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Author Topic: Ambient sound & Jecklin disc for quad?  (Read 2397 times)

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Offline m326

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Ambient sound & Jecklin disc for quad?
« on: November 21, 2020, 06:47:50 AM »
Hi all, I know what end result I want - but I don't know how to get there.

Let me explain.. I like relaxation recordings, especially nature based ones but often the music puts me off. I want to be able to record my own nature sounds with the idea of having random bird calls from various places in the room, a rustling in the leaves here and there, an animal scampering... you get the idea. Quiet and peaceful, no music & no dogs barking!

With my Dr100 I have made some progress with dual stereo recordings, Reaper is set up for 5.1 audio - but only using 4 channels. The resulting .wav file is then converted to .mp4 which then gets copied to my NAS and played through Plex to my Sonos PlayBar & 2 surround speakers. Not an ideal process or setup for outputting small signals. I would really like to have more discreet speakers placed further apart, any opinions or alternative (budget conscious) hardware recommendations on this?

I have made a Jeckin Disc which seems to work well for me with good stereo separation using a pair of EM172 omni's.

This Christmas I'm getting a Zoom F6 recorder and am contemplating getting a set of 4 matched EM272 XLR microphones. Beings the Jecklin Disc was successful, has anyone tried to make a quad version of it? It seems to be an obvious thing to try - or are there better solutions out there?
I would think that, looking downwards onto the discs & seeing a cross, the microphones would need to be located much more centrally and perhaps because of this, the discs need not be so big? In my current disc, the mic supports are removable which means it packs flat, a quad version would be much bulkier and wind noise protection will add further to this, perhaps reducing portability.

Thanks in advance for your comments and help, I'm fairly new to the audio scene.. technical wavelengths go straight through my skull  ;)

Offline heathen

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Re: Ambient sound & Jecklin disc for quad?
« Reply #1 on: November 21, 2020, 11:22:28 AM »
It seems like you're asking about playback setups and recording setups.  I'm pretty much just a two channel stereo guy when it comes to playback so I can't be much help there.  With regard to the recording setup, have you considered an ambisonic microphone?  If the Zoom F6 has an ambisonic mode like the F8, then something like the Sennheiser ambisonic mic would be a nice fit because the Zoom ambisonic mode is specifically designed to work with the Sennheiser mic ( it will also work with other ambisonic mics, though some mics like the Core Sound TetraMic don't let you take full advantage of the Zoom ambisonic mode capabilities).

For multiple mic setups, maybe look into things like IRT Cross and other arrays specifically intended for capturing ambience.
Mics: AT4050ST | AT4031 | AT853 (C/SC) | Line Audio CM3 | Sennheiser e614 | Sennheiser MKE2 | DPA 4061 | CA-14 omni Pres: CA9200 | DPA d:vice Decks: Zoom F8 | Roland R-05

Offline m326

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Re: Ambient sound & Jecklin disc for quad?
« Reply #2 on: November 22, 2020, 04:01:29 AM »
Thanks for your reply heathen.
Although ideal, the Sennheiser mic is way out of my budget. The IRT cross idea is something I will research.. but again cost of mics for what is an occasional hobby idea would be a limiting factor, hence my more DIY approach.

Offline kuba e

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Re: Ambient sound & Jecklin disc for quad?
« Reply #3 on: November 22, 2020, 09:53:47 AM »
I like primo Em172. I think they are great for nature recordings. I don't know if you have another use for FX6. If you only use it with Em172, maybe a Tascam Dr2d + Church audio preamp would suffice.

It is good idea to use four baffled omnis.  EDIT: Cross baffle with omnis in the corners is good idea. It should be similar to four coincident directional microphones. Also when the omni is placed in a corner, the direct/reverberant sound ratio increase and also the S/N ratio increase (the directivity and the improvement is only for frequencies where the baffle works). It's nicely explained by Gutbucket here https://taperssection.com/index.php?topic=186619.0
A baffle as a four sides box should be also good. When you use a box, you introduce a time difference into the signals.
The smaller the baffle, the higher frequencies will get around it. The larger the baffle, the lower frequencies are blocked and also, in the case of a box, the greater the time difference.

