Well since the last time my computer was well enough to edit this site much has happened. Most importantly, despite the invaluable assistance of my good friend, Tony Hodgson, economic realities have prevailed and all plans for any sort of commercial operation have been shelved. Custom built instruments of whatever style are still available so don't be shy. If you're holidaying in this area (gorgeous scenery and no airport security) why not drop in for a play of my prototype NMA which is approaching its eighth birthday and sounds lovely

 In the meantime here's a general overview of my New Model Acoustics theory.

New Model Acoustics (NMA); "A whole lot better without the hole!"

Why no "soundhole"? The question I asked was "Why have a soundhole when the sound obviously emanates from the soundboard?" (or "top" as it is commonly called). This had become clear to me when positioning microphones in front of acoustic guitars. All that comes out of the "soundhole" is a load of bass. This would suggest that it is in fact a bass-reflex port*.(see below)

How to correct this so that I could do away with this compromise and have true, natural bass? The resonant frequency of the top is what determines the depth of bass response so the obvious course would be to make the top more flexible to lower the resonant frequency (a thin, flexible top reproduces bass far more easily than a thick, stiff one; contrary to what one might think). The obstacle to this is that in a traditionally constructed guitar the top has a structural role and must resist the tension of the strings (around 180lbs for an acoustic guitar) leading to the use of braces to stiffen it; the very opposite of the ideal situation. The answer is to devise a method of construction whereby the string tension is catered for otherwise, which is exactly what I have done.

Doing away with the "soundhole" also deals with a second problem. The action of the vibrating string causes the top to vibrate up and down which causes a series of high and low pressure waves to be propagated outwards from it. This is how the top reproduces and amplifies the sound of the string. With a hole in the top we get a situation where , at certain frequencies, the downward motion of the top (causing a low pressure wave) pushes air out from the "soundhole" causing a high pressure wave which conflicts with the low pressure wave from the top (see diagram below). 

So, why have such a thing on an acoustic guitar? It could only be that, in its un-pierced state, a soundboards response would be lacking bass. This will a) reduce overall volume of sound and B) cause phase cancellation of some frequencies (usually in the mid-range). Not cutting a hole in the top deals with both these problems.

A method of countering string tension without involving the top was needed. The solution is to adapt the "thru-neck" design used on solid-bodied electric guitars so that a stiff structural member is placed between the heel of the neck and the tailblock so that the bridge can be braced to this separately, leaving the top free to vibrate.

Figure 1 shows a method of bracing the bridge from the interior, inspired by the popular "Bridge Doctor", that holds it firm in the plane of the string tension while leaving it free to vibrate up and down. The braces are made from Stainless Steel threaded bar and are arranged so that their tension can be adjusted so as to keep the bridge flat

Unfortunately the longish steel bars introduced unwelcome resonances. Figure 2 shows a method of bracing the bridge externally. The brace lies in a straight line through the bridge to the top nut. Its tension is adjusted via a turnbuckle. This has proved very successful except for a lack of control over the tendency of a bridge to rotate about the longitudinal axis. This is work in progress.

Her are some pix of Model No1

*bass reflex port. This is a means whereby the bass response of an enclosure (speaker cabinet, guitar body etc.) may be extended. As we all know, when we blow across the top of an open bottle a note is produced whose pitch changes according to how full the bottle is. The physicist Helmholtz discovered that the pitch also depends on the size of the hole. This pitch is in fact the natural resonant frequency of the system (i.e. the enclosure and the hole ).We can lower the resonant frequency of our guitar below the natural one by making a hole of the appropriate size in the instrument’s soundbox. Unfortunately all frequencies thus added to the range are synthetic, being produced by the mixing of the string’s sound with the sound produced by the box, and are not level in volume.

If you're interested in chatting about this then please email me  

Next.........

I keep reading and hearing about people, mainly Americans, who have devised modifications to top-nuts, saddles, frets and who knows what else in an attempt to make a guitar perfectly in tune.

What a waste of time!  Like all modern musical instruments, guitars are made using the "Equal Temper" system. This was devised to deal with the discrepancies in tuning that result from the fact that a pure fifth and a pure fourth add up to slightly more than a pure octave. This discrepancy is averaged across the octave so that all notes are very slightly out of tune resulting in an instrument that is to all intents and purposes in tune in every key. Added to this the pressure on the strings needed to sound the notes is less than that needed to press them down to the board. A few moments with an electronic tuner will demonstrate that between these two pressures lies as much as a quarter of a tone! Add a little inadvertent sideways pressure and the picture is complete.     

This area of uncertainty of pitch is where the actual playing of the guitar takes place. Here we add sweetness, raunch, blue notes even perfectly pure tones if our ears and touch are fine enough. In other words this is what makes it possible to have masters of the guitar who can move us to tears with their skill and others whose every note seems tired and pointless. This range of playing skill is what these "experts" would seek to eradicate. In my opinion they are mistaken.

By the way, equal temper also means that using harmonics (which are pure intervals) to tune a guitar is bound to leave it out  of tune. See "Complete Guitar Repair" by Hideo Yamimoto for a thorough expose of this phenomenon and see "tips and tricks" for my own method of tuning.