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Full range line array for wall or corner placement
Full range line array for wall or corner placement
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Old 21st July 2019, 01:27 PM   #301
nc535 is offline nc535
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Thanks. I hope you are right.

Also hope that multiple subs will neutralize effect of that 60 hz null.

Now here is boundary contribution prediction by Vituix for my array location in front of the garage door (green trace in middle graph):

Full range line array for wall or corner placement-boundary-interference-prediction-vituix-jpg

This showing a 71 hz null and another at 220. It does predict the hump in between that we see. 6 db effective absorption is a guess. There should be at least that much at 200 Hz, declining rapidly as frequency decreases.
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File Type: jpg boundary interference prediction vituix.jpg (223.0 KB, 119 views)
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Old 21st July 2019, 01:58 PM   #302
nc535 is offline nc535
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Here is the boundary prediction for the array tight to the corner.

Full range line array for wall or corner placement-tight-corner-boundary-jpg

With 2" thick pad, I believe I can get to the spacings shown which push the first null out to 720 Hz and reduce the null to a slight depression of 2.5 db or so. At lower frequencies there is a lot more corner support than shown as absorption drops off rapidly.
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File Type: jpg tight to corner boundary.jpg (237.8 KB, 119 views)
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Old 21st July 2019, 02:37 PM   #303
BYRTT is offline BYRTT  Denmark
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Full range line array for wall or corner placement
Thanks Vituix predictions where corner looks good and doable with bit of DSP management : )
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Old 21st July 2019, 03:39 PM   #304
nc535 is offline nc535
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Yeah, now if only I had a corner I could use out here. There is one inside though.

This morning it looks workable to rotate my listening axis so that sounds go across the garage . That gets one of the speakers away from the garage door where it restricts the opening. Any absorption I put on what are now un-insulated block side wall will benefit me thermally.
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Old 25th July 2019, 12:30 PM   #305
nc535 is offline nc535
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Ages ago it seems, I turned my room on its ear (well rotated it 90 degrees) because the 2nd array crowded the garage door too much and thinking it would be easier to treat the new rear wall.

Full range line array for wall or corner placement-garage-jpg

Since then its been a recovery operation trying to get back to where I was. the real challenge was implementing a circa 100 Hz XO in the presence of boundary interference near XO. Normally one would do this with outdoor measurements and/or nearfield of the LF but one can't nearfield an array...
But I persisted through several long days of trying again and again until I got something that seemed worth trying.

Full range line array for wall or corner placement-garage-minidsp-iir-eq-jpg

Full range line array for wall or corner placement-left-spectrogram-minid-eq-jpg

That isn't very impressive but it took all the miniDSP resources. Clearly there is work to be done both on the room and in DSP. But I listened anyway and was encouraged.
Attached Images
File Type: jpg across the garage.jpg (103.3 KB, 102 views)
File Type: jpg Across garage with MiniDSP IIR EQ.jpg (68.7 KB, 101 views)
File Type: jpg Left spectrogram with MiniD EQ.jpg (110.2 KB, 102 views)
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Old 25th July 2019, 12:54 PM   #306
nc535 is offline nc535
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This morning I got up with more energy and did a quick run through DRC Designer.

Full range line array for wall or corner placement-predicted-dsp-fr-jpg

Left channel
Full range line array for wall or corner placement-predicted-spectrum-left-jpg

Right channel
Full range line array for wall or corner placement-predicted-spectrum-jpg

DRC did a much better job on the right than the left but right was closer to begin with. This underscores the point that the better it is before DSP, the better the correction DRC does. That means more treatment. My 4" thick rigid absorbers don't go low enough, doing only a few db at 200 Hz. When I get time I will augment them with 8" thick pink and fluffy which porous absorber calculator tells me will be highly effective down to 100 Hz.

There is also a lot more to be done with DSP. This was just a quick check. Curious that DRC didn't flatten the phase at the low end.

Unfortunately duty will take me away for much of the rest of the day
Attached Images
File Type: jpg Before and predicted after DSP FR.jpg (98.1 KB, 101 views)
File Type: jpg Predicted spectrum on left.jpg (81.0 KB, 103 views)
File Type: jpg Predicted spectrum on right.jpg (79.8 KB, 102 views)
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Old 25th July 2019, 11:13 PM   #307
fluid is offline fluid  Australia
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Quote:
Originally Posted by nc535 View Post
Normally one would do this with outdoor measurements and/or nearfield of the LF but one can't nearfield an array...
You can significantly reduce the amount of "room" in a listening position measurement by impulse averaging 4 or more measurement s from different positions in a line around the listening position.

By impulse averaging you still keep the room resonances and nulls below transition but get rid of a lot of the positional dependent stuff above. About as close to an outdoor measurement as you will get indoors.

I showed how I did it in my thread somewhere around here
Full Range TC9 Line Array CNC Cabinet

REW calls it vector averaging, take the measurements align the impulses to the same point then vector average.
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Old 26th July 2019, 12:06 PM   #308
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Hi Fluid:
Thanks for that - this fresh point of view helps. I know the value of positional averaging but it never occurred to me to use it in crossover work. The closest I'm coming to that is using subs <100Hz both front and rear, which does help.

I'm actually surprised how little room shows up in the FR measurements compared to conventional speakers and smaller rooms, but then looking at the spectrograms, how much there is.

But most of that is front to back stuff and its the reflection from the rear wall that is making my life difficult. Side to side response variation is small enough for my purposes. Should I try averaging responses at different distances from the rear wall? Its worth a try...

So far all I've done is to try to find the optimal arrangement of rear wall absorption and the measurement distance with the least interference. If I build a couple more absorbers I might be there...
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Old 26th July 2019, 12:11 PM   #309
fluid is offline fluid  Australia
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You can measure anywhere you like and average it out, when changing front to back distance you can run into levels differences which might skew the results unless you normalize them. I tried with 12 points and found that 4 to 6 was the sweet spot for effort vs results. More points reduces the room in the measurement but becomes tedious and the most important stuff is down enough with 4 to 6 measurements.
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Old 26th July 2019, 01:21 PM   #310
nc535 is offline nc535
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yes, but my question was more to should I want to measure at various distances and then average. Think about the simplified case of a reflection from a boundary. At each distance you will get a null at a different frequency. If you average the multiple measurements with nulls at different frequencies, you pull down the response over the entire region spanned by those nulls. That doesn't get you closer to the direct response.

Instead let's say we have Mclose, a measurement taken close to the wall, which has a null at a high frequency and a Mdist, a measurement taken far from the wall which has a null at a low frequency. Perhaps we should merge these two measurements, like we do with a close mic and normal measurement, so that we use Mdist for the high range and Mclose for the low range and thus have a response relatively unaffected by the wall.
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