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?
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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?
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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.
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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?
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Originally Posted by localhost127 /forum/post/20767666
present ETC's from the listening position, measured one speaker at a time.
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Originally Posted by FOH /forum/post/20769341
This room;
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Originally Posted by FOH /forum/post/20769341
Damn, that last sentence in the last paragraph really sucks![]()
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.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.
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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....
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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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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.
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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".
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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!:
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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.
Originally Posted by fastl ![]() I'm not aware of any of the real pro acoustics designers using ETC as the basis of their designs |
Our hearing is basically frequency domain oriented, meaning that we don't directly sense sound waveform energy as presented by an ETC. |
Room mode analysis is probably the most effective thing you can use. |
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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.
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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.
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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.