Room Acoustics - Absorption Panels Behind ML's

MartinLogan Owners (MLO)

Help Support MartinLogan Owners (MLO):

bikerneil

Well-known member
Joined
Mar 3, 2011
Messages
88
Reaction score
7
Location
Carlsbad, CA
I have read much on this site about the importance of acoustic treatments of a room and how one can often make considerable improvements by making some simple changes.

I currently have ML Source electrostatics (and I am soon upgrading to a pair of Montis for my room). I have spent hours dialing in the position of my speakers to optimize sound stage & imaging and I am very happy with my current setup. The changes I made in position and toe-in have done wondrous things to improve the sound and imaging in my room. Based upon lots of reading on this site (and others) I am considering adding two absorption panels behind my ML's.

Some other info on my room:
- Room is 13' wide X 15' deep X 10' ceiling
- I cannot move speakers farther apart (due to room constraints near speakers)
- I currently have face of speakers about 30" from front wall (I used Martin Logan setup guide)

My current setup is shown below:
Current setup.jpg

I am considering adding a 2' X 2' sound absorption panel on the wall directly behind each of my two ML's.

The new setup would look something like this rendering (see the 2 black squares that I edited in to the pic):
Acoustic Treatment Final.jpg

I have a few questions for the experts and more experienced folks on this forum:

1. Would the addition of these absorption panels further improve the sound and imaging from my setup?

2. You will note that I have to keep the panels down near the floor, is this location too low to help my setup?

3. In theory, how does such a change work?

4. Last but not least, it sounds like acoustic treatments are 50% science, and 50% art. Is the change I am considering a "slam-dunk" to improve my sound or is it 50 / 50 as to whether it will make any change or improvement?

I love this forum and I look forward to hearing from some of the experts.

Thanks!
 
Last edited:

sleepysurf

Well-known member
Joined
Jan 11, 2005
Messages
2,564
Reaction score
38
Location
Tampa, FL
Unfortunately, those low panels would probably WORSEN the Montis soundstage (interacting with only the lower half of the panel, thus creating a non-uniform back wave). Given your room layout, it would be better to just place the Montis so the panel is at least 40" (if not more) from the front wall, so the reflected back wave doesn't "smear" the image.
 

Rich

Super Moderator
Moderator
Joined
Jul 8, 2006
Messages
4,138
Reaction score
2
Location
Huntsville, Alabama
I have used both absorption and diffusion behind my panels at different times. Here are my thoughts. If you can't get the panels more than three feet away from the wall, absorption is the way to go. If you can get them four to five feet away, then diffusion is the way to go. Absorption will give you an increase in clarity and precise imaging but flatten the soundstage. Diffusion will give you a wider and deeper soundstage, but imaging won't be as pinpoint precise. Neither is inherently "better." They are just different. The acoustic space sounds more natural with diffusion but the crystal clarity and pinpoint imaging with absorption is pretty cool.

Here's the thing, though. You have to absorb or diffuse the entire back wave of the speaker panel. So you need a panel that is as tall as the speaker panel and is directly behind it on the wall. You also need a panel that can absorb the entire frequency range of the speaker panel, down to about 500 hz., and not just the higher frequencies, for it to be truly effective. This generally means a panel that is about three to four inches in thickness.

The way you have it shown in your illustration would be entirely ineffective, as they are not set up to really absorb any of the back wave from the panel. The wall is still going to reflect that back wave to the listener and that is going to impair your clarity and imaging because there isn't enough lag time between the front wave and the rear wave reflection for your brain to distinguish them. Worse, because this rear wave adds to the total volume levels, you actually have to listen at a lower volume or it sounds too loud and harsh. So you are listening at a lower volume to muddied sound. This is bad for imaging and also for being able to hear all those wonderful details that electrostats are so good at providing. Proper absorption behind the panels will make a huge difference in the quality of your sound.

You may want to consider buying some 2'x4' absorption panels and hide them in a closet when you aren't using them, and then bring them out and lean them against the wall behind the speakers whenever you want to listen critically. This way you don't have to look at them all the time, but you have the ability to use them when you really want to.

Here is a bonus thought. I have also found that plopping down a 2'x4' absorption panel on its side in front of the rack (between the speakers and facing the listener) makes for a huge improvement in the sound, giving a much blacker background and improving imaging and sound staging. I have an 8' wide rack, so I actually use two bass traps for this purpose. I don't leave them there all the time. I just put them in place when I want to listen critically.
 

bikerneil

Well-known member
Joined
Mar 3, 2011
Messages
88
Reaction score
7
Location
Carlsbad, CA
Thank you both for the very detailed answers. I obviously will not proceed with my plan for 2X2 panels below my window. (But, I will look for a way to hang a 2X4 absorption panel behind my speakers when I am in the room by myself, or whenever the wife will allow.....)

