Topic: Boundary Mics - Recommendations?

[John Kelly]

I'm looking to pick up a boundary mic (maybe a pair) for recording some classical music and opera.  I'm not allowed to run a stand up front, not even a small stand, so my options are to pick up boundary mics or stealth it - and I'm not a fan of stealthing. 

Anyone used a boundary mic in that setting?  Any recommendations on a specific model?

[mfrench]

they're not boundary mics, but I use my DPA 4060's in the boundary layer technique, by simply spacing them and taping them to the rear wall of the venue. Depending on the room, I've had some fantastic results.

[DSatz]

I recently started using a pair of boundary microphones for opera recording, which I mix in with the main stereo pair. It makes a huge difference in the clarity and intelligibility of the singing, and I only wish I had started doing it sooner. I may also place the main pair a little farther back from now on, "just because I can."

The performances that I record are given in a church. The first time I used boundary mikes, they were Schoeps BLM 03 Cs, which are virtually invisible and built to resist damage even if stepped on. The sound was lovely, but the orchestra was directly in front of the slightly raised "stage" (altar) area, so I decided that some directivity and ability to aim the mikes away from the orchestra was desirable.

Schoeps makes a small accessory plate called a BLC, with a built-in holder for one of their CCMs or a capsule on a Colette active cable, so I've started using a pair of those with speech cardioid capsules on them. At first I was worried that people could step on the capsules and break them, but then Jerry Bruck gave me the idea of putting a headlight guard on top of the mike (see photo--this is from before I gaffer-taped stuff down, of course). I've also sent this photo to friends at Schoeps to see whether they might not want to come up with their own solution. Anyway, that has worked quite well and it's what I will very likely continue to use.

--best regards

P.S.: Looks as if photos are OK to upload again now, so:

[John Kelly]

they're not boundary mics, but I use my DPA 4060's in the boundary layer technique, by simply spacing them and taping them to the rear wall of the venue. Depending on the room, I've had some fantastic results.

I appreciate it, but I've already recorded from the back with my Senns and the results are less than optimal.  I need to be close, and in order to be close I need to be extremely low profile.  The 4060s aren't a bad choice and I'll definitely consider them, but I think boundary mics may work better in this scenario.

DSatz - I'll check into the Schoeps, thanks!

[mfrench]

While I'd agree with the rear of the room as being less than optimal - I think you'd be surprised with the technique. It produces allot better results than you might think.
I'll very typically fly one pair of mics up front (or closer) and use the boundary pair as a secondary reference. I can't properly express the amount of times that the musical director has suggested loving the rear of hall capture.

boundary mics are omnis used on a boundary - i don't see much of a difference at that level.

[John Kelly]

While I'd agree with the rear of the room as being less than optimal - I think you'd be surprised with the technique. It produces allot better results than you might think.
I'll very typically fly one pair of mics up front (or closer) and use the boundary pair as a secondary reference. I can't properly express the amount of times that the musical director has suggested loving the rear of hall capture.

boundary mics are omnis used on a boundary - i don't see much of a difference at that level.

I just recorded a recital at the rear of the room - the problem I have with it is the vocalist is not mic'ed, so I have to crank the gain from the rear and really ride the levels due to the crowd.  Kind of hard to enjoy the show if I'm constantly worrying about the recording.  From the front I'm pretty sure I can dial in to a comfortable level and leave it throughout the performance.

And the boundary mics I've been looking at (really only a few so far) are cards, not omnis. 

I was thinking about picking up a pair of Sennheiser e912s, but the frequency response graph didn't really impress me much.

[Walstib62]

If I'm not mistaken, boundary mics are neither cards nor omni's. They actually have a hemispherical pickup pattern, which is more similar in practice to an omni depending on placement. The advantage to boudary mics is that the surface they are mounted to becomes the pickup area. The larger the surface, the better the low end response is in particular.

[Walstib62]

mfrench,
Could you decribe how you are mounting those mics in a little more detail? Sounds interesting.
Thanks

[mfrench]

If I'm not mistaken, boundary mics are neither cards nor omni's. They actually have a hemispherical pickup pattern, which is more similar in practice to an omni depending on placement. The advantage to boudary mics is that the surface they are mounted to becomes the pickup area. The larger the surface, the better the low end response is in particular.

I was going to follow up my comment with something quite similar to this. The boundary takes a 360º pickup orb, and reduces it to a hemispherical pattern.

Let me see if I can find pictures; but, I literally take the 4060's, spread them about 4', and take a couple of inches of gaff tape and tape them to the surface, just behind the capsule.
In one venue, I have the ability to utilize the hall design as baffles. The hall design has tall vertical wood slats at the rear of the hall, spaced about 9" apart.  I can keep the mics closer together, and, baffle them from each other by nestling them tightly to the wood baffle slats.
let me see if I have any pictures available.

[John Kelly]

If I'm not mistaken, boundary mics are neither cards nor omni's. They actually have a hemispherical pickup pattern, which is more similar in practice to an omni depending on placement. The advantage to boudary mics is that the surface they are mounted to becomes the pickup area. The larger the surface, the better the low end response is in particular.

Typically, yes.  But the ones I was looking at were actually cardiod.  Odd, I know.

[DSatz]

Walstib, no, actually that's not what boundary layer microphones do. First of all, any pattern of microphone can be used, and its directional pattern will then be cut in half since the other half of it would theoretically lie behind/beneath/beyond the room boundary that it's mounted in/on. So for an omni mike the pattern becomes hemispherical, but that's only to be expected since sound can't reach the microphone from beneath the floor / behind the wall that it's flush with.

Second, if the microphone is mounted on (or within) a large enough, rigid enough surface, its frequency response will be the same as it would be with normal free-field mounting. But it won't have the usual narrowing of its pattern at high-frequencies any more, and it will now be 6 dB more sensitive to direct sound energy and 3 dB more sensitive to diffuse sound energy across the frequency range. The fact that the sensitivity to direct sound rises 3 dB more than the sensitivity to diffuse sound means that the pickup will be somewhat clearer, all other things being equal (which they won't be, since you don't normally record from positions near a floor or wall, do you? I didn't think so).

What you may be thinking of when you mention the (very real) relationship between the size of the surface that the microphone is mounted in/on and the low frequency response is that for flat frequency response down to a given low frequency, the size of the room boundary must be at least half a wavelength at that frequency in both dimensions. Since (say) 55 Hz has a wavelength in air of about 20 feet, you can well imagine that mounting a boundary layer microphone (say) on the lid of a piano is going to cause severe low-frequency losses (although advocates of "PZMs" do that all the time). And it's not just a simple rolloff--there can be peaks and valleys of 12 dB or more at particular frequencies.

So if you're trying to make a full-range recording, you need to be particular about where the microphones are located. For providing reinforcement for the vocalists in an opera recording, though, you don't need (or want) anything below about 80-100 Hz anyway.

--best regards

[John Kelly]

Oh noes!  Post with the Neumann boundary mic is gone. 

[Gutbucket]

John,
If you go the DPA miniature omni (4060/1/3) route, they have a boundary mounting acessory which is basically a tapered rubber disk into which the mic is inserted, which protects the capsule and makes for a smooth transition to the bondary surface.  The disks are lightweight and need to be gaffer taped down.  They are available seperately or as part of the stereo mic'ing kit.  I posted photos if them here a few years ago and will look for the thread.

DPA now makes a dedicated boundary model, which uses the same capsules in a weighted housing of similar dimentions which doesn't need to be taped down unless you choose to do so.

[Gutbucket]

Found those old 4060 boundary mount accessory photos-

top-


bottom-


mic inserted-


top with mic inserted (ignore the cork base and foam ball baffle)-


More photos and usage details are in this post from that original thread.

[John Kelly]

Very nice.  I think that may be the best way to go, that way I'll also have a set of tiny ass stealth mics as well when I don't want to run the Senns.