Design and Construction of Steel Stringed Guitars

Dave

Good to know I am not alone. My wife "doesn't do sums", so her view of my infinite series was, shall say, less than appreciate. I still don't know why she wasn't interested in the length and distribution of plains and purls of row n, where n was any number greater than the minimum necessary to establish the underlying pattern. I guess that women just aren't like other people...

I am glad you are treating yourself too. I only wish I had the skill to make mine too. For me, sadly, the "D" in "DIY" has always stood for "Destroy".

I am very interested in your point about the wood for my Fylde (I now feel safe to spell it out in full). Roger suggested Brazilian rosewood, in response to my original request for something "dark in tone and dark in appearance". I do not know what the tonal characteristics would be of walnut or mahogany, relative to rosewood.

By chance we have an old (early/mid 1800s) cuban mahagony dining table which my wife is keen to dispose of...

Brian

3. Body Shape and Size

Having chosen a scale length the next decision is how many frets on the neck will be clear of the body, the shape and size of the body and where the bridge will be on the lower bout. In the development of the steel string guitar a number of distinct body sizes and shapes have emerged as “standard”. One of the more well known are the Martin “nomenclature”: Size 5, O, OO, OOO/OM, and Dreadnaught but I prefer the more descriptive Parlour, Concert, Grand Concert, Auditorium, Grand Auditorium which gives a better indication of the size and where they were designed to be played. There is also the Jumbo and Small Jumbo (oxymoron?) from Gibson and specialist instruments such as Piccolo, Terz and Baritone guitars.

As you go up in size you generally get a larger top surface area, a bigger volume of air inside the box and a deeper guitar. The scale length tends to increase with body size but not always – this also depends on how many frets clear of the body are chosen. The larger top surface area means that the top has a lower main resonance as does the box with the larger air volume and this will tend to support bass notes better. The fullness and complexity of the sound also increases with body size with more natural reverberation present in the sound – you can hear this with hollow arm harp guitars even without their sub-bass strings, the main strings sound as though you are playing inside a church or cathedral. This does come at a cost though and you need to work at maintaining string clarity across the strings particularly for strumming – take the example of the large O series Lowdens strummed compared with the smaller F and S series. Conversely with smaller guitars you have to work at bringing out the bass and making the sound as full and complex as possible. One of the signs of good makers in my view is the ability to make small full sounding guitars that surprise and change the perception many players have that these instruments are “boxy”.

You can also shape the sound by altering the depth and taper of the box – a deeper box can help with bass and complexity and a shallower box can give an instrument more punch and mid-range focus and less susceptible to feedback when plugged in – useful in some live performance situations. Again there is a trade off though as the air movement inside the box is governed in part by the interplay of the back and top movement and when you go beyond a certain depth you loose a degree of clarity and focus across the strings. It’s also worth mentioning here that bigger guitars are not always going to be louder guitars. Loudness or perception of loudness is one of those interesting phenomena that occur in our brains. These have evolved to hear better in certain frequency ranges (usually related to hearing other human voices) and like vision, the human brain hears certain things and then “fills in” the rest. It is possible to make it hear a bass fundamental that the instrument doesn’t generate via a series of harmonics that the instrument does generate that are associated with the fundamental, or by accentuating the power of the mid-range frequencies – I’ll explain in more detail in a future article about Baritone guitars. It also explains why higher pitched instruments (like small yappy dogs) will cut through a mix of instruments and be perceived as loud. The way our brains “hear” also explain why it’s best to use you ears to tune a guitar rather than a precision tuner unless you are playing for an audience of Peterson strobe tuners.

Where the waist is positioned on the guitar and how “pinched” it is also shapes the tone. Guitars with curvy waists tend to have more focused mids and trebles whereas guitars with very little waist – like dreadnoughts – have a more bass focused sound. This is partly due to there being more air volume but it is also due to how the waist changes the motion of air inside the box. Where the soundhole is placed on the soundboard will also impact as the further towards the fretboard it is (which usually also goes with where the waist is positioned) the larger the lower bout active area of the top will be and the lower the Heimholz resonant frequency of the box. There is a trade off here as the total number of frets that can be on the neck is less. Finally the relative size of the upper bout to the lower bout will also shape the sound both in terms of box volume and air movement patterns – Dreadnaughts tend to have wider upper bouts in relative to the lower bout. The Modified Dreadnaught developed in the 1970’s by Ervin Somogyi took the dreadnaught shape, made the waist more pinched and moved the waist and soundhole towards the fretboard to make the instrument more suited to the Wyndham Hill fingerstyle guitarists and there type of sound.

