The Springboard (Pt. 4, Initial Prototype)

This is the fourth of a number of posts pertaining to the progress of my 21M.299 (The Social Lives of Instruments) final project, The Springboard.

With doubts and uncertainty growing, I needed to figure out whether this idea was actually going to work; I needed to develop a prototype. After keeping an eye open for free materials (at MIT you tend to find a lot of useful things being thrown out), I came across some leftover wood that could be used. Armed with a single janky drill and hand saws, I created the initial, somewhat sketchy, prototype (essentially a wooden plank with springs).


For mounting the springs on the board I had two possibilities- using metal J-hooks or machine screws with nuts. The J-hooks were simple, and would allow an amount of axial adjustment to the springs, however they provided no height adjustment and wouldn’t provide the best mechanical transfer of sound due to the minimal contact between spring and hook. The machine screws allow height adjustment of the springs and also provide better mechanical transfer of sound due to how they clamp the spring.

I decided to use both. On this initial prototype I placed the screw mounts at the top of the instrument and used the hooks as a sort of bridge. The result was the layout seen in the following pictures.

Drilling the holes for the springs and screws proved tedious. The wood, being old was dry and prone to splitting. The drill I borrowed from my lab proved inadequate; it would quickly stall, run out of charge, or spin without spinning the drill bit (due to a cheap chuck). Drilling holes involved stepping up from the smallest size drill bit to the size of the screw’s shaft. I was reminded of the value of good tools and a proper work environment, but alas I am but a poor college student.

The block used for the spring hooks (henceforth referred to as the hook block) was cut off from the end of the same board. While drilling holes for the hooks, the block inadvertently split in half. Frustrated and tired, I epoxied the wood block back together and let it sit overnight.

The next day I finished constructing the prototype by mounting the repaired hook block and stretching the springs. The small spring was inadvertently stretched too far in a previous experiment, necessitating that the deformed portion be cut off. This proved beneficial as the remaining portion of spring was now under more tension.

Knowing that the instrument would be too quiet (as it did not have a resonating chamber), I mounted a piezo sensor to the back near the screw mounts. This piezo sensor was attached using hot glue and its wires were twisted to a 1/4″ jack (the same kind found on guitars).

Piezo sensors use a piezo crystal to create a signal in response to deformation. The instruments vibrations are carried through the wooden body of the instrument and vibrate the crystal, thus creating a signal.

The instrument was ready for testing.


Upon trying to play the instrument I quickly found problems with my layout.

In order to get a good sound out of the springs, you have to bow near the screws. Bowing at the hooks does not work, as all the springs are at different heights and as mentioned earlier, the hooks do not provide good sound transfer.

The first problem I noticed was with bowing; since you bow at the screws and have to bow at an angle that’s near parallel to the spring’s length, this means the bow has to travel between adjacent screw heads, sometimes getting caught on the nuts and screws and pulling out hairs from the bow. The layout of screws needs to be rethought for prototype 2.

The next big problem was that the instrument was upside down! Because I placed the screws and sensors at the top of the instrument, it had to be played such that you bowed at the top and pitch increased as you moved up the “neck” (as opposed to down on every other stringed instrument ever). The layout will be flipped for prototype 2.

Playing actual pitches proved very difficult as your fingers tended to stretch the springs rather than slide above them. Stretching the spring lengthwise had no obvious effect on the sounding pitch- as alluded in my previous posts, I believe the spring vibrates differently than a string and doesn’t depend on tension, but rather mass.

Connecting it to my mixer and speakers resulted in an ok tone- no audio was recorded during prototype 1, however there will be audio for prototype 2. When played “correctly”, the instrument sounds sort of like a factory crossed with a cello. However, having never played a bowed instrument before, my bowing technique was inconsistent, sometimes creating screeching harmonics. After some practice I was able to get a serviceable and somewhat consistent tone. It had much less bass than I was anticipating- I believe this may be due to the mounting of the piezo sensor. Additionally the piezo sensor has the drawback of picking up every movement of the instrument- electromagnetic pickups may be an option on the final instrument.

Video of me playing will be provided when I write about prototype 2! Stay tuned.

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