Beginner smaart user la gasolina in english

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I’m new here and also to measurement software. I read a lot on this site and other forum and I finally started measurement. I have questions relative to my first experience. This is not a "real life" one, I just look at a monitor speaker at home and I have really basics question relative to this measures but I can’t find an answer on this forum or others. I know there is a lot of experienced guys here and I hope maybe one of you will have time to answer me.

On each measure I used the find delay function and inserted it. I noticed that when I move the microphone away from the speaker, the phase slope seems to increase. Why that ? As I inserted the delay I am supposed to see the same phase response, right? I consider this and thought that maybe the fact that I am in a small room result with 1 – very little time between the direct sound of the speaker and the reflections 2- Not a lot of level difference between reflections and direct sound. Also the more I put the microphone away from the speaker the more this is accentuated in the measure because I reduce level difference between direct and reflections. This can explain the mess in the phase response when I put more physical distance between monitor and measurement mic.

So I made another capture at 1,5meter but this time I decreased the FFT size to 1k , trying to exclude reflections of the measure. The result is on picture 4. And hurray ! the phases slope are more matching which make sense to me but I loose a lot of detail due to 1k FFT…

I understood that measurement is a lot of how to interpret the graph, can you tell me if my analyse is correct please ? Also when you are in real situation is this something to do to start taking a close up measure of the system giving us a "clean image" of the system that we can compare with the other measurements in the room and helping us to interpret the graphs ?

My last question concern picture number 5 where you can see all the measurements at once. The blue one and the pink one are respectively 30cm and 1,5meter from the speaker , MTW and 1k FFT. They match in the high frequencies. The green and light blue are 1 meter and 1,5meter both MTW, those two match in the high frequencies but differ from the 2 other measure. I don’t understand that …

On each measure I used the find delay function and inserted it. I noticed that when I move the microphone away from the speaker, the phase slope seems to increase. Why that ? As I inserted the delay I am supposed to see the same phase response, right? I consider this and thought that maybe the fact that I am in a small room result with 1 – very little time between the direct sound of the speaker and the reflections 2- Not a lot of level difference between reflections and direct sound. Also the more I put the microphone away from the speaker the more this is accentuated in the measure because I reduce level difference between direct and reflections. This can explain the mess in the phase response when I put more physical distance between monitor and measurement mic.

So I made another capture at 1,5meter but this time I decreased the FFT size to 1k , trying to exclude reflections of the measure. The result is on picture 4. And hurray ! the phases slope are more matching which make sense to me but I loose a lot of detail due to 1k FFT…

This is likely do to the positioning of the mic being somewhere in between the sample of the previous measurement. Please note that the difference in phase you are seeing is less that a .002 ms offset, and using the +/- delay buttons would vary the slope wildly, while only adjusting in .02ms increments.

The MTW takes choosing the appropriate FFT size out of the equation for you, as we’ve already chosen FFT sizes to have the appropriate time constants for their operation ranges, largely based on the past 2 decades of experience developing dual channel FFT based analysis. Pg.7 of the user guide goes into these concepts in greater detail, definitely an interesting read as a beginner user: http://www.rationalacoustics.com/dow…User-Guide.pdf

I understood that measurement is a lot of how to interpret the graph, can you tell me if my analyse is correct please ? Also when you are in real situation is this something to do to start taking a close up measure of the system giving us a "clean image" of the system that we can compare with the other measurements in the room and helping us to interpret the graphs ?

For a single speaker, phase is showing you that systems frequency response relative to the reference signal. In other words, what frequencies from the reference signal are on time with those from the measurement signal, which frequencies arrive before and after the reference signal. For a single system, asking if the phase is ‘correct’ is sort of the wrong question. Take the first image, if you want the analyzer to be timed to the energy at 8-10KHz then, yes, the phase response is correct. If you want the analyzer to be on time with the energy at 800Hz then, no, the phase response is not correct – at 800Hz the measurement signal lags the reference. (see Phase Response, in the User Guide, pg 102)