DIY sphere stereo mic

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k brown

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Sphere has developed into a system.

- Fitting at top for a 4.5' carbon fibre bar for wide AB omnis to add decorrelated 'envelopement' to the very sharp imaging from the sphere - especially helpful for adding 'size' and drama to the sound for loudspeaker reproduction. Being decorrelated and a bit delayed by being several inches above the sphere capsules, they don't shift the accurate localization for headphone repro.

- In instances where it isn't practical, or there's not sufficient time to find the optimum placement in the room, hypercardioids can be added just above the imbedded omnis to allow KFM 360-style pattern control - just one pattern (full fig 8) shy of the full range obtainable from the KFM 360: omni > subcardioid > cardioid > supercardioid > hypercardioid, by mixing the two pairs together. I've altered the KFM 360 pattern graphic (shown in a previous post) to illustrate stereo patterns achieved with the external hypers.

- For less critical applications, the ATM10a are very nice; for more demanding situations, higher quality mics can be suspended from the top bar, pointing straight up. This actually has an advantage over imbedded capsules in that sources in a full circle around the sphere arrive at the same angle to the capsules. Most SDC omnis with a top lift are quite flat at 90 degrees. Just needs diffuse field EQ in post.
 

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k brown

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Got the system in front of an orch rehearsal.

ATM10a in the sphere. AT853 omnis on the AB bar (delayed 2.5ms). AB mixed about -6dB. A bit of good ole' AU Matrix Reverb (band pass filtered) to 'stretch the tail' - room somewhat small and quite dry. Preamps/recorder was Tascam DR-70D.

Image is over-wide; system was too close. Check out the distance Jerry Bruck used with his KFM 360 sphere (photo below on the right).

Next time, Rode NT omnis in the sphere, and Okt MK-012s as the wide AB.

 

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k brown

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Quite so - the sphere hears just what one would hear standing in the same spot. On headphones, it's only less realistic than a binaural head in that there is no front/back distinction - but then not very many headphones resolve that distinction very well anyway.
 
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k brown

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Joined
Jul 7, 2021
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422
Location
San Francisco
Improved (in appearance, especially) attachment of external hypers for variable pattern.

'Chains' of silicone hair elastics (these things are insanely handy https://www.amazon.com/Scunci-No-Sl...dp/B00HSSBUJ2/ref=psdc_11058071_t2_B00UXNHQ92) anchored to deck screws on opposite sides of the sphere.

The 'grabby-ness' of the Plastidip coating keeps them from sliding around.

(Now I just need to order a pack of clear ones.)
 

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