Guitar Myths #002 - Are acoustic guitars' tops really flat?

Flat acoustic guitar top… really?

Once again urban myths strike again.

After making the big decision to part with one's hard earned money, a guitar was purchased. It was all perfect… was it? Playing the brand new guitar in private, admiring its beauty, savoring its tone… suddenly a slight bulge about the guitar bridges' area was sighted. Perplexed by it, immediately turning to internet to seek for an explanation.

Most people fear the unknown. Needless to say, many guitar owners assumed the worse. As such, it triggered their paranoia quests for solutions to this mysterious phenomenon. So the million dollars question; Are acoustic guitar tops really flat? If it isn't, so the guitar is not in perfect condition, right?

Total String Tension

First let's take a look at how much force is acting on a 6-string acoustic guitar's top board when all six strings are fully tuned to standard tuning. In D'Addario's website, the force in both pounds and kg for each string is listed. Below is an excerpt from D'Addario's EXP PB 12/53 string's technical specifications. 12/53 gauge is chosen because of its commonality.

Taken from: http://www.daddario.com/DADProductDetail.Page?ActiveID=3769&productid=87&productname=EXP16_Coated_Phosphor_Bronze__Light__12_53

There is no rocket science in determining the total force acting on a guitar top board. Just add them up.

In KG; (E)10.6 + (B)10.57 + (G)12.9 + (D)13.03 + (A)12.74 + (E)11.05 = 70.89kg or 156.29lbs

How much does a regular dude weigh?

Thickness of Top Board

Next, we shall consider the typical thickness of acoustic guitars' top boards. There are actually many considerations in determining the thickness of an acoustic guitar's top board. It isn't practical to go at length about it herein for obvious reason. Lets' take the word of a guru, Ervin Somogyi as a good guide. He mentioned in one of his many articles the preferred top board thickness is 3/32" or 2.34mm in thickness. You can read his full article here: http://www.esomogyi.com/top_thickness.pdf

We are going to rewind a little to figure out the reasons for guitar owners to assume that acoustic guitars' tops are flat.

Points of sale; firstly there is virtually no good reason for buying a guitar except for professional guitarists. We buy guitars on impulse, simple as that. Under impulse, no amount of intellect can help a guitar fanatic to discern facts from fiction. A guitar sales guy would say whatever the potential buyer wishes to hear. That includes generating an impression upon the potential buyer that the guitars in the shop are in perfect conditions. It isn't too hard to connect the dots right?

Acoustic guitars' top boards appear to be flat to our naked eyes. Most guitar buyers wouldn't question validity of this point. So it is not difficult for the sale guy to complete the sales with the buyer thinking and agreeing that the purchased guitar is in perfect condition which includes a perfectly flat top board.

Limited knowledge; while many guitar owners are passionate about playing guitars, however that has little to do with the motivation to learn adequately about guitar's construction. Flat Top guitar, this common jargon has convinced guitar owners that acoustic guitars' top boards are indeed flat or they must be flat. It is indeed factual that acoustic guitars' top boards are flat during the construction phase. All that will change when a constructed acoustic guitar gets into the quality control (QC) section. The freshly constructed guitar with a perfectly flatted top bulges immediately when the QC dude loads strings on it, for the purpose of inspection and setting up.

It isn't the end.

If this guitar gets shipped to regions with high humidity climate, the guitar continues to absorb moisture of the surroundings. Thus the bugle increases.

Answer to the million dollars question;

Lets' take a look at this picture.

Taken from: https://c3.staticflickr.com/3/2867/11215257453_6d98faf631_b.jpg

So does that answer the question? Just do an image search with this phrase "bulge guitar top" on any search engine to enlighten your mind.

Summing UP

Bulged top board is not a defect. It is an inevitable usage outcome of ALL acoustic guitars. It is perfectly normal for acoustic guitars to have a bulged top when in normal use.

Earlier we have found out the total six string force, that is 70.89kg or 156.29lbs as well the typical thickness of acoustic guitars' top boards, that is 3/32" or 2.34mm. It is also a common knowledge that wood would compress or flex under force loading.

If we put these facts together, it is not hard to understand that acoustic guitars will bulge under normal usage.

When a force of 70.89kg is allowed to perpetually act on a piece of wood of 2.34mm thickness, how would this piece of wood remain unchanged structurally?

In addition, when an acoustic guitar has absorbed excessive moisture from its surrounding, it will also contribute to the bulge.

