This page defines the many technical terms appearing in the literature on guitar design and making and on this site.
Action: the string clearance from the frets. Usually the action increases toward the higher frets, affecting playability and sharpness during fretting. If not further specified action is referring to the 12th fret.
Admittance: the ease of conversion of string force into plate velocity and sound pressure. The first part, from string to plate is also called mobility. A high admittance lets the string energy flow rapidly to the air, such as at a plate resonance frequency. Admittance is highly frequency dependent. Static admittance is the conversion of string force into plate deflection and is the inverse of stiffness. It can be considered as the baseline for the admittance spectrum.
Air cushion: the air enclosed in the soundbox, which pushes the plate back when compressed.
Anisotropy: ratio of across to along stiffness of a plate. When these are equal the plate is said to be isotropic. Anisotropy has great impact on the position of plate resonances on the frequency scale.
Archtop: plate with a hill shaped cross-section, with a dome at the top and flat at the bottom. The arch is longer than wide. Used in pressure resistant designs to accommodate tail end bridges.
Aspect ratio: ratio of length to width of the guitar body. The higher the aspect ratio the stronger the impact of cross stiffness of the plate on resonance frequencies. Classical guitars have a slightly higher aspect ratio’s than folk guitars.
A-type/ E-type tuning: guitar box tuning which shows resonances just under the A2 or E2 and at several successive overtones. The A-type is very common and usually has a back which is tuned higher than the top. The E-type is more rare and has the back tuned lower than the top.
Back: the back plate of the guitar box. It is usually made from the same material as the sides, using dense wood. Much of the timbre of the sustained tone comes from the selected back wood.
Balance: in general: two effects keeping each other in a desired equilibrium state. Many parameters in the guitar are traded against each other to aim for a tonal balance, to keep a frequency constant or to handle the weight of the guitar well.
Bass: a guitar type which starts at E1, a full octave below standard tuning. The term bass is also used for the perceived emphasis on the lowest frequencies, relative to the mid and higher spectrum. This concept is rather vague.
Baritone: a guitar type of which the tuning starts at A1.
Bending: the curve of a beam or plate under a torque or moment. The local curve is an infinitesimal circle segment and the radius becomes smaller as the torque is larger. If the torque is equal over the plate it bends in a circular shape. Usually the torque varies over the plate and the plate bends in a complex shape, called bending profile.
Bending stiffness: a quantity (noted as D) which is expressing how difficult it is to bend a plate. The underlying parameters are modulus of elasticity E of the material and the thickness of the plate. Also for a string bending stiffness is known, causing the higher harmonics of a string to become sharp.
Binding: the connection between plate and sides. Binding is made from a material which protects the end grain of the plate from moisture and impacts. The connection is reinforced with a lining (see there) and further decorated (and stiffened) with purflings (see there).
Binding stiffness: the rigidity of the binding for rotation around the edge. This does not only involve the binding itself, but also the near plate and side sections. If the binding is soft, the spectrum of resonances is stretched compared to a stiff binding.
Bottom: the lower end of the guitar body, when the guitar neck points up. Also called tail. The term bottom end is also used to indicate the lower part of the spectrum.
Brace shape: the cross sectional shape of the brace. Coarse braces are rectangular, but more elaborate round top, trapezium and triangular braces are applied as well. These have less stiffness and a little less mass.
Bracing: a brace is a local reinforcement of the plate stiffness, usually by a glued on, shaped bar. The arrangement of braces increases the strength of the plate, affects its tuning and affects the timbre. A particular arrangement is called a bracing style.
Break angle: the angle under which a straight element is deflected. Examples are the string break angle in tail end bridges and the neck break angle, which is adjusting the string height.
Break strength: when a plate or beam is bent, one surface is compressed and the other surface elongated. The compression or elongation may exceed the maximum which the material can bear, upon which it collapses. The break starts at the surface, where the deformation is the largest and progresses inward while the plate becomes weaker. Because the critical parameter is the compression of the material the maximum is called the compression break strength, in MPa (which in wood is lower than the tension break strength).
