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post #211 of 218 Old 11-20-2011, 10:46 PM
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Originally Posted by sdurani View Post

Remember, we're talking about consumer listening spaces, not studios. So most of us are starting out with a room that is already built. And yes, I would choose whether to treat or not, let alone what type of treatment, based on the contents and direction of the reflection.

...and yet you're posting such assuming commentary in the Dedicated Theater Design & Construction sub-forum...of which many design criteria (even down to trim-work and paint color!) are determined pre-build.

again, when you have nothing significant or of substance to add, you can always fall back on the "wife factor" or "living room" or "lowest common denominator" factor to dance around.

you can choose whatever acoustical response your heart or brain or ears desire. the particular user of this thread has signaled the goal of attenuating early reflections. how is the ETC not relevant or useful in such a scenario?

the fact is - i have repeatedly asked you what method or tool you would instruct a novice to use if they were to request such a goal. instead, you see such a simple tool as the 'ETC' as the enemy (and equate it with an acoustical model that you do not agree with), and as such, can't even bring yourself to recommend it when it is appropriate for the job. instead, you'll go far out of your way to distract and discuss differing acoustic models or responses such that the ETC (which is simply a tool) may no longer be relevant.
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post #212 of 218 Old 11-20-2011, 10:49 PM
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Originally Posted by sdurani View Post

The point is to take advantage of lateral reflections, so having off-axis response that is similar to the direct response (but tilted down, naturally) is helpful. It doesn't have to mimic the direct response precisely, as long as it doesn't look too different. Just looking for consistency, so that when the direct sound and reflections combine, it doesn't make drastic changes to the sound of the speaker.

dance dance dance - you completely ignore the effect that the boundary's acoustical impedance has on the spectral content of the reflection (until brought to your attention) - and i have yet to see you promote or recognize in any of your commentary the significance of the boundary on preserving such spectral information.

and now, you continue with such vague commentary such as "it doesn't look too different" .... "similar" ... etc. and you've yet to present any responses to my questions regarding the ideal early arriving energy...
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post #213 of 218 Old 11-20-2011, 11:04 PM
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ill quote myself one more time since you blatantly ignored the question the first few times i posed the question:

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Originally Posted by sdurani View Post

Actually, that is a good question, along the same lines as the one asked by test4echo101. In over a decade that this forum has been around, how on earth was anyone able to place treaments in their home theatres with any effectiveness without using ETC? Either: everyone who was using treatments had no idea what they were doing OR surgical precision in placement isn't all that critical in consumer listening spaces.

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I was merely pointing out that ETC was rarely discussed at this home theatre forum until folks came over from a studio forum..

then by all means - before the ETC was being "discussed" or "recommended" - how on earth were you objectionably verifying or communicating to a novice how to objectionably verify that their procured treatment was truly and sufficiently addressing the original problem that it was procured for ?!
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post #214 of 218 Old 11-20-2011, 11:07 PM
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Originally Posted by localhost127 View Post

the particular user of this thread has signaled the goal of attenuating early reflections. how is the ETC not relevant or useful in such a scenario?

What makes you think ETC is not useful in such a scenario?
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ill quote myself one more time

Everyone needs a hobby. Quoting yourself is as good as any.

Sanjay
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post #215 of 218 Old 11-20-2011, 11:13 PM
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Quote:
Originally Posted by localhost127 View Post

how is the ETC not relevant or useful in such a scenario?

Quote:
Originally Posted by sdurani View Post

What makes you think ETC is not useful in such a scenario?

reading comprehension 101.


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Everyone needs a hobby. Quoting yourself is as good as any.

keep dancing. looks like it is not possible to extract any more information from you regarding the questions that have been proposed...
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post #216 of 218 Old 11-21-2011, 05:00 AM
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could you please elaborate on how one would choose or select design characteristics of a diffuser based on a particular off-axis response?

"diffuser" is a very loose term which can have many distinct capabilities (spatial dispersion? temporal dispersion? bandwidth? hybrid absorber/diffuser?).

