Topic: Optimal Config for Side Address LDCs?

[StarkRavingCalm]

I had started a thread in the As The Tapers about achieving ORTF with side address LDC microphones.

http://taperssection.com/index.php?topic=167178.0

Near the end of the thread, DSatz explained that ORTF is not intended for use with these types of mics.

What would a more optimal configuration be?

I am using a pair of Oktava MK-319s.

[mepaca]

He didn't say that it would necessarily sound bad he just said it was not ortf.

[Gutbucket]

You can setup a pair of LDC microphones with a cardioid pickup pattern so their capsule elements are 17cm apart with a 110degree angle between them.  That places them in the same physical arrangement as ORTF, which specifies using a pair of SDC cardioids due to their better off-axis polar response behavior of the smaller diaphragms and pencil microphone configuration.  LDCs will still work.  Just refer to the setup as cardioids at 17cm/110° instead of ORTF and it's all cool.

The resulting recording may absolutely smoke.. or suck.. for any number of related or completely unrelated reasons.  The optimal configuration will be determined by the specifics of the recording situation, not the microphones.   ORTF may or may not be the best choice.  Specifying a configuration based upon the microphone type rather than the situation is putting the cart is before the horse.

[StarkRavingCalm]

You can setup a pair of LDC microphones with a cardioid pickup pattern so their capsule elements are 17cm apart with a 110degree angle between them.  That places them in the same physical arrangement as ORTF, which specifies using a pair of SDC cardioids due to their better off-axis polar response behavior of the smaller diaphragms and pencil microphone configuration.  LDCs will still work.  Just refer to the setup as cardioids at 17cm/110° instead of ORTF and it's all cool.

The resulting recording may absolutely smoke.. or suck.. for any number of related or completely unrelated reasons.  The optimal configuration will be determined by the specifics of the recording situation, not the microphones.   ORTF may or may not be the best choice.  Specifying a configuration based upon the microphone type rather than the situation is putting the cart is before the horse.

Agreed. I guess I should have framed it with "in a normally small diaphram, ORTF situation..."

[Gutbucket]

Regardless of the configuration, usually it's done with the LDC microphones oriented vertically and rotated to the achieve the correct angle, attached to a typical mounting bar with the spacing determined by the mounting locations chosen on the bar, or by rotating off-center microphone mounts seperately from the microphone bodies until the desired spacing is achieved. 

Can also be done with the bodies oriented horizontally as well, like on a Shure-vert bar or something.  I've run LDC's in both nearspaced and coincident configurations both ways.  If using shock mounts, often heavy LDCs will want to droop in the shocks if oriented sideways, which is probably the most significant practical implication to setting them up that way.  Technically, vertical orientation of the microphones is prefered, since that is more symetrical for sounds arriving from all directions in the horizontal plane, but that's pretty far down the importance list.

[DSatz]

Well--actually it's not just that the "ORTF" name no longer applies. There are two fundamental characteristics of microphones that affect the stereo image quite differently with most large-diaphragm cardioids versus most small-diaphragm cardioids.

One is the narrowing of the polar pattern at high frequencies. This occurs to some extent even with small-diaphragm microphones, but for each doubling of the effective diaphragm diameter, the narrowing sets in an octave lower. So with LDCs the narrowing typically begins in the upper midrange--an extremely sensitive range as far as localization of sound sources is concerned. To compensate for this problem, you could move your microphones slightly closer together and/or choose a somewhat narrower angle between them.

The other fundamental difference is the spreading out of pickup pattern at low frequencies (due not to large diaphragm-ness as such but to dual-diaphragm-ness; if you use Neumann TLM 103s, which are essentially single-diaphragm LDCs, this doesn't apply to you so much). What this spreading out of the pattern does is to make the stereo pickup more nearly mono in the bass, which detracts greatly from the sense of spaciousness in any recording. To compensate for this problem you could space your microphones apart somewhat farther and/or angle them outward a little more.

You may have noticed that there's a flat-out contradiction between the ways I suggested to compensate for each of these two problems. Unfortunately you can't solve both problems at the same time. It's an inherent dilemma that forces major compromises on anyone who uses large, dual-diaphragm microphones to make stereo recordings with coincident or closely-spaced microphone pairs. For that application most people prefer SDCs (and particularly for the cardioid pattern, single-diaphragm SDCs).

--best regards

[Gutbucket]

Thanks for the specifics! 

I've long had a question concerning the part quoted below from what you state above. Can you go into a bit more detail or point me to a resource describing the microphone design aspects which are behind this-
 

The other fundamental difference is the spreading out of pickup pattern at low frequencies (due not to large diaphragm-ness as such but to dual-diaphragm-ness; if you use Neumann TLM 103s, which are essentially single-diaphragm LDCs, this doesn't apply to you so much). What this spreading out of the pattern does is to make the stereo pickup more nearly mono in the bass, which detracts greatly from the sense of spaciousness in any recording. To compensate for this problem you could space your microphones apart somewhat farther and/or angle them outward a little more.

