A Sound Renovation for the Green Room - Page 3 - Home Theater Forum and Systems - HomeTheaterShack.com

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post #21 of 68 Old 03-03-17, 08:39 AM Thread Starter
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Re: A Sound Renovation for the Green Room

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:
Quote:
ajinfla wrote: View Post
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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post #22 of 68 Old 03-03-17, 09:27 AM
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Re: A Sound Renovation for the Green Room

Cant wait for pics!

I hate protesting! I just don't know how to show it.
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post #23 of 68 Old 03-03-17, 12:21 PM
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Re: A Sound Renovation for the Green Room

Quote:
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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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post #24 of 68 Old 03-03-17, 07:11 PM Thread Starter
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Re: A Sound Renovation for the Green Room

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
A Sound Renovation for the Green Room-img_2.jpg

Speaker's edges flush with rack's edge
A Sound Renovation for the Green Room-img_1.jpg

View of tweeter (above) and midrange (below)
Center of 4inch midrange is 4inches from top of shelf
A Sound Renovation for the Green Room-img_3.jpg

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post #25 of 68 Old 03-05-17, 06:13 AM Thread Starter
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Re: A Sound Renovation for the Green Room

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
A Sound Renovation for the Green Room-image00005.jpg

This view shows a row of crates along the left sidewall
A Sound Renovation for the Green Room-image00002.jpg

The subwoofer is behind the LP
A Sound Renovation for the Green Room-image00004.jpg

Looking back at the LP from behind the left main
A Sound Renovation for the Green Room-image00003.jpg

Crunched a lot of numbers
A Sound Renovation for the Green Room-image00001.jpg
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post #26 of 68 Old 03-05-17, 06:53 AM Thread Starter
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Re: A Sound Renovation for the Green Room

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.
A Sound Renovation for the Green Room-layout-1-fr-lr-only.jpg


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.
A Sound Renovation for the Green Room-layout-1-fr-c-only-12db-.jpg


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.
A Sound Renovation for the Green Room-layout-1-fr-sub-only.jpg


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.
A Sound Renovation for the Green Room-layout-1-fr-lrsub.jpg


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?
A Sound Renovation for the Green Room-layout-1-fr-centersub.jpg
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Last edited by Lumen; 03-05-17 at 10:20 AM. Reason: Added commentary for select graphs.
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post #27 of 68 Old 03-05-17, 03:17 PM Thread Starter
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Re: A Sound Renovation for the Green Room

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. 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?
A Sound Renovation for the Green Room-layout-1-fr-phase-l-only.jpg

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?
A Sound Renovation for the Green Room-layout-1-fr-phase-r-only.jpg

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?
A Sound Renovation for the Green Room-layout-1-fr-phase-c-only.jpg

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?
A Sound Renovation for the Green Room-layout-1-fr-phase-sub-only.jpg

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?
A Sound Renovation for the Green Room-layout-1-fr-phase-center-sub.jpg

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?
A Sound Renovation for the Green Room-layout-1-fr-phase-lrsub.jpg

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.
A Sound Renovation for the Green Room-layout-1-wf-l-only.jpg

Waterfall: R Only
See comments above for left channel.
A Sound Renovation for the Green Room-layout-1-wf-r-only.jpg

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?
A Sound Renovation for the Green Room-layout-1-wf-c-only.jpg

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?
A Sound Renovation for the Green Room-layout-1-wf-center-sub.jpg

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.
A Sound Renovation for the Green Room-layout-1-wf-l-r-sub.jpg

Group Delay: L Only
My understanding of group delay is limited. I gather that the flat sections indicate regions where EQ can be effective.
A Sound Renovation for the Green Room-layout-1-egd-l-only.jpg

Group Delay: R Only
My understanding of group delay is limited. I gather that the flat sections indicate regions where EQ can be effective.
A Sound Renovation for the Green Room-layout-1-egd-r-only.jpg

Group Delay: C Only
My understanding of group delay is limited. I gather that the flat sections indicate regions where EQ can be effective.
A Sound Renovation for the Green Room-layout-1-egd-c-only.jpg

Impulse Response: L Only
Any to understand/interpret this graph would be greatly appreciated.
A Sound Renovation for the Green Room-layout-1-ir-l-only.jpg

Impulse Response: R Only
Any to understand/interpret this graph would be greatly appreciated.
A Sound Renovation for the Green Room-layout-1-ir-r-only.jpg

Impulse Response: C Only
Any to understand/interpret this graph would be greatly appreciated.
A Sound Renovation for the Green Room-layout-1-ir-c-only.jpg

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!
A Sound Renovation for the Green Room-layout-1-etc-l-only.jpg

ETC: R Only
Same as above.
A Sound Renovation for the Green Room-layout-1-etc-r-only.jpg

ETC: C Only
Same as above.
A Sound Renovation for the Green Room-layout-1-etc-c-only.jpg

.
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Last edited by Lumen; 03-06-17 at 08:55 AM. Reason: Added graph titles and comments
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post #28 of 68 Old 03-05-17, 03:27 PM
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Re: A Sound Renovation for the Green Room

Wow you have generated some pretty colors Lumen.

Good Listening

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post #29 of 68 Old 03-06-17, 07:16 AM
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Re: A Sound Renovation for the Green Room

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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post #30 of 68 Old 03-06-17, 08:39 AM
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Re: A Sound Renovation for the Green Room

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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