Wall behind speakers amount of reflexion

[GW1800]

I am considering to switch from ordinary loudspeakers to dipole ones, and would need your help to clarify some questions on the matter.

It is my understanding that a dipole speaker needs a specific amount of reflecion from the back wall behind the speaker.

I am not sure if this back wall behind the dipole speaker should rather be absorbing or reflecting or a mix of the two?

Does there exist a precise physical measure ( oder: dimension) that helps to determine the optimal degree of reflection?

Currently the back wall behind my speakers consists of book shelves. Is it possible to find out if this book shelf is acting more as an absorber or more as a difusor? Some people say that bookshelfs act more as absorber some say that they act more as difusors. So I am kind of confused. Can someone please explain how this can be done?

Not sure my suggestion will work for you with the book shelves but I will give it a try. Ideally like most have stated is to have at least 4' behind or more and 2' or more on each side. That is great in a perfect setting or dedicated room but in the real world that most of us live in we do not have all that space particularly all the room behind even if our spouses would allow. In my situation I have about 27" behind and initially had no treatments at all behind first the Summit X's and now my CLX's. As I upgraded my system I started to get interested in room treatments and grounding. Grounding is another whole new subject that I will leave for another time. However I did spend quite a bit of time trying to maximize the sound quality in this space. Shawn had a old panel laying around that he sent me to try as there is no such thing as a demo or return period on treatments that I'm aware of. I noticed right away that it improved my sound stage. In doing the research I came across RPG and they recommended a BAD ARC panel which is a abfuser - not sure I spelled that right but its a combination of a diffuser and absorber but in a arc form. I ordered 2 panels 2'x5' and put them directly behind the CLX's and some smaller ones for first reflections point that were flat. They have special sound gem material etc.to wrap them in that come in many colors and to me they made a very nice change to the plus side. I'm very happy that I got them. The last room treatment was some type of a bass trap but I did not want some ugly corner filler like normal and decided to go with a black box from SR instead. I heard a demo at last Axpona and actually bought two but one made a difference and the second one really did not for my room. Lastly I had my panels perfectly straight and parallel to my listening position. Recently I updated my amps which really helped the depth of my sound stage and width all by themselves. I then toed in the CLX's ever so slightly like 1 1/2" (not quite the 1/3 that they recommend) and was very pleasantly surprised in the added depth of sound stage and just a touch more treble. Lastly I will most likely be added some BAD ARC's behind the Summit X's in my media room system #504.

 

[bikerneil]

I'm very interested in all of the information provided on this thread, as I am limited on how far I can move my ML Montis's out in to the room. The front plane of my speakers is 40" from the wall and that is very farthest I can get them away from the front wall (due to WAF and room geometry issues).

I am quite happy with my sound stage, but I enjoy tinkering and constantly trying to improve the sound, so I am now going to experiment with treatment of the wall behind my speakers. I saw a comment one thread that appear to state that if I absorb some of the back reflection I will improve the clarity (since smearing will be reduced), but I could sacrifice sound stage. Is this the case - do improvements in clarity come at the expense of sound stage imaging, or can I improve both simultaneously?

Thanks.

 

[C.A.P]

Give us more! Room size ! Speakers used!

Further out in a room can actually excite bass as waves can have time to clear each other as the bass is slower than the other frequencies.. When done right you don't get the over powered corner reinforced one note bass

In my room my Odyssey's are 8 feet out from back wall and have best bass response of all.. Along with that I get a HUGE stage and massive depth along with images well outside the speakers. its nothing to hear instruments 2 feet out from panels..

Try out Crowded House Recurring Dream.. Track 9 and when speakers are set up right the cars will actually circle you and they will be BIHIND you!

 

[bikerneil]

Give us more! Room size ! Speakers used!

My room is 13' wide X 15' deep.

I have Martin Logan Montis, which are moved out in to the room as far as possible, with the front face of the speakers about 40" from the front wall.

My main question is about the clarity vs. sound stage imaging - are they inversely related, or can you optimize both and improve both at the same time?

Thanks!!

