Posted by: recordingsofnature | March 12, 2010

Horn addons

Since the QTC40’s are extremely omni directional and with a flat frequency response, I have played with the idea of adding some sort of acoustic horn to the ends of the microphones.  In this way, I hope to be able to add a bit of directionality and, depending of the application, a bit of presence or diffuse field rise. This might also allow to emulate the acoustic effects of the human ear , and be a way to produce natural sounding recordings.

Film roll horn addon

An analogue film roll can be used as a horn

It is possible to make efficient horns by use of simple materials.

Film roll type: It is basically a roll of plastic or paper. If the roll is not too tight it is possible to change the shape of the roll, going from highly concave to highly convex. I’m using two old old film roll (Fujicolor film 36 images, 25mm…). When rolled around a 8 mm rod, the outer diameter is about 19 mm.  With this addon, the microphones get a diameter comparable to normal condenser microphones. The smooth surface and perfect edges of the this type of film roll makes it very good to work with, compared to similar horns made of a roll of paper.

The shape of the horn can be set freely, however it will always have a symmetrical geometry.

Flat film roll horn

Flat film roll horn

Highly concave film roll horn

Highly concave film roll horn

Toothpick type: Another type of horn addon, which is a bit more advanced, is the toothpick horn. Here I’m using a bundle of round toothpicks. The inner part connecting to the microphone  is again made of film roll, but here only 2.5 mm thick. On the outside the toothpicks are packed and fixed using rubber bands. The total outer diameter is approximately 36 mm. The toothpicks have a pointy end and a flat end, and the length is 43 mm.

Toothstik horn

Wooden toothpick horn

Toothstick horn

Toothpick horn flat and pointy side

The good thing about this setup is the ability to freely choose the horn geometry. It can be concave, convex, symmetrical or non-symmetrical. The toothpicks have a pointy tip and a flat tip. Using the pointy tips side, the horn will have a diffusive surface. Using the flat ends side, the horn will have a more reflective surface.

Toothstick horn mounted on microphone

Toothpick horn mounted on microphone

The high degree of freedom is a bit of a challenge with this horn. In order to make good use of it, its important to use horn geometries which can be easily reproduced.



  1. […] Horn frequency pickup – Part 1 In this post I will present the results the investigations of the connection between the frequency pattern and the horn shapes. This first part will show the results from the film roll horns. […]


  2. […] the tests are made using a ø=30 mm film roll (constructed by 3 old 36 picture Afga films, see this post), which can be formed to in wide range of concave and convex shapes, which however always will be […]


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