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Discussion Starter #1
Hi all!

wondered if you had any comments on the 8K to 10k plot dynamics..
I measured left, right and then both as you can see.

do you think this would be destructive interference from boundary early reflections, phase issue?

Adam p11a, studio control room, rta-m mic, room cal in place, mic cal not used...

(sorry if i dont post all relevant info, im very new to this!)
thanks!
brad
 

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Discussion Starter #2
I may have jumped the gun as I've rechecked the mic position and found it to be a bit forward (closer to the monitors) than it should be. I would say it's probably picking up reflections from the control surface and video monitors...
 

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Hi wayne!
yup, i guess they do!
hey, just to clarify: i dont have a lot of experience reading the results from tests, so im not sure how this plot stands up to others. is it out of whack, pretty good, real good etc...
because im new at this, i lack much of the understanding of interpreting the test results.
any comments on how i can speed up my progress of understanding? (ive been reading as much as i can find, but im not sure if im spinning my wheels a bit!)
thanks wayne!
b
 

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Your graph looks about average, except that you get a big depression at 8 kHz with both speakers operating (magenta trace). That’s pretty peculiar...
I wonder if the tweeter is wired out of phase in one speaker? Could reverse the connections to one of the speakers to see if the dip disappears when both play (will have odd effects lower down of course), if it does might want to rewire the tweeter.
 

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Discussion Starter #7
I wonder if the tweeter is wired out of phase in one speaker? Could reverse the connections to one of the speakers to see if the dip disappears when both play (will have odd effects lower down of course), if it does might want to rewire the tweeter.
thats an interesting thought!
do you think i would see more cancellation of at least higher frequencies in addition as well?

these monitors (adam p11a) are placed next to a set of yamaha ns-10's. the adam pair are set inside the ns-10's. and there's full equip racks below them and 2 mac 22" monitors in the middle.
i think im getting some kind of ER off the surfaces and the distance fits this 8k range in the space between monitor and measurement mic...
i do have the mic at about 35 degree up angle on the tests...
i tried absorption covering mac monitors and and the desk below them, but i saw difference in the result. i didnt try absorption on the face of the equip racks yet.

thanks for the advice! any help is appreciated for sure!!
b
 

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Yes to all of the above… could be driver polarity issue , could be 1st order reflection issue could be combination of both or… simply the laws of physics at play and nothing is really at fault.

When measuring high frequency content and as you well know, the wave lengths are relatively small. At 8000Hz (considering speed of sound at something like 1126 feet per second) the wavelength is approximating a whopping 1.69 inches.

Everything is fine and dandy when you are measuring a single source, but as soon as you add a second source all bets are off. The two sources have considerable driver spacing between them in context to the shorter wavelengths. You can’t assume (nor should you) that these two sources are arriving in perfect phase to the measurement microphone especially when the wavelengths are mere inches.

You have to take multiple measurements and move speakers or the measurement microphone around in very small increments to correlate “trends” rather than making assessments from a single snapshot at one static location when it comes to the high end band pass assessment.

You never mentioned any audible cancellation correlating to what’s seen on the magnitude response which leads me to believe it’s not as bad as it looks which goes to the point that we never let the graphs have the primary influence to make a change.

For near-field reflection possibilities you’ll have to evaluate the impulse response measurement that is better suited to indentify specifics about arrival times. You’ll see an obvious reflection if it’s there using the IR module of the software.
 

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Discussion Starter #9
hi bsa!
great comments!
-took about 10 tests with moving mic
the dip/peaks will change freq a bit on diff mic placements. (diff. wavelengths/ER cancellations??)
i think because the L and R tests are so sim. , ill use that data(one side) to try a eq correction curve.

audible correction:generally i have no prob. hearing the 8k range, actually now that you mention it, i have noticed i have to de-ess vocal recordings quite a bit. usually around 8200hz. maybe the tracks are not as bad as iv been thinking...more tests...

ill try the IR module...have not used it yet...
thank you!!!

Yes to all of the above… could be driver polarity issue , could be 1st order reflection issue could be combination of both or… simply the laws of physics at play and nothing is really at fault.

When measuring high frequency content and as you well know, the wave lengths are relatively small. At 8000Hz (considering speed of sound at something like 1126 feet per second) the wavelength is approximating a whopping 1.69 inches.

Everything is fine and dandy when you are measuring a single source, but as soon as you add a second source all bets are off. The two sources have considerable driver spacing between them in context to the shorter wavelengths. You can’t assume (nor should you) that these two sources are arriving in perfect phase to the measurement microphone especially when the wavelengths are mere inches.

You have to take multiple measurements and move speakers or the measurement microphone around in very small increments to correlate “trends” rather than making assessments from a single snapshot at one static location when it comes to the high end band pass assessment.

You never mentioned any audible cancellation correlating to what’s seen on the magnitude response which leads me to believe it’s not as bad as it looks which goes to the point that we never let the graphs have the primary influence to make a change.

For near-field reflection possibilities you’ll have to evaluate the impulse response measurement that is better suited to indentify specifics about arrival times. You’ll see an obvious reflection if it’s there using the IR module of the software.
 
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