The natural stone material used is serpentinite , a material that has an exceptionally high flexural strength on the one hand and very high vibration properties on the other. The gramorimba has 4 octaves from f - f4 and is tuned both fundamental and overtone. Rudolf Fritsche learned how to tune the individual stones from the Basel musician Lukas Rohner. The gramorimba has a pedal like a piano in order to be able to dampen the length of the notes.
The GramoEi is made of the same material as the Gramorimba. It is approx. 60 cm high and carved out of a solid stone block. Standing lamellae are created by making the milled groove. With wet hands you can make these slats vibrate and thus create a spherical sound. The GramoGong is made of the same material. The gong has a diameter of 135 cm with a hole of 45 cm, on the outside edge it is 2 cm thick and at the hole cutout 1.2 cm. The gong is ground convex on the back.
- Mineralischer Widerhall , Schweizer Musikzeitung, December 4, 2013