In closing, I would submit to all readers of this blog post that top board bulging in acoustic are caused by these factors,

1. String tension
2. Thin top board
3. Wood's natural compressible and flexible properties
4. Absorption of moisture

Don't loose sleep over your bulged acoustic guitars. They are in PERFECT conditions!

Saddle Materials For Guitars Part 2

Due to some technical errors, the previous posting has been deleted. This is a repost

Walrus Ivory Nut

Walrus Ivory Nut

Part 2 is expected to be slightly technical… While I am aware that not everyone will enjoy reading technical stuffs, such information does provide both wider and deeper comprehension of saddle materials in relation to tonal characteristics. This can further narrows the subjectivity tendencies in selecting the suitable saddle materials to match one's preference. During my study on saddle materials, I have reviewed several literatures written by anthropologists and other researchers that have conducted extensive study onto these materials. The sources are attributed at the end of this posting. For those who wish to know more, you're encouraged to read those resources. Herein I will attempt to elaborate the ever elusive saddle materials and tone from these perspectives.

1. Brief introduction of Acoustics
2. Acoustic properties of materials
3. Properties of the various saddle materials.
4. Sound clips - Bone and Ivory

About Acoustics

Particles transmitting vibration energy

Firstly, we all know that sound is produced when an object vibrates. The vibration pushes surrounding air particles, and these particles oscillate which spreads like ripple effects, the oscillation gets passed on between adjacent particles until the initial vibration energy is completely dissipated. Our ears detect such particle movements as sound. Guitar saddles function to transmit strings vibration energy to the guitar top plate (wood) resulting the vibration of top plate. We hear guitars through this energy transfer process. However energy loss is inevitable during the process of vibration transfers. Saddle materials are no exception to that. Perhaps it could very well be due to the inherent energy loss for each material that is different from others that sets each apart. While sound energy can be transferred via various mediums, this article concerns saddle materials, which are solids.

About Acoustic Properties of Materials

Many properties affect the eventual acoustic properties of any given materials. Herein I am featuring three prime properties in determining if a given material transfers sound energy or absorbs it. Understanding it is essential to predicting the tonal characteristics of saddle materials. However, there is no attempt to rank these featured saddle materials.

The three properties are density, rigidity and porosity.

1. Density - a measure of mass per unit volume of material. Dense materials allow efficient transfer of sound energy. Low density materials tend to absorbed part of the sound energy in making the particles within the material to vibrate.

2. Rigidity - a measure of resistance to deformation by external force of a given material. Malleable (Non-Rigid) materials can absorb sound energy in making the particles within itself to vibrate, which is similar to low density materials. Conversely, rigid materials can transfer sound energy through their material structure with little loss.

3. Porosity - a measure of the quantity of empty spaces (air gaps) in the total volume of a material. This is the most tricky property of the three. For a highly porous material, it is made up of very dense and rigid molecular structures. Adjacent to these dense and rigid molecular structures are air voids, too small to be observed by naked eyes. Rigid molecular structures promote efficient sound energy transfer with minimum absorption (loss). However the air voids within have created changes of energy propagating medium from solids to air voids (a.k.a. changes in surface impedances). This isn't good for energy transfers if the path way is subject to many impedance changes. Invariably materials of low porosity doesn't guarantee superb sound energy transfer because density and rigidity must promote it as well. Suffice to say that the relationships between porosity and efficient transmission of energy is far more complex.

Those who wish to read on, the following sections will cover the various saddle materials widely used in the present market. I have made no attempt to do any review but report the researched and known facts related to each featured material herein. There are unlimited literatures on this topic and my version may not align with many others. Also please don't take my writings wholesale, be curious to verify and even recommend corrections. In this way, everyone will learn and hopefully inclining to greater accuracy in creating such literatures. The following saddle materials will be featured in the next few sections.

Plastic (Synthetic)

Synthetic Ivory (Synthetic)
Pyrolytic Carbon (Synthetic)

Brass (Alloy)

Bones (Natural)

Horns (Natural)

Ivories (Natural)

Synthetic Materials

1. Plastic - Actually it is a by-product of crude oil refinement process. Polyethylene a.k.a. plastics have surely changed our lives. Its versatility has made it relevant. One such application is the injection molding process. Just about any plastic you hold in your hands is made through the molding process. By going in large volume, plastics products can achieve speed in production, volume in production, consistencies and most importantly reduction in cost per plastic product produced. While there are various grades of plastics, they are pretty much viewed by laymen as similar.

