# A Sound Renovation for the Green Room



## Lumen (May 17, 2014)

You may have come across my "Green Room" threads on this site, and let me tell you: I long for a proper HT with projector, 100+ inch screen, and multiple rows of seating. _Until then I can't think of a better way to enjoy what I have than to improve on the sound._ Believe me when I say I realize how much improvement the visual aspects need, but that's a derailment destined for another thread.

I'm rearranging my HT room to accommodate the matching center to my mains, so the upgrade bug hit and I just _had_ to get proper HT seating, too! All that led to designing a new layout minus extra furniture and clutter to take maximum advantage of the limited space in my 9 x 13 foot room. 
And space IS limited because 12 album crates have to stay by WAF decree :foottap: 
Bless her heart, though; she did let me take over almost every room in the house with audio gear and acoustic treatments. 

Now, some if not most of you would agree those massive speakers have no business in that small space, and you'd be right. Their performance is compromised, but not so much they can't develop convincing SS&I. It just takes more attention to detail. Which brings us to the point of this thread: I would like to graduate from REW frequency-domain basics (FR and XO phase) to time-domain analysis and correction (IR, ETC, and EGD). I don't have specific questions at this point, but wanted to start a thread to collect my thoughts - and hopefully your feedback - in one place. 

I plan to start my journey from self-proclaimed freshman to sophomore ( :nerd: ) REW user by trying to identify:
the best out of three possible subwoofer locations
the worst reflections
the best number/combo of bass and broadband traps

So welcome to my thread. I think you'll enjoy it as much as I hope to! :blink:
Here are some links to other threads which contributed to my progress:

Correcting aliasing during FR measurements
Adjusting phase tracking for ported mains
Fixing FR issues for center channel
Getting ASIO to Recognize the Soundcard and Offer Multichannel HDMI Capability


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## AudiocRaver (Jun 6, 2012)

Lumen said:


> You may have come across my "Green Room" threads on this site, and let me tell you: I long for a proper HT with projector, 100+ inch screen, and multiple rows of seating. _Until then I can't think of a better way to enjoy what I have than to improve on the sound._ Believe me when I say I realize how much improvement the visual aspects need, but that's a derailment destined for another thread.
> 
> I'm rearranging my HT room to accommodate the matching center to my mains, so the upgrade bug hit and I just _had_ to get proper HT seating, too! All that led to designing a new layout minus extra furniture and clutter to take maximum advantage of the limited space in my 9 x 13 foot room.
> And space IS limited because 12 album crates have to stay by WAF decree :foottap:
> ...


Goody! Carry on!


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## Lumen (May 17, 2014)

The most important part of my intro is missing. I'm such a people-person. :sarcastic::duh:
I can't say it any better than cadet did in Post #3 here:
_"If you could provide any details I'd greatly appreciate any feedback eager to learn & if someone like yourself is willing to help. I'm all ears."_


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## Lumen (May 17, 2014)

*Re: Eeek... Wife Moving at Light Speed!*

In preparation for speaker/LP positioning, I've been reviewing AudiocRaver's HTS 2ch Speaker Setup Guide for a Deep Soundstage. Following his advice for first-time use, I chose "The Simple Way," whose first step is to pick a spot for the LP. But in so doing, some immediate questions were raised:

ISSUES & QUESTIONS
With respect to the LP, the back "wall" is effectively made up of album crates.
But w.r.t. room modes, is the back wall the face of the filled album crates, or is it the physical room boundary? I think the albums provide more absorption than reflection or diffusion, so their presence essentially creates an irregular-shaped room, correct?
Considering the seat back protrudes over my ears by about 3 inches, doesn't that place the back wall there instead of at either 1 or 2 above? I imagine the answer lies in the spirit of the method: uncompromised placement, which includes unobstructed listening.

So knowing I can only throw a thick blanket over the back of the seat to ameliorate those reflections, and assuming the back wall is at the front face of the filled crates, choosing a spot for the LP went something like this:
0.25ft = Worst-case distance required between seat and wall for full recline (worst case: inconsequential?)
1.17ft = Best-case distance required behind seat for album crate (best case)
1.42ft = Worst-case distance required behind seat for sub (worst-case: possible location not in stone)
3.00ft = Minimum recommended distance from back wall to center of head
4.67ft = Distance between room's physical back wall and center of head (sum of previous worst-case quantities)
8.58ft = C = (13.25 - 4.67)ft.

Therefore, 
dimension "A" = C / 2.4 = 3.6ft
dimension "B" = A x 1.4 = 5.0ft


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## Lumen (May 17, 2014)

*Re: Eeek... Wife Moving at Light Speed!*

...(continued from last post)...
*Calculation results are approximate until seats arrive!*

Because the room is small, the previously derived quantities aren't practical. Separating the speakers by only 5ft on-center, would visually encroach on the display area. What's more, the speakers would be much too close to the seats to allow comfortable ingress/egress. No worries, though, as the guide is quite flexible and has a contingency plan: just determine A, B, and C the best you can given a fixed LP or speaker location. The guide tells us that dimension "C" is not super critical, but that the C/A ratio of 2.4 helps reduce room mode interaction. So in the following calcs, I reduced LP distance to the back wall by a couple feet (increased distance to front wall), and kept the same average ratio of C/A=2.4:
10.6ft = C = Previous value plus 2 feet
dimension "A" = C / 2.4 = 4.4ft
dimension "B" = A x 1.4 = 6.2ft

That's obviously going in the right direction. 
The speakers now clear the line-of-sight to the display, but are still not far enough away to fully recline the seats. 
For that I'll need Amin=6ft, which now dictates:
C = 13.25 room length - (1.42 sub width behind seat + 0.25 recliner clearance) = 11.58ft
and
C / A = 1.93, which is still within the acceptable range.

So far, so good until we notice this pushes the speaker roughly a foot from the front wall - not a desirable condition from an SBIR perspective. And it also precludes using my tube traps in the corners (should they become needed). Am I approaching this the correct way so far?


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## willis7469 (Jan 31, 2014)

Ummmmm. Yes?


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## AudiocRaver (Jun 6, 2012)

The _correct_ way is always some set of compromises that still gives a good result.

My own listening area is far from perfect, even far from symmetrical, but still sounds amazing, in my opinion. So the correct way is going to be the way that makes best use of available resources and gets the best sound possible.


One might prioritize like:

spkr and LP placement for convenience AND good sound
symmetry of direct and _desired_ first/early reflection paths
treatment of all _unwanted_ first/early reflection paths
bass trap treatment
for general LF absorption (easier)
for frequency-specific treatment (harder)

Dirac Live


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## Savjac (Apr 17, 2008)

Ummm No ??

As I mentioned earlier kinda, it seems you are doing your best to work with the stuff you have but it seems a bit like trying to fit a C5 cargo plane into a Submarine. It might could be done but to what end. Upon reading your post several times I think it comes down to placing your chairs in the room at the back wall and then fitting or removing everything else so as to provide you with the sound you like....as best can be expected of course. 

It seems obvious you and your wife like to watch movies together so FIRST and FOREMOST make the room fit your hobby not the other way around. If album racks have to move out, so be it, if the equipment has to be moved forward...so be it. Ensure that the room is comfortable for the Lumen family and use placement and your dirac to make the sound acceptable or even likeable. I am not sure where you sub should end up, i thought the right side near the front wall seemed very good but with the larger speakers it may need to go against the wall which will increase the bottom end which again may require an adjustment. 