Wait if Gutbucket joins. He experimented with 4 baffled microphones and also his oddball technique is very similar to it. I think he is also one of the few here who has done recordings for surround playback. Once, when I was inspired by Gutbucket and his oddball microphone technique, I pinned 4 microphones on me - a pair on the my shoulders, one center forward, one center backward. It was at a concert. But I wasn't in a good place, the microphones on the shoulders hadn't enough separation to create space for mixing in the center microphones (I am mixing only for stereo playback). But I would like to try 4 baffled microphones again. I need to get some bigger inconspicuous box.

Oddball microphone technique:https://taperssection.com/index.php?topic=191953.0
I can't find it now, but I know that someone sent a picture from a recording studio - a large box of transparent plastic that served as a baffle, with musicians sitting around.
« Last Edit: November 23, 2020, 07:26:59 AM by kuba e »

Offline m326

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Re: Ambient sound & Jecklin disc for quad?
« Reply #4 on: November 25, 2020, 04:32:07 AM »
Seems the EM172 stocks are depleted now, EM272 being an almost direct replacement.
I originally bought a Clippy EM172 stereo pair with 3.5mm jack plug and was quite impressed by them so when I bought my DR100 I got a XLR pair of 172's with XLR.. another improvement in sound.
The F6 has been purchased and wrapped for Christmas - so no changing that now. Must admit though, I'm a bit concerned about the reports that say the DR100 has quieter preamps.

Thanks for the info and links, I'm trying to take it all in.
Over the holiday period I'm going to make and try a cross baffle, I have all I need for it but I need to think of a way to make it fold flat for more portability.. 3D printer to the rescue no doubt.

Offline kuba e

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Re: Ambient sound & Jecklin disc for quad?
« Reply #5 on: November 25, 2020, 10:18:10 AM »
I mixed two things together. The baffle may be rigid - 'boundary microphone' and the baffle may be damping - 'Jecklin disc'.

'Boundary microphones' in corners of a cross.  Edit: I thought more about it. It should work. The cross should be 90 deg (theoretically, problems arise at angles lower than 45 deg) and the microphones have to be placed exactly in the corners to avoid unwanted reflections. It's interesting. When I find plexiglass, I'll try it. A rigid baffle as a box or sphere is also fine. In all cases, the boundary microphones must be placed directly on the baffle surface to prevent unwanted reflections. And the rule of amplification and the improvement of the direct/reverberant ratio should apply to the frequencies at which the baffle works. Which can be a disadvantage when the baffle size is small. Because only the high frequencies are amplified, the low frequencies remain unamplified.

'Jecklin disc' as a cross. The material of the baffle must dampen a lot to prevent reflections. Then you don't have to put microphones right in the corners, they can be in the space between the baffle. The farther from the baffle, the smaller its influence. I think Jecklin discs in the cross is fine.

The third possibility is that you install the omnis in spheres, this will increase their directionality. When you have individual omnis in separate spheres, you can easily place them in space.
https://schoeps.de/en/products/accessories/filters-pads/ka-40.html
https://reverb.com/item/28102645-schoeps-kfm6-sphere-stereo-microphone

For a basic idea of ​​what frequency the baffle will affect, it is possible to use an approximate relationship - the baffle will affect sound wavelengths that are as long as the baffle dimension and shorter. E.g. a baffle of 60 cm will start to affect frequencies from 570Hz (wavelength 60 cm) and higher.

I am writing here what I have read here on the forum. Try waiting for someone who has experience with it to advise more.

You have a very nice present for Christmas!
« Last Edit: December 01, 2020, 01:05:44 PM by kuba e »

Offline Gutbucket

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Re: Ambient sound & Jecklin disc for quad?
« Reply #6 on: February 08, 2021, 12:06:11 PM »
I must've overlooked this thread until today. Its right up my alley. I do a lot of suuround recording and I agree with most of what has been posted previously. Following are a few thoughts and clarifications from my experience-

First bear with me through a breif philosophical underpinning, as I think a rudemenatry inderstanding at that level really helps to point the way at each practical step.

