Physics of Music PHY103 Lab Manual Making a Fretted Monochord Using the Tempered Scale EQUIPMENT and MATERIALS • Guitar pegs (Economy guitar tuners) • Wood board 8’ x 1.5” x ¾” (hardwood) • Guitar strings • #6 flat washers to hold string end • Pieces of wood, plastic and rubber to make bridge and nut pieces • 1” diameter drills, hand drills • Miter boxes, files, rulers, clamps, vices • Fret wire, Fret saw (that has width the same as needed for the fret wire) • Snippers for cutting fret wire flush to the neck. • Digital Tuners • Small screwdrivers, extra tuner screws • Utility knifes • Hand saws • Example monochords from last year Materials 1 monochord per lab group. I ordered the fret wire, saws, snippers and economy tuners from Stewart McDonald. I am still not sure what the best materials are for the bridge and nuts. Popular seems to be ¼”x ¼” wood (pickup at hardware or hobby shop) and same in plastic (ordered from Plastruct?). Also slightly smaller squares are good in plastic. The ¾” poplar does bend, affecting the pitch. I have recently ordered rectangular files from Stewart McDonald for making grooves for the bridge or nut. Satefy Warning: use safety glasses when using power tools. Wear protective eyewear when near an operating drill press. If you are drilling and other people are watching the drill, please make sure they too are wearing protective eyewear. INTRODUCTION In this lab we will construct a monochord. We will use the tempered scale to calculate the location to place frets along the neck of the monochord. After we make a working fretted monochord, we will measure the accuracy of our scale. Half notes in the tempered scale have frequency that differ by a factor of 21/12 = 1.05946. For a string the fundamental mode frequency is proportional to the inverse of the string length. Figure 1: Our monochord will use one of these economy guitar tuners so that we can adjust the tension on the string. We will mount the tuners perpendicular to their normal orientation so that we do not have to have the headstock (see Figure 2) at a different angle than the guitar neck. metal sleeve Screws go here to fix the tuner to the boardPhysics of Music PHY103 Lab Manual Figure 2. Parts of an acoustic guitar. CONSTRUCTION 1. Cut a board. Cut a piece of 1 ½ x ¾” (actual size) hard wood to a length of about 2’ 8”. Guitar strings are only 3’ long so your board cannot be longer than that. Please use a hand saw, not a fret saw. The fret saws are a specific width to fit the fret wire and are best used for delicate cutting, not sawing boards in pieces. We are using a hard-wood so it is harder to bend and so that the frets will not slip. 2. Installing the tuner Drill first a 11/32” and then a 1” hole as shown in Figures 3,4. Center the 1” hole so it will be centered on the center of the tuner. Insert the metal sleeve into the 11/32” hole face that is in the 1” hole edge. The metal sleeve will help keep the tuner from tilting. Drill 2 very narrow holes for the 2 tuner screws. Install the tuner. Screw the two holding screws into the tuner. A note on drilling: Remember to put a piece of scrap wood below the piece you are drilling into when you are using the drill press. Otherwise you will wind up drilling into the metal table. Start by drilling a small and precisely located hole before you drill a large hole. Use safety glasses. Be aware that the wood can catch on the drill and start spinning. It is good to drill large holes with the drill press. You can start a large hole by drilling a small well positioned hole first.Physics of Music PHY103 Lab Manual Figure 4 We are side mounting the tuner so that the monochord will lay flat on a table top. 11/32” hole that does not need to go all the way through the board 1” diameter hole or square slot Figure 3 Showing 2 holes needed to install the tuner shown in Figure 1. The metal sleeve shown in Figure 1 is inserted into the inner side of the 11/32’’ hole so that the tuner does not wiggle. I recommend that the 1” hole be more distant from the edge of the board that has the tunerPhysics of Music PHY103 Lab Manual 3. Fixing the end of the string First drill a hole small enough that the string can pass through the hole (e.g., about 5/64” diameter) but not the round bead at the end of the string. Then drill a hole on the backside of the board just large and deep enough to hold the washer (about 7/16”; see Figure 5). The washer is there to spread the weight from the end of the string out over a larger area. The washer and bead on the end of the string (diameter ~4mm) are sunk into the backside of the monochord so that the board can lie flush against the table. 4. The frets Mark the locations where you would like to put the bridge and nut and measure the distance (L) that the string will have between the nut and the bridge (see Figure 2). Don’t make the nut too far away from the tuner, otherwise the string will touch the wood and buzz. Using the tempered scale calculate the location of at least 6 frets. The first fret should be at a distance L/21/12 from the bridge, the second fret L/22/12, the third L/23/12 from the bridge, etc….. The frets should be getting closer together as you move away from the tuner. Using the fret saw and miter box, saw narrow shallow groves into the neck at your marked fret locations keeping the saw perpendicular to the neck. Carefully tap or push the fret wire into each grove. Snip off the ends of the fret wires so the ends are flush with the board edge. File the edges of the frets so the neck edges are smooth. The fret saw should Guitar string Bottom side of monochord #6 Washer to keep the string end from digging a hole into the wood Recessed larger hole to hold washer and bead on the end of the string. The recessed larger hole makes it possible for the monochord to lie flush on the table. Figure 5: Two more holes must be drilled so that the end of the string can be held. Figure 6. A fretted guitar neck. Notice the frets are closer at the bottom.Physics of Music PHY103 Lab Manual exactly match the width of the fret wire. Try to saw smoothly. If the saw bends while you are sawing the slot cut will be too wide and the fret wire will tend to fall out of its groove. Remember the fret saws are matched to