Remember that when you get in a pickle trying to plan this layout, just ask us and we will confuse you even more. 0


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## Lumen (May 17, 2014)

AudiocRaver said:


> The _correct_ way is always some set of compromises that still gives a good result.
> 
> My own listening area is far from perfect, even far from symmetrical, but still sounds amazing, in my opinion. So the correct way is going to be the way that makes best use of available resources and gets the best sound possible.
> 
> ...


I like the way you think! Your high standards lend me no doubt you've synergistically tuned your system/room. Thanks for spelling out the priorities for me. I'm eager to get started with the nuts and bolts of working with reflections, and will try my best not to shortchange intermediate steps. Speaking of reflections, I revisited your Psycho Pillow thread and am intrigued. I'd rank introducing Psycho Pillow last in the list of priorities. _But not because its unimportant_; rather, because it's no substitute for careful setup as I'm sure you'd agree. Incidentally, what material would you use if you started from scratch without the Acousta-Stuf material from the LXmini?

As far as I know, identifying reflections is not as straightforward as the mirror or string "tricks" would have one first believe. There are measurement tools (like REW) that can generate plots that make identification easier, but require skill in execution and interpretation - something I hope to someday achieve. Energy Time Curve and Excess Group Delay plots come to mind. Could you please tell me a little more about identifying first/early reflections? Maybe provide a summary like you did for the set-up priorities? As an aside, I'm familiar with the mirror trick - but that just confirms a reflection's existence, not it's desirability. To identify all reflections, you'd have to cover the whole room in reflective tape (lol)!


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## AudiocRaver (Jun 6, 2012)

Lumen said:


> I like the way you think! Your high standards lend me no doubt you've synergistically tuned your system/room. Thanks for spelling out the priorities for me. I'm eager to get started with the nuts and bolts of working with reflections, and will try my best not to shortchange intermediate steps. Speaking of reflections, I revisited your Psycho Pillow thread and am intrigued. I'd rank introducing Psycho Pillow last in the list of priorities. _But not because its unimportant_; rather, because it's no substitute for careful setup as I'm sure you'd agree. Incidentally, what material would you use if you started from scratch without the Acousta-Stuf material from the LXmini?
> 
> As far as I know, identifying reflections is not as straightforward as the mirror or string "tricks" would have one first believe. There are measurement tools (like REW) that can generate plots that make identification easier, but require skill in execution and interpretation - something I hope to someday achieve. Energy Time Curve and Excess Group Delay plots come to mind. Could you please tell me a little more about identifying first/early reflections? Maybe provide a summary like you did for the set-up priorities? As an aside, I'm familiar with the mirror trick - but that just confirms a reflection's existence, not it's desirability. To identify all reflections, you'd have to cover the whole room in reflective tape (lol)!


The Psycho Pillow fill is simply pillow poly fill stuffing from a craft store, in a mesh laundry bag. You can scrunch (an audiophile term) it as needed for best result.

The idea on reflections is to determine the kind you want and the kind you don't want, carefully work with the timing of the wanted ones, and absorb/diffuse the ones not wanted in a way that does not disrupt imaging. First reflections only, after that, the delay is generally enough that imaging is not affected. The first part involves careful measurements, first physically with a tape or laser distance measurer, then refining with REW and a mic. The second kind are eyeballed, because that is good enough. See where they appear most likely and use panels on those surfaces - ensuring that ALL diffused reflections are aimed AWAY from the LP.


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## Lumen (May 17, 2014)

Savjac said:


> As I mentioned earlier kinda, it seems you are doing your best to work with the stuff you have but it seems a bit like trying to fit a C5 cargo plane into a Submarine. It might could be done but to what end.


The "end" is I get to keep the Revels instead of the B&Ws. No brainer. My current plan is to find a new room for them before I die! lddude:



Savjac said:


> Upon reading your post several times I think it comes down to placing your chairs in the room at the back wall and then fitting or removing everything else so as to provide you with the sound you like....as best can be expected of course.
> It seems obvious you and your wife like to watch movies together so FIRST and FOREMOST make the room fit your hobby not the other way around. If album racks have to move out, so be it, if the equipment has to be moved forward...so be it


That room is the albums' home. Without it they are, well... homeless. The original plan was to have my favorites converted to digital format and sell them. It took about 3 months to finish only 15% of them. Now that project is on hold until after new carpeting is installed in the living room. Then I can reassemble the required gear. Anyway, the albums are there to stay. I'll definitely experiment with your suggestion to pull some of them out a little at random intervals so as to create a diffuser effect.



Savjac said:


> . . . so as to provide you with the sound you like....as best can be expected of course.
> . . . use placement and your dirac to make the sound acceptable or even likeable.


Jack, Jack, Jack. I don't expect perfection. Are you under the impression that very good SQ and SS&I are not possible in my room? But I've witnessed just that. My previous set up developed respectable SQ and convincing SS&I. I'm certain I can do better with this renovation. Time-domain measurements will help identify reflections which rob the system of good SS&I. 



Savjac said:


> Remember that when you get in a pickle trying to plan this layout, just ask us and we will confuse you even more. 0


I'm counting on it :wink2:


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## Savjac (Apr 17, 2008)

Lumen said:


> Jack, Jack, Jack. I don't expect perfection. Are you under the impression that very good SQ and SS&I are not possible in my room? But I've witnessed just that. My previous set up developed respectable SQ and convincing SS&I. I'm certain I can do better with this renovation. Time-domain measurements will help identify reflections which rob the system of good SS&I.
> 
> 
> I'm counting on it :wink2:


Not at all Lumen, I would expect you to obtain good SQ and SS&I in that room, albeit there may be little to no soundstaging/imaging outside the speakers themselves. That of course does not in any way preclude obtaining good sound in the room. It is hereby your sword duty to wring every ounce of goodness from your equipment in the Green Room. Others have done so with worse rooms.


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## Lumen (May 17, 2014)

Savjac said:


> Not at all Lumen, I would expect you to obtain good SQ and SS&I in that room, albeit there may be little to no soundstaging/imaging outside the speakers themselves. That of course does not in any way preclude obtaining good sound in the room. It is hereby your sword duty to wring every ounce of goodness from your equipment in the Green Room. Others have done so with worse rooms.


Now you've gone and done it: making me understand! Too bad you had to draw me a picture, though.

You're right, of course. It's physically impossible to get a decent spread between the mains with the walls in the way! And speakers less than three feet from a boundary will have both bass and imaging issues. If we were staying there, I'd seriously consider knocking down the adjoining bedroom one. 

With things being as they may, I'd like to try my hand at measurements with help from the fine folk here at HTS. It may not get the system where I'd like it to be, but it just has to be better than tuning by ear. It's just gotta! 

Thanks for the vote of confidence, and for reminding me listening is as important as measuring, if not more so. That last comment may invite a barrage of opposing viewpoints, but what's progress without controversy? It would be boring if everything were easy.




Sent from my iPhone using Tapatalk


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## willis7469 (Jan 31, 2014)

Listening is indeed at least as important as measuring. 
Did you say demo? Wooo hoooo!!!!


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## AudiocRaver (Jun 6, 2012)

Lumen said:


> Are you under the impression that very good SQ and SS&I are not possible in my room?


I believe that with the proper TLC, very good SQ and SS&I are possible in any room.


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## Lumen (May 17, 2014)

willis7469 said:


> Did you say demo? Wooo hoooo!!!!


You're a hoot! :rofl:


AudiocRaver said:


> I believe that with the proper TLC, very good SQ and SS&I are possible in any room.


You're an inspiration! 
I now have newfound confidence, and will be starting my measurement regimen this weekend after getting the new HT seats situated. If you like, check out the delivery here.


