This is a vibraphone “rescue” project I completed for a local musician. The instrument was given to him by a friend in derelict condition, and only had the bars (the part that is struck by mallets), the damper bar and the frame intact. It did not include a pedal to operate the damper, or, more importantly, resonators.  Because it was given to him by a friend, the instrument has special sentimental value, and it is affectionately called the “Red Vibes”.

MAIN IMPROVEMENTS/FEATURES:

Damper System

Damper Bar – New felt on damper bar

Pedal- Completely new, wide damper pedal for easy access while playing through whole range of instrument.

Resonators

Dimensions – 1/4 wavelength one-end-open, one-end-closed (half open) aluminum tubes, 1 3/4″ outer diameter (equal to the bar width).

Tunable – Tube stops made with aluminum discs with rubber o-ring as a seal (similar to a piston in a combustion engine). Each tube stop has a 1/4″ hex bolt through it, allowing each resonator to be tuned individually with a hex wrench.

End Correction – Gap between bar and tube provides end correction for 1/2 open tube resonators. This ensures the vibrating bar is at the anti-node of the wave, which is slightly (about 1/2″) outside the open end of the tube.

Finish- I investigated several finish options, (anodizing, lacquer, etc.), but decided a “brushed” finish would be best (least expensive and cool looking).

Bars (keys)

I cleaned the keys (along with cleaning and lubricating other existing metal parts) using Scotch-Brite, steel wool and acetone.

THE PROJECT

Design

I designed a pedal mechanism which would mate to the existing damper bar hardware and that would be easy to remove and reassemble at performances. I had it machined from aluminum at Wagner Machine Co. in Champaign, IL (they were in Urbana, IL at the time). This was the easy part…

Because the resonators are part of the sound-producing system of this instrument, designing and building them was particularly challenging. They needed to work with the existing frame and be easy to assemble/disassemble, in addition to making the instrument sound better.

The operating principle of resonators in keyboard instruments is that when a vibrating bar is situated near the end of a tube of equal fundamental frequency (f₀₎, the column of air in the tube will vibrate sympathetically. Because the bar and tube resonate sympathetically at f₀, but have different resonances at the harmonics (f_n), f₀ is amplified more than the higher harmonics. This means that the loudness of f₀ is greater than the loudness of f_n, making the instrument sound less “bright” or more “mellow”. There may be matching of higher harmonics between the resonator and bar, along with the vibraphone, but the main amplification is at f₀. This is the signature sound of the vibraphone, and what I sought to achieve in my design.

Fabrication and Assembly

As mentioned above, the damper pedal was machined at Wagner Machine Co.:

Note that significant mass has been removed from the pedal to keep the action lighter.

Wagner was also the site of drilling the holes for the resonator tubes and rails. The tubes were cut using a plumbing pipe cutter. The brushed finish was achieved using sandpaper, steel wool and Scotch-Brite with the tube spinning on a metal lathe. The tubes are attached to the rails by round head hex bolts and nylon-insert lock nuts.

U-Channel aluminum was used for the endpiece on each resonator set. The original instrument included a small metal bracket with a raised knob in the middle. The U-Channel endpiece has a hole into which the knob fits, holding the resonators in place.

The curve of the resonators made smoother after the “rough” photo above was taken.  The curve was made more smooth.

The vibes on a sunny fall day before being returned to their owner!