Simplified REW Setup and Use (USB Mic & HDMI Connection) Including Measurement Techniques and How To Interpret Graphs - Page 930 - AVS Forum | Home Theater Discussions And Reviews
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post #27871 of 28124 Old 09-15-2019, 10:43 AM
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Originally Posted by Lesmor View Post
Yeah I checked and double checked the wiring and it is ok
Not good enough. While not likely, there have been cases of reversed internal wiring. The only way to be sure of polarity is to use the REW impulse response to compare polarity with the other mains.
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post #27872 of 28124 Old 09-15-2019, 11:19 AM
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Quote:
Originally Posted by Lesmor View Post
Yeah I checked and double checked the wiring and it is ok
I get where you are coming from though as it looks to start with a phase shift but there is no evidence of that past the XO point
plus the cancellation is < of the XO which suggests it is somehow caused by the subs but only affecting the left speaker
a work in progress

I wouldn't rule that out either. The 80 Hz XO is not that far away.

I'd increase the sub's distance 1 meter in the AVR setup and see what happens to the dip (in case of two subs, switch one off). Don't forget to measure the center and R, too with the distance tweak.
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Good sound is always the result of engineering. And engineering always starts with measuring. Consumer industry and mainstream will never tell customers about that: improvements in room acoustics are worth roughly ten (10!) times the amount spent on equipment like speakers and receivers. For example: only $500 in room treatment is worth more than spending $5000 (fivethousand) on equipment.
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post #27873 of 28124 Old 09-15-2019, 12:17 PM
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Quote:
Originally Posted by AustinJerry View Post
Not good enough. While not likely, there have been cases of reversed internal wiring. The only way to be sure of polarity is to use the REW impulse response to compare polarity with the other mains.
Impulse responses posted

Quote:
Originally Posted by Skinfax1 View Post
I wouldn't rule that out either. The 80 Hz XO is not that far away.

I'd increase the sub's distance 1 meter in the AVR setup and see what happens to the dip (in case of two subs, switch one off). Don't forget to measure the center and R, too with the distance tweak.
REW seems to suggest adding 1 foot to the subs,as I understand it this would mean 1 foot to each sub?

As always I appreciate the comments
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Last edited by Lesmor; 09-15-2019 at 12:23 PM.
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post #27874 of 28124 Old 09-15-2019, 01:20 PM
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Originally Posted by Lesmor View Post
Impulse responses posted



REW seems to suggest adding 1 foot to the subs,as I understand it this would mean 1 foot to each sub?

As always I appreciate the comments
I was more interested in seeing whether the LCR speakers are all the same polarity, which requires zooming in on the Impulse responses as shown in the first attached screenshot. When zoomed in, it is easy to see whether the initial impulse is positive or negative (negative indicating reversed polarity).

As for the alignment of the subs with the mains, the usual practice is to use the sub distance tweak rather than the impulse response. Notice in the second screenshot the effect of varying the sub distance, which results in a flatter response near the crossover (100Hz). The center+subs impulse response for the flattest frequency response (third screenshot) clearly shows the subs are not time aligned with the center (they don't need to be). The subs, however, need to be aligned with each other (see fourth screenshot).
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post #27875 of 28124 Old 09-15-2019, 03:13 PM
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Quote:
Originally Posted by AustinJerry View Post
I was more interested in seeing whether the LCR speakers are all the same polarity, which requires zooming in on the Impulse responses as shown in the first attached screenshot. When zoomed in, it is easy to see whether the initial impulse is positive or negative (negative indicating reversed polarity).

