Posted by: recordingsofnature | March 13, 2010

Horn frequency pickup – Part 1

In this post I will present the results from the investigations of the connection between the frequency response and the horn shapes. This first part will show the results from the film roll horns.

A setup was made consisting of two microphones side by side with distance of 11 cm. Only one of the microphones would have a horn fitted. The other stayed clean. The next task was to get a white noise source. Noise produced by a speaker seems to be very sensitive to movements from side to side. The best alternative I could find was crunching a thin crispy plastic bag. This produces a quite reproducible noise ranging well above 20kHz and with a good spreading of the sound . The noise was produced appx 90 cm from the microphones.

The picture below shows the resulting frequency pattern measured when both microphones were clean. Post processing was easy in this case, -the frequency spectrum of the two channels was readily obtained using the old excellent CoolEdit Pro audio software.

This reference measurement curve shows that both microphones pickup the same pattern when they both are clean. The gallery below shows the results from various geometries, going from convex to concave, of the film roll.

Conclusion

I think the film roll horns show some interesting effects on the frequency pickup. The horn influences only frequencies above 4 kHz. Below that value the effect is very limited. Typically the horns produce a rise in frequencies from 5kHz to 11kHz. Where the peaks are found depends on the shape. I really cant figure out the full logic behind. I think the film rolls might be useful in situations where you need a HF rise, when recording on longer distances. With the modified frequency response there will also be a change of the directionality, normally into a more directional pattern (see later posts). For long distance recordings a higher directionality will be an advantage.

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Responses

  1. […] frequency pickup – Part 2 This post is a continuation of the previous Horn frequency pickup – Part 1 which described the results from the film roll horn. This post will present the frequency spectrum […]

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  2. […] 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 […]

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