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post #1 of 29 Old 08-29-2019, 09:17 AM - Thread Starter
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DIY speaker placement

All-

I posted over in the media room design sub-forum and it seems a bit more dead than the DIY guys. Since the speakers are all DIY, hopefully ya'll won't stone me for posting here for advice too!

This is what I shared with them:

My friend and I are building out his basement with the following DIY components:
LCR: Titan 615LX
Surround: Volt 10's
Atmos: Volt 10's
Subwoofer: dual full Marty's with UM18s

The atmos situation is pretty straightforward. There is already wiring in the ceiling from the previous install, and we will just move the holes to fit our needs. We will be doing the Volt 10's in an infinite baffle type setup.

I am more stuck with the positioning of the surround and surround back speakers.

Below are two images....one is a top-down view of the basement space (not entirely to scale...) Briefly, 15ft viewing distance for main seat. Atmos will be positioned based on Dolby recommendations. Ceiling is 9ft. LCR and sub will behind screen (acoustically transparent screen/wall) There are two doors on the viewer's left that makes it near impossible to mount the speakers at ear height. This is shown in the second picture.

Where would you position the surround channels? On the ceiling but angled down at listener? The wall to the right of the viewers is completely empty.
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post #2 of 29 Old 08-29-2019, 10:44 AM
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My first thought would be to use something like these mounted from the ceiling;
https://www.amazon.com/OmniMount-10-...45040647&psc=1

Don't know if these will support the weight of Volt 10's, but there are several sizes available.
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post #3 of 29 Old 08-29-2019, 11:02 AM - Thread Starter
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So a bracket solution. That could work pretty well.

However I think it's still likely to be mounted up higher on the wall rather than directly ear level. Same for the surround back speakers. How much of an impact do you think I would notice on soundstage performance?
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post #4 of 29 Old 08-29-2019, 11:57 AM
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Quote:
Originally Posted by mtnboydl View Post
Where would you position the surround channels? On the ceiling but angled down at listener?
The point of Atmos is to separate sounds around you versus sounds above you. Impossible to get that separation when the height speakers AND surround speakers are all mounted on the ceiling.

One solution would be do a 5.1 base layer with the Surrounds mounted on the side walls, just rearward of the stairs. If you're determined to do a 7.1 base layer, the Sides can go just forward of the equipment closet and the Rears in the back corners of the room.

For smoother bass response (fewer/smaller peaks & dips), consider moving the seating forward so that the listeners' ears end up 2/5 room length (13') from the front wall. The current seating position has the listeners right near the loudest peaks & deepest nulls of room length.

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post #5 of 29 Old 08-29-2019, 12:01 PM - Thread Starter
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Thank you. That's extremely helpful from a contextual standpoint.

We've considered the possibility of adding sound-deadening curtains to divide off the back of the long room where there is a bar top. Would bring things forward maybe 10ft (as far as a back wall is concerned)

How much impact would that have on the listening experience?
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post #6 of 29 Old 08-29-2019, 12:36 PM
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As sdurani mentioned, the issue with high mounted "bed" surround channels is the lack of separation. I would strongly suggest going ear height if you are doing 4 Atmos channels by their specs. I have 4 overheads dead on with Dolby specs and they do a good job enveloping you with ear height side and rear surrounds. If my surrounds were not at ear level, I could easily imagine the surround-effect being less......surrounding haha. More voice-of-god like.

The left surround seems like it could be mounted in the door and matching wall placement on the other side. If it's storage, that would be effectively as much IB as between studs in a wall. Maybe a custom door/shelf solution like a hidden door?

Once you settle on distance to screen for MLP, check the angle for your rear surrounds and see which gap in the walls are least compromised and angle them toward the MLP.

