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Resonators on North American Marimba

By Jim McCarthy | October 10, 2011

One of the main differences between building a marimba in North America and making marimbas in Australia, is in the resonators. The materials available are simply a little different. That is one of the main reasons that I explain the principles in the building guides as well as use specific examples – to allow for some variations. In building this P524 marimba in Canada though, I wanted to show how one can overcome some of the common potential issues!

The first issue is simply that of different types of pipe commonly used. Mostly throughout North America, plumbing is not in fact done with PVC pipe at all, but with Black ABS pipe which is softer and more importantly has a thicker wall. Because the resonator and the bar are best matched when internal diameter of the pipe is roughly the same width of the bar… this creates a problem. By the time you add the wall thickness to the internal diameter… THEN also add the thick wall of an end cap, the whole thing ends up to wide and the bottom of the resonators don’t fit in the space. I’ve seen people come up with all sorts of time consuming solutions for this, but there are easier ones! So here goes!

The top two octaves of a five octave marimba use 1 ½ inch pipe. The metric standard is 40mm – and both are available generally in North America but only in that thicker pipe. The solution here is simply to not use standard caps for this pipe, but to use instead the thin plastic “test caps”. These work just fine and in fact look even better than normal thin wall caps when painted up nicely. Because the plastic is so thin though, it can be tough to accurately produce a tone by striking these on the end of the higher tubes though. This means that a few more than usual need to be “passively tuned” – ie tested for good resonance under the finished bar, rather than tested with a tuner or stroboscope. The photo here shows some high resonators using these test caps – sometimes they come in orange colour also.

This photo here, basically shows the next two octaves down C#3 to C5 use 2 inch pipe. Here’s the super easy solution! You CAN GET THIN WALL PIPE IN 2”!! Even in a basic hardware store like Home Depot thin wall pipe is readily available with perfect end caps to suit. BUT don’t lok for it in the plumbing section. Look for it in the section that deals with ducted vacuuming systems – that’s what this type of pipe is used for in America and Canada. Using this solves the space problem, and is a whole lot cheaper and lighter to boot!

Shown here are two specific problem notes… C3 and B2. On this marimba they are on the end of the middle row of resonators. In Australia I simply use a 60mm PVC pipe for this which Is a medium wall thickness, and although not as common as others – still reasonably available and inexpensive. In the small city I was building in though in Canada… I could find virtually NOTHING between 2 inches and 3 inches that would do the job. Now actually you could get away with using just the same 2inch vacuum pipe for these two notes, but the bars ARE just a bit too wide and I like to match things up properly. SO I found this solution here… which is a 60mm electrical conduit. I could not find caps to suit, so for these two tubes I will have to make internal plugs – a pain – but it means the pipe is well matched. As this pipe has a thick wall, caps would likely take up too much space anyway.

This photo here shows the bottom row of resonators – the big ones! The highest of these was no major problem. In Australia we have a very common and cheap PVC pipe that is 75mm (3 inches) in diameter. It is used for stormwater and is very thin wall and the 90 degree fittings are very tight turns. Now mostly in North America, the black ABS is standard for 3inch pipe BUT you can get a thinner wall white PVC. It is even labelled with the metric 75mm! Admittedly I could only find this pipe in one of the major stores in the city I was in… but I have seen it in other American cities a fair bit. The Home depot stores I looked at had the fittings for the PVC pipe… but not the pipe!! Crazy!

There was still a small problem though because the 90 degree bend fittings available are different – they are more like pressure pipe fittings and do not turn so tightly. This means that when you put them together they make a wide U bend that might not fit under your instrument without hitting the frame. My solution was twofold – firstly the frame modification to use a single lower strut – (read the last blog entry). Secondly, I made these fittings a fraction shorter by sawing the joining area in half on the two bends before gluing them. You can see from the close up photo here that the extra inch that it gave me in room was just enough!

The bottom resonator on the prototype was a 4inch (100mm) pipe – and this pipe is available in both ABS and PVC generally. As it is just the bottom note you have a little flexibility in room because you can always shift things over a little – so it doesn’t matter much what you use. Actually I ended up using this pipe for the bottom tube on the other row also – the C#2 – as it helped solve an issue there which I’ll write about below. The bends on this pipe were not very tight either, so I repeated my trick of sawing away some of the join area. Even so though, there was no way I was going to be able to neatly fit this tube with the bend going inwards… so for this bottom resonator I went towards the player instead, and angled just a little outwards – it comes just inside the frame so I’m happy. The C# is not fitted yet, but I anticipate it fitting ok with the bend going the normal way because there is a little more room to twist it towards the frame end – it does after all start half a bar width further up!

This left still a couple of resonators in the middle of this bank that would normally be made with 90mm pipe. In Australia, 90mm is another stormwater grade so cheap and easy and tight bends. I could not find ANY pipe though that would really do this job – what is needed is something in between the 4 inch and the 3 inch pipe. There just wasn’t any where I was buying! My solution was to use the 3 inch pipe which at least fit.. BUT I made sure that the mouth end of the tubes under the bars.. was the flanged bits that come at the end of a whole length of tube. You can see in this photo here that the top sections of two tubes are wider. This is not ideal, but it does at least correctly match the impedance of the tube mouth to the bar – and with the thicker wall tube, it does not look silly making a one inch jump in diameter for the last note on the row.

ONE more thing I wanted to do differently with this marimba.

Normally I use sealed rivets to construct the resonator banks, but it seems these are not popular the world over. In most major cities etc in the USA and Canada they are reasonably available BUT not so much in Saskatoon where I was building this one. I could have purchased them online or chased some down probably, but I wanted to find an alternative. This is what I used shown here in this photo. Short screws designed for sheet metal. I needed to drill holes for these that were a little smaller than the screw size – that way they grip well and make an air tight seal going in. The down side of this is that there are sharp points inside the top of the tubes which could grab your fingers when dismantling the instrument – so I am going to find a small grinding wheel for the end of my drill, and grind these reasonably flat to the wall of the tube – then they will be safe and look neat!

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