Bowmen of Skelmersdale

Bow Resonance

Vibrating systems - wine glasses, road bridges, stabiliser rods and so on - have a natural frequency (usually more than one) at which they will vibrate if disturbed.

Resonance is a condition in which two or more separate systems with similar natural frequencies of vibration will tend to vibrate in concert. Under these circumstances, energy transfers efficiently from the most strongly vibrating system to the other(s).

This effect can be used effectively to make sure that TFC s or other stabiliser components are efficiently controlling unwanted movement in the bow.

The same effect can amplify or exaggerate movement, sometimes disastrously. An archer with a muscle tremor at around 15 Hz will transfer energy efficiently into a bow/stabiliser system with a natural frequency close to 15Hz, resulting in greatly increased bow oscillation during aiming. In these circumstances, we need to change the offending natural frequency of the bow to avoid the archer s natural frequency.

Avoiding resonance

Avoiding resonance when it occurs is simple. Almost any change in the system - increasing or decreasing weight, changing rod stiffness or length, or changing limb stiffness in either direction - will change the natural frequency of the bow. Changing stabiliser length or weight is usually the most effective as there is scope for larger changes.

Finding resonance

Deliberately achieving resonance is harder. But the options are the same; change any part of the system you want to tune . The difficulty is simply that to identify resonance, one or other part of the system must be allowed to vibrate, and the other part observed. When the undisturbed part immediately picks up and continues the vibration of the first, resonance has been located. To tune a damping system,

damping is most effective when the damping system matches the vibration frequency - the system stops vibrating fastes when the vibrating and damping parts are close to resonance. This needs to be repeated for a series of small adjustments, and is easiest with a continuously adjustable unit - like the ubiquitous TFC.

What bow behaviour needs controlling?

Bow  movement

Timing - When is movement important?

Time and Motion

Controlling bow displacement

Weight, Mass and Inertia

Static and Dynamic properties

The misnamed TFC

Controlling bow balance

Centre of Gravity

Finding the centre of gravity

Changing the balance using weight

Weights and Distances

Rods, weights and risers

Controlling bow vibration

Causes of Bow Vibration

Reducing Vibration - Damping

Bow Resonance

Tuned damping - more on TFC’s