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

49283 Views 291 Replies 27 Participants Last post by mtbdudex, Nov 10, 2014

mtbdudex

Discussion Starter · Aug 1, 2011

I'd like to read a primer on HT enthusiasts using energy time curve (ETC) charts/graphs for their acoustic analysis.

Not some REW help files or theory in books/online either, I've read all those and .... sorta get it.

What I'm looking for is a thread that details some peoples journey thru the acoustic rabbit hole, jumping in, getting really small once realizing how much info/data there is.

Then, growing and using energy time curve charts/graphs for their acoustic analysis.

The "final step".

I searched but can't find a thread here.

I've taken lots of measurements, freq/H20, for my IB sub, but for some reason I've steered away from energy time curve charts for my side wall/ceiling acoustic treatments.

I'm willing to be "Alice", who will lead me thru the acoustic energy time curve (ETC) charts/graphs rabbit hole?

Show me what you done, how you've analyzed your room acoustics, and made changes until you've said "I'm done".

My (4) LH and (2) RH side wall panels are easily removable, and while the (2) ceiling clouds are sorta big/bulky hanging there, I could cover their facing downside with kraft paper to negate their effects for measurements.

I'm thinking this would help others also as I go thru this acoustic learning journey.....

http://www.santafevisions.com/csf/ht...considerations

[edit Feb-28-2012] Plan to re-boot this thread March/April 2012:

Come spring, when I re-do my 130" screen due to humidity induced warping of the screen , , I will totally remove all my existing side wall/ceiling panels and start from baseline of no treatments on the room

(besides my corner superchunks, which all have front facing reflective treatment on them)

I also will do the following:

-Pure reflective room baseline

-baseline of "the mirror tricK", as I did, with side wall 2" panels + 2" air gap

-Pure ETC approach and using 4" panels + 4" air gap at specific locations verified by ETC

-compare and make objective and subjective assessment

All above is being done utilizing porous absorbers.

Come 2014/2015, when it's new PJ time (4k +LED light engine), and I go AT front screen - with DIY L/C/R main speakers in a baffle wall, then the whole HT acoustic treatment strategy will change; diffusion, membrane absorbers, etc....but that's topic for a different thread.

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fastl

· #2 · Aug 1, 2011

ETC analysis was the fad back in the late 70's early 80's. Basically doesn't work. You know that old saying about re-inventing the wheel?

localhost127

· #3 · Aug 2, 2011

Quote:
Originally Posted by fastl /forum/post/20767403

ETC analysis was the fad back in the late 70's early 80's. Basically doesn't work. You know that old saying about re-inventing the wheel?

the ETC is a tool that details a room's specular response. it is not a fancy analysis; it merely displays gain vs time. that is all.

Quote:
Originally Posted by SAC /forum/post/0

Its time more people looked at the time domain ETC and focused on what it shows.Its characteristics are displayed in terms of gain and time. There is no frequency scale. There is a reason the time domain takes precedence here, as the time relationships are causal with regard to the derivative anomalies that appear in the frequency domain.

the ETC is used to identify energy (eg specular reflections that are modeled as rays), and where it impedes the listening position after the original signal, with respect to time.

it also allows you to see how your diffuser (eg if it performs spatial and temporal dispersion - is actually performing and how a particular specular reflection now impedes the listening position as a diffused return.

control rooms and critical listening rooms employ the LEDE (and now RFZ) room models to achieve a particular response. this response is measured with the ETC.

if one is seeking to emulate the Reflection-Free-Zone room model, then early-reflections which must be attenuated are identified (and their incident boundary) with the ETC.

if one is seeking to induce a haas kicker, then this is measured to arrive at the correct time after the original signal with the ETC.

you'll fancy this comment by george massenberg regarding
blackbird studio C 's ETC response:

http://www.gearslutz.com/board/6834790-post49.html

RFZ is an evolution of LEDE - and now, blackbird studio c's room response (ambechoic) is an evolution of RFZ.

but good luck emulating that response in your room.

for your pleasure (take note to SAC's commentary):

http://www.gearslutz.com/board/studi...c-impulse.html

http://www.gearslutz.com/board/bass-...absorbers.html

http://www.gearslutz.com/board/6202822-post67.html

http://www.gearslutz.com/board/studi...s-trigger.html

http://www.gearslutz.com/board/6118734-post48.html & http://www.gearslutz.com/board/6145795-post60.html (troubleshooting for early specular reflections and their elimination).