In making guitar saddles, the moldable nature of plastic has overwhelmed all other materials regardless of their merits. Just about any shape can be made out from plastics. As such, plastic saddles of any kind are seen flooding the guitar markets relentlessly. A huge attraction to guitars manufacturers indeed. In terms of properties relating to acoustic qualities, due to plastics' general low rigidity, it will be hard to claim that plastic saddles can enable a guitar to fully express herself. The density and rigidity of plastics are usually not close to regular natural materials like bones, ivories and horns. While these two attributes are main influences to acoustic properties of any given materials but they are still not the determinant ones.

It is also difficult to describe the tonal characteristics from plastic saddles except to predict more sound energy loss is expected. Suffice to say that changing to harder and denser materials with known acoustic properties, improvements are noticeable immediately. However plastic is here to stay regardless..

Plastic parts

Taken from: http://img.alibaba.com/img/pb/675/406/328/328406675_380.JPG

2. Pyrolytic Carbon - it is a diamond like carbon base synthetic material that has undergone a treatment process call pyrolysis. The treated materials are enhanced in certain mechanical properties. The patent of this process is held by James M. Guthrie and Jonathan C. Stupka, both are based in Austin Texas, USA. The company behind the development of this material is Obbligato Inc. also based in Austin Texas, USA (http://www.obbligatoinc.com/).

Elaborated in the patent, pyrolysis is inducing decomposition of hydrocarbon at temperature in excess of 1000˚ C. In this state, carbon molecules can be coated on a suitable substrates of dense isotropic graphite, also of suitable size and shape which include various guitar parts. The coating can be of structural or surface nature. The process in which they are made will likely result in increase in rigidity and density but porosity is not conclusive. This carbon base material bears a trademarked name "Black Diamond" because of the way the material is synthesized. These are the claims regarding tonal and functional enhancements for applications to musical instruments.

≈ significant increase in volume

≈ gives richer harmonics

≈ clearer sound, reduce muddiness

≈ strings sound lively for a loner period before going "dead"

≈ gives strings coming to contact with such materials longer life-span

Pyrolytic Carbon a.k.a. Black Diamond

Taken from: http://www.obbligatoinc.com/images/Saddle_FV.jpg

A Black Diamond Saddle

Taken from: http://www.obbligatoinc.com/images/DiamondSaddlecrop.jpg

Source: Pyrolytic Carbon Components for Stringed Instruments Patent, USPTO # is 8,110,729.

I wasn't able to obtain any empirical data to verify the above claims but given the method which it is synthesized, the Black Diamond is likely to give any organic material a run for its money.

Clarification; the above section has been amended from synthetic ivory to pyrolytic carbon. Factually, it is incorrect to classify pyrolytic carbon as synthetic ivory.

3. TUSQ, a material well known to many guitar players, also widely called man-made ivory, is produced by Graphtech, a Canadian company. Graphtech has employed this patented TUSQ technology for more than 30 years in producing many guitar parts. TUSQ has similar enhancements as claimed by the pyrolysis process. Likewise I wasn't able to find any empirical date to support those claims. However the popularity of TUSQ has certainly been established strongly among musicians. Anecdotally, one may find it hard to deny its qualities by the sheer popularity.

Taken from: http://graphtechsblog.com/wp-content/uploads/2010/11/AcKitA.jpg

3. Brass - it is an alloy of copper and zinc known for its superior acoustic properties. This wonderful materials carries many favorable properties that have magically fitted into man's evolution. As man became more knowledgeable, the application of brass also widens and deepens. Its great versatility in industrial and commercial applications has made it indispensable.

Brass nut

Taken from: http://theguitarshow.files.wordpress.com/2009/08/lap-slide-conversion_1.jpg

While many musical instruments are made out of brass, it is not known if it was the malleability or acoustic properties of this materials that made brass the top choice for making metal musical instruments, perhaps both characteristics have contributed. As for acoustic properties, brass does carry certain properties like strength, elasticity, density that are favorable to sound energy transfer too. There are other metals that possess similar basic properties but they don't make the grade of musical instruments. The history of brass in relation to metal musical instrument is indisputable. Brass saddles are rare but nuts are commonly seen.

Natural Materials

The next sections, I will provide a simplified summary of each natural saddle materials. Instead of focusing on merely acoustic properties and tonal qualities when applied as guitar saddles, understanding the fundamental make up will help in making sense of the tonal characteristics of these natural saddle materials when in use. After all, acoustic properties of any given materials are all but an extension of their fundamental make up.

