Gents' C7 Pulsynetic............................81dB(C)....78dB(A)
Synchronome 1920 no GA buffer..........74dB(C)....70dB(A)
ECS double contact.............................76dB(C).....70dB(A)
Gents' WT C40A 20VDC.......................80dB(C)....80dB(A)
Synchronome turret slave No4...............75dB(C)....73dB(A)
PO36 below background noise. The slave dials predominate.
Background noise level ~55dB(A)
All masters were mounted on a 4" breeze block wall.
All measurements made at ~1' (30cm) using a Galaxy 140 digital SPL meter using Max Hold. C-weighting records deeper sounds and is more typical of human hearing. A-weighting is generally used for noise measurement but does not favour the lower frequencies.
Lowering drive voltage is a popular way to reduce noise with all electric clocks provided reliability is maintained.
The pendulum drive predominates in the sound picture of the WT. Frequency of drive impulsing will depend on the load. Up to two minutes between impulses is possible with a lightly loaded / rigidly mounted WT movement. It might be possible to damp the sound slightly with rubber buffers to the armature. This may require undesirable modification! There is very little room to play with.
Today, a humble rubber band was simply stretched around the rocking armature. The band intervenes between the electromagnet cores and the armature. Thereby stopping the very noisy metal-to-metal contact completely. If the rubber band wears out then another can be easily slipped in its place without dismantling anything. Absolutely no skill is required. Just watch your fingers if the pendulum is still swinging!
Stopping the heavy and powerful pendulum is a very good idea while working on any WT. Otherwise the pendulum could easily cause severe crushing injury to the extremities!
Damping the fall of the armature, height-adjusting screw is also important in noise reduction. The screw adjustment ensures that the impulse roller does not run continuously on the underside of the pendulum hook. However, the domed screw head falls heavily in metal-to-metal onto the WT's mainframe casting.
By raising the screw sufficiently a rubber pad can be placed under the rounded screw head. This rubber buffer can be glued to the WT mainframe with contact cement. Something like bicycle, puncture repair, rubber cement will do. A small, plain, rubber, tap washer would suit perfectly. You must use glue or the tap washer will quickly fall off. Clean the frame locally before applying the contact glue. The paint may be greasy.
It is an essential part of WT set-up that the impulse roller just clears the underside of the pendulum impulse hook. Too much clearance leads to a loud metallic clonk as the roller finally catches up with the pendulum hook. Close roller clearance ensures a quiet take up and strong push over the maximum possible distance.
The armature, height adjusting screw is a tight friction fit in the armature but amenable to pliers. The nut is permanently fixed so leave well alone. Removing the front bearing block allows easy armature removal. The rear bearing can be safely left in place.
By such very simple means a WT can be made almost fully domesticated from the noise point of view. The sound of the Hipp toggle now predominates. One must hope that the rubber band does not wear out and snap in the middle of the night! Nothing untoward will happen but the noise levels will probably quadruple!
The thickness of the rubber band is not particularly critical. Though its length may affect its lifetime if stretched too tightly. Apply thinner bands to taste but ensure the pendulum receives a decent push to achieve a reasonable period between drive impulses. The angular nature of the armature movement will dictate whether a rubber band is too thick. Avoid oil as it will quickly degrade the rubber.
My WT showing the position of the rubber band (orange). The position of the tap washer buffer is arrowed in red. The rubber washer sits under under the head of the armature height adjustment screw. Where it normally rests (metal to metal) on the main frame. (better picture to follow when my TZ7 camera is repaired (again!))
The WT toggle damper is also useful in obtaining further noise reduction. I used silicone rubber tube on the end of the damper rod to considerable effect. Old, hardened, rubber tube will not achieve much in the way of noise damping.
Tolerance of noise is highly personal. Even the quiet tinkle of a Hipp toggle on a PO36 can drive one to distraction when trying to sleep in the room above.
As a background noise to other daytime activities the sound of master clocks is soon forgotten. As is witnessed by master clocks frequently being fitted in manager's, headmaster's and supervisor's offices for security.