UBC Undergraduate Research

Effects of Wood Attributes on Acoustic Guitar Sound Quality Bartolome, Jan Emanuele 2016-04

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	Effects	of	Wood	Attributes	on	Acoustic	Guitar	Sound	Quality	Jan	Emanuele	Bartolome	ABSTRACT	The	guitar	is	a	classic	instrument	that’s	been	around	for	hundreds	of	years.	The	sound	quality	of	a	guitar	can	be	attributed	to	the	wood	used	to	construct	it.	However,	sound	quality	is	more	qualitative	than	quantitative.	A	more	expensive	guitar	is	not	necessarily	a	better	guitar.			 		 	 Jan	Bartolome		Graduation	Essay	 	 2	Introduction	The	guitar,	which	is	“a	stringed	musical	instrument	with	a	long,	fretted	neck,	a	flat	somewhat	violin	like	body,	and	typically	six	strings,	which	are	plucked	with	the	fingers	or	with	a	plectrum”	[1]	is	one	of	the	most	well	known	instruments	in	the	world.	Researchers	believe	that	the	guitar	originated	from	the	guitarra	latina,	an	instrument	invented	in	Spain	in	the	early	16th	century	[2].	Those	guitars	were	composed	of	four	strings,	tuned	to	the	notes	C-F-A-D	[2].	Nowadays,	guitars	are	made	with	six	strings,	and	are	tuned	to	the	notes	E-A-D-G-B-E.		The	primary	material	used	in	making	guitar	bodies	is	wood,	and	the	two	main	parts	of	the	guitar	that	use	wood	are	the	neck	and	the	body.	Different	species	of	wood	can	be	used	for	each	part,	or	the	same	can	be	used.	The	species	of	the	wood	greatly	changes	the	sound	and	tone	of	the	instrument.	Some	of	the	common	woods	used	include	Alder,	Ash,	Basswood,	Korina,	Mahogany,	Maple,	Poplar,	Rosewood	and	Walnut.	Woods	of	the	same	species	cut	from	different	trees	(or	grown	in	different	regions)	will	sound	slightly	different,	and	have	different	weights,	different	densities,	and	so	on	[3].	Taylor	Guitars	is	one	of	the	largest	and	most	popular	producers	of	guitars.	The	three	most	popular	models	are	the	114ce,	214ce,	and	814ce.	Table	1	shows	a	summary	of	the	price,	and	wood	types	of	these	three	guitars.		Guitar	 Price	(USD)	 Wood	Type	Used	114ce	 1,058	 Back/Side	–	Layered	Sapele	Top	–	Sitka	Spruce	Neck	-	Sapele	Fretboard	-	Ebony	214ce	 1,328	 Back/Side	–	Layered	Rosewood	Top	–	Sitka	Spruce	Neck	-	Sapele	Fretboard	-	Ebony	814ce	 4,498	 Back/Side	–	Indian	Rosewood	Top	–	Sitka	Spruce		 	 Jan	Bartolome		Graduation	Essay	 	 3	Neck	–	Tropical	Mahogany	Fretboard	-	Ebony	Table	1:	Comparison	of	price	and	wood	type	used	for	three	different	models	of	Taylor	guitars	From	Table	1,	it	can	be	observed	that	the	top	three	most	popular	guitars	made	by	Taylor	all	have	a	Sitka	spruce	top	and	sapele	or	rosewood	backs	and	ebony	or	mahogany	fretboards.			Taylor	Guitar	says	that,	“While	the	rich	tones	of	solid	wood	remain	unmatched,	a	layered	wood	construction	can	yield	great	sound	in	a	beautiful,	durable	and	affordable	instrument.	Such	is	the	case	with	layered	sapele,	in	which	we	use	interior	and	exterior	veneers	of	sapele	with	a	core	layer	of	poplar	between	them”	[4].	 There	have	been	many	recent	developments	in	guitar	technology	over	the	years.	One	such	example	is	layering	woods	for	the	neck	instead	of	using	one	solid	piece.	This	allows	for	more	flexibility	where	guitars	with	better	sounds	using	lower	quality	wood	could	be	achieved.	Other	innovations	include	the	use	of	materials	that	are	not	necessarily	wood,	but	are	carbon	fiber	or	fiberglass,	or	graphite.	