Marimba Resonators

Hey
Colin

The keys will
always sound a little ‘dead’ until you have two things in place (a) a mounting
mechanism that will allow it to vibrate freely and (b) something to amplify the
sound, i.e. a resonator.

(a) Temporary
mounting

Place the bar
resting on its nodes on some rope or a couple of part-inflated long balloons or
some light sponge, you should hear a clearer note then.

(b) resonators –
this is a more complicated element of the build. Basically you require a sealed
‘vessel’ open at the end directly below the marimba key. This can be
anything really as long as it fits under the bar and can be cut to length. Go
for the widest vessel that you can physically fit in there as this will maximise
volume. Reso length will affect the pitch of the resonator and reso width will
affect amplitude (volume) with wider being louder. The reso needs to be really
tight to the key 1" – too tight will flatten the resonated note, too far will
make the note weak.


There is a formula for
calculating the reso length

  1. Take
    the Speed of sound (33,500mm/s)
  2. Multiply the Desired frequency (hz) by 4
  3. divide
    the speed of sound by the result of step 2
  4. The
    result in mm is the length of the resonator.

Ok so if maths
isn’t your thing, try this… Take a plastic bottle and cut it off on the
vertical bit below the shoulder. Place the bottle with the open end beside your
ear. Sing a glissando, a sliding note from high note to low note. At certain
points you will clearly hear the bottle pick up on your voice and make it
significantly louder – that’s it resonating the note, each time it does that you
have matched either an harmonic or the fundamental. If you place a marimba bar
of the same note over the bottle and hit the bar then
the magic happens.

To tune the bottle
you simply use scissors to trim the plastic away and raise the resonated
frequency until it is resonating at the pitch you want. I used this singing
technique to build resonators (seen above) at home near Belfast for an
instrument that was 500miles away in the Stomp workshop – it worked
perfectly.

You will notice on
the assembled instrument to the left that the last two resonators are about the
same length. In this case, the lower one has had the top closed over slightly.
Restricting the size of the opening will also lower the note – I uses this a lot
on the bass and baritone marimbas otherwise the resonators would be many feet
long. It does have an effect on volume however so you need to work out effective
ranges.

Hope this
helps

Paul

Cola Bottles


Materials
Required –

  • One x 2 litre
    Coke bottle per note –
    Wash the bottle and leave it upside down to drain and
    dry overnight
  • One tyre (tire)
    valve per note
    – ask at your local tyre repair shop
  • Bicycle
    pump
    – to fit the tyre valve of course

Tools

  • Drill &
    drill bit
    (10-12mm or 3/8″- 1/2″)
  • Silicone
    sealant or similar.

Method

  • Make a hole in the
    bottle cap that is 2mm smaller than the bottom of the tyre valve. This is to
    enable the valve to squeeze tightly into position.
  • Push the valve
    through the cap from the inside until it is jammed in the hole. The tighter the
    better as this gives the best air seal
  • Squeeze the
    silicone sealant into the back of the cap until it reaches about 5mm or 1/4″
    deep. Be careful not to get any into the airway.
  • Turn the cap
    upside down, gently lower the bottle into it and slowly screw the cap on – watch
    out for sealant entering the airway.

    • It’s best to put a
      little pressure in the bottle as the silicone dries
  • I’d not play them
    too hard until the day after and even then…

Tuning the
bottles

  • Attach the air
    pump and pump once. It is surprising how little air it takes to increase its
    musical note significantly
  • Raise the note
    until it is above where you want it to be
  • release air from
    the valve to lower the note to the desired pitch

Playing the
bottles

  • Normally the
    bottles are struck against the opposite hand, against the body, against each
    other (produces a chord) or against whatever won’t damage them.
  • You will find that
    there are different places to strike the bottles, any of its lower rounded
    surface are good but the lower base itself is too stiff.
  • They can be
    mounted in a frame and played like a percussion keyboard – I’ve seen Evelyn Glennie do this
  • There are infinite
    ways to play them but imagine sword fights, juggling routines….

Extras

They can be made
without the sealant but they are often leaky and hard to keep in tune