Breathing: when the top moves out and the back as well, the volume of the guitar box increases. Air may be sucked in and this pattern of motion is called the breathing mode or f1. Air may also flow against the pressure, flowing out, and this is called the anti-breathing mode or f2.
Bridge: the bridge is the part which transfers the string forces to the top. Two constructions are popular, one in which the string ends at the bridge, while the bridge is glued to the top (classical bridge) and the other where the strings run over the bridge to a tail end. This bridge is kept in place by the string tension and called the tail end bridge.
Buzzing: when a string swings, while touching the next fret a rattling sound is produced, called buzzing. It stems from incorrect fret height, worn nut, too low action or suboptimal neck profile.
Center of mass (CoM): The imaginary point where the mass of a physical body could be concentrated without changing anything to force moments or forces.
Chladni pattern: vibration mode shape made visible by sprinkling (contrasting) dust on a vibrating plate so that the dust collects in the nodal lines.
Claim: in a patent statements are made what the patented invention is doing. These have the legal status of claims and are compared to previous claims, in other patents.
Clearance: free space between two parts. The clearance is used up when the parts start to vibrate, limiting the vigor of the vibration.
CNC: Computer Numerical Control. This is a method used in automated cutting, in which a shape is described mathematically and transferred to a cutter by defining small mechanical steps.
Coupling: mechanical connection between vibrating units to make them vibrate in sync. In the guitar box the internal air and the elasticity of the sides cast soft coupling between top and back. In the violin the sound post is a hard coupling device.
Cross flush: see flush.
Cross mode: integral mode in which the top is in a different mode than the back. There are many types of cross modes but the resonances involved are not higher than of the second order: (0,2) or (2,0) or (1,1).
Damping: the absorption of energy by internal friction in vibrating materials. Damping occurs in constructions, in solid materials and in fluids and thus pertains to every part of the tone generation process.
Dead note: a note which is muted because of a coincidence of neck vibration resonance and string resonance, when a string is pressed at a particular fret.
Density: the mass per volume of a material. For tonewood the density of tops and braces is around 400 kg/m3, for backs between 600 and 900 kg/m3.
Dipole: sound source which radiates sound in two opposite directions mainly, with little sound across. Higher guitar resonances are of the dipole type and are not directed to the audience frontal to the guitar.
Dome: the spherical shape of a plate. At the edges the shape rests on the sides. When the dome bends away to end flat at the sides it is called an arch. Domes resist pressure but also the twist of a torque better than a flat plate. Domes have stiffness inversely to the radius and are frequently applied to make a plate move with humidity changes rather than crack.
Dreadnought: large guitar shape, immensely popular with folk guitarists. Because of its sheer size, it increases the loudness of bass notes. Named a bit boyish after the notorious British steel battleships.
Effective area: the fraction of a plate which, when moving at maximal deflection, has the same volume displacement as a full plate moving with graded deflection. It is also loosely called the piston equivalent.
Efficiency: the amount of acoustic energy leaving the guitar, relative to the energy put into the plate. For a continuous flow of stimuli this is equivalent to the acoustic power relative to the power put in the plate. For a sequence of discrete notes the latter is approximated, which is easier to measure than the energy of decaying notes. Another efficiency measure in use is a measurement in which the acoustic power output of a plate is compared to that of a moving piston, both per unit area.
Elasticity: the stretch or compression per unit of force. Elasticity is the inverse of (linear) stiffness. The elasticity modulus E (also known as Young’s modulus) is expressing the elasticity as the force per surface area, divided by the length change per unit of length. The usual dimension is GPa = 109N/m2.
End effect: amount of air which sticks to both ends of a defined air column in a Helmholtz resonator. The shape of the end matters: the end effect is different for an open tube, a baffled tube, a horn etc.
Energy: the amount of joules which is involved. The energy of a vibrating mass is continuously transformed from kinetic to potential energy and back again. The total of the two remains the same. Energy is lost by emission or absorption, turning energy into heat. It cannot be converted back, so this is a one way process.
FEM: Finite element modelling. This is an engineering technique in which a mechanical construction is split in small but not infinitely small elements, for which the neighbouring relations come from the theory of elasticity. It is a powerful but computer heavy technique.