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## willis7469 (Jan 31, 2014)

Thanks Lou! I'll be here all week. Is this thing on.....? 
Hey, I'm just glad you keep sharing your journey. Not all of us are so brave.


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## Savjac (Apr 17, 2008)

willis7469 said:


> Thanks Lou! I'll be here all week. Is this thing on.....?
> Hey, I'm just glad you keep sharing your journey. Not all of us are so brave.


Some of us are brave.......but broke. I guess that is the 3 B syndrome, Brave But Broke. :huh:


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## willis7469 (Jan 31, 2014)

Savjac said:


> Some of us are brave.......but broke. I guess that is the 3 B syndrome, Brave But Broke. :huh:




Yep. Put me in the club!


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## Lumen (May 17, 2014)

I am now, so +1.
And oh yeah, that's hilarious! :rofl:


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## Lumen (May 17, 2014)

Getting closer to some real action! 

I've got the TV wall-mount installed, the equipment rack assembled, and the center channel perched upon it. HT seats arrived yesterday, and are present in the room as well. So I'm standing there at the room's entrance juggling my options, and realize I can start listening trials! First order of business is to pull those mains off the wall, where they've been pushed out of the way for "construction." A significant amount of toe-in may be necessary to overcome sidewall proximity. But I want to keep an open mind and not let preconceptions cloud my judgement; so I'll be starting from scratch with no toe-in at all during my first listening sessions. You'd probably like a picture from the LP to give a better idea of placement options. They're certainly not abundant:
The LP is equidistant from the sidewalls to match system symmetry
The LP is also fixed from the back wall to maximize space between the speaker and the recliner's footrest.
Proximity of the mains to the sidewalls is dictated by the extent of the display's edges.

Aside from LP and mains placement, I'll need to decide on where to aim the center channel (at or above the LP). The middle of the tweeter/midrange centerline is a couple inches or so below ear level, so that's a good a place as any to start. Throwing a couple different degrees of tilt into the listening trials should help zero-in on a preference. I'm tempted to just tilt the center up and be done with it. Why? I'm worried about midrange "floor" bounce resulting from the driver practically sitting on the shelf's surface. Scooting the speaker cabinet forward to align or overhang the shelf's edge is unsightly because of the cabinet's curved surfaces, but may be something I have to live with. Yet again I'd like to keep an open mind with no preconceptions; so I'll plan on measuring FR and phase for both straight and tilted center channel positions. Which brings me to my first question of the day: *Is the reflection from the midrange off the shelf surface even an issue since the driver's so close to it (think precedence effect)?*

Another member posted about measurements vs. listening in Post #112 here:


ajinfla said:


> If you wish to please your eyes or an "ETC" measurement pressure mic, treat away. If you wish to please your ears, read Floyd Tooles writings and videos, which are a nice compilation of a large body of work by many many scientists in the field of acoustics study.


There are those with opposing viewpoints, of course, and it's not my intention to start a feud; but I'd like to hear some opinions regarding tilting a center channel.


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## scotts2014se (Dec 29, 2016)

Cant wait for pics!:grin2:


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## ajinfla (May 10, 2009)

Lumen said:


> *Is the reflection from the midrange off the shelf surface even an issue since the driver's so close to it (think precedence effect)?*


It shouldn't be but a picture of exactly what is going on would help.


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## Lumen (May 17, 2014)

Glad you checked-in, AJ! The pics below show the center atop the rack as far forward as it should probably go. Any further and the rack starts to wobble. Probably has something to do with the center's near 100lb weight. I've always thought this type of installation was prone to "floor bounce," and so recommend inching the speaker to the edge. Now I'm not so sure. I'm also unsure if the reflections would be strong enough to be significant (greater than -20dBFS) on an ETC graph, or even if that's the best way to approach dialing-in the center channel.

*Birds-eye view of center speaker on rack's top shelf*








*Speaker's edges flush with rack's edge*








*View of tweeter (above) and midrange (below)*
*Center of 4inch midrange is 4inches from top of shelf*


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## Lumen (May 17, 2014)

It became obvious after a few listening sessions that the center needed to be aimed higher. A couple of regulation hockey pucks under the center did the trick nicely. Listening trials were conducted with the mains in the corners (1-star), beside the equipment rack (3-stars), and then out into the room according to Option-3 of Wayne's Setup Guide (4.5 stars):
_"Option 3 - 3rd Best - Other Conditions, Exceptions
If the LP or speaker location is set, use it as your starting point and determine A, B, and C the best you can given that limitation, also following the other guidelines in Options 1 and 2 the best you can. Remember that C is not critical as long as it is "big enough," so if conditions force it to be bigger than 2.4, that is fine."_​
Noting that the LP is fixed at 38" off the back wall forces C=10ft.
Change (C/A) ratio from average of 2.4 to near-minimum of 1.75, then A=5.7ft.
Change (B/A) ratio from average of 1.4 to minimum of 1.08, then B=6.16 ft.

Moving the mains into those positions put the baffle approximately 4.5ft off the front wall, and puts the tweeters about 17in off the sidewall. Starting with the drivers firing straight ahead and increasing toe-in a half-inch at a time, I listened to my demo material until the drivers' centerline crossed in front of the LP. I decided the best balance between image specificity and soundstage expansiveness occurred when the tweeters were 18inches from the sidewall. 

*Here's what it looks like now from the LP* 








*This view shows a row of crates along the left sidewall* 








*The subwoofer is behind the LP*








*Looking back at the LP from behind the left main*








*Crunched a lot of numbers*


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## Lumen (May 17, 2014)

So the listening trials to set SS&I went well. They just took a long time. I had hardly any left for sub tuning, REW measurements, and a Dirac calibration. I could wax poetic about the SQ, but suffice it to say that when the sound locked-in, a smile crept upon my face and my foot started tappin' - before I knew it a whole album side had gone by! If I had to boil it don, I'd say that images are the right size and stay planted, and also that they're more layered than I remember. Stage depth is the best I've witnessed with these speakers, but the room's interaction still gives away their location. I expect that to improve as I fine-tune speaker locations, and add acoustical treatments. 

Before looking at my charts below, notice how the average SPL seems elevated. That's because I measured at a test level of 90dB SPL per this AVS post:
_"Taking measurements at this level will do a few things. First, and most importantly, it will get you above the noise floor so you can get accurate decay times and secondly it will show you how flat your subwoofer truly is down at 15-20hz when played at this volume. ...<snip> ... If you cannot run a measurement at 100db and you cannot get your noise floor below 40db your measurements aren’t totally invalid, but you may not be able to get the full picture or capture your true in room decay times to 60db."
_
So here is my 1st shot at the FR plots, but I'm discouraged because I couldn't make sense of the phase or the IR graphs. Both look innocent enough in the online guides, but just try to interpret one for yourself the first time! So right now I think I'll limit myself to frequency response and waterfall graphs. More to come!

*Left and Right Channel (Overlayed)*
Both channels track each other fairly well until the left one (red trace) exhibits a suck-out around 3.5kHz. I suspect it may be because of its close proximity to the album crates along the sidewall. I plan to move them and try again, but I'm surprised to see they have an effect on the tweeter, which is crossed at 2.2kHz and sits a good foot and a half above and behind the nearest crate.









*Center Channel*
This is interesting. Notice the dips at 100Hz, 200Hz, and 400Hz? Are they related, other than harmonically? I do think the 100Hz dip may be due to SBIR, since the center's baffle is about 2.5ft from the front wall.









