Simplified REW Setup and Use (USB Mic & HDMI Connection) Including Measurement Techniques and How To Interpret Graphs - Page 280 - AVS Forum
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post #8371 of 12293 Old 01-26-2014, 09:29 AM
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Originally Posted by Brian Fineberg View Post

Funny you should talk about phase at this point

Last week I was doing some tweaking and my graph looked awful!! I though maybe the cleaning lady moved the couch and put it in a null so I was trying everything to get me flat response back.

Then out if no where I tried reversing the phase in the MINIdsp. BAM!!!! That was it flat response again.

Not sure how it happened but it was in reverse for some reason Lol

 

Odd. Good job you noticed it though.

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post #8372 of 12293 Old 01-26-2014, 10:05 AM
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Originally Posted by kbarnes701 View Post

It's an interesting idea to have the sub on the front wall in reverse phase to the sub on the rear wall. We also have to take account of the subs' interactions with the room, and with each other as well, so it's quite a complex thing I reckon.

I am in the UK too - I got a UMM-6 when Herb was prepared to ship them overseas. I think now the option is just the UMIK-1, but AFAIK they both give similar results.

I'm just hovering over the 'buy now' button for the UMIK-1 this evening. The older I get, the longer it seems to take me to make a decision though. redface.gif

As I see it I have a number of permutations to try when I have something more accurate to measure with:

1. The front sub's phase relative to the main speakers.
2. The rear sub's phase relative to the front sub.
3. The rear sub's delay relative to the front sub (via the sub amp's DSP).
4. Any pre EQ of the DIY subs prior to running Audyssey.
5. The overall sub distance setting (via my Onkyo 818) WRT it's effect on the crossover region..

After this I still can tweak the EQ via the sub amp's DSP if I want to create a house curve, but I think that REW will be a great help with items 1-5. Even some rough and ready tweaking using the SPL meter/spreadsheet resulted in an improvement in the sound, though it's to be expected going from a single BK Monolith to a pair of 15" sealed subs.

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post #8373 of 12293 Old 01-26-2014, 10:06 AM
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Quote:
Originally Posted by kbarnes701 View Post

It's an interesting idea to have the sub on the front wall in reverse phase to the sub on the rear wall. We also have to take account of the subs' interactions with the room, and with each other as well, so it's quite a complex thing I reckon.
This is an area where timing info really comes into it as then you can see there may be n different alignments that give good results with respect to frequency response and phase alignment but that different alignments might be optimal for each main channel. Obviously you then have to compromise.

When I had 2 subs, they were both near the front of the room but the best alignment was found with the polarity flipped on one of them.

This all assumes phase differences are audible (which seems a subject of some debate) of course.

Timing info means you can do the calcs offline rather than endless remeasuring btw.

There are multiple long threads on the subject on HTS for further reading if interested.
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post #8374 of 12293 Old 01-26-2014, 12:01 PM
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Quote:
Originally Posted by kbarnes701 View Post

Quote:
Originally Posted by AustinJerry View Post

Uh oh. Just when I thought I could relax, now I have something new to test out. It should be easy enough to flip the polarity switch and measure the results. Question is, should the test be made with Audyssey off, or do we flip the switch, re-run a calibration, and then test the results with Audyssey on?


Yes, funnily enough I was just wondering about that myself. I was thinking that the proper way to proceed would be to get the subs in phase with each other and with the mains (not necessarily the same thing or even achievable, so some compromise may need to be made here) with Audyssey OFF. The problem is, though, that we cannot retain the settings when we run Audyssey because Audyssey ignores all settings we have made. So Audyssey will EQ the subs in its own imperfect way (never measuring the combined response of the subs and mains) and undo all our good work. This means that we have to run independent measurements post-Audyssey so that we can get the phase relationships right again.  So the short answer to your question is IDK.  OR... do we get the phase relationships right before running Audyssey, run Audyssey and then set the settings to whatever we determined them to be before running Audyssey, and then measure to confirm that Audyssey hasn’t buggered them up (Limey term: to spoil)?

Interesting post. I had the same thoughts when trying to give advice about optimizing crossovers between mains and subs (i.e. Pre or post Audyssey and then do you just revert to your findings pre Audyssey?!).

