Vibration speaker cylinder

It took about 25 years that a special type of loudspeaker – vibration speaker – came to widespread use.

In 2022 I was to give technical help to realize a set of light transmitting and receiving devices. On the receiver side a vibration speaker was to be used (namely: Dura Mobi Speaker Hummingbird bone conduction speaker). In further research I came across a larger 20W version of a vibration speaker.

With vibration speaker the sound is created by transmitting vibrations to any material of much larger dimensions than the vibration surface of the speaker motor. One approach is to use it as driver for the planar surface.- this method is well documented and was also presented in photo-sound installation by Miha Godec D•Still later that year. This is a so-called directive loudspeaker.

Immediately I got the idea to bend a special, particularly light wooden panel into a cylinder sleeve and thus achieve uniform sound radiation on all sides of the vertical axis of the cylinder. This is a so-called omnidirectional speaker.

The wooden sleeve has been closed at the bottom and top to create an additional resonant space that amplifies the lower mid frequencies. The sound check results so far are specific, and sometimes even brilliant.

What I feared the most is the self-resonance of the wooden material. This was to be evaded by the tension which is built into the cylinder. It is a sandwich construction – the fatter vertical soft wood is on the outsides, and the quality thin layer of the two criss-crossed laminate quality wood is in the middle – to hold everything together. So: In bending the panel into a cylinder compresses the inner soft wood layer and expands the outer layer. A veneer was added on the outside to stabilize the cylinder structure.

Speaker driver was mounted on the insides – at the point where the lowest frequency was detected (with the thump of a finger). This was at one edge of the vertical cylinder. A half-hole was made to allow for the inner mounting – and to lessen the effect of the closed hollow box.

There are still possibilities to tame the material: the technologies of building an acoustic guitar.

The good side is clearly the full-range speaker driver that is superb from the highest notes, down to the lows of a male voice – there the problem start.

This is a photo-sequence of my actions: