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Can you do Blumlein adjacent, not vertical?
Old 1st August 2014
  #1
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Can you do Blumlein adjacent, not vertical?

I was just wondering the following. It is my understanding that in a Blumlein setup two figure 8 mics are positioned vertically at 90 degrees with no horizontal offset.

What would happen if you were to position the two fig.8 mics side by side, (almost) touching each other, at 90 degrees. No vertical offset. If for example we were talking about an AT4081 (of which I own one) or one of the Royers (I sure would like to be able to say I own one of those ), the horizontal distance would be something like one inch.

Would that for practical purposes still be considered a Blumlein? Any problems in doing it that way if it turns out to be the more practical way to position the mics under the circumstances?

For that matter, could you do MS the same way? I am aware that the mics would be "shielding"/"shadowing" each other slightly, but would it be such that it would be a problem?

Regards, Christine
Old 1st August 2014
  #2
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I do MS this way with 2 x mkh 30
They are sdc and I have no shadowing problems,the capsules are teflon coated fabric
Im not sure ribbons would behave the same way
The AT s can be a little noisy for distant sources
The mkh are very quiet and this rig is very unobtrusive in a Rycote Universal Mount
Old 1st August 2014
  #3
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Plush's Avatar
Quote:
Originally Posted by connloyalist View Post
I was just wondering the following. It is my understanding that in a Blumlein setup two figure 8 mics are positioned vertically at 90 degrees with no horizontal offset.

What would happen if you were to position the two fig.8 mics side by side, (almost) touching each other, at 90 degrees. No vertical offset. If for example we were talking about an AT4081 (of which I own one) or one of the Royers (I sure would like to be able to say I own one of those ), the horizontal distance would be something like one inch.

Would that for practical purposes still be considered a Blumlein? Any problems in doing it that way if it turns out to be the more practical way to position the mics under the circumstances?

For that matter, could you do MS the same way? I am aware that the mics would be "shielding"/"shadowing" each other slightly, but would it be such that it would be a problem?

Regards, Christine
No, it would not be Blumlein, but instead, called "near coincident."
Blumlein is a defined standard where the capsules are coincident at the same point in space.

You can still get good recorded sound with figure-of-eight microphones at 90 degrees. But it is not Blumlein, strictly speaking.
Old 1st August 2014
  #4
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Quote:
Originally Posted by connloyalist View Post
I was just wondering the following. It is my understanding that in a Blumlein setup two figure 8 mics are positioned vertically at 90 degrees with no horizontal offset.
Don't overlook the option to have the two mics in orthogonal arrangement, for example:
- one Fig8 mic body being _vertical_, but rotated on its body axis so that the main axis of its Fig8 pattern points 45° left of target
- the 2nd Fig8 mic body placed atop and _horizontal_, with its body axis pointing 45° left - and rotated on its body axis to have its Fig8 pattern main axis pointing horizontal and 45° right of target. .

This permits capsule coincidence (w.r.t. sounds arriving in the horizontal plane). It would be a slightly more difficult, though, to accurately point the main Fig8 axis of the vertical body mic.
Old 1st August 2014
  #5
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Sound-field mics produce coherent MS
They are not stacked.
They are spaced
The implementation of the matrix is important.
I have tried orthogonal, vertical and horizontal it makes little difference imho
Old 2nd August 2014
  #6
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Quote:
Originally Posted by Rolo 46 View Post
Sound-field mics produce coherent MS
They are not stacked.
They are spaced
The implementation of the matrix is important.
I have tried orthogonal, vertical and horizontal it makes little difference imho
My understanding, though, was that the Soundfield had clever time delay compensation incorporated in the matrixing mathematics, so that all four capsules in the tetrahedron array delivered signals as if the capsules were all located at the exact same point in space (but of course with their aiming direction retained). Can't quite get my head round how that could ever be done.

But if true, it would be fairer to say: "no differences can exist for the Soundfield because the spacing gets fixed in post.'' :-)

p.s. Returning to the proposed two Fig8 orthogonal array (one body vertical; the other horizontal), it would be better on L/R symmetry grounds to run that oriented as MS, then derive classic Blumlein from matrixing.
Old 2nd August 2014
  #7
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Quote:
Originally Posted by connloyalist View Post
Would that for practical purposes still be considered a Blumlein? Any problems in doing it that way if it turns out to be the more practical way to position the mics under the circumstances?

