Simplified REW Setup and Use (USB Mic & HDMI Connection) Including Measurement Techniques and How To Interpret Graphs - Page 442 - AVS | Home Theater Discussions And Reviews
Forum Jump: 
 316Likes
Reply
Thread Tools
post #13231 of 13336 Old 01-20-2015, 12:15 PM
AVS Special Member
 
jim19611961's Avatar
 
Join Date: Mar 2011
Location: Texas
Posts: 1,499
Mentioned: 6 Post(s)
Tagged: 0 Thread(s)
Quoted: 202 Post(s)
Liked: 96
Quote:
Originally Posted by tvuong View Post
So my 8-9% distortion level at my normal listening level down to 14hz isn't bad after all. Now is that 8-9% distortion audible is my next question.
The problem is you have high distortion at significantly higher frequencies than 14hz.

My Room
My Music
Rega - Apollo, Rega - DAC, Goldpoint Passive, (2) Classe CA-100 bridged power amps (350w)
Jenzen Next
jim19611961 is online now  
Sponsored Links
Advertisement
 
post #13232 of 13336 Old 01-20-2015, 12:40 PM
AVS Special Member
 
tvuong's Avatar
 
Join Date: Dec 2000
Posts: 2,048
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 369 Post(s)
Liked: 150
Quote:
Originally Posted by 3ll3d00d View Post
Most people are going to have to accept more distortion, in the sub region at least, than that because most people rely on EQ to flatten the response. The room amplifies harmonic distortion after all and you can't address this with EQ. To give an example, here's a pretty high output sweep from my room (roughly equates to 0dBFS output at my max listening level). I've annotated with red arrows to show room modes that amplify harmonic distortion and green arrows to show the effect of a null, you can't see most of this in the fundamental because that's been EQed but you can see it in the distortion traces.



Therefore there are at least 2 Qs here

if the Q is "what's the capability of my sub?" then I look outside of those areas and see 3-4% THD at 10Hz and <1% THD around 40Hz which says to me my sub has plenty of headroom.
if the Q is "what's the capability of my room?" then I look at those areas and see 15% THD at 20Hz & 8% at 10-13Hz and remember that I have a honking great big mode at 40Hz.

In particular the 60Hz distortion is boosted by a mode at 120Hz but coincides with a null in the fundamental hence shows up as relatively massive distortion.

Personally I'm going to try out the VBA (virtual bass array) approach to see if I can cancel that 40Hz room mode completely, the rest I'll live with.
Good explanation. Thanks.
Quote:
Originally Posted by jim19611961 View Post
The problem is you have high distortion at significantly higher frequencies than 14hz.
I see. Is it audible at 75hz with 8-9% distortion? I think Audessey boosts too much there. I am going to bump up around 70-75hz using my subs built in pEQ and then rerun Audessey to see if it helps with distortion. Speaking of running Audessey, I will only need to optimize my very own seating, would you guy recommends running all positions closed mic, ~3 inches from MLP? Thanks.
tvuong is offline  
post #13233 of 13336 Old 01-20-2015, 02:01 PM
AVS Special Member
 
AustinJerry's Avatar
 
Join Date: Jan 2003
Location: Austin, Texas
Posts: 8,545
Mentioned: 13 Post(s)
Tagged: 0 Thread(s)
Quoted: 1613 Post(s)
Liked: 1022
Quote:
Originally Posted by tvuong View Post
Good explanation. Thanks.

I see. Is it audible at 75hz with 8-9% distortion? I think Audessey boosts too much there. I am going to bump up around 70-75hz using my subs built in pEQ and then rerun Audessey to see if it helps with distortion. Speaking of running Audessey, I will only need to optimize my very own seating, would you guy recommends running all positions closed mic, ~3 inches from MLP? Thanks.
The lower the frequency, the harder it is to hear distortion. I agree with Jim, you have some distortion levels at frequencies where the distortion could be noticeable.

WRT mic spacing, I optomize for a single seat, but my mic spacing is 12". I don't think 3" will get an improvement.

