DIY sphere stereo mic

[k brown]

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.

 

[k brown]

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.

https://www.idrive.com/idrive/sh/sh?k=o1a7e8w1k7

 

[ccaudle]

Image is over-wide; system was too close

It probably is an accurate representation of what it would sound like standing in that location.
Some people like the conductor view style of recording.

 

[k brown]

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.

 

[k brown]

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.)

 

[Gutbucket]

I realise this thread is 3-1/2 years old now, but just came across it, and the arrangement being discussed here is similar to some setups I use. Similarly, my original intent was the emulation of KFM360-like directionality control with the addition of fig-8's placed coincidently with each omni. I never ended up adding the fig-8's, but would still like to achieve both forward AND rearward-facing directional patterns. I have considered using cardioids or super/hypercardioids in place of fig-8 as you are doing here, except with one forward facing and the other rearward facing. However, I'd rather not have to use two additional mics coincident with each omni.

My question is if you ever tried to create a rearward-facing directional pattern via differential summing of the omni and the forward-facing directional mic? - That is to say, inverting polarity of the directional mic prior to summing in order to to subtract its output from that of the omni, such that upon careful balancing of the levels from the two a virtual polar pattern is produced that is directed toward the rear, with highly attenuated pickup toward the front?

To achieve sufficient attenuation in the forward-facing direction, I imagine it may be necessary to EQ match the response of both channels with regards to wavefront arrival from the front, in addition to careful level matching and differential summing. If the resulting response after that EQ match filtering is less than desirable, one could apply a second instance of EQ post sum.

Hope that makes sense and thanks for the time-warp

 

[k brown]

I realise this thread is 3-1/2 years old now, but just came across it, and the arrangement being discussed here is similar to some setups I use. Similarly, my original intent was the emulation of KFM360-like directionality control with the addition of fig-8's placed coincidently with each omni. I never ended up adding the fig-8's, but would still like to achieve both forward AND rearward-facing directional patterns. I have considered using cardioids or super/hypercardioids in place of fig-8 as you are doing here, except with one forward facing and the other rearward facing. However, I'd rather not have to use two additional mics coincident with each omni.

My question is if you ever tried to create a rearward-facing directional pattern via differential summing of the omni and the forward-facing directional mic? - That is to say, inverting polarity of the directional mic prior to summing in order to to subtract its output from that of the omni, such that upon careful balancing of the levels from the two a virtual polar pattern is produced that is directed toward the rear, with highly attenuated pickup toward the front?

To achieve sufficient attenuation in the forward-facing direction, I imagine it may be necessary to EQ match the response of both channels with regards to wavefront arrival from the front, in addition to careful level matching and differential summing. If the resulting response after that EQ match filtering is less than desirable, one could apply a second instance of EQ post sum.

Hope that makes sense and thanks for the time-warp

No, I haven't tried it, but if you do please post the results here!

 

[MidnightArrakis]

I realise this thread is 3-1/2 years old now, but just came across it, and the arrangement being discussed here is similar to some setups I use. Similarly, my original intent was the emulation of KFM360-like directionality control with the addition of fig-8's placed coincidently with each omni. I never ended up adding the fig-8's, but would still like to achieve both forward AND rearward-facing directional patterns. I have considered using cardioids or super/hypercardioids in place of fig-8 as you are doing here, except with one forward facing and the other rearward facing. However, I'd rather not have to use two additional mics coincident with each omni.

My question is if you ever tried to create a rearward-facing directional pattern via differential summing of the omni and the forward-facing directional mic? - That is to say, inverting polarity of the directional mic prior to summing in order to to subtract its output from that of the omni, such that upon careful balancing of the levels from the two a virtual polar pattern is produced that is directed toward the rear, with highly attenuated pickup toward the front?

To achieve sufficient attenuation in the forward-facing direction, I imagine it may be necessary to EQ match the response of both channels with regards to wavefront arrival from the front, in addition to careful level matching and differential summing. If the resulting response after that EQ match filtering is less than desirable, one could apply a second instance of EQ post sum.

Hope that makes sense and thanks for the time-warp

>> Way back during the mid-1970's, I used to do "LIVE" recordings of jazz-bands and symphony orchestra's using the SENNHEISER "MKE 2002" Triaxial Binaural Microphone System and achieving astounding and unbelievable aural results!!! See below:

>> SENNHEISER MKE-2002 Triaxial Binaural Microphone:


This microphone system not only picked-up and recorded "High-Fidelity" audio, but it also picked-up and recorded an amazing amount of very specific "directional audio" details. As an example, one of the jazz-bands I had recorded ("LIVE" to a CROWN SX-722 half-track stereo reel-to-reel tape-recorder), the band was on-stage about 15-feet in front of me, while I was setup on a 4-foot high raised podium-section directly in front of the band.

