ECM8000 microphone measuring techniques and usage discussion - Page 9 - Home Theater Forum and Systems - HomeTheaterShack.com

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post #81 of 170 Old 01-29-09, 07:18 PM Thread Starter
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Re: ECM8000 microphone measuring techniques and usage discussion

Okay we've merged the threads back together since they both ended up being a discussion of the ECM8k mic and its usage (originally they were split b/c I thought one would end up being a MobilePre discussion).

So back to one big thread folks!

Carry on!
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post #82 of 170 Old 01-29-09, 07:34 PM
 
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Re: ECM8000 microphone measuring techniques and usage discussion

Quote:
hifisponge wrote: View Post
Spearmint -

Both Anthony and I have concluded that the issue we were experiencing had nothing to do with the Mobil Pre. It works as advertised.

- Tim
Quote:
Anthony wrote: View Post
Yeah, the MobilePre is a great portable sound card. I even use it to tie into my laptop as a mobile music station (laptop to MobilePre to stereo). Good for measurements.

It does have some flaws if you want to use it for speaker building. The line out sags its voltage under even light loads, which makes it tough to measure impedance. It is also a bit noisier than some of its counterparts (again unless it's for really serious speaker testing it's not an issue). But the portability aspect and phantom power make it worth it.
Thanks, very much appreciated...
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post #83 of 170 Old 02-03-09, 09:12 AM
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Re: ECM8000 microphone measuring techniques and usage discussion

An interesting response from Cross Spectrum Labs here in regard to mic orientation for measuring.

Does it mean we should stop recommending vertical orientation of the ECM8000 type mic when measuring from the listening position?

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post #84 of 170 Old 02-03-09, 09:59 AM
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Re: ECM8000 microphone measuring techniques and usage discussion

The question might be for those measuring 5.1 or 7.1 full room response, for something like Audyssey type measuring, does the mic need to be turned and pointed at each speaker as the tones/pulse moves from speaker to speaker? Or should we assume Audyssey has accounted for vertical placement of the mic?

And how do you point the mic at a sub, since it is omnidirectional? What if you have subs scattered about the room?
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post #85 of 170 Old 02-03-09, 10:25 AM
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Re: ECM8000 microphone measuring techniques and usage discussion

Quote:
does the mic need to be turned and pointed at each speaker as the tones/pulse moves from speaker to speaker?
Well, Herb has clarified my incorrect interpretation of what he said. His recommendation is that the mic is vertical (straight up and down) with a slight 10-20 degree tilt toward the mains speakers.
And, if you're measuring a specific speaker near field, then it's as we already understood - point the mic horizontally on-axis at the source and gate the impulse response.

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post #86 of 170 Old 02-04-09, 07:23 AM
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Re: ECM8000 microphone measuring techniques and usage discussion

Quote:
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The question might be for those measuring 5.1 or 7.1 full room response, for something like Audyssey type measuring, does the mic need to be turned and pointed at each speaker as the tones/pulse moves from speaker to speaker? Or should we assume Audyssey has accounted for vertical placement of the mic?

And how do you point the mic at a sub, since it is omnidirectional? What if you have subs scattered about the room?
As far as Audyssey, Chris co creator of Audyssey has stated that the position of the mic supplied for use with Audyssey should be at Ear hight and pointed verticaly directly at the ceiling, because it is designed for Grazing..

This works fine unless you have A speaker such as center channel tilted slightly up then it "MAY" be best to adjust the mic angle to match the angle of the center speaker, but that creates A huge hassle ....

Cheers....
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post #87 of 170 Old 02-04-09, 03:56 PM
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Re: ECM8000 microphone measuring techniques and usage discussion

Quote:
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Or should we assume Audyssey has accounted for vertical placement of the mic?
I would presume that Audyssey has accounted for their suggested orientation of the mic and has their system optimized for that placement.

Quote:
And how do you point the mic at a sub, since it is omnidirectional? What if you have subs scattered about the room?
For low frequencies it won't matter since pretty much any (condenser) mic will omnidirectional below 1000 Hz. Point it where ever you like.
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post #88 of 170 Old 02-04-09, 05:30 PM
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Re: ECM8000 microphone measuring techniques and usage discussion

In my years in pro-audio, both professionally and dabbling around the fringes before and since, I’ve never seen anyone use a vertical mic orientation when shooting a room. Typically the mic is aimed at the speaker, so when I first saw the vertical-orientation recommendation here I thought it was the most ridiculous thing I had ever heard. However, when I found out that we were recommending vertical because the ECM8000 was calibrated that way, I let the matter drop, even though I don’t buy into it.

