Posted by: recordingsofnature | March 15, 2010

Horn directionality

Beside the change of frequency response, the horn addons have a high influence of the directionality pattern of the microphones.

Directionality test setup
Setup for test of directionality

The human ear is equipped with a sophisticated horn/pinna geometry, which modifies the received frequencies according to the direction of the sound. Optimal reception is found right in front of the person. Directionality perception is very important for many animals. E.g. bats, cats, owls and lizards. There is a lot of inspiration to find in nature.

In order to investigave the directionality of the microphone horns, I attempted some direct measurements.

Setup

The setup was made using a speaker and a microphone (Earthworks QTC40 / QTC1) which could rotate. When rotating, the tip of the microphone stayed in the same center position. Distance between speaker and microphone was ~78 cm and SPL-A was 67 dB. It was very important to keep the microphone in the same position during rotation, since even very small displacements leads to changes of the high frequency pattern from the speaker.

I used a noise sequence which was optimized to produce approximately ‘white’ noise in the range of 500Hz to 35000Hz on the given speaker. As seen on the frequency curves this noise is not perfectly white. This is only due to the speaker, not the microphones which are flat from 4 – 40 kHz +/- 1 dB.

Having a dial disk indicating the angle of the microphone, and by following the second hand of a watch it was possible to make one rotation in one minute with the right speed. The final polar plots were made using CoolEdit Pro to produce a spectral view and then GIMP for converting this into polar coordinates. This polar plot give a nice view of frequency response with respect to the direction. The lowest frequencies are in the center, while the highest are in the outer ring. The plots show the relative frequency gain.

Results

The below charts show the directional behavior of the various horn addons.

Discussion of the charts will follow…

If you have ideas on how to interpret the results you are very welcome to leave a comment!

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Responses

  1. […] the directional testing method from the earlier post Horn directionality it is possible to get at good overview of the frequency response and directionality. Dummy head […]

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  2. […] has one side with flat endings and one with pointy endings (see also earlier post here, here and here) . In the middle, a film roll (Ø=13 mm) serves a fitting for the Earthworks microphone head (Ø=8 […]

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