How does the D-damp device work?

Around 1970 a german engineer and double bass player, Professor Gerhard A. von Reumont, was doing stress tests on welded steel frames. He and his group of researchers found that trating these frames with vibrations, making them vibrate by force, increased their resistance to structural failure. A stress-free structure resists better. He liked the idea and started to apply this techique, called “vibrational de-damping) on his double bass with good results.
His method consists of a small dc motor with an eccentric weight (just like the vibrator in a cell phone) which is driven by a benchtop power supply that indicates voltage and current draw. The amount of excentric weight has to be carefully adjusted for the instrument and frequency we want to treat. For any given type of instrument we then need a proper fixture to keep the vibrator in place. Once we start treating a specific frequency we’ll notice that, after a while, the frequency starts to raise! We then need to lower voltage to keep the frequency stable. The fact that the frequency is raising on its own is a clear indicator that the “resistance” in structure and material is diminishing!
Keeping log if this process, we will always find a behaviour like in the graph below.

Since we have the measurements, we can also calculate the amount of improvement. Below you can see a complete log of a treatment with some exeptionally high values: an average improvement of over 30% with a maximum of 50% (last column)!

Now this original method, patented by Von Reumont in 1977, goes very deep and allows for a special experience of the instrument: you can pratically feel the instrument vibrate at each frequency and you can litterally experience the “resistance” to vibrate at certain frequencies. It takes about two days to treat 12-14 frequencies and is very labour-intensive and takes some experience as you need to adjust weight properly.

For this reason the commercially available devices often work with one weight for one frequency. The effect, these devices have on the instrument, is therefor often neglectable and you don’t have any measurements to verify it’s effect.
In my device the motor is controlled by PWM (pulse width modulation) trough a microcontroller and not by voltage. Motor speed (frequency = rpm/60) is kept constant by a sensor feedback so you don’t need to adjust frequency by hand. PWM is the same technology used to dim LED lights and consists of sending shorter or wider impulses of full voltage to the motor. In programming microcontrollers, the width of the pulses is expressed in a number from 0 to 255 and is proportional to the energy consumption of the motor! This PWM number is displayed (along with “actual frequency” and “set frequency”) on the frontpanel of the device and we can keep log of it to measure improvement percentages.
The frequency to treat can be set manually for maximal flessibility or automatically following a preinstalled program (a chromatic scale about one forth and fixed weight of the duration of 3,5 -4 hours). In the latter case we only need to establish the weight at maximum frequency manually.