With me being on this 4-foot high podium-section, there were several chairs placed directly onto the dance-floor below me and along its wall. Behind me was the separate seating area where people could sit and enjoy a meal, while being able to still see the band, but not be bothered by the dancing crowd. The entrance to this nightclub was 20-feet or so from me, but at a 45-degree angle to my left. The bar and cash register were about 20-feet or so away from me, but around a 30-degree angle on my right. I mention all of this in order to provide you with a "hint" that I had at least 5 different audio signals and angles coming at me from where I was positioned on this raised podium-section.

Playing the recording back on a pair of SENNHEISER "Open-Aire" headphones was jaw-dropping!!! However, I did embellish the audio playback by adding in some low-end that headphones simply cannot reproduce.....no matter what. And, what I had done was this.....I split the "Tape-Out" stereo audio with one feed going to a CROWN D-60 power-amplifier to drive the headphones. The other audio-split first went to a CROWN VFX-2 electronic crossover where I took just the LOW-END OUT signal that only had 100Hz and below and that then went to a BOSE 1800 Power Amplifier that drove a pair of JBL 4320 Studio Monitors.....that I had disconnected the high-frequency driver from. Ya got all of that now???.....

So.....when you put the headphones on and adjusted the volumes "just right".....not only could you very clearly hear the band performing just as though they were right there in front of you, but you could also literally "feel" the kick-drum against you coming from the JBL's!!! In addition, the audio playing within your head had all of the "spatiality" within it as though you were there sitting right there in the nightclub!!! Not only that, but.....you could literally "hear and differentiate the location" of people laughing >> IN FRONT OF AND DOWN BELOW YOU << like.....coming from below your chin!!! That was from the people sitting in the chairs on the dance-floor down below me!!!

You could hear the obnoxious and kind of loud -- CR-R-R-E-E-E-E-A-K-K-K!!! -- of the entrance door as people came in and left and the sound was DEFINITELY at a 45-degree angle to your left!!! Other laughter and guffaws would fill your head and you would instinctively -- turn-around -- to see what's going on!!! THAT laughter was coming from the people sitting at the tables located behind me!!! And, finally.....there was the -- CHA-CHING!!! - CHA-CHING!!! -- coming from the cash-register.....located at a 30-degree angle off to your right!!! In other words.....

>> AS FAR AS YOUR BRAIN WAS CONCERNED.....YOU WERE RIGHT THERE SITTING IN THE NIGHTCLUB AS THOUGH YOU WERE ACTUALLY THERE!!! <<

You had "true-to-life" audio reproduction in your ears, with all of the various directional audio signals coming at you from their respective directions and -- NOT -- just "Left/Right Stereo"!!! Then, you also had the -- THUMP & RUMBLE -- of the kick-drum and the stand-up bass rattling you, just as though you were actually there listening to the band itself, thanks to the JBL 15" studio woofers!!! I'm telling ya.....SUCH AN AMAZING SOUNDING RECORDING AND ACTUAL PHYSICAL PLAYBACK EXPERIENCE!!!

Anyway.....that's my humble contribution!!!

/

>> CROWN SX722 Tape Recorder:


>> CROWN VFX-2 Electronic Crossover:


>> BOSE 1800 Power Amplifier:


>> CROWN D60 Power Amplifier:


>> JBL 4320 Studio Monitor (Used only the woofer. High-Frequency Driver was disconnected):


>> SENNHEISER "Open-Air" Headphones:


/

 

[k brown]

>> Way back during the mid-1970's, I used to do "LIVE" recordings of jazz-bands and symphony orchestra's using the SENNHEISER "MKE 2002" Triaxial Binaural Microphone System and achieving astounding and unbelievable aural results!!! See below:

>> SENNHEISER MKE-2002 Triaxial Binaural Microphone:
View attachment 146040

This microphone system not only picked-up and recorded "High-Fidelity" audio, but it also picked-up and recorded an amazing amount of very specific "directional audio" details. As an example, one of the jazz-bands I had recorded ("LIVE" to a CROWN SX-722 half-track stereo reel-to-reel tape-recorder), the band was on-stage about 15-feet in front of me, while I was setup on a 4-foot high raised podium-section directly in front of the band.