I consider live music performance and environmental ambient recording, via either 2-channel stereo or multichannel surround, as all being rooted in capturing the sound arriving directly from the sourc(es) and the indirect diffuse sound that arrives from all directions. Those are the basic things that must be in balance. With 2-channel recording we generally arrange things to achieve a good set balance of those things via the recording location, microphone pickup pattern, stereo mic'ing cofiguration, etc. With a multichannel microphone arrangement, we can set things up in ways that achieve a less compromised pickup of each of those aspects and allow a degree of freedom over how they are combined for 2-channel reproduction, or manipulated for discrete multichannel playback,  after the initial recording was made.

Practical things-
I find good capture of surrounding ambience generally requires space between the microphones, and that the direct sound component from each individual source is not being picked up by all microphones (there is minimal direct sound in at least some of the other channels). That means some spacing combined with some directionality imparted by microphone directivity or baffling.

Ambisonic mics are compact and convenient and a 1st order ambisonic microphone is great at capturing direct sound from all directions and retaining directional info. But they are not great at conveying the diffuse ambience that gives one the  distictive realistic feeling of "being there" immersed in the sound environment.  You need some space between the microphones for that.  Sure folks use them for ambient recording, but that is mostly about convenience and/or VR compatibility, rather than representing an optimal approach

The IRT cross is a great starting point for that and what I'd recommend if using 4 cardiods or supercards for the type of ambient recording you are doing. If using 4 omnis, use a similar spacing to IRT cross with baffles to produce directionality. Mounting to the surfaces of a box works well. Mounting to four sides of your torso does too. A cross-shaped intersecting Jecklin disk will work, as will two of them separated by a fore/aft baffle. They may provide sharper direct sound imaging, but a box is simpler and effective. You essentially want sufficient directionality/spacing between each adjacent pair of microphones similar to that of a 2-channel recording atrangement. That means any two opposing channels in a 4-channel ambient pickup arrangement is angled twice as wide and spaced twice as much as a typical 2-channel arrangement. With that in mind, using 4 omnis, I'd use a box before choosing a sufficiently large beachball sized spherical or vertical round column baffle, but use what you have available.

For ambient recordings an L,R,Ls,Rs (quad format) recording and reproduction works well. For things like music where there is a definite forward direction I prefer to turn that 45 degrees (L,C,R,S), which achieves better front/back differentation,  imaging across the front, and keeps the loud front arriving sound in the front. For LRCS playback it helps to distribute the S channel to as many surround speakers as possible.
musical volition > vibrations > voltages > numeric values > voltages > vibrations> virtual teleportation time-machine experience
Better recording made easy - >>Improved PAS table<< | Made excellent- >>click here to download the Oddball Microphone Technique illustrated PDF booklet<< (note: This is a 1st draft, now several years old and in need of revision!  Stay tuned)

Offline Gutbucket

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Re: Ambient sound & Jecklin disc for quad?
« Reply #7 on: February 08, 2021, 12:25:07 PM »
Any of the essentially symmetric 4 channel microphone arrangements above are picking up both the direct sound from a specific direction as well as diffuse sound from all directions. For sources in front the C channel contains the primary direct sound, with a bit less in L,R, and the the S channel exclusive of the direct sound as much as possible, where as the ambient component of that sound is picked up bu all channels.  For any source located behind the recording position it is the opposite situation. And the same goes for sources to the far left and right.

Playback of these recordings can be really impressive. I've recorded frog choruses in the back yard and then immediately played them back in surround inside the house and it was astoundingly transporting. Walked around the block with the windows open and from all sides it souned like the house was filled with frogs. Walking the street in back the actual frogs were stimulated to join in, creating a super croaker chorus. Good fun
musical volition > vibrations > voltages > numeric values > voltages > vibrations> virtual teleportation time-machine experience
Better recording made easy - >>Improved PAS table<< | Made excellent- >>click here to download the Oddball Microphone Technique illustrated PDF booklet<< (note: This is a 1st draft, now several years old and in need of revision!  Stay tuned)

Offline kuba e

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Re: Ambient sound & Jecklin disc for quad?
« Reply #8 on: February 11, 2021, 05:40:19 PM »
I will also have to get surround playback one day. The frog concert must be enjoyable.