As for the alignment of the subs with the mains, the usual practice is to use the sub distance tweak rather than the impulse response. Notice in the second screenshot the effect of varying the sub distance, which results in a flatter response near the crossover (100Hz). The center+subs impulse response for the flattest frequency response (third screenshot) clearly shows the subs are not time aligned with the center (they don't need to be). The subs, however, need to be aligned with each other (see fourth screenshot).
hopefully got this right
this certainly looks different to what you posted
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post #27876 of 28124 Old 09-15-2019, 03:18 PM
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Originally Posted by Lesmor View Post
hopefully got this right
this certainly looks different to what you posted
All three impulses are pointed in the same direction, which means the speakers have the same polarity, which is good. The peaks don't line up exactly, which means there is a slight alignment difference. Holding the CTRL key down, and simultaneously right-clicking the mouse, REW will measure the distance between the peaks. Depending on the result, you may, or may not, need to adjust the speaker alignment. It depends on how big the measured distance is, which I can't tell from the screenshot you posted.
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post #27877 of 28124 Old 09-15-2019, 03:45 PM
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Quote:
Originally Posted by AustinJerry View Post
All three impulses are pointed in the same direction, which means the speakers have the same polarity, which is good. The peaks don't line up exactly, which means there is a slight alignment difference. Holding the CTRL key down, and simultaneously right-clicking the mouse, REW will measure the distance between the peaks. Depending on the result, you may, or may not, need to adjust the speaker alignment. It depends on how big the measured distance is, which I can't tell from the screenshot you posted.
this is with CTRL > right click and drag
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post #27878 of 28124 Old 09-15-2019, 03:48 PM
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Quote:
Originally Posted by Lesmor View Post
this is with CTRL > right click and drag
That is an insignificant distance, likely smaller than the distance adjustment on your AVR. Not an issue at all, safe to ignore.
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post #27879 of 28124 Old 09-15-2019, 03:53 PM
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Quote:
Originally Posted by AustinJerry View Post
That is an insignificant distance, likely smaller than the distance adjustment on your AVR. Not an issue at all, safe to ignore.
good to know thanks
subs tweak will have to wait until I use REW again
I maybe also need to revisit your guide
well its midnight here so wish you all a goodnight
Regards
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post #27880 of 28124 Old 09-15-2019, 03:58 PM
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Originally Posted by Lesmor View Post
good to know thanks
subs tweak will have to wait until I use REW again
I maybe also need to revisit your guide
well its midnight here so wish you all a goodnight
Regards
Andy
Let me know if you need instructions for the sub distance tweak.
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post #27881 of 28124 Old 09-16-2019, 03:29 AM
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Originally Posted by AustinJerry View Post
Let me know if you need instructions for the sub distance tweak.
thanks Jerry
if it is still current I did find a link in the REW guide

Audyssey Sub Distance Tweak Procedure Oct 2013.pdf

I will have to check the time alignment is correct on both my subs (one at the front right corner and one at the rear left back wall)
Is there any written guidance for doing that?

I must say that this has been a invaluable exercise for me if only in building up confidence with using REW and the presentation of the graphs
thanks to all concerned for sticking with me
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post #27882 of 28124 Old 09-16-2019, 06:26 AM
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Originally Posted by Lesmor View Post
thanks Jerry
if it is still current I did find a link in the REW guide

Audyssey Sub Distance Tweak Procedure Oct 2013.pdf

I will have to check the time alignment is correct on both my subs (one at the front right corner and one at the rear left back wall)
Is there any written guidance for doing that?

I must say that this has been a invaluable exercise for me if only in building up confidence with using REW and the presentation of the graphs
thanks to all concerned for sticking with me
Page 22 of the 2x4 implementation guide linked in my sig has a description of how to use REW to align the subs.

In a nutshell, the sub distance tweak involves adjusting the combined sub distances in small increments while measuring center + Subs, and picking the sub distance the yields the flattest response curve in the crossover region. Typically, there will be a distance that results in an obvious improvement.
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post #27883 of 28124 Old 09-16-2019, 01:31 PM
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Originally Posted by AustinJerry View Post
Page 22 of the 2x4 implementation guide linked in my sig has a description of how to use REW to align the subs.

In a nutshell, the sub distance tweak involves adjusting the combined sub distances in small increments while measuring center + Subs, and picking the sub distance the yields the flattest response curve in the crossover region. Typically, there will be a distance that results in an obvious improvement.
I will read the 2x4 guide I am also considering getting a 2x4 HD
I manged to take some readings this afternoon before reading your post this is with Audyssey
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post #27884 of 28124 Old 09-16-2019, 02:01 PM
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I will read the 2x4 guide I am also considering getting a 2x4 HD
I manged to take some readings this afternoon before reading your post this is with Audyssey
The alignment looks pretty close. Depending on the granularity of your distance setting, you might be able to get the peaks to line up exactly. If you can’t, I think what you have is close enough.
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post #27885 of 28124 Old 09-17-2019, 10:17 AM
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Acoustic Treatments

It's been awhile since I examined the sound in my room with REW, but I now finally have clearance from the wife for "some" acoustic treatments so I'd like to revisit here.