I'll also follow this discussion with great interest. Thanks for the find Keith!
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post #8375 of 12293 Old 01-26-2014, 12:28 PM
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I finally got my UMM6 from CSL and I have been playing around with REW. Here are the measurements I took today with my Denon X4000, EmpTek E55Ti, and Rythmik F15HP.


The E55Ti's are 6'9" apart (from inside edge to inside edge) roughly toed in 5-10 degrees with about 8 ft from MLP to TV. I know my room is pretty acoustically awful. The full length windows behind the TV/speakers face a street and get a fair amount of street noise. Not much I can do about that though. mad.gif

So what can I do to improve this?
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post #8376 of 12293 Old 01-26-2014, 12:30 PM
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Quote:
Originally Posted by kbarnes701 View Post

Quote:
Originally Posted by AustinJerry View Post

You may well be correct, but the method by which Audyssey corrects for phase issues is not clear to me. As I have reported on a number of occasions in the Pro thread, I ALWAYS get a phase error warning on the sub channel, even though both subs are set to zero phase. IF I reverse the phase switch and run a fresh calibration, I have noticed that the sub response is significantly different, so Audyssey is unable to reverse the switch from zero to 180 phase.


While I have experimented with phase before, I don't recall if I actually tried front subs set to zero, and rear subs set to 180 degrees. For someone like myself who always enjoys investigative work, I think it is worth a try. If I run the test, I'll report back here, of course.
My Submersives don't have phase or polarity controls so I have to adjust phase by varying delay in the prepro. Same result, different method. I think I will give it a try and see what, if any difference it makes.
My FV15hp defeats the phase variable knob when LFE input is connected. I would like to know how much distance tweak for my rear sub is needed to have it act like it is being inverted as compared to the one upfront. Thanks.
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post #8377 of 12293 Old 01-26-2014, 01:19 PM
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Originally Posted by Kelvin1965S View Post
 
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Originally Posted by kbarnes701 View Post

It's an interesting idea to have the sub on the front wall in reverse phase to the sub on the rear wall. We also have to take account of the subs' interactions with the room, and with each other as well, so it's quite a complex thing I reckon.

I am in the UK too - I got a UMM-6 when Herb was prepared to ship them overseas. I think now the option is just the UMIK-1, but AFAIK they both give similar results.

I'm just hovering over the 'buy now' button for the UMIK-1 this evening. The older I get, the longer it seems to take me to make a decision though. redface.gif

As I see it I have a number of permutations to try when I have something more accurate to measure with:

1. The front sub's phase relative to the main speakers.
2. The rear sub's phase relative to the front sub.
3. The rear sub's delay relative to the front sub (via the sub amp's DSP).
4. Any pre EQ of the DIY subs prior to running Audyssey.
5. The overall sub distance setting (via my Onkyo 818) WRT it's effect on the crossover region..

After this I still can tweak the EQ via the sub amp's DSP if I want to create a house curve, but I think that REW will be a great help with items 1-5. Even some rough and ready tweaking using the SPL meter/spreadsheet resulted in an improvement in the sound, though it's to be expected going from a single BK Monolith to a pair of 15" sealed subs.

 

Once you get the mic (UMIK-1 is fine) you can jump right down the rabbit hole and join the rest of us - plenty of room for more :)

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post #8378 of 12293 Old 01-26-2014, 01:22 PM
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Originally Posted by jkasanic View Post
 
Quote:
Originally Posted by kbarnes701 View Post
 
Quote:
Originally Posted by AustinJerry View Post

Uh oh. Just when I thought I could relax, now I have something new to test out. It should be easy enough to flip the polarity switch and measure the results. Question is, should the test be made with Audyssey off, or do we flip the switch, re-run a calibration, and then test the results with Audyssey on?


Yes, funnily enough I was just wondering about that myself. I was thinking that the proper way to proceed would be to get the subs in phase with each other and with the mains (not necessarily the same thing or even achievable, so some compromise may need to be made here) with Audyssey OFF. The problem is, though, that we cannot retain the settings when we run Audyssey because Audyssey ignores all settings we have made. So Audyssey will EQ the subs in its own imperfect way (never measuring the combined response of the subs and mains) and undo all our good work. This means that we have to run independent measurements post-Audyssey so that we can get the phase relationships right again.  So the short answer to your question is IDK.  OR... do we get the phase relationships right before running Audyssey, run Audyssey and then set the settings to whatever we determined them to be before running Audyssey, and then measure to confirm that Audyssey hasn’t buggered them up (Limey term: to spoil)?