Thanks!

bikerneil
 

GW1800

Well-known member
Joined
Sep 3, 2011
Messages
327
Reaction score
14
Location
WI
I have read much on this site about the importance of acoustic treatments of a room and how one can often make considerable improvements by making some simple changes.

I currently have ML Source electrostatics (and I am soon upgrading to a pair of Montis for my room). I have spent hours dialing in the position of my speakers to optimize sound stage & imaging and I am very happy with my current setup. The changes I made in position and toe-in have done wondrous things to improve the sound and imaging in my room. Based upon lots of reading on this site (and others) I am considering adding two absorption panels behind my ML's.

Some other info on my room:
- Room is 13' wide X 15' deep X 10' ceiling
- I cannot move speakers farther apart (due to room constraints near speakers)
- I currently have face of speakers about 30" from front wall (I used Martin Logan setup guide)

My current setup is shown below:
View attachment 18514

I am considering adding a 2' X 2' sound absorption panel on the wall directly behind each of my two ML's.

The new setup would look something like this rendering (see the 2 black squares that I edited in to the pic):
View attachment 18515

I have a few questions for the experts and more experienced folks on this forum:

1. Would the addition of these absorption panels further improve the sound and imaging from my setup?

2. You will note that I have to keep the panels down near the floor, is this location too low to help my setup?

3. In theory, how does such a change work?

4. Last but not least, it sounds like acoustic treatments are 50% science, and 50% art. Is the change I am considering a "slam-dunk" to improve my sound or is it 50 / 50 as to whether it will make any change or improvement?

I love this forum and I look forward to hearing from some of the experts.

Thanks!
I may have a few suggestions but your room with the windows make doing something difficult. I agree with pretty much everything that Rich has suggested with one change. I have found that RPG BAD ARC to be superior product. This sound panel does both absorb and diffuse with a unique arc shape. My system is only 2' away and it helped tremendously. I also agree with Rich that you need to cover the whole panel from behind to get the results that are needed. You also need to address the first reflection points on the side walls. If you have I did not see that mentioned?
 
Last edited:

Norway84

Banned
Joined
Jan 1, 2016
Messages
22
Reaction score
0
Location
Texas
I'm not sure anybody can tell you what you need as far as passive treatment goes they have not heard your room. What is the problem with the sound, is the room dead? Is it to lively just putting asc tube traps or a absorption panels won't guarantee you better sound. It depends on the the problem you have in the room and what frequencies are the problem. You can have asc tube traps made to absorb or reflect certain frequencies depending on your room problem. Or they ncan do both at the same time.
 
Last edited:

Rich

Super Moderator
Moderator
Joined
Jul 8, 2006
Messages
4,138
Reaction score
2
Location
Huntsville, Alabama
I'm not sure anybody can tell you what you need as far as passive treatment goes they have not heard your room. What is the problem with the sound, is the room dead? Is it to lively just putting asc tube traps or a absorption panels won't guarantee you better sound. It depends on the the problem you have in the room and what frequencies are the problem. You can have asc tube traps made to absorb or reflect certain frequencies depending on your room problem.
In general, this is true. But as concerns the rear wave of a dipolar speaker, the physics are pretty well understood and are going to apply regardless. You either have to absorb the rear wave, or you have to bring the speaker panels four feet or more away from the front wall and diffuse the rear wave. If you don't do one of these two things, your imaging and soundstage will suffer due to the rear wave reflection arriving too soon in relation to the front wave. No matter the room. Simple as that.

Mind you, this point doesn't address other room interaction issues such as side wall reflections, bass nodes, etc. It simply addresses dealing with the acoustic issues generated by the rear wave of a dipolar speaker. Which is one of the first issues any ML owner should consider if they want to take advantage of the spectacular imaging and soundstaging these speakers are known for.
 

Norway84

Banned
Joined
Jan 1, 2016
Messages
22
Reaction score
0
Location
Texas
Again every room is different whether we are talking about panel speaker or dynamic drivers. It's impossible to say what is right for somebody because the sound of their speaker are reflecting both direction. It's all the same speaker react to different shapes in the acoustic environment. If that were the case all rooms would be acoustically perfect. Which could not be further from the truth!! Even the size of the bass driver can have a huge impact on how a speaker interacts in a room. I have Hales T-8 Hales rev 3's and the rev 3 sounds way better in my room than the 8's. I also have a pair of Sonus Faber Extremas with a passive radiator in the back that has to much bass and it's the smallest of two said speakers. If you are putting panels or traps even the height of placement can effect sound. So many variables take effect so just throwing passive adjustment in a room is a crap shoot.
 
