R/E/P Community

Please login or register.

Login with username, password and session length
Advanced search  

Pages: 1 [2] 3 4 ... 10
 11 
 on: April 06, 2019, 07:56:16 pm 
Started by klaus - Last post by Jeffrey
My name is Jeff. I am the person messing around with Mr. Blumleinís array. Klaus was kind enough to post my Blumlein ideas in this forum. I didnít think anyone would be interested. I can say that it works for me, and Iím pleased to try to answer any questions if Iím able to.

To hopefully address Daveís concern, here are the two alternatives Iíve investigated for vertically stacking the 4 cartioid Blumlein array. It is easier to visualize by drawing a schematic:

1st Arrangement:
The two forward facing mics  are immediately one above one other. And the two rearward facing mics are immediately above one another. This arrangement necessitates the  mics participating in each of the two figure 8 components to be separated from one another by one of the microphones, a little less than an inch in the case of KM84 mics. i.e., this arrangement is optimized for coincident phase at the expense of a less symmetrical Blumlein sound field. I would like to put in perspective  Daveís concern vis-a-vis the Blumlein sound field created from four cartioid mics may be compromised, I would point out that the Blumlein composed of the 4 cartioid mics  Iíve described would be no less symmetrical than a traditional Blumlein array sound field composed from ribbon mics or multi pattern condenser mics that place the ribbons or diaphragms of the two mics a minimum of approximately 2 inches apart. This is often  necessitated by the minimum distance between the  ribbon or diaphragm to the cage of each microphone. This distance multiplied by 2 is the distance between the transducers of both mics in the traditional Blumlein array. Although the ribbon mics do not suffer from the asymmetry of two diagrams to create the figure 8 polar pattern, ribbon mics and side address multi pattern mics often necessitate greater separation between their transducers as compared to small diaphragm condenser cardioid mics of approximately  1 inch diameter.  The small effect it has on the sound field asymmetry and  phase relation consequences are regarded as negligible in these traditional Blumlein arrays. So to is the case with a Blumlein array composed from 4 cartioid mics with similar dimensions as the KM84 mic.. - jeff

2nd Arrangement:
The two mics participating in each figure 8 component are immediately one above the other. This arrangement is optimized for a more symmetrical Blumlein sound field at the expense of a less coincident relationship between the forward facing mics and the coincident relationship of the rearward facing mics respectively.
For what itís worth, I usually prefer the 1st alternative because the degree of coincidence in the 2nd alternative is audible but small in the top octave or so. A separation of 21 mm diameter mics by about a wavelength of 1 inch will effect frequencies above approximately 13KHz, although diffraction of frequencies above this are to some degree mitigated by diffraction at the diaphragm depending on the diameter of the diaphragm.

Regarding shadowing, although I have never experienced any audible shadowing effect using the KM84s, if anyone does hear shadowing with their mics, one could always use detachable miniature cardioid capsules or try a mic with a smaller foot print.

 12 
 on: April 06, 2019, 03:38:19 pm 
Started by klaus - Last post by klaus
Quote
Another point of reference for this discussion is the Neumann KM 86 which had back-to-back, separate cardioid capsules that were combined for its "omni" and figure-8 settings. (In fact those two capsules were each the same as a KM 84's capsule--just with shorter pins--though as I recall, the reflectors behind/between the capsules in the KM 86 were shaped more like a convex lens than the hemispherical-shaped reflector of a KM 84.) The dual capsules and the spacing between them helped account for the microphone's strong low-frequency response in the figure-8 mode.

Correct about the shapes of the reflectors.
But there is another issue not yet mentioned in the discussion about the KM86's frequency response and suitability for Blumlein: it sports 4 screens in front of the capsule! Three of them are in the outer head basket, and one more in front of the diaphragm platelet.

I speculate that the predominance of lower mids and lows in that mic (or the relatively soft representation of high frequencies and its overall cotton-mouth dynamic behavior) is a direct result of these acoustic impediments, even it that is not clearly reflected in the graphs.

 13 
 on: April 06, 2019, 07:17:29 am 
Started by klaus - Last post by afterlifestudios

P.S.: It would be interesting to take a stereo microphone that has vertically aligned, single-diaphragm capsules, such as a Schoeps CMTS 301 or 501, and measure its frequency and polar response when its capsules are set to cardioid and combined into a figure-8 as in this experiment. One could also do that for dual-diaphragm capsules as in various stereo microphones from Neumann or AKG.


Thanks for the great thoughts and info.  Thatís an excellent idea.  I have a sm69 I could try that with.

 14 
 on: April 06, 2019, 05:53:07 am 
Started by klaus - Last post by David Satz
Right. But conventional stereo recording takes only the horizontal plane into account. So if the two microphones' diaphragms are aligned one above the other, and precisely equidistant from the sound sources, then (as far as conventional stereo recording is concerned) the microphones are effectively "coincident"--just as with stereo microphones that have one capsule above the other.

Actually I share your doubts to some extent, and wish I knew more about the listening tests that didn't turn up any audible shadowing effects. I believe the sincerity of the report--but one would expect some wavelength-dependent problems in the top octave, depending on exactly how the microphones were arranged. It would be good to quantify those effects even though they might be small.

--best regards

P.S.: It would be interesting to take a stereo microphone that has vertically aligned, single-diaphragm capsules, such as a Schoeps CMTS 301 or 501, and measure its frequency and polar response when its capsules are set to cardioid and combined into a figure-8 as in this experiment. One could also do that for dual-diaphragm capsules as in various stereo microphones from Neumann or AKG.