FFT: Fast Fourier transform. This is a method to convert a signal which varies in time to a spectrum of contained frequencies. The signal is monitored for a time interval and correlated with harmonics which fit in that interval. With a FFT resonance frequencies are detected instantly.
Flush: air in the soundbox moves in and out, but may also move sideways, with no net volume change. If the air is passing the waist the motion is called long flush, if it is passing the centerline, it is called cross flush. Some use the term slush.
Force: force is the driver for mechanical motion, expressed in Newton. Force times travel is energy. Distinction is made between static force, which involves no energy change and dynamic force, involving energy changes. As an example, string tension exerts a static force on the bridge, the dynamic force of the string vibration makes the bridge move. The static force is often much higher than the dynamic force, in case of the string a factor of 100 or more.
Fret: metal elevation marking a certain pitch at the fretboard. The distance between frets is a fraction (5.95%) of the string length. Because the string becomes shorter with each fret, the spacing of the next fret is 5.95% of the shorter string length and so on, resulting in a decreasing series of spacing.
Fretboard: also called fingerboard, because the fingers press the strings on the frets to cast pitch. Usually the fretboard is straight in the length and flat to slightly convex across (bulging out). The radius depends on musical style and preference, but the profile in both length and across may be exploited to enhance playability and manage string clearance.
Frequency: the number of vibration cycles per second, expressed as Hz. The base for the modern scale is the A4 at 440 Hz.
Friction: the force needed to make two components which are in contact to slip. String slip may happen at nut, saddle and frets. The friction increases with pressure on the contact.
Fundamental: the base of the harmonic series of which a tone consists. If the harmonics follow the pattern n*f0, where n is the wave number, 1*f0 is the fundamental, whether it is actually present or not.
Hardness: measure for the resistance of wood against denting. The Janka hardness scale is the force which it takes to press a 11.3 mm steel ball halfway in the wood. Hardness is related to wood density and varies with the orientation relative to the grain (cross or end).
Harmonics: the motion components of a vibrating body. The resonances start with the fundamental frequency. The harmonics are the integer multiples of the fundamental, with the fundamental thus as first harmonic. If an harmonic deviates from this scheme it suffers from inharmonicity.
Headstock: the extension of the neck on which the strings are mounted.
Heel: the construction by which the neck is mounted to the shoulder of the guitar body. Here the analogy with the human body fails. The name must have been inspired by its shape. Some necks have no heel because they use another construction.
Helmholtz resonance: the fundamental resonance of a fixed volume of air, with a defined soundhole. The soundhole casts a vibrating air mass and the enclosed volume of air a cushion. The soundhole air plug vibrates on the elasticity of the cushion. Tubes and baffles connected to the soundhole modulate the Helmholtz resonance as they change the air plug mass.
Inharmonicity: the inverse of Purity. Inharmonic notes sound interesting to harsh to dissonant to double notes.
Inlay: Short brace end protruding from the lining to a couple of cm under the plate. Inlays can be used to increase the plate resonance frequencies when they have become too low. The term inlay is also used for veneered decoration.
Innovation: new designs of guitar construction or guitar parts, which enhance existing functions or provide new functions. Innovations come in big and small, but big innovations become more and more rare in guitar design.
Integral resonance: resonance in the guitar body in which top plate, back plate and internal air collaborate.
Interaction: when the combined effect of two parameters is not equal to the sum of their separate effects, they are said to interact. In statistical variance analysis interaction is tested and frequently found.
Interface: a system which connects the output from one system to the input for another. Human interfaces deal with human expression and perception in relation to machines and instruments. For acoustic guitars, strings and fretboard are the main interface for expression and the sound pressure for perception. An example of an instrumental interface is MIDI, Musical Instrument Digital Interface. The interface of the classical guitar includes position, speed, force and timing of multiple fingers to activate the sound generation and perception of the sound by human ears. MIDI can monitor these actions to control sound synthesis, as is done in some high tech guitars. Although MIDI is a signal standard which can support complex interfaces, MIDI guitar interfaces tend to miss out the richness of expression of the fingers.
Intonation: a correction on scale length to compensate for string tension increment due to fretting the string. Strings have individual intonation because they differ in core gauge and action, thus in tension increment.