For	example,	Adamas	graphite-top	acoustic	is	better	protected	against	temperature	and	humidity	changes	compared	to	the	traditional	spruce	top	[5].	Thermowood	is	another	innovation	being	used	for	making	guitars.	Essentially,	the	wood	is	baked	in	an	oven	to	create	a	vintage,	crisp	sound	[6].	Lastly,	Acoustic	Resonance	Enhancement	(ARE)	is	a	new	way	of	treating	wood.	It	is	similar	to	thermowood	in	that	“new	wood	matured	with	this	technology	produces	a	tonal	richness	like	that	of	well-used	vintage	instruments”	[7].	Guitar	Anatomy	In	a	guitar,	the	sound	comes	from	plucking	or	strumming	the	strings.	The	strings	are	connected	to	the	neck	and	the	body	of	a	guitar	through	the	saddle	and	the	headstock.	Figure	1	shows	a	diagram	of	a	guitar	and	its	different	parts.			 	 Jan	Bartolome		Graduation	Essay	 	 4		Figure	1:	Diagram	of	a	guitar	[8]	The	body	is	what	resonates	the	sound	of	the	strings	being	plucked	or	strummed.	The	generally	accepted	design	is	for	the	sound	hole	to	be	in	the	center	of	the	body,	as	this	makes	it	more	symmetric	and	appealing.	However,	this	actually	structurally	weakens	the	soundboard,	or	top	of	the	body	[9].	One	important	part	of	the	body	is	the	heeljoint.	“The	heeljoint	refers	to	the	curved	block	of	wood	that	is	usually	found	on	an	acoustic	guitar	at	the	point	where	the	neck	joins	the	body”	[10].		“Steel	strung	guitars	with	a	‘traditional’	neck	joint	have	a	wood	block	inside	the	guitar	and	the	neck	is	joined	to	this	block	with	a	dovetail	join.	The	dovetail	is	carved	into	the	inside	face	of	the	heel	and	secured	to	a	matching	cavity	in	the	body	block	with	glue”	[10].		The	neck	is	what	holds	the	fretboard	of	a	guitar.	It	is	connected	to	the	heeljoint	of	the	body	and	on	the	other	end	is	connected	to	the	headstock.	This	is	one	of	the	most	important	parts	of	the	guitar	because	this	is	where	the	feel	of	a	guitar	and	its	playability	are	most	observable.	Another	part	of	the	neck	is	the	truss	rod.	It	is	a	metal	rod	that	is	placed	inside,	along	the	length	of	the	neck.	It	is	used	to	stiffen	the	neck	of	the	guitar	as	well	as	to	“counteract	the	force	of	the	strings,	which	tends	to	bend	the	neck	forward”	[10].	The	truss	rod	can	also	be	adjusted	to	bend	the	neck	at	a	higher	or	lower	angle	from	the	heel	joint.	This	can	change	the	feel	of	the	guitar	by	either	increasing	or	decreasing	the	space	between	Heeljoint		 	 Jan	Bartolome		Graduation	Essay	 	 5	the	strings	and	the	fretboard.	A	higher	space	makes	the	guitar	harder	to	play,	however	if	the	space	is	too	small,	there	is	a	risk	of	the	strings	hitting	the	fretboard	and	producing	an	unpleasant	buzzing	sound.		Different	woods	are	used	for	the	body	of	the	guitar.		“The	top	of	soundboard	woods	are	usually	chosen	for	their	strength	and	acoustic	properties	while	the	sides,	or	rims,	and	back	woods	are	chosen	more	for	their	appearance	and	ability	to	be	steam	bent	into	curves	for	the	sides“	[9].	For	the	neck,	the	most	commonly	used	wood	is	mahogany	as	it	carves	easily	and	has	good	longitudinal	strength.	Taylor	uses	another	wood	called	sapele,	and	according	to	them,	“it’s	sometimes	mistakenly	referred	to	as	African	mahogany	because	it	closely	resembles	the	West	African	wood	khaya,	which	is	commercially	known	as	African	mahogany”	[11]. Tonewoods	Tonewood	is	wood	that	creates	a	certain	sound	or	tone	when	struck.	