The 2nd Plate. Experiments prior to reeds.

After making a working plate, i decided to develop its design.

Next i decided to solder to 'tabs' to the rear of the plate.

The Theory is to increase the surface area of the plate to try and achieve a larger reverb time as with the existing plate being 6 inch's by 6 inch's with a surface area of 24 inch's (6 inch x 6 inch = 12 inch x 2 surfaces = 24 inch's ) there isn't enough area for reverb to occur.

Also this is a test to see if the sound is transmitted to the tabs, which are 2 and a half inch square in diameter which will add an extra 25 inch to the total surface area (2.5 inch x 2.5 inch = 6.25 inch x 2 surfaces =12.5 x 2 tabs = 25 inch's). This will also prove weather or not these tabs will resonate at a particular frequency.

To ensure this is a fair test the same speakers, frame, drum samples, springs and tension have been used.

The results of exciting this plate were pleasing. Not in the sense of sonic quality or a good effect but, the results proved my theory. The tabs added an extra resonance to the plate, however as the tabs are large in dimensions, unfortunately they produce bass frequencies, which for a reverb effect is not desirable.

The two tabs did not seem to increase the size of the reverb time, there effect was to lower the resonant frequency of the plate. To ensure this was true I placed the contact microphone on to one of the tabs and the effect was an increased resonant frequency which proved my theory.

The issues with this design are that still large amounts of gain re required so the signal is noisy. The plate is still not earthed which adds to the noisy signal. And the tabs are to large and therefore increase the low frequency resonance.

Next i attempted to build my own speaker system to excite the plate. For this i used a piezco driver with a capacitor soldered into the positive feed and screwed into a terminal block into which a guitar lead is used to drive the speaker.  

I decided to solder a capacitor into the circuit as this stops low frequencies (generally under 1khz) from being produced by the driver, the reasoning behind this is, if no low frequencies reach the plate, i should rectify any low frequency resonance. 

This driver had a rubber tube attached to increase its directionality and therefore improving its performance.

This driver was mounted close to the plate to ensue the maximum sound pressure level was exciting the plate.

I have since tested this design and it is a failure, this because the driver simply cannot generate enough sound pressure to excite the plate enough to receive a signal from the contact microphone.

I have since removed the speaker.

In my next design I intend to place 25 "reeds" which will be placed in a grid 1 inch away from each other and will be 0.5 cm in width and approximately 7.5 cm in length. I will then test this design to see what effect these 'reeds' have. Thy will increase the surface area by 66.96 inch's (0.5 cm x 7.5 cm = 3.75 cm x 2 surfaces = 7.5 cm x 25 reeds = 187.5 cm. To convert to inch's 187.5 / 2.8 = 66.96 inch's) which means the surface area is nearly 2.8 times greater.  

The total surface area = 66.96 + 24 = 90.96 inch's  

I am also hoping that the small width of the reeds will decrease the low frequency resonance and help boost harmonics across the length of the reeds.

I intend to trim each reed down to different lenghts as smaller reeds will resonate at higher frequencies and help counter the low frequency resonance. 

However a side effect maybe that the reeds act in the same way as a spring reverb as the sound will be carried down the reed, and reflect back of its boundary.

Thats all for now.

Testing continues.