*Sub Only*
Can this be considered to be a good response? I think so - fairly flat except for the "ripple" down low. But even that is only about a 2dB difference peak to peak.









*Left + Right + Sub*
Except for the slight ripple from 18Hz to 25Hz, I'd say this is very good performance; all based on only the FR, of course. I plan to examine the waterfall plot later.









*Center + Sub*
This is a mess. This is a very big mess. Do not pass GO, etc. etc. What happened from 75Hz to 125Hz? Is this just a case of poor support through the xover region? Or could it be due to a floor front wall cancellation?


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## Lumen (May 17, 2014)

Okay - pretty sure I figured out how to plot SPL & Phase, IR, ETC, and GD. Please let me know if any of these seem peculiar, and what I might have done wrong. I would also greatly appreciate any advice based on these measurements.
My latest mdat file is attached.
View attachment 137882


*FR & Phase: Left Channel Only*
FR was analysed in Post #26. Does phase for Left Channel Only need to be taken into account to determine acoustic treatments or room/speaker layout?








*FR & Phase: Right Channel Only*
FR was analysed in Post #26. Does phase for Right Channel Only need to be taken into account to determine acoustic treatments or room/speaker layout?








*FR & Phase: Center Channel Only*
FR was analysed in Post #26. Does phase for Center Channel Only need to be taken into account to determine acoustic treatments or room/speaker layout?








*FR & Phase: Subwoofer Only*
FR was analysed in Post #26. Does phase for Subwoofer Only need to be taken into account to determine acoustic treatments or room/speaker layout?








*FR & Phase: Center + Sub*
FR was analysed in Post #26. Does phase for Center+Sub need to be taken into account to determine acoustics or room/speaker layout?








*FR & Phase: L + R + Sub*
FR was analysed in Post #26. Does phase for L+R+Sub need to be taken into account to determine acoustics or room/speaker layout?








*Waterfall: L Only*
My novice analysis tells me decay for the left and right channels is essentially the same. I think the ringing in the upper frequencies is caused by bare walls, minimal furnishings, and the fact that the rear tweeters were active (an oversight on my part, I meant to leave them off). I also think the absence of decay in the lowest frequencies is caused by traffic on a nearby highway, and slow decay by room modes above that. I'm planning on introducing special bass traps to help control ringing in both regions. The round traps have integral broadband diffusion/absorption which can be focused by rotating them.








*Waterfall: R Only*
See comments above for left channel.








*Waterfall: C Only*
I'm unsure how or if I should treat the front wall behind the center. I think SBIR is at work here at around 100Hz where the big trough occurs. I haven't measured the center channel location yet, but I think its baffle is around 2 ft from the front wall. Can anyone please help me confirm that?








*Waterfall: C + Sub*
REW's input level had to be reduced from -12dBFS to -24dBFS in order to avoid clipping during this measurement. Does that invalidate it?








*Waterfall: L + R + Sub*
IIRC, this is traditionally the most important waterfall measurement, but I may have gotten the scale wrong (maybe should only be from 15-200Hz?). There seems to be good correlation between predicted room modes and the ringing indicated here at:
43Hz, 85Hz, 128Hz (length modes)
62Hz, 124Hz, 187Hz (width modes)
71Hz, 141Hz, 212Hz (height modes)
Manufacturer specs for the 20" and 16" diameter traps state a rolloff frequency of 30Hz and 55Hz, respectively. But because no SPL figure is given (i.e. 3dB down), real-world performance is most likely less.








*Group Delay: L Only*
My understanding of group delay is limited. I gather that the flat sections indicate regions where EQ can be effective.








*Group Delay: R Only*
My understanding of group delay is limited. I gather that the flat sections indicate regions where EQ can be effective.








*Group Delay: C Only*
My understanding of group delay is limited. I gather that the flat sections indicate regions where EQ can be effective.








*Impulse Response: L Only*
Any :help: to understand/interpret this graph would be greatly appreciated.








*Impulse Response: R Only*
Any :help: to understand/interpret this graph would be greatly appreciated.








*Impulse Response: C Only*
Any :help: to understand/interpret this graph would be greatly appreciated.








*ETC: L Only*
Derived from the impulse response, my understanding is that peaks above -20dBFS represent reflections that should be investigated. Distances can be directly determined on the graph per the Getting Started with REW guide. Then use the string method to find the reflection's location for possible absorption or diffusion. In this case, there are so many reflections I don't know where to begin. I think the wild swings are caused by the rear tweeter firing into an untreated corner and sidewall (i.e. comb filtering). If so, then a little broadband absorption should compensate. If not, then turning the rear tweeter down or even off should help. More listening tests are warranted!








*ETC: R Only*
Same as above.








*ETC: C Only*
Same as above.


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## Savjac (Apr 17, 2008)

Wow you have generated some pretty colors Lumen.:scratchhead:


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## willis7469 (Jan 31, 2014)

Louie!!!! Hi. 
To my eye, the sub only FR looks nice. The weird thing is mains and sub rises from 20hz to about 70 where it falls down. I agree that, big gully is bad XO support, and I would start with the distance setting in the avr, or phase on the sub. You might want raise the xo on the center just to see what it does. As far as the FR, I would prefer it rises, as it descends from 200 down to 20. Yep, house curve. Yours seems to be the opposite by about 10(on the center). Do you have the lfe trim bumped or flat(75). What happens if you raise it by say 5db and sweep? IMO 10db roll off from 70 on down isn't going to sound good. 
Afaik, the phase plots will only be helpful with the full FR plots above and below XO. That setting is somewhere in the graph tab??? Not sure. Ok that's it for me. I'm sure smarter guys will help soon. 
Good job ol buddy.


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## ajinfla (May 10, 2009)

Glad you figured out center position. Nice looking setup.
You have very good speakers, do not touch anything above 400hz or so, unless you find the overall balance a bit bright or dull.
Do not try to fill sharp nulls in the bass. Concentrate mainly on bass peak issues *if they are audibly offensive*.

cheers


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## AudiocRaver (Jun 6, 2012)

Lumen said:


> This is interesting. Notice the dips at 100Hz, 200Hz, and 400Hz? Are they related, other than harmonically? I do think the 100Hz dip may be due to SBIR, since the center's baffle is about 2.5ft from the front wall.
> View attachment 137722


The 100 Hz dip could be from a reflection / cancellation, as you suggest. The 2.5 ft path for the delayed wave would result in a cancellation at 100 Hz, and higher frequency dips could also result from that same delayed path, but higher frequencies would be at 300 Hz, 500 Hz, etc.


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## Lumen (May 17, 2014)

willis7469 said:


> To my eye, the sub only FR looks nice. The weird thing is *mains and sub* rises from 20hz to about 70 where it falls down. I agree that, big gully is bad XO support, and I would start with the distance setting in the avr, or phase on the sub. You might want raise the xo on the center just to see what it does.


Troublemaker! :neener:
Thanks for pointing that out. But did you mean to say "center and sub" for the 20-70Hz rise/drop? *The response for L+R+Sub seems to have good fill through the xover region, correct?* I agree there's a big gully around 70Hz, but it applies to C+Sub. My AVR has distance settings, but only for manual EQ. I plan to use Dirac Live, which has none. I think I'll need to experiment with sub phase and/or center location to iron out that gap. I imagine the phase setting can satisy one or the other, not both; so any phase manipulation is going to be a compromise.



willis7469 said:


> As far as the FR, I would prefer it rises, as it descends from 200 down to 20. Yep, house curve. Yours seems to be the opposite by about 10(on the center). Do you have the lfe trim bumped or flat(75). What happens if you raise it by say 5db and sweep? IMO 10db roll off from 70 on down isn't going to sound good.