Last edited:

Rich

Super Moderator
Moderator
Joined
Jul 8, 2006
Messages
4,138
Reaction score
2
Location
Huntsville, Alabama
Again every room is different wether we are talking about panel speaker or dynamic drivers. It's impossible to say what is right for somebody because the sound of their speaker are reflecting both direction. It's all the same speaker react to different shapes in the acoustic environment. If that were the case all rooms would be acoustically perfect. Which could not be further from the truth!!
Sorry, but I disagree. Did you happen to notice the pictures and other info that he posted? Dipolar speaker panels less than three feet from a front wall that consists entirely of hard, reflective surfaces, in a 13'x15' listening room. I can't speak to all the possible room interactions, but I can guarantee you this: the rear wave of those speakers (sounds from about 500 hz. on up) will reflect off that front wall and arrive at the listener's ear very shortly after the front wave, and this reflection will muddy the imaging and soundstaging the listener would normally get from that front wave. This is simple physics and psycho-acoustics. If the waves arrive too closely in time and energy levels, the brain can't separate them and properly interpret the spatial cues inherent in the audio signal.

There are two ways to fix this particular issue: decrease the energy of the rear wave and/or increase the distance to the front wall, thereby increasing the latency of the rear wave. If the speakers stay in place, absorption of the rear wave is the only viable option to get proper imaging and soundstaging from these speakers. If the speakers can be moved another foot or two out from the wall, that will help tremendously with the issue by further delaying the arrival of the rear wave, but diffusion panels behind them would help even more to get the ultimate performance the speaker panels are capable of.

You seem to be caught up in the notion of predicting overall room response, bass response, etc. That's not what I am doing. I am not talking about or giving recommendations on bass performance or other possible room interaction issues. That's a whole 'nother ball of wax and very complex. I am simply referring to the effect of the rear wave of a dipolar speaker, which is a specific property of Martin Logan and similar panel speakers. Your suggestion that "it's impossible to say what is right" in the situation presented by O.P. is poppycock. Again, the physics are very simple, straight-forward, and long-proven. Anyone that's seriously experimented with ML speaker placement is going to understand the need to ameliorate the deleterious effects of the rear wave. You have to get the speakers far enough from the front wall to adequately delay the rear wave for best imaging and soundstage presentation. If you can't do that, your next best option is to absorb the rear wave. If you do neither, I guarantee you will not get the imaging and soundstaging performance these speakers are capable of. Period.
 

Norway84

Banned
Joined
Jan 1, 2016
Messages
22
Reaction score
0
Location
Texas
Psycho acoustics I'm out of this conversation. One last thing I can't predict anything I'm not there! Enjoy your music!
 
Last edited:

Rich

Super Moderator
Moderator
Joined
Jul 8, 2006
Messages
4,138
Reaction score
2
Location
Huntsville, Alabama
Psycho acoustics I'm out of this conversation. One last thing I can't predict anything I'm not there! Enjoy your music!
From Wikipedia: "Psychoacoustics is the scientific study of sound perception. More specifically, it is the branch of science studying the psychological and physiological responses associated with sound (including speech and music). It can be further categorized as a branch of psychophysics."

You may not be "there" but you can still predict that if OP drops a ball it is going to fall to the ground. The rules of physics don't change simply because you are not there to witness them.
 

Norway84

Banned
Joined
Jan 1, 2016
Messages
22
Reaction score
0
Location
Texas
Psychology of lateral posistion is low voltage but vibration occurance = the physics of introduction of electocustic of low voltage miliwatts. Vibration dissipates to heat when I'm not there of the back wave of total reflection of the pyramid.
 

Rich

Super Moderator
Moderator
Joined
Jul 8, 2006
Messages
4,138
Reaction score
2
Location
Huntsville, Alabama
Psychology of lateral posistion is low voltage but vibration occurance = the physics of introduction of electocustic of low voltage miliwatts. Vibration dissipates to heat when I'm not there of the back wave of total reflection of the pyramid.
If you don't understand technical concepts, it's ok to just admit that and defer to those who do. Trying to make fun of science simply because you don't understand it just kind of makes you look pathetic. Especially on a forum like this where there are quite a few technically-savvy individuals.

I've got 16 years of experience working with and listening to over half a dozen models of ML speakers, experimenting with positioning them in multiple rooms and sound systems, and using bare walls, diffusion and absorption behind them. I'm offering the OP solid advice that is based in science and experience on how to deal with a well known property of ML speakers - the back wave of a dipolar speaker. You come into this thread with less than a dozen posts on the forum and and all you offer is: no one can say because they haven't heard the room.
 

