Treeter and Wooder, Wooden Loudspeakers for Violins

This is a long on going project to design new loudspeakers which better resemble the sound of the original instruments. The idea here is to create simple loudspeakers which are dedicated to a single instruments and be able to route the sound independently. We start with the violin where the cones are not suited to spread a planar sound as a vibrating membrane.

Audio got somehow stuck into taking all the instruments, route them into a mixer, output a stereo signal to be sent to an amplifier which routes into loudspeaker which separates the signal again through an expensive cross over. Expensive loudspeaker are built to have a flat response by mixing their mechanical properties together with the cone typical spectrum profile.

If you play a violin you realize the sound is completely different, you chose to use amplification knowing that the sensation and the dynamic will be different. Everything passes through a mixer and you have a stereo output with all frequencies mixed up. The loudspeaker you are going to use it's a vibrating cone which expands the sound in a spherical direction, not like the vibrating boards of a string instrument. The sound is localized instead of spread all over the room.

This sensation is difficult to show on video (which was made to represent stereo audio) but I tried with a shotgun microphone https://www.youtube.com/watch?v=camNdWhXdD0

This project uses mainly exciters which are loudspeakers without cone and are used to let wood vibrate.

The loudspeaker is simply made of a wooden box, two panes of different thickness, two tweeters and an exciter. A sound post (like in a violin) is used to couple the two boards.

Part list:

1. 1 exciter (here I use a monacor AR 30)
2. 2 spare tweeters (4Ω each)
3. 1 class D amplifier
4. 1 sound post
5. a wooden box (60x37 cm)
6. 2 piezo disks (1cm + 2cm)
7. 2 wooden panes (7mm and 3mm)

Total cost of material is around 50EUR depending on the quality of the components.

The schematics is simple. The violin has 2 piezo microphones, one attached to the lower board (larger with a lower resonance frequency) and the other (smaller with an higher resonance frequency) to the upper board.

The upper board passes through the amplifier on the left channel which is connected to upper tweeters and represents the high pitch. The lower microphone is attached to the lower board and routed to amplifier and then to the exciter screwed to the thicker pane. The sound post is screwed to both panes and transfer the sound between the two.

The upper tweeters have a bamboo resonance boxes. The left one has a skin on the top which can be tighten by a peg and can resonate on specific frequencies. The right one is open.

The sound of the lower board is spread across the room in planar waves while the sound of the upper board is spread vertically apart from the left tweeter which uses the skin to resonate horizontally as well.

The effect is difficult to render on video but I'll think at other ways to convey the experience.

First of all you build a squared box of length 60cm times 37cm. The golden section helps to avoid resonances.

You drill two upper holes for the tweeters and glue the bamboo segments.

You cut the bamboo segments on the upper end around 45 degrees and stretch and glue a skin. A thread passes from the skin in the middle and is winded around a peg which is used for tuning.

The tweeters are then screwed on the box and the connected in series.

The exciter is screwed at the start of the Fibonacci spiral. The exciter and the tweeters are then connected to the class D amplifier.

The sound post is put in the middle and screwed to both panes.

The panes are then screwed to the borders and the tension of the screws tunes the loudspeaker as you would do in a cajon

The treeter is a tweeter made out of a bamboo segment with skin stretched on the top. I wind the coil with a screwdriver and use a magnet hanged to the skin of the bamboo. As it can be seen in the video the sound is really low and a better effect is reached by putting an exciter glued on the skin of drum

I tried other forms of wooders. One idea was to build one to be used as violin cover but the result was a bit dangerous for the violin and a bit too heavy. I even made a version where the panes had dedicated exciters.