“If	a	guitar’s	body	shape	produces	the	sonic	equivalent	of	a	meal,	think	of	tonewoods	as	the	seasoning”	[12]. There	are	many	types	of	wood	available	in	the	world,	however,	tonewoods	are	special	because	they	create	a	sound	when	struck	and	resonate	that	sound	well.	“Because	of	the	dynamics	of	the	guitar,	tonewoods	for	faces	need	to	be	different	than	tonewoods	for	backs,	if	the	instrument	is	to	have	the	best	and	most	even	sound”	[13].	“Lighter woods like mahogany are said to have a dry and woody sound. The denser Rosewoods have a rich and bell-like sound, while the denser-still Ebonies and Blackwoods are said to impart a deep, piano-like sound to the guitar” [14]. 	For	the	top,	spruce	is	the	most	popular	wood	to	use	(Table	1).	“As	a	guitar	soundboard,	or	top,	Sitka	spruce	is	the	tonewood	standard	of	the	modern	era.	It’s	used	on	85-90	percent	of	the	guitars	that	Taylor	makes.	Its	combination	of	strength	and	elasticity	translates	into	a	broad	dynamic	range,	yielding	crisp	articulation	and	allowing	for	everything	from	aggressive	strumming	and	flatpicking	to	fingerpicking.	Sitka	spruce	is	Bob	Taylor’s	personal	favorite	for	an	all-around	great	guitar”	[15].	There	are	two	types	of	spruce	woods		 	 Jan	Bartolome		Graduation	Essay	 	 6	used:	(1)	European	Spruce,	when	bent	or	stressed,	will	crack	and	break	because	it	is	brittle.	However,	it	creates	very	good	overtones	and	a	more	full	sound.	(2)	American	Spruce	is	strong	and	will	not	break	when	bent	or	stressed,	however	it	creates	less	overtones	and	a	warmer	feel.	This	is	good	for	music	such	as	folk.			Usually	the	top	of	the	body	is	a	different	wood	compared	to	the	back	of	the	body.	“The	best	guitar	backs	are	made	of	high	quality	hardwoods	such	as	rosewood,	ebony,	maple,	walnut,	koa,	mahogany,	or	a	number	of	other	suitable	body	woods”	[13].	In	the	case	of	Taylor,	their	three	most	popular	models	have	either	a	sapele,	or	a	rosewood	back.	Traditionally,	Brazilian	rosewood	has	been	used	because	of	its	high	quality	resonance.	“When	struck,	a	properly	cut	sample	rings	like	a	plate	of	glass”	[13].	This	is	a	great	quality	for	a	guitar	because	it	helps	with	the	resonance	and	will	allow	the	guitar	to	sustain	the	sound	for	a	longer	time.		The	alternative	to	Brazilian	rosewood	is	Indian	rosewood.	This	has	the	same	properties	as	the	Brazilian	rosewood,	but	is	not	as	good	at	resonating	and	sustaining	sound.	The	reason	for	an	alternative	is	the	declining	amount	of	Brazilian	rosewood.		To	obtain	wood,	trees	must	be	cut	down	from	the	forest.	In	the	case	of	rosewood,	Brazilian	rosewood	is	one	of	the	best	choices.	Because	of	this,	Brazilian	rosewood	has	become	more	scarce	and	is	on	CITES	Appendix	I,	which	means	that	even	finished	products	of	this	wood	are	not	allowed	to	cross	international	borders	[16].	This	is	the	main	reason	that	Indian	rosewood	has	been	used	as	a	substitute.	The	sound	is	very	similar	and	Indian	rosewood	is	more	available.	Another	example	of	woods	used	in	guitar	that	is	becoming	scarcer	is	Ebony.	Ebony	is	used	mostly	in	the	neck	and	on	fret	boards.	“The	issue	isn’t	rocket	science:	ebony	trees	(in	the	Diospyros	genus)	are	generally	small	and	slow	growing.	Demand	for	ebony	wood	is	very	high:	it’s	a	high	quality	hardwood	that’s	very	hard,	very	strong,	and	most	of	all,	very	black”	[17].	Most	of	the	world’s	ebony	comes	from	third-world	countries	and	so	it	has	been	exploited	to	near	extinction.	Taylor	uses	Macassar	ebony	and	African	ebony	in	their	guitars.	To	obtain	this	ebony,	they	have	purchased	“Crelicam,	an	ebony	mill	located	outside	of	Yaoundé,	Cameroon”	[18].	This	is	to	ensure	“that	ebony	is	legally,	sustainably,	and	ethically	harvested”	[18].		 	 Jan	Bartolome		Graduation	Essay	 	 7	Scientific	analysis	of	sound	The	sound	of	a	guitar	is	produced	in	the	strings.	The	body	is	what	resonates	the	sound	and	the	type	of	wood	is	what	‘colors’	the	sound.	The	bridge,	which	connects	the	strings	to	the	body	(more	specifically	the	top),	“transfers	the	vibrational	energy	of	the	strings	to	the	top	plate”	[19].	The	top	then	vibrates	and	transfers	the	vibrations	to	the	air	inside	the	body	of	the	guitar	and	out	the	sound	hole	amplifying	the	sound.	“The	top	plate	is	made	so	that	it	can	vibrate	up	and	down	relatively	easily.	On	the	inside	of	the	plate	is	a	series	of	braces.	These	strengthen	the	plate”	[20].	It	is	also	necessary	to	note	that	the	body	does	not	“amplify”	the	sound	in	the	traditional	sense	of	the	word.	For	comparison,	in	electric	guitars,	the	vibration	from	the	string	disrupts	the	magnetic	field	around	the	pickup,	which	is	a	series	of	magnets,	and	the	pickup	sends	this	disruption	to	the	amplifier	to	create	a	louder	sound	that	can	be	heard	through	speakers	[21].	In	acoustic	guitars,	“all	of	the	sound	energy	that	is	produced	by	the	body	originally	comes	from	energy	put	into	the	string	by	the	guitarists	finger”	[20].	The	body	then	does	the	equivalent	of	what	an	amplifier	does	by	strengthening	the	sound	inside	the	body.		 One	of	the	main	factors	that	affect	the	acoustic	properties	of	wood	is	its	density.	“The	most	important	acoustical	properties	for	selecting	materials	for	sound	applications,	such	as	musical	instruments	and	building	interiors,	are	the	speed	of	sound	within	the	material,	the	characteristic	impedance,	[and]	the	sound	radiation	coefficient”	[22].	The	grain	of	the	wood	and	its	direction	affects	the	speed	of	sound.	In	a	guitar,	characteristic	impedance	is	important	between	the	bridge	and	the	body.	The	two	mediums	have	different	impedances	to	sound	and	a	careful	ratio	must	be	made	by	changing	thickness	of	each	medium.	“Sufficient	vibratory	energy	must	be	transmitted	form	the	string	to	the	soundboard	to	make	the	strings	vibrate	audibly,	while	the	energy	should	not	be	transmitted	too	readily	or	too	rapidly,	causing	the	vibrations	of	the	string	to	die	down	quickly	and	their	sound	to	resemble	that	of	a	thud”	[22].	The	sound	radiation	coefficient	refers	to	the	dampening	of	a	vibration	in	a	body	due	to	sound	radiation.	This	is	important	in	guitars	for	how	long	they	can	sustain	a	sound.				 	 Jan	Bartolome		Graduation	Essay	 	 8	With	these	properties	in	mind,	a	difference	can	be	measured	between	new	guitars	and	aged	guitars.	Luthiers	and	experienced	guitar	players	will	say	that	vintage	guitars	have	a	better	tone	and	sound	quality	because	of	the	aged	wood.	“One	bit	of	science	[Luthier	Alan	Carruth]	has	brought	to	the	attention	of	the	lutherie	community	is	that	wood	consists	mainly	of	cellulose,	lignin,	and	hemicellulose,	and	that	all	wood	gradually	loses	hemicellulose—a	soluble	polysaccharide—to	evaporation	over	a	long	period	of	time”	[23].	