Isotropy: a plate is isotropic when its bending stiffness is the same along as across the grain, otherwise it is anisotropic. Anisotropy is defined as the across over the along stiffness.
Kerfing: a type of lining which is made flexible by repetitive incisions (kerfs) to follow the curves of the sides.
Knocking: inharmonic sound at the start of a note, in particular with percussive guitars.
Laminate: a plate construction, consisting of two or more layers, bonded together. The layers are often oriented perpendicular, to make the plate less anisotropic in strength and stiffness. Its elasticity modulus is lower than that of a solid wooden plate along the grain and glue may hamper sustain. There exist also laminates with non-wood layers, with good acoustic properties, such as with an aramid honeycomb middle layer or carbon outer layers.
Lining: reinforcement of the connection between plate and sides with a triangular strip of wood, increasing the glue surface.
Long flush: see flush.
Loudness: the perceived level of sound intensity. For a given level of sound pressure the loudness varies with the frequency. The ear is most sensitive to about 1000 Hz and a given sound pressure is loudest there. By definition at 1000 Hz the loudness is equal to the sound pressure level (SPL).
Lower bout: the wide part of the guitar body below the waist. This part is most active during resonances.
Machine: winch to put the string under adjustable stress. Usually the machines are located on the headstock, but this is not necessarily so. Machines are designed to maintain the string tension despite the stress.
Mass: Inertia to acceleration. It is expressed in kg. It is commonly confused with weight, which is the force that gravity exerts on a mass. A scale indicates weight, a force, assuming that gravity is the same everywhere (which is not exactly true), but gives the result in recalculated kg of mass. Mass is also used in related concepts, notably surface weight (the mass of a plate per unit of surface area, kg/m2) and string weight (the mass per unit of length, kg/m). Also the vibrating mass is important: not the full mass is in effect, but only the mass in proportion to its deflection.
Mid: the frequency range roughly between 200 and 400 Hz. Beyond the midrange the guitar sound pressure drops and becomes highly directional. Also used for the subjective emphasis in this range, such as in ‘strong mid’.
Missing fundamental: when several harmonics ring in phase they produce a rhythmic pulse at the fundamental frequency, even when the fundamental vibration mode is absent. The pitch is then being perceived as if the fundamental were present.
Mobility: the maximum physical velocity of the plate or bridge for a given force. See also admittance.
Mode: a body, such as a beam, a plate or a soundbox may vibrate in several patterns, called modes. The fundamental mode is the largest pattern and has the lowest frequency. It is noted by 0, meaning: nil nodes. Higher modes split the body in sections, separated by nodes. Linear bodies like a beam or string are split along the length, where the node is a point. Surfaces split in two-dimensional arrays or in radial sections, separated by nodal lines. Volumes split in three-dimensional arrays, separated by nodal surfaces. Modes are by convention noted as 0, 1, 2, 3 and so forth for linear bodies like strings, neck or braces and (0,0), (0,1), (1,0) etc. for guitar plates, where the first number counts the intersectional nodes in the width and the second number in the length. Integral guitar body modes are more complex and specify top mode, back mode and air mode separately.
Modulus of elasticity (Young’s modulus): see elasticity.
Moment: the tangential force which causes bending or rotation. Its value is force times arm so that a large force acting on a short arm may have the same moment as a small force on a long arm. The guitar top is bent under the moment of the string tension times bridge height. Also called torque, in a technical context.
Monopole: a sound source which radiates sound equally in all directions away from it is called a monopole. The importance of monopole radiation (or projection as it is called sometimes) is that everyone in the audience hears the same, be it at lower intensity farther away.
Neck: the slender part between headstock and guitar body, parallel to the strings. The fretboard is mounted on the neck and it can be disputed where the neck ends. Some would argue that neck bending and the fretboard extend to over the upper bout of the guitar body, others could counter that the neck ends at the heel.
Neck bending: the neck is an elastic element with resonance frequencies of its own. The appearance of neck resonances, fired by the body resonances, is called neck bending. Neck bending is also used in a quasi static way: applying force to the neck to make the tone vibrate.