Poking around the internet to bolster my case, I was surprised I wasn’t able to find much of anything to support either method. I looked up the manuals for several pro-audio hardware RTAs and even a couple of software-based programs like TrueRTA, and nothing specifically mentioned mic orientation.

The only thing I could find supporting a horizontal orientation was a picture in the manual of my AudioControl R-130 RTA that showed the calibrated mic pointed directly at the speakers, angled slightly upward. My RTA shows that response at the listening position starts drooping as far down as 1200 Hz with vertical mic orientation, and it gets really severe above 8000 Hz. Having used this RTA for well over 10 years, I trust it enough to know that if I EQ’d my system from a vertical mic orientation, it would be horribly inaccurate.

Likewise, the only thing I could dig up supporting vertical orientation was something on Goldline’s website mentioning that THX recommends it for home theater systems. I find that a bit problematic, however, given the wide range of shapes and sizes of rooms that home theaters find themselves in - high ceilings, low ceilings, cathedral ceilings of different angles and pitches, shoe-box rooms, family rooms open to other areas of the house, etc.

I don’t know how THX, Audyssey or anyone else can in good faith recommend a mic orientation that relies on reflections for upper frequency information to be applicable for all residential situations. Let us not forget that reflected sound will exhibit a certain amount of high frequency loss due to a certain amount of absorption from the walls and ceilings. If room treatments are present, the high frequency loss in reflected soundwaves will be even greater. Did Audyssey figure that into their “grazing” theory? Just a few of the reasons why I prefer horizontal orientation: You know what you’re getting with direct soundwaves.

Quote:
brucek wrote: View Post
Does it mean we should stop recommending vertical orientation of the ECM8000 type mic when measuring from the listening position?
As long as our ECM8000 calibration file was generated using a vertical position, I don’t have a problem with us recommending it for that mic.

However, a while back someone was asking about orientation who was using a dbx mic from one of the company’s RTAs, and we recommended vertical. I think we need to make it a point to tell people to use the orientation that was used to generate their calibration file. If that information is unknown, horizontal should be the standard recommendation, at least for anyone taking full-range measurements. Even if it’s not specifically stated anywhere “on record,” it’s generally accepted that any mic calibration is performed horizontally, unless specifically stated otherwise.

Regards,
Wayne



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post #89 of 170 Old 02-06-09, 10:25 AM
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Re: ECM8000 microphone measuring techniques and usage discussion

Interesting information and discussion... although you guys are the experts, my thoughts...
I fully agree with using the mic in the orientation the cal file was generated in, in ALL cases... anything else has potentially zero accuracy...
Assuming you can get a cal file generated for any orientation you want, if you're willing to pay for it, the question of preferred orientation for different applications, has to depend on the characteristics of a given mic... starting the the ECM8000...
Seems to me that any measurement intending to be a direct measurement, i.e. either ignoring/minimizing reflections and/or in an anechoic setup, point the mic directly at what you're measuring, use a cal file taken in that orientation, and go...
But I question the validity of room response measurements taken horizontally as it seems the body o fthe mic would obviously affect the response to room reflections ... polar plots could prove me wrong...

For low freqs the effects of the case surrounding the mic shouldn't affect things significantly, and at high freqs, when talking about room response, are we really looking for a kind of accuracy where a cal file taken in the verticaly orientation would not adequately account for the diffraction/grazing affects?

I can't comment on Audessey as I have no first-hand experience, but I hesitate to trust any automatic process to do it's job without taking manual measurements to confirm results... "trust, but verify"
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post #90 of 170 Old 07-01-09, 10:18 AM
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Question Re: ECM8000 microphone measuring techniques and usage discussion

Herb,
Perhaps, you could enlighten us.
Are your recommendations for mic placement during measurements based upon some literature that you might share or based upon your experience?
What position do you place the mics in during calibration?

Thanks,
Jay
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