a request (challenge?) for Aholics

[ratso]

don't make me beg here. i recently bought the omnimic measuring system. it is simple and intuitive to take fr sweeps, waterfall graphs, etc. but there is a problem i am having and i'm not alone. from the AVS forum on omnimic, a sample of quotes:

"I was hoping that I'd find a good 'How To...' on the net somewhere but I haven't so far. I'm a total noob at all this measuring stuff - I know how a first-time Audyssey user feels now!"

"I've searched high and low for a 101 on acoustic measuring but, so far, without success..."

"I do not think there is a "HOW TO Read measurements" thread or document online. THere should be!! I think everyone learns over time from looking at 100's of plots and reading 100s of discussions."

"So far, the Omnimic has not really helped me. This was my fear before I bought it - that the learning curve would be very steep, that there is no online 101 on room measurement and how to use the graphs."

i could go on but i think you get the idea. there is very little BEGINNER information online on how to take standard measurements (nearfield? farfield? which weighting? which smoothing? what range? - yes there are some instructions for this, but they all assume you know what all these are and what your doing). and there is almost zero, nada, zilch info online on how to use and apply these pretty graphs - how to read a waterfall, decay plots, fr response, how do i interpret these when moving my speakers and subs around the room, should i have my subs on or off, should i measure one channel at a time, should i be using rta or snapshots, etc etc). audioholics would be doing a lot of people a real service with an article (or better, series of articles for each major graph type) for NOOBS. true, not everyone will take room measurements, but all of us could learn how to look at a waterfall chart and know what it means. how about it? please? pleeeeezzzzzzz.....

 

[ratso]

from audioholic's own multiple sub setup guide:

"It is assumed the reader is knowledgeable on how to properly use an FFT or RTA analyzer to properly measure system response. Instructions about how to use such equipment can fill an entire article on its own, which is outside the scope of this article."

so ummm where is that?

 

[lsiberian]

You might check out the REW guide.

Essentially a F-R is the level for each frequency at the position of the listener.

Multiple measurement positions are used to provide the best average sound.

Just remember this rule, Keep it Simple Silly. Measurements can be very helpful, but at the end of the day your mind is pretty good at helping correct for room issues.

 

[Alex2507]

A guy named MikeZ over at the Parts Express Tech Talk forum has an Omnimic set up. You might want to shake that tree. I'm sure others there are familiar with it as well. As far as articles are concerned I have no idea where you would find them.

 

[Irvrobinson]

i could go on but i think you get the idea. there is very little BEGINNER information online on how to take standard measurements (nearfield? farfield? which weighting? which smoothing? what range? - yes there are some instructions for this, but they all assume you know what all these are and what your doing). and there is almost zero, nada, zilch info online on how to use and apply these pretty graphs - how to read a waterfall, decay plots, fr response, how do i interpret these when moving my speakers and subs around the room, should i have my subs on or off, should i measure one channel at a time, should i be using rta or snapshots, etc etc). audioholics would be doing a lot of people a real service with an article (or better, series of articles for each major graph type) for NOOBS. true, not everyone will take room measurements, but all of us could learn how to look at a waterfall chart and know what it means. how about it? please? pleeeeezzzzzzz.....

I'm not going to write an intro article, but to answer some of your questions:

1. I recommend putting the mic on a stand with a boom and position it at ear-height at your listening position.

2. I measure the system as I listen to it, with the sub active.

3. I measure one channel at a time only if I think I need to for micro-positioning the mains. What I found is that I micro-position the mains for imaging, and micro-position the sub(s) for best frequency response. I use both noise and sine sweeps, but I prefer the A-weighted noise chart.

4. I use the frequency response screen with 1/6th octave smoothing the most. For noise analysis I find A-weighting to be most useful.

5. The bass decay plot is for advanced work (like figuring out room treatments). I don't use it, but this link explains it if you are mildly technical:

Decay and Waterfall Plots

6. I use the RTA display for analyzing the background noise of the room. When my HVAC system runs, for example, it has a very annoying spike at 57Hz.

There is a lot of understandable information available easily from a Google search, as long as you have just a smidgen of knowledge about sound propagation.

 

[ratso]

thanx irv, actually i thought that you would be the guy to do this guide after reading some of your posts. maybe a case of beer? seriously though, i thank you for the time for the response. and it is helpful, i actually have read everything i can get my hands on about this and know a little bit about it. it just amazes me that for all the talk about graphs, charts, RTA, etc. that there is NO definitive A-Z guide on this. you would think SOMEONE out there would have done it by now. maybe if i can become more knowledgeable i will tackle it someday. hmmm....

 

[Irvrobinson]

thanx irv, actually i thought that you would be the guy to do this guide after reading some of your posts.

I'm not really an expert, so I shouldn't write it. I'm just technical enough in other fields to understand what experts write.

 

[ratso]

i may have misunderstood isiberian's post - this may have been what he was refering to. i thought he was refering more to the REW manual? not perfect but this is better than anything else i've seen:

RealTraps - Room Measuring Series