And for sound deadening curtains.......don't waste your time or money lol. They will do nothing for bass frequencies and make your rear area "dead" for frequencies that might actually benefit from some reflections (maybe someone else could back this up, my understanding of absorption for multichannel format is that too much can still be an issue). As I understand it, the front wall is the only one that should be considered for 100% coverage.
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post #7 of 29 Old 08-29-2019, 12:47 PM - Thread Starter
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When you say 100% coverage of the front wall, do you mean using something like rockwool to fill all of the spaces not occupied by the speakers?
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post #8 of 29 Old 08-29-2019, 01:09 PM
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And behind the speakers if not doing a baffle wall where the face of the speaker is flush with the wall. But generally, yes. I'm sure this isn't law of the land, but more for reference that the curtain at the rear probably isn't necessary or beneficial.
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post #9 of 29 Old 08-29-2019, 01:19 PM - Thread Starter
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Thanks for your input.

I told him with no uncertainty that we will need to do some sound treatments given his empty walls and echoes that exist in the basement now
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post #10 of 29 Old 08-29-2019, 05:15 PM
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Quote:
Originally Posted by mtnboydl View Post
We've considered the possibility of adding sound-deadening curtains to divide off the back of the long room where there is a bar top. Would bring things forward maybe 10ft (as far as a back wall is concerned)

How much impact would that have on the listening experience?
Curtains would have no effect on low frequencies, so it won't be like moving the back wall forward. Rather than attempting to change acoustics by shortening room length, easier to place the seating so that it is less affected by acoustical problems.

I'm sure you've blown across an empty bottle and made the air in that small chamber resonate (make that booooh sound). If you enlarge that small chamber to the size of your room, the air inside will still resonate (of course at different frequencies than the empty bottle). The 32-foot length of your room is going to result in resonances (room modes) at specific frequencies: 18Hz, 35Hz, 53Hz, 70Hz, 88Hz, 106Hz, etc. The first 4 of those length modes are mapped on the graph below:



Any number with Hz after it is a problem frequency. Each problem frequency is colour coded, so you can see the locations of its peaks & nulls. The other numbers are distances from the front wall.

Notice that the midpoint of room length (pretty close to the 15-foot distance you were planning on sitting) has the worst frequency response: everything is either peaking or nulling. Also notice that all the nulls are at even divisions (half, quarters, sixths) of room length. To avoid them, it's a good idea to place the listeners' ears at one of the odd divisions (thirds, fifths) of room length, where things aren't all-peaks and all-nulls. That's why I suggested putting the listeners at 13 feet from the front wall, because it was one of the odd divisions (2/5ths) of room length.

The smoother bass response will give a big head start to the room correction system in your receiver. And it's free (doesn't cost anything to move the seating a couple feet forward).
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post #11 of 29 Old 08-29-2019, 05:28 PM - Thread Starter
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Thank you for such spectacular advice. Very well explained.

So if we move the main listening position up two feet, I can put the surrounds directly to the left and right of the MLP at ear level (in between the two doors and on a bracket) and then position the surround backs somewhat further back and angled in although not directly behind the listener.

Moving to 13' also seems to require a decreased screen size of 135 over the previously planned 150. It would also mean that I would bring the LR channels in more narrow than originally planned. About a foot less to each side. Does that seem reasonable? Was sorta excited about a 150 screen, but don't want viewing fatigue. (I realize I'm asking this in the audio section...)
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post #12 of 29 Old 08-29-2019, 05:42 PM
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Quote:
Originally Posted by mtnboydl View Post
Thank you for such spectacular advice. Very well explained.

So if we move the main listening position up two feet, I can put the surrounds directly to the left and right of the MLP at ear level (in between the two doors and on a bracket) and then position the surround backs somewhat further back and angled in although not directly behind the listener.

Moving to 13' also seems to require a decreased screen size of 135 over the previously planned 150. It would also mean that I would bring the LR channels in more narrow than originally planned. About a foot less to each side. Does that seem reasonable? Was sorta excited about a 150 screen, but don't want viewing fatigue. (I realize I'm asking this in the audio section...)
Why would you need to decrease the screen size? Also I don't believe that the small changes, i.e. a foot would be that noticeable.

How about moving the left door to inside the cubby? That way you would have that whole wall to place the surround and maybe a cool absorption panel.
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post #13 of 29 Old 08-29-2019, 05:46 PM - Thread Starter
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That's a great question. I will check the next time I get over to his house on the door options.

