The Soundboard

Choosing Wood for the Soundboard

A true quarter-sawn cut of wood will have rays which are intricate little cross stripes running perpendicular to the vertical grain lines on the face. They appear as ripples and are known as silk (pictured on the spruce top on the right).

These rays are an indication that the top is perfectly quarter-sawn. This means the end grain is 90 degrees to the face. Additionally, having little or no run-out (read about run-out) along the length of the top would make the piece ideal for a soundboard. These characteristics are typically present in AAAA or master grade tops.

Some builders might not have used this top because of the color streaks. I would never let a few  color streaks stop me from using a perfectly quarter sawn top like that one. That guitar sounded great. Besides, the wood will eventually darken to an even color as the guitar ages.

Guidelines in selecting a soundboard:

• Look for quarter sawn wood with silk as described above.
• Check for run-out. Ideally you are looking for little to no run-out.
• Stay away from tops covered with bear claw. It has been my experience that tops with tons of bear claw just don’t sound good. They are popular because they look cool. Yes, they are visually striking but its about sound isn’t it? I will only use a top if it has just a hint of bear claw, nothing more.
• Avoid flaws such as bark inclusions and knots. If these flaws are present in your top check that they fall outside the boundaries of the top. If the knot is small and without voids I may allow it on the top because the wood around a knot is always stiffer than it is anywhere else on the board. Again its a personal choice.
• Width of the grain lines is not as important as people think. I have used wood with many grain lines per inch as well as wood with not so many. I have not noticed any differences as long as the other criteria were met.
• The wood used for a top should be stiff. The stiffer the better. This should be checked both with the grain and across the grain. It will be much less stiff across the grain that it is along the grain. We are talking relative comparison from top to top.
• Density is another factor to consider. I avoid using very light tops as they tend to have a punchy sound in my opinion.
• Tap tone is the subject of much debate. Some builders swear by it others don’t consider it at all. In a tap tone I look for a musical tone with sustain. That’s as fancy as it gets for me. Pitch is not important.
• Contrary to popular belief

These things are just guidelines and there are occasionally exceptions. Things will vary from top to top.

Wood Grades for Soundboards

If you intend to build the best sounding instrument possible, you  must begin with the best wood possible. If you are buying your wood from a reputable dealer most likely the soundboards will be graded. The criteria for grading should be standard but seldom is. Therefore there can be grading variations from supplier to supplier. You should ask for the grading descriptions where you buy your wood to be sure.

On the right is a AAA grade top. Each supplier its seems has their own grading criteria. I purchased this top from a saw mill in Idaho. One half has the grade written on it, the other was planed to reveal the grain. Notice the one instance of bear claw at the top of each piece.

Wood Grading Critieria

Below are the grading descriptions that Allied Lutherie uses:

•  AAAA (master grade) is as good as it gets, about 1 to 2 percent of soundboard material grades out as master, with cosmetics (which are based on structural integrity) and runout differentiating this grade from AAA.
• AAA is a good professional grade soundboard, with good cosmetic appearance and little if anyrunout. (Runout, commonly understood these days, was a little known subject before Bill Lewis wrote about it in his supply catalog of 1975.) We find that about 5% of tops fall into this category.
• AA is a good grade, but may not be as perfectly quartersawn as AAA grade, or may have more grain variation, or some slight coloration. This is a grade that the US factories commonly use.
• A grade is a decent top but few guitar builders ever use it, and few of the factories in the States use this grade. It’s more of an export grade, although one can find some nice tops in this grade if cosmetics are not of great importance.

Advise

Most luthiers look for a soundboard with specific characteristics because they know it will work well with their design and the way they work. For instance, some will look for stiff tops that are very dense ( heavy). Others will look for tops that are stiff, light and have a good tap tone with nice sustain. Everyone is different. It depends on how you relate to the material.

If you are an inexperienced guitar builder go around and look at as many soundboards as you can. Many suppliers will let you check out the wood in person. Look at the different grades and see for yourself what the differences are as far as visual, touch and the sound it makes as you tap it with your knuckle. Does the wood make a musical sound or is it a dull thud? Does the sound sustain and trail off or does it just die out quickly? Select a range of tops and see which ones work for you. With time you will begin to develop your own criteria.

Picking out the right wood is a process that will take time to develop. You simply cannot ask someone to tell you what is good and what is not, you need to find out for yourself and your guitars. If you are short on experience it may be a good idea to purchase only master grade material since it will be difficult at this point to find a real bargain in the lesser grades of wood.

Spruce and Cedar

Classical guitars typically have either spruce or cedar for soundboards. The species of spruce that are most commonly used are European and Englemann. Sitka spruce is not typically used on a classical guitar.

Western red cedar is the choice of cedar for classical guitars. Some luthiers have also begun to use redwood which looks very similar to western red cedar but is a bit less dense and has different tonal characteristics. Tonal characteristics are a matter of personal taste.

Physical Differences between Spruce and Cedar

The main difference in the physical characteristics of spruce and cedar is strength and density.  Spruce is stronger, stiffer  and more dense than cedar.

There is also a vast difference in appearance. This is sometimes overlooked by some luthiers when selecting a color scheme for the details on their guitars. Cedar is a medium  brown with a good amount of red in it. This brown will darken with a finish applied to it. Spruce is a whitish yellow in color. This will turn a golden yellow when a finish is applied to it.

It may take a few tries to be able to closely judge how much the colors will change when finished, but it is important if you are trying for that eye catching look. Th same colors that go with a cedar top may not look so good on a spruce top guitar and vice versa.

Acoustical Differences

Cedar is typically described as a warmer darker sound and spruce as a sound brighter sound with more interesting overtones. There are vast differences in sound between these two species of wood. What are they precisely? It will be different for everyone. Its all a matter of opinion. This is compounded by the fact that two people may use the same words to describe the same thing.

The words used to describe sound character are very subjective and the same words used by one person to describe what they are hearing can be very different that those used by someone else. My best advise is to go and hear for your self an don’t listen to what other people say. If you listen to enough guitars you will develop your own opinions.

Measuring the Properties of Your Soundboards

Trying to get precise measurements of the different characteristics of your wood is kind of a waste of time. A more useful approach for measuring properties of your guitar wood is to make comparative measurements, or normalized measurements.

Normalized measurements begin with picking a number you consider normal. What it is does’t really matter as this is will be used to ultimately tell you which way to go and by how much.

To make proper comparisons on things like stiffness and density the tops should be the same size (H x W x L). If they are not your comparison is meaningless.

So for instance, say you are weighing your tops.  Weigh a few and select the middle weight as your normal and give it a value of 1. Write down what that weight was and for what speicies. Then weight tops of the same species and divide the result by your normal weight. The result will tell you how much more or less it is to the normal. Numbers below 1 such as .9, .8 and so on are lighter than your normal. From the resulting fraction you can also determine by what percentage.  So in this case a .9 will be 10% less dense than your normal.

As you accumulate data and you find that your are always choosing tops that are more dense than your norm you can make a new norm and start from there. Over time you will have a pretty good idea of what works for you and you won’t have to remember a whole lot of numbers.