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localhost127

· #4 · Aug 2, 2011

Quote:
Originally Posted by mtbdudex /forum/post/20766356

I'm willing to be "Alice", who will lead me thru the acoustic energy time curve (ETC) charts/graphs rabbit hole?

present ETC's from the listening position, measured one speaker at a time.

FOH

· #5 · Aug 2, 2011

This room;

"The lows and the highs are easier to perceive because they have roughly the same ambience, the same reverberation time. We don't have any fiberglass on the walls it absorbs largely at high frequencies and is less likely to absorb at low frequencies. Any absorption in this room is caused by several processes, including the air turbulence around all these edges, and the scattering of reflective sound from all these surfaces. Dr. D'Antonio has referred to our principle in action as ambechoic.' "

The room is conducive to accurate work because we have taken away the boundary effect by eliminating' the walls. The boundary effect is usually a speaker set away from the wall, which causes comb filtering because the sound hits the wall and bounces back at a different time than the direct signal from the speaker. Certain frequencies are canceled and certain frequencies are enforced, which is not a good idea in a critical listening environment.

Then again;

"the room is hardly anechoic, though. just listening to music in there is extraordinary; ensemble musicians report that it's easier to play live in the room because it's easier to hear in the room.

those that appreciate it use it to it's utmost. the "sound" is more or less like an "acoustic white-out", and the decay is extraordinarily linear with higher frequencies (the Schroeder curves are remarkably linear) having more decay than any other room i've ever experienced. i made the best record i ever made in my life in there (from which that video clip came). unfortunately, Nashville's short-sighted and inept "music" industry will not tolerate innovation of any kind, and i'm told that the room now has heavy curtains hung in front of the diffusors.

i now live in Montreal, by the way.

George Massenburg

Damn, that last sentence in the last paragraph really sucks

Thanks for the links

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mtbdudex

Discussion Starter · #6 · Aug 2, 2011

Quote:
Originally Posted by localhost127 /forum/post/20767666

present ETC's from the listening position, measured one speaker at a time.

Hopefully I can get to it this weekend.

Below is my HT and it's current acoustic layout, I have 8 listening positions.....

I will take 3 readings from each seating position, one for each of the mains R/C/L, one at a time, and of course labeling them.

3 x 8 = 24 charts... @ approx 3 minutes/measurement + label graph/etc, this is at least a 2 hour data gathering session.

Upload, organize a post.....yea need to do it at night while the kids are sleeping.

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mtbdudex

Discussion Starter · #7 · Aug 2, 2011

Quote:
Originally Posted by FOH /forum/post/20769341

This room;

FOH....my wife would totally negate that........I'd love to listen in it though, with the curtains off of course.

localhost127

· #8 · Aug 2, 2011

Quote:
Originally Posted by FOH /forum/post/20769341

Damn, that last sentence in the last paragraph really sucks

stifling innovation at its finest!

fastl

· #9 · Aug 3, 2011

localhost - Thank you for the information. I know what ETC is. Pro sound magazines of the era I mentioned, such as dB, REP and Studio Sound were infested with articles on the topic. There were all these "experts" running around with Techcron analyzers (and the like) making ETC measurements and charging big bucks. I think most folks eventually figured out that it was basically just another audio consultant scam and it eventually fell out of vogue. Doesn't surprise me at all that it gets "discovered" again.

GGA

· #10 · Aug 3, 2011

fastl,

What do you prefer instead of ETC?

Thanks.

aackthpt

· #11 · Aug 3, 2011

Very nice, Mike! I don't know where you read about it but ETC analysis is one of the things I was going to go through with you.

Are you trying to make every seat in the house equally good? My intention is to make all of the seats good seats, but not amazing seats. Therefore while I may measure ETC from all of the seats, I am not going to fuss over the finer points of achieving the desired response from the cheap seats.

And, as the ambechoic response was mentioned... you need to decide what you are trying to do with the tool.

-Verify your ISD gap?

-Strongly terminate the ISD gap?

-Add to the sense of spaciousness in the room?

-Decrease the sense of "deadness" in the room?

-Improve the quality of the decay characteristic?