For that matter, could you do MS the same way? I am aware that the mics would be "shielding"/"shadowing" each other slightly, but would it be such that it would be a problem?
Plush is right, that it is not Blumlien (or MS). The capsules have to be
aligned as close horizontally as possible (to be called Blumlien or MS). Spaced near coincident array can work but will sound different than Blumlien. As MS the further apart they are spaced the less coherently the pair can be matrixed.
Old 2nd August 2014
  #8
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More important in my book is the similarity of transducers
The classic mkhs are great for this, especially if you use 2 x 30s
The matrix is what I have found to make a considerable difference
Firstly I used transformers, and then the 3 ch mixer aux send and nulling with none, and final software derived.
The latter in the Nagra VI is excellent , this combined with the Nagra pre amps is spot on, the results best yet.
Vertical or horizontal is academic in practice ,imho.
Old 2nd August 2014
  #9
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Quote:
Originally Posted by aracu View Post
The capsules have to be
aligned as close horizontally as possible (to be called Blumlien or MS). Spaced near coincident array can work but will sound different than Blumlien.
Agreed, but unfortunately in the OP's case we are dealng with a "psychoacoustically wrong implementation of nearness." For the intensity clues would then be contradicting the arrival-time clues.

When direct sound from a source hits the two mics of a properly near-spaced array, the mic that generates the stronger signal is always the mic that also generates the earlier signal. (That's, after all, why people have been obliged to layer and cross over mics whose barrels are awkwardly longish.)

Moreover, I suspect the spacing of the OP's mics may actually have been greater than the reported one inch: for though those AT4081's may well be arranged with their barrel-ends almost touching, the spacing that is relevant is the spacing between their acoustic centre...and that is a few cm. further down the barrel?
Old 2nd August 2014
  #10
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I am enjoying this discussion, thank you.

Quote:
Originally Posted by Tom McC View Post
Agreed, but unfortunately in the OP's case we are dealng with a "psychoacoustically wrong implementation of nearness." For the intensity clues would then be contradicting the arrival-time clues.

When direct sound from a source hits the two mics of a properly near-spaced array, the mic that generates the stronger signal is always the mic that also generates the earlier signal. (That's, after all, why people have been obliged to layer and cross over mics whose barrels are awkwardly longish.)
This is true, hadn't considered that. It will be either correct for the front, or for the back, but not both at the same time.

Quote:
Originally Posted by Tom McC View Post
Moreover, I suspect the reported spacing of the OP's mics may actually be greater than the reported one inch: for though those AT4081's may well be arranged with their barrel-ends almost touching, the spacing that is relevant is the spacing between their acoustic centre...and that is a few cm. further down the barrel?
Just to be clear, what I have in mind is to have the long side of the two mics against each other, not the tops end to end.

The AT4081 has a diameter of 2 cm. So if you put two of these right against each other, the center-to-center distance will be 2 cm. The clamp adds 4mm. If you position the two clamps so they are above each other and not side by side you only need to add the 4mm once. So that comes to 2.4cm (assuming the ribbon is in the exact center of the mic when looking at it from the top and that it is the acoustic center).

According to the Sengpiel site those 2.4 cm will result in a time difference of 0.049ms and a level difference of 39.99 dB. The phantom source shift from level difference will be 97.8%, the phantom source shift from time difference 2.16%. This 2.16% will be correct for the front (or back) and be opposite to the level difference for the back (or front).

Regards, Christine
Old 2nd August 2014
  #11
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Quote:
Originally Posted by Rolo 46 View Post
More important in my book is the similarity of transducers
I assume you are referring to MS. I find that certain capsules work better as mid and others work better as side, and that they do not have to be similar.
Of course in Blumlien they have to be the same.
Old 2nd August 2014
  #12
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Quote:
Originally Posted by connloyalist View Post
Just to be clear, what I have in mind is to have the long side of the two mics against each other, not the tops end to end.

The AT4081 has a diameter of 2 cm. So if you put two of these right against each other, the center-to-center distance will be 2 cm. The clamp adds 4mm. If you position the two clamps so they are above each other and not side by side you only need to add the 4mm once. So that comes to 2.4cm (assuming the ribbon is in the exact center of the mic when looking at it from the top and that it is the acoustic center).
Christine, I'll have to partially retract my comments on the arrival-tme vs intensity psychoacoustics because I'd forgotten that those Fig8 barrel mics are side-address. Duhh! (But avoidance of a toed-in arrangement is certainly advisable in most typical near-coincident arrays that involve end-address unipolar mics such as cardioids.)

