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Author Topic: Naiant x-x as boundary  (Read 426 times)

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Offline carpa

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Naiant x-x as boundary
« on: September 11, 2020, 09:35:25 AM »
I've read around that small omnis may be set up as boundary and I wonder if Naiant X-X's ( I think quite a few here own them) could be arranged that way.
I would be very interested in knowing what kind of mount ( even DiY) could serve at the purpose. Apart from the fact that it seems helping to increase the S/N ratio in the recording, what are other applications/benefits ( close/distant) ? Mostly recording piano here.
Thank you so much

Offline Gutbucket

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Re: Naiant x-x as boundary
« Reply #1 on: September 11, 2020, 11:10:44 AM »
No reason Naiant X-X should not work. 

To clarify- It's the ratio of of direct-sound to reverberant-sound pickup which is increased via boundary mounting, not as well as S/N.

You want the microphone element as close to the boundary surface as possible, ideally flush-embedded into it.  The Crown PZM implementation mounts the element a hair's width above the surface facing toward it.  A microphone with a small enough diameter element facing sideways and taped directly to a flat surface is sufficiently close to the surface in my experience.  Closer = smoother high frequency response.

The boundary surface should ideally be smooth and relatively hard.  Size of the boundary surface (it's area and geometric shape) determine the low-frequency cutoff where the frequency and polar response returns to free-space-mounted (non boundary mounted) condition.

If recording piano with freedom to place the mics, it could be useful on the underside of the lid in a room with compromised acoustics.  When recording from a considerable distance, it can be useful on a wall of the venue when one cannot otherwise get the microphones sufficiently close.  Might be useful to try on a hardwood stage floor.
« Last Edit: September 11, 2020, 03:25:26 PM by Gutbucket »
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<<

Offline carpa

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Re: Naiant x-x as boundary
« Reply #2 on: September 11, 2020, 12:50:54 PM »
@Gutbucket
Thank you very much for your response. The main think I'd like to understand, and which I didn't get from googling for pictures, is the position of the mics on a surface. Some pics show the head of the mic directly aiming at the surface ( as if the hard surface was the sound source ) with just a mm or two of air.  That should be a bit difficult to achieve, while just taping the mic laying on the surface could be much easier; are you meaning this option by  "facing sideways"?

In your example of application you have indicated taping underneath the piano lid or, on the much more distant option, the idea of taping the mics on a wall like ambience mics.
Does have a sense using them on a DiY thing having sort of  two square pieces of hard surface with one mic each and using them at, let's say, AB or other configuration at 1,5/2  meters distance from the instrument or players? What will the difference be in respect of using them not boundary like? 
Should it make some sense, what size of surface would you suggest? Something like a CD cover?
I hope I didn't mess up misunderstanding everything!
Thanks again

Offline DSatz

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Re: Naiant x-x as boundary
« Reply #3 on: September 11, 2020, 03:19:21 PM »
The microphone should definitely not be aimed at the backing surface. That was a big defect in the design of the old Crown (and Radio Shack) "PZMs", which caused a number of problems in the high frequency response.

Ideally the membrane should be parallel to the backing surface and as nearly flush with it as possible, but facing into the space that contains the sound sources. See for example the designs from manufacturers such as Schoeps and Neumann (sample photos shown below; the actual products have normal-length cables). The asymmetry of both designs is deliberate; the base of the microphone has a non-zero thickness so there are some minor diffraction effects at the edges, and the idea was to spread those around so that they wouldn't affect any one narrow band of frequencies as much.

Neumann no longer makes or sells this type of microphone, and Schoeps has discontinued its original, larger model (the BLM 3), but the BLM 03 C has the identical capsule. It's a damn nice-sounding microphone, as well as being my ready answer to any complaints about the phallic shape of most microphones. -- Sennheiser introduced the actual first commercial microphone of this type, which had its (electret) microphone element built into a cylindrical cage that sat above the flat base of the microphone. That's shown in the fourth photo. I don't know what the internal arrangement of the parts was inside the dome.

If you have to lay the capsule down on the floor or prop it up against a wall, with the membrane perpendicular to the sound sources, that's still better than having it face away from them and into an air gap. This type of setup can also be done with other types of microphone capsule; they don't have to be pressure transducers (omnis). I've recorded with cardioids or supercardioids on the little circular plate shown in the third photo below; of course I put something over them to protect the mikes from being stepped on.

--best regards

P.S.: Actually, placement on a boundary does increase the s/n ratio in addition to the similar increase in direct sound pickup relative to reflected sound, since the sensitivity increases while the self-noise does not. It's not an either/or situation; both improvements occur at the same time.
« Last Edit: September 11, 2020, 03:56:25 PM by DSatz »
music > microphones > a recorder of some sort

Offline Gutbucket

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Re: Naiant x-x as boundary
« Reply #4 on: September 11, 2020, 04:18:53 PM »
D-
Thanks for the clarification on S/N which I should have remembered but had forgotten about.  I suppose that's because unless the noise floor is audible that aspect is not perceptually apparent, whereas the increase in direct sound pickup relative to reflected sound is immediately obvious at all levels.