Agreed again. I forgot to mention earlier that these graphs represent measurements taken without EQ, so what we're seeing is natural speaker/room interaction. I've always wondered about the slightly rising response, but never got serious about it until now. *Might that be a type of room-gain?*


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## Lumen (May 17, 2014)

AudiocRaver said:


> The 100 Hz dip could be from a reflection / cancellation, as you suggest. The 2.5 ft path for the delayed wave would result in a cancellation at 100 Hz, and higher frequency dips could also result from that same delayed path, but higher frequencies would be at 300 Hz, 500 Hz, etc.


Being that low, the 100Hz null may respond well to bass trapping on the front wall behind the center channel. A trap effective at 100Hz is going to be too large to fit between the wall and the rack, so I'm hoping traps placed in the nearby corners may have some "residual" effect. Another option would be to move the center, which would change the cancellation frequency according to the SBIR formula: fc = c / 4dfwall, where c=1125ft/sec and dwall is the distance between the speaker and the front wall. It would be ideal to move the center away from the wall, which would drive the cancellation frequency down - preferably below the speaker's low frequency cutoff. But since the rack stays where it is, the speaker can only be moved back about a foot. That would push the quarter wavelength cancellation frequency up to 187.5 Hz, still too low to be treated with traditional acoustic panels. I think a frequency-specific panel/trap might be needed.

I don't understand how you arrived at 300 and 500Hz for higher cancellation frequencies. Is it just a matter of odd-order harmonics? Why not even order? Please explain.


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## AudiocRaver (Jun 6, 2012)

With a delayed signal path and a reflection that re-combines with the original signal and causes cancellation, the frequencies at which that occurs are defined as:


F1 = 1 / (2 * D)
F2 = 3 / (2 * D)
F3 = 5 / (2 * D)
F4 = 7 / (2 * D)

A 5 ft delay path will give (roughly)

F1 = 1 / (2 * 5ms) = 100 Hz
F2 = 3 / (2 * 5ms) = 300 Hz
F3 = 5 / (2 * 5ms) = 500 Hz
etc


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## willis7469 (Jan 31, 2014)

Wow Lou! I can hardly keep up with you. Sheesh! Lol. 
Sorry, I don't know how to multi quote your post without butchering it. 
Yes I was referring to center and subs for the rise, but the mains and sub exhibit a similar rise. The XO on the mains looks excellent. I am surprised that Dirac locks out the manual delay thing. At least you have the phase knob on the sub. You asked(Wayne?) about good for the goose and gander lol. I think you'll end up with a balance in the middle somewhere. Interested to see what Dirac does. Especially with that bottom end. If I'm not mistaken(very easily I may be), room gain(or vessel pressure) starts with the longest room dim /565. If your ceiling is 8' that is 70hz, but also your shortest length so...idk! Also that these graphs are without EQ is really good. I also don't think the waterfalls are too bad either, but I've spent the least amount of time with them. Glad Wayne's here.
This link references rhythmik subs, which stands to reason since it's from their site. However, the principles apply. Just some more to stuff in that big brain. 
http://www.rythmikaudio.com/phase1.html


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## Lumen (May 17, 2014)

willis7469 said:


> Yes I was referring to center and subs for the rise, but the mains and sub exhibit a similar rise. The XO on the mains looks excellent.


I'm curious about the rise. It's present in the mains, the center, and the sub. The room is the common denominator, so if no one checks-in I'll just accept it. A house-curve with an inverse slope should make short work of it!



willis7469 said:


> I am surprised that Dirac locks out the manual delay thing.


You and at least one other person - though I've also heard it elsewhere (you may want to check out Posts #8, 14, and 15 here).



willis7469 said:


> At least you have the phase knob on the sub. ... <snip> ... I think you'll end up with a balance in the middle somewhere. Interested to see what Dirac does. Especially with that bottom end.


Yes, and there's fortunately a wide range of phase angles from which to choose that work well for the mains. I'm also considering reversing the direction of the sub's port so that it's "loaded" by a nearby wall, rather than firing into an open corner. Failing that, I'm also considering swapping it with the album crates on the side wall. That might help to restore symmetry and so raise the dip seen for the left speaker.


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## willis7469 (Jan 31, 2014)

Lumen said:


> I'm curious about the rise. It's present in the mains, the center, and the sub. The room is the common denominator, so if no one checks-in I'll just accept it. A house-curve with an inverse slope should make short work of it!
> I noticed in the center+mains thread, you mentioned to Brian that you reduced the sub level. Just grasping, but could that be what we're seeing? Yes a house curve would take care of that!
> 
> 
> ...




At those wavelengths, I'd be amazed if the port orientation would matter. Wait, where is your port located?


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## Lumen (May 17, 2014)

willis7469 said:


> At those wavelengths, I'd be amazed if the port orientation would matter. Wait, where is your port located?


See how much I know! Side-firing port on bottom-firing sub. I think you mentioned sub orientation to me a while back. When would port location make a difference, if at all?


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## ajinfla (May 10, 2009)

Lumen said:


> To identify all reflections, you'd have to cover the whole room in reflective tape (lol)!


No need. Human beings have evolved in reflective spaces for millennia. I've posted this before, but I'll oblige again: http://www.audioholics.com/room-acoustics/room-reflections-human-adaptation
and http://www.audioholics.com/room-acoustics/room-reflections-human-adaptation/what-do-listeners-prefer
Reflections aren't create spontaneously, they are created by your loudspeakers. The exact pattern is determined wholly by the source(s) of their creation. So you can't look at "room" reflections independent of what is creating them...or you may miss half the picture ;-).
Your loudspeakers have reasonably smooth off axis responses http://www.stereophile.com/content/revel-salon-loudspeaker-measurements-2#Y7Y8LkfuuYfoYxb1.97
Our brains constantly compare the "direct" onset sounds coming from the speaker and the reflections coming from all around. The summation affects the perceived timbre and of course spatial rendition of the sound. When the off axis is a mangled mess and the reflections contain little DNA of the sound origin, it become more difficult if not impossible for the brain to ignore them. Not good.
You should not have such issues. If this is primarily a MCH HT setup, by all means turn it more into an iso-ward and allow the various channels to do their thing. However, if you're trying to strike a balance and want good 2CH front sterophonic sound, be very wary of this approach. There is of course a matter of taste. One mans visually over reflective room, may be another mans lifeless studio stereo construct....to the ears.

cheers


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## Lumen (May 17, 2014)

ajinfla said:


> Glad you figured out center position. Nice looking setup.
> You have very good speakers, do not touch anything above 400hz or so, unless you find the overall balance a bit bright or dull.
> Do not try to fill sharp nulls in the bass. Concentrate mainly on bass peak issues *if they are audibly offensive*.


