Room Modes

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Abby72

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Room Modes
« on: 7 Oct 2021, 02:48 pm »
I'm hoping for a bit of help understanding them room Modes/ Waves of my room. I'm posting the reading for my room and need help understanding the data. For example, considering the width of my room if I was trying to clean up the null between the 2nd and 3rd axial standing wave, would I want to place my speaker between the 2nd and 3rd (red and black) or avoid that area? To make matters a bit more confusing I running magnepan 3.7i's and a pair of svs sb3000 subs in this room ( 9' ceiling, 13', 8" width, 43' length ).




JLM

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Re: Room Modes
« Reply #1 on: 8 Oct 2021, 11:39 am »
Where are the Maggies and SVS's placed in the room?  And where is the primary listening position?  What is/are your listening complaint(s)?  Have you tried any (effective) absorption treatments?  Your room is very long, would expect it to behave more like a tunnel than a room (similar to the vastly under appreciated issue in most floor standing box loudspeakers).

Tyson

Re: Room Modes
« Reply #2 on: 8 Oct 2021, 02:44 pm »
You can predict or you can just measure.  Nowadays it's easy to download an FFT app on your phone, play some full range pink noise through your speakers and simply walk around the room with your phone.  It'll tell you exactly where there are issues with your room and give you a better idea of where the ideal locations are for your speakers and subs. 

Are your subs placed in the front corners behind your speakers?  If so then that's a problem (usually).  If you want to stick with box subs, then you should buy 2 more subs and place one along a side wall and one along the back wall (not in corners).  That will give you a nice 'swarm' approach that will even out your room nodes.

The other option is to sell the SVS subs and get a pair of Servo OB subs to replace them.  That's the approach I would recommend.  You still get a pair of them and you place them as close to the main speakers as possible (NOT in corners).  Because they are OB, they have 2 advantages over box subs.  First, they don't excite room modes in the same way that box speakers do, so you have much faster and more detailed bass.  Second, because they are OB, they match the radiation pattern of your main speakers, making integration with them MUCH easier and more seamless. 

youngho

Re: Room Modes
« Reply #3 on: 8 Oct 2021, 03:35 pm »
I don't know what you mean by "For example, considering the width of my room if I was trying to clean up the null between the 2nd and 3rd axial standing wave, would I want to place my speaker between the 2nd and 3rd (red and black) or avoid that area?" I wonder if you're not thinking about it correctly.

The sidewalls result in standing wave (mode) formation. The first-order width mode is 41 Hz, so if a sound source "drives" this mode (maximally so if if the source is at a sidewall), then a listener positioned in the midline of the room will experience a null or relative suckout at this frequency. However, if the sound source is placed in the midline of the room, then it will not energize this mode. Alternatively, instead of moving the sound source, if a second sound source is placed on the opposite sidewall, then it will cancel out this mode. The tops of the curves are the antinodes, so sound sources placed at these locations will energize the modes, unless they're cancelled, and listeners placed at these locations will experience the maximal boost, so to speak, of the mode. The bottom "rebound"-looking parts are the nodes, so listeners at these locations will experience the most null or suckout, and sound sources at these locations will not activate the mode.

The second-order width mode is 83 Hz. A listener placed in the midline of the room will experience a peak at this frequency if the mode is driven. Unless the listener moves to the side of the midline, they will not experience a null, but they certainly would if they moved 3.375 feet to the side. Are you trying to "clean up" this null at such locations? If so, move the sound sources (I don't know where you have your crossover set) for this frequency so that they're approximately 1/4 of the way from the side walls. This would reduce variation of the frequency response curve at this frequency for listening positions both at and lateral of midline.

Etc for the third-order width mode, but if you're using dipole planar speakers, they tend to radiate much less sound to the sides, so they're probably not energizing this mode as much as a conventional speaker would, so you may not need to be concerned, anyway.

