Pio2001
Senior Member
Hi,
Just in case, here are some measurements that I made with my JBL 305P mkII and Neumann KH-120 AW.
I took the measurements at tweeter's height, and also at mid-height between the tweeter and the woofer's axis, at a distance of 70 cm, holding the microphone by hand.
The MMM (Moving Micro Measurements) from the listening position are averages over one seat, 2 meters away, in an ordinary room, far from walls, with room eq below 600 Hz, with 0.45 RT60 speakers-to-listening-position at 500 Hz.
The listening position is located 6° above and 10° sideways the speaker's axis.
The darkened area must be ignored. I think that this peak at 350 Hz is a boundary effect of the windowing of the impulse response.
We can see that the choice of the reference axis has little effect of the frequency response, at least at a distance of 70 cm.
For the JBL, the only difference is the little peak at 9500 Hz. For the KH-120, the part from 2500 to 8000 Hz is smoother at the reference axis. Above 8000 Hz, the effect is the opposite of what we expect : highest frequencies are about 1 dB stronger on the reference axis than on the tweeter's axis. I hope I labeled my curves correctly
We can also see that the result at the listening position, if we neglect the general treble attenuation, is a bit different for the Neumann, while it looks exactly like the anechoic response for the JBL from 1000 to 10000 Hz. This questions the importance of the choice for a reference axis in a non-treated room.
On the other hand, we must remember that the anechoic response is more important than the listening position response for perceived sound quality. And this correlates well with my listening impressions. The Neumann sound more realistic, on human voices, than the JBL.
Last, and this puzzles me a lot more than the reference axis question, at listening position, the oscillations of the anechoic frequency response above 5000 Hz are canceled. But if we look at the spinorama of the JBL, these oscillations exist on all curves, in all directions. It should be impossible to smooth them.
It correlates with my listening impressions : if I equalize the JBL curve given by the spinorama, it works up to 5000 Hz. Above that, if I equalize them, it sounds weird, and the measurement from the listening position shows that the result is grossly incorrect : the correction destroys the curve instead of improving it.
The same phenomenon occurs as soon as 1500 Hz if I make close-field MMM measurements in the early reflection direction or in the sound sound power directions. The permanent oscillations of the frequency response of the speaker all disappear !
Jean-Luc Ohl, a french acoustician, has noticed the same phenomenon while performing measurements in an anechoic chamber: measuring the frequency response moving the microphone around the speaker cancels some oscillations in the frequency response that, according to the spinorama data, can never be canceled.
Just in case, here are some measurements that I made with my JBL 305P mkII and Neumann KH-120 AW.
I took the measurements at tweeter's height, and also at mid-height between the tweeter and the woofer's axis, at a distance of 70 cm, holding the microphone by hand.
The MMM (Moving Micro Measurements) from the listening position are averages over one seat, 2 meters away, in an ordinary room, far from walls, with room eq below 600 Hz, with 0.45 RT60 speakers-to-listening-position at 500 Hz.
The listening position is located 6° above and 10° sideways the speaker's axis.
The darkened area must be ignored. I think that this peak at 350 Hz is a boundary effect of the windowing of the impulse response.
We can see that the choice of the reference axis has little effect of the frequency response, at least at a distance of 70 cm.
For the JBL, the only difference is the little peak at 9500 Hz. For the KH-120, the part from 2500 to 8000 Hz is smoother at the reference axis. Above 8000 Hz, the effect is the opposite of what we expect : highest frequencies are about 1 dB stronger on the reference axis than on the tweeter's axis. I hope I labeled my curves correctly
We can also see that the result at the listening position, if we neglect the general treble attenuation, is a bit different for the Neumann, while it looks exactly like the anechoic response for the JBL from 1000 to 10000 Hz. This questions the importance of the choice for a reference axis in a non-treated room.
On the other hand, we must remember that the anechoic response is more important than the listening position response for perceived sound quality. And this correlates well with my listening impressions. The Neumann sound more realistic, on human voices, than the JBL.
Last, and this puzzles me a lot more than the reference axis question, at listening position, the oscillations of the anechoic frequency response above 5000 Hz are canceled. But if we look at the spinorama of the JBL, these oscillations exist on all curves, in all directions. It should be impossible to smooth them.
It correlates with my listening impressions : if I equalize the JBL curve given by the spinorama, it works up to 5000 Hz. Above that, if I equalize them, it sounds weird, and the measurement from the listening position shows that the result is grossly incorrect : the correction destroys the curve instead of improving it.
The same phenomenon occurs as soon as 1500 Hz if I make close-field MMM measurements in the early reflection direction or in the sound sound power directions. The permanent oscillations of the frequency response of the speaker all disappear !
Jean-Luc Ohl, a french acoustician, has noticed the same phenomenon while performing measurements in an anechoic chamber: measuring the frequency response moving the microphone around the speaker cancels some oscillations in the frequency response that, according to the spinorama data, can never be canceled.
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