This	means	that	as	wood	ages,	it	loses	weight	and	tensile	strength	over	time,	but	the	stiffness	is	not	lost	as	quickly.	“As	long	as	the	tensile	strength	remains	sufficient	to	withstand	string	tension,	there	is	a	net	gain	in	one	of	the	most	important	features	of	tonewood:	the	stiffness-to-weight	ratio,	which	is	known	as	Young’s	modulus”	[23].	Primary	Research	One	of	the	biggest	opinion	differences	in	guitars	comes	in	how	a	guitar	sounds.	This	is	because	each	person	hears	things	differently	than	the	person	next	to	them	listening	to	the	same	thing.	They	will	hear	the	exact	same	soundwaves,	however	their	brain	will	interpret	it	differently	and	the	sound	will	give	them	a	different	feel.	The	sound	of	a	guitar,	while	it	can	be	somewhat	quantified	in	terms	of	decibels,	is	more	qualitative.	For	this	very	reason,	I	went	to	a	music	store,	Long	and	Mcquade	located	in	Vancouver,	BC,	and	tested	out	the	three	Taylor	guitars	mentioned	earlier.	I	played	each	one	for	about	20	minutes	and	played	the	exact	same	thing	on	each	guitar.	Here	are	the	results.	Taylor	114E	(899	CAD)	The	only	difference	that	this	guitar	has	with	the	Taylor	114CE	is	that	it	lacks	the	cutaway	in	the	body	that	allows	players	to	reach	higher	frets	with	more	ease.	“The	114e	defies	the	logic	of	most	starter	guitars	by	providing	a	really	great-sounding	instrument	that	extremely	well-built.	Laminated	sapele	back	and	sides	and	a	solid	spruce	top	make	for	crisp	and	well-defined	sound	in	this	versatile	mid-priced	guitar”	[24].	In	my	opinion,	this	guitar	felt	heavier	than	the	other	two	models.	Purely	on	aesthetics	alone,	I	was	not	a	big	fan.	The	dots	on	the	frets,	as	well	as	the	design	on	the	soundhole,	looked	like	they	were	painted	on	or	were	stickers.	The	sound	was	not	too	powerful,	but	good	for	plucking	softly.	I	was	hoping	to	hear		 	 Jan	Bartolome		Graduation	Essay	 	 9	the	bright	warm	sound	that	is	associated	with	Taylor	guitars,	however	I	found	the	sound	to	be	slightly	dampened	and	more	‘twangy’.	I	could	not	hear	the	overtones	as	much	and	the	notes	were	sustained	for	only	a	short	time	before	sounding	dead.	This	guitar	is	good	for	beginners	because	it	was	the	easiest	to	play.		Taylor	214CE	(1,399	CAD)	It’s	“a	glossy,	solid	Sitka	spruce	top	meets	gorgeous	Indian	rosewood	laminate	back	and	sides,	delivering	an	experience	of	sight,	sound	and	touch	that’s	unmistakably	Taylor”	[24].	In	my	opinion,	this	was	exactly	what	Taylor	guitars	should	sound	like.	It	was	bright	and	warm,	perfect	for	strumming	and	light	plucking.	This	guitar	would	play	nicely	with	folk	music	or	slow	jazz.	The	playability	was	really	easy	and	I	found	that	I	lost	track	of	time	while	playing	it.	The	sound	was	very	full	and	filled	the	little	room	I	was	in	with	no	effort.	There	was	a	slight	hint	of	overtones,	but	nothing	too	obvious.	I	really	liked	the	aesthetics	of	this	guitar’s	neck	due	to	the	wood	grain	of	the	layered	rosewood.	Overall,	this	was	my	favorite	of	the	three	and	it	was	the	most	reasonably	priced.		Taylor	814CE	(4,899	CAD)	This	guitar’s	“balance,	warmth	and	articulation	are	great	for	fingerstyle,	it	has	enough	punch	as	a	strummer	to	front	a	band,	and	the	top-end	power	will	fuel	lead	runs	without	getting	shrill.	