 

[C.A.P]

lots of potential issues in that room IMHO! That bar table is really a issue with standing wave and image width.. The TV will cause reflections out of timing.. Id Toe them with a flash light too.. Its always hard making a room a listening room that is not really made for one.. Getting them past that bar would help clear up center image and covering the TV with a blanket will dull reflections as well as a slight toe

 

[bikerneil]

lots of potential issues in that room IMHO! That bar table is really a issue with standing wave and image width.. The TV will cause reflections out of timing.. Id Toe them with a flash light too.. Its always hard making a room a listening room that is not really made for one.. Getting them past that bar would help clear up center image and covering the TV with a blanket will dull reflections as well as a slight toe

Believe me, if I had any idea a few years ago that I would get in to this music hobby I would do things differently in this room. At the time, the room was our formal living room (which never saw any use) and I convinced my wife to allow me to convert it in to my office and hobby room. I installed a custom made, built-in desk on one wall, and a work bench on the other wall , and I hung a big tv on the opposite wall. Fast forward a few years and now I have to work with what I have..... In the long term, I may end up making some big changes to the room like getting rid of the workbench, but for now I gotta work with what I have.

It's hard to see from this picture, but the speakers are toed in. Also, I spent several hours measuring with a laser and flashlight to ensure the speakers have the same exact angle and are equidistant from my primary listening seat.

My real question on this thread was - if I manage to install some sound absorbing panels and drapes behind the speakers it is my understanding that those changes would eliminate the back reflection and improve the sound CLARITY of my system. Will this improvement wreck the beautiful sound stage that I currently enjoy??

Thanks.

 

[Rich]

My real question on this thread was - if I manage to install some sound absorbing panels and drapes behind the speakers it is my understanding that those changes would eliminate the back reflection and improve the sound CLARITY of my system. Will this improvement wreck the beautiful sound stage that I currently enjoy??

It is quite possible that it will reduce the size of the soundstage, but enhance imaging. Quality diffusers would maintain and even enhance the size of the sound stage while maintaining good clarity, assuming you can place the panels four to five feet out from them. If the panels have to be three feet or less from the back wall, absorption is a better option. Note that you would need a panel that absorbs midrange as well as high frequencies for best results.

 

[bikerneil]

It is quite possible that it will reduce the size of the soundstage, but enhance imaging.

Thanks Rich. I am trying to do as much studying and learning as I possibly can before I take any next steps. It's not possible for me to move my ML's out 4-5', so I will focus on absorption. I'm very happy with what I have today, so worse case I will try a few changes and go back to what I currently have.

 

[Rich]

For absorption panels, I recommend one panel 2'x4'x4" behind each speaker panel. Something like GIK's 242 panels or RealTrap's Mondo Traps. Place them on a small stand or pedestal so they cover the full height of the speaker panel. Worst case scenario, if you don't like the sound with them behind the panels, you can always use them to tame side-wall reflections.

At first, it will seem that the sound is less "lively" but give yourself time to adjust. You have to realize that your ears are hearing a lower volume level (as if you turned down the preamp volume) because the added sound from the rear wave is no longer hitting your ears. So you should be able to turn up the preamp volume beyond your normal listening levels to get back to the levels of sound you are used to listening to. You may also need to make minor adjustments to speaker positioning and toe-in to fine tune the sound. At this point, you should notice much improved clarity and imaging, two areas where electrostatic speakers shine. Putting some bass traps in the corners of your room would improve the sound tremendously as well.

 

[bikerneil]

Thanks Rich - that's the kind of information I was looking for. I will begin working on some treatments today. I wanted to make sure I was not going to lose my sound stage imaging. If I can improve both clarity and the imaging, it's worth a try.

Thanks. I will report back after I make some changes.

 

[Brad225]

If you are looking for a DIY approach. There must be a supplier in the area that sells Owens Corning 705 fiberglass panels. 2" thick x 24" wide x 48" long is the most common size for these panels. You can make a frame for them to fit in and wrap it in a fabric of you choice.

Owens Corning 703 will absorb a bit more low end but is very soft must have a frame work to place it in.

In my room I used 705.