Edit: Actually, my mic spacing is on a circle around the MLP, where the circle has a 36" diameter. I am using Dirac Live now.
AustinJerry is online now  
post #13234 of 13336 Old 01-20-2015, 02:13 PM
AVS Special Member
 
Alan P's Avatar
 
Join Date: Jan 2003
Location: Rapid City, South Dakota
Posts: 3,584
Mentioned: 9 Post(s)
Tagged: 0 Thread(s)
Quoted: 1212 Post(s)
Liked: 611
Quote:
Originally Posted by AustinJerry View Post
The lower the frequency, the harder it is to hear distortion. I agree with Jim, you have some distortion levels at frequencies where the distortion could be noticeable.

WRT mic spacing, I optomize for a single seat, but my mic spacing is 12". I don't think 3" will get an improvement.

Edit: Actually, my mic spacing is on a circle around the MLP, where the circle has a 36" diameter. I am using Dirac Live now.
Is that with the MLP in the center of the circle, or.....?

AVR: Denon 4520ci, FL/R: Klipschorn, CC: Klipsch RC64ii, SUR: Polk LS F/X x 4, SUB: PSA T-18 x 2, DISP: Mitsubishi WD-73740, BluRay: PS3 & BDP-S5100, Remote: URC MX-700
--------------------------------------------------
Getting Started with REW
Audyssey 101
Audyssey FAQ
Alan P is online now  
post #13235 of 13336 Old 01-20-2015, 02:13 PM
AVS Special Member
 
AustinJerry's Avatar
 
Join Date: Jan 2003
Location: Austin, Texas
Posts: 8,545
Mentioned: 13 Post(s)
Tagged: 0 Thread(s)
Quoted: 1613 Post(s)
Liked: 1022
Quote:
Originally Posted by AustinJerry View Post
I think we need to ask Stuart to describe the sounds he is hearing. There is a known issue with REW that it occasionally will output a distorted tone, not a pure tone. That is what you are describing, Alan, and I experience this in almost every REW session I have. Like you say, getting rid of the distorted tone involves toggling the output channels a couple of times, and then everything is OK again.

But I didn't get the impression this is what Stuart was experiencing. Stuart, perhaps you could explain what you are hearing in more detail or, better yet, take a recording of the static and post the file here so we can listen to it.
Here is an audio clip of what I am calling a "distorted REW sweep": https://dl.dropboxusercontent.com/u/...EW%20sweep.zip

I believe a number of people have reporting hearing this.
AustinJerry is online now  
post #13236 of 13336 Old 01-20-2015, 03:12 PM
AVS Club Gold
 
sdrucker's Avatar
 
Join Date: Feb 2006
Location: Chicago, IL
Posts: 2,321
Mentioned: 3 Post(s)
Tagged: 0 Thread(s)
Quoted: 216 Post(s)
Liked: 170
Quote:
Originally Posted by AustinJerry View Post
Here is an audio clip of what I am calling a "distorted REW sweep": https://dl.dropboxusercontent.com/u/...EW%20sweep.zip

I believe a number of people have reporting hearing this.

That's the one - I had to turn the volume up on my PC speakers to capture what I heard on Sunday, but yes.

Audio Gear: Sherwood R-972 (Trinnov Altitude - coming soon!), NAD M27 amp
Display: Panasonic VT50, Lumagen Radiance Mini
Misc.: Oppo 103, Apple TV, JRiver ID NUC
PSB Imagine T2, Center, and Surrounds; HSU ULS-15 subs (2)
sdrucker is online now  
post #13237 of 13336 Old 01-20-2015, 03:41 PM
AVS Special Member
 
Alan P's Avatar
 
Join Date: Jan 2003
Location: Rapid City, South Dakota
Posts: 3,584
Mentioned: 9 Post(s)
Tagged: 0 Thread(s)
Quoted: 1212 Post(s)
Liked: 611
Yup, that's exactly what I hear too.

AVR: Denon 4520ci, FL/R: Klipschorn, CC: Klipsch RC64ii, SUR: Polk LS F/X x 4, SUB: PSA T-18 x 2, DISP: Mitsubishi WD-73740, BluRay: PS3 & BDP-S5100, Remote: URC MX-700
--------------------------------------------------
Getting Started with REW
Audyssey 101
Audyssey FAQ
Alan P is online now  
post #13238 of 13336 Old 01-20-2015, 04:45 PM
AVS Special Member
 
AustinJerry's Avatar
 
Join Date: Jan 2003
Location: Austin, Texas
Posts: 8,545
Mentioned: 13 Post(s)
Tagged: 0 Thread(s)
Quoted: 1613 Post(s)
Liked: 1022
Quote:
Originally Posted by Alan P View Post
Yup, that's exactly what I hear too.
Known issue. Perhaps I should ping JohnM once again for an explanation?
AustinJerry is online now  
post #13239 of 13336 Old 01-20-2015, 04:59 PM
AVS Special Member
 
Alan P's Avatar
 
Join Date: Jan 2003
Location: Rapid City, South Dakota
Posts: 3,584
Mentioned: 9 Post(s)
Tagged: 0 Thread(s)
Quoted: 1212 Post(s)
Liked: 611
Couldn't hurt.

