Using energy time curve for acoustic analysis: developing a Home Theatre primer - Page 9

Okay I figured out how to get the impulse graph I want in REW, using the %FS rather than db FS mode.

Oye!
Where is the mic when you are measuring those 1/6th oct FR's?
At the listening position?

cheers,

AJ

All measurements taken at the main listening position. Using a ECM8000 mic pointed straight forward and an M-Audio FastTrack Pro. I bunched several blankets loosely around the mic to reduce the effect of the seat back.

Right now the room has 2" of acoustic cotton lining all the surfaces behind the screen wall (as per Dennis Erskine design recommendation) and no other treatments yet.

I suspect some of some reflections at 1.5ms are coming off the 2x4 framed false wall that hides the speakers, I might need to line that framing with some cotton.

kromkamp,
please start your own thread for your particular situation or questions.

regarding the ETC,

Running in circles. Cool!
How will you when you get to the end then? Is there one? Or more laps?

cheers,

AJ

And how does it sound to you at the LP?
What speakers btw?`


What was the result perceptually? Did you prefer it to your memory of the untreated wall?


Seems possible.

cheers,

AJ

That's quite an assumption...


Can we assume you started due to something wrong with the sound, or...?
And thus the stop will be when that something is sufficiently absent?


So your unknown end goal will be applicable to others? It won't just be some arbitrary preference point of yours?

cheers,

AJ

Will do.
And as long as the "and related" doesn't extend to perception, you should be fine. Stick with the "for acoustic analysis" abstract and this should run for a while, with the usual cast of characters.

cheers,

AJ

my apologies localhost/mtbdudex - It seemed to me this discussion would benefit from more concrete examples of ETC analysis. I can certainly move them to another thread if you prefer.

Cheers

We've had bucketloads of those. Now we just need the Local Host and Dragon et al analyzers to give us those concrete "ETC as it correlated to perception" examples/studies. Those seem to be AWOL.

cheers,

AJ

Me neither. But I'm more of an expert on what I prefer, than any other "expert" out there will ever be. How 'bout you?


I don't do it on purpose.


Eh? What does that mean? Why did you "establish RFZ" in your home??


For the sake of "acoustic analysis", or...??


Sure. What relevance do they have to your perceptual end goal? The sound you desire.
Or is your end goal simply "analysis" of your HT/room, cause it's fun to do?

cheers,

AJ

No problem Mike. Here's a(nother) non-philosophical ETC q for you.
What perceptual relevance do ETCs have?
Thanks in advance for your non-philosophical ETC a

cheers,

AJ

this article doesn't really "say much", either. im not interested in "absorber placement" either via the "mirror trick" or by actually utilizing the ETC (there is nothing of difficulty with such processes). we solved how to use the ETC to identify high-gain early reflections and their attenuation once an absorber has been placed ages ago. and why would a band-limited ETC even be necessary or required for "absorber placement"?

not to mention, the article basically just uses broadband absorption of varying thickness, without so much as mentioning the flow-resistivity values of the material...there is nothing to be gained from that section of the article and im not sure why it was presented?

where is the analysis of treatment design based on speaker radiation patterns or information generated from the band-limited ETC?

from the conclusion of your online publication (http://www.hifizine.com/2011/12/list...-time-curve/):


what i'm after is examples of "appropriate acoustic treatment" for varying examples of speaker radiation patterns and/or band-limited ETC measurements. i'd like to see an example of what custom treatment you designed for a particular room via measured band-limited ETCs - or even the room in question of which the graphs were generated on your online publication.

I moved my measurements to my own build thread Here

Thanks!

I only referenced the linkwitz article and the other one i linked out to because it seemed localhost was having problems understanding band limited etc measurements. I was trying to show that I'm not the only one using these types of measurements for analysis and that the time domain 'data' can be analyzed in many complementary ways.

Aj

All the perceptual effects are summarized clearly by Arthur Benade, "From Instrument to Ear in a Room: From instrument to ear in a room: Direct or via recording," Journal of the Audio Engineering Society, Vol 33 Nr 4, 1985., who wrote:

"The auditory system combines the information contained a set of reduplicated sound sequences (authors note - i.e. the direct sound and its reflections) and hears them as if they were a single entity, provided:
a. that these sequences are reasonably similar in their spectral and temporal patterns,
and
b. that most of them arrive within a time interval of 40 ms following the arrival of the first member of the set.
The singly perceived composite entity represents the accumulated information about the acoustical features (tone color, articulation, etc) shared by the set of signals. It is heard as though all the later arrivals were piled upon the first one without any delay - that is, the perceived time of arrival of the entire set is the physical instant at which the earliest member arrived (authors note - this is known as the precedence effect).
The loudness of the perceived sound is augmented above that of the first arrival by the accumulated contributions from the later arrivals.
The apparent position of the source of the composite sound coincides with the position of the source of the first-arriving member of the set, regardless of the physical direction from which the later arrivals may be coming."

