So I have a pair of AKG 451B's and a stereo bar which only allows you to place the mics side-by-side in XY configuration when in actual fact they should be one over the other.

Where can I get a thread adapter to raise the hight of one of the mics? And are they available in different sizes as presumably I need one to match the width of the mic itself (about 2cm).

Thanks!

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Excess makes the heart grow fonder

Quote siderealxxx:

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So I have a pair of AKG 451B's and a stereo bar which only allows you to place the mics side-by-side in XY configuration when in actual fact they should be one over the other.

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Really? Have you thought about this?

I know the received wisdom is that you should raise one mic above the other so that they remain parallel when the capsules are aligned one above the other... but have you actually worked out the angular error if you don't bother, and instead simply angle one mic slightly down and the other slight up?

The diagram below is a scale drawing of a pair of neumann KM184s demonstrating the angular error if you arrange one capsule above the other, but with the mounting points in the same plane. It amounts to +/- 7 degrees.



And that's with the stubby little KM184s which suffer the problem far more than a longer-bodied mic like the C451.

I don't believe anyone anywhere could tell the difference in frequency response between an on-axis source and one that is 7 degrees off-axis when using a relatively wide cardioid, especially within the context of an large scale source like an orchestra or choir... and that being the case, I no longer bother to add spacers when arranging crossed cardioids. It really makes no practical or audible difference in 99% of applications.

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Where can I get a thread adapter to raise the hight of one of the mics?

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If you must, then CANFORD do a good range of adapters, but they are generally quite widly available.

A standard 5/8 socket to 3/8 stud adapter, fitted with an internal 3/8 to 5/8 adapter does the job quite nicely(assuming your stereo bar has 3/8 fittings).

hugh

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Technical Editor, Sound On Sound

Thanks Hugh - thats very insightful, I had wandered about this approach and actually done it on numerous occasions. Good to know I've not ruined any recordings yet... I will obtain said adapter anyway, I'd be curious to try it. Thanks!

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Excess makes the heart grow fonder

Now I have to say there are *some* situations where I'd disagree with Hugh about this. I recorded a Mozart Requiem with just two beyer MC930s in ORTF. (Things were too cramped to fit in any spots.) Having perfected the angle of the mics in terms of pointing them at the more distant choir to keep it bright over the orchestra, I also tried to position the mic stand so the soloists in front of the orchestra were covered by the mics' cardioid pattern.

However, the two outer soloists moved forward a little for the actual concert. This meant that on the right side, which was covered by the mic pointing more up than down (even in ORTF mics get displaced by their own width on stereo bars) the outer soloist just missed the edge of the cardioid pattern. As a result he came out dramatically quieter on the recording than the other three soloists, which was disappointing.

Ideally I would use soloist spots so this would never have been an issue. However, since that recording I bought one of these: http://cgi.ebay.co.uk/Stand-Accessory-5-8-3-8-Mic-Microphone-Thread-Adapto r-/370523114819?pt=UK_Music_Instruments_Microphones_MJ&hash=item5644e60d43

Now I'm confident that if any errors like this happen again they will at least happen consistently across the stereo image! Basically if you use two cardioids as a distant X/Y or ORTF pair keeping the angle the same in my experience is important.

Hmmm. The displacement caused by lack of an adaptor is probably less than 7 degrees with the MC930s and yet according to their polar pattern, you only get around 1.5db attenuation at 30 degrees. I can't see how your fourth soloist was 'dramatically quieter' because of this displacement. Surely other factors were at play?

Bob

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www.bickerton.co.nz

Quote Bob Bickerton:

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Hmmm. The displacement caused by lack of an adaptor is probably less than 7 degrees with the MC930s and yet according to their polar pattern, you only get around 1.5db attenuation at 30 degrees. I can't see how your fourth soloist was 'dramatically quieter' because of this displacement. Surely other factors were at play?

Bob

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Well the singer was more off-axis than 30 degrees (closer to 90) but you're probably right. Just the fact the mics were quite high meant the singer was projecting more past the mic rather than into it. But in general I have noticed for more distant miking (to try and capture more bloom or blend an amateur ensemble or whatever) it can be audibly noticeable when the mics aren't at the same angle.

Quote mjfe2:

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....the outer soloist just missed the edge of the cardioid pattern. As a result he came out dramatically quieter on the recording than the other three soloists, which was disappointing.

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Clearly, we are talking here about someone who was probably closer to 90 degrees off axis right at the extreme edge of the stereo acceptance angle. In that situation, the (less than) 7 degree offset really wouldn't make a lot of difference. You're going to be in the poo regardless!

Clearly, there will always be an angle beyond which the mic's pickup pattern starts to become unacceptable. Usually it's the frequency response drop-off that becomes too bad, rather than absolute level. And there's always a compromise to be made between how much of the stereo acceptance angle is filled by the source, the distance between the mic and the source, and the acoustic perspective. That's the art of microphone placement!

In the case you describe, it sounds like the distance was too short for the size of the source when the soloists moved forwards. Life can be a bugger that way sometimes

But I stand by my previous comments. In the vast majority of cases, the small angular offset caused by overlapping mic capsules with both mics mounted on the same plane is generally insignificant in terms of imaging.

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Basically if you use two cardioids as a distant X/Y or ORTF pair keeping the angle the same in my experience is important.

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We'll have to agree to disagree on that one...

Hugh

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Technical Editor, Sound On Sound

Quote Bob Bickerton:

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Hmmm. The displacement caused by lack of an adaptor is probably less than 7 degrees with the MC930s

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Yes, I would estimate below 5 degrees.

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you only get around 1.5db attenuation at 30 degrees. I can't see how your fourth soloist was 'dramatically quieter' because of this displacement. Surely other factors were at play?

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Absolutely. Clearly the soloist was significantly far around the side of the mic... and given we're talking about an ORTF arrangement with the mics at 55 degrees to the centre line anyway, that implies that either the soloist was very far forward indeed, or the mic array was extremely close to the stage.

Hugh

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Technical Editor, Sound On Sound

Err...Right.

Maplin also do a range of adaptors!

Dave.