 

[bikerneil]

Based upon input from others on this thread, and other websites too - I decided to implement some acoustic treatments in the front of my listening room (in the area behind my Martin Logans). I am limited on what I can do in this room with placement of my speakers and the room layout, so I decided to seek improvements treating the room.

I built base traps for the front corners and absorption panels to go behind my Montis speakers. I built the traps and the panels using 2 inch thick, 2X4 sheets of Owens Corning. The traps are 24" tall and are 6" thick. The absorption panels are 2' wide, and 4' tall (I had to do a cut-out to squeeze the panel between my window frame and the fireplace, but I placed the section that I cut out behind the shutter, just in front of the glass window pane). The panels and traps passed the wife approval test, and we hung them on the walls. I think they look pretty good.

I am very pleased with the results. I notice a definite improvement in overall imaging and clarity - especially with my bass. I'm still playing around with toe-in and final placement of my speakers. In a perfect world I would move my speakers outward, but my room won't allow for that. (The room is 13' wide X 15' deep.)

Thank you to everyone for input in thread above.

 

[C.A.P]

well done . Room is the second biggest part of a system to fix .. How far is your seat from the back wall as it can reinforce bass to.. Its a great tool that many do not use as most sit their char or sofa WHICH is a big sound absorbing blob in the center of the room and wonder why they have no bass. Bass waves are big and need time to get to the rear and reflect

 

[bikerneil]

.. How far is your seat from the back wall as it can reinforce bass to.. Its a great tool that many do not use as most sit their char or sofa WHICH is a big sound absorbing blob in the center of the room and wonder why they have no bass. Bass waves are big and need time to get to the rear and reflect

My ears are about 24" from the rear wall when I'm sitting in my chair. I used to have a large piece of artwork (framed with a pane of glass) on the wall behind this chair, but I have removed that picture and now the wall is just drywall. I can't move my chair forward or to the rear much at all.

 

[C.A.P]

24 is fine your getting room gain and that sense of air with rear early reflections.. Well done CHAP!

 

[bikerneil]

With regards to the back wall - is it best to leave it as bare drywall, with no absorption panels or other treatments?

 

[Rich]

With regards to the back wall - is it best to leave it as bare drywall, with no absorption panels or other treatments?

Normally, I would recommend diffusion on the rear wall. But since you are only sitting two feet away from it, diffusion would likely be ineffective. I would place an absorption panel on it, horizontally oriented at ear level behind your seating position. I expect you would get better clarity and imaging by reducing the rear wall reflections. These reflections, because they come back to your ears so soon after the initial sound wave, will confuse your brain and muddy the imaging. Any "sense of air" they may provide is not worth ruining the excellent clarity and imaging provided by electrostatic speakers.

 

[twich54]

With regards to the back wall - is it best to leave it as bare drywall, with no absorption panels or other treatments?

Normally, I would recommend diffusion on the rear wall. But since you are only sitting two feet away from it, diffusion would likely be ineffective. I would place an absorption panel on it, horizontally oriented at ear level behind your seating position. I expect you would get better clarity and imaging by reducing the rear wall reflections. These reflections, because they come back to your ears so soon after the initial sound wave, will confuse your brain and muddy the imaging. Any "sense of air" they may provide is not worth ruining the excellent clarity and imaging provided by electrostatic speakers.

also to add what Rich has said given your close proximity to the back wall with regards to all things 'reflective', if it were me I'd be treating the corners as well.

 

[bikerneil]

And one final question:
You can see in the picture above that I have a large plasma TV on the wall behind my speakers. It's located between the speakers, and above the speakers. I suspect I am getting some amount of sound reflection off this glass screened TV. I am considering placing a blanket or something similar over that TV screen when I am not using the TV (which is 99% of the time). Does the type of blanket I use make a big difference, or can I get 80% of the absorption with any blanket? (or do I need to go and buy a thick wool blanket?)

Thanks.

 

[C.A.P]

A Blanket that has had a fan blowing on it for a week ! :ROFL:

Those in the know will Know!

Quilted will work.. No yarn as it wont help.. Just use it for two channel listening and tell your wife the TV was cold !