History

All-aluminum and hybrid wood-aluminum guitar construction has been around since the inception of the electric guitar. In fact, the first commercially viable guitar was all aluminum. The Electro Hawaiian Guitar Company (Rickenbacker) produced an all-aluminum body lap steel guitar The Frying Pan in ~1931.

  • Walter L. Fuller finalized the design of Gibson’s first pickups for an all aluminum electric lap steel guitar, E150, introduced in 1935.

A large aluminum and hybrid manuf. list, is located at JediStar and some history can be found at MugWumps and Appleton.

Sound

The bottom line is a guitar’s sound can’t be categorized solely by body material; it is a lot more complicated. Lots of characteristics effect the body’s resonant nodes, anti-nodes, dampening, and feedback to the neck and the strings (via the bridge).These characteristics include the bodies shape and structure, stiffness, moment of inertia in all axes, alloy/material, alloy heat treatment, bolted on dampeners-masses (neck, pickup module, pickups), etc. etc.… All of these contribute to the instrument’s complex harmonics.

Aluminum doesn’t have a lot of dampening compared to wood. So, where different woods selectively damped some frequencies, aluminum does not. We use our wood necks and wood pickup modules for this flavoring.

Tap Tuning” our body… With our constantly changing 3D curving surfaces, material, bolt-on choices, etc., a tap tuning impact gives a thunk rather than a single-note bell ring.

Hybrid manufacturing is not unusual in instruments. Check out the plate, the “corner stone” of a Steinway grand piano; which is 400lb of cast iron.

A small bodied wood guitar tends to flop around eating string energy (killing sustain and dropping volume on various resonant notes). The lack of mass and material on bending axes combined with wood’s poor stiffness means they’re rarely seen in studios. Aluminum and carbon fiber’s stiffness give them a special advantage here.

Stiffness

Young’s modulus is Stress/Strain, describing the stiffness of a material. For maple bending with-the-grain = 1.8×106 psi, whereas aluminum is at 10.5×106 psi; a ~6x higher stiffness advantage!

It is not very easy to bend a note by bending our body. The stiffness together with the shape, help us build a high-end instrument on a small body. Also, this allows smaller dimensions around the neck heel pocket, for better ergonomics reach-around at high notes.

General Durability

Aluminum bodies have far less problems with cracks than wood, with far higher unit strength, not in just the grain direction. Yield stress is a mechanical property describing the limit after which a part doesn’t return to its original shape. For maple, yield stress in bending is 5 kpsi with the grain and .75 kpsi perpendicular to the grain; with our aluminum it is 20 kpsi.

So, a 4X strength advantage compared to wood with-the-grain, and a huge 25X compared to cross grain. Anywhere wood gets thin, loads in a non-grain orientation, and especially areas of hi stress, it will crack. A few typical heel pocket cracks here. Wood Properties here.

Tuning Stability -> from Temperature changes, Hybrids rule!


Our hybrid’s high expansion rate of aluminum body combines with the low temp expansion of our wood neck to get close to the medium temperature expansion of string steel music wire; almost self-compensating for temperature!

Let’s compare an All-Wood, All-Aluminum, and our Hybrid construction:

Expansion coefficients for our example; maple at 2.1, aluminum at 11.9 and music wire at 6.7 uin/in*F. Our hybrid’s wood neck makes up 16.7in and Al body makes up 8.8in of a typical 25.5” scale length.

So, with a 30degF (16.6C) change:

  • All-wood body, length difference = StringGrowth- WoodGrowth=
    • 5” x (6.7-2.1uin/in*F) x 30F= +.0035”, 25 Cents Flat!
  • All aluminum body, length difference = StringGrowth – AlBody Growth=
    • 5” x (6.7-11.9) x 30F = -.0040”, 28 Cents Sharp!
  • Hybrid, Wood neck and Aluminum; body length difference = StringGrowth –(WoodGrowth+AlBodyGrowth)=
    • [(25.5”x6.7) – (16.7”x2.1 + 8.8”x11.9)] x 30F = +.0009”, 6 cents slightly flat

So, the Hybrid combination of a wood neck and an Al. body gave a ~4x reduction in differential expansion, for significantly more tuning stability; compared to all wood or all aluminum.

Notes:

  • A standard headstock guitar would fare worse, from using a longer total string (including overhung string) and body length.
  • Calcs assume even temp changes, such as thru a case. Open air fast warmups and chill downs would depend on surface/volume ratio, masses, and conductivity. Generally, the steel strings would change temp fastest, aluminum body next, then wood the slowest.
  • An all carbon fiber guitar’s low expansion coef. (close to wood) puts it going flat 25cents in our example.

Tuning Stability –Humidity changes, all Aluminum or (Carbon Fiber) wins


Steel strings and aluminum bodies don’t grow with increasing humidity. The all-aluminum guitar would fare best, and our hybrid wood/Al would be middle of the road while still far better than the all wood guitar as 35% of the length isn’t affected by humidity.

Wood grows with increasing humidity depending on direction to the grain, cut (quarter sawn or flat sawn), preparation, and coating. Although humidity dependency for wood in the grain direction is low, other grain direction dependencies can fight the truss rod and change tuning from bending.

Our standard neck is roasted (torrefaction) maple. This heat-treating process gives the wood much less response to humidity changes, less weight, and increased long term stability.

Roasted links… Bourgeois page , Commercial Forest Products , Guitar.com

General:

  • Sounds must be judged on a case by case basis, (like people). The design details typically rule, and generalizations don’t work with appropriate materials. (sure, rubber wouldn’t be a fun starting point)
  • All material choices have trade offs

Aluminum Body-Wood Neck Hybrid

  • Pros
    • The bridge can be built into the body for a more direct string to body connection for less mud and cleaner separation of notes
    • Lower dampening = more sustain
    • Higher Stiffness, 6X
      • Helps raise resonant frequencies
      • Lets a small body do its job, like a bigger massive one
      • More contouring can take place around the neck’s heel for better hand access ergonomics, without sacrificing flex
      • Mass reduction in body can made up with the improved stiffness
    • Built-in electric shielding
    • Greater durability from higher strength material, 4->25X!
    • Better tuning stability, 4X, temp driven
    • Aluminum is a great recycling material
  • Cons
    • More expensive to make
      • Large tooling costs don’t encourage design changes, whereas a wood body design is a far simpler CNC program change
    • Some Al guitars are heavy
      • Only in a non-optimum design. (our guitar is ½ the typical wood guitar wt.)
    • Body contact
      • Forearm feels hot/cold against guitar depending on temps, from the higher heat transfer coefficient. Designs can mitigate this with other materials and coatings in the resting forearm location.