By going down to a 135" screen, I was thinking I'd be closer to the THX spec of 36" view field. The THX spec seating distance would be 15ft so I was already stretching it to a 150" screen.

Am I thinking about that wrong?
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post #14 of 29 Old 08-29-2019, 08:15 PM - Thread Starter
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Quote:
Originally Posted by sdurani View Post
Quote:
Originally Posted by mtnboydl View Post
We've considered the possibility of adding sound-deadening curtains to divide off the back of the long room where there is a bar top. Would bring things forward maybe 10ft (as far as a back wall is concerned)

How much impact would that have on the listening experience?
Curtains would have no effect on low frequencies, so it won't be like moving the back wall forward. Rather than attempting to change acoustics by shortening room length, easier to place the seating so that it is less affected by acoustical problems.

I'm sure you've blown across an empty bottle and made the air in that small chamber resonate (make that booooh sound). If you enlarge that small chamber to the size of your room, the air inside will still resonate (of course at different frequencies than the empty bottle). The 32-foot length of your room is going to result in resonances (room modes) at specific frequencies: 18Hz, 35Hz, 53Hz, 70Hz, 88Hz, 106Hz, etc. The first 4 of those length modes are mapped on the graph below:



Any number with Hz after it is a problem frequency. Each problem frequency is colour coded, so you can see the locations of its peaks & nulls. The other numbers are distances from the front wall.

Notice that the midpoint of room length (pretty close to the 15-foot distance you were planning on sitting) has the worst frequency response: everything is either peaking or nulling. Also notice that all the nulls are at even divisions (half, quarters, sixths) of room length. To avoid them, it's a good idea to place the listeners' ears at one of the odd divisions (thirds, fifths) of room length, where things aren't all-peaks and all-nulls. That's why I suggested putting the listeners at 13 feet from the front wall, because it was one of the odd divisions (2/5ths) of room length.

The smoother bass response will give a big head start to the room correction system in your receiver. And it's free (doesn't cost anything to move the seating a couple feet forward).
Since your message I've spent some time reading about modes and nulls. It's a fascinating concept that makes sense but was not on my radar at all.

One of the longer articles also talked about LCR positioning and how it affects the size of the sweet spot for imaging. Does Dolby's recommended 22-30 deg angle spread to the listening position match that consideration? I sort of had a rudimentary understanding years ago that your distance to the screen was essentially equivalent to the distance between the left and right channels.
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post #15 of 29 Old 08-30-2019, 08:49 AM
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Quote:
Originally Posted by mtnboydl View Post
So if we move the main listening position up two feet, I can put the surrounds directly to the left and right of the MLP at ear level (in between the two doors and on a bracket) and then position the surround backs somewhat further back and angled in although not directly behind the listener.
I prefer the Sides a little forward of my seating position, so in your room I would put them at the front edge of the equipment closet door. The rears would go just rearward of the stairs.
Quote:
Moving to 13' also seems to require a decreased screen size of 135 over the previously planned 150. It would also mean that I would bring the LR channels in more narrow than originally planned. About a foot less to each side. Does that seem reasonable? Was sorta excited about a 150 screen, but don't want viewing fatigue. (I realize I'm asking this in the audio section...)
If you sit at the sweet spot of a typical movie theatre, roughly 2/3 back form the screen, you'll have a 45° viewing angle. Your planned 150" screen from 15' away would give you a 40° viewing angle. To get that same 40° viewing angle from 13' away would require a 130" screen. So, using a 135" screen will give you a bigger image than what you would have seen with your planned 150" screen from 15' away. Let's not confuse screen size with image size.

The THX recommendation of 36° is for the very back row of a movie theatre (i.e., the minimum viewing angle, NOT the recommended viewing angle). In this day and age of high def, I would have at least a 50° viewing angle. Won't be fatiguing at all.
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post #16 of 29 Old 08-30-2019, 09:02 AM
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Originally Posted by mtnboydl View Post
One of the longer articles also talked about LCR positioning and how it affects the size of the sweet spot for imaging. Does Dolby's recommended 22-30 deg angle spread to the listening position match that consideration?
Different folks have different priorities when considering L/C/R placement. Some place the speakers to get the soundstage width they want. Others place the speakers for mode cancelling (i.e., minimizing peaks & nulls across the width of the room/seating). Dolby's recommended range reflects the L/R spread in movie theatres (45°) and for typical home stereo layouts (60°).
Quote:
I sort of had a rudimentary understanding years ago that your distance to the screen was essentially equivalent to the distance between the left and right channels.
Not sure what you get from that, except a 53° spread between the L/R speakers.

