Posted on August 1, 2022March 24, 2023 by Dale Phillips Questions: Significance of Q Questions: Significance of Q by Brian Burns Originally published in American Lutherie #86, 2006 John Belluci of Baltimore, MD asks: Please explain what “Q” is when referring to wood or instruments. The definition I’ve seen is, “internal damping.” Brian Burns of Fort Bragg, CA responds: “Q” is one of the basic qualities of the materials we use to make stringed instruments. The traditional low-tech Q test is to listen to the tap tone of a piece of wood and hear how long it takes for the sound to die away. The longer the tap tone lasts, the higher the Q, and the greater the potential of that piece of wood to make a loud instrument with long sustain. The design and construction of the instrument of course determine the ultimate result; the Q test just gives you an idea of the potential of that particular piece of wood. Become A Member to Continue Reading This Article This article is part of our premium web content offered to Guild members. To view this and other web articles, join the Guild of American Luthiers. Members also receive 4 annual issues of American Lutherie and get discounts on products. For details, visit the membership page. If you are already a member, login for access or contact us to setup your account. Questions: Significance of Q by Brian Burns Originally published in American Lutherie #86, 2006 John Belluci of Baltimore, MD asks: Please explain what “Q” is when referring to wood or instruments. The definition I’ve seen is, “internal damping.” Brian Burns of Fort Bragg, CA responds: “Q” is one of the basic qualities of the materials we use to make stringed instruments. The traditional low-tech Q test is to listen to the tap tone of a piece of wood and hear how long it takes for the sound to die away. The longer the tap tone lasts, the higher the Q, and the greater the potential of that piece of wood to make a loud instrument with long sustain. The design and construction of the instrument of course determine the ultimate result; the Q test just gives you an idea of the potential of that particular piece of wood. It’s important to hold the sample as close to the center as possible, between thumb and middle finger, halfway from the end, and reaching in so that the palm of your hand almost touches the edge. Tap with a fingernail to hear the high frequency response. For bass response, hold about one-forth of the way from one end and tap with the pad of your finger. I test all my top and back woods for stiffness, density, and Q before deciding whether to build with them. The stiffness and density tests take about fifteen minutes per sample. Density is just weight divided by volume. On rough stock I take a number of thickness readings around the perimeter with a cheap digital caliper and average them. This is important if you are to get accurate stiffness numbers, as stiffness varies by the cube of the thickness. Multiply the thickness by the length and width of the piece, and divide that number into the weight. I work in English units, and end up with pounds per cubic foot. If you want specific gravity, divide by 62.6. I test stiffness, both long grain and cross grain, by supporting the wood on metal rods and measuring the deflection when weights are placed in the center. If you’re interested in more information, I can mail you a copy of the handout from my talks at the Healdsburg Guitar Festivals. It’s not yet a “how-to” manual, but it has more detailed descriptions of the setups and procedures. (See contact info on Authors’ page.) If the wood has a relatively high stiffness-to-density ratio, I go on to a Q test using electronic equipment. This is much more precise than the traditional tap-tone test, but is a bit spendy, and depending on the method you choose, can take up to a half hour per sample. One thing that can be said for sure about tonewoods is that they vary — a lot. All of the qualities I test for are largely independent of each other, and can vary by as much as a factor of five from one sample to the next. I’m trying to sort out the excellent wood from the good, and my experience is, that for nylon string instruments, it’s really worth the trouble. The jury is still out, but evidence is mounting that wood with high stiffness-to-density ratios and high Q numbers makes superior instruments. Wood that doesn’t test well goes back to the supplier, who, with some exceptions, only grades the wood by appearance. I strongly urge builders to test their woods, at least for stiffness and density, which is quick and cheap. Knowing the qualities of the wood that went into an instrument that turned out well can really help you to repeat the performance. Additional information can be found on my website: www.lessonsinlutherie.com. [/wcm_restrict]