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Transfer Function Measurements With Smaart v8

Why measurements are a quicker and safer way to optimize a sound system than doing it by ear...

By Joan La Roda January 30, 2019

Image courtesy of Rational Acoustics

Acoustical measurements, unless performed in an anechoic chamber, will always show bands where coherence is not 100%. As explained earlier, one should not trust the readings at those frequency bands. Once we have finished doing these practice measurements and start doing real life measurements, it’s advisable that we measure at several positions so as to give us a better idea of the average system response across the audience area.

If, when running the measurement, the coherence trace disappears at frequencies where coherence is low, this is due to Smaart’s default Blanking Threshold for coherence, which hides coherence at frequencies where it falls below 20%. This threshold can be adjusted by dragging the arrowhead on the left; we’ll move the arrowhead down if we want to see the trace for those frequencies where coherence is very low:

Figure 24: Modifying the coherence blanking threshold.

Frequency Smoothing

Loudspeaker specification sheets often use 1/3rd-octave smoothing for displaying frequency response curves. With such wide frequency smoothing, important details can be lost. Measurement software such as Smaart allow for a more detailed frequency display. Smoothing can be selected down to 1/48th-octave, or even no smoothing at all. I would start with a smoothing of 1/12th-octave and, depending on what we see or what we intend to measure, increase or decrease that.

This 1/12th-octave smoothing will typically be enough to appreciate reflections or temporal mismatches, but, if we detect a problem, to check how serious it is even less smoothing may be necessary.

Figure 25: Frequency Smoothing drop-down menu.

Temporal Averaging

If we are looking for a stable graph, especially when using music as a Reference Signal or when in a noisy environment, it may be appropriate to use high temporal averaging. In these cases, you may want to start with averaging of 1 to 3 seconds and then decide whether you need more or less.

However, when adjusting EQ or phase we’ll need for the graph to respond immediately to the changes being introduced to the system. In this case we’ll need shorter temporal averaging. We can start with the 16 FIFO option, which shows the last 16 “frames.”

Figure 26: Temporal Averaging drop-down menu.

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Fedele says

For now i have just read only introduction and... desagree.
Sofwares are just tools based on numbers! Calculations on numbers, made across many kayers of approximation and errors.
Reality, the Sound Phenomena, the Human way to ear, are more complex tan that.
In a concert, there are many forms of energies that analyzer don’ t measure ( remember...also just calculations on numbers and a 1/4 capsule here or there) but that caracterize our complex sensation.

Seth Morth says

Fedele is missing the point, and should have read the rest of the article before commenting.

This is a helpful guide in how to use Smaart8 to get the sound system to an (objectively) calibrated baseline. Occasionally this is referred to as "flat" but that is rather misleading; consider it "time aligned, checked for phase, and compensated for detrimental artifacts".

From this milestone you can then trust your ears to make (subjectively) changes as desired to have it sound the way you would like it to.

I would in fact like to hear more from Joan La Roda, as well as José Brusi, Xesc Canet, Pepe Ferrer, José Moldes, Germán Ramos, James Woods, and Jamie Anderson. They always have an open invitation to visit my workplace and command my attention when they publish an article.

Fedele says

And also.....
There are other conditions for cancellation!! It is not only problem of relative time As it is writed.

Fedele says

Good evening.
In addition to what I have already written, and which I will soon write,...
I also have to underline how, quoting this part of the text:
"When two acoustical waves reach the same point with a time difference, there will be a total cancellation ...etc"
There are other conditions for cancellation!! It is not only problem of relative time.
Fedele De Marco

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