Nsm1979

Re: Room Modes
« Reply #4 on: 8 Oct 2021, 03:52 pm »
Requesting a little more clarification from Tyson on his post.

In regards to placement of the open baffle subs being as close as possible to the Magnapans, is the recommendation to place the subs to the side of the main speakers and keep the voice coils of the subs aligned with the drivers of the main speakers?  Is there a preference to put the subs inside or outside the main speakers?  With the sound wave cancelling at the edges of open baffle designs, is it less of an issue to place the subs near the sidewall, as long as they are pulled out from the front wall?

Tyson

Re: Room Modes
« Reply #5 on: 8 Oct 2021, 08:08 pm »
Sure thing.  The Servo OB subs I'm referencing are the GR Research subs, IMO the very best subs on the market.  I run planar OB speakers downstairs and the servo OB sub integration is the best I've heard. 

You are exactly right - the figure 8 radiation pattern of OB speakers (and subs) allows them to be placed next to each other with less interference.  Personally I think that the subs sitting 'almost' in line with the outside edge of the speakers (but every so slightly behind) is best, because it gives you better imaging from the main speakers while still integrating the bass wave launch with the main speaker location.  But the nice thing is this - you can play around with them and see what you like best in your room.  As long as the subs are at least 3 feet off the front wall, you are fine.  Side wall interactions are pretty much null.

Here's the problem with the Maggies, they are so fast and so clean and so detailed it is almost impossible for a regular sub to keep up with them.  I ran into this problem myself before I had my current setup.  It's really nice to have subs in my setup (the servo OB subs) that are just as blazing fast and detailed as my planar OB sections in my speakers. 

Don't get me wrong, I don't hate box subs, but rather I think they are a good match for box speakers.  And the servo OB subs are the best match for OB speakers, particularly ones that are at a reference level like Maggies. 

WGH

Re: Room Modes
« Reply #6 on: 8 Oct 2021, 10:12 pm »
I have heard Magnepan 3.7i's with the REL Gibraltar G2 sub (discontinued) and it is definitely fast enough to keep up, that is why I bought one. Generally speaking most people who buy REL subs without talking to the factory first end up buying one size too small for their room. REL customer support is always very friendly and knowledgeable because all they do is subs.

I'm partial to the Reference Series because the handheld remote allows you to fine tune the crossover frequency and volume in 1 dB increments without getting up, great for 1950's jazz recordings with no bass or modern pop with too much bass.

https://rel.net

From reviews I have read REL subs are faster and better for music; SVS are great for home theater.


WGH

Re: Room Modes
« Reply #7 on: 9 Oct 2021, 06:48 pm »
The papers by Floyd E. Toole, Ph.D., Vice President of Acoustical Engineering at Harman International Industries will help you interpret the room mode graph.

Part 2 of "Maximizing Loudspeaker Performance in Rooms" has detailed information about the Room Mode Calculator

https://www.audiocircle.com/index.php?topic=58304.0

Abby72

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  • Posts: 6
Re: Room Modes
« Reply #8 on: 12 Oct 2021, 12:16 pm »
Where are the Maggies and SVS's placed in the room?  And where is the primary listening position?  What is/are your listening complaint(s)?  Have you tried any (effective) absorption treatments?  Your room is very long, would expect it to behave more like a tunnel than a room (similar to the vastly under appreciated issue in most floor standing box loudspeakers).

I apologize about the delayed response on my end, I took a few days off for my birthday. My room is a bit odd, so let me try to explain. The length of the primary room is 21' and than 1 step up it opens up to a 22' long kitchen area, thus the 43' length calculation to the back wall. Also the ceiling height in the primary room is 9' but once we get to that kitchen area the ceiling opens up to 18'. Right now I have the maggies out 5'4" from the front wall, and 2' from the side walls. I have my subs on risers placed in-board about 8" to the side of the maggies . I'm running bass traps in the corners and in the center I have diffusion panels.