Interesting post. I had the same thoughts when trying to give advice about optimizing crossovers between mains and subs (i.e. Pre or post Audyssey and then do you just revert to your findings pre Audyssey?!).

I'll also follow this discussion with great interest. Thanks for the find Keith!

 

I spent a couple of hours trying different things and I could not improve on what I already had. Of course, this may not be the case for everyone. If the SubMs had a polarity switch it would have been a lot quicker to do it. I tried pre and post Audyssey adjustments - no difference in end result.

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post #8379 of 12293 Old 01-26-2014, 01:27 PM
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Originally Posted by MarsianMan View Post

I finally got my UMM6 from CSL and I have been playing around with REW. Here are the measurements I took today with my Denon X4000, EmpTek E55Ti, and Rythmik F15HP.


The E55Ti's are 6'9" apart (from inside edge to inside edge) roughly toed in 5-10 degrees with about 8 ft from MLP to TV. I know my room is pretty acoustically awful. The full length windows behind the TV/speakers face a street and get a fair amount of street noise. Not much I can do about that though. mad.gif

So what can I do to improve this?

 

Never seen a black REW graph before :)

 

The magenta trace doesn't look too bad.  If you had DEQ on when you ran the tests, ideally you are supposed to have DEQ off and this will affect the outcome somewhat, at the bottom end. I measure without DEQ and make all adjustments that way and then run one final measurement of mains + subs with DEQ on just to see what it is doing in listening conditions. Mind you, I listen typically at -5.0dB and I am reluctant to set REW to play the tones at that level so it's no more than a guide as to how DEQ is working when MV is set to -9.0dB (my usual setting for REW measurements).  What crossover are you using?

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post #8380 of 12293 Old 01-26-2014, 01:45 PM
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Quote:
Originally Posted by kbarnes701 View Post
My Submersives don't have phase or polarity controls so I have to adjust phase by varying delay in the prepro. Same result, different method. I think I will give it a try and see what, if any difference it makes.
My FV15hp defeats the phase variable knob when LFE input is connected. I would like to know how much distance tweak for my rear sub is needed to have it act like it is being inverted as compared to the one upfront. Thanks.

 

It's not simple.

 

Switching the polarity changes phase by 180 degrees globally. if you adjust delay then you change the phase of every frequency as well, but each by a different amount. For instance, 180 degrees shift at 80Hz is 7 feet. That same 7 feet is 90 degrees at 40Hz, 45 degrees at 20Hz.

 

The formula for this is:

 

Speed of sound / Frequency = Wavelength

1126 ft/s / 80 Hz = 14 feet

Phase shift / full cycle (360 degrees)

180 degrees / 360 degrees = 2

14 feet / 2 = 7 feet

 

(Divide by 2 because you are 180 degrees out of phase at 1/2 cycle, which, theoretically, is complete cancellation.)

 

If you plug the distance between your two subs into the equation above you should get an idea of the distance required at, say, 80Hz.

 

The room and reflections etc also come into it. so the best thing to do, IME, is to adjust delays while watching the response change in REW or OmniMic and look for the smoothest response at the XO area. As you can see above, you can only get it right for one frequency at a time by adjusting the delays, so aim for the XO frequency. All of this only matters when two sources are playing the same signal - which is around the XO.

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post #8381 of 12293 Old 01-26-2014, 01:56 PM
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^^ thanks Keith. Can you look at my graphs on post 8345 and let me know what you think please? Thanks.
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post #8382 of 12293 Old 01-26-2014, 02:12 PM
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^^ thanks Keith. Can you look at my graphs on post 8345 and let me know what you think please? Thanks.

I see very little wrong with this (blue trace):

 

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^^ thanks. What about my main LR and subs graph? Based on the graph, would you choose 60 or 80hz Xover for my main? Thanks again.
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post #8384 of 12293 Old 01-26-2014, 02:55 PM
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I'm joining the rabbit hole; just ordered my UMIK-1. smile.gif

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post #8385 of 12293 Old 01-26-2014, 03:24 PM
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OK, I did some quick measurements, playing with the Polarity switch on the two rear subs.  Setting the polarity to 180 resulted in worse measurements, as you can see.

