A marimba project in Shymkent

So today I finished fine tuning all the keys to within 1 Hertz of their fundamental frequencies.  As for the harmonics, I got lucky with one or two of the seventeen which show strong resonance at four times the fundamental but for most these harmonics were not correct.  Most were flatter than they should be so the keys don't sound so creamy sweet as they might have done had I got this right.  Next time I make a test key I will try different cuts with the router.  I will still take 6mm of wood out between the 25% lines, but my second cut will be inside the 40% lines in the first instance, and probably a little deeper than 12mm to get the fundamental down.  Hopefully by leaving wider shelfves from the first cut the harmonic frequencies will be more in play.... Watch this space! Today I also fitted the catch on the mouth of the 'crocadile' so the rails don't raise by accident in transport.  Then I sanded down any rough corners and brushed the whole instrument...

So today I cut the resonator pipes.  These were made from 50mm diameter plastic  plumbing pipe.  Assuming a speed of sound of 344m/s in dry air at 21 degrees Celcius, I used the basic wave formula to calculate the wavelength for each note frequency - i.e.  Wavelength equals 344/frequency. Once I knew the wavelength in metres, I was able to calculate the tube lengths.  I know that in a closed pipe resonator the air in the pipes has to be 1/4 the wavelength... In other words, the plugs stoppering the pipes should be positioned at these calculated lengths.  It doesn't actually matter what length of pipe you choose if the pipes are closed by plugs, as it's the air column we're interested in....so this allows for some aesthetic proportioning of the tube lengths to create a nice visual affect of increasingly longer pipes as you go down the octaves. I was pleased with the way the instrument packs down.

The outer frame, seen here, allows the legs to fold flat because, with the sides being parallel, the legs are also parallel and remain parallel whether they are out or folded away.  Now the legs at each end don't get wider apart or closer together when opened, I will be able to add cross bars to join each pair together and make them into a more rigid unit. They are also wider apart so offer more integral support. With the rails hinging upwards, thanks to some big door hinges I will be able to cut out a couple of groves betwen the hinges at the end  of the leg frame.  These grooves will accommodate the rails ithat will support the resonators  which I will now be able to drop nto the leg space before lower the tone bar rails back down on top....

While shopping for bolts at the weekend I had a good idea.  Rather than bolting the rails to the leg frame, I realised that by using hinges at the bass end I could keep the rails attached to the legs whilst still allowing me to drop the resonator rack into the leg frame by raising up the rails like a credit opening its jaws.  The rails and legs would flat pack once the resonators are removed. Today I put this plan into practice and made good progress.  The photo shows where I got to by the end of the day.  I still need to finish screwing down some of the leg supports and I also need to add struts to keep the legs together at each end to increase their structural strength...

I have also finished putting legs on the rails.  However, I am now having second thoughts and am about to enact an alternative plan. Why?  Well, the legs look nice and the instrument is level and light ...but due to the tapering sides of the rails, legs that fold flush to these get narrower on closing and wider at the feet on opening at the wide end, and you get the opposite problem at the other end.  This will not work as lateral support bars are needed between the pairs of legs to give structural integrity to the marimba.  If the feet get closer together or further apart on opening, then fixed lateral supports cannot be fitted. So the new plan is to deconstruct these rails and build a frame that incorporates legs that are in parallel so that they fold without the above issues.  The new frame will act as support for the resonator rack, and having put the resonators in place I will drop a set of rails, pre-strung with all the keys, on top.  I will secure ...

I used a small craft drill to remove channels from the woods, which I then painted white to define the note names.  I will sand them down when the  paint is dry.  I have yet to test if removing this small amount of material has altered the pitch significantly, but as the notes have not had their final tuning yet I have some leeway and can hopefully still do some manual sanding to smooth their surfaces before applying a thin layer of shoe polish.