Neck mount: the construction to unite neck and body. Roughly three constructions are used: set neck, which is a dovetail or mortise and tenon glued joint, bolted neck, in which the neck and neck block are bolted together and through necks, where the neck extends to deep into the body, sometimes all the way to the tail. The Spanish guitar has a through neck, but not very deep.
Node: a place between vibrating sections which does not move. An antinode is the top of a vibrating section.
Nut: the division between neck and headstock, also known as fret 0. The difference with a fret is that the nut keeps the stings restricted sideways.
Parameters: a parameter is a measurable variable which affects a design in a consistent way. A set of parameters tries to encompass all designs, although this is never complete. The more design variation depends on a single parameter, the more useful the parameter is.
Patent: a legal document, describing the claims made by the inventor on how to achieve a certain goal. Not the goal but the route to it is patentable. Patents require initial and annual fees and the patent holder may license use rights to others against an appropriate compensation, for a legally defined time period.
Pitch: the frequency of a tone. Pitch is also used to indicate the neck break angle, in the plane perpendicular to the top and through the guitar axis.
Pick-up: vibration sensor, of which the signal is amplified and converted to an electrical signal and can be used to create stronger vibration, for instance of a loudspeaker cone. Different pick-ups sense string, plate, air, bridge and other vibrations.
Pluck: finger stimulus in which the string is pulled and suddenly released. This gives the string a certain amount of energy. The pluck may stimulate the string in a particular transverse direction.
Poisson coefficient: a material parameter υ (nu) describing how the thickness of a plate of that material changes under bending stress. It appears in the stiffness of that plate.
Power intensity: the amount of energy which passes a surface per unit of area and per second. The ear has a defined threshold for power intensity of air waves above which loudness increases.
Principal component: a statistical term in factor analysis, for a cluster of mutually dependent factors which is independent of other principal components. In this way the variance in the data is attributed to principal components. The first 3 or 4 usually together explain the bulk of the variance.
Prior art: existing knowledge, laid down in previously published patents.
Projection: the way sound energy is spatially distributed. Somewhat sloppy, projection is often used to express how strong the sound is to back in the audience.
Purfling: decorative strips which are used to highlight the outline of the guitar, but which also reinforce the joint of plate and side. Luthiers take pride in applying their unique purfling designs.
Purity: degree to which higher harmonics have integer multiples of the fundamental frequency. The measure of purity is the just noticeable difference (jnd) to the human ear.
Q-factor: one measure of damping in a resonance. For a high Q the damping is low and the resonance peak is sharp. Q is simply measured as ω/Δω, in which Δω is the width of the peak.
Resonance: although a body may be stimulated with any frequency, the response is not even. For some frequencies the mechanical resistance between stimulator and body drops to zero, upon which the energy transfer is high and the body vibrates vigorously. The frequency is called a resonance frequency and the pattern on the body is characteristic for the resonance mode. Resonance modes depend on the shape of the body. Thus top plate resonances are not the same as guitar body resonances since they refer to different bodies. Technically a resonance is one eigenvalue of the matrix of forces in the body.
Resonator: a guitar part which is tuned to a certain resonance, to enhance the loudness in a particular frequency band. Resonators have been made from various materials, but aluminum became the standard. They are designed to have a strong voice for a limited spectral band.
Roll: rotation of the neck relative to the body, around the guitar axis.
Rosette: decoration of the soundhole edge and near top area. In many guitars this decoration is regarded as a trade mark, often of intricate design and made of coloured materials. The decoration is about half a plate thickness deep, which can only be afforded because the soundhole is fenced by braces.
Saddle: the material between the string and the bridge. In some guitars the saddle is constructed to move the contact point in length direction of the string for intonation. The shape of the saddle top affects wear and tonal purity. The saddle is meant to reduce bridge mass.
Scale: the length of the string between nut and saddle. Shorter scales produce higher tones in general, but this also depends on the string gauge and tension. Within limits of playability it is the scale which sets the tuning, while the string and body add timbre.
Scaling: increasing or decreasing overall body size, to convert a design from one tuning to another. Thus a family of instruments with similar characteristics results, for instance, baritone – standard – treble.