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post #17 of 29 Old 08-30-2019, 09:26 AM - Thread Starter
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Originally Posted by mtnboydl View Post
One of the longer articles also talked about LCR positioning and how it affects the size of the sweet spot for imaging. Does Dolby's recommended 22-30 deg angle spread to the listening position match that consideration?
Different folks have different priorities when considering L/C/R placement. Some place the speakers to get the soundstage width they want. Others place the speakers for mode cancelling (i.e., minimizing peaks & nulls across the width of the room/seating). Dolby's recommended range reflects the L/R spread in movie theatres (45Â&#176 and for typical home stereo layouts (60Â&#176.
Quote:
I sort of had a rudimentary understanding years ago that your distance to the screen was essentially equivalent to the distance between the left and right channels.
Not sure what you get from that, except a 53° spread between the L/R speakers.
If I'm crossing the Titans at 60hz, most of the nulls will be subwoofer sensitive (right?) because of the shorter wavelengths with higher frequencies. Having two subs will also smooth that out somewhat.

Should I get a mic and do some angle/width adjustments once things are all assembled?

Looks like a 150" screen at 13' is under your suggested 50deg angle, so I'll stay with 150.
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post #18 of 29 Old 08-30-2019, 12:04 PM
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If I'm crossing the Titans at 60hz, most of the nulls will be subwoofer sensitive (right?) because of the shorter wavelengths with higher frequencies. Having two subs will also smooth that out somewhat.
Your 17'9" is room width is going to result in width modes at 32Hz, 64Hz, 95Hz, 127Hz, 159Hz, 191Hz, etc. See graph below for locations of the peaks & nulls for the first 4 of those problem frequencies.



When looking at the graph, imagine the width of your couch superimposed on the middle 7 or 8 feet (or however wide your couch is). Some listeners will be sitting in loud peaks while other listeners will be sitting in deep nulls. To address length modes, the couch could be moved away from the midpoint of room length (where frequency response is worst) to a location where the peaks & dips were less intense. Can't use that approach to address width modes because the midpoint of room width (where frequency response is worst) happens to be the money seat. So have to use a different approach, one that actively cancels the width modes.

The locations of the modal peaks & nulls are fixed (which is why room modes are sometimes called standing waves), but their intensity can be changed by placing the sources of bass (subs & speakers) at null locations, which will prevent modes from resonating. IF you decide to place your 2 subs and 3 front speakers for mode cancelling, here are the nulls to place them in:

Centre the subs at 1/4 room width in from the side walls.



Centre the woofers of L/R speakers at 1/6 room width in from the side walls. Centre speaker at the midpoint of room width.



Should minimize the peaks & nulls of first 5 width modes (32Hz, 64Hz, 95Hz, 127Hz, 159Hz), resulting in smoother bass response AND greater consistency across the seating area. Again, it's free (placement doesn't cost anything). I would cross over the L/C/R speakers to the subs at 80Hz, so that the 64Hz width mode is cancelled mostly with the subs rather than the speakers.
Quote:
Looks like a 150" screen at 13' is under your suggested 50deg angle, so I'll stay with 150.
IF you decide to place your L/R speakers in the above locations, they will be spread 142" apart (centre of woofer to centre of woofer). A 150" screen is 131" wide. So the speakers will end up just outside the screen. You might need to shrink the screen size by a few inches to accommodate the speaker cabinets.
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post #19 of 29 Old 09-26-2019, 03:59 PM
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All great advice!

I’ve been studying acoustics and theory and have a mode question that has been on my mind.

Where should membrane type bass traps be placed when width and/or length room modes are the target.

