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What size bars for a Bass Marimba? - (Qs Max de Wardener and Rob Vialle)

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-----Original Message-----
From: Max De
Sent: Thursday, 11 October 2007 9:07 PM
To: jim@percussionclinic.com
Subject: ...bass marimba SOS....
Hi Jim

Me and my friend are struggling with trying to build a bass marimba in London England. We found your amazing website and were wondering if you might be able to answer some brief questions as we have never made a marimba before.

We initially thought we would like to copy Max Krimmel's Fan Marimba where the bars are triangular in shape but this seemed to making things even harder. We wondered if you had any thoughts about triangular bars.

We are thinking now of sticking to rectangular bars but are slightly bemused about why there appears to be so much variety in bar measurement between each marimba we read about. For example Harry Partch's low C bar on his bass marimba is about 4 feet long where as a standard orchestral low c on a 5 octave marimba is about a foot and a half long. I assume the size effects amplitude therefore allowing the fundamental to be heard more clearly . Is this the reason for such diversity between bar lenghts?

We were wondering if you had any approximate measurements for a chromatic marimba with rectangular bars. We want to start at F , 7 semitones below the stanard C you get on orchestral 5 octave instruments . If you had any guide lines that would be superb. We're not afraid of making the bars quite big(like Partch's).

Any help would be very appeciated. thanks once again for such an informative website. It's a real, real help.

Yours
Max de Wardener and Rob Vialle


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Hi Max & Rob Pleasure to hear from you, and I'll do my best to help out.

Firstly I am not clear about the range of notes you wish to make. You mention a 5-octave marimba which is the maximum standard range for a concert instrument. That means that the low C you are talking about is two lines below the bass stave - or to put it another way, two octaves below middle C - the lowest note on a cello. The first Bass marimba I made had a lowest note E below that, which is another 8 semitones. Sound similar to what you are after? I chose the E because that is also the lowest note a double bass (or contra-bass if we are naming it correctly!) which means it enables you to transcribe orchestral bass parts. Am I correct in assuming that you mean the F you are talking about is the lowest note? You said start, but does that mean highest or lowest? It is surely a pretty low note for a marimba. If you visit the percussionclinic dot com website at http://www.percussionclinic.com/art_marimba.htm you can read a little about this marimba - incidentally the page doesn't mention, but the bars were 2cm thick at the ends - the same as for a normal instrument. The entire surface area of the bar effects the amplitude of the note, but in practice the amplitude is essentially down to the bar width. Length has very little direct relationship to amplitude as it is really just the middle part of the bar that counts - above the resonator. The bar can be wider or narrower than the diameter of the resonator, but it is generally considered that having them equal is best. This means that a wider bar not only has more moving timber over the resonator, but it will also have a bigger diameter resonator which of course makes a louder sound. Just like a bar..... a resonator's length determines the note frequency, and the width determines the amplitude. Having the bar width and resonator diameter similar, means that the resonator takes energy away from the bar at about the correct rate. Bigger resonators mean the fundamental resonance sound is louder, but the note doesn't last as long because all the energy is used up quickly.

You will have noticed that low bars are very thin in the middle. Obviously a longer bar gives a lower note, but without this carving of timber from the middle, the bar would have to be extremely long indeed for low notes - impractical. The variance in bar length you are seeing is normal. Some manufacturers have longer bars with less timber removed, and others have shorter bars that are very thin indeed. These tend to be easier to play as there is less distance to reach for the "black" notes, and they also tend to sound a little better in my opinion. The disadvantage is that these really thin bars are quite fragile and can crack. You can't play them very hard without risk so in one way you could say they are capable of less volume.