I've attached my left, centre and right speaker sound waves from my last readings over a year ago. I will be measuring again and posting here just to get a more current reading, but wanted to get this discussion going sooner.
At that time, I positioned my two SVS PB-12 subs to get the smoothest bass response, so that's already done.

I've also posted here:https://www.avsforum.com/forum/19-de...l#post58560682

with picture of my room and details which should help.

I've since measured my first reflections (mirror trick), including the ceiling.

My thoughts were that I'd just buy the following bass traps and place them as indicated below: This is pretty much the extent of the WAF so couldn't go beyond.

GIK Acoustics Monster Bass Trap with Flex Range - 7.31" thick - 24"x36" - I'd mount two end to end on the ceiling at the measured reflection point between the FL/C/FR speakers and the main viewing position (blue couch).

GIK Acoustics 244 Bass Trap with Flex Range - 5.25" thick - 24.25" x 48.25" - I'd mount 3 vertically side by side on the big green wall to the right of the screen (behind the other blue couch that's perpendicular to the screen wall) at the measured reflection point there which is about centre on that wall

Is this a good approach? Should I be measuring or trying other things first?
How likely are the acoustic treatments going to be at improving my sound in the room I have?
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post #27886 of 28124 Old 09-17-2019, 12:35 PM
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It's been awhile since I examined the sound in my room with REW, but I now finally have clearance from the wife for "some" acoustic treatments so I'd like to revisit here.

I've attached my left, centre and right speaker sound waves from my last readings over a year ago. I will be measuring again and posting here just to get a more current reading, but wanted to get this discussion going sooner.
At that time, I positioned my two SVS PB-12 subs to get the smoothest bass response, so that's already done.

I've also posted here:https://www.avsforum.com/forum/19-de...l#post58560682

with picture of my room and details which should help.

I've since measured my first reflections (mirror trick), including the ceiling.

My thoughts were that I'd just buy the following bass traps and place them as indicated below: This is pretty much the extent of the WAF so couldn't go beyond.

GIK Acoustics Monster Bass Trap with Flex Range - 7.31" thick - 24"x36" - I'd mount two end to end on the ceiling at the measured reflection point between the FL/C/FR speakers and the main viewing position (blue couch).

GIK Acoustics 244 Bass Trap with Flex Range - 5.25" thick - 24.25" x 48.25" - I'd mount 3 vertically side by side on the big green wall to the right of the screen (behind the other blue couch that's perpendicular to the screen wall) at the measured reflection point there which is about centre on that wall

Is this a good approach? Should I be measuring or trying other things first?
How likely are the acoustic treatments going to be at improving my sound in the room I have?
Couple of comments. The low frequencies below 300Hz do not look very smooth. And I believe the measurements you posted have smoothing applied. If you were to post 15-300Hz measurements without smoothing, I think the situation would look even worse. Bass traps help with resonance in the low frequencies, but are only marginally effective in smoothing out the frequency response. Typically, positioning the subs will get a smoother frequency response, but you say you have already done that. I don't know what to say, except that more subs would be a logical next step.

As far as the effectiveness of treatments, we need to see the waterfall to assess bass resonance, and the ETC to assess higher frequency reflections. I would defer making any decisions until you get feedback on these additional measurements.

Edit: I took a look at the pictures of your listening room. It seems like it would be quite a challenge from an acoustic perspective.
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post #27887 of 28124 Old 09-17-2019, 01:39 PM
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Originally Posted by AustinJerry View Post
Couple of comments. The low frequencies below 300Hz do not look very smooth. And I believe the measurements you posted have smoothing applied. If you were to post 15-300Hz measurements without smoothing, I think the situation would look even worse. Bass traps help with resonance in the low frequencies, but are only marginally effective in smoothing out the frequency response. Typically, positioning the subs will get a smoother frequency response, but you say you have already done that. I don't know what to say, except that more subs would be a logical next step.

