Yamaha Duplex Scale

[Ron Overs]

Hi list,

Yamaha C5 rear duplex lengths are inappropriately set to enable them to 
be tuned to the intended harmonic of the fundamental tones.

I find the 'chorus' effect of 'out of tune' duplexes, in the extreme 
treble sections of Yamaha and Steinway pianos (and others), to be 
moderately annoying. However, should a tech wish to tune the duplexes of 
these pianos, it would be necessary first to replace the rear duplex 
blocks, which are cast in multiple note sections at 'out of tune' 
harmonic lengths, with individual blocks placed at a ratio of the 
fundamental's speaking length.

We have rebuilt several grand pianos with individual rear duplex blocks 
set and tuned to specific harmonic lengths (it takes six months of 
refinement post_rebuild to get them exactly to the correct lengths and 
tuning_stable). While these instruments seem to have cleaner and better 
defined treble sections, I am not sure whether its due the fact that the 
harmonics are in tune, or whether it is due to the superior seating of 
the individual duplex blocks on the iron plate. We have found that poorly 
seated group rear duplexes can lead to a propensity to falseness. 
Furthermore, the 'benefits' of a tuned rear duplex system seem to be 
better when the hitch pins behind the duplex blocks are not further than 
20mm from the duplex block. We recently rebuilt a Kawai KG6 incorporating 
shorter than OEM and tuned duplex lengths, relocating the hitch pins to 
20mm behind the blocks. We were delighted with the result. For those of 
you who have been unlucky enough to tune a factory KG6, they are 
typically disastrously false in the treble and mid sections. I have 
always believed that the unusually long rear duplex lengths (similar to 
the '70s CF Yamahas) were responsible for these problems. It appears to 
be so.

I should perhaps add that rebuilding Kawai KG6 pianos with appropriate 
modifications, including appropriate action geometry changes, can 
transform them into one of the finest 7' pianos one can experience (even 
when compared with product from the world's leading manufacturers).


Ron E. Overs

Email: ron@overspianos.com.au
Website: www.overspianos.com.au