It's very startling (and potentially dangerous) when it happens at higher SPLs.

AVR: Denon 4520ci, FL/R: Klipschorn, CC: Klipsch RC64ii, SUR: Polk LS F/X x 4, SUB: PSA T-18 x 2, DISP: Mitsubishi WD-73740, BluRay: PS3 & BDP-S5100, Remote: URC MX-700
--------------------------------------------------
Getting Started with REW
Audyssey 101
Audyssey FAQ
Alan P is online now  
post #13240 of 13336 Old 01-20-2015, 05:08 PM
AVS Special Member
 
AustinJerry's Avatar
 
Join Date: Jan 2003
Location: Austin, Texas
Posts: 8,545
Mentioned: 13 Post(s)
Tagged: 0 Thread(s)
Quoted: 1613 Post(s)
Liked: 1022
Quote:
Originally Posted by Alan P View Post
Couldn't hurt.

It's very startling (and potentially dangerous) when it happens at higher SPLs.
Yes, scary. I am in the habit of hovering the cursor over the "Cancel" button every time I run a sweep.
AustinJerry is online now  
post #13241 of 13336 Old 01-20-2015, 05:29 PM
Advanced Member
 
ggsantafe's Avatar
 
Join Date: Feb 2008
Location: Solar Powered in the Land of Enchantment
Posts: 724
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 33 Post(s)
Liked: 72
Quote:
Originally Posted by AustinJerry View Post
Here is an audio clip of what I am calling a "distorted REW sweep": https://dl.dropboxusercontent.com/u/...EW%20sweep.zip

I believe a number of people have reporting hearing this.
Yup - I believe we've had an earlier discussion of this "phenomena" and it is disturbing - I found that in many cases, if I simply repeated the measurement the "static" disappeared. Listening to the clip reminded me that the other day while I was working out in my gym, I noticed a song playing on the speakers that included a segment that very much reminded me of a 15-20,000hz sweep with a very techno pop feel to it - no idea what the name is - but somehow I think the sound engineers have played with REW at some point in their recording careers!

ggsantafe is online now  
post #13242 of 13336 Old 01-21-2015, 04:28 AM
Advanced Member
 
3ll3d00d's Avatar
 
Join Date: Sep 2007
Location: London, UK
Posts: 881
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 420 Post(s)
Liked: 105
Quote:
Originally Posted by tvuong View Post
Is it audible at 75hz with 8-9% distortion?
based on my experience, I think such levels of distortion, in the subwoofer passband, can be audible under certain conditions (content, volume). I don't believe it is possible to say "yes, x% of distortion is always audible with all content in all conditions by all people" so you need to determine whether you can perceive it or not.

To refer back to my graph as an example, there is considerable harmonic distortion at the 40Hz room mode which affects <=20Hz content. This means that a certain subset of films, when played back at substantial levels, do exhibit a certain "buzz" that seems out of place. The elevated distortion around 60Hz is much harder to pick out, it might be making certain guitar heavy music tracks a bit fatiguing when you really crank it up but that could also simply be the fact that it is quite loud at this point.
3ll3d00d is online now  
post #13243 of 13336 Old 01-21-2015, 10:07 AM
AVS Special Member
 
jim19611961's Avatar
 
Join Date: Mar 2011
Location: Texas
Posts: 1,499
Mentioned: 6 Post(s)
Tagged: 0 Thread(s)
Quoted: 202 Post(s)
Liked: 96
Quote:
Originally Posted by tvuong View Post
Good explanation. Thanks.

