Do It Yourself audio: Jecklin/Schneider disc!

11 Jan

First of all, happy new year for everyone! Hope everything’s going fine for you. It has been hectic back in Spain for holidays those last weeks, seeing friends and enjoying time as much as I could but also working my ass off to prepare University assignments for the next 2 weeks. I guess it’s time to get to it…

One of the things that I had left for when I was back home was recording my fellow friends and bandmembers of Sweet Q playing in our rehearsal room. And not recording them in the usual way, but in Surround! I’ll have to bring that tracks back to Salford University’s studios and produce a 5.1 mix where I can recreate the room so a listener can feel like he or she is just there listening them play. More technical details on the recording process and technique will come in the next post, in a few days.

While I was doodling about which microphone technique to use for the surround recording, I came to remember something that I always wanted to try and do myself: construct a Jecklin disc with my own materials! Let’s go to the first stop: what’s a Jecklin disc?

As it name says, it is just a disc that is placed between two separated microphones to recreate a natural stereo image that is convincing both when listening in headphones and in loudspeakers. It does so because it is a baffle, made of acoustically absorbent material that creates a shadow area at high frequencies between those microphones, such in a way that recreates more or less accurately the amplitude, time-difference and frequency response between the ears. Low frequencies don’t represent an obstacle to the disc due to their large wavelengths so they reach both microphones more or less at the same time. Difference comes with high frequencies: the disc is an obstacle to them, so that the sound source becomes directional at that point and one of the pair of microphones will capture it before the sound wave arrives to the other one, giving us the idea of localization of the source.

My own DIY Jecklin disc

There are lots of ways to construct a Jecklin disc, since it’s the cheapest and easiest Do-It-Yourself project out there for home recordists. The inner layer of the disc can be made from a lot of materials (plexiglas, vinyl discs glued together, a wood panel…). Mine was done glueing together three layers of carton with the same diameter. For the acoustically absorptive material on the sides of the disc, there are also lots of variations but it is very popular around internet forums to construct them with acoustic wool and then cover the whole disc with a lamb fleece cushion to further improve high frequency attenuation from one side to another.

Lamb fleece on a Jecklin disc

The original specifications given by Mr. Jürg Jecklin (inventor of this device) date from the 1970s, as he was trying to achieve an Optimal Stereo Signal (OSS), which gave name to this method of stereo recording. Under Jecklin’s first specifications the disc must be 30.5 cm in diameter and 2 cm thick, using two omnidirectional microphones at its sides just in the center, 16.5 centimeters apart from each other (to simulate the human head’s difference in arrival times ) and each pointing 20 degrees outside. He rectified these specifications some years later, as he thought the distance between microphones was too small and thus the stereo image too narrow. That’s why he thought of making a 35 cm diameter disc and placing the omni microphones at a distance of 36 microphones between them, this time with both parallel and facing directly to the front.

Lots of really good people at DIY tasks even drill small holes on the sides to mount the microphone holders and make room for the cables to go through a single tube that holds the disc. That’s pro, man. My poor Jecklin disc has been made with carton and acoustic material on the sides, and it will stand in place with a regular microphone stand fitted with a regular mic clip as we can see next…

My Jecklin disc on its stand

Another variation on this is the Schneider Disc which adds a semispehere at each side of the disc, in the center, to further improve the similarity with the human head’s absorption characteristics, making it more suitable for binaural recordings that are going to be played through headphones afterwards.

Schneider disc: the binaural variation of the Jecklin disc

I was thinking of further improving my primitive design, but I didn’t have time for that and my Jecklin disc has had to stay in Madrid, so I guess I’ll get back to the project when I get back again in April maybe. I’d have loved to make a recording with it and try if it’s working or not, but it’ll have to be next time… Next post will be talking about Surround recording and a particular mic technique that I chose to use. Stay tuned!

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One Response to “Do It Yourself audio: Jecklin/Schneider disc!”

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  1. Surround recording techniques: Double M/S and IRT Cross « Ruido Blanco by Jorge Polvorinos - January 17, 2012

    […] Ruido Blanco by Jorge Polvorinos The art of Audio Production and music enjoyment HomeAbout me ← Do It Yourself audio: Jecklin/Schneider disc! […]

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