So to resume, there are three ways to arrange a Blumlein pair from two identical barrel mics:
A. Layered: both mics horizontal, one atop the other, barrels aimed 45° L and R; capsule centres coincident as seen from above.
B.orthogonal: one mic vertical; one horizontal
C. end-butted: one mic vertical upwards; one vertical downwards; barrel front ends almost touching

- The spacing between the mic acoustic centres would generally increase along the series A -> B -> C (but that spacing would lie in the less important vertical direction)
- The ease of correct aiming decreases along the series A -> B-> C (since the barrel lengths can't be utilized to help aim).
- Method 'B' has poorer symmetry - inviting MS to be used.

My wrong(?) take was that you had difficulties setting up 'A' or 'C" and had been pondenng a set-up 'D':
D. Both mics on same horizontal layer, each toed-in 45°; front barrel ends almost touching (and mic acoustic centres thus with a bigger spacing).

But - penny finally droppng for me - you were really contemplating arrangement "Ë":
E. Both mics with long barrel sides almost touching; parallel and vertical; equidistant from frontal sound source; barrels swivelled +/- 45°.

Right?. Aiming and shielding issues aside, that mightn't be too bad. Just 'suck it and see'.If you can't do it as you must (ABC), then you must do it as you can. :-)
Old 2nd August 2014
  #13
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Time difference of .049 ms I understand Christine,level difference of 39.99 dB implies a sonic barrier unsuitable for MS.
The diffusion loss through a MKH 30 is far less...
I can't measure it with my limited tools.

Same physical size mics and similar capsules / gains are essential for MS imho.
These are all practical observations from 30 yrs of Mid Side I should add.
Old 2nd August 2014
  #14
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These are some of my arrays
All of which work.
The first is the best .
Attached Thumbnails
Can you do Blumlein adjacent, not vertical?-dsc_0001.jpg   Can you do Blumlein adjacent, not vertical?-dsc_0018.jpg   Can you do Blumlein adjacent, not vertical?-dsc_0016.jpg  
Old 2nd August 2014
  #15
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Quote:
Originally Posted by Tom McC View Post
But - penny finally droppng for me - you weree really contemplating arrangement "Ë":
E. Both mics with long barrel sides almost touching; parallel and vertical; equidistant from frontal sound source; barrels swivelled +/- 45°.

Right?. Aiming and shielding issues aside, that mightn't be too bad. Just 'suck it and see'.If you can't do it as you must (ABC), then you must do it as you can. :-)
Correct, that is what I was thinking. My thinking was along these lines: If I do only a Blumlein (or MS) then I can do it as option C (or A or B) by taking a stereo bar and tilting it vertically.

However, if I have a long stereo bar, then I might like to do an AB pair of omni's at whatever is appropriate, and in the center try to get a Blumlein using two ribbons. That would give me two stereo recordings of the same thing. Except that using a horizontal stereo bar (required for the AB) I won't be able to reach the ribbons across to be in configuration C. But it might be able to go as configuration E. Reconsidering, I might be able to set it up as configuration A by clamping each mic at the end of the barrel near the XLR connector. Might just be long enough. I will have to try

I have found that with these things, it never hurts to try things out. If it doesn't work, then that's just a little more experience I have gained As they say, you learn more from your mistakes than from what went well.

Quote:
Originally Posted by Rolo 46 View Post
Time difference of .049 ms I understand Christine,level difference of 39.99 dB implies a sonic barrier unsuitable for MS.
The diffusion loss through a MKH 30 is far less...
I can't measure it with my limited tools.

Same physical size mics and similar capsules / gains are essential for MS imho.
These are all practical observations from 30 yrs of Mid Side I should add.
Forget I mentioned the 39.99 dB. On closer consideration I suspect an error in that program the webpage is running. Considering the difference in level between cardioid, supercardioid and bidirectional microphones for the same pattern, I suspect there might be an error with respect to the bidirectional mics which spits out this 39.99 dB. According to that website, an XY with cardioid mics gives a level difference of 6.02 dB. Supercardioid mics gives a level difference of 8.73 dB. Replace that with bidirectional mics and it gives 39.99 dB (subcards gives 3.517 dB).