I see. Is it audible at 75hz with 8-9% distortion? I think Audessey boosts too much there. I am going to bump up around 70-75hz using my subs built in pEQ and then rerun Audessey to see if it helps with distortion. Speaking of running Audessey, I will only need to optimize my very own seating, would you guy recommends running all positions closed mic, ~3 inches from MLP? Thanks.
Click image for larger version

Name:	distotion 75.GIF
Views:	30
Size:	73.1 KB
ID:	492874

Hard to say. But your 75hz distortion is about 40X higher than mine (no joke). So its something to be looked into.

My Room
My Music
Rega - Apollo, Rega - DAC, Goldpoint Passive, (2) Classe CA-100 bridged power amps (350w)
Jenzen Next
jim19611961 is online now  
post #13244 of 13336 Old 01-21-2015, 11:03 AM
AVS Special Member
 
Alan P's Avatar
 
Join Date: Jan 2003
Location: Rapid City, South Dakota
Posts: 3,584
Mentioned: 9 Post(s)
Tagged: 0 Thread(s)
Quoted: 1212 Post(s)
Liked: 611
I know it's generally frowned upon to adjust speaker distances post-Audyssey, but last night I was going through the sub distance tweak (for the ump-teenth time) and was trying to get a good compromise between subs+CC and subs+FL (or FR) and thought I'd just see what happened if I adjusted the Front L/R speaker distances. I was surprised by the results.

This graph compares the before and after for the front right speaker. It made a drastic difference in the FR!





I wasn't able to get much of a change on the front left speaker:




And this compares the subs+CC (red) and subs+FL/R (blue). I've got almost the exact same response, which I was never able to get using the sub distance tweak alone.





I did some listening afterwards and couldn't detect anything being way out of whack. As a matter of fact, I think it sounds better than ever.

Will I be branded a heretic? Is this such a horrible thing to do??


Here is a drawing of my room. Audyssey first mic postition was dead center of MLP1 (where my head would be) and yes, it is off-center by about a foot. I have new subs now, both in the rear corners, so disregard the XS15s in the drawing.

I only got to listen for about an hour last night after I did this, but I swear my center sounds more intelligible now (along with a few other improvements, mostly in the bass).





Here are the changes I made to the speaker distance settings:

FL - from 18.2' to 16.2'
FR - from 17.6' to 12.6'

Audyssey's distances are pretty much spot on to the actual distances BTW.

Maybe it has something to do with the irregular acoustic properties of using corner-horns...?

AVR: Denon 4520ci, FL/R: Klipschorn, CC: Klipsch RC64ii, SUR: Polk LS F/X x 4, SUB: PSA T-18 x 2, DISP: Mitsubishi WD-73740, BluRay: PS3 & BDP-S5100, Remote: URC MX-700
--------------------------------------------------
Getting Started with REW
Audyssey 101
Audyssey FAQ
Alan P is online now  
post #13245 of 13336 Old 01-21-2015, 11:29 AM
AVS Special Member
 
tvuong's Avatar
 
Join Date: Dec 2000
Posts: 2,048
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 369 Post(s)
Liked: 150
^^ Glad it sounds better. Let me make sure it's clear: you also changed subs distance, correct? I would try to put your MLP death center by moving the table. Have you tried to calibrate and measure with mic at death center?
tvuong is offline  
post #13246 of 13336 Old 01-21-2015, 11:36 AM
AVS Special Member
 
Alan P's Avatar
 
Join Date: Jan 2003
Location: Rapid City, South Dakota
Posts: 3,584
Mentioned: 9 Post(s)
Tagged: 0 Thread(s)
Quoted: 1212 Post(s)
Liked: 611
^^^

Yes, I changed sub distances as well.

- optimized both subs by "moving" one sub, however the Audyssey distances proved to be the best here
- ran through the sub distance tweak for subs+CC, subs+FL and subs+FR
- then decided to get crazy and "move" the front speakers

Putting the MLP in the center of the room just ain't gonna happen, not only due to WAF, but due to my own AF as well.

