Every instrument built presents the builder with specific challenges, and at Chestnut Hill Presbyterian Church it was the desire for an organ on the gallery of adequate size but with a restriction in height. Initial designs suggested that the Swell Organ be placed behind the Great Organ but this presents disadvantages for the egress of sound and balance between the manual departments. By making the console slightly projecting, and dropping the Swell above the trebles of the Great Organ, it proved possible to achieve a vertical disposition. However, this made the case wider than it might otherwise have been. Wide organ cases are always difficult to make elegant and required some ingenious work on the part of the case designer. Fortunately, the assistant designer at Mander Organs, Aidan Nutter, is a trained architect; and he in combination with Geoff McMahon, the head designer, a suitable compromise was realised.
Aidan Nutter writes: "To make a wide case elegant it is vital to emphasize the vertical elements; to this end the heavy entablatures (cornices) on the round towers serve to create a series of strong vertical components which contrast with the visually subservient pipe shades in between. The contrast in colour of the timber and their curved top also reinforces this effect. The case also has a strong hierarchy, which serves to break up the large area of the case, starting with the Choir case, moving on to the Great and Swell in the centre and finally the Pedal at the sides. The Pedal towers are joined to the rest of the case by low flats which creates this visual distinction. The carved foliage shades to the top of the pipe flats gave the opportunity to create visual counterpoint by the opposing directions in which they slope." The projecting console also makes the conducting of the choir easier and it was provided with curved terraces for the stops also in an effort to keep it as low as possible, whilst ensuring that the stops were accessible.
The key action is balanced and all the manual pipework is planted in major thirds from the middle of the tenor octave, a feature which improves tuning stability and blend. The organ is tuned to Kellner's proposed temperament for the performance of Bach which is gaining a great deal of popularity in America as a temperament with good all-round flexibility. Bach's seal, reproduced below the Choir case, is recognition of this as well as the 250th anniversary of his death.
|Double Diapason||16||Open Diapason||8|
|Open Diapason||8||Hohl Flute||8|
|Viola da Gamba||8||Celeste||8|
|Fifteenth||2||Sesquialtera II||2 2/3|
|Fourniture IV-V||1 1/3||Plein Jeu III-IV||1 1/3|
|Mounted Cornet V||8||Bassoon||16|
|Swell to Great||Tremulant|
|Choir to Great|
|Chimney Flute||8||Open Diapason||16|
|Nazard||2 2/3||Bass Flute||8|
|Recorder||2||Mixture IV||2 2/3|
|Cromorne||8||Great to Pedal|
|Tremulant||Swell to Pedal|
|Swell to Choir||Choir to Pedal|
|* Playable from Great and Choir keys, an existing stop now placed behind a screen in the Chancel|
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Case Design Aidan Nutter
Technical Design Geoff McMahon (Team Leader), Aidan Nutter
Construction Leslie Ross (Works Manager),
Mike Smith (Workshop Foreman)
Scaling John Pike Mander
Tonal Preparation Michael Blighton (Team Leader),
Site Installation Ralston Bryan (Team Leader)
Tonal Finishing John Pike Mander, Michael Blighton