And thanks for the warning.. I didn't mean to suggest trying to mount them so as to face the boundary in my attempt at providing some historical background of how it has been done and why.  I imagine that unless otherwise compensated for, mounting a capsule in such a way could produce a significant HF peak relative to the gap spacing and capsule surface area.  Might that be the source of the high frequency response problems in those designs?

C-
Yes, I mean the microphone diaphragm facing sideways in relation to the surface on which it is mounted. [edit- like the csm-BLC image 3rd from the top in the post above]

Assuming the use of omnis, if both microphones of a stereo pair are mounted on the same surface it acts as a spaced A-B configuration.  If mounting each microphone on a separate boundary "plate", those plates can be faced in different directions and like directional microphones will begin to produce level-differences as well as time-of-arrival differences.  That directionality will manifest only within the effective bandwidth of the boundary-effect region, determined by the area of the boundary at the low frequency end of that range and the spacing between diaphragm and boundary surface at the high frequency end of things.

A CD case cover is too small to be effective below the kHz region.  It would act like the pressure modification attachments used on some omnis to change their presence range and higher frequency response and directionality.   Those range from circular disks to spherical attachments.  Some of the wooden circular disk ones I've seen are close to the diameter of a CD.

Generally an area of a few square feet at minimum are needed to be effective down through the lower midrange frequencies.

For stereo configurations, other than A-B mounting to a single surface, mounting to squares or rectangular pieces of polycarbonate (Plexiglas) is common, and the two can be arranged in a wedge shape, which achieves a similar angle/spacing relationship to a stereo pair of directional microphones.

Below are a couple examples of how Pierre Sprey of Mapleshade records small ensembles this way-



« Last Edit: September 11, 2020, 04:40:21 PM by Gutbucket »
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<<

Offline Gutbucket

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Re: Naiant x-x as boundary
« Reply #5 on: September 11, 2020, 04:34:44 PM »
With a small, lightweight microphone such as you are asking about, gaffer taping it directly to the surface with the micrphone laying parallel to the surface generally works with minimal effort.  If SPLs are high it might be beneficial to put something thin yet compliant under the microphone to prevent rattling if the surface starts vibrating.  I sometimes put a strip of gaff tape flat on the surface first, then position the microphone, then add another strip of gaff-tape holding it down atop the other piece.  The tape on the boundary surface protects both the surface and micrphone from getting scratched, and cushions the microphone enough to eliminate vibration against the surface.  If that's a significant concern you could use a couple strips of tape or even a thin piece of neoprene.
« Last Edit: September 11, 2020, 04:41:36 PM by Gutbucket »
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<<

Offline carpa

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Re: Naiant x-x as boundary
« Reply #6 on: September 11, 2020, 06:35:16 PM »
@DSatz and @Gutbucket,

I appreciate your explanations very much. I finally understood in a few words what I couldn't figure out googling quite a bit.
You are a true source of inspiration. I'll give a try to some possible configuration and hear the results.
carlo

Offline Limit35

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Re: Naiant x-x as boundary
« Reply #7 on: October 13, 2020, 11:28:35 PM »
I have used these mics in this setup before, they sounded quite nice. Naiant sells a handy surface mount for the X-X at $29.00 a mount, although Gutbucket's suggestions are the way to go for infrequent use or on walls. If I used them on stage more often I would get the mounts to weight them down a bit and not worry about tape lifting up. They are good little mics.

Offline Gutbucket

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Re: Naiant x-x as boundary
« Reply #8 on: October 14, 2020, 10:20:30 AM »
This can be a good strategy on a column in a good position in the room, placed either on opposing or adjacent sides depending on the size and shape of the column and its orientation.  With a larger column it may be beneficial to shift both mics closer to the front edge or corner to achieve the correct overlap between channels.  With a round column consider its diameter in relation to a person's head.  If the same size or smaller mount on opposing sides, if larger diameter, shift them towards the front somewhat to reduce the spacing and acoustic shadowing.

I once did that with a 4 channel arrangement of miniature omnis  on a column I had previously assessed at a small music venue. I placed one microphone on each side of the square column, which was about 16" wide. The microphones, wiring, small recorder and preamps (2 x CA-Ugly > tascam DR2d) were all fixed using a couple long strips of industrial-grade velcro.  It was quick and easy to setup by simply wrapping the velcro strip around the column once then adjusting the positions of the microphones as needed before making a second wrap to secure them and the in place.  No wire runs down the column, and I was able start and stop the recorder from a few tables away using the IR remote. I made sure the red record LED on the top of the DR2d was visible for visual confirmation from my table.  This made for a very nice boundary/baffled L/C/R/S arrangement in a near optimal location.  The folks who had reserved the seats at the table surrounding the base of the column showed up after I'd set up and departed just after the concert ended and never noticed it just over their heads.  Worked out really well.
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<<

 

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