 

Starting point:  phase=0 on all four subs, main speakers off, Audyssey off

 

 

Now flip phase switch on two rear subs to 180, main speakers still off, Audyssey still off (Green line is phase=180, red line is phase=0):

 

 

Now turn on center speaker, rear subs phase still 180, Audyssey still off (green line is phase=180, red line is phase=0):

 

 

Center+subs, Audyssey on, phase=0:

 

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post #8386 of 12293 Old 01-26-2014, 03:26 PM
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Yup. That's the exact response I was getting with my subs out of phase

Looks like that theory you posted was wrong lol

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post #8387 of 12293 Old 01-27-2014, 02:08 AM
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Yup. That's the exact response I was getting with my subs out of phase

Looks like that theory you posted was wrong lol
Late to the party, but if you think about it logically, it's going to be extremely setup dependent.

View it in this manner. What do people do when they're trying to break-in woofer spiders quickly without blowing the neighbors away?

You place a pair of speakers facing each other and reverse the polarity on one of them. As one cone moves out, the opposite cone moves in. You get cancellation. It allows you to turn up the volume for greater excursion with significantly lower in-room SPLs.

Inverting the phase on the rear subs (and delaying the rear signal the exact time of travel of the bass signal from the front sub array) is the exact technique used to cancel the planar wave in a Double Bass Array as it arrives at the rear wall. If this ISN'T the goal, why would it be a good idea?

Think about it a little more: In a perfectly symmetrical room, with the MLP in the center, the time of arrival of both waves would cancel in the center. If the setup is not symmetrical (MLP not in the center, rear subs closer than fronts etc.) but the delays are set so both waves arrive at the MLP simultaneously, the theoretical effect is the same. The real world effect is going to be affected by the room of course, and how the waves reflect and interact (unless you ARE going for a DBA).

Leave all the subs in the same phase unless you're attempting a DBA.


Max
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post #8388 of 12293 Old 01-27-2014, 03:41 AM
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Yup. That's the exact response I was getting with my subs out of phase

Looks like that theory you posted was wrong lol

 

Yes - glad we got it sorted. Max's response makes perfect sense too. The theory seems to have a lot of followers - I have since found different posts putting it forward. 

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post #8389 of 12293 Old 01-27-2014, 03:44 AM
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^^ thanks. What about my main LR and subs graph? Based on the graph, would you choose 60 or 80hz Xover for my main? Thanks again.

Oh, I didn’t look too closely at that one!  Because I am 'movies only' I attach much more significance to the centre channel. As you know, with movies, the centre channel is the 'anchor' for the entire presentation with the other channels creating the 'soundscape' around it, so if my centre and subs is good I leave it that way. I can usually make a bit of an improvement to the LR and subs as well but at the expense of the centre and subs, so I don't mess with it.  This may be entirely different for music, IDK.  I'll look at your LR and subs later and report back.

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post #8390 of 12293 Old 01-27-2014, 05:16 AM
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^^ thanks. What about my main LR and subs graph? Based on the graph, would you choose 60 or 80hz Xover for my main? Thanks again.

 

I’d go with Red based purely on the FR I think. But be aware that an 80Hz XO may be more beneficial in other ways than a 60Hz XO so at the end of the day the 80Hz (blue) might be preferable overall. I don't think there's all that much in it TBH based on the graph below and I'd be happy with either. I am much more influenced by centre + subs as I said, and that looks very good to me indeed. Beware of graphitis nervosa....

 

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post #8391 of 12293 Old 01-27-2014, 06:30 AM
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Leave all the subs in the same phase unless you're attempting a DBA.

Max

Well articulated, Max. As I was observing my measurements, my first thought was, if this works it must be highly room-dependent. Your explanation confirms this.
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post #8392 of 12293 Old 01-27-2014, 06:39 AM
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Leave all the subs in the same phase unless you're attempting a DBA.

Max

Well articulated, Max. As I was observing my measurements, my first thought was, if this works it must be highly room-dependent. Your explanation confirms this.