I do have a listening chair about 11' from the front speakers, but my wife and I do most of our non-critical listening in the kitchen area which is located 33' from the front wall. I guess I'm shooting for a balance between these two listening spots, rather than just perfection at 1 spot. I started playing with the room mode calculator and it lead to a bit more confusion than I had anticipated. I do have a laptop running REW and taken a few measurements, which wern't all that bad. I will post up a pic of the primary listening room even though things are a bit of a mess.




Tyson

Re: Room Modes
« Reply #9 on: 12 Oct 2021, 02:46 pm »
With that setup you definitely should switch out the SVS subs for some servo OB subs.  It will give you much cleaner (and better) bass.

Abby72

  • Jr. Member
  • Posts: 6
Re: Room Modes
« Reply #10 on: 12 Oct 2021, 06:14 pm »
You can predict or you can just measure.  Nowadays it's easy to download an FFT app on your phone, play some full range pink noise through your speakers and simply walk around the room with your phone.  It'll tell you exactly where there are issues with your room and give you a better idea of where the ideal locations are for your speakers and subs. 

Are your subs placed in the front corners behind your speakers?  If so then that's a problem (usually).  If you want to stick with box subs, then you should buy 2 more subs and place one along a side wall and one along the back wall (not in corners).  That will give you a nice 'swarm' approach that will even out your room nodes.

The other option is to sell the SVS subs and get a pair of Servo OB subs to replace them.  That's the approach I would recommend.  You still get a pair of them and you place them as close to the main speakers as possible (NOT in corners).  Because they are OB, they have 2 advantages over box subs.  First, they don't excite room modes in the same way that box speakers do, so you have much faster and more detailed bass.  Second, because they are OB, they match the radiation pattern of your main speakers, making integration with them MUCH easier and more seamless.

I really appreciate your info on the OB subs. I thought about them prior to buying the pair of svs, but at that time I had the Magnepan .7's and I was not sure how that was going to work out, and opted to play it safe $$$$ to start. I've had a few issues with my svs subs/ 2 plate amps replaced and now they are sending me out a new sub which has me thinking about selling the pair and upgrading. Big bonus if the OB wont excite the room nodes, but will they hit near as hard and low as the svs I have now? Rythmik and GR is what I should be looking at, or are there others?

Tyson

Re: Room Modes
« Reply #11 on: 12 Oct 2021, 08:15 pm »
The GR Research are the ones I'm referring too.  And yes, they hit very hard and they go very low.  In some ways, they hit even harder than the SVS subs. 

Here's the physics of it - your main speakers are radiating sound in a figure 8 pattern because they are OB. But your SVS subs are radiating sound like a pulsing sphere.  So your bass will never match up very well to your speakers, not matter how good the subs.  Box subs will always produce bass that sounds slow and bloated when trying to pair with OB main speakers. 

On the other hand, OB subs match up perfectly because they radiate sound in a figure 8 pattern too.  Plus, they don't excite room modes nearly as much (particulalry the side to side room modes) so you naturally end up with less boomy and cleaner bass.

But, how hard do they hit?  OK, I have a confession to make.  I'm a bit of a bass head.  I know that might lose me some audiophile cred, but there it is.  To me, bass is the foundation of all music and I'm simply not interested in a speaker or system that can do bass really, really well.  I had heard OB bass before GR Research came out with their Servo OB solution.  And I'm sorry but most OB bass systems suck.  They are nicely detailed and clean but they are seriously lacking in impact and punch. 

So when I first heard the GR Research Servo OB subs I was stunned because those things freaking punch you in the chest.  They are monsters in that respect.  And they go deep (20 hz in my room, flat).  And they still have all the traditional strengths of OB bass (clean, detailed, fast).  These things have literally no weaknesses.  And for a bass-snob like me, that's incredibly impressive. 