As far as the effectiveness of treatments, we need to see the waterfall to assess bass resonance, and the ETC to assess higher frequency reflections. I would defer making any decisions until you get feedback on these additional measurements.

Edit: I took a look at the pictures of your listening room. It seems like it would be quite a challenge from an acoustic perspective.
Thanks, I will defer any decisions until I analyze further. I'll look to produce those measurements and post over next few days or by weekend - I have a new projector, screen material and DCR lens coming so may be busy with that first.

When you say it would be quite a challenge, what strikes you the most for that opinion? Is it the size? Or just how the back wall isn't there maybe?

My thoughts here are (and I know I'm jumping to the end again prematurely) that if I can't provide a significant sound quality improvement with just the few acoustic treatments I've mentioned, then I'll just leave it all as is. Overall, the sound isn't bad to my ears for HT - I just know it can be vastly improved, especially for music listening.
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post #27888 of 28124 Old 09-17-2019, 01:56 PM
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Based on the pictures, the open back of the room will be a challenge. And it doesn’t look like a lot of flexibility WRT sub placement. Let’s withhold any further comments until you take some new measurements. I would like to see left+subs, right+subs, center+subs, all with room correction turned on (if you are using room correction). And both subs by themselves, then sub1 by itself, and sub2 by itself. Consider uploading the REW MDAT file to a file sharing site so others can download it and run their own analysis.

Are you using room correction? If yes, what type? Audyssey? XT or XT32?
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post #27889 of 28124 Old 09-17-2019, 04:37 PM
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Originally Posted by Sittler27 View Post
...
GIK Acoustics ...
There's a vendor that will work pretty closely with you to ensure you get the appropriate panels. I don't recall if it's Gik or not.
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post #27890 of 28124 Old 09-17-2019, 04:54 PM
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When you say it would be quite a challenge, what strikes you the most for that opinion? Is it the size? Or just how the back wall isn't there maybe?
Lack of back wall means the subs have to energize a large room. Also the general asymmetry and openness of the space makes it difficult when it comes to predicting results from subwoofer placement as well as getting a symmetrical soundstage. Will require some trial & error to find better subwoofer locations. Are you mostly concerned with a single seat (main listening position) or consistency across multiple seats?

Sanjay
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Based on the pictures, the open back of the room will be a challenge. And it doesn’t look like a lot of flexibility WRT sub placement. Let’s withhold any further comments until you take some new measurements. I would like to see left+subs, right+subs, center+subs, all with room correction turned on (if you are using room correction). And both subs by themselves, then sub1 by itself, and sub2 by itself. Consider uploading the REW MDAT file to a file sharing site so others can download it and run their own analysis.

Are you using room correction? If yes, what type? Audyssey? XT or XT32?
Audyssey XT32. I have a Marantz SR7010.

I'll run all those checks through this weekend. Thanks!
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post #27892 of 28124 Old 09-17-2019, 05:30 PM
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Lack of back wall means the subs have to energize a large room. Also the general asymmetry and openness of the space makes it difficult when it comes to predicting results from subwoofer placement as well as getting a symmetrical soundstage. Will require some trial & error to find better subwoofer locations. Are you mostly concerned with a single seat (main listening position) or consistency across multiple seats?
MLP only, no one else cares about this stuff...lol

I'm open to adding another sub if that is what would help, let's see where we go with this. I have two SVS PB-12s now, but maybe I need more.
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post #27893 of 28124 Old 09-18-2019, 06:35 AM
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Hi Jerry,

For speaker timing alignment do you have to take a sweep of each speaker individually with a timing reference in place and then overlay all the impulse response graphs ?

So to align the centre channel with the sub, I'd have to a measurement of each individual speaker - i.e Centre without sub and sub alone ?

