Posted by: recordingsofnature | April 15, 2010

Wind screen experiments

In this post I will report on some investigation on a wind protection system. The general idea is to enclose the microphones with a thin fabric shield, e.g. the typical nylon stocking material. I was quite curious to see how different thin materials affect the sound transmission, especially for the higher frequencies. There should be at least to effects present; 1) a transmission coefficient of sound waves going through the fabric which is dependent of the frequency, and 2) reflections of sound waves when hitting the fabric (causing effects in the cavities).

The following garage tests were made.

The transmission test: An item to be tested (15 x 20 cm) was inserted in between the speaker and the microphone, 15 cm from the microphone. Distance from speaker to microphone was 70 cm. The two curves show the noise spectrum with and without the item inserted. The spectra are purely relative. The noise sent out from the speaker is not very white (my old white noise calibration seems to be quite helpless nowadays).

The reflection test: Here the item was placed 3-5 cm behind the microphone, which now was facing 90 degrees to the speaker. The two curves is a comparison of when the item is behind the microphone and when nothing is behind.

Tests with different types of materials:

1 layer stocking, flat and smooth type

1-layer stocking transmission reflection test

1-layer stocking transmission reflection test

2 layers stocking,  soft touch type

2-layer stocking transmission reflection test

2-layer stocking transmission reflection test

Wool – non woven fabric 4 mm thick

wool fabric transmission reflection test

wool fabric transmission reflection test

Heavy textile – woven fabric

heavy textile transmission reflection test

heavy textile transmission reflection test

Thin plastic film (soft polyethylen, ~7 micron thick)

thin plastic transmission reflection test

thin plastic transmission reflection test

Thicker plastic film (30 um thick)

thicker plastic transmission reflection test

thicker plastic transmission reflection test

The stocking materials have a very minute effect on the sound. Surprisingly, the two layered test had less effect than the 1-layered test.

Going to thicker materials, the wool fabric also showed good transmission/low reflection, however some HF effect is starting to be seen.

For all the rest, heavy textile and even the very thin plastic film, a high reflection and high blocking of the sound is observed.

Construction of the wind screen

Wire grill for wind shelter

Wire grill for wind shelter

I’m aiming for a system which can be mounted if needed and is easy to transport. A steel wire was folded in a square wave style (20 x 4.5 cm) and connected with electric tape.  The result is seen above. These structures are easy to mount on the sides of the dummy head by sticking the ends of the wire into the head.

Wire grill mounted on Dummy

Wire grill mounted on Dummy

A pair of stockings with the legs cut off can readily be mounted.

Final wind protection

Final wind protection. Considering a name change to E.T.

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

Categories

%d bloggers like this: