ttocs
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Post by ttocs on Apr 17, 2022 14:09:20 GMT -5
GoTo bottom for the quick read of problem/solution. CENTER SPEAKER, it goes in the middle, right? Got a new center channel speaker and after some initial break-in hours it was time to figure out where it should be placed. Not much choice here as it's gonna go in the middle, but there are some considerations to be made that impact in-room frequency response at the MLP. I use REW for measuring frequency response. A little about my room. It’s a multi-purpose great room, an odd-rectangle, almost square-ish that can be imagined as two conjoined-rectangles of different length with the Front Wall being the only common wall, sloped cathedral ceiling with a 16” beam at the peak. The A/V system uses the right half of the common 23’ wide wall with one window at the right end in the corner that meets the right wall which is over 80% glass from floor to ceiling. That window at the right end of the front wall, which is 40” wide and 7’ high, is totally covered with 3-1/2” thick rock wool and fabric. The new center speaker, Martin Logan C18, comes with a wall mount bracket and is designed for wall mounting, or can be placed on a table or stand. I tried on a stand (petrified tree stump that I purchased just for a center speaker but never used it as such, until now), got some bad results, so I mounted it on the wall just under the tv with just about the same results. I figured that the wide and fairly deep null is due to SBIR (Speaker Boundary Interference Response) and would benefit from wall mounting, but with SBIR, there’s more than one source to consider. So I tried putting absorption panels in various spots to see if there would be any chance of a change to the FR (Frequency Response) curve in REW. The only location that proved to change anything was when a panel was placed on the floor between the speaker and MLP (Main Listening Position). The depth of the null was reduced a little bit. I’m not keen on leaving absorption panels on the floor, so I mounted a couple on the ceiling and got the same result (these are called “clouds”), plus got the added benefit of reducing ringing/reverb. The clouds are 30”x48” and 3-1/2” thick. Doubling up the panels for extra thickness had no additional measurable effect, so single thickness is fine. I’m now certain that I’m dealing with a placement issue for both the speaker and MLP. I decided to use REW’s Generator and RTA. I set the REW Generator to play Periodic Pink Noise limited to 100-800Hz to more than cover the null from 200-500Hz. Playing Periodic Pink Noise from Generator and “Recording” with RTA will display a Live FR Curve on the computer screen, which in this case is my 85” tv so it’s very easy to see. With the speaker still wall-mounted I started playing the Periodic Pink Noise and watched the screen while moving the mic closer to, and farther from, the center speaker looking for changes in the FR curve where the null is. I had to move way behind the MLP to get some better results, which is not going to work for me. So I removed the speaker from the wall and put it on the stump so I could move it around easily (the stump has furniture pads on the bottom so it slides nicely). I started with the speaker as close to the front wall as possible, measured while moving the mic, then moved the stump out from the wall about 6” at a time. After the speaker got in the range of 2-1/2’ to 3’ from the front wall I saw some good results happening, so I knew I was on the right track. So I put the mic on a stand and started moving the sofa, along with the mic in the proper MLP location relative to the sofa, for a more definitive representation of how things really are. This kept the mic at a consistent elevation above the floor, and a consistent relative position to the sofa. Moving the mic/sofa a little at a time until things started looking better and then began looking worse, I’d put it back to the last known good position and then moved the speaker while looking for its better/worse comparison. This back and forth went on for a few iterations until it was clear that the sweet spot for both the speaker and MLP vs distance from front wall were close at hand. Next, I setup for running normal REW sweeps for better accuracy and did the same back and forth moving of both the speaker and MLP, but this time I only moved things 2” at a time being that things were very close already. It wasn’t too long before the best spots for both were found and the null was fixed! The front edge of the C18 is 31” from the Front Wall, and the MLP is 10’-11” from the Front Wall which is one foot farther than before. These locations for Center Speaker and MLP reduced the null by being in a “good” distance from Front Wall and “good” distance from each other causing no destructive or constructive interference at the MLP. As I have often said, speaker location is most important. I’ve also said that if speaker location alone doesn’t help entirely, move the MLP. My example here demonstrates both pretty well. But, this is only in consideration of the Center Speaker, so I now need to re-check the Left and Right speakers to see how they sound and remeasure. The MLP is a little farther from the front wall than before, and from my experience in having done this exercise with the L&R in the past, this should end up being ok with a little relocation of the speakers, but needs to be confirmed. The lesson here is that room treatments are good for reducing some effects of reflections and ringing, but can’t take the place of finding the best speaker placement and listening location in the first place. Also, an inch of movement can change things and can easily be overshot if one is too hasty and moves using larger increments. The room showing the new clouds and current location of MLP and C18.  Problem/Solution Wide deep null. Fixed by moving the Center Speaker fore/aft relative to Front Wall, and, moving the MLP fore/aft relative to Front Wall and Center Speaker. Measurements were used to find the best spots for Speaker and MLP. Speaker Location, MLP Location. Nothing beats it! |
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Post by leonski on Jun 9, 2022 16:58:58 GMT -5
Of what material are the clouds? Did you find some in OC703 or some kind of RockWool?
Great idea BTW. I'm glad you measured and recorded. This is good since you may end up moving stuff in order to clean.....that sort of thing.
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Post by Boomzilla on Jun 9, 2022 22:26:55 GMT -5
I’ve found that even in a mostly symmetrical room I get better results with my left speaker slightly more toed in than the right. To look at, it bugs me to death, but when I close my eyes and listen, it’s toe-in imbalance is clearly right. The reason, so far as I can tell, is that the left speaker faces a hallway on the opposite side of the room from it and some of its sound escapes down the hall. Toe in prevents some of this from happening.
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Post by novisnick on Jun 9, 2022 23:06:32 GMT -5
I’ve found that even in a mostly symmetrical room I get better results with my left speaker slightly more toed in than the right. To look at, it bugs me to death, but when I close my eyes and listen, it’s toe-in imbalance is clearly right. The reason, so far as I can tell, is that the left speaker faces a hallway on the opposite side of the room from it and some of its sound escapes down the hall. Toe in prevents some of this from happening. I have a similar situation where my left is toed differently then the right. I’ve not noticed the looks in some time do to this setup being this way for some time. At first it just bugged the heck out of me but like you stated the sound imaging is everything. 🎶🎶she may be ugle,,,🎶🎶,,, but she sure can cook!🎶🎶😂😂🤣 |
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Post by marcl on Jun 10, 2022 6:15:53 GMT -5
I’ve found that even in a mostly symmetrical room I get better results with my left speaker slightly more toed in than the right. To look at, it bugs me to death, but when I close my eyes and listen, it’s toe-in imbalance is clearly right. The reason, so far as I can tell, is that the left speaker faces a hallway on the opposite side of the room from it and some of its sound escapes down the hall. Toe in prevents some of this from happening. I have a similar situation where my left is toed differently then the right. I’ve not noticed the looks in some time do to this setup being this way for some time. At first it just bugged the heck out of me but like you stated the sound imaging is everything. 🎶🎶she may be ugle,,,🎶🎶,,, but she sure can cook!🎶🎶😂😂🤣 + boomzilla Toe in certainly affects imaging. And along with physical symmetry, so does the timing of direct and reflected waves. I found using REW that there are asymmetric reflections that affect imaging. Not surprising to have asymmetric reflections even in a seemingly symmetrical room. The key is that with REW you can see them and then track down the source. Example: A couple years ago - after repositioning speakers and changing some room treatment - I found that my right speaker (only) had a strong reflection at 18ms on the REW impulse response. I also observed that the image overall was shifted to the left, irrespective of balance (level) settings or toe in. Frequency response of left/right speakers was essentially the same with no indication of anything that would cause an imaging issue. I placed a 2x4ft absorber in various locations until I determined that the source of the sound was the back wave from my right (Magnepan) speaker; the source of the last reflection before reaching the MLP was the side wall immediately to the right of the MLP. So ordered a 3x3ft absorber to fit the space, and the problem went away ... until I moved the speakers and treatments again a year or so later. I noticed some asymmetry again with the image on the right side. The REW impulse response showed a slight reflection at 8ms but nothing at 18ms. I took the 3x3ft absorber down, and the imaging improved. I replaced the absorber with two diffusers and it improved further. I determined that the repositioning I had done (and addition of a larger TV) had blocked the back wave from the right speaker. And apparently now in the whole scheme of things the absorber was now causing the image shift. Listening tests with several benchmark recordings confirmed that the imaging was now symmetrical again. Note that my room and speaker positioning are anything but conventional! The Rooze setup has the front speakers pointed 45 degrees toward the side walls with highly reflective panels bouncing the waves toward the MLP. The rest of the room has a LOT of diffusion. But I proved it - correlated it - with listening tests and repeated measurements and experiments.   |
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Post by marcl on Jun 10, 2022 7:02:15 GMT -5
GoTo bottom for the quick read of problem/solution. CENTER SPEAKER, it goes in the middle, right? ........... Hmmmm how did I miss this post!?  Oh yeah, THAT was the day I got locked in the quarantine room for a week!  |
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Post by 405x5 on Jun 10, 2022 8:17:20 GMT -5
“GoTo bottom for the quick read of problem/solution. CENTER SPEAKER, it goes in the middle, right? Got a new center channel speaker and after some initial break-in hours it was time to figure out where it should be placed. Not much choice here as it's gonna go in the middle, but there are some considerations to be made …….” …..but not yours….. Immensely and needlessly complicated. You would do much better by reading up from experienced HT users and Tips also from Martin Logan on getting the most out of it. You could kick yourself for how simple and elegant some of the solutions are. |
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KeithL
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Post by KeithL on Jun 10, 2022 9:17:15 GMT -5
Interesting... but I sort of have to agree that you're somewhat "overthinking" the situation... A good start is to stop worrying about the graphs and think about how it sounds... and what you find problematic there... and how to fix it. Your goal is to have a room that sounds good... not to have one that measures good. (They may coincide... but you may also end up expending a lot of effort fixing things you can't hear.)
For example... you ended up with a sound absorber on the floor halfway between that center speaker and the main listening position. This is a relatively common and well-known solution to problems with "dialog that isn't clear and intelligible". (And the first piece of advice many experts would have given you is "try a throw rug on the floor in front of the center speaker".)
This is true basically because the midrange frequencies are critical for dialog clarity... The sound bouncing from the floor at that spot tends to cause cancellations with the direct sound coming from the speaker in that range of frequencies. (You may get a similar improvement if you put an absorber at a similar location on the ceiling.) (The next thing to try would be absorbers at the "first bounce spots" on the walls... for both the center and the main speakers.)
However this is something you could have guessed at without taking all those measurements. (And many folks suggest that one easy way to locate those "first bounce locations" is with a LASER pointer and a buddy holding a mirror.)
Likewise, what most people advise regarding "boundary issues" is "most speakers sound best when out a few feet from the side and back walls - adjust to taste".
(You will also find that this tends to vary with different brands and models of speakers... but, as 405x5 said, it's often easier to just see what other folks with the same speakers found to work well.)
It is worth noting that, as someone else mentioned already, our brains integrate both short term and long term reflections.
This is a fancy way of saying that symmetry matters... and not only in terms of speaker placement and toe-on. You WILL hear a difference if your room is "live on the left and dead on the right"... even if the speakers are not pointed directly at those walls.
But, again, you don't need to make especially fancy calculations, or make lots of measurements, to get a good idea what's going on. In very simple terms... if your left and right sides are different you're going to hear different amounts of sound coming from those directions at different frequencies and times. This is true if your left and right speakers have different toe-in... But it's also true if you have a hallway on one side and not the other... Or if you have a stucco wall on one side and a window on the other... Or a window on one side and a tapestry on the other... Or even an opening behind you on one side and not the other...
One very simple rule of thumb is to eliminate the asymmetry (block the hallway; put drapes over the window; or hang a tapestry on that opposite wall). And, if you can't eliminate that opening on one side behind you, consider a listening chair with a high upholstered back.
And, if you cannot do that, minimize the effect the difference has, by increasing the toe-in of the speakers, so less sound reaches those asymmetrical spots... Or use speakers with narrower horizontal dispersion...
“GoTo bottom for the quick read of problem/solution. CENTER SPEAKER, it goes in the middle, right? Got a new center channel speaker and after some initial break-in hours it was time to figure out where it should be placed. Not much choice here as it's gonna go in the middle, but there are some considerations to be made …….” …..but not yours….. Immensely and needlessly complicated. You would do much better by reading up from experienced HT users and Tips also from Martin Logan on getting the most out of it. You could kick yourself for how simple and elegant some of the solutions are. |
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Post by marcl on Jun 10, 2022 9:35:00 GMT -5
Interesting... but I sort of have to agree that you're somewhat "overthinking" the situation... A good start is to stop worrying about the graphs and think about how it sounds... and what you find problematic there... and how to fix it. Your goal is to have a room that sounds good... not to have one that measures good. (They may coincide... but you may also end up expending a lot of effort fixing things you can't hear.)
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…..but not yours….. Immensely and needlessly complicated. You would do much better by reading up from experienced HT users and Tips also from Martin Logan on getting the most out of it. You could kick yourself for how simple and elegant some of the solutions are. + ttocs 405x5 When I was in engineering school one of my classmates was ranting about why we had to study all the math and theory ... he was a long-time electronics hobbyist and he said "you just look that stuff up in a book". Another classmate responded "who do you think writes the books?" So sometimes we do measurements to gain a broader understanding and then correlate what we hear/perceive to the data. Sure, the shortest path to a solution might be to look for a similar situation and copy it. But you don't learn the fundamentals that way and you may not actually solve the problem. And, you miss gaining a broader understanding which cumulatively may help you solve some future problem. But then there is the immortal wisdom of some guy in some post I read on some forum somewhere, as he laughed at us and seriously said "Why measure what you can hear with your own two ears?" |
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Post by 405x5 on Jun 10, 2022 10:21:01 GMT -5
“Interesting... but I sort of have to agree that you're somewhat "overthinking" the situation... A good start is to stop worrying about the graphs and think about how it sounds... and what you find problematic there... and how to fix it. Your goal is to have a room that sounds good... not to have one that measures good. (They may coincide... but you may also end up expending a lot of effort fixing things you can't hear.)”
What he said
…..but not yours….. Immensely and needlessly complicated. You would do much better by reading up from experienced HT users and Tips also from Martin Logan on getting the most out of it. You could kick yourself for how simple and elegant some of the solutions are. |
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KeithL
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Post by KeithL on Jun 10, 2022 16:44:35 GMT -5
I don't disagree at all.
Although I would add the exception that sometimes you don't always need or want to know all the details. For example I personally like to know what's going on with my audio gear... But, when I cook a steak, I generally settle for looking up how long to cook a steak of a given weight and thickness at a given temperature. I'm not going to spend hours taking multiple series of measurements at different depths and at different times...
(Although I do know at least one person who tracks the temperature of his grill with sensors and an app on his phone.)
In the case of audio I always make the distinction between wanting to learn and wanting to find an expedient solution. For example, sometimes it's simpler and quicker to ensure that a room is "acoustically symmetrical from left to right", than to actually measure it. So, if there's a tapestry on one wall, and a window on the opposite wall, I'm going to try drapes on the window (or moving the tapestry). Likewise, if the center channel dialog is somewhat muddled, and there's a bare floor in front of the listening position, I'm going to try a throw rug first. I happen to know the theory behind that... but it's not such an awful thing to take it as "an expert suggestion" either.
(I would only resort to taking dozens of measurements if I am unable to conveniently employ the simpler solution or it doesn't work for some reason.) (Also, to be blunt, based on my personality type, if I want to learn the finer details, I'll probably read a book rather than spending hours doing my own experiments.)
I absolutely applaud someone who wants to learn... But it's also possible to "dive so far down the rabbit hole that you spend too much time there"...
Or even "never find your way back out"... 
Interesting... but I sort of have to agree that you're somewhat "overthinking" the situation... A good start is to stop worrying about the graphs and think about how it sounds... and what you find problematic there... and how to fix it. Your goal is to have a room that sounds good... not to have one that measures good. (They may coincide... but you may also end up expending a lot of effort fixing things you can't hear.)
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+ ttocs 405x5 When I was in engineering school one of my classmates was ranting about why we had to study all the math and theory ... he was a long-time electronics hobbyist and he said "you just look that stuff up in a book". Another classmate responded "who do you think writes the books?" So sometimes we do measurements to gain a broader understanding and then correlate what we hear/perceive to the data. Sure, the shortest path to a solution might be to look for a similar situation and copy it. But you don't learn the fundamentals that way and you may not actually solve the problem. And, you miss gaining a broader understanding which cumulatively may help you solve some future problem. But then there is the immortal wisdom of some guy in some post I read on some forum somewhere, as he laughed at us and seriously said "Why measure what you can hear with your own two ears?"  |
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Post by leonski on Jun 10, 2022 20:46:34 GMT -5
During my career in semiconductor processing, I found it FAR more valuable to be able to find stuff out rather than just stuff my head with information. You can find out nearly anything if you know where to look... I only rarely remembered formulas. But did have a huge take on color / thickness relation of the commonly applied films. A good working knowledge and ability with shop math went further than you'd think.... I kept the 'Sand To Silicon' book at my desk. And would spend a few minutes weekly with one very forthcoming Phd who knew a LOT. This kind of stuff helped fill-in-the-gaps and made me better at my task. This 'pick and choose' was the most productive way to go. download.intel.com/newsroom/kits/chipmaking/pdfs/Sand-to-Silicon_32nm-Version.pdfthis intel publication is a FINE example. |
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Post by Jean Genie on Jun 11, 2022 11:21:46 GMT -5
Throughout my 40+ year career as a letter carrier, I had access to and enjoyed reading, on breaks & lunchtimes, many technical journals and magazines replete with obscure facts, jargon and references as varied as snowflakes and blades of grass, some of which I understood and many that were merely words on the page.
