A tenor bridge conversion

[alan forsyth]

Hi Andre and welcome back to the list from lurk mode!!

When the strings in the low tenor are not long enough for a short piano, the designer lowers the tension so that the string can achieve the required frequency.  Unfortunately when this happens, the string makes more of a boing...boing...  type sound when it is at such low tension. This would explain the voicing difficulties. Also when a string is at such low tension it induces tuning instability because a very slight expansion or contraction of the soundboard produces a much greater effect on a low tension string than a high tension string. Take for example the case of the Yamaha GH1; you will always find that the low tenor is always the first part of the scale to go out of tune and is usually way out more than any other part of the scale. The transition bridge is a remedy for this tuning instability; by decreasing the length of the tenor strings so that they can be converted to wound strings which will be heavier and therefore produce the required  low frequency at a much higher tension. 

As to why the manufacturers did it their way, I can only assume that it was to keep the harmonics in line as far down the scale as was possible. No matter how well a scale is designed there will always be a noticeable change in the harmonic content of the sound as soon as you reach the bass crossover point i.e. the change from plain strings to wound strings.

AF

See next post; I have a question for you?

From: Concert Piano Service 
  To: Pianotech List 
  Sent: Monday, January 22, 2007 7:40 PM
  Subject: Re: A tenor bridge conversion




  On 22-jan-2007, at 1:52, Ron Overs wrote:


    Hi all,


    I've just loaded a couple of images onto my webspace which show the layout for a tenor bridge conversion of a Bechstein model C grand, and an image of the new tenor bridge in place prior to stringing.


    Here is an image link taken at the layout planning stage;


    http://members.optusnet.com.au/ronovers/bech_c_tenor1.jpg


    Here is an image link, taken last Friday which shows the finished tenor bridge in place, awaiting strings.


    http://members.optusnet.com.au/ronovers/bech_c_tenor2.jpg


    The original Bechstein C (circ 1953) was one of the most outstanding examples of a poor scale I've ever measured in a mid sized grand. The tension dropped down to around 18% at note E20 (the lowest note on the long bridge). To rectify this problem, a new tenor bridge was designed from the first original trichord plain note, E20, up to note D#31. The new lowest plain-strung trichord is at a respectable tension of 36%. This will transform the model C from one of the worst crosses in the business, improving it to the point where it is about equivalent to the cross of a model D Steinway (in terms of percentage of tension deviation - the lower the deviation the better the tuning stability). Should have it strung and playing in a couple of weeks.


    Ron O.








  Hi Ron,
  I have a question :


  You cut off the treble bridge in the tail. Did you do that because that last part of that treble bridge is so close to the rim?
  I worked on a brand new Bechstein C and I noticed that those first treble notes (nr 21 to appr. nr 30 sounded weird and were difficult to voice correctly, as usual).
  I also wonder what kind of string thickness you use on that new bridge you built. Do they get thicker in size because they are shorter?




  friendly greetings
  from
  André Oorebeek


  Antoni van leeuwenhoekweg 15
  1401 VW Bussum
  the Netherlands


  tel : 0031 35 6975840
  tel : 0031 652388 008


  where music is, 
  no harm can be



-------------- next part --------------
An HTML attachment was scrubbed...
URL: https://www.moypiano.com/ptg/pianotech.php/attachments/20070123/52daf1ba/attachment.html