im having problems understanding how you are "carefully selecting appropriate acoustic treatment to correct for dissimilarities in the spectral balance of reflected sounds."

what treatments were selected for the example room of which the band-limited ETC's were presented in the online publication? is there post band-limited-ETCs as well, once the treatment has been placed?


they used those types of measurements under a section titled: "absorber placement". of which, band-limited ETC's are not even necessary (and they also revert back to using a mirror, when they're already using the ETC). not to mention - within the article, they simply apply broadband porous absorption ! how are appropriate treatments being selected or build based on particular speaker radiation patterns or information gained from the band-limited ETC? are concepts now being validated based simply on the fact that "someone else" is doing it too?

Was this thread killed, or did it die of natural causes?

It died as there are not enough familiar with what the response represents as well as not enough folks who could use Google fast enough to find sufficient out of context statements in order to sustain the nonsense.

I don't think there's much more to say after dragonfyr explained why we don't need to use bandlimited ETC. That made perfectly sense to me.

But can someone point me to dragonfyr's explanation of this? I want to read it again, but I can't find it.

If a reflection does not show up in the ETC in lower bands (lower resolution), but it does show up in the higher bands (higher resolution), would that suggest that the object that is reflecting is smaller with respect to the wavelengths being used?

A lot of using ETC measurements, and wanting to read about others, and relating them to REAL ROOMS and seeing how they solved problems, is educational.

In my case, I'd like to post before-after when I get better ceiling tile up. The stuff I was left with when I bought my home feels more like drywall, probably the cheapest stuff at Menards: Chalky, painted paper surface with no orifices.

I want to replace a couple rows of tile with better-absorbing ones, and probably lay some insulation on top of them to absorb lower.

Maybe everyone else is doing the same, waiting until they have more of their own real examples and measurements to post?

A lot of his posts seem to have disappeared from this thread. Anyone know why?

When the Experts disagree, it's like Mommy and Daddy fighting. There's a cloud in the house.

When the teachers trying to teach 4th grade concepts also pedantically hold students accountable to 8th grade standards, and strike down from an ivory tower with finger of god force, it gets tough to learn. We've seen that here.

Being an expert on something doesn't automatically make one a good teacher.

Despite the moaning about the fractious recalcitrant AVS users, I see arguing and dissent and repetition at GearSlutz forums too.

Although it looks like AJ has an agenda, I don't begrudge his looking for examples of relating perceptual quality improvements to treatment. I don't think Nyal's pointing to a paragraph explaining the precedence effect helped. And I understand people looking for more examples of ETC in a real room, relating the measurements to how the room initially didn't follow a given model, how the problem surfaces were found, what was done to treat them, what the ETC looked like afterwards (which should follow the model), and how the new conformance to the model was qualitatively & perceptually then enjoyed by all.

On the other hand, I understand the Experts' frustration with students not trying this stuff out on their own rather than arguing so much. It's true, that many people have spent a lot of hours talking and thousands of dollars on other aspects of a theater's sound. So it suggests that a few tens of hours and a few hundred dollars are easily affordable.

Personally, I'd reinforce the utility in performing measurements in one's home. It has helped to make it all "real" and tie concepts together for me.

It was edifying for me to look at the ETC, remove some panels and see that they weren't doing much. Then put those panels in other areas I hadn't gotten around to treating yet, and seeing a dramatic removal of a reflection. Then removing ceiling tiles and putting blankets (which I felt should use band-limited high frequency ETC because blankets aren't 4" thick insulation) or insulation up there.

I struggled mightily with one reflection that I couldn't find. Using the blocking method on a center speaker, I had to bound the left and right of the speaker with 2' x 4' panels to kill the reflection. Move the panels out farther and farther, and the reflection would appear. Move a panel in front of stuff that I thought might be reflecting, no joy. Then, even though I was by myself, I rigged a sloppy string method setup. Low and behold, I traced the reflection to my surround speakers (Paradigm ADP-170) that stick out of the wall as trapezoids. The front and bottom of the speaker was reflecting. I was surprised that one to two square feet would make that big of a reflection (I was trying to get the reflections down 15dB under the direct signal).

Just like other things in life, practical example and practice is part of the education process.

I've also read the Toole book, the Alton Everest book, and the freely available pages of the Acoustic Absorbers & Diffusors book referenced here.