The statement was clear ... the off axis response of the speaker will determine the type of treatment (absorption, diffusion). You know the answer to, or have an opinion about, your question. I am not taking the bait and being sucked into your vortex. Further, the answer to your question is the subject of multiple texts, AES, ASA, and other academic texts, the total of which is thousands of pages. I have neither the time, nor the desire to regurgitate this massive body of work done by others. If you have original, vetted work, please feel free to entertain the audience.

Dennis Erskine CFI, CFII, MEI
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post #217 of 218 Old 11-21-2011, 08:04 AM
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The following post by SAC seems to me to very well summarize everything being discussed here, from value of measuring with ETC to treatment methods:

"Thus, if I understand you correctly, assuming hardware loopback (automatic device correction) is used to account for hardware latency/propagation delay, if one does not apply FM's minimum phase origin translation, then each energy peak displayed in the ETC will correspond to the actual Time Of Flight (TOF) from the acoustical origin (source speaker) to the measurement mic.

Folks, for our acoustic purposes here, that is exactly what we need to be using.

Normalization relative to the direct arrival point, Td, where time=0 is assigned to the Td, is NOT useful for our particular application here. While for delay settings and for a few alternative purposes it is very useful feature, is it NOT useful for our purposes in this application.

So, if you are using FuzzMeasure, (and if I understand the implementation properly),please be sure to enable the Automatic device correction (hardware loopback in order to compensate for hardware latency/propagation delay) and do Not use the minimum phase setting. If this configuration is followed, the time of each energy arrival will correspond to the actual time of flight.

In order to determine the actual distance of travel for each direct and indirect specular energy path, one multiplies the actual TOF x 1.13 ft/ms or .344 m/ms for the distance in feet or meters respectively. This will be useful if one is not using one of the blocking methods for identifying the correlation between ETC and thee various specular paths.

If one is not empirically determining the path(s) of the indirect signal(s) by blocking, and want to know the actual distance of the indirect signal, you need to know the Total time of Flight (TOF).

This information may make the process a little easier to visualize as you can now know the actual time and the actual distance traveled from acoustic source (your speaker) to the measuring mic.

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...."

Floyd

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post #218 of 218 Old 11-21-2011, 09:58 AM
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Floyd;
Your post above reminds me I have homework still in my HT, and before Thanksgiving (Wed 11/23, I'm burning my last vacation day) will be re-doing measurements and trial/error based on dragonfyr's post there (from Oct-5, 2011).
http://www.avsforum.com/avs-vb/showt...2#post21041842
Quote:


For continuous nonperiodic signals (noise) use the Hanning window.

Select Use Loopback as Timing Reference
Unselect Set T=0 at IR Peak
Unselect Sub-Sample Timing Adjustment
Unselect Decimate IR

As suggested before, displaying 400 ms of time is interesting, but hardly useful considering that this corresponds to looking at signals travelling ~452 feet.
Either window the display in the Limits window to
Left: -.001; Right .045 (which will easily capture 2x the length of the room)
Top: 5; Bottom:-35

And post the .mdata source files so that we can open in REW

I might suggest zooming in to see more detail of what is actually happening and focusing on identifying the specific paths and points of incident of anomalous high gain early sparse arriving peaks.

But in any event, I would first seek to focus in on the display with adequate resolution to see greater detail. Then I would seek to identify the paths of the high gain anomalous sparse reflections. And I would also seek to determine and mitigate the very early arriving reflection that exists almost immediately after the direct signal arrival.

Once we can see the display windowed in more detail, it will be easier to proceed with more specificity.

Now, I can't let anyone enter the HT on Thanksgiving day to watch the Detroit Lions BEAT the Green Bay Packers till this is done, or the gods of acoutsic-ness will never let me by their pearly gates when my time comes....
(side bets on the game anyone )

And no, I won't be showing them any graphs/charts, learned my lesson on that already

Mike R,P.E. clickable DIY hot links:

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