P.P.S.: Another point of reference for this discussion is the Neumann KM 86 which had back-to-back, separate cardioid capsules that were combined for its "omni" and figure-8 settings. (In fact those two capsules were each the same as a KM 84's capsule--just with shorter pins--though as I recall, the reflectors behind/between the capsules in the KM 86 were shaped more like a convex lens than the hemispherical-shaped reflector of a KM 84.) The dual capsules and the spacing between them helped account for the microphone's strong low-frequency response in the figure-8 mode.

But the down side was irregular polar response at high frequencies. This made the KM 86 sound rather shrill (as I can unfortunately attest) if it was used for Blumlein stereo recording, since the front of a Blumlein pair is at a Ī45į angle to each of the capsules--and that is just where the KM 86 had a substantial high-frequency rise followed by a considerable fall (see graph below; I've drawn a circle at 315į, where the microphone's Ī45į polar response is shown for the higher frequencies, and attached another graph where I've run a curve through data points for 4 kHz, 8 kHz and 12.5 kHz to infer the microphone's Ī45į frequency response from its 1 kHz frequency response as well as I can).

Neumann recommended that the KM 86 be used only at miking distances greater than one meter--but I think that they meant that for the patterns that used both capsules, since there's no great problem with the pattern in the cardioid setting.

 15 
 on: April 06, 2019, 04:39:30 am 
Started by klaus - Last post by afterlifestudios
... their directional patterns have a common center point.

Thatís the part I canít see being the case in the above suggested array... 

 16 
 on: April 05, 2019, 08:48:55 pm 
Started by klaus - Last post by klaus
Microphonics encountered in the use of microphones, especially in sensitive condenser microphones, is still a relatively unexplored and little-understood subject. But their detrimental effect on the sound of a mic is considerable, and should be addressed.

A microphone becomes microphonic when any of its components other than the capsuleís membrane resonates in response to  sound waves, and the parasitic signal thus triggered interferes with the signal captured by the capsule.

Microphonics in microphones can be grouped, in descending order of annoyance, and I give suggestions how to eliminate them:

Tubes. The assumption that tubes selected for microphones are quieter, longer-lasting, or feature other qualities compared to non-selected ones is false. F. ex. Neumannís EF86, AC701, 13CW4 or VF14 M selected for low-microphonics, and identified as such with a special label or a stamp, are usually identical with the same tube type, except their filament construction went through a Ďpingingí test. Samples with lower than average microphonic tendencies were then selected out as suitable for use in mics.

Pinging a tube by flicking a finger against its body midway, while you hold the tube to your ear, is an excellent method to pre-select a microphone tube. Nothing fancier is needed to predict whether the tube is likely to be triggered into ringing inside a mic.

All tubes resonate or ring to a degree, due to the various unsecured wire filaments inside, so the goal is to find the specimen with the lowest resonance. If even a light knock will trigger extended ringing, the tube, once installed, will become a serious obstacle to a clean recording.


Passive components.  When resistors, capacitors, switches, wires and other microphone components are not secured from vibrating, they will contribute microphonics to the output signal of the mic. Usually, good mounting and soldering techniques will prevent components from ringing, but sometimes free-standing parts need to be secured with an adhesive that connects them to adjacent components or to the circuit board.

I use Eclectic E6000 to prevent components from vibrating. This Styrene-based glue stays flexible, can be removed completely and without residue, and with one pull, and has an extremely high electrical resistance, preventing any lowering of high impedance circuits in condenser mics.

Other often overlooked causes for microphonics.

* Mono-filament wires. They should not be used as capsule lead-outs. They can hum like a bass guitar string

* Mechanical switch contacts in attenuator and pattern switches. They should not be free-floating, but their contact tongues
   should rest against a firm surface

* Mesh layers of double or triple-layer head baskets.  One of them should be slightly bent inward or outward, so that the layer rests
  firmly against an adjacent one, to prevent resonating                                             

The ultimate test whether you successfully removed all sources of microphonics: hold the mic against your ear and knock its housing with your knuckle. If all you can hear is a dull thud, you are done.

You will appreciate the added clarity the mic delivers once microphonic artifacts are removed from the signal.

© Klaus Heyne 2019

 17 
 on: April 02, 2019, 11:39:42 am 
Started by klaus - Last post by David Satz
A forward-facing cardioid is (1 + cos θ)/2, a backward-facing cardioid is (1 - cos θ)/2, and a figure-eight is simply the cosine function by itself.

If you subtract a backward-facing cardioid from a forward-facing one, the two half-"1"s cancel each other out, while the two half-cosines reinforce one another to become a whole cosine--a figure-8. That assumes that the microphones are well matched and that their directional patterns have a common center point.

 18 
 on: April 01, 2019, 11:23:40 pm 
Started by klaus - Last post by opacheco
That sound interesting set up!

Do exist a method o way in order to simulate the response or the resultant pattern of  an array like this conforming 4 Cardioid Mics for a Blumlein System with the control for each Cardioid??...I mean use a Geometric Angular Graphing in order to get the Directional Pattern in a cylindrical type plot.

What would be the angular equation for something like that mics arrangement?

Thanks


 19 
 on: March 30, 2019, 03:47:42 pm 
Started by Spindrift - Last post by Spindrift
This post is related to the recent thread regarding snipping the jumper on the C414EB to lock it to 48V and ease the load on phantom supplies: 

https://repforums.prosoundweb.com/index.php/topic,37331.msg538131.html#msg538131

Does the AKG C451EB have a similar modification which can be performed which limits it to a 48V supply?  48V is the standard in phantom supplies in this day and age and I'm looking to lessen the load on my phantom supplies when employing these mics. I understand that the C452 was the strict 48V model but I'd like to not have to go hunting down more mic bodies.

Thanks,
Keith Banning

 20 
 on: March 28, 2019, 05:49:57 pm 
Started by mikezietsman - Last post by klaus
Kai,
Can you check your messages. please?

Pages: 1 [2] 3 4 ... 10