Do you know how the boundary layer behaves on the sphere? Is it the same as on the flat surface?
I like the boundary layer theory. Acoustic boundary layer reminds me of the boundary layer in aerodynamics. In aerodynamics, it is explained by the boundary layer why objects have resistance in a fluid stream. The resistance is determined by a thickness of the boundary layer. The aerodynamic boundary layer is also separated from object at high velocity. This could be compared to an "acoustic shadow". Although one is a wave, the other a flow, there may be some distant resemblance.

It seems useful that a boundary layer microphone amplifies direct sounds over diffuse sounds. This would be good for audience recording. It is a pity that a large surface is needed for this. All those boundary microphones that are on a smaller board have 6db drop for lower frequencies. There are probably also problems with the polar pattern in this transition.

Offline DSatz

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Re: Ambient sound & Jecklin disc for quad?
« Reply #9 on: February 11, 2021, 11:03:08 PM »
kuba e, exactly so--the surface that a boundary microphone is placed on has to be large w/r/t the wavelength of the lowest frequency that you hope to capture with it, or else you'll just get a 6 dB shelving rolloff somewhere in the range. Crown used to show their PZMs on music stands; PZMs on piano lids were commonplace at one time; et cetera ad nauseam.
music > microphones > a recorder of some sort

Offline Gutbucket

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Re: Ambient sound & Jecklin disc for quad?
« Reply #10 on: February 12, 2021, 10:47:53 AM »
kuba e, I certainly see parallels between aerodynamic and acoustic boundary phenomena, although I dont really know how truely analogous they are or how far the analogy holds.

Similar to what you describe, at the acoustic boundary surface above the corner frequency determined by the area of the bounary there is no velocity component and only pressure component w/r/t a wave front arriving perpendicular to the surface. There will be incresing velocity component for acoustic wavefronts as they ecounter the boundary at angles approaching parallel rather than perpendicular.

A sphere or vertical column boundary will produce the smoothest polar response above the corner frequency determined by the area of the boundary, while a flat sided box with corners will make for a somewhat tighter pattern in each direction, and a 4-pointed star shaped boundary tighter still, each with increasing boundary gain.  If the boundary is acoustically absorbent across that frequency range, the polar modification remains but there is less boundary gain.

I've made lots of recordings using 4 omnis in a cross formation without any baffles or boundaries (other than using 2" sphere attacments on each microphone), increasing the spacing to about a meter (3') between oposite sides to compensate. The result is somewhat less specific directionality of the direct sound but a very enveloping ambient sound that might work very well for the OP's stated intent. It is certainly practically easier to setup and transport without use of a central boundary or baffles.. unless you are the baffle.. or if their happens to be something already in place that can be used as suitable boundary/baffle such as a column or big tree trunk or rock or something.
musical volition > vibrations > voltages > numeric values > voltages > vibrations> virtual teleportation time-machine experience
Better recording made easy - >>Improved PAS table<< | Made excellent- >>click here to download the Oddball Microphone Technique illustrated PDF booklet<< (note: This is a 1st draft, now several years old and in need of revision!  Stay tuned)

Offline kuba e

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Re: Ambient sound & Jecklin disc for quad?
« Reply #11 on: February 12, 2021, 03:34:15 PM »
Thank you for your comments.

I asked about the difference between the sphere and the flat surface because I was thinking about recording with the ball as in the link. When someone records with this ball or dummy head, are the high frequencies also increased by 6db because boundary layer? Is it corrected by eq?
https://reverb.com/item/28102645-schoeps-kfm6-sphere-stereo-microphone
https://taperssection.com/index.php?topic=187681.msg2336073#msg2336073

Edit: I thought about it more. There is probably no analogy between the boundary layers. The aerodynamic boundary layer is formed due to friction. But the theory of aerodynamics, where friction is not considered (potential flow), should be similar to acoustic.