I can definitely tell you that the ETC has been getting progressively "better" in my room as I do more. And if you do want to see some "journeys to the center of the earth" I could point you to a couple of studio build threads on gearslutz where people did just that.

@fastl, can you provide a reference for "basically doesn't work"? Or just PM me with _your_ methodology and requirements/expectations for room acoustics? I'm quite interested to hear what causes you to say it "doesn't work".

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localhost127

· #12 · Aug 3, 2011

Quote:
Originally Posted by aackthpt /forum/post/20772250

Very nice, Mike! I don't know where you read about it but ETC analysis is one of the things I was going to go through with you.

And, as the ambechoic response was mentioned... you need to decide what you are trying to do with the tool.

precisely. the ETC is the tool that details your room's total specular response. you modify your room as needed to achieve the particular room response you desire - and re verify with ETC once treatment has been applied.

it would likely be wise for a starting-point (mtbdudex) to pick a single listening position and focus on the L/R for the time being until the process is fully understood.

take note!:

Quote:
Originally Posted by SAC /forum/post/0

Thus if you choose to determine the specular energy paths in the most basic and accurate manner, you can, depending upon the amount of separation in time of the various reflections, more easily determine which boundary surface correlates to each energy spike. And from there, (omitting a few mechanical steps*) you can determine precisely the location of the center of the incident region.

And, assuming one knows the acoustical model** they are working to satisfy; one indeed knows where to place treatment. The type of treatment is then determined by the effect one desires to create.

Absorption will damp the reflection.

Reflection will redirect the energy which will effectively cause incidence later in time at other location(s) - in other words, it will both reduce the gain of the spike and it will effectively be 'moved' to a later time.

Diffusion will do two things. One, it will decrease the gain of the spike. And two, it will break the primary reflection into 'smaller' reflections of lower gain and spread them out in time. Thus you will have a nesting of distributed lower gain spikes, generally with the distribution in time being skewed to a later time.

(See graphics below)

Thus, if you know the target acoustical response desired, reading and interpreting the ETC correctly will indeed provide information as to the precise point of incidence, and this point is where treatment is applied to mitigate said energy in the manner desired. And knowing the acoustical response desired, you can appropriately choose which kind of treatment is useful at the location.

Note, I say what type of treatment may be useful rather than what is necessarily best. The reason is that there are often multiple ways to achieve similar results depending upon the context of your space. For instance, if your acoustical model is that of a NE room, then you will most generally want to use absorption to reduce the reflection. On the other hand, if you are building according to the LEDE model, and you want to preserve the energy while simultaneously controlling its dispersion; then you may want to employ either reflection or diffusion in order to create the acoustical response appropriate for that portion of the ETC response. But a comparison of the actual ETC with the acoustical model template will help you to determine what behavior is optimal with respect to time and gain for the given incident point in the room.

Does that make sense? The ETC provides a total picture of the specular response in the room - from early arrivals to the 'last' of the energy, be it totally damped or a decaying diffuse soundfield. And this is all done with respect to time.

The ETC allows you to see exactly what kind of energy distribution you have currently, and allows you to select and precisely place the treatment you have chosen in order to create the effect you desire - be it damping, redirection, or diffusion. It also allows you, upon repeating the measurement, to see the precise impact the positioning of the chosen type of treatment has. from this you may be satisfied, or you may want to further refine the positioning in order to insure the proper response is accomplished.

Oh, and one more important point here. It will also show you if, and to the degree, that your treatment does not act completely in the manner you suspect. In particular, this is most common with absorption, which to many folks surprise, will often exhibit a stronger degree of reflection than anticipated - especially if the angle of incidence at the boundary is great. you can also determine the actual degree of diffusion versus scattering a diffusor or a scatterer such as a poly-cylinder exhibits. With this information, you may decide to modify or use another type of treatment if , for instance, the resulting reflections are not sufficiently diffuse.

But in any case, if one becomes proficient in using the ETC, the days of blindly assuming a treatment based simply by virtue of its name, performs exactly and solely as one expects, should be over. you will discover that absorbers have a reflective quality. And that diffusors exhibit an absorptive component (often more than one would like if your goal is to diffuse and retain said energy!) and that they may also act as reflectors (especially is the incident signal is perpendicular to the unit). In other words, you will not only know what is happening within the room, but you will quickly learn a great deal about the real, as opposed to ideal, behavior of the various treatments.