Cheytak.408

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Re: Room Modes
« Reply #12 on: 12 Oct 2021, 11:05 pm »
The GR Research are the ones I'm referring too.  And yes, they hit very hard and they go very low.  In some ways, they hit even harder than the SVS subs. 

Here's the physics of it - your main speakers are radiating sound in a figure 8 pattern because they are OB. But your SVS subs are radiating sound like a pulsing sphere.  So your bass will never match up very well to your speakers, not matter how good the subs.  Box subs will always produce bass that sounds slow and bloated when trying to pair with OB main speakers. 

On the other hand, OB subs match up perfectly because they radiate sound in a figure 8 pattern too.  Plus, they don't excite room modes nearly as much (particulalry the side to side room modes) so you naturally end up with less boomy and cleaner bass.

But, how hard do they hit?  OK, I have a confession to make.  I'm a bit of a bass head.  I know that might lose me some audiophile cred, but there it is.  To me, bass is the foundation of all music and I'm simply not interested in a speaker or system that can do bass really, really well.  I had heard OB bass before GR Research came out with their Servo OB solution.  And I'm sorry but most OB bass systems suck.  They are nicely detailed and clean but they are seriously lacking in impact and punch. 

So when I first heard the GR Research Servo OB subs I was stunned because those things freaking punch you in the chest.  They are monsters in that respect.  And they go deep (20 hz in my room, flat).  And they still have all the traditional strengths of OB bass (clean, detailed, fast).  These things have literally no weaknesses.  And for a bass-snob like me, that's incredibly impressive.
Oh, yeah!   :thumb:

Abby72

  • Jr. Member
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Re: Room Modes
« Reply #13 on: 13 Oct 2021, 11:38 am »
The GR Research are the ones I'm referring too.  And yes, they hit very hard and they go very low.  In some ways, they hit even harder than the SVS subs. 

Here's the physics of it - your main speakers are radiating sound in a figure 8 pattern because they are OB. But your SVS subs are radiating sound like a pulsing sphere.  So your bass will never match up very well to your speakers, not matter how good the subs.  Box subs will always produce bass that sounds slow and bloated when trying to pair with OB main speakers. 

On the other hand, OB subs match up perfectly because they radiate sound in a figure 8 pattern too.  Plus, they don't excite room modes nearly as much (particulalry the side to side room modes) so you naturally end up with less boomy and cleaner bass.

But, how hard do they hit?  OK, I have a confession to make.  I'm a bit of a bass head.  I know that might lose me some audiophile cred, but there it is.  To me, bass is the foundation of all music and I'm simply not interested in a speaker or system that can do bass really, really well.  I had heard OB bass before GR Research came out with their Servo OB solution.  And I'm sorry but most OB bass systems suck.  They are nicely detailed and clean but they are seriously lacking in impact and punch. 

So when I first heard the GR Research Servo OB subs I was stunned because those things freaking punch you in the chest.  They are monsters in that respect.  And they go deep (20 hz in my room, flat).  And they still have all the traditional strengths of OB bass (clean, detailed, fast).  These things have literally no weaknesses.  And for a bass-snob like me, that's incredibly impressive.

Great info, however I wish there was a simpler solution, as I'm not much of a carpenter. It looks like OCD HI-Fi Guy was going to put together a kit prebuilt but that was almost a year ago and I do not see him offering them up for purchase on his website.  :scratch:

Tyson

Re: Room Modes
« Reply #14 on: 13 Oct 2021, 02:54 pm »
There's probably a few people over on the GR Research circle that might be willing to do a build for you.  If not, there's very simple/easy flat packs you can order and then just have someone local (a woodworker or other skilled handyman type) assemble them for you.  An H-frame assembly should be very simple.  And it looks like your main speakers are black, so I'm guessing you'd just paint the subs black to match, again that's very easy for anyone local to you with even minimal skills/experience. 

It's a little more of a hassle doing it this way but that's the only way to get this level of performance for a reasonable cost.  If they were made commercially available (finished), they'd cost at least 3x what they do now.  Ouch. 

