Fitting the sound blade: the coupling decides everything

The coupling decides everything

A blade only vibrates if the energy is transmitted to it correctly. The quality of the contact between the exciter and the surface governs the result more than the choice of either one taken alone.

The bearing must be firm and free of play

An approximate contact dissipates energy in friction instead of transmitting it. The symptom is recognisable: the level drops in the midrange and a dry noise appears on transients.

Tightening

Too loose, it leaves play. Too tight, it constrains the blade and restricts its vibration. The right tightening lies between the two, it is repeatable from one piece to the next, and it is checked rather than judged by hand.

The position on the blade

It is not a matter of indifference. Depending on where the energy is injected, certain vibration modes are favoured and others are not, and that position is determined by trial rather than set at the centre by default.

The direction of the grain

It orients the stiffness and therefore the propagation within the blade. Fitting a piece without regard to its grain amounts to ignoring half of what distinguishes a wooden blade from any other plate.

The check after assembly

A listening test on a voice, a few minutes, before closing anything up. It is the last moment when a coupling defect can be corrected without dismantling, and it shows on no visual inspection.

The principle is developed on the Magic Speaker page, and ceiling sound on the dedicated page.