Posted by: recordingsofnature | July 22, 2010

Directionality response of inclined angle horns

This post describes some measurements made on a set of different horn geometries. This time the horns, made of a bundle of toothpicks, have an inclined angle and is not symmetrical. The frequency response was measured as a function of the angle of incoming noise, -90 to +90 degrees. The microphone horn tested here the typical ones used in the up to now posted nature recordings. However here the tests have been made without the dummy head.

top view microphone horn test

top view microphone horn test

Setup

The measurements were made with one microphone with a horn fitted, and another microphone close just clean.

Setup for microphone horn test

Setup for microphone horn test

In the tests the effect of quite small adjustments of the microphones position in the horn was investigated. The general form of the horn is a cylinder with inclined end-planes. The toothpick horn 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 mm). The exact position of the microphone end and the film roll has a clear effect on the recorded sound.

Noise was generated by crunching a thin crispy plastic bag at 1 meters distance and in angles of -90, -45, 0, +45 and +90 degrees. By comparing the received signal in the two microphones, the effect of the horn can be evaluated.

Results

Details on the precise test setups can be found in the posters below:

Discussion

The green curve shows the spectrum of the noise from the plastic bag, which has a typical envelope. The red curve shows the response from the microphone with a horn fitted. The difference between the two curves is the effect of the horn.

The horns have a clear effect on the sound down to 2-3 kHz. Adjusting the position of the film roll and microphone end has a clear effect on the range 5 kHz and up.

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