of straight-grain Brazilian back when luthiers could just as easily have obtained highly-figured stuff.

    It’s the job of builders to educate customers about the advantages of using less-figured woods. But first, we have to convince ourselves because we all love to build gorgeous guitars and figured woods are hard to beat for eye candy.

  4. Mario DeSio

    I’m building a Gibson J45 style guitar and found the koa a dream to bend. It is not highly figured but has some light flame. The dark and light brown streaks will be wonderful when finished. I have a friend with a koa Martin D41 I believe and it’s got oodles of tone!

  5. Addendum: Despite the caveats on koa, I must say that it is my favorite tone wood. The better sets have all of the advantages of both rosewood (depth) and mahogany (warmth) with bell-like trebles. When I finally build the guitar of my dreams, it will be all koa. It’s worth all the trouble, and the drawbacks (difficult bending and splitting over time) can be overcome if properly built. Side splints are a must!

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