Yes, I would be using two identical (but not strictly "matched") ribbon mics.

Regards, Christine
Old 2nd August 2014
  #16
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Quote:
Originally Posted by Rolo 46 View Post
These are some of my arrays
All of which work.
The first is the best .
Yes, the first is what I had in mind The green dot is the positive side, red dot negative?

Regards, Christine
Old 2nd August 2014
  #17
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Red is +M
Green is +S
They really help in a dark hall.
There is a Large Rycote USM which I would recommend to you
I use it for addition MKH 20 plus 2x MKH 30s
Roger
Old 2nd August 2014
  #18
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Quote:
Originally Posted by Rolo 46 View Post
Red is +M
Green is +S
They really help in a dark hall.
There is a Large Rycote USM which I would recommend to you
I use it for addition MKH 20 plus 2x MKH 30s
Roger
Do I see some kind of holder in picture number 1 to hold the two mics together stable in the Rycote USM? It seems that without something to stabilize things they would roll and move against each other?

Regards, Christine
Old 2nd August 2014
  #19
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Wouldn't one mic shadow the other being in front of one of the fig.8 lobes?
Old 2nd August 2014
  #20
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That's a Sennheiser MS clip, Rycote do one to,not as good though.
Shadowing was discussed earlier in the thread heva,I discount it to a degree, with the MKH 30s capsule.
Old 3rd August 2014
  #21
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Some ones edited this thread, why ?
Old 3rd August 2014
  #22
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Quote:
Originally Posted by Rolo 46 View Post
Some ones edited this thread, why ?
Rolo, In post #12, besides a typo correction, I did add a tiny phrase "barrels aimed 45° L and R" to clarify my description of array A. Is that what you were referring too? Mea culpa. Probably should have made an "Edited.." comment, but I wasn't altering any arguments, merely tightening a vizualization, which I noticed was still ambiguous in the absence of a pic.
(I've on occasions dived in - within a minute of a post appearing - to quickly repair an ugly, glaring fat-fingered typo, without feeling the need to append a "last edited..." footnote.)
Old 3rd August 2014
  #23
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Sorry Tom,
Got confused with another adjacent thread, Opera how did they do it in the 50s
Roger
Old 3rd August 2014
  #24
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Quote:
Originally Posted by connloyalist View Post
Forget I mentioned the 39.99 dB. On closer consideration I suspect an error in that program the webpage is running. Considering the difference in level between cardioid, supercardioid and bidirectional microphones for the same pattern, I suspect there might be an error with respect to the bidirectional mics which spits out this 39.99 dB.
Those huge dB figures are correct - and the resolving power, noise level or overload capability of the microphones isn't an issue.

If a sound source is sited at the transition edge into the ambiophonic region of a stereo array (+/- 90deg for a Blumlein pair), it will lie on the node for one mic (thus generating zero voltage to that channel), while still delivering a significant voltage to the other mic channel. Thus the mic voltage ratio will be "something divided by zero" = infinity...and the dB channel level diffeence also infinity. If you take some time to calculate channel voltage ratio's or dB differences for various XY and MS arrays, at several XY angles or M/S ratios, you will observe large calculated dB numbers emerging as you venture beyond the SRA, and a steep rise as you approach the ambiophonic frontier. (It's nothing to do with dB(A) sound intensities from speakers.)
Old 2nd November 2014
  #25
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Roger...just to be clear, on the MKH30, the side on which the switches are located is the + side, correct?

Quote:
Originally Posted by Rolo 46 View Post
Red is +M
Green is +S
They really help in a dark hall.
There is a Large Rycote USM which I would recommend to you
I use it for addition MKH 20 plus 2x MKH 30s
Roger
Old 2nd November 2014
  #26
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Quote:
Originally Posted by bwanajim View Post
Roger...just to be clear, on the MKH30, the side on which the switches are located is the + side, correct?
Correct.
Old 2nd November 2014
  #27
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The side with the switches on is +.
Im about to mark my PGS ribbons (see my thread about Blumlein mount for 4038s) with the red and green dots for identification in dim halls
The response of a ribbon 1/4" wide and 1- 1/4" long is very different from 16mm Teflon coated MKH.
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