Scalloping: shaping the brace height to create spots of higher flexibility along the brace.
Second moment of area: a physical concept I, describing the effect of the cross-sectional shape of a beam on its bending stiffness D: D = IE, where E is young’s modulus. Examples are the guitar neck and a braced plate.
Shoulder: the upper part of the guitar body when the neck is pointing up.
Shrinkage: the dimensional change of wood with humidity. Radial (perpendicular to the annual rings), Tangential (along an annual ring) and Longitudinal (in the direction of the grain) changes are different, among which R is the largest, T somewhat smaller and L small. Expressed in percentages the volumetric shrinkage is V= R+T+L.
Slip: sliding movement of a string over a fret or the saddle with every vibration cycle or every fret press. Slip is shortening sustain and causes wear of the nut, fret or saddle.
Soundhole: the gateway of the soundbox. Size, shape and number of openings affect the Helmholtz frequency. The air plug in the opening vibrates on the cushion of the trapped air. The soundhole is essential for the lowest resonances of the guitar body.
Sound pressure: the air pressure (Pa) of a sound wave at its top. Usually the sound pressure level is (SPL) is used, which is 20 times the logarithm of the ratio of the actual sound pressure to the sound pressure at the threshold of hearing. SPL is frequency dependent. For low frequencies larger pressures are required to sound equally loud as a 1000 Hz tone. For higher frequencies the required pressure rises also. Sound pressure is directly related to admittance by taking the differential.
Sound pressure factor: spf, the amount of sound pressure created by top, back and soundhole together, divided by the sound pressure of top and back alone. Spf takes into account that top and back may move to very different magnitudes.
Sound quality: an intuitive expression of how a guitar is liked. Important components of sound quality are loudness, dynamics, frequency spectrum and sustain, but how a guitar sounds is up to individual vocabulary and personal preferences.
Spectrum: the frequency response curve when a guitar is stimulated with a frequency sweep. In the spectrum the resonances and their loudness’ are visible. When the guitar construction is such that the peaks are closer together than for another guitar, its spectrum is said to be compressed.
Spectral factor: a parameter describing compression or expansion of the spectrum, relative to that of a neutral plate. The neutral plate is an isotropic, stiff bound plate. Compression and expansion are mainly caused by bracing style and binding stiffness.
Spring mass system: a system of connected masses, which each have their elastic drivers. When stimulated, the masses interact to reveal amplitude and phase relationships between the masses, which change with the frequency. In a guitar the string-bridge-plate system and the string-plate-neck system are important examples.
Stiffness: the force needed to displace an elastic element a unit of distance (N/m). This may pertain to elongation of a string, deflection of a plate, movement of a bridge. Its rotational counterpart is bending stiffness, the torque needed to bend an elastic element over a unit of angle (Nm). Bending stiffness is a plate or beam property, taking its thickness into account. When a mounted plate or brace is depressed under a force it has a pressure stiffness, which depends on the bending stiffness, but also on the plate dimensions (N/m). When a plate is twisted by a bridge also the dimensions of the plate are involved, resulting in twisting stiffness (Nm).
Stress: the external force on a mechanical system, creating a deformation called strain. The ultimate strain is a crack, confusingly called a stress fracture.
String: steel or nylon wires, always round and of even thickness. Strings may be wound with metal (often phosphor bronze) to increase the mass per unit of length.
String bending: playing style in which one or more strings are pushed sideways, so that the pitch goes up, while staying on the fret.
String stiffness: the force needed to stretch a string over a certain distance (Dstr, N/m). This depends on the length of the string l. Thicker strings are stiffer. Although string gauges are measured at the outside, string stiffness depends on the core gauge because the wound part is much more elastic.
String tuning: standard tuning for a six string guitar is E2-A2-D3-G3-B3-E4. A treble guitar is tuned a perfect fourth higher by which the series shift one string: A2-D3-G3-C4-E4-A4. The bass is tuned one octave lower than standard: E1-A1-D2-G2 and the baritone again shifts one string: A1-D2-G2-C3-E3-A3. Variations are common, depending on the music.