The analogies are interesting. I remember, I was unable to understand electricity at school. I only understood electricity when I learned hydrodynamics. The whole basics of electricity- voltage, resistor, current, capacitor, coil - can be learned to compare to water - pressure, velocity, resistance.
I remember when I was learning aerodynamics, there is another interesting analogy. It was used before when there were no computers. Older models in aerodynamics neglected friction because it has simpler equations. And friction-free fluid models and electricity are described by the same type of equations. This was used in practice. A conductive plate was taken and a non-conductive material was pressed into it, for example in the shape of a wing profile. Voltage was applied to the plate and the voltage potentials around the non-conductive part - the wing profile - were measured. And then these voltage potentials were recalculated to pressure and velocity potentials in aerodynamics. In this way, the wing lift could be roughly estimated.
Maybe there is something similar in acoustic.


« Last Edit: February 12, 2021, 05:26:33 PM by kuba e »

Offline kuba e

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Re: Ambient sound & Jecklin disc for quad?
« Reply #12 on: February 13, 2021, 09:38:28 AM »
I tried to figure it out. I mistakenly thought that the dummy head is just for creating an 'acoustic shadow'. But the dummy head also uses boundary layer reinforcement.
And my second misconception was that the gain in the boundary layer is the same for all directions. But that's not true. The maximum gain is for perpendicular directions only. And conversely, the sound in the tangential direction is not affected by the boundary layer.
« Last Edit: February 13, 2021, 09:41:04 AM by kuba e »

Offline DSatz

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Re: Ambient sound & Jecklin disc for quad?
« Reply #13 on: February 13, 2021, 10:20:41 AM »
Now that is really interesting, and makes general sense although I haven't seen or heard it mentioned before. The polar response patterns of boundary-layer microphones have always been represented by their manufacturers as if they were simply the original patterns "cut in half" at the boundary. But from what you say that should not be so; rather, the relative "selectivity" of the directional pattern should be emphasized by the boundary effect to some extent, even if only by a few dB, sharpening the patterns somewhat.

I'll try to find out more about this; I don't have the educational background to know about it on my own, nor the time right now to experiment. As I said, the way you're describing the situation (which makes sense enough to me) is at some variance to what I've always seen (and for Schoeps' technical literature, translated). As you may know, some of the leading microphone manufacturers offer not only special-purpose microphones--or more often nowadays, capsules designed for boundary-layer placement with extension cables for existing modular amplifiers, and/or accessories that facilitate the placement of their existing microphones and/or capsules on a boundary layer (Schoeps example shown below). And decades ago Shure used to offer an interesting little tripod stand for near-floor mounting of microphones (scan from an old catalog page also attached, from long before Crown made "PZMs" into a thing).

I've used both as problem-solvers in situations where the visual obstruction of a microphone stand couldn't be tolerated, as well as in one political situation of another kind that I can tell you about. I can't say that they worked any sonic miracles beyond allowing me to make somewhat decent recordings; 3 dB increase in sensitivity and reduction in diffuse-sound pickup is nice, of course, but only a modest effect overall.

--best regards
music > microphones > a recorder of some sort

Offline kuba e

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Re: Ambient sound & Jecklin disc for quad?
« Reply #14 on: February 13, 2021, 11:19:47 AM »
I'm just guessing, I don't want to cause any confusion.

I have wanted to use a boundary microphone for a long time to record lectures. I wanted to put it on the floor (it's yoga, we sit on the floor during lectures). But now I'm not sure if it will have any advantage, because the lecturer is further and sound hits the microphone at a small angle. On the other hand, if the angle of incidence into the boundary layer does not matter, then a correction should be made to the dummy head recording. But these are just my imagines, it may be completely different in reality. I'll try to read something about it on the internet. If I found out more, I would write.
« Last Edit: February 13, 2021, 11:29:14 AM by kuba e »

 

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