 

 

Agreed. It certainly didn't effect any improvement at all here.  

 

I think the idea is potentially dangerous as it is simple and has a sort on internal logic. "Sub at front pushes out, sub at rear needs to 'push in' or the two will tend to cancel each other out."  As usual, the reality seems to be much more complicated. Still, it's something else that some people might consider if all else is failing them. Depending on their circumstances it may even work ;) 

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Really, two identical speakers facing each other and fed the same content at the same SPL will completely cancel out and won't make ANY sound? rolleyes.gif
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post #8394 of 12293 Old 01-27-2014, 07:40 AM
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Theoretically, yes, exactly in the middle.

Or in a vacuum.

;) 


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Did you really need to quote that entire post in your reply?
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post #8395 of 12293 Old 01-27-2014, 08:31 AM
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Really, two identical speakers facing each other and fed the same content at the same SPL will completely cancel out and won't make ANY sound? rolleyes.gif

 

Yeah - we used to do that in the old days to check that a stereo pair as in or out of phase.

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post #8396 of 12293 Old 01-27-2014, 09:33 AM
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Theoretically, yes, exactly in the middle.
Or in a vacuum.
wink.gif  

With no one around to hear it.
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Quote:
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^^ thanks. What about my main LR and subs graph? Based on the graph, would you choose 60 or 80hz Xover for my main? Thanks again.

I’d go with Red based purely on the FR I think. But be aware that an 80Hz XO may be more beneficial in other ways than a 60Hz XO so at the end of the day the 80Hz (blue) might be preferable overall. I don't think there's all that much in it TBH based on the graph below and I'd be happy with either. I am much more influenced by centre + subs as I said, and that looks very good to me indeed. Beware of graphitis nervosa....


Thanks for your inputs. Is that dip at about 45hz audible? I can try with my subs built in peq to flatten it further.
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post #8398 of 12293 Old 01-27-2014, 10:49 AM
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Agreed. It certainly didn't effect any improvement at all here.  

I think the idea is potentially dangerous as it is simple and has a sort on internal logic. "Sub at front pushes out, sub at rear needs to 'push in' or the two will tend to cancel each other out."  As usual, the reality seems to be much more complicated. Still, it's something else that some people might consider if all else is failing them. Depending on their circumstances it may even work wink.gif 
an awful lot of sub setup wisdom that gets parroted around are essentially examples of old wives tales though and referred to as gospel ignoring the fact that rooms are complex environments. Is there anything that is actually invariant to the room?

For example, one of the latest memes is that corner loading is a good thing because it reduces temporal distortion arising from the delayed reflection off the nearest wall even if it exacerbates the modal response. This also has a certain logic to it yet also seems suspicious given the wavelengths involved. I don't know enough about the dynamics of a wave in a room to say one way or the other so I just measure and see what works best & go from there smile.gif
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Thanks for your inputs. Is that dip at about 45hz audible? I can try with my subs built in peq to flatten it further.

 

It's about 5dB so it could be - just about. A change of 5dB is easy enough to hear when it is isolated, but when stuff is going on, less so. If you could PEQ it away of course, so much the better.

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post #8400 of 12293 Old 01-27-2014, 11:19 AM
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Agreed. It certainly didn't effect any improvement at all here.  

I think the idea is potentially dangerous as it is simple and has a sort on internal logic. "Sub at front pushes out, sub at rear needs to 'push in' or the two will tend to cancel each other out."  As usual, the reality seems to be much more complicated. Still, it's something else that some people might consider if all else is failing them. Depending on their circumstances it may even work wink.gif 
an awful lot of sub setup wisdom that gets parroted around are essentially examples of old wives tales though and referred to as gospel ignoring the fact that rooms are complex environments. Is there anything that is actually invariant to the room?

For example, one of the latest memes is that corner loading is a good thing because it reduces temporal distortion arising from the delayed reflection off the nearest wall even if it exacerbates the modal response. This also has a certain logic to it yet also seems suspicious given the wavelengths involved. I don't know enough about the dynamics of a wave in a room to say one way or the other so I just measure and see what works best & go from there smile.gif

 

That tends to be my approach too quite often. Sometimes it is easier than figuring out the theory. HST, I am always happy to receive theory-based suggestions from those who understand these things. 

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