Thank you for the advice and kind words! :T
The restriction over 400Hz you mention has to do with the Schroeder frequency, yes? Is it unwise to manipulate the upper frequencies because unequal EQ in L/R channels might damage SS&I in some way? And is the reason for not trying to fill sharp LF nulls that they're regions of destructive interference (room modes), which can only be tamed with acoustic traps? I like your last qualifier about leaving bass peaks alone unless they're audibly offensive. Human hearing is not all that reliable at low frequencies, so good SQ can easily be ruined with heavy-handed EQ.




ajinfla said:


> No need. Human beings have evolved in reflective spaces for millennia. I've posted this before, but I'll oblige again: http://www.audioholics.com/room-acoustics/room-reflections-human-adaptation
> and http://www.audioholics.com/room-acoustics/room-reflections-human-adaptation/what-do-listeners-prefer


Interesting reading! I especially like the section on Toole's discussion of bass buildup being mistaken for treble rolloff where he says, "The key is to have the right amount of broadband absorption, and find ways to tame frequency-specific resonances without making the room overly dead." It's of special interest to me because that is my new goal. EQing and trapping can easily become an exercise for their own sake. For instance, conventional wisdom has it that first reflections should _always_ be treated to improve SS&I, and that bass traps should _always_ be added in the corners on the front wall to help tame bass resonances. How many of us blindly follow that advice as "given" before the first measurement is even considered? As one of your referenced articles states: "The widespread belief that first reflections in listening rooms are bad originated in the recording industry, where many mixers felt that they were better able to do their jobs when they were in a strong direct sound field; reflections attenuated." Some people may need a lot of persuading to overcome that deeply entrenched notion.




ajinfla said:


> Our brains constantly compare the "direct" onset sounds coming from the speaker and the reflections coming from all around. The summation affects the perceived timbre and of course spatial rendition of the sound. When the off axis is a mangled mess and the reflections contain little DNA of the sound origin, it become more difficult if not impossible for the brain to ignore them. Not good.


Coherent reflections, uncorrelated packets, incident waves - all very cerebral! And all very necessary for Toole's research: "If the spectra of the direct and reflected sounds are significantly different, the reflections are likely to be more noticeable, from subtle timbral effects up to a premature breakdown of the precedence effect, at which point listeners may be aware of two simultaneous sound images, one located at the loudspeaker and one located at the point of reflection." But I'm unsure I'm totally convinced, or even concerned. Perhaps I should be if I'm ever to reap the benefits of taming frequency-specific resonances. I already know too well how easily my room becomes overdamped using my current acoustic treatments. What worked well in my old listening room does not translate well into my currently smaller space. A different approach is obviously needed, and I thank you for making me question the validity of my past practices. I now prefer to fix the problems than to let the room/speaker/treatment system editorialize all content played through it. That's easier said than done and I may not reach my goal in this room, but the journey will be fun.




ajinfla said:


> Your loudspeakers have reasonably smooth off axis responses ... <snip> ... You should not have such issues. If this is primarily a MCH HT setup, by all means turn it more into an iso-ward and allow the various channels to do their thing. However, if you're trying to strike a balance and want good 2CH front sterophonic sound, be very wary of this approach. There is of course a matter of taste. One mans visually over reflective room, may be another mans lifeless studio stereo construct....to the ears.


Yes, I'll be trying for good balance with an emphasis toward music. I was pleasantly surprised at the level of performance afforded by the new setup in the untreated room. Not apples-to-apples since the center channel came up off the floor onto its own stand. And not apples-to-apples since I secretly (...ooops, cat's outta the bag) brought in a different complement of acoustic treatments for comparison. But I do think there are issues. The trouble comes in properly identifying them as reflection-based or as something else.

EDIT: Since posting the above I've done a bit more digging and came across some good explanations (in posts 24-27 here) of why a room treated for HT will not perform well for stereo. HT needs an absorbent front-wall to keep the ambient info from creeping forward, whereas stereo needs the right balance and type of reflections to preserve spatial cues for robust SS&I. Both benefit from diffusion on the back wall.


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## Lumen (May 17, 2014)

UPDATE:
This last weekend was a mixed bag of tricks in terms of progress. On one hand I was able to rearrange the room to take acoustic measurements for two more layouts. On the other hand, I encountered a major setback when discovering a dead left-channel tweeter. Something went wrong between the first listening trials and measurements for Layout-1. Long story short: a new tweeter is on its way. That's the bad news. The good news is that the blown tweeter explains the wide response dip around 3.5kHz (the rising response from there to 20kHz is due to the rear tweeter). 

The other room arrangements I tried basically experiment with subwoofer location. Layout-2 swaps album crate and subwoofer locations. It has three stacks of crates along the back wall, and the sub along the left sidewall. Layout-3 puts the sub between the last stack of album crates and the door, leaving just enough room for a person to squeeze in. Listening trials for these layouts didn't last long, partly because of the blown tweeter, and partly because of my resultant foul mood. Despite the setback, I listened for bass quality and measured low FQ. The graphs showed a steep 20dBSPL drop from 40Hz down through 15Hz, and many peaks/dips from 40 through 300Hz - not at all like the fairly flat response observed for Layout-1. Different locations along the sidewall did not help. Listening to my bass test tracks told me all I needed to know:
Bass was generally boomy
Subwoofer could be frequently localized
Punch factor was gone

Realizing that lowered treble can be perceived as an increase in bass and vice-versa, I'll conduct more listening tests after repairing the tweet. But I doubt an improved frame of mind is going to change the overall bass quality I heard in music and movies from Layouts-2 and 3. I'd like to try one more sub location right next to the LP (Layout-4) before declaring Layout-1 as the SQ winner. I can publish some graphs if anyone is interested, just ask.


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## willis7469 (Jan 31, 2014)

Bummer about that tweeter Lou. Glad you got to experiment with the sub though. I hate guessing with stuff.


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## Lumen (May 17, 2014)

Thanks willis, it's all good! 


Sent from my iPhone using Tapatalk


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## Lumen (May 17, 2014)

willis7469 said:


> Glad you got to experiment with the sub though. I hate guessing with stuff.


Yeah, same here. And speaking of guessing, I'm still a novice when it comes to many things HT, subwoofer setup included. I thought that moving a sub a few inches can make a big difference, but I'm finding that's not the case (at least in my room so far). Guess I could have saved myself a lot of REW measurement heartache by moving the sub a foot at a time instead of inches. Do you know if that should make a difference? I'd like to know because I'll need to start my subwoofer location tests all over again. 

But why, Lou? Well, because I made another mistake, but this one brings good news! My curiosity got the better of me last evening... how could bass plummet from satisfying into boomy, localized slop? What changed? Then I remembered I engaged the LOUDNESS function for a late-night movie, thinking it would only be active for that "session." Boy was I wrong! The LOUDNESS setting stayed active through the next power-up sequence. I was expecting it to act like the L/C/R/Sub trims, which only retain their setting for the active session. That'll learn me to expect logic from an AVR! So just take a wild guess what happened during my next listening session when the volume was cranked with LOUDNESS engaged. Yup, an overabundance of low-quality bass which I chalked-up to subwoofer positioning instead of an AVR setting. And to make matters worse, I realized my rear "wall" was now a matrix of filled album crates. My measurements and listening tests were being conducted from a "secret" LP much closer to the back wall than was thought or planned. It's no wonder turning down the subwoofer trim didn't help much. The good news is the drop in bass SQ now has a good explanation.


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## willis7469 (Jan 31, 2014)

Well Lou. IME moving a subwoofer by inches instead of feet yields very minimal changes. I'm sure that's dictated by room size. In my gymnasium, even one foot shows no changes in measurements. But in my bedroom smaller changes are evident. 
So glad you figured out the boom and bloom! I HATE when settings don't go back after powering down. I've been burned by that too. As to the LPs.(sufferin mind), I'm kinda guessing, but imo the density created by stacking them tightly in crates, would crest a barrier. Probably even more so than drywall and wooden studs.


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## Lumen (May 17, 2014)

The scary thing is that no one's making fun of me. Well? C'mon - I ain't scared, I have teenagers! 


Sent from my iPhone using Tapatalk


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## willis7469 (Jan 31, 2014)

Lou, Lou, Lou...
If we started making fun of you, you might stop sharing!!! Lol!!!
Most of us aren't professionals either(of course some are), and there is much to be learned from your trials and tribulations. Doin good!


