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Thinking About Power Response (?) at Listening Position

RayDunzl

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#1
I may be unclear on what Power Response is, or how it is measured, so correct me.

Anyway, I was thinking about it.

Assuming one way of looking at it is the difference between direct and direct+reflected sound energy at the listening position...

I compare the swept sine SPL of two speakers in this room, with 500ms and 4.3ms right window Impulse Response timing in REW.

The EQ applied was "flat", no slope. The averaging is 1 octave (lots of averaging).

First, JBL LSR 308. Red line is 500ms window, black line is with 4.3ms window - seems to be just under the time of the first reflection from wall/ceiling/floor.

1551834620408.png



Observation:

The SPL of the windowed measurement is 2dB lower in the mid and higher frequencies.




Next, the MartinLogan reQuest electrostatic hybrids. I pick the same right window, 4.3ms. (Changing it a bit doesn't change the measure, so, I'll just be consistent).

1551834585600.png


Observation:

Only a .2dB difference in the higher frequencies. Direct, or Direct+Reflected SPL is nearly identical.



Conclusion:

I dunno, but there are the measures.

Comment?
 

RayDunzl

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#2
After thinking about it some more, my still-functioning neuron reinvents the wheel and comes to this conclusion:

The black lines, being time limited to exclude reflections, represents the direct SPL.

The red lines, represent the combined direct and reflected sound level.

So, what is the level of the reflected alone?

1552067227541.png


Using the calculators
http://www.sengpielaudio.com/calculator-coherentsources.htm
http://www.sengpielaudio.com/calculator-leveladding.htm

Where Direct + Reflected = Total, and solving for Reflected

At 3.4kHz:

JBL

Coherent reflected SPL= 71.4dB
Incoherent reflected SPL = 81dB

Martin Logan

Coherent reflected SPL= 53dB
Incoherent reflected SPL = 72dB

Conclusion:
ML (dipole) has an 18.4dB advantage (my opinion of the result) of Direct to Reflected Coherent sound over the JBL in this room.
ML has a 9dB advantage in Direct to Reflected Incoherent sound.

So, the reflected sound is about half as loud ML vs JBL - dipole vs wide dispersion.

The imaging difference - I perceive the JBL as fuzzily wide, the ML as narrowly focused. Detail is lost with the JBL but it sounds big, switching, the ML initially sounds narrower, but becomes just as wide as you hear the detail that's not obscured.

Treating the walls and ceiling reflections should narrow the gap, but that's not in the plans for this room.

The calculation above supports the observed ETC difference - Red, JBL, Blue ML, 500ms

1552068418529.png


And the Impulse - later wiggles are reflections

1552069771348.png


Does it make a difference?

Soon after the JBLs arrived, we were listening on Beer Saturday, and Audio Buddy suggested they were out of phase, because the stereo was so mushy.

Changing between in and out of phase didn't make nearly the difference as noted with the ML that evening.

I may have gotten used to them, or tuned them up a little better, the effect doesn't seem as strong now. Or it was just good beer.
 
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Krunok

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#3
If I remember correctly recently you cought yourself listening to your JLBs but thinking it was the MLs doing the job, so the question seems to be - does all this acoustic science really matter? :D
 

RayDunzl

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#4
That was casual listening, mostly TV, mostly from the desk in the corner, and moving around, in and out of the room, to do stuff.

DSP/DRC gives them essentially the same frequency response, so that isn't noticeable.

Sitting in the sweet spot and paying attention to a stereo source, the differences are obvious.

But, if the room were dead, it would probably be a much closer contest at moderate levels. Too loud, the little JBLs audibly distort.

If science didn't matter I'd just pray everything into submission, and throw in a few Hail Mary's for safety. But, so far, that hasn't worked.

1552071730500.png
 
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Krunok

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#5
That was casual listening, mostly TV, mostly from the desk in the corner, and moving around, in and out of the room, to do stuff.

DSP/DRC gives them essentially the same frequency response, so that isn't noticeable.

Sitting in the sweet spot and paying attention to a stereo source, the differences are obvious.

But, if the room were dead, it would probably be a much closer contest at moderate levels. Too loud, the little JBLs audibly distort.

If science didn't matter I'd just pray everything into submission, and throw in a few Hail Mary's for safety. But, so far, that hasn't worked.

View attachment 23260
IMHO there is no doubt that your MLs are very competent speakers and you set them up really well. THere is absolutely no doubt that MLs would leave in smoke your little JLBs at first 10 seconds of serious listening but it is still a huge compliment for them to be able to fool you with casual listening.
 
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#6
I think what you're seeing there is the difference in the critical distance between the two speakers (a discussion we were just having in another topic). The critical distance for something like a dipole is much farther back than a box speaker, if memory serves. The horizontal and vertical dispersion is quite limited for a variety of reasons. Thus, you're likely listening in the nearfield for most of the frequency range, and at the measurement position the direct sound is significantly higher in output than the diffuse field. If you measure farther to get past the critical distance (if that's even possible in the room) the plot for the MLs will start to look more like that of the JBLs.
 
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