source file: m1607.txt Date: Fri, 18 Dec 1998 17:52:07 -0500 Subject: Re: steel bar tunings by Rick Sanford From: "Darren Burgess" Rick Sanford writes: >>> Question number one is - How are the bars suspended thus where are the nodes? ( are they held only at one end or are they drilled at two (or more) points and suspended there) >>> Darren Replies: Rather than approach this one question at a time, I have included below all of the characteristics of the bars. The main problem I have encountered with tuning them is that grinding between the nodes causes a phase or beating effect. I want to tune the bars, but preserve their timbre. I have tried a few things which are detailed below. Any ideas you have, Rick, or any one else on the list, would be greatly appreciated. These bars comprise 1961 bell instrument that attempts to mimic cast bell carillons. Characteristics of the bars: 1. Each has two solenoid strikers. One primarily emphasizes the fundamental (placed at the end of the bar), the other the second harmonic (place just inside the vibrational node). This creates an overlap ofoctaves between the adjacent octave racks of bars. (5 racks of bars) 2. The bars are varying lengths from about 20 cm to about 56 cm. 4 mm square at the end (3/16th") 3. the bars each have 3 brass (or bronze?) collars firmly attached along predictable but somewhat inconsistent places between the vibrational nodes. They follow a general pattern but are not in exactly the same relative postion from bar to bar. It is my theory that these collars are used to tune and/or supress the inharmonic partials. The Collars are larger on the longest bars 5/16th" wide, 3/32" wide on the shorter bars I have experimented a little with moving them and have found doing so creates significant changes in the timbre of the bar. I have also noted that moving one collar further from its original position causes a "beating" effect -- the further from original, the faster the beating. This is not a very predicable, consistent effect. 4. Tuning of the bar by grinding metal from between the vibrational nodes lowers the fundamental frequency as expected. It has the unfortunate effect of causing a slight phasing of about 2 cycles/second, and significant loss of the original timbre of the bar. ****What is the cause of this effect?**** This effect is somewhat corrected by moveing the brass collars, but not perfectly. Placing weight on the end of bar also lowers the frequency, but that also causes a phase effect. I am experimenting with various tuning methods to determine how tune without causing a phase effect. 5. There are five octaves of bars. 6. There is a notch cut away on either side of each bar at the vibrational nodes (20% of the length of the bar) effectively making the bars thinner at the nodes. About 1/16th" thick at the nodes. 7. The bars are suspended with string. On one end the suspension point is close to the vibrational node. On the other end, it is at bit further from the node, and closer to the end of the bar. The suspension points are consistent, relative to the total length of each bar. The longest bar is 56.6 cm. Each of the nodes are at 11.6 cm (20%). The suspension point on the "magnet" end is at 7.5 cm (13% of the total length). The suspension point on the "solenoid" end is at 10.6 cm (18%) 8. Each bar has a small but strong magnet one end that pokes up thru a coil of magnet wire.