Absorb or reflect behind ML

MOON said:

Having absorbtion behind Logans really defeats the purpose of having a rear wave in the first place.

Click to expand...

People who use their M/L's for H.T. only might not notice a difference?

Just a thought.

I agree 100% with your statement, just trying to widen the application.

Interesting idea on the shutters for diffusion. Got me to thinking about the antique doors I've been searching for in the house I'm building. We came across decorative antique doors and antique shades that might serve the same purpose as the home depot shutters, with much more aesthetic style. Many of the shades did not have all of the panels and would have to be modified to become doors, but could be individually hung on the wall behind the speakers unmodified. Here in Austin, there are all sorts of eclectic furniture stores that carry these kinds of things.

DTB300 said:

I would agree with your statement if the wall behind the speakers was completly covered with absorption sucking up every bit of the rear wave. I do not think any of us here using absorbtion, have ever stated that.

Having "some" absorption or "some" diffusion is what people need to try out. We are not trying to "completely" absorb, or "completely" diffuse the sound.

Dan

Click to expand...

I agree and some of the best absorbtion has a slightly reflective face side and underneath is a different layer of absorbing material.

I would recommend abfussion, as the combination of slight dispersion of the rear wave combined with some absorption of the highest frequencies will clean up the sound from the front of the panels a bit. The idea is to not have strong, fixed delay rear wave co-mingling with the front (causing combing and cancelations).

By adding diffusion, we are spreading out the rear wave into many specular angles and thereby distributing the reflection points and associated delays. While still causing combing, it is distributed more and therefore less objectionable and sounds more like natural ambience.

Be careful that the diffusion tool you use does so only in the horizontal range and is not a 3D diffusior like the RPG Skyline. The idea is to maintain the nice vertical null’s the ML’s have and not have to deal with the ceiling or floor reflections as well as lateral walls.

Auralex and RPG have 2D diffusiors that would work well behind the panels.
I generally recommend trying to keep the rear reflections from coming back around and between the two fronts, as that will smear the center image. To achieve this, I’ve experimented with angling the 2D diffusers a bit towards the side walls. This seemed to help, but I did not do measurements. Nor is it how my rig runs now. I have mostly absorption behind the Monoliths, letting portions of the flat wall do the reflections.

For the rear channels, I do have a totally different set up, with full 2D diffusers behind the Sequels and 3D diffusers (4x Skylines) between them. This works really well for rears, but is not recommended as a setup for fronts for the reasons listed above. Look in the thread describing my system for a pic that shows the rear wall treatments.

This is more of a request for clarification than an assertion...but my understanding of a dipolar line array, is that the line array aspect of it causes nulls at the top and bottom that minimize ceiling and floor reflections, while the dipolar nature of it gives you a more focused horizontal dispersion, because of nulls created starting at the edge of the baffle and radiating outward where the waves meet. Thus, I would think that the only places you would really have to deal with reflections would be your front and back walls...and you'd want absorbtion there, if your goal is to have just a pure clean wave with minimal reflections. I would think that you would theoretically (if accurate reproduction is your goal) want as close to an anechoic chamber as possible, in order to accurately reproduce the environment as well as the music...because the microphones doing the recording would also be recording any reflections that were occuring in the room the recording was made in. By adding other reflections, you're merely simulating a different listening environment, as opposed to accurately reproducing the recorded one...

I just pieced these things together from various sites I was reading regarding open baffle line arrays, so may be COMPLETELY wrong about some or all of this...and please do correct me if I'm wrong.


Of course, if you compare the two, and like diffusion better...because it spreads the stage, etc...then that's the best option, purely because you like it better

"In your room, we tried something startling for a dipolar design—we damped most of the backwave. Then we opened up the dispersion a bit by putting the reflective side of the Studio Traps near either side of the SL3s. We emphasized that energy, but we had enough absorptive material in the room so that the energy died rapidly and was quite evenly distributed. That gave us better imaging, better focus, and a better sense of space.

"That whole experience has altered the way I think. I used to depend upon the backwave, but absorbing it showed me that we can free ourselves from it. We can start to work closer to that back wall as long as we can emphasize that midfield energy."

Click to expand...

That was Gayle Sanders speaking. Of course, it's not necessarily the last word, but helpful reference for experimenting...

Posted this some time ago, here's the link to the full article again:
http://www.stereophile.com/floorloudspeakers/145/index6.html

I just want to say that I'm following this good and informative thread as I know that backwave manipulation is the next step in my system.

Thanks guys....

Joey

This weekend I tried to place absorbtion material behind the CLS II's. I've put some square meters of it, attached to the walls behind the speakers. Half a minute of music, then I stood up and removed everything. YMMV with other ML's... I must say I'm happy to know that, because my wife's veto was loud and clear anyway - but I had to try it.

lugano said:

This weekend I tried to place absorbtion material behind the CLS II's. I've put some square meters of it, attached to the walls behind the speakers. Half a minute of music, then I stood up and removed everything. YMMV with other ML's... I must say I'm happy to know that, because my wife's veto was loud and clear anyway - but I had to try it.

Click to expand...

What exactly did you use as absorption?

i used this:

garmtz said:

What exactly did you use as absorption?

Click to expand...

See attached picture.

lugano said:

See attached picture.

Click to expand...

Did you place the entire panel behind each speaker?

Looks to be 2' x 4' (.6m x 1.2m or so) and is it made for Acoustics, or is it just some foam packing material in sheets?

Dan

DTB300 said:

Did you place the entire panel behind each speaker?

Looks to be 2' x 4' (.6m x 1.2m or so) and is it made for Acoustics, or is it just some foam packing material in sheets?

Dan

Click to expand...