Abby72

  • Jr. Member
  • Posts: 6
Re: Room Modes
« Reply #15 on: 13 Oct 2021, 05:27 pm »
I don't know what you mean by "For example, considering the width of my room if I was trying to clean up the null between the 2nd and 3rd axial standing wave, would I want to place my speaker between the 2nd and 3rd (red and black) or avoid that area?" I wonder if you're not thinking about it correctly.

The sidewalls result in standing wave (mode) formation. The first-order width mode is 41 Hz, so if a sound source "drives" this mode (maximally so if if the source is at a sidewall), then a listener positioned in the midline of the room will experience a null or relative suckout at this frequency. However, if the sound source is placed in the midline of the room, then it will not energize this mode. Alternatively, instead of moving the sound source, if a second sound source is placed on the opposite sidewall, then it will cancel out this mode. The tops of the curves are the antinodes, so sound sources placed at these locations will energize the modes, unless they're cancelled, and listeners placed at these locations will experience the maximal boost, so to speak, of the mode. The bottom "rebound"-looking parts are the nodes, so listeners at these locations will experience the most null or suckout, and sound sources at these locations will not activate the mode.

The second-order width mode is 83 Hz. A listener placed in the midline of the room will experience a peak at this frequency if the mode is driven. Unless the listener moves to the side of the midline, they will not experience a null, but they certainly would if they moved 3.375 feet to the side. Are you trying to "clean up" this null at such locations? If so, move the sound sources (I don't know where you have your crossover set) for this frequency so that they're approximately 1/4 of the way from the side walls. This would reduce variation of the frequency response curve at this frequency for listening positions both at and lateral of midline.

Etc for the third-order width mode, but if you're using dipole planar speakers, they tend to radiate much less sound to the sides, so they're probably not energizing this mode as much as a conventional speaker would, so you may not need to be concerned, anyway.

Yes, I believe I was thinking of things a bit wrong. Your comment "Alternatively, instead of moving the sound source, if a second sound source is placed on the opposite sidewall, then it will cancel out this mode." This is what I was trying to understand. I was not sure to place speakers on a certain node point in the room or not, but I guess that all depends if I'm getting a null or not. Not sure if I explained my understanding of that correctly, but I believe it makes sense in my mind.

And this is very informative... "Unless the listener moves to the side of the midline, they will not experience a null, but they certainly would if they moved 3.375 feet to the side. Are you trying to "clean up" this null at such locations? If so, move the sound sources (I don't know where you have your crossover set) for this frequency so that they're approximately 1/4 of the way from the side walls. This would reduce variation of the frequency response curve at this frequency for listening positions both at and lateral of midline."

Thank you for your help!

youngho

Re: Room Modes
« Reply #16 on: 13 Oct 2021, 11:13 pm »
Yes, I believe I was thinking of things a bit wrong. Your comment "Alternatively, instead of moving the sound source, if a second sound source is placed on the opposite sidewall, then it will cancel out this mode." This is what I was trying to understand. I was not sure to place speakers on a certain node point in the room or not, but I guess that all depends if I'm getting a null or not. Not sure if I explained my understanding of that correctly, but I believe it makes sense in my mind.

I only have a very basic understanding of modes and standing waves, but I'm happy to try to help further, if you'd like.

Quote
And this is very informative... "Unless the listener moves to the side of the midline, they will not experience a null, but they certainly would if they moved 3.375 feet to the side. Are you trying to "clean up" this null at such locations? If so, move the sound sources (I don't know where you have your crossover set) for this frequency so that they're approximately 1/4 of the way from the side walls. This would reduce variation of the frequency response curve at this frequency for listening positions both at and lateral of midline."

Thank you for your help!

I don't believe that there are many commercial dipole subwoofers readily available. You could possibly consider the Magnepan DWM or one of the Gradient Quad subwoofer units that occasionally come up on the used market from time to time.