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Discussion Starter · #1 ·
John: Wouldn't it be simple to implement a timer function in the RTA to support this (below)?
  • A countdown timer - like now is in the measurement panel - so the operator can click GO and have X seconds to get in place.
  • And a duration timer that stops the RTA after Y seconds - up to several minutes - of analysis.
Is that something you would consider implementing?

Here is the idea:

With pink noise running and RTA in averaging mode, the measurement mic is is slowly moved by hand at random through a broad area around the LP. Results are fast, easy, accurate. Not a brand-new idea, but well explained and documented.

Just received notice of a recent paper explaining the Moving Mic Measurement (MMM) method of accurate frequency response measurement with pink noise and an RTA. Not usable where phase or time info are needed, but a good alternate or cross-check method for LP frequency response validation. It is a little technical but also down-to-earth enough to be useful. A very worthwhile read.

Here is the paper explaining it: MMM Moving Mic Measurement method.

Jean-Luc's BLOG PAGE. A lot of interesting ideas, some freeware VSTs and audio software. I have been following his work for years, good stuff. Jean-Luc is a very outside the box thinker.
 

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The time doesn't seem to particularly matter, could just have the RTA on Forever averaging, reset the averaging at the start of the measurement and stop the RTA (or save the result) when you're happy you've moved the mic about enough.
 

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Discussion Starter · #4 ·
The time doesn't seem to particularly matter, could just have the RTA on Forever averaging, reset the averaging at the start of the measurement and stop the RTA (or save the result) when you're happy you've moved the mic about enough.
You are right, actually I thought of it and tried it and it does work just fine, as long as the beginning and ending times are kept to a minimum with the mic kept in the target area the whole time.

Thanks, John. Don't you just love all my nutty requests?
 

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Discussion Starter · #5 ·
Assuming it could be done, what is the benefit? Just time saved compared to taking several separate measurements?

Regards,
Wayne
Benefits, according to Jean-Luc's well-supported paper, and it all makes good sense:
  • Time saved (just?), which can be significant.
  • The accuracy - or better than - of a large number of broadly-spaced individual measurements averaged.
  • A good and easy cross-check for what to expect from multiple measurements to be averaged.
The technique, which gives no time or phase information, will not replace individual measurements, but looks like a good alternative technique for some applications.
 

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Yes, EQ to a single mic position may be very helpful in some cases, but is a relatively poor method. All the commercial "automated EQ" methods I am aware of utilize multiple positions in the listening area.

The MMM is suitable for hobbyists intending to spend time to fine tune their house curve using manually adjusted EQ to best satisfy their preferences.

1. Very high repeatability (extremely low standard deviation of the SPL variability) without concern for micro locations of the mic positions.

2. Insensitivity to mic movement pattern or reasonable mic speed differences.

3. Low sensitivity to differences in window/volume size selected. In my room I can change the volume of the measurement area 50% or more without significant change to the MMM measurement. I prefer to cover a window/volume surrounding 1-1/2 listening positions and the difference is insignificant if I change to covering 1 or 2 position areas.

4. There is high correlation to averaging SPL of a large number of individual measurements within the same area.

5. Measurement time is only approx. 30 seconds for my situation. 10 measurements would take much longer and be significantly less repeatable. [I've taken roughly a thousand MMM measurements in my room so it adds up for me.]

I was puzzled only by the comment in the paper that the 90° mic cal was important with mic direction random or 90° to the speaker. I find only a negligible difference in doing that, verses using 0° cal and pointing the mic in the general direction of the speaker during the MMM. Even if the difference is more significant in some rooms and makes a small, but significant change to the final house curve shape, I don't understand why the end results would not be the same. Maybe this could be a problem if a preconceived notion of what the correct house curve is? It's best to keep in mind that there is wide variability in music recording studios. Things are better defined for theater, but there are still differences due to; room volume, listening distance, and speaker dispersion. Even preferred listening volume impacts the house curve that is preferred. In the end, the house curve is a compromise decision.

If one intends to spend the time needed to fine tune a house curve then having an easy and repeatable measurement method is critical. This is probably only a very small percentage of the hobbyists here.

If manually fine tuning the house curve using repeated measurements/listening sessions is not the intent, then this method provides little value.
 

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Discussion Starter · #8 ·
Thanks for your viewpoint, jtalden. I kinda glossed over the mic direction instructions, making the assumptions you mentioned. My main mic has a small tip diameter so little directional variations are not a huge factor.

I have heard of the MMM method but never used it or seen it documented so well. I also see it as a crosscheck before starting multiple measurements for Dirac Live or Audyssey MultEQ or other purposes - "what should I expect to see?"
 

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Yes, that is a good point. Any before/after measurements that are intended to show an SPL change needs a highly repeatable measurement method from setup to setup.
 

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Yes, EQ to a single mic position may be very helpful in some cases, but is a relatively poor method. All the commercial "automated EQ" methods I am aware of utilize multiple positions in the listening area.
fwiw acourate uses a single measurement position but produces quite sublime results. I think, in the end, it's what you do with it that counts.
 

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Interesting.
I have looked at their info, but I didn't catch that only one position is recommended.

There are lots of good comments about the results, so...
 

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Discussion Starter · #12 ·
When experimenting and trying not to get too bogged down in tedium, I like the MMM for finding the "area average," then finding a centered single point that is CLOSE to that average, then can use that single point for ongoing quick measurements. NOT for reference work, just for messing about.
 
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