And with this combined knowledge of both what is happening in the room, having the information of where to place treatment appropriate to your acoustical response design goals, knowing what specific affects your choice of treatment actually achieves - while becoming aware of any residual artifacts of the treatments, you will be well on your way to creating the response you desire....

Quote:
Originally Posted by SAC /forum/post/0

There seems to continue to be some persistence in looking at specular responses in the frequency domain and worrying about EQ.

If you address the time domain issues in the specular region, you don't have to worry about the frequency domain or EQ! EQ is appropriate ONLY for adjusting the direct signal that comes out of the speaker - NOT the speaker-room interaction

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aackthpt

· #13 · Aug 3, 2011

Quote:
Originally Posted by fastl /forum/post/20772169

localhost - Thank you for the information. I know what ETC is. Pro sound magazines of the era I mentioned, such as dB, REP and Studio Sound were infested with articles on the topic. There were all these "experts" running around with Techcron analyzers (and the like) making ETC measurements and charging big bucks. I think most folks eventually figured out that it was basically just another audio consultant scam and it eventually fell out of vogue. Doesn't surprise me at all that it gets "discovered" again.

Maybe it just became well known as a tool so it was no longer media-worthy. There are many tools for acoustics, including your ears. They should all be used judiciously and in ways for which they are fit for purpose.

I'm all for someone gaining another tool in their toolbox. Even more so, I'm for people learning how to do acoustical analyses that include time. What we are actually seeing here is amateurs becoming able to use analyses that professionals were using 20 years ago.

mtbdudex

Discussion Starter · #14 · Aug 3, 2011

Quote:
Originally Posted by aackthpt /forum/post/20772250

Very nice, Mike! I don't know where you read about it but ETC analysis is one of the things I was going to go through with you.

Are you trying to make every seat in the house equally good? My intention is to make all of the seats good seats, but not amazing seats. Therefore while I may measure ETC from all of the seats, I am not going to fuss over the finer points of achieving the desired response from the cheap seats.

And, as the ambechoic response was mentioned... you need to decide what you are trying to do with the tool.

-Verify your ISD gap?

-Strongly terminate the ISD gap?

-Add to the sense of spaciousness in the room?

-Decrease the sense of "deadness" in the room?

-Improve the quality of the decay characteristic?

I can definitely tell you that the ETC has been getting progressively "better" in my room as I do more. And if you do want to see some "journeys to the center of the earth" I could point you to a couple of studio build threads on gearslutz where people did just that.

@fastl, can you provide a reference for "basically doesn't work"? Or just PM me with _your_ methodology and requirements/expectations for room acoustics? I'm quite interested to hear what causes you to say it "doesn't work".

John;

I'll have to take some ETC first then I can answer your q/statements with educated response.

-Verify your ISD gap? Yes - as starting point with my treatments as they are need to know this

-Strongly terminate the ISD gap? Need to see what it is to determine

-Add to the sense of spaciousness in the room? Subjectively I'm amazed at the 3d seemless of the sound as is compared to w/o treatments. Objective chart should help quantify that.

-Decrease the sense of "deadness" in the room? Subjectively my HT room does not appear overdamped to me, but ETC should help quantify that

-Improve the quality of the decay characteristic? tbd

I've got some reading to do @ gearslutz ......

Quote:
Originally Posted by localhost127 /forum/post/20772476

precisely. the ETC is the tool that details your room's total specular response. you modify your room as needed to achieve the particular room response you desire - and re verify with ETC once treatment has been applied.

it would likely be wise for a starting-point (mtbdudex) to pick a single listening position and focus on the L/R for the time being until the process is fully understood.

take note!:

Advice taken.

For now, I'll focus on 2 seat positions.

seat #6 in 2nd row, as that is the best for 10-200hz, so that is where measurements will be taken and any acoustic treatment changes will be initially based on that

seat#2 in 1st row, as reference to seat #6.

Keeping in mind this is a HT, so while seat#6 will be my "learning seat", final goal is overall "improvement" to as many seat positions as possible, or at least coming to terms with the HT acoustic state and then accepting it as "done" and "good to go" for a DIY amateur basement HT.

(some people would stop now, but the OCD inside of me says "get more fact based data".....)

I'm open to adding some strategically placed diffusors in the HT....the DIY ones seem to involve much time to research/build, but I'm ok with that as a ongoing learning project.