Let’s just use the OP room and dry carbon membrane traps with tuning around 32hz and the other tuned to 64hz. Where would be optimal placement of said traps? These type of traps have the best results when dealing with low frequencies so have wanted to find optimal ways to use them even though I doubt the above scenario wouldn’t be the best case to use as an example.


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post #20 of 29 Old 09-26-2019, 04:51 PM
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All great advice!

I’ve been studying acoustics and theory and have a mode question that has been on my mind.

Where should membrane type bass traps be placed when width and/or length room modes are the target.

Let’s just use the OP room and dry carbon membrane traps with tuning around 32hz and the other tuned to 64hz. Where would be optimal placement of said traps? These type of traps have the best results when dealing with low frequencies so have wanted to find optimal ways to use them even though I doubt the above scenario wouldn’t be the best case to use as an example.


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Place the traps on the walls. Put them on short walls for length modes, and on the long walls for width modes.

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post #21 of 29 Old 09-26-2019, 05:10 PM
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Let’s just use the OP room and dry carbon membrane traps with tuning around 32hz and the other tuned to 64hz. Where would be optimal placement of said traps?
Both are width modes, so place the membrane traps on the side walls.
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post #22 of 29 Old 10-13-2019, 07:30 PM
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DIY speaker placement

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Originally Posted by Augerhandle View Post
Place the traps on the walls. Put them on short walls for length modes, and on the long walls for width modes.
And @sdurani

Right I get the basic idea just concerned with exact placement locations for optimal efficiency. Say for the mode that is the null in the dead center which shows it at the top of the wall intersection, should that trap which is spec’ed for that frequency range be placed at the wall intersection up near the ceiling for optimal performance? Then follow that basic principle on all walls at the point of where the mode trace line is meeting the wall? That is my thinking but just can’t find it actually laid out in such simple terms in any book/white paper etc....


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post #23 of 29 Old 10-14-2019, 08:34 AM
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Anywhere on the side walls would be fine. At those low frequencies, we're talking about pressure against the side walls. If the trap is tuned for a specific range, it won't help to place them in corners unless the length or height modes have modes in the same range.

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post #24 of 29 Old 10-30-2019, 01:39 PM
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@sdurani where did you plot those graphs from?

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post #25 of 29 Old 10-30-2019, 01:49 PM
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What goes in the cubby? If you can get away with a speaker that overhangs the corner a bit, you'd be set mounting it on-wall with a french cleat.

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post #26 of 29 Old 10-30-2019, 02:10 PM
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@sdurani where did you plot those graphs from?
Harman room mode calculator (free download).

https://www.harman.com/room-mode-calculator

Added arrows in MS Paint.

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post #27 of 29 Old 11-05-2019, 09:28 PM
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Originally Posted by sdurani View Post
Harman room mode calculator (free download).

https://www.harman.com/room-mode-calculator

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THANK YOU!

I am not sure how well it works for "open floor plan" rooms but perhaps it will give me a starting point so I know what to look for.

How many Db change am I looking for when manually trying to find a null, or peak in my room?

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post #28 of 29 Old 11-06-2019, 11:13 AM
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Originally Posted by kagtha View Post
I am not sure how well it works for "open floor plan" rooms but perhaps it will give me a starting point so I know what to look for.
It's designed to calculate room modes between parallel walls.
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How many Db change am I looking for when manually trying to find a null, or peak in my room?
There is no dB scale on the calculator. When you look at the graphs, those are not so much acoustical peaks & nulls but more a graph of coupling functions: how strongly the source of bass couples with the room mode. If the source of bass (subwoofer or speaker) is placed at a peak location, it will couple strongly with that particular room mode (loud peaks, quiet nulls). If you put the source of bass in a null location, it won't couple with that room mode at all (that mode won't be energized, so that frequency won't have any peaks or nulls).

What do you mean "manually" trying to find a null or peak?
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post #29 of 29 Old 11-07-2019, 08:40 PM
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Well that makes a little more sense. I was considering walking around with a DB meter to see how certain frequencies behave but it looks like an impossible mission for a genius like me considering my area has some 20 more walls than an enclosed room.

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