problems with salt test - Discussions with Anthony
-----Original Message----- From: Anthony Sent: 28 April 2010 To: email@example.com Subject: problems with salt testHi Jim,
Since our last e-mails I'm pleased to let you know that I did indeed manage to make some outdoor instruments, and had a great summer last year taking them to festivals, often locate dnearby the childrens' space.
Now we're in year 2, and I'm making bigger and better things. So far Ive made a giant copper chime, a pvc batonka, melody the cow bell cow, whispering pipes, tongue drums, a giant triangle, a giant rainstick. Today I finally finished my first giant xylophone. Hooray!!
It's pretty straight forward- 6 notes, A major pentatonic. Made from sapele, 40mm thick, 150mm wide.
I watched your you tube video for finding nodes with salt- something i'd read about. The next day I did exactly as instructed but had some interesting reults--
1- the nodes were not equi-distant from the ends of the bars on any of the 6 bars.
In the end I drilled perpendicular holes 22.5% in from the ends of the bars and this seems to work fine for all but 1 of the bars- the lowest note (A). It was in tune before we drilled the holes, now it's a fraction sharp.
Question- If I sand out a little arch will the pitch be lowered?
Hope you can help.
Anthony James Brown
Hi Anthony - great to hear from you, and thanks so much for taking the time to get in touch and send a photo. Great work by the way!
Ok now for your salt test result findings.
Point one - well the nodes can be a little different in distance from the ends of the bars, although they should not be a great deal so. If they Are different, it might be partially due to those same grain variations but more likely because of an uneven arch shape - but even this should not make a BIG difference between the two ends. If you find there IS a big difference, you may find that you are actually reading one of the nodes in the bar from a different mode of vibration - one of the overtones.
And to answer your last question - yes - sanding a little out of the middle of the bar will definitely lower the pitch - sand just a little though as it should not take too much.
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answers by Jim MCCarthy - 28/02/2008
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