Harry Partch's marimba notes (mostly just a few notes and not chromatic his instruments!) are often cited as being an octave lower than they really were. He did use very big bars with not so much carving, but the range of most of his notes was actually in the same area as we are talking - in the octave below the bass stave. I must admit however that I was inspired in part by Partch many years ago when reading about his dream to one day have a staircase in his house with each tread a functioning marimba bar. He thought that sedate moods would deliver scales, but energetic mornings might produce arpeggios! He did produce a few lower single-note style instruments, but they were generally considered to not sound that great. The problem is all in getting enough amplitude at the fundamental when we go lower. The range I suspect you are talking about is about what I would call the practical range for a bass marimba - any lower than that and things get exponentially more difficult. The predominant sound we are after in a marimba note is the fundamental. Unlike other instruments, the upper partials are not exact divisions of the bar length - ie they do not fall where our brain expects them to within a harmonic series. This means that we actually rely on the amplitude of the fundamental itself for recognition of the note. Most bass instruments seem to make plenty of volume at the fundamental, but in fact there is not enough for our ears to adequately hear - what happens is that we hear the upper harmonics and our brains re-create the fundamental for us subconsciously. With a marimba bar this can't happen, so you need a heck of a lot of the actual fundamental to hear and recognize the note properly. This problem is what gets exponentially worse as we go lower. You might have read about my one-note "Gus" - G below the piano range (25ish Hz) - http://www.percussionclinic.com/art_marim3.htm Check out his dimensions and how much trouble I went to, to get maximum vibration - in reality this was still very tricky to make sound good in an actual performance situation despite all the efforts. There was often issues with the size of the building he was in, and where both the bar and listener were in the room. This was because of standing wave effects in the room. Stand in one spot, and the sound would be satisfyingly big, but stand a few meters away in a different spot, and you couldn't hear him at all!

As far as triangular bars are concerned - I will admit ignorance - I've never even heard of them! Sorry can't offer anything there.... Does SOUND like it would be more complex.

Hope this is some help, and feel free to ask more if required!

Jim McCarthy


Thanks Jim,

Thanks for such an informative email. That makes it much clearer. Sorry for our vague information regarding the intended pitch of our instrunment and you were correct in thinking that we are trying to emulate the range of the bass guitar (minus a semi tone).

Have been looking at your 2 octave bass marimba - The tubing looks incredible! Would you be able to reveal the bar lenghts for this instrument as it would really help us as we are a bit scared of commiting to cutting up our rose wood!

Here's a link to the triangular bass marimba that we originally wanted to copy. It's amazing to look at but Max has'nt made any recordings of it.

www.maxkrimmel.com/Marimba/Bass/BassMarimba.html

thanks again for all your help.
Max


Hi again Max...

I no longer own that particular instrument so I can't tell you exact measurements, except for that bottom note which was 9.8cm wide, 63cm long. One octave above that you are in the range of a five octave or even 4 & 6th concert instrument, so you could use those bar measurements. My concert 4 & 6th low E is 7x50cm. If I was going to build these instruments again, I would go for 20% bigger (well 20% wider anyway and maybe 10-15% longer) than this in the bottom octave and 1/2. I would start with a bottom E say 12cm wide and 70cm long and evenly graduate the bars over 2 octaves to E(space) at 42 x 5 & 3/4cm. Any notes above this would graduate more, but perhaps not as sharply - just using tried and tested concert instrument dimensions would be prudent. The reality is, that the exact measurements don't matter that much - as long as they are in the ball park you will be able to tune them correctly. It is often more a matter of practicality - ie how long is your arm/mallet - how wide the doorway you need to wheel the instrument through etc. What I WOULD recommend, is practise the tuning of bars on cheaper timber before you start carving your rosewood. There is quite an art to it if you want to get your upper partials in tune as well as just the fundamental. The trick is to get all the notes correct in relation to each other well before the fundamental is as low as you need it to be, then work them all down gradually together. And BEWARE the last steps - it always seems that the notes get exponentially lower as you carve or sand the timber, so its very easy to go too far, and it's always much harder if not impossible to bring the bar back up again!

I had a look at the link - thanks for that! Ok, so those bars are not really triangular as such - I guess they do taper a little, but just enough to create that semicircular shape without big gaps between the bars at the outside. They would be a little harder to tune like that, but not too much harder if you practised a few that shape. If the notes were in the middle range this sort of shape would be impossible to tune, but at the lower end the frequency of the transverse vibrational mode is not going to be in the troublesome range. That shape would certainly be harder to cut and finish though, and would tend to cause a little more wastage, even if you DID (as you would) alternate thin ends with wide ends on your template. In reality this might not even be possible, because your rosewood or padouk tends to come in planks that are just as wide as you need them anyway. (That's if you can even get hold of any at all these days!) Those instruments look quite impressive I have to admit - but of course it would be even more impressive if the instruments were fully chromatic! Now THAT would be a design!

