Posted on June 6, 2024January 21, 2025 by Dale Phillips Questions: Measuring Guitar Efficiency Questions: Measuring Guitar Efficiency by Alan Carruth Originally published in American Lutherie #73, 2003 and Big Red Book of American Lutherie Volume Seven, 2015 Buck Montoya of Wichita, Kansas asks: I’ve heard and read that acoustic guitars are horribly inefficient (less than 10% if I remember correctly). Is there a method of measuring a guitar’s efficiency that could be performed by the average luthier without the resources of a fully equipped lab? Al Carruth of Newport, New Hampshire responds: I think most instruments are pretty inefficient. Neville Fletcher and Tom Rossing discuss this in their book, The Physics of Musical Instruments. The figure that I’ve been given for the violin is about 2%, and Ervin Somogyi said at the GAL convention in ’92 that guitars run around 5% efficient. It’s not easy to measure the efficiency of a guitar. For one thing there is so little power involved: any source of noise will throw the measurement off. For another thing, guitars are complex sources: even the headstock radiates some sound. You have to take measurements all around at all different frequencies and add them up to find the total. And you can’t take the measurements from close up, since the phase cancellation of the different radiating areas can skew the results. The cheapest calibrated microphone and preamp combination I know of costs several hundred dollars, and it’s probably the wrong kind of mike for this. I wish it were an easy measurement to make: I’d love to know how efficient my instruments are. But try as I might I can’t think of an easy way to do it.
Posted on June 6, 2024January 21, 2025 by Dale Phillips Questions: Measuring Soundboard Vibration Questions: Measuring Soundboard Vibration by Alan Carruth Originally published in American Lutherie #73, 2003 and Big Red Book of American Lutherie Volume Seven, 2015 Gregory Furan of Toronto, Ontario, Canada asks: Over the past several years there have been numerous articles written in many different guitar mags regarding measuring soundboard vibration, that is, tuning tops. Can you give me a reference for where all of the different elements can purchased? Al Carruth of Newport, New Hampshire responds: For tuning plates on guitars or violins, the equipment you need is fairly simple: a signal generator capable of producing a reasonably “clean” sine wave signal over the range from about 20Hz to 1000Hz, an accurate frequency counter, an amplifier that can boost the output of your signal generator to around 12w or more, and a loudspeaker that is matched to the amp and rated for the power. To be on the safe side, I’d get a speaker that was rated for about 1½ times the nominal power of the amp: sine waves have high peak-to-peak voltages. Become A Member to Continue Reading This Article This article is part of the Articles Online featured on our website for Guild members. To view this and other web articles, join the Guild of American Luthiers. Members also receive 3 annual issues of American Lutherie and get discounts on products. For details, visit the membership page. MEMBERS: login for access or contact us to setup your account.
Posted on June 6, 2024January 16, 2025 by Dale Phillips Questions: Guitar Rib Depth Questions: Guitar Rib Depth by R.M. Mottola Originally published in American Lutherie #85, 2006 Mark Korsten of Hastings-on-Hudson, NY asks: The article concerning how the rib depth of guitars should be adjusted when plates are domed was clearly written and illustrated (AL#84). I truly appreciate the insights offered by author R.M. Mottola. Being a neophyte luthier, however, I have what is probably a naive question. How does changing the depth of the guitar’s ribs modify the manner in which the bindings are fitted to the binding ledge? It’s a fairly easy operation to bend the binding when the plates are flat. However, when the depth of the ribs are varied, doesn’t that introduce another plane to the geometry? Do you simply use more flexible, thinner bindings or stronger binding tape to keep things tightly apposed in the ledge? R.M. Mottola responds: Although the doming of the plates means that the side depth of the ribs must be varied so the ribs and plates can be glued, this type of construction has little effect on binding. The ledges can be routed using a router resting on the plate or inverted in a router table. In either case the doming is so slight that the routing can be done just as if the plates were flat. And although the bindings must be bent vertically to accommodate the varying rib depth, the amount is so small as to be inconsequential. ◆
Posted on June 6, 2024January 17, 2025 by Dale Phillips Letter: Side Soundhole Guitar Letter: Side Soundhole Guitar by Marc Connelly Originally published in American Lutherie #93, 2008 Dear GAL Family, Thank you Cyndy Burton for the exploration of side-ported instruments. It was a terrific affirmation for this most interesting fenestration option. Like Mr. Montelone, at some point I laid my head on the side of my old Martin, strummed, and wondered how to get more of that big wood and bronze sound into my face. I started experimenting with a “side hole” variant, and it changed the way I think about what I am doing — not because it was “better,” but because it was clearly different in a thought-provoking way. In fact, this exercise has finally purged the word “better” from my lutherie vocabulary, and that’s a good thing. My side-hole instruments (which I call “Atlas”) are from the same plantilla as my front-hole models, so I can make some general comparisons. At first, the Atlas models seemed a bit too percussive and weighted toward the bass. So I made some small modifications in the way I tune the box and tamed the bass. The percussive nature of these guitars is simply a component of getting a more direct blast of wavy air into the player’s face. I have come to like this. Several Atlas owners have agreed it has an appeal and have readily adapted to it. But a truly freakazoid experience is to stick your left ear in the hole and play! There isn’t a prewar D-45 on the planet that sounds like that! Until I read Montelone’s article, I never even considered the possibility of weakening the side. What was I (not) thinking! None have folded up, but future Atlas models will have some consideration for this possibility. Fusion jazz player Don Mock owns an Atlas and loves it. Don enjoys having people ask “What’s that?!” Of the folks who play my guitars with some interest in commissioning one, the Atlas is always the first off the rack. But guitar players are an amazingly conservative lot, I find. Selling a side-hole guitar is like selling a blonde guitar. You are either open to them or you are not. It is personally rewarding to watch the tug of war between the conventional and the unconventional. ◆ Photo by Marc Connelly.
Posted on June 6, 2024January 17, 2025 by Dale Phillips Questions: 17″ Scale Length String Questions: 17" Scale Length String by R.M. Mottola Originally published in American Lutherie #87, 2006 Rob E. of Lexington, MA asks: Does anyone know of a string that can be put on a 17" scale length instrument, with an after length to the tailpiece of about 6", that is strong enough to reach a mandolin E tuning without breaking? “Questions” editor R.M. Mottola answers: A string with a small enough diameter to be tuned to this pitch at this scale length will have a breaking tension that is too close to its static tension to be of much practical use. When specifying the scale length for a new type of instrument, use a length similar to that used by existing designs with the same pitch range. For high-pitched instruments with long scales (such as the instrument in question) the issue is finding a string with high enough breaking tension to be useful. Unfortunately there are no simple solutions short of having strings custom-made of high-tensile-strength materials. For low-pitched instruments with short scale lengths the issues are tone and, for fretted instruments, intonation. Short, fat bass strings don’t behave much like ideal strings and their partials tend to skew way sharp as they are further shortened by fretting. There is a mathematical relationship among scale length, pitch, tension, and mass per unit length of a vibrating string. Download the paper entitled “Catalog Supplement / String Tension Specifications” from the D’Addario website. The paper (in PDF format) can be found at www.daddariostrings.com/Resources/JDCDAD/images/tension_chart.pdf. It contains comprehensive info on the string formulae as well as mass-per-unit-length (unit weight) data for every string D’Addario makes. Unfortunately, breaking strength data is not available in this paper as the issue of specifying the tension at which a real string will break is more complicated than it might appear. Tensile strength data is available from wire manufacturers but the best bet is to design high-pitched instruments using short enough scale lengths.