I understand your explanation of how that affects microphone setup and the resulting recording.  I understand the basic concept of how signals from two back to back cardioid elements are combined to derive various first-order pickup patterns in an electrically switchable microphone.  I've noted the pattern distortions in the polars of the omni position of those microphones, and I can grasp some of the issues of the real-world patterns varying with frequency due to those elements not being able to be arranged so that they are perfectly coincident.  What I don't understand is this- doesn't the cardioid pattern use signal from only the front element, with the back one switched off and completely out of the circuit? Wouldn't that make the cardioid pattern the least affected by the inevitable (if tiny) spacing difference between the two diaphragms that would necessarily effect any other non-cardioid switchable patterns?  Does it have nothing to do with spacing between the diaphragms and I'm totally missing something basic here?

[DSatz]

gutbucket, you're right, in dual-diaphragm cardioids (or multi-pattern dual-diaphragm microphones in their cardioid setting), with only one exception that I'm aware of, the rear diaphragm is simply left unpolarized. However, acoustically, for the front half of the capsule it's one thing to have a delay labyrinth behind the backplate, and quite a different thing to have another backplate and diaphragm in that position. The dual-diaphragm arrangement isn't as efficient at canceling rear-incident sound at low frequencies.

See the attached polar response graph for the dual-diaphragm, large-diaphragm Neumann U 87 in its cardioid setting, which clearly shows both effects I was describing; compare this to the single-diaphragm, small-diaphragm KM 84 graph on the right. (These happen to be the two best-selling microphones that Neumann has ever made.) In each graph, the traces for 1 kHz and above are shown in the left half of the circle while 1 kHz and below are on the right. Both microphones excel at many tasks around the studio, but there's no question which microphone is better suited for coincident or near-coincident stereo recording.

--best regards

P.S. added later for those who aren't sure they know how to read polar diagrams: The KM 84's pattern is a cardioid (or very nearly so) all across the frequency range, while the U 87's pattern varies rather greatly depending on which frequency you're looking at. -- The low-frequency response is represented by the dashed line on the right side of each of the diagrams (omitted from the KM 84 diagram because it's identical to the 1 kHz pattern), and (thinking in terms of a clock face) if you look in the 3:00 to 6:00 range, you'll see what has fooled so many people into believing that LDCs sound "warmer" or "have better low-frequency response" than SDCs: With a cardioid you expect a "null" in the response at 180 degrees, but in dual-diaphragm microphones this is not so clearly defined below the midrange. That's OK, or even potentially beneficial, for spot/solo miking. But if you set up a pair of mikes like this for stereo recording, in fairly close proximity to one another and angled apart, at low frequencies the difference between what the two mikes pick up becomes less and less because the pattern becomes broader and broader. At the lowest frequencies both microphones are picking up nearly the same signals; the two channels increasingly blend into one another at lower frequencies--and that's exactly the opposite of what you want for most stereo recording.

[Gutbucket]

Thanks for that explanation.

-regards

[JimmieC]

Last Saturday, I ran ADK TL Hypercardioid (DINa) > Littlebox (OT) at the lip of the stage.  I also ran AKG ck61 (DINa) > Naiant Couplers > V2.  I was wanting to compare the two setups so ran the same mic configuration.  The ADKs were a little more bass heavy and thought possibly it was the preamp but may be not after reading this.  Both recordings sound great and gave them to the band leader.  He liked both but preferred the AKG recording due to cleaner mix (flatter response).  Next time I will try spacing the ADKs more apart and / or increase angle.

[Gutbucket]

I suspect what you are hearing is due mostly to differences in frequency response between the different pairs of microphones, and less related to the situation described above.

The discussion above doesn't really concern the overall frequency balance of the microphone pair (although that is also an important qualification for appropriate microphones to use for ORTF) but is more concerned with the resulting stereo imaging and how well balanced it is across all frequency ranges.   The issue described above with using LDCs for coincident or near-coincident configurations can basically be re-stated as "a lot of stereo seperation at high frequencies and not so much at low frequencies" using LDCs instead of achieving a similar amount of stereo seperation across all frequencies using SDCs with more consistant polar patterns.

However, changing the spacing and angle between microphones can also affect the tonal balance of the recording for various reasons, so those changes can affect the general frequency balance too, as well as affecting the imaging and sense of 'openess'.  It's all somewhat interrelated, you can rarely just change one aspect when you adjust the microphone setup and keep all other aspects exactly the same, multiple things change.

