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Difference between on-axis and MLP measurements

Zedly

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I'm seeing an unexpected difference between on-axis measurements of my speakers (Klipsch RP-280F) and measurements from the MLP. I took the on-axis measurements at a distance of 1m. The MLP is 2.5m (8.5 feet) from each speaker and 25 degrees off-axis. The speakers are in a family room area that is open on the right side, and there is a stairwell on the left side.

The on-axis measurements show that the speaker is pretty flat above 350 Hz (more so in the left than in the right), except for a wide dip from 550 Hz to 2 kHz (more pronounced in the left than in the right).

on-axis.png


The MLP measurements have a big peak around 650 Hz, a smaller peak around 1250 Hz, and then settles down just under 2 kHz. I'm wondering what might be causing these peaks.
mlp.png


I noticed that 640*2=1280 and 640*3=1920, which suggests that the peaks might be the harmonics of a 640 Hz fundamental, but I have no idea why I would be getting such a strong fundamental here. My understanding is that room modes are weak/non-existent at this high of a frequency, so I'm not sure this could be caused by a mode (and why at the MLP but not on-axis).

What are the likely/possible causes of this, and what is the best way to treat it? Should I rely on EQ or is there a good way to find out where to place treatments to absorb some of the energy?
 

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richard12511

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I'm seeing an unexpected difference between on-axis measurements of my speakers (Klipsch RP-280F) and measurements from the MLP. I took the on-axis measurements at a distance of 1m. The MLP is 2.5m (8.5 feet) from each speaker and 25 degrees off-axis. The speakers are in a family room area that is open on the right side, and there is a stairwell on the left side.

The on-axis measurements show that the speaker is pretty flat above 350 Hz (more so in the left than in the right), except for a wide dip from 550 Hz to 2 kHz (more pronounced in the left than in the right).

View attachment 122870

The MLP measurements have a big peak around 650 Hz, a smaller peak around 1250 Hz, and then settles down just under 2 kHz. I'm wondering what might be causing these peaks.
View attachment 122872

I noticed that 640*2=1280 and 640*3=1920, which suggests that the peaks might be the harmonics of a 640 Hz fundamental, but I have no idea why I would be getting such a strong fundamental here. My understanding is that room modes are weak/non-existent at this high of a frequency, so I'm not sure this could be caused by a mode (and why at the MLP but not on-axis).

What are the likely/possible causes of this, and what is the best way to treat it? Should I rely on EQ or is there a good way to find out where to place treatments to absorb some of the energy?

In my experience, the room still influences the sound up to about 1kHz. I believe that the Schroeder (transition point) frequency is just the frequency at which the room gains more control than the speakers, but the room still definitely messes with the response above that.
 
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Zedly

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Is there a good way to determine where to place treatments to minimize this mode? Or should I just try to use the Audyssey app to bring down the peaks?
 

rynberg

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Is this a single mic position measurement? If so, I would take the average of a few measurements centered around your head position and see if it is actually a real problem first. Your room measurements indicate a very bright speaker.
 
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Z

Zedly

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Yes, it was at a single position, so that's a good idea. It is a Klipsch speaker, so it is on the bright side.
 
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