Attached is a graph of the C+Sub with front L being the timing ref speaker. As you can see the alignment with 0 (zero) is very slightly off.
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post #27894 of 28124 Old 09-18-2019, 06:57 AM
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Hi Jerry,

For speaker timing alignment do you have to take a sweep of each speaker individually with a timing reference in place and then overlay all the impulse response graphs ?

So to align the centre channel with the sub, I'd have to a measurement of each individual speaker - i.e Centre without sub and sub alone ?

Attached is a graph of the C+Sub with front L being the timing ref speaker. As you can see the alignment with 0 (zero) is very slightly off.
In the measurement that you posted, the center channel is showing a very slight alignment difference from the channel used for the timing reference (i.e. the left channel). But the difference is extremely small, likely smaller that the granularity of your AVR distance adjustments, and should be no cause for concern.

If you wanted to look at the alignment of the center channel with the sub, you would measure each individually and overlay the impulse responses. But remember, one would typically use the "sub distance tweak" to achieve the flattest response between the subs and mains, and the flattest response is rarely achieved by aligning subs and mains using the impulse response. For example, my setup yields the flattest response with a sub distance tweak of 6ms. The first attachment shows the improvement that can be obtained by tweaking the sub distance. The second attachment shows that the center and subs are not aligned WRT the impulse response, even though the frequency response is best.
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post #27895 of 28124 Old 09-18-2019, 07:56 AM
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MLP only, no one else cares about this stuff...lol
In that case, no need for more subs. Just find locations for your current subwoofers that result in the fewest/smallest dips. Peaks can be EQ'd down.

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post #27896 of 28124 Old 09-18-2019, 08:07 AM
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Originally Posted by sdurani View Post
In that case, no need for more subs. Just find locations for your current subwoofers that result in the fewest/smallest dips. Peaks can be EQ'd down.
One would think that XT32 would have done more to smooth out the low frequencies, no? Assuming the measurements were with Audyssey turned on.
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post #27897 of 28124 Old 09-18-2019, 09:03 AM
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Originally Posted by AustinJerry View Post
One would think that XT32 would have done more to smooth out the low frequencies, no? Assuming the measurements were with Audyssey turned on.
Yes, Audyssey should at least have brought down some of those peaks (can understand if it didn't do much to boost dips). But I didn't know whether the measurements were with or without Audyssey.

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post #27898 of 28124 Old 09-18-2019, 11:18 AM
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Originally Posted by AustinJerry View Post
That is one way to do it.
Is there a better way to do it? I can't see a way in REW to select Left+Sub or L+R+Sub or anything like that for a measurement. Am I missing something easy? thanks
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post #27899 of 28124 Old 09-18-2019, 11:46 AM
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Is there a better way to do it? I can't see a way in REW to select Left+Sub or L+R+Sub or anything like that for a measurement. Am I missing something easy? thanks
If speakers are set to "small", then a REW sweep from 15Hz to 20KHz automatically includes both the mains and the subs by virtue of bass management. Frequencies below the crossover are reproduced by the subs.
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post #27900 of 28124 Old 09-21-2019, 04:19 AM
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Could someone wiser than me check my REW measurements after ARC and see if they can figure why there is so big dip in response on front channels between 100-200hz compared to what Anthem's ARC calculated. All crossovers are set to 80hz for FR/C/FR and subwoofer. Attached a picture of fronts+sub sweeps.


REW measurements,

https://drive.google.com/file/d/1Tl0...8Qsw97A31_sxBV

Allso looking at the impulse response from REW, it shows FR and Surrounds impulse going opposite from FL, C and Subwoofer. Does that indicate those speakers are at wrong phase / polarity ?

Too much things happening after buying miniDSP and UMIK. Atleast finally i got to see what ARC does and how should go forward with room acoustics etc. ARC doesn't seem to do well on taming 300Hz - 1000Hz range so i guess that could use some room threatment?


Allso subwoofer is far from ideal and has to be done starting with possible moving things around, but would like to first set the front stage correct and go from there.
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Attached Files
File Type: pdf ARC Room Correction miniDSP_flat.pdf (657.9 KB, 10 views)

HTPC - MRX 520 - Gallo Reference 3.1 & Strada - SVS PC4000 - Sony 65" 4k TV 8505C
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