I find the ADK TL set to the hypercardioid position has a flatter frequency response through the bass region than a lot of other super/hypercardioids when used for this type of recording ('this type of recording' meaning stage-lip or more distant placement of a stereo pair, as opposed to close-mic'ing where the proximity effect comes into play emphasising bass frequencies).  I frequently use the TLs in the hypercardioid pattern for on stage or stagelip recording partly because its frequency balance works well for me.  Sometimes I'll substitute a pair of supercardioid Microtech Gefell M21 which are SDCs.  I can hear the differences in imaging between the MG M21s and the ADK TLs set to super/hypercardioid when both pairs are positioned identically, which is probably attributible to the effect described above, as well as slight differences in their overall polar patterns (regardless of pattern consistancy differences, one is probably somewhat closer to the cardioid side of thingsand the other somewhat closer to figure-8), but the more apparent difference is simply the overall tonal difference due to the slightly different frequency responses of the microphones.

If the comments were more about the differences in imaging, openness, reverberance and that sort of thing rather than focusing on tonal differences, then this might be more applicable.  For most listeners tonal differences will be more obvious than imaging differences.

[JimmieC]

Gutbucket, true and may be hyper vs cardioid?  I would be surprised so much difference between polar pattern.  If interested, I can see if I can post a link to samples (if OK with band).  Next time, I'll do same polar pattern for one set of music and then change spacing to see if I can hear a difference.  Thanks for response and correcting my thinking.  I bought the ADK mostly for experimenting polar patterns, M/S, etc.

[JimmieC]

I have ran the ADK (forget the pattern) > DR-680 (Phantom on) and AKG ck61 > Naiant.. > V2 > DR680.  For that show, I thought the ADKs sounded pretty similar to the AKG but thought the ADK bass response was a little lacking.  I like the ADK better with the Littlebox but may be situation too.

[Gutbucket]

Oh right, the ck61 is a cardioid (I don't use those AKGs and forget which capsule number indicates which pattern) and not a super/hypercardioid.  I just assumed both pairs were the same nominal pattern.  Even if they are the same nominal pattern, and regardless of how well they hold that pattern through the full frequency range (which was the jixt of the discussion above), the general patterns may be somewhat different.  Some manufacturer's supercards are closer to the cardioid side of things, others a bit further towards the figure-8 side.  A 'supercardioid' is generally taken to be somewhat more towards the cardioid side and a hypercardioid somewhat closer to the figure 8 side, but there is no standard convention agreed upon by all microphone manufacturers for where those patterns land along the continuum.  That's why I'm using 'super/hypercardioid' to generally describe the pattern, indicating 'something between cardioid and figure-8'.  Its the same situation over on the omni side of the contiuum- thre are subcardioids, open-cardioids, etc. and all those have patterns are somewhere in between taht of an omni and a cardioid.

A closer comparison in your scenario would be with the TLs set to the cardioid pattern, and both the TL and ck61 pairs spaced/angled identically and as close to the same physical position as possible without interfering with each other.  Say mounting the AKGs directly over the ADKs. 

If shooting to maintain similar imaging as much as possible while substituting a cardioid pair for a super/hypercardioid pair, you'll want a tad less more spacing, a tad less more angle, or a bit of both with the cardioids.  Remember that other things things change too in addition to the imaging.  The reververant pickup of the diffuse room sound will sound somewhat different, if the sax player wanders over and stands directly above the microphones which are just above stage level, she'll sound slightly farther away using the super/hypers than cards since the combined pattern of the stereo pair will be slightly less sensitive to sound from directly above and below than it would be if using cardioids.

All this technical stuff helps with understanding what's going on and why things might sound different, but there is no substitute for trying things out and listening for the differences.  The technical stuff just informs that process and helps in making smart choices to get what you want.

[typo edit, correcting less to read more ]

[Gutbucket]

Jimmie, please note the edit to my last post above if you've already read it.  I accidentally had it backwards.

I bought the ADK mostly for experimenting polar patterns, M/S, etc.

I originally picked up a matched pair of ADK TL years ago for the same reason as you, and also because they are relatively inexpensive yet generally comparable in both sound and pattern selection to the AKG 414.  I’ve kept and still use them because they sound good and provide that pattern flexibility when I need it.  I picked up a third one a few years ago for the same reason when I started playing around with three channel stereo configurations on-stage, which tend to have more spacing between each of the microphones than typical two channel stereo setups.

BTW, keeping the caveats of pattern consistency issue noted above in mind, I still find the ADK TL a very good tool for playing around and getting a hands-on understanding of various patterns and stereo configurations.  It's four selectable patterns (omni, cardioid, super/hypercardioid, figure-8) all sound good to me and are generally consistent in their overall frequency response, so they provide a lot of flexibility in trying various setups using a single pair of microphones with a more or less consistent sound signature across all patterns.  That eliminates some variables compared to using a bunch of different microphones from a variety manufacturers, allowing me to better focus on the effect of the pattern alone, and was also more affordable than buying all four capsule types in a single interchangeable SDC microphone line from one manufacturer with a similar or better sound quality than I can get from the TLs.