Off axis response SDC microphones

[MicUlli]

Hello all,
it would be fine to catch some opinions regarding the effects of off axis response on the sound (stage) of different stereo mic setups. As a good starting point I have attached some off axis responses of 4 different mic types:
Audio Technica AT2031 (107€), Neumann KM184 (750€), Telefunken TC600 (50 years old, former price 158DM), Primo EM21 (40 years old, former price 98DM).
We all know that the response on axis can (and should) be easily corrected by proper EQ. That is NOT true for off axis response.
For my taste the 50 years old Telefunken TC600 performs best. This mic was developed by MB Electronics, now better known as MBHO

Comments very welcome

 

[kingkorg]

It doesn't make much sense unless you publish the off axis responses together with 0°. 0° normalized of course, and off axis adjusted for level in respect to 0°.
That Telefunken looks like almost omni or wide cardioid. Off axis will also vary widely with distance from the source.

It would make sense to provide 180° as well, which would indicate type of capsule.

If a capsule is a hypercardioid it would logically show better rejection and FR at 90°, but a cardioid would beat it at 180°.

 

[MicUlli]

@kingkorg: ???

The responses ARE already normalised to 0° frequency response. So you can imagine 0° FR for all 4 mics as a straight line at 0dB in the diagrams.

The capsule type is self explaining thru 90° response: AT2031, KM184 and EM21 are cardioids (approx. -6dB) , TC600 is hypercardioid (approx. -8,5dB).

The dB-values in the legend are for 1 kHz. Mesasurement distance was 1m, data were taken in a church (2500m3 volume), quasi anaechonic, by windowing impulse responses before first echo arrived.

As already stated 0° FR is not of importance for this discussion because it can be corrected by proper equalisation.

The diagrams show the differences of the 4 mics very clearly. What do you think, is it (barely) audible?

 

[kingkorg]

If i understand you correctly, you used each mic 0° as a reference for it's off axis response? You divided off axis responses by the 0°, or used 0° as a cal file.

I am a big proponent of importance of off axis response! It's not just important it's crucial even when recording at 0°. It makes much sense that TF will have better rejection at those angles since it's HC. Thanks for heads up on that mic, i wasn't aware of it. But as a HC it will have less rejection from 180°. The energy has to go somewhere, it would be interesting to see how it performs at 180° compared to others.

 

[MicUlli]

Yes, all graphs are scaled to 0° FR. Find attached the responses at 135° and 180°.
For low frequencies the FR is influenced by the proximity effect, should be always kept in mind..
At 1kHz and 135° TC600 has the maximum rejection because of hypercardioid construction.
AT2031 has poor rejection at 180° and high frequencies.

 

[MicUlli]

Here are the graphs for 0° frequency response to complete the measurement set..

 

[kingkorg]

Awesome!

 

[ubxf]

Would the MB Electronic C527 have a similar capsule ?

 

[Paul W]

But as a HC it will have less rejection from 180°. The energy has to go somewhere, it would be interesting to see how it performs at 180° compared to others.

I don't know what you mean by "the energy has to go somewhere."

Is there a conservation law at work that I don't understand?

I would think that when you're combining front and rear signals to create a polar pattern, you're combining information, not energy, and you can combine them in ways where things cancel out, or reinforce, without the missing energy necessarily poking out somewhere else.

For example, at low frequencies where front and back both act more like omnis, flipping the polarity of the back signal will switch between mostly reinforcing low frequencies and mostly cancelling them out.

It also seems like your very neat trick of EQing the back signal differently to make rejection more consistent across different frequencies is another violation of the idea that "the energy has to go somewhere."