Introduction: Scrap Metal Rhumba Box
The rhumba box, also known as the marimbula or lazy bass, is an Afro-Carribean folk instrument. Like many American folk instruments, it's a product of poverty, cultural cross pollination and innovation. When the African slaves were brought to the Americas they carried nothing but their memories and traditions. One of these traditions was their music. In this new land they crafted instruments from whatever materials they could find or recycle. The music they created was based on the rhythmic tradition of their homeland, but it also freely incorporated melodic and structural forms from the European music of their captors. This new music called for new instruments.
The kalimba, or thumb piano, is an instrument from the western regions of Africa. In its simplest form, it consists of a small hand-held plank or gourd with thin metal tines attached across a wire bridge. The tines are of different lengths and are plucked with the thumbs to create notes. Traditionally, the kalimba is tuned to the players voice to accompany singing and is played in small, intimate settings.
The rhumba box is a kalimba on steroids. When the rhythmic African music met Latin musical traditions in the cane fields of Cuba, something amazing happened. African musicians suddenly had new influences and musical inspirations. While the terrible circumstances of slavery prohibited them from having guitars and pianos, they were able to adapt their traditional instruments to recreate these new sounds. The orderly keys of the piano resembled the tines of the kalimba so they started tuning it to European scales. While the kalimba was usually a solo instrument, the new music was played in ensembles so it had to become louder. They increased the size of the tines and attached them wooden boxes to create a resonator chamber. This soon evolved into the marimbula, a large kalimba tuned to a bass register to emulate a bass guitar (quatrobasso) or left hand of a piano player. Tines could be fashioned from metal strap, thin wood or shaved bamboo. resonators could be packing crates or other discarded boxes. With a few scraps of hardware and some simple tools anyone could build a musical instrument. Rhumba boxes combined with skin drums, cajons, claves, hand-carved guitars and woodwinds to create the roots of popular carribean music- from reggae to salsa.
Here's how I made a bass rhumba box from stuff on my scrap pile.
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Step 1: The Parts
I cleaned out a garage for a lady a few years ago. Her father had passed away, leaving a large metal workshop full of old outboard motors and marine parts. It may have been valuable at one point, but it was all disassembled in piles with no clue what was what. Unfortunately, most of it went right to the scrap yard.
Of course I had to set aside some choice pieces. This old gas can made an awesome sound when it tumbled off of a pile of junk so I kept it. It's probably 30-40 years old- made of thick steel with quality welds.I also grabbed a couple of pull starter units. These have a flat steel spring inside that causes the pull rope to wind itself back up. I decided to combine these two parts with some other scrap materials to make a rhumba box.
Step 2: Preparing the Gas Can
I was planning to cut the spring into strips and affix them to the top of the can on a wooden bridge. I removed the intake tube from the gas can with four screws. I drilled out the rivets holding the handle on and removed it. I turned the can upside down and shook it to remove as much rust and dirt from the inside of the can as possible. I tapped the corner of the can nearest the intake hole on the table top so all the rust and dirt would collect there. I then wrapped my finger tip with masking tape sticky side out and wiped out the remaining rust.
I liked the worn finish of the gas can, so I used a plastic bristle brush to remove any loose material and rust then I wiped the whole surface down with an alcohol soaked rag to remove all grease and dirt. I hung the can from a beam in my shop with a length of wire and coated the outer surface of the can with polyurethane and let it cure overnight..
Step 3: Building the Harp
I cut the tines into pieces about 4-5" long with an angle grinder using a c-clamp to steady the spring. I chucked a 1" grinding wheel into my drill and rounded and smoothed one end of each tine.
The harp refers to the tines and the wooden bridge they are attached to. I cut a scrap piece of 1x2 oak (from a salvaged waterbed frame I butchered a few years ago) about 8" long. I dug around in my parts bins and found a steel rod with a knob on one end. It was the pull tab to close the drain on a lavatory faucet. This would act as a nut for the tines to rest on. A section of aluminum U channel salvaged from a security company yard sign would become the pressure bar to hold the tines in place.
I used my table saw to cut a shallow groove in the oak strip. This will hold the nut in place when the tines are mounted. Next I marked out the screw locations. This instrument would have eight tines with a screw between each one and at the ends. I marked out nine holes on the aluminum channel and drilled pilot holes. I used this as a guide to drill pilot holes in the oak and then drilled out the holes in the aluminum channel to the size of the screws I used. I installed the tines under the aluminum channel and over the top of the nut and tightened the screws. I put the harp on the can top to determine the final location and then I disassembled it to mount it on the can.
Step 4: Mounting the Harp to the Can
I mounted the wood to the can top with JB Weld and screws. I scraped the finish and drilled several holes in the can top to increase adhesion. I drilled a hole in each end of the oak for the mounting screws and used it as a guide to drill pilot holes in the can top. Next, I mixed up equal parts of the JB Weld and smeared it on the under side of the oak piece. I put the wooden piece on the can and tightened it down with two screws. I reassembled the harp and let it sit overnight to cure.
Step 5: Tuning the Rhumba Box
The next day I tuned the Rhumba Box. I used an old shareware program on my laptop with a quality microphone. I loosened the tines slightly so they could slide back and forth a bit and tuned them one at a time. The notes start in the center and go outwards alternating left and right. I tuned it to E minor, so the note arrangement is D, B, G, E, F#, A, C and E2. Tuning is pretty straight forward- make the tine shorter to raise the pitch or longer to lower it. I may help to dampen the other tines with tape to isolate the desired note. Once the tines were tuned I tightened down the screws carefully to keep the pressure even and prevent unwanted vibration and rattles. The backs of the tines can be ground smooth with a Dremel tool, but I left mine rough and covered the bare ends with a strip of gaffer tape. This way I can remove the tape and drop the pitch of the whole instrument a few more steps if I want.
Step 6: Playing the Instrument
I play it one of two ways depending on the sound I want. I can tuck it under my right arm with the tines pointing to the left and play it with my left hand for simple bass lines. This allows me to tap or knock it with my right hand for a percussive sound. I can also lay it face up in my lap and play the tines with both hands for more complex melodies and even chord structures. Also the bottom of the can can be dampened with my knee to control the 'ring' of the notes. This is a very expressive instrument and it's a blast to play. It can be retuned for a variety of scales.
This rumba box gives more bang for the buck than most anything at Guitar Center! I used less than a dollar's worth of glue and hardware for something that will give me years of fun. Give it a listen-