AVR: Denon 4520ci, FL/R: Klipschorn, CC: Klipsch RC64ii, SUR: Polk LS F/X x 4, SUB: PSA T-18 x 2, DISP: Mitsubishi WD-73740, BluRay: PS3 & BDP-S5100, Remote: URC MX-700
--------------------------------------------------
Getting Started with REW
Audyssey 101
Audyssey FAQ
Alan P is online now  
post #13247 of 13336 Old 01-21-2015, 11:38 AM
Advanced Member
 
3ll3d00d's Avatar
 
Join Date: Sep 2007
Location: London, UK
Posts: 881
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 420 Post(s)
Liked: 105
What are the before and after distances for each channel? That is a pretty big (ie massive) difference between time of arrival for L and R. I take it you don't listen in stereo in this setup at all?
3ll3d00d is online now  
post #13248 of 13336 Old 01-21-2015, 11:52 AM
AVS Special Member
 
tvuong's Avatar
 
Join Date: Dec 2000
Posts: 2,048
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 369 Post(s)
Liked: 150
Quote:
Originally Posted by Alan P View Post
Putting the MLP in the center of the room just ain't gonna happen, not only due to WAF, but due to my own AF as well.
Unless it provides a much better FR, correct?
tvuong is offline  
post #13249 of 13336 Old 01-21-2015, 11:52 AM
AVS Special Member
 
Alan P's Avatar
 
Join Date: Jan 2003
Location: Rapid City, South Dakota
Posts: 3,584
Mentioned: 9 Post(s)
Tagged: 0 Thread(s)
Quoted: 1212 Post(s)
Liked: 611
dood,

I didn't write down the distances for all the channels, only the ones I changed and I listed those above:

Quote:
FL - from 18.2' to 16.2'
FR - from 17.6' to 12.6'
No, I never listen in 2 channel. I prefer Dolby PLIIx Music.

AVR: Denon 4520ci, FL/R: Klipschorn, CC: Klipsch RC64ii, SUR: Polk LS F/X x 4, SUB: PSA T-18 x 2, DISP: Mitsubishi WD-73740, BluRay: PS3 & BDP-S5100, Remote: URC MX-700
--------------------------------------------------
Getting Started with REW
Audyssey 101
Audyssey FAQ
Alan P is online now  
post #13250 of 13336 Old 01-21-2015, 11:52 AM
AVS Special Member
 
Alan P's Avatar
 
Join Date: Jan 2003
Location: Rapid City, South Dakota
Posts: 3,584
Mentioned: 9 Post(s)
Tagged: 0 Thread(s)
Quoted: 1212 Post(s)
Liked: 611
Quote:
Originally Posted by tvuong View Post
Unless it provides a much better FR, correct?
Even I will only go so far.

AVR: Denon 4520ci, FL/R: Klipschorn, CC: Klipsch RC64ii, SUR: Polk LS F/X x 4, SUB: PSA T-18 x 2, DISP: Mitsubishi WD-73740, BluRay: PS3 & BDP-S5100, Remote: URC MX-700
--------------------------------------------------
Getting Started with REW
Audyssey 101
Audyssey FAQ
Alan P is online now  
post #13251 of 13336 Old 01-21-2015, 12:09 PM
Advanced Member
 
3ll3d00d's Avatar
 
Join Date: Sep 2007
Location: London, UK
Posts: 881
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 420 Post(s)
Liked: 105
I thought you said you moved the sub as well? Anyway if you like it then that is what matters. I would have thought it will shift any phantom image somewhat though without a minor change in level (time intensity trading might be the thing to look at there, not 100% sure). It is probably difficult to do rapid back to back comparisons though.
3ll3d00d is online now  
post #13252 of 13336 Old 01-21-2015, 12:13 PM
AVS Special Member
 
Alan P's Avatar
 
Join Date: Jan 2003
Location: Rapid City, South Dakota
Posts: 3,584
Mentioned: 9 Post(s)
Tagged: 0 Thread(s)
Quoted: 1212 Post(s)
Liked: 611
Oh, sorry....yes, I did "move" the subs:

From 6.5'/7.8' to 12.5'/13.8'

AVR: Denon 4520ci, FL/R: Klipschorn, CC: Klipsch RC64ii, SUR: Polk LS F/X x 4, SUB: PSA T-18 x 2, DISP: Mitsubishi WD-73740, BluRay: PS3 & BDP-S5100, Remote: URC MX-700
--------------------------------------------------
Getting Started with REW
Audyssey 101
Audyssey FAQ
Alan P is online now  
post #13253 of 13336 Old 01-21-2015, 01:03 PM
AVS Special Member
 
ambesolman's Avatar
 
Join Date: Jun 2009
Location: Atlanta, GA
Posts: 3,899
Mentioned: 10 Post(s)
Tagged: 0 Thread(s)
Quoted: 509 Post(s)
Liked: 501
In my setup, just changing the distance 0.1' of the L or R shifts the phantom image close to a foot.