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## Savjac (Apr 17, 2008)

Not making fun of you ?? Why nonsense my friend, I would surely make fun if I was smarter and could understand your missive's. I am left behind in the dust here. :scratch:


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## Lumen (May 17, 2014)

Well, at least I can laugh at myself! You guys are too kind; thanks for the encouragement. Now I'm starting to understand why you called me brave! What was I thinking? But I'm not ready to crawl away in shame yet!! 

This thread isn't turning out as planned. The forum's big fish aren't taking my measurement bait - maybe because the thread's title needs focus, or maybe because it seems off-topic to REW measurements. In any case, I'm moving it to a less-technical forum and will continue to post measurement questions individually.


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## Savjac (Apr 17, 2008)

I am sorry Lou but I cannot do the measurement thingie just yet. Next time we get together you can show me or....maybe I could just read the manual :laugh2:

I dont learn as well by reading something as by doing it...so you have left me done and dusted. :crying2:


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## Lumen (May 17, 2014)

The tweeter's failure mode leaves me with a nagging sensation. Why hadn't I noticed it sooner? Of course, hindsight's always 20-20! It's clearly evident in the SPL graph, but on my behalf the tweeter hasn't totally given up the ghost. It still functions at the lower end of its crossed frequency range! The dip is not as noticeable to these ears as the graph would have me believe. Again to my credit, I think it took a while to detect because of the masking effect presented by the right and center channels. I've never heard of such a failure mode, though. Can a tweeter fail "halfway" so it's only reproducing part of it's normal range, or would that be a crossover problem?


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## Lumen (May 17, 2014)

Savjac said:


> I am sorry Lou but I cannot do the measurement thingie just yet. Next time we get together you can show me or....maybe I could just read the manual :laugh2:
> I dont learn as well by reading something as by doing it...so you have left me done and dusted. :crying2:


You're not alone. Seeing is easier than doing for me as well. Once I get the hang of it, I won't mind sharing; so no worries, we can take a look at your setup during our next audio get-together!


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## Savjac (Apr 17, 2008)

Lumen said:


> The tweeter's failure mode leaves me with a nagging sensation. Why hadn't I noticed it sooner? Of course, hindsight's always 20-20! It's clearly evident in the SPL graph, but on my behalf the tweeter hasn't totally given up the ghost. It still functions at the lower end of its crossed frequency range! The dip is not as noticeable to these ears as the graph would have me believe. Again to my credit, I think it took a while to detect because of the masking effect presented by the right and center channels. I've never heard of such a failure mode, though. Can a tweeter fail "halfway" so it's only reproducing part of it's normal range, or would that be a crossover problem?
> View attachment 138634


Good Morning Lou

I am not sure but it would be my thought that either the tweeter works or it does not. I am not sure I have ever encountered a driver like your tweeter working over a selected frequency and not the rest of its inherent range.

I wonder if maybe there is an actual crossover issue in the one speaker ? Let me rephrase that statement, It would appear that there may be a crossover issue in the one speaker.


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## Lumen (May 17, 2014)

I initially considered drivers to be digital in nature - that is, they either work or they do not. However, further investigation reveals that some engineers believe in partial failure modes which leave the driver damaged, yet operational. An example of a failure mode similar to my own appears in this Speaker Failure Analysis article, where the author states:

_"For a host of reasons, glue attachment of the voice coil to the cone or spider may fail. The immediate result of even a partial failure is the voice coil is no longer precisely centred. An off-centre voice coil will scrape against the pole pieces and this soon damages the wire it is wound from, possibly creating shorted turns in the process. This highly audible defect is called "poling" by repairers. Broken or cracked attachments vibrate severely under normal drive forces, so this is also highly audible as buzzing noise or distortion. Repair is sometimes possible but re-coning or replacement is often needed."_

While I have heard HF distortion, it's difficult to tell whether it originates from the tweeter, midrange, or source material. But that still doesn't explain the main failure mode of partial output. I did find related posts on the Electrical Engineering Stack Exchange, which support my recent experience:

_"...However, one can imagine a scenario where something else in the speaker is damaged, such as the surround (the rubber coil that allows the cone to vibrate freely) or the spider (cloth "guide" inside the speaker, behind the cone) or leads leading into the cone are damaged, but the coil still operates. Any of these issues have the ability to reduce the volume level of the speaker."_

and

_Another part of the speaker that can fail is the joint between the coil and the cone. If the force on the coil exceeds the strength of that joint, it's possible that it may fail partially or completely. If this happens, motion of the coil will not be properly conveyed to the cone, causing the speaker to sound rather weakly. Additionally, the speaker will likely be more effective at producing sound when driven in the direction that would pull the coil against the one, than when driven in the opposite direction. Thus, the sound will not only be quieter than it should, but distorted as well._

I know there are smarter and more experienced enthusiasts than I who may present evidence and arguments against what I have found so far. But in the end, I still have a partially functioning tweeter, whose failure mode was verified by swapping drivers in the left and right mains - the problem followed the driver! Installing a totally new driver in place of the malfunctioning one solved the problem. This should be confirmed with my next round of measurements.


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## Lumen (May 17, 2014)

Success! Both tweeters are now functional:


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## Lumen (May 17, 2014)

* Please feel free to add your comments and/or suggestions! These charts show the improvement realized first by adding 2 bass traps (2T), and then by adding 3 more (5T). As more traps are added, frequency response starts flattening out and resonant modes start decaying more rapidly.*

*Frequency Response Improvement (Left Channel)*
Maybe quotes should go around the word improvement. Adding traps sure doesn't make the FR plot look pretty. You'll need to turn to the waterfall for that. A quick glance at the Sub-Only plot shows that the sub dominates the combined responses (L+R+Sub and Center+Sub).








*Frequency Response Improvement (Right Channel)*
Same here! Maybe quotes should go around the word improvement. Adding traps sure doesn't make the FR plot look pretty. You'll need to turn to the waterfall for that. A quick glance at the Sub-Only plot shows that the sub dominates the combined responses (L+R+Sub and Center+Sub).








*Frequency Response Improvement (Center Channel)*
My novice eye has yet to detect much improvement here as well. The traps' effectiveness down low is extremely limited to nonexistent, as is expected.








*Frequency Response (Subwoofer Channel)*
As expected, there's only slight improvement where FR is leveled from about 75 to 150Hz. Larger and/or more traps would be needed to make a significant dent above 40.








*Bass Resonance Improvement (Left+Right+Sub Channel)
LEFT = 0 Traps & 2 Traps / RIGHT = 0 Traps & 5 Traps*
These waterfall comparisons are best viewed "live" in REW, but I tried to make them as revealing as possible. The baseline measurement with 0 traps is always the same color, and is shown transparent. Examining the first slice of the 5T plot reveals that FR is smoothed from around 65Hz to 120Hz, and to a lesser extent from around 120Hz to 300Hz. Noticing where the distance increases between succeeding slices tells us if and where ringing has been improved. Ringing has been totally subdued by trapping at around 300/210/180Hz and partially subdued at 205/150/130/95/75Hz. Severe ringing still exists at 45/22/19Hz, which are too low for traps to be effective.