This brings me neatly onto the positioning of the bridge in the lower bout area and the discussion about “sweet spots”. There tends to be a view that positioning the bridge close to the middle of the lower bout at its widest point is a “sweet spot” to drive the top. This is not necessarily the case – it depends on the top bracing. The best spot is likely to be the centre of the “active” part of the top and this depends on where the bracing is put. On classical guitars where the energy available from the strings is much less than on a steel string, the active top area is generally reduced to the soundhole downwards by putting a large transverse brace there as well as the one on the upper bout, and so classical guitar bridges are further down in the lower bout than on steel strings. With steel string guitars the large upper transverse brace in the upper bout will generally define the active top area and with makers such as myself that believe in the importance of the upper bout to tone this is a tonal rather than structural brace.

So once the maker has the scale length and view of required body shape/size/volume and has determined the best tonal position for the bridge based on his building style the number of frets clear on the neck usually comes out in the wash as it were.

With both small and big bodies there can be issues of ergonomics and player comfort. Generally fewer frets clear of the body tends to feel easier for people to fret but there are issues of upper fret access that cutaways can help to address. Small people can find bigger bodies more awkward to play and so features like the Manzer style wedge (where the treble side is wider than the bass side of the guitar for the same body volume), armrests and bevels can make them more manageable. Some bigger players can envelop smaller guitars and straps that attach to the guitar and rest on the players knee holding the guitar in the “classical” position can also help here.

One thing to bear in mind when designing different body styles – as well as aesthetics – is the availability of hard cases that will fit the instrument. It helps to design around commercially available case sizes unless you want to go down the custom case route. Also for a maker that uses heating blankets and bending forms together with external moulds it helps to have a manageable number of body shapes and sizes that can be used with different scale lengths and frets clear of the body to produce a wide range of models. This is what I now do and have five basic body sizes for my guitars. You can read more about this here on my website.

Finally here’s a photo illustrating my five main guitar body sizes – left to right “Treebeard” (baritone), “Buachaill Mór” (Modified Deadnaught), “Lughnasa” (Small Jumbo), “Samhain” (Grand Concert) and “Féileacán” (Concert):

Leo,

Thanks - I'm glad you find it interesting. Sybil shares the same body as "Treebeard" my baritone but with a smaller scale length and 12 frets clear of the body. It is the same as "Treebeard" capoed at the second fret.

I was going to start a campaign for Dave White to be featured in the next 'Meet The Maker' interview, but it looks like this is it on steroids!

Thank you very much for the wonderful insight Dave - this will be printed up and placed in the old resource folder with your first article. As I have now found my 'unique tone' with the guitars I build, there is certainly room for improvement and I am looking forward to applying some of this new-found knowledge.


Which leads me to a question for Dave; when did you feel you achieved your own 'signature' tone?

To clarify, there is a moment in a guitar builder's life when they discover each guitar has the same 'tonal theme' - which is why we can sometimes pick out an Avalon guitar from a Lowden, a Brook from a Taylor, etc. (apologies to those who are thinking I'm facilitating a geriatric to munch on poultry ovum )

Please keep this series going Dave.

This is like "The Wire"...can't wait for the next episode...thabnks from here too Dave!

Has Keith swallowed some glurk/garlic inadvertently?!

ANdrew and Keith - thanks.




Sam - I think it arrived with the first guitar I made. I say think as I'm currently doing some work on its neck and hope to have strings back on it again after many years without. I can check then. My "signature sound" was pretty much there in it and I have been through a process since then of refining it and knowing how to reproduce it with each instrument I make. It has been there in my small and large guitars, with X or ladder bracing, in harp guitars, bouzouki's, lap slides and mandolins and also in the ukulele's I've made. I think it's in my dna/gnome