With me being on this 4-foot high podium-section, there were several chairs placed directly onto the dance-floor below me and along its wall. Behind me was the separate seating area where people could sit and enjoy a meal, while being able to still see the band, but not be bothered by the dancing crowd. The entrance to this nightclub was 20-feet or so from me, but at a 45-degree angle to my left. The bar and cash register were about 20-feet or so away from me, but around a 30-degree angle on my right. I mention all of this in order to provide you with a "hint" that I had at least 5 different audio signals and angles coming at me from where I was positioned on this raised podium-section.

Playing the recording back on a pair of SENNHEISER "Open-Aire" headphones was jaw-dropping!!! However, I did embellish the audio playback by adding in some low-end that headphones simply cannot reproduce.....no matter what. And, what I had done was this.....I split the "Tape-Out" stereo audio with one feed going to a CROWN D-60 power-amplifier to drive the headphones. The other audio-split first went to a CROWN VFX-2 electronic crossover where I took just the LOW-END OUT signal that only had 100Hz and below and that then went to a BOSE 1800 Power Amplifier that drove a pair of JBL 4320 Studio Monitors.....that I had disconnected the high-frequency driver from. Ya got all of that now???.....

So.....when you put the headphones on and adjusted the volumes "just right".....not only could you very clearly hear the band performing just as though they were right there in front of you, but you could also literally "feel" the kick-drum against you coming from the JBL's!!! In addition, the audio playing within your head had all of the "spatiality" within it as though you were there sitting right there in the nightclub!!! Not only that, but.....you could literally "hear and differentiate the location" of people laughing >> IN FRONT OF AND DOWN BELOW YOU << like.....coming from below your chin!!! That was from the people sitting in the chairs on the dance-floor down below me!!!

You could hear the obnoxious and kind of loud -- CR-R-R-E-E-E-E-A-K-K-K!!! -- of the entrance door as people came in and left and the sound was DEFINITELY at a 45-degree angle to your left!!! Other laughter and guffaws would fill your head and you would instinctively -- turn-around -- to see what's going on!!! THAT laughter was coming from the people sitting at the tables located behind me!!! And, finally.....there was the -- CHA-CHING!!! - CHA-CHING!!! -- coming from the cash-register.....located at a 30-degree angle off to your right!!! In other words.....

>> AS FAR AS YOUR BRAIN WAS CONCERNED.....YOU WERE RIGHT THERE SITTING IN THE NIGHTCLUB AS THOUGH YOU WERE ACTUALLY THERE!!! <<

You had "true-to-life" audio reproduction in your ears, with all of the various directional audio signals coming at you from their respective directions and -- NOT -- just "Left/Right Stereo"!!! Then, you also had the -- THUMP & RUMBLE -- of the kick-drum and the stand-up bass rattling you, just as though you were actually there listening to the band itself, thanks to the JBL 15" studio woofers!!! I'm telling ya.....SUCH AN AMAZING SOUNDING RECORDING AND ACTUAL PHYSICAL PLAYBACK EXPERIENCE!!!

Anyway.....that's my humble contribution!!!

/

>> CROWN SX722 Tape Recorder:
View attachment 146054
>> BOSE 1800 Power Amplifier:
View attachment 146049

>> CROWN D60 Power Amplifier:
View attachment 146050

>> JBL 4320 Studio Monitor (Used only the woofer. High-Frequency Driver was disconnected):
View attachment 146052

>> SENNHEISER "Open-Air" Headphones:
View attachment 146056

/

Yes, binaural is awesome, but I don't see what this has to do with the post you are replying to (directionality conrtrol of a sphere mic).

 

[k brown]

I realise this thread is 3-1/2 years old now, but just came across it, and the arrangement being discussed here is similar to some setups I use. Similarly, my original intent was the emulation of KFM360-like directionality control with the addition of fig-8's placed coincidently with each omni. I never ended up adding the fig-8's, but would still like to achieve both forward AND rearward-facing directional patterns. I have considered using cardioids or super/hypercardioids in place of fig-8 as you are doing here, except with one forward facing and the other rearward facing. However, I'd rather not have to use two additional mics coincident with each omni.

My question is if you ever tried to create a rearward-facing directional pattern via differential summing of the omni and the forward-facing directional mic? - That is to say, inverting polarity of the directional mic prior to summing in order to to subtract its output from that of the omni, such that upon careful balancing of the levels from the two a virtual polar pattern is produced that is directed toward the rear, with highly attenuated pickup toward the front?

To achieve sufficient attenuation in the forward-facing direction, I imagine it may be necessary to EQ match the response of both channels with regards to wavefront arrival from the front, in addition to careful level matching and differential summing. If the resulting response after that EQ match filtering is less than desirable, one could apply a second instance of EQ post sum.