Sent using Tapatalk since the mobile version is still
ambesolman is online now  
post #13254 of 13336 Old 01-21-2015, 01:22 PM
Advanced Member
 
3ll3d00d's Avatar
 
Join Date: Sep 2007
Location: London, UK
Posts: 881
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 420 Post(s)
Liked: 105
Quote:
Originally Posted by Alan P View Post
FL - from 18.2' to 16.2'
FR - from 17.6' to 12.6'
Sub - 6.5'/7.8' to 12.5'/13.8'
why are there 2 distances for the subs?

anyway assuming an 80Hz XO then ~3.5' is a 90 degree phase shift (assuming no major discontinuities in the phase response which might be quite a heroic assumption but still...), therefore you've applied

FL - ~+45 degrees
FR - ~-130 degrees
Sub - ~-150 degrees

(+/- is arbitrary there, just using it to indicate direction of distance shift)

this nets at FL/sub at -105, FR/sub at -280 and FL/FR at -85

Another way to put this is a) loads, and b) every which way but loose

This sort of change is simple (ish) with a loopback so one approach is to try holmimpulse timelock and working fast to take measurements. Failing that, I would consider flipping the polarity on the sub and trying again.

Alternatively trust your ears (but you're in the wrong thread for that advice )
3ll3d00d is online now  
post #13255 of 13336 Old 01-21-2015, 02:21 PM
AVS Special Member
 
Alan P's Avatar
 
Join Date: Jan 2003
Location: Rapid City, South Dakota
Posts: 3,584
Mentioned: 9 Post(s)
Tagged: 0 Thread(s)
Quoted: 1212 Post(s)
Liked: 611
2 subs distances because I have dual subs and my AVR has XT32 + SubEQ HT.


Quote:
this nets at FL/sub at -105, FR/sub at -280 and FL/FR at -85

Another way to put this is a) loads, and b) every which way but loose
Sorry, but you lost me here.

Quote:
Failing that, I would consider flipping the polarity on the sub and trying again.
My subs don't have phase/polarity adjustments on them (theoretically, shouldn't be needed with SubEQ HT). I do have a MiniDSP that I'm currently not using (haven't had much luck with it in the past, but thanks to Jerry's new guide I might be talked into giving another go).

AVR: Denon 4520ci, FL/R: Klipschorn, CC: Klipsch RC64ii, SUR: Polk LS F/X x 4, SUB: PSA T-18 x 2, DISP: Mitsubishi WD-73740, BluRay: PS3 & BDP-S5100, Remote: URC MX-700
--------------------------------------------------
Getting Started with REW
Audyssey 101
Audyssey FAQ
Alan P is online now  
post #13256 of 13336 Old 01-21-2015, 02:23 PM
AVS Special Member
 
Alan P's Avatar
 
Join Date: Jan 2003
Location: Rapid City, South Dakota
Posts: 3,584
Mentioned: 9 Post(s)
Tagged: 0 Thread(s)
Quoted: 1212 Post(s)
Liked: 611
Quote:
Originally Posted by ambesolman View Post
In my setup, just changing the distance 0.1' of the L or R shifts the phantom image close to a foot.


Sent using Tapatalk since the mobile version is still
I'll see what some 2 channel sounds like with the different distance settings (Audyssey set vs. modified) tonight and report back.

AVR: Denon 4520ci, FL/R: Klipschorn, CC: Klipsch RC64ii, SUR: Polk LS F/X x 4, SUB: PSA T-18 x 2, DISP: Mitsubishi WD-73740, BluRay: PS3 & BDP-S5100, Remote: URC MX-700
--------------------------------------------------
Getting Started with REW
Audyssey 101
Audyssey FAQ
Alan P is online now  
post #13257 of 13336 Old 01-21-2015, 02:29 PM
AVS Special Member
 
AustinJerry's Avatar
 
Join Date: Jan 2003
Location: Austin, Texas
Posts: 8,545
Mentioned: 13 Post(s)
Tagged: 0 Thread(s)
Quoted: 1613 Post(s)
Liked: 1022
Quote:
Originally Posted by Alan P View Post

Will I be branded a heretic? Is this such a horrible thing to do??
Yes. Absolutely. Putting you on my ignore list now, Alan...
Alan P likes this.
AustinJerry is online now  
post #13258 of 13336 Old 01-21-2015, 04:58 PM
Advanced Member
 
