TEF analysis versus using the more typical MLS

[dragonfyr]

CATT_A1.pdf

[dragonfyr]

[dragonfyr]

MLSSA-Brochure1.pdf

[dragonfyr]

While I am trying to locate and scan a few other articles, there is an exceptionally useful tool and technique (and it especially is wonderful when dealing with large rooms featuring HIGH ceilings to which you might not want to be running up and down ladders or scaffolds!), and that is the Polar ETC/PET software that generates polar coordinate plots from ETC (Energy Time Curve) data.

This software allows one to locate the direction and intensity of reflections in an acoustic environment. And with the aid of a POGO laser alignment transit, one simply dials in the 3space coordinates and the laser points to the spot corresponding to the reflection. The reflections are ploted in a 3space volumetric coordinate system, or you also have the option to move the cursor along the ETC curve and the locations on the response corresponding to the secondary arrival times are rsloved into their 3 space coordinates allowing for quick identication of the location of the spots to be diffused, absorbed or abfused, depending upon the specific needs. No more repeated trial and error and repeated trips to the ceiling!

...Talk about taking the fun out of an otherwise tedious exercise!

And while the POGO 'setup' is described in the attachment includes a rangefinder, its addition merely adds to its versatility, as the distance calculations have already been performed. While a simple laser pointer could be utilized, the incorporated laser sight in the range finder laser sight can be aligned as an accurate 'pointer' providing accurate alignment and distance measurements for other 'what if' scenarios, especially via the use of mirrors for ray tracing experiments. So while the range finder is not absolutely necessary for the TEF component and could be replaced with a simple laser pointer, the inclusion of the range finding capability adds functionality for other related functions and makes the tool that much more versatile. An example is included in the home theater example following where they use the POGO for related functions.

POGO_Room_Models2.pdf

[dragonfyr]

An example of the POGO being used in a home theater room setup (without the polar resolution tools of the TEF software...)

HmThtreDesign.pdf

[dragonfyr]

On 3/31/2005 8:48:52 PM Gramas701 wrote:

It is my understanding that with a TEF and using the software to plot the measurements (Nyquist Points), that it will also plot on the z-axis. Now, plotting on the z-axis will reflect time over the course of taking measurements and therefore give a 3-d model. Is this correct? What is the benefit of having a 3-d plot with a time reflection?

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Yes, if you refer to the previously posted SynAudCon newsletter attachment you will see an article about the Nyquist & Heyser spirals. Included is a picture of one of the views afforded in the TEF analyzer showing a 3space diagram with the spiral as well as the projections onto each of the 3 planes. As the cursor is moved along the spiral, perpendiculars are extended to each plane and the corresponding values are displayed.

The BIG advantage is clarity! And, from this diagram (and the description) you can also discover the meaning of "imaginary" numbers in math, electronics & physics!

You may recall the 2space graph (common in electronics) where a complex number represented a point in a 2 dimensional plane with reference to 2 axes. This point is also represented as a vector, drawn from the origin to the point. The x axis is the real axis and the y is the imaginary axis. And it involved a bit of calculation to transpose the rectangular representation (C=A +-jB) to the polar perspective C= C(angle sign)Theta (so much for rich text!)In this perspective the x axis corresponded to the Real (resistance) and the reactance to a positive (1st Quadrant resultant) imaginary impedance XL=jwL, and the capacitor to a negative (4th Quadrant resultant) imaginary impedance XC= -j.1/wC = 1/jwC. Confused? Weren't those classes fun!? No? Well, now, if you understand the significance of those calculations, you don't have to pull out your trusty HP calculator or P-Spice! You can see them within a changing time frame rather then as discrete static calculations. And the rate and pattern of change provides much more info that the static calculation! But doing all that math sure built character!

So, the display the TEF affords with the Nyquist (and Heyser variant) corresponds to the classic phasor diagrams for complex impedance, but in a time variant 3space view.

So you see, in addition to the potential and kinetic energies, this viewpoint contains quite a bit of information that varies with frequency! Quite a meaningful expansion of the traditional frequency domain or 2space phasor view! And without all the gobblygoop calculations!

Multiple display options include: Impulse, Doublet, Intensity, ETC, Log-Squared Impulse for the Time Domain, and Magnitude, Phase, Heyser Spiral, Nyquist for Frequency Domain.

Another advantage, is that as the information varies in time (and since frequency is simply the change in phase with regards to time), frequency dependent values are easily ascertained, as well as time variant data. Other views (the classic waterfall plot which displays the 'ringing' - or resonances of the system while displaying the decay times of the various frequencies offers yet another view of the classic frequency response yet with additional useful information.