It’s	a	great	choice	for	a	gigging	player	looking	for	one	guitar	that	can	cover	it	all”	[25].	Aesthetically,	it	had	pearl	inlays	on	the	marbled	fretboard.	The	colors	of	the	guitar	were	very	eye	catching	and	looked	vintage.	The	sound	was	full	and	filled	the	entire	room	effortlessly,	meaning	you	didn’t	need	to	strum	or	pluck	the	strings	as	hard	as	you	would	on	the	other	two.	The	overtones	were	very	obvious	and	the	sound	was	sustained	for	a	longer	period	of	time.	The	downside	to	this	was	that	the	neck	was	not	as	smooth	because	of	a	finishing	varnish	on	it	and	the	action	(space	between	the	fret	and	the	strings)	was	much	higher.	This	made	the	guitar	less	playable	and	it	did	not	feel	as	nice	to	play	as	the	Taylor	214CE.			After	trying	these	three	guitars,	my	favorite	guitar	in	terms	of	sound	and	playability	was	the	Taylor	214CE,	although	aesthetically,	the	Taylor	814CE	was	the	best.	I	am	not	an	expert		 	 Jan	Bartolome		Graduation	Essay	 	 10	when	it	comes	to	guitars,	however	I	have	been	playing	for	more	than	ten	years	and	so	I	think	this	qualifies	the	observations	I	made	about	each	guitar.			One	interesting	thing	that	I	noticed	was	that	all	the	guitars	sounded	the	same	when	plugged	in.	This	is	probably	due	to	the	guitar	pickup	system	being	the	same	in	all	three	guitars.	When	plugged	into	an	amp,	all	the	guitars	sounded	exactly	the	same,	so	the	qualitative	observations	I	made	about	the	sound	were	nullified.		Technological	Advances	New	and	innovative	technology	is	being	released	everyday	and	this	holds	true	for	guitars.	These	technologies	can	range	from	improving	the	sound	system	that	allows	a	guitar	to	plug	into	speakers,	new	materials	for	strings,	and	most	importantly,	changing	the	way	the	wood	used	for	guitars	is	treated.			One	innovative	way	of	changing	the	wood	in	a	guitar	has	been	mentioned	earlier.	Layered	wood,	or	more	commonly	known	as	laminated	wood,	is	used	in	many	guitars	(for	example	the	Taylor	114CE	and	Taylor	214CE).	The	laminated	wood	is	composed	of	a	layer	of	an	expensive	piece	of	wood	over	layers	of	cheaper	pieces	of	wood.	This	makes	the	guitar	less	expensive.	According	to	Taylor,	“One	of	the	benefits	of	layered	wood	for	guitars	is	extra	resilience	in	the	face	of	fluctuating	humidity	conditions”	[4].	One	drawback	of	layered	wood	is	that	it	has	a	flatter	sound	and	does	not	produce	as	much	volume	as	compared	to	a	solid	piece.	This	is	because	it	does	not	vibrate	as	well	due	to	its	layers.			Yamaha	is	also	developing	a	technology	called	ARE	or	Acoustic	Resonance	Enhancement	This	new	technology	is	a	way	of	treating	wood	to	make	it	have	a	mature	sound	and	the	tonal	characteristics	of	vintage	wood.	One	of	the	biggest	things	the	affects	wood	in	instruments	is	heat	and	humidity.	What	Yamaha	found	was	that,	“Young	wood	gives	an	edge	and	hardness	to	the	sound,	but,	as	the	years	pass	by,	it	becomes	more	and	more	difficult	for	changes	to	occur	and	it	produces	a	good	deep,	rounded	sound”	[26].	The	way	that	Yamaha	discovered	to	create	this	sound	in	young	wood	was	by	controlling	the		 	 Jan	Bartolome		Graduation	Essay	 	 11	humidity,	temperature,	and	atmospheric	pressure.	This	treatment	affects	the	grain	of	the	wood.	