Hammered Bass

Designers: Cory Weiner, Lindsay Johnson
Client Coordinators:
Supervising Professor: Dr. Larry N. Bohs

The Hammered Bass (HB) is an electronic instrument designed for the client, who was a professional electric bass player before an accident left him paralyzed. Since he can no longer play the bass, a custom instrument was designed to be played with hammers, using the techniques the client currently uses to play the hammered dulcimer. The HB consists of two rows of rubber pads, representing two octaves of notes, which when tapped trigger digital MIDI signals that create synthesized bass sounds.

How this project helped
The HB gives the client the freedom to continue a career using his talent with the bass guitar. The casing is designed with the proper dimensions, weight, and tilting options to accommodate his limited range of motion, and allows for the most comfortable and effective playing position. The HB has been easy to learn because of the client’s previous experience with a piano keyboard layout and his use of dulcimer hammers. With the HB, the client is able to play with maximum speed gain, giving him the ability to have fun making a living playing the music he loves.     In addition, the client can create new effects such as “rolls”, which were not possible on the electric bass.

The HB (Fig. 1) is a Musical Instrument Digital Interface (MIDI) controller that plays two full octaves below middle C.

The HB has 24 1.5 inch neoprene rubber trigger pads protruding 1/4″ above the top surface. Below each pad is a thin rigid disk that is attached to a piezoelectric sensor.  The  piezoelectric sensors are then attached to circular silicone rubber pads which have been quartered and glued to a Lucite board. The silicone pads inhibit the propagation of vibrations along the board, which can cause cross-triggering of notes.

Each sensor is connected to a voltage divider, peak detector and gain circuit (Fig. 2). The voltage divider allows the sensitivity of each sensor to be adjusted, and the
peak detector allows the positive peak amplitude of the hit to be fed to an analog-to-digital converter after a gain of 2.2. The amplifier allows the client  to produce a wide range of amplitudes with a small range of striking forces.

Signals from the sensor circuits are connected to MIDI brains (PAiA Electronics, Edmond, OK), which were purchased in kit form. Each brain accepts 8 sensor inputs; three brains accommodate all 24 sensors. The eight inputs are monitored by an ADC8609 Analog to Digital Multiplexer, which also converts the input analog pulse to a digital sequence. The MIDI Brain assigns each of its inputs to a note, stored in an on-board EPROM. When a voltage is detected at an input, the brain translates the voltage amplitude into MIDI velocity data. This information is then combined with the assigned note number to construct the proper corresponding MIDI signal, which is then transmitted through the Brain’s MIDI Out port. The EPROM is programmed to play notes commonly used on a bass guitar. The MIDI brains are daisy chained together, having the MIDI out of the previous brain going into the MIDI of the next. The output of the third brain connects to a synthesizer, which can be programmed to produce any desired sound. The MIDI input of the first brain also allows input from other MIDI instruments.

The HB is enclosed in a black acrylic case, 32″x8″x4.125″. An aluminum bar is placed within ridges on the bottom to allow for different playing angles: 20°, 30°or 45°. A 6VDC adapter port provides power from a standard wall outlet. The total cost of the HB is $819.

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