Combining Microphones to Form Cardioid Pattern

In various product applications, it is often desirable to combine an omnidirectional microphone with a dipole microphone. With some basic software, users can then combine the two microphone outputs to create any type of polar pattern they desire, such as a cardioid. Ideally, both microphones would be perfectly aligned, enabling the creation of a perfect cardioid shape that remains consistent across all frequencies. However, in practice, due to physical limitations when integrating the microphones into a product, this is not possible. For example, if both sound ports of the dipole microphone are brought to the same surface using a V-gasket, as seen in AN-300, there might be a spacing of 10mm between the two dipole ports.

Furthermore, due to the physical nature of these components, it's not feasible to position the omnidirectional microphone directly atop the dipole microphone. Consequently, a gap exists between the sound port of the omnidirectional microphone and the two sound ports of the directional microphones.

Interestingly, specific relative positioning between the sound port of the omnidirectional microphone and the sound port of the dipole microphone yields superior results when attempting to create a cardioid pattern by combining their signals. The interactive GUI below offers the capability to adjust the placement of the omnidirectional microphone both horizontally and vertically, relative to the sound ports of the dipole microphone. You can also switch between different frequencies to see how the cardioid polar pattern changes as a function of frequency for different relative positions of the two microphones. As you will be able to see, the cardioid pattern maintains greater consistency across frequencies when the omnidirectional microphone’s sound port is placed directly on the y-axis, centered between the two dipole microphone sound ports, ensuring equidistance from both ports.

Interactive GUI Chart