Also, I've got "left over" 6 sheets of OC703 2' x 4' board.

This will be a 2-4 month term project, as summer is still here and a few weekend camping trips coming up, then outdoor movie weekends, etc.

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test4echo101

· #15 · Aug 3, 2011

Lolz,

I would LOVE to contribute mtbdudex but this is :

Test,

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aackthpt

· #16 · Aug 3, 2011

Quote:
Originally Posted by mtbdudex /forum/post/20774006

I'm open to adding some strategically placed diffusors in the HT....the DIY ones seem to involve much time to research/build, but I'm ok with that as a ongoing learning project.

I'd suggest you consider polys as well as Schroeder diffusers. Both have their merits. I'm actually investigating putting up quite a few polys in my theatre. If I don't like them I'll pull some down and put in something else.

As for the room being overdamped... well it depends on what you're going for, to whose acoustic philosophy you prescribe, and what sort of environment you find comfortable. Plenty of people would suggest that near-anechoic is the best response model for a multichannel environment. I don't really have a strong opinion on it personally. Then again I haven't read Toole's book yet so I don't know the details of his philosophy.

localhost127

· #17 · Aug 3, 2011

Quote:

Originally Posted by aackthpt

I'd suggest you consider polys as well as Schroeder diffusers. Both have their merits. I'm actually investigating putting up quite a few polys in my theatre. If I don't like them I'll pull some down and put in something else.

additional reading on polys (for those interested):

AcousticAbsorbers & Diffusers.10.4.Polycylinders..pdf 462.1220703125k . file

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fastl

· #18 · Aug 4, 2011

...What do you prefer instead of ETC?...

It depends on what you're trying to do. Room mode analysis is probably the most effective thing you can use. I'm not aware of any of the real pro acoustics designers using ETC as the basis of their designs, but they do use room mode analysis. Our hearing is basically frequency domain oriented, meaning that we don't directly sense sound waveform energy as presented by an ETC. If you really want to get into ETC, I would suggest trekking down to a library that carries dB or REP magazine back issues and reading through all the old "stories", so you can at least experience all of the wild claims that were being made.

aackthpt

· #19 · Aug 4, 2011

Quote:

Originally Posted by fastl

I'm not aware of any of the real pro acoustics designers using ETC as the basis of their designs

Of course not, because they use super-duper simulation packages such as CATT. But they use analyses in it that provide ETC or equivalent (as well as other acoustical measures), plus being able to actually listen to the room sound from the simulation. They're also usually working on a room that isn't built yet, allowing them to tailor the (apparent) room boundaries to do half the acoustic work for which the rest of us rely upon "treatments".

Quote:

Our hearing is basically frequency domain oriented, meaning that we don't directly sense sound waveform energy as presented by an ETC.

LOL, that is epically untrue. If the ear/brain system were not time-oriented, we would not hear echoes. Sound is waves, and waves are inherently time-based. FR is actually just one way to characterize a system, and only a part of the characterization. FR is derived from a recording of what really does exist, which is pressure versus time, making it the representation more removed from physical reality. Not making it unuseful, though.

I'm actually somewhat interested to know what wild claims were being made. Unfortunately I'm not interested enough to head to a library. I know that I've seen some making it sound like it's an acoustical panacea on forums, and I actually object to that. Time is important in acoustics, and ETC is one of the tools that helps visualize and analyze it. Just another tool, full stop.

Quote:

Room mode analysis is probably the most effective thing you can use.

Please, for the sake of clear discussion define what you mean by "room mode analysis".

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localhost127

· #20 · Aug 4, 2011

Quote:
Originally Posted by fastl /forum/post/20772169

There were all these "experts" running around with Techcron analyzers (and the like) making ETC measurements and charging big bucks.

Quote:
Originally Posted by fastl /forum/post/20776750

I'm not aware of any of the real pro acoustics designers using ETC as the basis of their designs, but they do use room mode analysis.

so, if i follow your commentary correctly, the "experts" who charge the "big bucks" have simply moved on to another tool?

Quote:
Originally Posted by fastl /forum/post/20776750

Our hearing is basically frequency domain oriented, meaning that we don't directly sense sound waveform energy as presented by an ETC.

Helmut Haas and Dr. Manfred Schroeder would like to have a word with you...

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