RUR

Well-known member
Joined
Aug 12, 2007
Messages
1,020
Reaction score
1
Location
SoCal
Psychology of lateral posistion is low voltage but vibration occurance = the physics of introduction of electocustic of low voltage miliwatts. Vibration dissipates to heat when I'm not there of the back wave of total reflection of the pyramid.
I'm with Rich. Rather than mock the very real, and very important concept of psychoacoustics, do some research e.g. google "Haas effect" or "precedence effect". Understanding how your brain processes and interprets sound, i.e. psychoacoustics, is part and parcel of proper set up in any audio system.
 

bikerneil

Well-known member
Joined
Mar 3, 2011
Messages
88
Reaction score
7
Location
Carlsbad, CA
Thank you Rich (and others) for your input. I will try pulling them out from the forward wall another 8-12" to see how they sound. The sound field is already fantastic, but I would love to see it get even better. It's interesting to note that the ML literature says to place them >24" from front wall, so I figured my setup at 28" was good enough. I will report after I move them to 36".

Thanks again.

bikerneil
 

Rich

Super Moderator
Moderator
Joined
Jul 8, 2006
Messages
4,138
Reaction score
2
Location
Huntsville, Alabama
Thank you Rich (and others) for your input. I will try pulling them out from the forward wall another 8-12" to see how they sound. The sound field is already fantastic, but I would love to see it get even better. It's interesting to note that the ML literature says to place them >24" from front wall, so I figured my setup at 28" was good enough. I will report after I move them to 36".

Thanks again.

bikerneil
The problem with a hybrid design like ML has is that the best placement for the woofer box is not necessarily the best placement for the panels and vice versa. So you may move them out and find that imaging improves but bass response gets worse. Or not. A lot depends on your room. Will be interested to hear your impressions.

In general, best imaging and soundstage presentation is going to come with the panels 48" or more from the front wall. Even if you can't keep them there, I would suggest you try them at that distance just to get an idea of what they are capable of.
 
Last edited:

twich54

Forum Administrator
Moderator
Joined
Nov 25, 2005
Messages
6,729
Reaction score
114
Location
SE Pa
The problem with a hybrid design like ML has is that the best placement for the woofer box is not necessarily the best placement for the panels and vice versa. So you may move them out and find that imaging improves but bass response gets worse. Or not. A lot depends on your room. Will be interested to hear your impressions.

In general, best imaging and soundstage presentation is going to come with the panels 48" or more from the front wall. Even if you can't keep them there, I would suggest you try them at that distance just to get an idea of what they are capable of.
totally agree with Rich on this and with that being said subwoofer placement combined with proper integration will do wonders for the bottom two octaves !
 

sb6

Well-known member
Joined
Apr 23, 2010
Messages
235
Reaction score
0
Location
Round Rock, TX
Agree with Rich. Also, in that size room, you probably can't get far enough way from them and pull them out from the wall enough to justify diffusion. I would simply absorb that back wave, be done and be very happy!
 

bikerneil

Well-known member
Joined
Mar 3, 2011
Messages
88
Reaction score
7
Location
Carlsbad, CA
I moved my ML's out away from the front wall to a distance of 36" from the forward wall. The sound quality is noticeably improved. I listened to a series of recordings that I consider to be my baseline CD's for evaluating music in my room and I hear more base and the sound stage is wider and more precise. The overall "sound quality" is improved as well - I now hear small and subtle things that I did not hear before.

My baseline set of songs includes: Diana Krall - Fly Me To The Moon (from Live in Paris), Spanish Harlem & Isn't She Lovely (from Chesky's "The Worlds Greatest Recordings"), Several songs from Roger Water's "The Pro's and Con's of Hitch Hiking", Linda Rondstadt - What's New & I've Got A Crush on Your (from What's New), and Several songs from Pink Floyd's "The Wall".

Now that the location of my Source speakers is perfect, I will finally make the move to new ML Montis speakers that I have eyed for the past 2-3 months. I am hoping to see a local retailer run a special on them as I hear ML is discontinuing the Montis line this month or next. I have spent countless hours at all of the audio stores in the San Diego and Orange County areas listening to many, many different lines of speakers and to me - none of them come close to the sound of ML's. For my room size, the Montis seem to be a great match. I actually had a larger budget than I will spend on the Montis's but to me they sound better than any of the $15K speakers that I auditioned. I considered the ML Summit's, but I think the Montis will be a better match for my 13' X 19' room (especially if I am pulling them 3' into the room's depth).

Thank you again to everyone for your advice. I am somewhat of a newby, but I am coming up the learning curve quickly and appreciate advice and shortcuts to the finish line (if there is such a thing).

bikerneil
 
Top