By Jim McCarthy | July 14, 2009
This week saw me finish things up on the Five Octave Marimba project. Actually there are a few more things I will do slowly over the next few months, as I discover some of the subtlties of this particular instrument – BUT I have now arrived at the point where I can actually play the marimba – and it LOOKS really great too! Here’s what this post will cover:
- Getting the wheels on.
- Finishing all the horizontal struts with felt strip and bar posts.
- Trying some different strings and stringing the bars.
- adjusting resonator height.
- Testing and making small adjustments.
With all the woodwork protected by estapol, I could finally screw the castors onto the bottom of the frame. The particular wheels I’ve chosen were quite expensive but I wanted these ones as the quality is very good and they also have a good combination of a base plate small enough to screw on to the frame without TOO much extra timber just for that purpose – AND – a decent size actual wheel. Small wheels are not much use on a marimba of this size unless you are only ever rolling it along a super smooth glass-like surface – yeah right! These ones will work fine on carpet or concrete surfaces without vibrating themselves and the instrument to bits. It also helps that they are made from a hard rubber compound which has a slight suspension effect. These wheels came in a version with and without a locking mechanism. The ones with were more expensive, so I got two of each. The idea is that you really only need one locking wheel at each end of an instrument to hold it firmly in place. I was careful to make sure the wheels with locks went on the side of each frame end that would end up closest to the player. This means that the locks can be kicked on and off by the performer without moving out from behind the instrument.
The other task needs to be done AFTER the estapol goes on, is putting all the string holding bar posts into the timber struts. I touched on this in the last post, so you can check out the details there. This week however saw me have the time to actually finish the process with all four struts. In total it’s almost 150 bar posts so it takes more than a few minutes!
Then the joyous moment – time to string the bars! This photo to the left shows the top bars loosely strung into position. Notice how the string goes around the two brass support posts at the end. Notice also that I’m stringing the “white” notes first. This may seem obvious but it certainly is easier this way and I’ve seen people try it the other way!
This photo to the right shows the bottom bars strung up. At first I used a double plaited 4mm nylon cord which is actually called “starter cord” – the sort used on lawnmover pull starts. I often use this as it is really strong and durable and it also has the added bonus that you can work it with a flame to melt it. This means it’s easy to tidy the ends and prevent fraying, but more importantly you can mend it quickly! I carry a cheap cigarette lighter as part of my small gigging repair kit. If a nylon cord breaks it makes the instrument unplayable, and in the middle of a show it takes too long to re-string a set of bars even if you happen to have a spare lengthy of cord. Thats where the cigarette lighter comes in. You just trim the cord ends where it has snapped, then melt the ends together using the flame. You may have to adjust the cord a little to make up for the missing length and ensure the join is not in a position where it interferes with a bar’s vibration – BUT it is a quick fix which works really well.
Unfortunately for me, I was unsatisfied with the result using the nylon cord in this particular instance. The reason was that some of the bars made a slight rattle or buzz on the cord when it was strung tightly. This is a reasonably common issue. It tends to happen more on bars where the natural nodal lines don’t match up perfectly with drilled holes – as is common – but in general it can happen anyway. Sometimes it can be just a bit of a click sound on the initial impact of the note – caused by the inside of the hole striking the hard surface of the cord – but still undesireable. Strangely enough I have found that this tends to happen more on bars with holes that are drilled really well – those holes that have a bit of a bend in them hold the cord a little and don’t buzz. Of course the downside is that they also can choke the vibration a little as well. Using a smaller diameter hole through the bars can help this problem as well as there is less room for movement on the cord. Obviously I can’t make the holes smaller at this stage, and in any case I made them the size I did for a good reason. That little bit bigger means the bars are easier to string and also that they are a little more free to vibrate. This really plays a crucial part of the instrument’s sustain.
So my solution was one I’ve used many times before – I changed the cord to a 4.5mm plaited cotton variety. This is called “sash” cord or “venetian blind” cord. It comes in various diameters but you don’t want one actually big enough for a window sash! The 4.5mm is just big enough to fill up a little more of those holes in the bars. More important though is the fact that it is made of cotton. Even under high tension the cotton cord does not have a hard exterior surface like the nylon does. This acts a bit like felt would – it dampens any hard contact sounds. The photos here actually show the cotton cord in use. With the bars restrung with cotton, all the problems went 100% away. Great! Notice the spring between the tension posts at the bottom end of the instrument. This keeps tension on the cord as well as makes it easy to remove the bars without untying anything.
Here we see the finished instrument! Looks pretty good I reckon. The next step was to make some minor adjustments. Firstly I adjusted the resonator height at the low end to best suit the room. This will change from venue to venue as temperature changes. It was only a subtle difference as the starting height was pretty close to as good as possible for “normal” condidtions – as intended. For more extreme temperature conditions the adjustment will be useful. It’s easy to do with this cool system I made which you can see in the photo above right, and just involves twiddling a couple of screws with the allan key. It’s a simple listening test. Hit a couple of low notes – adjust height – hit same notes – compare sound. Do this a few times till you arrive at the best sound.
The next step was to play each note a few times. A couple of notes were sounding just a little muted owing to their bar posts being slightly off position and pulling the string firmly against the side of the bar’s hole. It is a small imperfection, but one worth fixing. One of the reasons I prefer making my bar posts from aluminium rather than steel, is that it makes these things easy to adjust. I went over every post with a screwdriver and small hammer giving them a tiny tap one way or another to make sure the cord came through the center of each bar’s hole and into the middle of the bar post’s slot without any sideways tensions at all. This made sure all the bars were perfectly free to vibrate fully with no muting from the string at all. Once again – it’s worth mentioning that I’m talking about very subtle improvements here, but why not?
Here we see the view from the audience side of the marimba. Notice how the dummy resonators at the low end hide all the bends and twists in the tubes behind them.
I’ll post some more info for you later on down the track, but for now this five octave marimba is finished and ready to enjoy! All that remains to be done is to write up the building guide and finish the instructional videos so YOU can easily make one of these marimbas yourself. This will take me a little while, but put your name and email address in the box at the top right of this page, and you will get a couple of email updates along the way. Don’t miss out on the super deal I’ll be offering the earlybirds when the building guide is launched!
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