Dan, these are 1m x 1m pieces of sonic absorbtion material used in the industry to acoustically isolate noisy machines. A friend of mine which builds such stuff uses them on a regular basis. He gave me 4 pieces in order to see what happens. I preferred these over regular, pyramidal ones, because when rotated 90 degrees they offer a different profile. I could not hear any difference by rotating them, though. Yes, I placed 2 of them against the wall, behind each CLS II. A lot of silence between notes, yes, but it is not what I need when listening to music and trying to recreate a live performance. They are probably a very good idea for recording studios, and I got my lesson about what to expect when using such stuff. They did not fit my bill, but I must say that I don't have reverberation problems in my listening area. The clapping hands test does not bring echoes in my case - there are plenty of objects all around the room already. In my case, it was like looking at a movie with my sunglasses on....

lugano said:

Dan, these are 1m x 1m pieces of sonic absorbtion material used in the industry to acoustically isolate noisy machines. A friend of mine which builds such stuff uses them on a regular basis. He gave me 4 pieces in order to see what happens. I preferred these over regular, pyramidal ones, because when rotated 90 degrees they offer a different profile.

Click to expand...

Thanks for the information on the panels. Hard to tell what they were by the picture.

Dan

Here are the slatted door rear wave diffusser pictures I promised to post. The camera is low resolution, but hopefully the pictures help. These diffiusers work excellent and if anyone is interested I will post the Stereophile article on the slatted door diffussers.Just ask and I shall post it. It is in the March 2002 issue under the fine tunes section.

I had to buy a new set of slatted doors for my newly aquired Oddessy's as I had cut my previous set down in size for my Aerius i's. I finished the doors on Friday and put them in place on Saturday. Tried to post the pictures asap. I bought the 2 doors for $70 at a home recyling center, they were in excellent condition already painted white. Therefore I didn't have to primmer them and just painted them the color of my walls.

You will notice, in the Oddessey front close up picture that the center of the stator is directly in line with the center of the slatted door disperssing the rear wave back to the center of the room and to the side as well. The door halves slant back to the wall on a 30% angle. Also, there is a half slatted door in each corner on a 45 degree angle in the corners as well.

The wall on the right side of the Oddessey is one shade darker than the wall behind the speakers, just thought I would mention it if you were wondering about the color variance.

The stained glass window over the stereo rack is made by me , it's a side hobby.

Cheers, Greg

Zip3kx07 said:

My preference is to defuse the back wave and absorb the sidewalls.

Click to expand...

HI All,
Yes, I agree. I have gone further. I Broke the Rules bigtime. After experimenting with the CLS's with the space between empy, i tried something that the rules of the HIGH END says should not work. I beg to differ.

I had a 45" rear projection TV way off to the side on the end of the room. I could not enjoy the sound system and the TV at the same time. Just for the hell of it, I decided to put this large console TV square beween the CLS's. I had just acquired my Kinnergetics SW-800 subs so I made several changes at the same time.

The order of the components as seen from the listening position is Left CLS, 1 Kinnergetic's Subwoofer, TV Set, 1 KInnergetics SW-800 Subwoofer, Right CLS. The speakers, subs and the TV set effectively formed a wall since the Subs and CLS's were moved out into the room. The panels and subs are aimed exactly at the specific ear for that channel. Space behind the CLS's was about 3.5 feet, not enough, I'm afraid. To the left side wall it is 4.5 feet while to the right side wall it measures about 12 feet.

The effect of moving the TV into the equation was to prevent the back waves from each channels speakers from mixing. As I switched the system on, I did not l know what to expect knowing that what I was doing was a big NO-NO.

Well, what I found was most unexpected. The system sounded better. The image was more focused and the sound staging lost nothing. After a few hours of listening I decided that the TV was staying.

The moral: Try breaking the rules. Sometimes it pays.

Sparky

karma said:

The moral: Try breaking the rules. Sometimes it pays.

Click to expand...

Agreed. There really are no rules, just ideas to try out and hear the results.

Dan

MOON said:

Here are the slatted door rear wave diffusser pictures I promised to post.

Click to expand...

They look very nice in your room - great job matching them up. But I would call them more of a "redirector - reflector" than a diffusor. But like anything in this great hobby, if it helped create a better sound in your room, then it was worth the effort.

A diffusor is designed using specific mathematical data to create the different peaks and valleys helping to scatter or diffuse the sound properly. A badly designed diffusor can make things worse rather than better. People have tried pop/soda cans, PVC piping, pieces of wood, etc. Some of the successful ones are basically copies of existing products - "Skyline diffusor like panels" have plans out there on the net to help make the different pieces of wood the right or close to right sizes.

Discussions about diffusors has been going on over at Ethan Winer's forum as Real Traps is just about ready to release their diffusor panels. There is another company/person who is also adding to the thread, and they already make diffusors.

Dan

I`ve tried damping behind the Summits and that took all life out of the sound, I now use 2 diffusors behind each Summit at 60cm x 150cm which makes a big leap in performance of the Summits. These are made by Svanå at Svanå Miljøteknik
Here`s a pic of them.

Here's a very interesting new product... diffusor "tiles", apparently made of recycled paper products. Introductory pricing is very reasonable... $30 for a dozen tiles. They might even be paintable, though not sure. They also offer some other abstract designs, but ?? what acoustic properties.

Here's the website...
http://mioculture.com/store/pc/viewPrd.asp?idcategory=2&idproduct=9

Hi Dan,

The slatted door panels have separate 1 inch slats all the way up on a 45 degree angle, I assume they do some diffussion as well as redirect the wave at the same time.

Viking,

I didn't see that diffusser on the site, possible I overlooked it. What is the name of that specific diffusser and what is the cost for 2 of them ?They look really nice.