Bone parts

4. Bones - It is a dense type of connective tissue made up of 1/3 organic tissues and 2/3 inorganic salt components. This wonderful substance provides functions like support, protection, movement assistance, mineral storage, blood cells production and chemical energy storage. Porosity and density of bone are not uniform for all bones. It is because of the unique functional applications of various bones located at different body parts that render its variable porosities and densities. Besides the structural function undertaken by our bones, blood irrigation is one of the many essential functions as well. This explains the porosity nature of bones.The bones for making guitar saddles are compact bones that has the mechanical and acoustic properties to meet the expectations.

Horn saddle

5. Horns - It is composed of a sheath of keratin overlying a bony core. Keratin is a class of resistant and insoluble fibrous protein. These keratin tissues are usually associated with various essential biological functions e.g. offense, defense, display, communication, temperature and water regulation. In fact, there are other body parts which constitute keratin tissues as their make up, e.g. feather, hair, claws, nails but in this article, the feature item is bovid horn. It is not regenerative unlike nails or hair. The growth of horn is also made possible because of the presence of organic tissues which deliver nutrients and minerals to it. Unique to bovid horns, moisture content within can have significant influences on its overall strength.

FMI Nut

FWI Saddle

6. Ivories (Elephant, Mammoth, Mastodon, Walrus) - It is a calcified substance which possesses a complex chemical and structural composition. In material science terms, ivory is a rigid biological composite, has a rigid matrix reinforced by elastic fibers. Its strength comes from calcium phosphate found in the rigid matrix and its elasticity is due to discontinuous collagen fibers. The application of tusk (before they become ivory) during their active days include functions like pushing, piercing, bending and bearing its own weight. The make up of ivories is also like bones or bovid horns consist of both inorganic and organic tissues. It is almost made entirely of dentine, coated with a layer of cementum. Within the dentine core, pulp cavity takes up about 1/3 of the entire tusk length, beginning at the pulp rostral. The growth of tusks are enabled by the delivery of nutrients and mineral via the dentine pulp.

Tonal Characteristics

The above three natural saddle materials are found to be dense in general. Each one possesses high strength and elasticity due to the functional requirements during the active days of each. It may not be squarely considered as a rigid material nor soft as well. Within each one, it is made up of both organic and inorganic constituents for its initial growth years. The porous nature of each enables nutrients irrigation thus growth is possible.

In relation to the tonal characteristics of each material, it is all about recognition and differentiation. This is also the main issue. The process of recognition and differentiation is all but a subjective preferential cognitive process. Far from perfect but this is what we have. Not withstanding our subjective preferences, each material does carry it unique characteristics that are influenced by the fundamental make up, density, rigidity, strength and porosity. As objective and factual as I can, below are my two cents of each material, largely base on my experiences in working with them and the data table below.

Data Table

Taken from: http://www.springerlink.com/content/l3112460j86446nx/

Bones are denser than ivory (see above table), thus also heavier for a given unit of volume. In terms of rigidity, bone has higher Elastic Modulus than ivories which accounts for its stiffness and hardness. Taken from Maury Music's website on saddle materials' review, "Bone saddles offer very pure tone, nice volume and an increase in sustain…" I interpret pure tone as loud, clarity and unaltered. What is yours? In relation to bone's acoustic properties, its high density and rigidity are likely contributive to the tonal characteristics. As for porosity, it is inconclusive.

Ivories, the common ones use in acoustic guitars are Fossilized Mammoth, Fossilized Walrus and Elephant. Compared to bones, usually their densities and rigidities are less but not far from it. However ivories are known to be tougher than bones in terms of fractures, i.e. high in elasticity strength. While bone is observed to give pure tone, ivories tend to influence the tonal signature of guitars. Taken from Maury Music website on saddle materials' review, "They add warmth and fullness, fatting up the notes and compensating for any brittle qualities one might hear…" and also " If there is a downside to fossilized ivory it is found in highest highs. Some of the brightness and sparkle, what I call the angels in the harmonics over top of the voice, is sacrificed in exchange for that added warmth and meat in the undertone and fatness in the fundamentals."

The link to Maury Music's saddle review article: http://www.maurysmusic.com/fossilized_mammoth_ivory_saddle___todd_s_review

We can loosely conclude that ivories are softer than bones because bone fractures more readily than ivories. In a paper written on the physical characteristics of mammoth ivory (Heckel C., 2009), bone specimens when subjected to percussions by hammerstone fractured. Whereas ivories were able to take more blows and cracks were seen propagating before fractures finally set it. This amazing property is indicative of ivories ability to absorb mechanical energy. Personally, I think this unique ability has resulted in the tonal distinction mentioned in saddle materials review article.

