Experience learns that if omnidirectional microphones are placed relatively far from the musical instruments that you want to record, the result sounds somewhat dull. This also applies to the Sonodore RCM-402. To solve this problem, Rens Heijnis developed a grid that boots the higher frequencies more than the lower ones; it can be considered an acoustical tone control.

The standard grid of the Sonodore RCM-402 (type PG-68) provides an almost flat frequency characteristic.

The PG-78 grid, on the other hand (made of titanium) shows a rise of the high frequencies with a peak at approximately 15 kHz and a gain of 3.5 dB (please refer to the graph below). These values should be added to the frequency characteristic of the Sonodore RCM-402 used in combination with the PG-78 grid. The increase of the high frequencies does not introduce any additional noise, which means that the signal-to-noise ratio even improves slightly when the PG-78 grid is being used.

The directional characteristic is slightly influenced by the PG-78:
from 5 to 10KHz the directional characteristic is a little better than it is with the standard grid (0.1-0.3dB); at 20kHz, the directional characteristic is slightly worse (depending on the angle: 0.1-1.5dB).

The PG-78 differs from the standard grid in height (7.8 mm compared to a 6.8 mm standard grid), it has no slots at the edge, and it has a slightly different tint(less shiny).