“The	hardening	in	the	direction	of	the	grain	and	softening	across	the	grain	of	the	wood	achieved	by	the	ARE	treatment	improves	the	clearness	of	the	sound,	making	it	unmuffled,	and	produces	excellent	resonance	by	enhancing	low	range	sustain	and	increasing	the	attack	in	the	medium-	to	high-range	frequency	bands”	[26].			Another	innovation	that	is	worth	looking	at	is	thermowood,	which	is	a	process	that	was	developed	in	Finland.	Thermowood	is	essentially	wood	that	has	been	heat-treated	to	increase	its	strength	properties.	The	wood	is	treated	at	low	oxygen	levels	to	prevent	it	from	burning.	“Temperatures	for	the	actual	heat	treatment	period	range	from	150	°C	to	240	°C,	the	time	of	the	period	is	0.5	to	4	h”	[26].	A	company	named	‘Sago’	is	using	this	thermowood	in	their	guitars	because	it	gives	it	a	more	vintage	sound	and	makes	it	more	durable.	According	to	Sago,	“balance	between	strings	and	frets	will	increase.	Thermowood	processing	keeps	the	body	size	stable	in	humid	Japan,	preventing	deformation	of	your	instrument	at	home	or	in	a	car,	or	even	against	spotlights	and	heat	of	the	audience	at	a	performance”	[6].	Summary	The	guitar	is	a	timeless	instrument	that	is	only	getting	more	popular	as	the	years	go	by.	This	popularity	can	be	attributed	to	its	convenient	size,	it’s	playability,	and	the	great	sounds	that	it	produces.	There	are	many	types	of	guitars	and	they	are	all	made	with	the	same	general	blueprint	in	mind.	The	differences	are	based	on	the	wood	chosen	for	specific	parts	and	the	shape	in	which	each	one	is	built.	Other	notable	instruments	that	have	a	similar	build	and	style	of	play	include:	ukuleles,	mandolins,	basses,	and	banjos.		The	science	behind	the	sound	of	a	guitar	can	be	summarized	into	the	wood’s	density	and	the	stiffness	to	weight	ratio	(also	known	as	Young’s	modulus),	as	well	as	how	the	sound	acts	and	moves	inside	the	body	of	the	guitar.	The	factors	of	the	speed	of	sound	in	the	guitar,	its	characteristic	impedance,	and	sound	radiation	coefficient,	all	play	a	large	part	in	the	acoustic	properties.	These	are	specific	things	that	can	be	measured	with	scientific		 	 Jan	Bartolome		Graduation	Essay	 	 12	instruments	inside	a	lab.	Many	works	of	literature	go	more	in	depth	on	the	specifics	of	sound	in	an	instrument;	however,	I	have	found	that	the	sound	of	a	guitar	is	dependent	on	the	ear	and	sound	perception	of	the	person	listening.	When	describing	how	a	guitar	sounds,	the	terms	used	are	more	qualitative	than	quantitative.	The	average	guitar	player	would	not	be	able	to	tell	you	the	acoustic	properties	of	the	wood	in	their	guitar,	but	they	can	tell	you	that	it	“sounds	warm”	or	“it	creates	a	bright	tone	and	produces	loud	overtones.”	None	of	these	descriptive	qualities	are	quantitative	and	is	all	based	on	the	guitarist’s	perception	of	the	sound.	Within	the	guitar	community,	there	are	disagreements	on	whether	a	vintage	guitar	sounds	better	than	a	newer	guitar	because	of	its	aged	wood.	There	has	been	research	done	to	support	this,	such	as	the	increase	in	stiffness	as	wood	ages,	but	the	advancements	in	wood	treating	technology	is	making	those	arguments	null.	Treatments	have	advanced	to	the	point	new	or	young	wood	is	“aged”	and	thus	the	sound	it	produces	is	vintage.	These	advancements	are	also	affecting	new	guitars	in	that	cheaper	guitars	are	sounding	better	even	with	lower	quality	wood.	