Here are two audio clips for your listening pleasure. The only difference between both clips is the saddle material. Here is the recording chain regarding the clips. Remember to raise your device volume if you can't hear the clips optimally.

Guitar: Gibson Western Classic

Mic: Zoom Q3

Amplificaton: Unplugged

Instrumental Tune: 31-91 by Hardline

Clip one: With FMI saddle

Clip two With Bone saddle

What is your take?

Buffalo Horn Saddle

Bovid horns are least rigid compared bones and ivories. In handling the blanks, they can be readily bent, unlike the stiffness of bones and ivories. However, bovid horns' are still considerable stiff, tough and strong because of the functional demands of horns. Hydration significantly affects the stiffness. Water penetrates the intertubular matrix, acting as plasticizer thereby reducing density and stiffness of bovid horn. Well in laymen terms, horn feels softer. Sound energy transfers 101, more sound energy loss is expected from bovid horn materials. When translated to tonal characteristics of guitar, one would expect less volume but the other characteristics are anyone's guess.

Brass possesses higher levels in strength, rigidity and density than all natural saddle materials. Moreover brass's acoustic properties are indisputable. When used as guitar saddles, the heavy weight is expected to increase sustain, boost clarity and volume. However, it is harder to make a brass saddle by hand than those natural materials. It might be this practical reason that brass is not commonly used as guitar saddles.

Closing

My conclusion is similar to part 1 in essence. While we can put in tremendous effort in quantifying the properties and normalizing the way we describe the materials, there is no escaping from our preferential judgment on such intrinsic attributes. There isn't much difference in loving someone where it is all in the eyes of the beholder. In my effort to condense the abundance of literatures that are related to the topic of saddle materials, I hope this article is able to provide fresh angles and insights to all guitar lovers. To some individuals, judging should be solely base on irrefutable facts and data whereas on the other end of spectrum, some individuals are totally comfortable in using subjective perspectives, jargons and intuition. Part 1 has given attention to subjectivities and part 2 has attempted to link mechanical properties and acoustic properties of various saddle materials to the eventual tonal characteristics of guitars. If you are able to find your preferred tone and saddle materials after reading this article, it would be the greatest reward for me. It was indeed an interesting ride for me. Thank you for reading!

Sources

Acoustic Properties of Materials: http://www.crecim.cat/portal/images/MaterialsScience/public/Acoustics_module_3rd_version_en.pdf

Measurement of the Acoustic Properties of Acoustic Absorbers: http://www.inceusa.org/nc07/links/Muehleisen_plenary_acoustic_properties_materials.pdf

Bone Structure and Composition: http://www.eng.tau.ac.il/~gefen/BB-Lec1.PDF

Tensile Properties and Facture of Ivory: http://www.springerlink.com/content/l3112460j86446nx/

Physical Characteristics of Mammoth Ivory and their Implications for Ivory Work in the Upper Paleolithic: http://www.urgeschichte.uni-tuebingen.de/fileadmin/downloads/GfU/2009/071-092.pdf

Experimental study on the mechanical properties of the horn sheaths from cattle: http://jeb.biologists.org/content/213/3/479.full.pdf

Classical Guitar Forum thread about nut and saddle material: http://classicalguitar.delcamp.net/viewtopic.php?f=11&t=61655&start=15

The effects of material in brass instrument: http://la.trompette.free.fr/Smith/IOA/material.htm

Acoustic properties of common metals: http://www.efunda.com/materials/common_matl/Common_Matl.cfm?MatlPhase=solid&MatlProp=Acoustic#Acoustic

Physics of musical instruments: http://hyperphysics.phy-astr.gsu.edu/hbase/music/musinscon.html#c1

About brass: http://www.copperinfo.co.uk/alloys/brass/brasses-properties-and-applications.shtml#s3

Measurement of the toughness of bone: A tutorial with special reference to small animal studies: http://www.lbl.gov/ritchie/Library/PDF/bone_tough_bone_08.pdf

Structure and functions of bones: http://www.ivy-rose.co.uk/HumanBody/Skeletal/Skeletal_System.php

What is bone? : http://www.mananatomy.com/basic-anatomy/bone

What are cow horns? : http://www.cowboyway.com/What/CowHorns.htm

Structure and innervation of the tusk pulp: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1571488/

Microstructure, elastic properties and deformation mechanisms of horn keratin: http://www.rhinoresourcecenter.com/pdf_files/126/1263373670.pdf

Maury Music, FMI Guitar Saddle Review: http://www.maurysmusic.com/fossilized_mammoth_ivory_saddle___todd_s_review