After work, I would go home and sit in my comfy chair and put an Allman Brothers or a Bela Fleck album on the stereo, and by the next day, I'd have forgotten all that useless information completely, my mind an empty vessel, eager to embrace the new day's bounty.🙌
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Post by 405x5 on Jun 11, 2022 11:46:25 GMT -5
Throughout my 40+ year career as a letter carrier, I had access to and enjoyed reading, on breaks & lunchtimes, many technical journals and magazines replete with obscure facts, jargon and references as varied as snowflakes and blades of grass, some of which I understood and many that were merely words on the page. After work, I would go home and sit in my comfy chair and put an Allman Brothers or a Bela Fleck album on the stereo, and by the next day, I'd have forgotten all that useless information completely, my mind an empty vessel, eager to embrace the new day's bounty.🙌 I disagree about “useless information” but I understand completely where you’re coming from. Here, (and most other forums I frequent) the “real” sound of the instruments that reach your ears gets run over by measurements and technical data. |
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Post by Jean Genie on Jun 11, 2022 12:03:34 GMT -5
Throughout my 40+ year career as a letter carrier, I had access to and enjoyed reading, on breaks & lunchtimes, many technical journals and magazines replete with obscure facts, jargon and references as varied as snowflakes and blades of grass, some of which I understood and many that were merely words on the page. After work, I would go home and sit in my comfy chair and put an Allman Brothers or a Bela Fleck album on the stereo, and by the next day, I'd have forgotten all that useless information completely, my mind an empty vessel, eager to embrace the new day's bounty.🙌 I disagree about “useless information” but I understand completely where you’re coming from. Here, (and most other forums I frequent) the “real” sound of the instruments that reach your ears gets run over by measurements and technical data. Point taken. I should have said useless "to me", since I've neither the knowledge, equipment nor inclination, not to mention the time, to measure or quantify what I hear and enjoy. |
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Post by monkumonku on Jun 11, 2022 12:52:32 GMT -5
Throughout my 40+ year career as a letter carrier, I had access to and enjoyed reading, on breaks & lunchtimes, many technical journals and magazines replete with obscure facts, jargon and references as varied as snowflakes and blades of grass, some of which I understood and many that were merely words on the page. After work, I would go home and sit in my comfy chair and put an Allman Brothers or a Bela Fleck album on the stereo, and by the next day, I'd have forgotten all that useless information completely, my mind an empty vessel, eager to embrace the new day's bounty.🙌 Just think, if you'd retained all that you could have been a star on Jeopardy! |
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Post by leonski on Jun 11, 2022 14:29:40 GMT -5
Throughout my 40+ year career as a letter carrier, I had access to and enjoyed reading, on breaks & lunchtimes, many technical journals and magazines replete with obscure facts, jargon and references as varied as snowflakes and blades of grass, some of which I understood and many that were merely words on the page. After work, I would go home and sit in my comfy chair and put an Allman Brothers or a Bela Fleck album on the stereo, and by the next day, I'd have forgotten all that useless information completely, my mind an empty vessel, eager to embrace the new day's bounty.🙌 Information is useless only until it is needed. Or perhaps corrolates with something Else.....Than stuff starts dropping into place and making sense.... For me? Patterns. |
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DYohn
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Post by DYohn on Jun 11, 2022 15:43:30 GMT -5
To paraphrase Einstein, "It is useless to memorize things when there are books."
To the OP: Just remember that there are "rules of thimb" for setting up audio and home theater systems showing a "proper" starting point for loudspaekr placement. But every installation is unique, and the rules of thumb only give you a starting place.
1. Install however you need to so it works for your installation
2. Adjust so it measures as well as possible in your installation
3. But above all, make it sound good to YOU. Nothing else matters.
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