*Bass Resonance Improvement (Center+Sub Channel)
LEFT = 0 Traps & 2 Traps / RIGHT = 0 Traps & 5 Traps*
I'm unsure if this speaker combo even needs scrutiny. I only included it because it was a recommended measurement in the REW 101 Guide. As before, these waterfall comparisons are best viewed "live" in REW. Examining the first slice of the 5T plot reveals that FR is smoothed from around 70Hz to 170Hz. Noticing where the distance increases between succeeding slices tells us if and where ringing has been improved. Ringing has been totally subdued by trapping at around 200Hz and greatly improved at 150/125/95/75Hz. Severe ringing still exists at 45/22/19Hz, which are too low for traps to be effective.














*Decay Improvement (Left+Right+Sub Phase=0)
LEFT = 0 Traps / RIGHT = 5 Traps*
On the left we see that ringing at 45Hz does not decay 20dB within the recommended 160msec target. On the right we see that 5 traps brought the decay under control even though ringing still exists! This is actually proof of the traps effectiveness in action. To quote The ABC's of ASC's Tube Traps: "It’s worth keeping in mind that ASC’s tube traps aren’t bass absorbers per se, they are resonant absorbers. They won’t remove the bass energy from your room, rather they will tame the resonances caused by this energy. _Bass peaks will still be strong at the room’s resonant frequency, but the absorption of this resonance will reduce their severity._"














*Decay Improvement (Left+Right+Sub Phase=90)*
Dialing in the sub's phase control for proper support through the 80Hz xover region shows that decay times are greatly improved and well within target.


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## Lumen (May 17, 2014)

*And here are the plots showing subwoofer phase support through the 80Hz crossover region. Which would you choose?*


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## Lumen (May 17, 2014)

Results of the room/system calibration and center channel upgrade are impressive so far:
line-of-sight to surrounds established for first time
semi-nearfield LP eliminates many damaging reflections
bass has regained it's punch
speech intelligibility has been greatly improved

Yet I'm left with only a lukewarm feeling. The system could be taken up another notch, but I'm not sure how to proceed. Maybe it can't be done with my current gear (is a miniDSP in my future)? I'm hoping to learn enough from my REW threads to find out!


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## Lumen (May 17, 2014)

I updated the graphs above with observations. Please feel free to critique or comment!


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## Lumen (May 17, 2014)

And just to put your suspicions to rest, no it's not business-as-usual. I plan on taking your advice rather than asking for it, but then doing what I want anyway. The current 5-trap layout with sub next to the LP is a temporary solution until I develop something better. So far, it's my favorite.

*Room Layout #1 (original before this renovation): 
Well-integrated bass with reasonably flat FR and excellent support through xover region. Fair SS&I. But too many traps required, so fairly lifeless.*









*Room Layout #2: 
Very poor LF response. No amount of good symmetry/aesthetics makes up for sound this bad!!*









*Room Layout #3: 
Good LF response with engaging tactile feedback. Very good SS&I. Least aesthetic of options, but who cares!*









*Room Layout #4: 
Fair LF response with some extreme LF feedback (expected more sitting right next to sub). Very good SS&I. Good symmetry/aesthetics.*


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## tonyvdb (Sep 5, 2007)

Lumen said:


> *And here are the plots showing subwoofer phase support through the 80Hz crossover region. Which would you choose?*
> 
> View attachment 139514


The lighter pink line would be the one I would choose, You still have that dip at 70Hz and again at about 140Hz but its less noticeable I am sure.


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## Lumen (May 17, 2014)

tonyvdb said:


> You still have that dip at 70Hz and again at about 140Hz....


Hi Tony! Yup, 70 and 140 show up as room modes according to the calculators. Below 100 are tough to deal with. I thought my specialized ASC traps would make a bigger dent. Turns out subwoofer phase has a much greater impact! I learned from this Room Modes 101 article that room modes can be identified through peaks in the frequency response and slow decay in the time domain. It suggests that modal problems can be solved by:
Acoustic treatment
Positional equalization (changing the location of the listening positions and speakers/subs)
Electronic equalization
Room mode cancellation

*Modes for 13.25'L x 9.1'W x 8.0'H room:*


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## Lumen (May 17, 2014)

But first.... I should be working on controlling early reflections. As an FYI to myself, I included a few related articles below. _Please feel free to suggest more reading, and as always, your questions/comments are welcome!_
Early Reflections 101
Understanding Small Room RT Measurements
How to Choose Acoustic Panels
Acoustic Measurement Standards

I also owe you pictures of Layout 4 (which is what we're currently analyzing), along with the accompanying measurements for comparison.


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## Lumen (May 17, 2014)

AudiocRaver said:


> The idea on reflections is to determine the kind you want and the kind you don't want, carefully work with the timing of the wanted ones, and absorb/diffuse the ones not wanted in a way that does not disrupt imaging. First reflections only, after that, the delay is generally enough that imaging is not affected. The first part involves careful measurements, first physically with a tape or laser distance measurer, then refining with REW and a mic. The second kind are eyeballed, because that is good enough. See where they appear most likely and use panels on those surfaces - ensuring that ALL diffused reflections are aimed AWAY from the LP.


Do you think this is something best learned through formal training and/or experience? The literature I've come across so far seems to lean in that direction. Care to comment on where I should head after getting good ETC measurements? I realize my questions are probably like a passenger expecting a pilot to teach them to fly by asking how to get on the plane!


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## Lumen (May 17, 2014)

I think I found the answer in your recommendations on early reflections in the thread HTS Two-Channel Speaker Setup Guide for a Deep Soundstage. It seems that I do need to generate an ETC from the IR graph. According to the REW101 Guide, these should be "... measurements that isolate one speaker, e.g. left front, right front, center, etc. Do not use measurements that combine multiple speakers, or measurements that include the subwoofer(s). .... Any peaks above -20dB represent reflections that should be researched."



AudiocRaver said:


> Early Reflection Guidelines:
> 
> Perfect room symmetry is not absolutely necessary. General symmetry plus a few treatments probably do the trick. A room with longer RT60 times might have "unbalanced spaciousness" effects where one side sounds bigger than the other. My own listening area is far from symmetrical, but RT60 is quite low and I do not notice anything like this. With longer RT60, absorptive treatment can help balance this effect out.
> 
> ...


Also see: 
Creating A Reflection Free Zone
The Importance of Timbre in Sound Reproduction Systems
Listening Room Reflections and the Energy Time Curve


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## Lumen (May 17, 2014)

Promised pics!!

*PREPARATION (Got a good workout doing squat-pushups to change REW connections)*














*LAYOUT OPTIONS*


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## Lumen (May 17, 2014)

Lumen said:


>


In the name of all that is sane, what on earth is the meaning of this? Well, I'd like to think it's helping tame a floor-to-ceiling axial mode but truth be told, it's primarily acting as a diffuser for the back wall. It also doesn't hurt to hide the mess left on the back wall from dismounting the surrounds.


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## Lumen (May 17, 2014)

My attempts to advance into the realm of speaker timing and ETC-driven reflection remedies have dissolved. Well actually, they've morphed into iterative tuning cycles to find the best balance between theory and practice. I at first reached an acceptable configuration with all speakers crossed at 80Hz and sub phase adjusted for good SPL support through the crossover region. Measurements said that FR was not particularly good, but remembering that time domain behavior plays an important role told me that listening was important as well. I tried a 60Hz crossover configuration - which looked better on paper - but didn't sound nearly as good. Granted, the Dirac calibrations could have skewed results, but I strived for identical protocols. Moving back to the 80Hz setup with a modified house curve and slightly repositioned center channel went a long way toward imparting punch, clarity, and immersion. I'm very satisfied with the results and couldn't have done it without your help! Now it's time to kick back and become acclimated to the new sound. Do you think it'll take long to develop a re-tuning itch?

That's setting up a sequel, don't you think?


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