Paul Chambers Guitars - Luthier and Maker of Fine Acoustic and Classical Guitars

CM - 1   ( Chambers Model-1 )

Design

The CM-1 Small Jumbo is designed to be a big sounding but sensitive concert guitar that will appeal to fingerstyle guitarists as well as more general acoustic players. This guitar presents a deep bass on top of strong middles & sparkling trebles. It is a sensitive instrument, with good attack and sustain, and separation across the strings that works well for solo fingerstyle work, but holds together when strummed for rhythm work. The CM-1 is a loud instrument, with a broad dynamic range and good projection.

This guitar also lends itself to altered tunings. The design characteristics combined with the option of an extended scale length of 650 mm enable the guitar to hold good string tension and tone when played in altered tunings. Many guitars falter with the lower string tensions involved with these tunings. The CM-1 is musical even when the "E" string is tuned down to a low "C" tuning.

Woods

I have used all variations of soundboard woods with great success on the CM-1, including Sitka, Engelmann & European spruce, as well as Western Red Cedar. The back & sides variations include Indian Rosewood, Madagascan Rosewood & Cocobolo. Typically I use ebony for both the fingerboard & bridge, with options for Indian or Madagascan Rosewood. The necks can be either Honduran or African Mahogany. The rosette inlays are either shell, including New Zealand Paua, Abalone or Pearl, or are a decorative wood inlay, surrounded by purfling lines of various wood species. All bindings, purflings & headstock veneers are of wood. Species used include Indian Rosewood, Madagascan Rosewood, Rio Rosewood, Ebony, Maple, Cocobolo & Snakewood. Solid wood bridge pins are used of either Ebony or Rosewood, most often with Paua, Abalone or Pearl dot inlays.

Acoustic Tuning

All instruments are individually acoustically tuned. The top plate, back plate, bracing, bridge geometry, scale length, string tension and body size are all carefully optimised during design and construction.

I employ a number of acoustic tuning techniques ( see the menu link Methods ) that look at both the mechanical & acoustical characteristics of each guitar. The stiffness & weight of the top, back, brace wood and bridge are all measured and the data used to make decisions throughout the build process.

The top & back plates are thinned towards the outer edge to lower the resonant frequency. The braces are scalloped to tune the finished plates, which should have their respective resonant frequencies tuned to within a tone of each other to achieve acoustic coupling. This coupling creates a guitar with balanced across the range of the fingerboard. The acoustic properties of the assembled body are then measured and any final thicknessing of the plates can be undertaken prior to fixing the bindings and purflings.

The design of the bridge torque model (see link Tuning ) is also a critical factor to consider when tuning the instrument. The scale length, string gauge & tension, and the break angle of the strings over the bridge must all be taken into account. The greater the scale length and / or string gauge the greater the torque forces at the bridge and therefore on the top. The height of the saddle determines the break angle. Again, the greater the height the greater the break angle and therefore the greater the force on the bridge and the top. All of these factors must be considered during the construction process.

A finally tuned instrument will produce a fine sounding instrument.

Body Arching

Part of the design which affects the sound is the arching of the back & top, often referred to as radiusing or doming. By radiusing the top & back plates a stronger & stiffer structure is created. This enables both the plates and bracing to be have a lighter construction, which enhances the acoustical properties. A lighter built guitar will have a reduced mass to stiffness ratio, with less inertia. This in turn results in greater sensitivity and a fast attack with greater volume & projection.

The radiused plates also provide a more ergonomic body shape, with a reduced depth to the sides at the extreme wings of the lower bout, making for a more comfortable guitar for the player.

Playability

As well the ergonomic body shape detailed above there are a number of options available to match the guitar to the player.

  • The fingerboard can be radiused options of 16", 18" or 20" to suite the player.
  • The string spacing at the nut & saddle can be custom sized, standard size is 45mm at the nut & string spacing of 57 mm at the saddle.
  • The neck profile can be selected from a "D", "C" or soft "V" profile. The neck is stabilised with carbon fibre rods, and adjustable with a 2 way truss rod.
  • Scale length can be chosen from 650 mm, 645 mm or 632 mm.
  • Compensation is added at both the saddle and the nut for more accurate intonation. Both are made of bone.
  • Side markers of pearl are used to denote fret positions.
  • The fingerboard can be bound for a smooth feeling edge with no fret ends protruding.
  • The choice of Waverly or Gotoh 510 tuners provide accurate and stable tuning.