3ll3d00d's Avatar
 
Join Date: Sep 2007
Location: London, UK
Posts: 881
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 420 Post(s)
Liked: 105
Quote:
Originally Posted by Alan P View Post
Sorry, but you lost me here.
I don't know if this will illuminate or confuse further but here's an example

blue is the original measurement
green is just with the polarity reversed, it's an exact mirror image



now the phase response, if you were to check you'd see it is 180 degrees out of phase at every single point. If you were to sum those two responses then they would cancel each other out completely everywhere



now lets say we delay one signal relative to the other based on our 80Hz crossover frequency. The wavelength is 4.3m at this frequency so half a wavelength is 2.15m which is (2.15/343*1000)ms = 6.268ms. We introduce this shifted impulse to our view in red, now it looks like the blue line but shifted in time.



Now look at the phase response vs the inverted response (which we said was a mirror image of the original), it is exactly aligned to the polarity reversed response *AT 80Hz ONLY*. The phase variance increases as you move further from that crossover frequency.



Ultimately the point is that a polarity change substantially changes the phase response (by 180 degrees even) but *does not change* arrival time. Hence you may find that a polarity flip + a small distance change can give the same, or better, results vs large timing changes (which can destroy imaging).

FWIW I don't know how you'd do this by trial and error, it's time consuming enough when you have phase responses to look at!!
Attached Thumbnails
Click image for larger version

Name:	ir_invert.jpg
Views:	111
Size:	155.8 KB
ID:	493282   Click image for larger version

Name:	ir_invert_phase.jpg
Views:	113
Size:	177.1 KB
ID:	493290   Click image for larger version

Name:	ir_shift.jpg
Views:	113
Size:	173.3 KB
ID:	493314   Click image for larger version

Name:	ir_shift_phase.jpg
Views:	116
Size:	165.5 KB
ID:	493322  
3ll3d00d is online now  
post #13259 of 13336 Old 01-21-2015, 05:06 PM
AVS Special Member
 
Alan P's Avatar
 
Join Date: Jan 2003
Location: Rapid City, South Dakota
Posts: 3,584
Mentioned: 9 Post(s)
Tagged: 0 Thread(s)
Quoted: 1212 Post(s)
Liked: 611
Quote:
Ultimately the point is that a polarity change substantially changes the phase response (by 180 degrees even) but *does not change* arrival time. Hence you may find that a polarity flip + a small distance change can give the same, or better, results vs large timing changes (which can destroy imaging).
OK, got it!

I guess I'll have to give the MiniDSP another day in court.

AVR: Denon 4520ci, FL/R: Klipschorn, CC: Klipsch RC64ii, SUR: Polk LS F/X x 4, SUB: PSA T-18 x 2, DISP: Mitsubishi WD-73740, BluRay: PS3 & BDP-S5100, Remote: URC MX-700
--------------------------------------------------
Getting Started with REW
Audyssey 101
Audyssey FAQ
Alan P is online now  
post #13260 of 13336 Old 01-21-2015, 09:03 PM
AVS Special Member
 
ambesolman's Avatar
 
Join Date: Jun 2009
Location: Atlanta, GA
Posts: 3,899
Mentioned: 10 Post(s)
Tagged: 0 Thread(s)
Quoted: 509 Post(s)
Liked: 501
Decided to do a little measuring yesterday to try and tweak my sub. After dialing it in, I took a few sweeps with just my rx8s set to large without the subs to see what the freq response looked like in my room. There was a good hump at 70 and 40hz with it steeply rolling off after that with no audyssey xt32 engaged. With it on, it smoothed out that hump and extended the roll off point to about 28hz! Not bad for a couple of 6.5 inchers

Green is w/o audyssey, black is with

Click image for larger version

Name:	ImageUploadedByTapatalk1421899285.033006.jpg
Views:	41
Size:	254.4 KB
ID:	493706

And yes, I know you can take a screenshot but I never get on AVS anywhere but my phone


Sent using Tapatalk since the mobile version is still
ambesolman is online now  
Sponsored Links
Advertisement
 
Reply Audio Theory, Setup, and Chat

Tags
Dayton , Dayton Audio , Room Equilizer Wizard Rew

Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page


Forum Jump: 

Posting Rules  
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off