Hope that makes sense and thanks for the time-warp

There may be some useful info in this thread: https://groupdiy.com/threads/making...ni-and-a-cardioid-capsule.87941/#post-1157874

Same principals would apply whether there's a sphere between the mics or not.

I assume you were interested in a sphere mic with directional control, not an actual surround mic like the KFM 360.

 

[MidnightArrakis]

Yes, binaural is awesome, but I don't see what this has to do with the post you are replying to (directionality conrtrol of a sphere mic).

[what this has to do with the post you are replying to] -- I seem to remember that you are a "Party-Pooper" in some other threads from last year. I guess I need to keep an eye-out for your screen-name in any threads I visit and stay far away from YOU!!!.....

I merely provided my actual experience using this particular binaural microphone because I occasionally read comments from other budding recordists who believe that you cannot obtain either a high-quality audio recording and/or any type of good "stereo" sound when using a binaural microphone. I figured that since there is a high likelihood that someone like that may end up reading this thread for whatever reason, I just thought I would include my actual true-to-life recording experience here in hopes that someone else may want to try it for themselves and then also experience their own amazement as I did 40+ years ago!!! GEE!!! I am so sorry that you are so easily offended. It must be awful being so dismal all of the time.

/

 

[k brown]

[what this has to do with the post you are replying to] -- I seem to remember that you are a "Party-Pooper" in some other threads from last year. I guess I need to keep an eye-out for your screen-name in any threads I visit and stay far away from YOU!!!.....

I merely provided my actual experience using this particular binaural microphone because I occasionally read comments from other budding recordists who believe that you cannot obtain either a high-quality audio recording and/or any type of good "stereo" sound when using a binaural microphone. I figured that since there is a high likelihood that someone like that may end up reading this thread for whatever reason, I just thought I would include my actual true-to-life recording experience here in hopes that someone else may want to try it for themselves and then also experience their own amazement as I did 40+ years ago!!! GEE!!! I am so sorry that you are so easily offended. It must be awful being so dismal all of the time.

/

I made no objection about responding in this thread; my point was that you replied to a specific post that was not about binaural in general, but a specific question about controlling directionality of a sphere mic, and your reply had nothing to do with that - hence the question.

Sincerely, k brown (pooping on parties since 1955).

 

[Gutbucket]

@k brown-
Thanks for the link to the other thread. I'm well versed with the underlying Mid/Side / Ambisonics techniques using sum/difference processing and know how to go about doing this from a technical standpoint. I'm asking because I'm curious to hear about the real world experience of others concerning how well it actually worked for them when subtracting the output of a cardioid from a coincidently placed level-matched omni in order to form a cardioid-ish pattern facing the opposite direction as the cardioid. In ambisonic arrangements output of all capsules need to be closely matched for the summing to work correctly, else the virtual patterns and responses are a mess. In these simpler arrangements summing on-axis is easy enough, but differential summing to form a virtual pattern facing the opposite direction seems closer to getting the trickier ambisonic arrangements working correctly.

Why and how am I using this?
I use various 4 to 8 channel microphone arrays in ways that provide both stereo mix down output and multichannel "surround" playback. Some of the 4-channel arrangements use a baffle which is non-spherical, but the microphone arrangement is essentially the same, only doubled with the inclusion of forward and backward-facing omnis in addition to Left and Right facing. Conceptually, the addition of four fig-8s placed coincidently with the four existing omnis will provide a lot of mix-down / routing flexibility via the ability to derive virtual polar patterns with various directionalities using such an arrangement, while capping the total channel count at 8 channels. The front and back facing omnis (made semi-directional by the sphere) become traditional M/S pairs, with the left and right facing omnis operating like the KFM360.

My current 8 channel arrangements use increased spacing and microphone directivity rather than omnis around a baffle. Some of those use a Mid/Side microphone in the center surrounded by four near-spaced supercardioid microphones (two of them forming a forward-facing triplet with the center M/S mic, two rearward facing), along with two wide-spaced omnis about 2 meters apart.


@Midnight Arrakis-
I relate! These recordings produce an incredible "you are there" experience. With multichannel playback they are truly immersive and 360-degree directional, acting as an acoustic "teleportation time machine" of sorts. I have a recording friend who uses the Sennheiser binaural head like yourself. He informs me that placing the head on the storage box (as shown in your photo) is intended to emulate the human torso and its resonance. I understand the microphone's can also be worn on one's own head. Fun stuff.

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