[Lumen]

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:

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.

 

[scotts2014se]

Cant wait for pics!:grin2:

 

[ajinfla]

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.

 

[Lumen]

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

 

[Lumen]

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

 

[Lumen]

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?

 

[Lumen]

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.

 

[Savjac]

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

 

[willis7469]

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.

 

[ajinfla]

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

 

[AudiocRaver]

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.

 

[Lumen]

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.

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?

 

[Lumen]

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.

 

[AudiocRaver]

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

 

[willis7469]

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

 

[Lumen]

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!

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).

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.

 

[willis7469]

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!





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).



I'll look. I believe you, but it just seems odd.



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.

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

 

[Lumen]

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?

 

[ajinfla]

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

 

[Lumen]

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.

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.

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.

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.