All the best...
Jim

Jim Reccomends www.makeamarimba.com for comprehensive blueprints and building guides to make your own marimbas.


HI Jim

You very kindly answered questions about triangular bars about 2 years ago. Thank you. Strangely we appear to still be working on the bass marimba dream.

I have a short question. We are copying Partch's bass marimba design and have been progressing well. We have been using Sitka spruce (as specified by Partch) and were surprised how effective it is.

We're hit a small (and probably familiar) problem now in trying to create the lowest note(cello C). Firstly we're not sure how much of the resonator should cover the bar. Any thoughts? Does making the mouth very big effect the volume of the amplification.

Also do you have any idea how much the distance should be between the bar and resonator mouth?

At the moment the fundamental is not really as loud as we'd expected. We're ok with resonator length as we have a plunger so we can adjust to find the right distance.

We are hearing the first overtone much much louder than the fundamental.

I expect this sort of thing with low pitches but I thought as we are not going very low it might have been louder.

Do i need to tune the overtone first? would this help?

If you have any thoughts then that would be smashing.

Best
Max de Wardener and Robert 'chisel' Vialle

P.s. the measurements for the long C bar are as follows.

5 5/8" wide and 1 11/16" thick (at thickest points which is far less than half) 51 3/4" long on the flat top of the bar. The bottom length is shorter by approximately 3 3/4" - 1 7/8" on each end - due to curved filing of bar underneath.


Hi Guys - great to hear you are still going.

The dimensions for the bar you mention don't make much sense to me - probably my bad interpretation sorry. Certainly the thickness of a marimba bar will vary along its length… but the length should be the same top and bottom - can't see how that can vary….? You are certainly using a massive bar as far as I can make out, so volume should not be an issue at all. Just for reference, a standard commercial 5 octave marimba would have cello C as its lowest note and would have dimensions about ¾ x 20in5/8 x 3in1/8. Obviously much much thinner in the middle.

Now onto resonator and the coupling of it to a bar.
Yes the size of the resonator mouth will affect the overall volume a great deal. The bigger the diameter of the resonator the greater the amplification. A wider tube will also take energy away from the vibrating bar quicker though, so overall the sound tends to be shorter. On low notes the sustain is more though, so this is not usually a problem. There is some psychological effects that can play a part in the subjective effects as well but in general don't worry too much about it - the wider the tube the louder the sound. The generally accepted practise is to have a round tube with a diameter the same as the width of the bar - or equivalent surface area of cross section.

Having the surface of the underside of the bar arch about 30mm (1in3/16) from the resonator mouth is about standard on commercial instruments. You may have problems with such a big heavy bar as I think you are using, because there is likely to be so much movement at the middle of the vibrating bar that it might start clunking against the tube. Taking the tube further away from the bar will not affect the pitch, but will lower the amplification effect. Putting the resonator mouth closer to the bar will cause more amplification, but you need to be careful because it also has the effect of lowering the resonant frequency of the resonator itself - by effectively starting to close off the mouth. Sometimes you can compensate for this to a certain degree by shortening the tube a little. I actually did this when I made the bottom octave of my contra-bass marimba - Boris. The bars were about 20mm (3/4) from the tubes and the tubes were fine tuned purely by testing their effective resonance under the bar. Overall it resulted in a louder punchier sound with a little less sustain than you would normally have.

There is quite an art to the process of tuning overtones in bars, but essentially the secret is this: START by getting the RELATIVE positions of the overtones correct first. Chisel/sand in the correct places to get those relationships/intervals correct as early as you can - well before the final target pitch has been reached. Once you have the relationship correct, you can gradually take the pitch of all the modes down together making sure they stay in the correct ratios. If you tune the fundamental to pitch first without considering the overtones, it's 99% sure that you can do nothing now to change the overtones without also affecting the fundamental significantly.

Hope this helps guys.
Jim McCarthy


Making Marimbas, Xylophones & Vibraphones is now Easy
Building Guides for Making Marimbas, Xylophones, Vibraphones and Metalophones
Get These Comprehensive Plans & Instructions with Video!


answers by Jim MCCarthy - 01/12/2005

For more help on instrument building you can email Jim.

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