Mic Location / Orientation / Cal File for Horn Speaker measurements?

[Robbie010]

Hi all,

I am going round in circles with this basic question so I have turned to the horses mouth, so to speak.

Before posting, I have read loads of threads, asked lots of questions and watched lots of videos. I am asking the question specifically for my own use with horn speakers, as I was told by a knowledgeable individual that my speakers should be measured with the mic pointed at the speakers, due to the directivity of the horns.

Now, if my understanding is correct, with my Umik mic, the standard calibration file is to be used with the mic positioned vertically and the 90 degree file when positioning it horizontally. However, when specifically measuring a 2 channel stereo system, using the 90 degree calibration file and positioning the microphone horizontally, should the mic be orientated centrally, measuring both speakers at the same time, or should the mic be orientated towards each speaker seperately and measured individually?

Finally, given the directivity of the horn speaker design, is there anything to be gained from taking measurements on the vertical axis using the standard calibration file?

Thanks

 

[Wayne A. Pflughaupt]

Now, if my understanding is correct, with my Umik mic, the standard calibration file is to be used with the mic positioned vertically and the 90 degree file when positioning it horizontally.

No, that’s backwards. The 90-degree calibration file is for a vertical orientation. A vertical orientation of the mic is naturally going to attenuate the high frequencies, since it is severely off-axis from the sound source (the speaker). The 90-degree calibration file compensates for that by appropriately boosting the highs. Use the 90-degree file with horizontal (0-degree) orientation and you will get a reading with exaggerated highs – IOW, the highs will read “hotter” than they really are.

As far as which is the proper orientation, I’m a voice crying in the wilderness on this one, but I’ve always preferred 0-degree orientation, typically pointed at the speaker you’re measuring. That’s the way it has been traditionally done, if you review the manuals of vintage room-measurement RTA hardware and manufacturers of measurement mics. And, that’s the way we did it once upon a time when I worked as an installer at a pro-audio company. (REW author John Mulcahy and Herb Singleton of Cross Spectrum Labs have long recommended 0° orientation for in-room frequency response measurements of main-channel speakers, and 90° for acoustics measurements.)

The popular consensus now, put forth on popular guides and Youtube videos by people with no background in pro audio, is to use 90-degree for all measurements, I assume because that allows measurement of all speakers without changing the orientation. My main issue with 90-degrees is that if you have a ceiling that’s more reflective than most, you can see readings with exaggerated highs. Seems to me that even with a “normal” ceiling, if you have speakers positioned high on the wall (like surround speakers often are), 90-degrees can also give a reading with exaggerated highs for those speakers.

Thus, I recommend experimenting with both orientations, using the appropriate calibration file. If they both look the same, then pick the method you find most convenient. But if there is a difference between them, I’d be more inclined to trust the 0-degree reading over the 90.

Regards,
Wayne

 

[DanDan]

You are not alone Wayne. IMO Mics work best pointed at the source. Great mics require minimal or correction, but if there is some HF build up, easily fixed. The mic now hears at least the front hemisphere pretty much equally.
Worth noting that for surround 90 degrees ignores/diminishes all speaker HF equally. At least the speaker is corrected by the Cal file but of course this boosts all of the HF off axis reflections. Pointing the mic down at the carpet would eliminate your very strong very early reflections.