List, A colleague and I were discussing duplex modifications recently, when the subject of applying a drop of glue to a noisy duplex to detune it came up. While this topic has been covered previously by Jim Coleman snr and others. It occurred to me that some list recipients may be interested in revisiting this topic. Included below is a copy of my recent reply to my colleague regarding this matter. >Thanks for your reply. What is this glue on the duplexes thing? I >have not heard of it. What kind of glue? How and where do you >apply it? Any glue will do, it's the mass effect we're after not it's adhesive qualities. You apply it to the center of the duplex string segment of the offending duplex unison. As I mentioned in my previous reply, the principal factor which causes duplex noise, apart from poor duplex and capo bar shape, is that the duplex length is close to in-tune with a harmonic of the speaking length. There are two ways you can alter the resonant frequency of a duplex segment; 1) Change the length of the duplex. 2) Change the mass per unit length of the duplex string segment. Changing the duplex length you already know about. While you can change the mass per unit length of the duplex by using a different gauge wire, the duplex frequency won't change in this case since the speaking length will also be at a higher or lower tension, and the duplex frequency will not change with respect to that of the speaking length harmonic. However, if you mass load the duplex only, the resonant frequency of the duplex will be lowered without effecting that of the speaking length. Here enters the idea of putting a drop of glue on the offending duplex string length (Jim Coleman senior mentioned this on the list last year - and a great idea it is too). The glue drop will lower the frequency of the duplex, moving it out of tune with the harmonic of the speaking length. This is a very neat work around for noisy duplex unisons in 'the field'. Furthermore, with pianos such as Steinway and Yamaha, where the duplex sections are a continuous bar for each duplex section, the frequency of each duplex unison, of the same note, will vary considerably since their lengths also vary. This is why on these pianos you will often find that one unison is making most of the noise while the other two might be quite acceptable. Try this glue on the duplex trick, it's a ripper. The other good thing about it, when compared to the commonly employed - tape across the offending duplex group, is that the sustain of the note will not be affected. In fact, I have found that the elimination of the string noise with a glue drop on a duplex unison can actually yield a longer sustaining tone. Ron Overs -- _________________________ Website: http://www.overspianos.com.au Email: mailto:ron@overspianos.com.au _________________________
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