TOPIC: UMIK-1 mic position and polar plot

Question: when using the UMIK-1 pointed vertically (90-degree calibration), should the blue power LED be facing towards the source of the sound, or vice-versa?

...and now some context to help explain why I'm asking

We know that the UMIK-1 is an omnidirectional mic, meaning that it should in theory pick up sound with equal gain from all sides or directions.

However, it seems that in practice the polar patterns of omnidirectional mics are never truly equal on all sides. For example, here's the polar plot of an M30 Earthworks Audio mic - and we can see that one side of the capsule is slightly less consistent/accurate:



I'm unable find a copy of the polar plot for the UMIK-1 - it doesn't seem that one is published - so I'm wondering whether the UMIK has a similar plot to the M30, with one section of the mic's diaphragm/circumference being slightly less accurate? And if so, are we correct to assume that it's the 'bottom' edge of the mic that is less accurate - i.e. in the case of the UMIK, the edge opposite the little blue power LED?

This would have implications when using the UMIK-1 mic at 90-degree orientation (pointing to ceiling). In which case, we'd most likely want the more accurate side of the capsule facing towards the main speakers. So again, when the mic is angled at 90-degrees (pointing upwards to the ceiling), should the little blue power LED be facing the source of the sound we wish to measure, or vice-versa… or doesn’t it matter either way?!

Grateful if anyone can shed some light on this question

? 180 is behind the mic

john.reekie wrote:
Thanks John. The voice of sanity

I’ve just realised that I’ve been misinterpreting the mic polar plots… and that what I thought was a ‘less accurate’ section of the mic diaphragm (e.g. at “6 o’clock” on the polar plot above) is in fact the response from behind the mic at 180 degrees.

Cue facepalm...!


Thanks again for clarifying. Its good to learn something new each day...

No worries I'll get a badge made

Skol303 wrote:
I'm wondering why you are pointing the mic to the ceiling - or the floor - instead of pointing it straight at the centre point between the speakers (ie. horizontal)?

Andy

Hi Andy. Happy to explain.

Short answer - the team at Dirac Live recommend 90-degree mic orientation when calibrating their software, no matter whether it's a 2-channel or surround sound set up (albeit contrary to what is written in miniDSP user manuals, as I discovered for myself). Here's an example response from their HelpDesk:

“By pointing the microphone upwards you will get the same coloration on the sound coming from the backward/side/front wall as the direct wave from the speaker. This is important in the filter deign process so we don't do any wrong decisions. If you point the microphone to the speakers instead, the coloration of the room will differ from the direct wave, this could result in filters which are overcompensated in certain frequencies. For our room correction system I would always recommend to point the microphone upwards.”

I've discovered that this view is also supported by most professional acousticians (through discussion on other forums), who tend to recommend pointing the mic at 0-degrees for speaker measurements (when you want to focus on the direct wave) but at 90-degrees when taking room measurements (when you want to more evenly capture the direct wave plus reflections). Dirac Live software is concerned with the whole room, not just the speakers, for the purpose of its time/frequency domain corrections. Hence 90-degree orientation seems most logical.

Longer answer is available in this thread if you want to read it…

www.minidsp.com/forum/dirac-series-suppo...field-monitoring-how

Skol303 wrote:
Thanks, Skol - but I read the last link you provided and it said (the Dev Team post, no. 2) that for stereo ... you point it horizontally, "direct at the speaker".

Not sure quite that means when you have a stereo setup - but I would assume it means pointed directly between the speakers - so mid way between them?

(Only when you have a 360-like speaker arrangement (i.e. 5.1/7.1) would you point the mic up, to able to hear all speakers with the same angle of incidence.)

Maybe only when one is using Dirac Live does one point it vertically (I just have a 10x10HD)?

Andy

Hi Andy,

“Devteam” is miniDSP support and their recommendation is indeed to point the mic on-axis (0-degrees) for two channel stereo set up of their Dirac Live products.

The Dirac team’s own recommendation is to point the mic vertically (90-degrees), using a suitable calibration file, for both stereo and multi-channel set ups.

So there’s a contradiction between the advice given by miniDSP and Dirac Live.

Ultimately, from my own testing it doesn’t appear to make much difference (my test results are included in the thread above). But when calibrating Dirac Live software, it seems sensible to follow the advice of the Dirac team themselves and point the mic upwards.

If you’re not using Dirac Live - perhaps another DSP/DRC software? - then the advice may differ, depending on how that software is configured. Sonarworks for example recommend pointing the mic at the speakers... but they also suggest it’s ok to just hold the mic in your hand, so they’re perhaps less concerned about accuracy.

Nearly all acousticians I’ve spoken with also recommend angling the mic upwards for room measurements (usually at an angle of 70-degrees in fact). This of course applies to diffuse field mics, which are designed to work that way. But I also see the same recommendation for free-field mics (like the UMIK-1) providing you have a calibration file. This is because when angled vertically, the mic captures a more balanced picture of the whole room response - not just the speakers - and that’s a good thing in terms of DSP/DRC calibration.

Hope that helps.

Thank you, skol303.

I'm not using Dirac Live yet but when I next do an REW measurement, I will angle the mic vertically, if this enables a more balanced capture of the whole room response.

Andy

You’re welcome!

It doesn’t make a huge difference whichever way you angle the mic (and the difference is only in the high end above 5kHz or so). But angling upwards does help to capture a more balanced picture of the room reflections combined with the direct signal from the speakers, which is most useful for the purpose of setting up ‘room correction’ software. Even more so if your room has no acoustic treatment.

Either way in most cases the difference will be small (in my room <1 dB), but there will be a difference.