Strum: stimulus of multiple strings with an ongoing one-way movement, starting strings in sequence.
Sustain: the duration of the tone until it is dead. Guitarists have a good ear for its estimate, but the perceived sustain depends on the background noise. Putting your ear to the sound box reveals much longer sustain than noticeable in the air. Technically, the decay time (the time for its level to fall 63%) is a better measure.
Tapering: reduction in brace height towards the brace end. Tapering is used to reduce the plate stiffness towards the sides.
Tension: an internal stress state of a material. It may be thought of as two equal, opposite forces at any place pulling at, for instance, a string. This cannot be observed directly, but the string elongates a little. The tension increases the speed of propagation of a wave in the string and thus the resonance frequency. Something similar happens in plates and membranes.
Tentalones: small triangular blocks which fit in the corner between plate and side. If a lining is not just kerfed but cut through, you are left with tentalones. Also called peones.
Timbre: the type of sound as results from the composition of harmonics of a tone and the way they change over the duration of the tone. The higher harmonics die faster than the fundamental, making the timbre change from percussive to rich to mellower, like a flute. Moderating the harmonics is a main function of the soundbox.
Tone brace: light braces which are mounted in between constructional braces to make the plate stiffness more even.
Tonewood: wood, selected for acoustic purposes. If a tonewood is good depends on its purpose. For tops light, stiff wood is selected, for sides and backs denser and prettier wood. The decisive physical parameters of tonewood are density, Young’s modulus, compression break strength and damping.
Top: plate of the guitar on which the bridge is placed. The top is a few mm thick and often reinforced with braces. The top is to a high extent responsible for the loudness and dynamics of the guitar.
Tornavoz: Spanish for voice reflector, a tube end mounted from the soundhole down. It increases the mass involved in the Helmholtz resonance, lowering its frequency. Some luthiers claim also other voicing effects.
Torque: see Moment.
Transposing: change of the open tuning of the guitar with a number of halftones, to play in a different key with the same finger positions.
Treble: a guitar type which starts at A2. Treble is also the general term for the high frequency emphasis in the spectrum, as the counterpart of bass and mid.
Tremolo: device to change the tuning of all strings continuously over a few semitones, with a single handle. It is common on solid body guitars and on guitars with sound cavities. Acoustic guitars don’t have a tremolo as it exerts large forces on the body. During operation, chords run out of tune if not the string elongation is carefully adjusted to the string stiffness for each string. Acoustic guitarists swing the neck as a substitute.
Tuning: adjustment of the string tension to arrive at a target frequency. For the strings to sound in harmony they must have precise frequency ratios. However, this is not possible for all keys alike. The western ear has got used to the equal temperate tuning, which is an approximation. The term tuning is also used for the fine adjustment of the bracing, when they are shaved to produce a kind of chord upon a knock on a braced plate.
Values: properties with the highest significance for a user or buyer, depending on his personal believes.
Variance: statistical measure for the variation in a data set. The essence of statistical analysis is to attribute variance to certain variables (said to ‘explain’ a portion of the total variance).
Vibration: repetitive motion of a body, where a deflection creates a force that makes the vibration decelerate, stop and reverse. At the stop the force is maximal. When the body goes through the neutral position the force is zero and the speed maximal. Without energy loss, such as by making a sound wave in the air, the vibration would go on forever.
Vocabulary: in general: list of words, but here specifically used for terms which musicians, listeners and instrument makers use to describe timbre and sound. The same term means different things to different persons and many terms used by different people mean the same. This makes vocabulary ambiguous to describe sound.
Waist: narrowest point of the guitar body, in analogy to the human torso. The width and location of the waist are important for the resonance spectrum, but technically a waist is not necessary to sound as a guitar, since other design parameters may have the same effect.
Weight: the effect of gravity on an amount of mass. The term mass is the common factor in several accelerations, among them not only gravity but also elastic (plate, string, air) accelerations or stimulation (by a finger).
Wolf note: a note which sounds harsh and loud due to a coincidence of string frequency and plate resonance frequency.
Yaw: neck angle with the guitar axis, in the plane of the top.
Young’s modulus: the modulus of elasticity, see Elasticity