A	more	expensive	guitar	does	not	necessarily	mean	that	it	is	going	to	be	better	sounding	or	more	playable	than	an	expensive	one,	as	per	my	observation	between	the	Taylor	814CE	and	Taylor	214CE.			The	guitar	is	a	classic	instrument	that	has	undergone	many	changes	over	the	years.	There	are	always	more	improvements	to	be	made	to	bring	it	to	the	next	level.	It	is	exciting	to	see	where	technology	is	pushing	the	boundaries	of	guitar	making	and	the	sounds	it	can	produce.	From	thermowood	to	acoustic	resonance	enhancement,	the	future	of	guitars	looks	bright.	As	a	guitar	player,	I	believe	that	the	current	state	of	the	guitar	is	perfect,	but	I	am	eager	to	see	the	developments	being	made	and	where	it	will	take	this	instrument	that	has	been	around	for	hundreds	of	years.					 	 Jan	Bartolome		Graduation	Essay	 	 13	Appendix	A	–	Common	Tonewoods	Common	Name	 Latin	Name	 Average	Dried	Weight	(kg/m3)	Sapele	 Entandrophragma	cylindricum	 670	Sitka	Spruce	 Picea	sitchensis	 425	Macassar	ebony	 Diospyros	celebica	 1,120	Brazilian	Rosewood	 Dalbergia	nigra	 835	Indian	Rosewood	 Dalbergia	latifolia	 830	African	Mahogany	 Khaya	spp.	 640															 	 Jan	Bartolome		Graduation	Essay	 	 14	References	[1]	"The	Definition	of	Guitar."	Dictionary.com.	Web.	06	Apr.	2016.			[2]	"History	of	the	Guitar."	History	of	the	Guitar.	Web.	06	Apr.	2016.			[3]	Hunter,	Dave.	"All	About	Tonewoods."	All	About	Tonewoods.	Web.	06	Apr.	2016.			[4]	"Layered	Sapele."	Taylor	Guitars.	Web.	06	Apr.	2016.			[5]	Potts,	Paul.	"Geek	Versus	Guitar."	Recent	Developments	in	Guitar	Technology.	Web.	06	Apr.	2016.			[6]	"Thermowood:	About	Sago's	Neck	Material."	Sago.	Web.	06	Apr.	2016.			[7]	"A.R.E.	Technology."	Yamaha.	Web.	06	Apr.	2016.			[8]	Acoustic	Guitar	Parts.	Squarespace.	Web.			[9]	Relph-Knight,	Terry.	"The	Acoustic	Guitar	Body	–	Part	1."	Acoustic	Masters.	Web.	06	Apr.	2016.			[10]	Relph-Knight,	Terry.	"The	Guitar	Neck	&	Fretboard."	Acoustic	Masters.	Web.	06	Apr.	2016.			[11]	"Sapele."	Taylor	Guitars.	Web.	06	Apr.	2016.			[12]	"Woods."	Taylor	Guitars.	Web.	06	Apr.	2016.			[13]	Somogyi,	Ervin.	"Tonewoods	in	Guitars."	Esomogyi.	Web.	06	Apr.	2016.			[14]	Brill,	Andrew,	and	Drew	Beeson.	"The	Acoustical	Properties	of	Wood."	(2007).	Web.			[15]	"Sitka	Spruce."	Taylor	Guitars.	Web.	06	Apr.	2016.			[16]	"Brazilian	Rosewood."	The	Wood	Database.	Web.	06	Apr.	2016.			[17]	Meier,	Eric.	"Ebony:	Dark	Outlook	For	Dark	Woods?"	The	Wood	Database.	Web.	06	Apr.	2016.			[18]	"Sustainable	Ebony."	Taylor	Guitars.	Web.	06	Apr.	2016.			[19]	"Acoustic	Guitar."	Hyperphysics.	Web.	<http://hyperphysics.phy-astr.gsu.edu/hbase/music/guita.html>.			[20]	Wolfe,	Joe.	"How	Does	a	Guitar	Work?"	The	University	of	New	South	Wales.	Web.			 	 Jan	Bartolome		Graduation	Essay	 	 15		[21]	"How	Electric	Guitars	Make	Sound."	Sound	Called	Music.	Web.	06	Apr.	2016.			[22]	Wegst,	Ulrike	G.K.	"Wood	for	Sound."	American	Journal	of	Botany	93.10	(2006).	Web.			[23]	Turner,	Rick.	"Acoustic	Soundboard:	The	Sonic	Effect	of	Time	and	Vibration."	Premier	Guitar.	Web.	06	Apr.	2016.			[24]	"Acoustic	Guitars."	Long	&	Mcquade.	Web.	06	Apr.	2016.			[25]	"814ce."	Taylor	Guitars.	Web.	06	Apr.	2016.			[26]	Homan,	Waldemar	J.,	and	Andre	J.M.	Jorissen.	"Wood	Modification	Developments."	(2003).	Web.					

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