Also, the ability to display the arrival times of reflections and to resolve the reflections into 3space geometric paths is extremely useful for tuning anomalies (see the references to using the POGO laser pointer). And it is interesting that some of these complex impulse responses include, not only the direct and reflected from the driver itself, but ALSO secondary emissions originating from the walls of the enclosure itself - some significant enough to require attention! Diffraction effects, whereby an edge acts as a secondary point of origin can also be identified. As you see, the more you can identify, the more complex our awareness of reality becomes. And each situation presents differing levels of complexity depending upon our goals and the systems employed.

And lest you wonder, the TEF can measure the transform (function) of electrical as well as acoustic devices.

With the PrecisionEQ software, a TEF analyzer, and a parametric equalizer, one can quickly and accurately equalize a sound system to a high degree of accuracy, accomplishing in a matter of minutes what might realistically take hours with real time analysis. And since only minimum phase regions can be equalized, the software offers a mode allowing you to highlight those regions on the equalized graph.

Additionally, tools are present to perform Noise Level Analysis in order to analyze environmental background noise as well from sources such as heating, ventilation, and even crowds. This provides for statistical noise information for periods as short as 1 minute or as long as 24 hours. It is also useful when designing and installing sound systems in places like meeting rooms and gymnasiums, where ambient noise is the primary inhibitor to intelligibility.

I fear that without seeing the displays and watching that which the TEF 'shows', that the significance and usefulness of these tools may be lost in the 'translation' As the visual mode, coupled with the derivation of values is very powerful in identifying relationships and for quickly identifying many individual points of focus from a unified picture.

One other aspect that I will mention is the mapping of various domains to one another, as we are viewing the same proverbial elephant from many different perspectives! It is this ability to view the same phenomena in so many perspectives, each offering increased insight that makes the TEF so powerful. As it is able to cover all of the differing domains, each perspective may be employed relative to its strengths, and additional perspectives can be brought to bear when a particular point of view may be inconclusive.

I will post one more attachment that shows a relationship of the various points of view between the time & frequency domains...

And I am still working on posting a copy of Don Davis' process or looking at a room with the TEF that will walk you through a classic room analysis presenting a much clearer way several of the tools are routinely employed and explaining other practical considerations...

[formica]

Thanks for the wealth of info. I wanted to tell you up front that your effort is appreciated. It'll take me awhile to get though it, digest it, and post any follow up questions... so I wouldn't want you to get the feeling it fell on deaf ears.

It's nice having others members who agree at getting better sound through better science (BTW, Klipsch forum has a higher than avg number of these compared to most home audio forums)

Thanks again...

Rob

[dragonfyr]

I hope I didn't bury you with confusing 'stuff'.

But I am still working on getting the Davis paper posted which will provide a great overview of the general process and tie everything together...

Maybe this evening!

[sunnysal]

thanks for posting and typing all that useful info on this subject! I will begin to wade through it tonight. warm regards, tony

[dragonfyr]

Here, finally!, are the pages for the Davis LEDE concept utilizing the TEF measurements and showing a general process for analyzing a room...

By following this process you will be introduced to alot of the method to the madness (process) as well as how many of the measurements are used and what they mean.

Of course this is for a small acoustic space (these exhibit no reverberant fields as the dimensions are such that the time delay of the reflected signals are is not sufficiently large enough to constitute a reverberent field). The rules change slightly for large acoustical spaces that exhibit a reverberant field.

[dragonfyr]

Davis LEDE p2

[dragonfyr]

Davis LEDE p3

[dragonfyr]

Davis LEDE p4

[dragonfyr]

Davis LEDE p5

[dragonfyr]

Davis LEDE p6

[dragonfyr]

Davis LEDE p7

[dragonfyr]

Davis LEDE p8

[dragonfyr]

Davis LEDE p9

[dragonfyr]

Davis LEDE p10

[artto]

Nice post Dragon!

I must admit Ive not been an advocate of Live-End/Dead-End rooms (I tried it in the early 80s and it sucked with Khorns!). But that was also based on the earlier documents from the 70s and early 80s which primarily dealt with absorption as the major component of the Dead-End in LEDE rooms. I see Davis has (had) updated the definition of LEDE rooms in this more recent presentation from 1987 (which I never saw because I was deeply involved with other business/professional commitments at the time) to include the directionality of the speaker, speaker placement (ie: corner and/or flush with wall), as well as producing adequate time delay between the speaker and reflected sound through specular diffusion (can you say polycylindrical?). So it looks like I basically accomplished the same thing in my room, albeit through diffusion instead of absorption. Either way, the goal is the same, to make the room disappear from the equation. And as mentioned, this can bring out the worst in a recording, or reveal all its beauty and transport you to the place it was recorded.

I would be interested in running full time domain/energy tests on my system/room some time, if anything, just to see how close or far off I am from ideal for the conditions present, by tuning the room using basic acoustic principals and listening.