[ebag4]

Gents:
I have a room used as a home office.  I have done some basic (unfinished) treatment to it and it sounds OK.  I get good imaging but my soundstage is primarily between the speakers.  My bass control is pretty good, my OB speakers have a lot to do with reducing the boom, but I have purchased some additional 8lb rockwool, my plan is to replace what I have currently with 2 solid rockwool corners all the way to the ceiling.  Is there anything else I can do to improve the soundstage or the overall acoustics of this room?  Any help is appreciated.  See below for a room sketch and photo of speakers in the room.

Best,
Ed

[mcgsxr]

Now those are some funky OB speakers, nicely done!

I assume they bass drivers are Auggies?

Have you tried playing with the toe in?

Wish my DIY finishes were as nice...

[ebag4]

Thanks Mark, yes they are Augies.  I have tried messing with to in, distance from walls, etc.  While the sound is good, it seems to me that the sounstage should be better.  I am hoping that some acoustic treatment can show me the light!

Best,
Ed

[bpape]

Treatment may help some but I think most of it is going to be placement related. 

Doing the chunks instead of panels will extend the botom of the efficient range of absorbtion of the corners but not offer any more from say 100Hz up.

Have you played with even crude diffusion yet behind the speakers?

Bryan

[ebag4]

Hi Bryan, thanks for chiming in.  No, I haven't played with any typed of diffusion, I thought my room was too small for diffusion to be effective.  Is there something specific I might try to determine if diffusion will take care of my problem?

Thanks again,
Ed

[bpape]

Diffusion behind you in a typical sense wouldn't likely work well.  Behind an OB, it can help spread the soundstage and minimize some comb filtering. 

Unfortunately, trying diffusion isn't as easy as trying absorbtion.  One can fold up blankets and pillows to simulate an absorber.  Simulating a diffusor is pretty tough.  If you want to try it and see, you can get try a crude poly - though that will be very different in sound than a QRD/well type diffusor.

Get a pc of 3/4" plywood.  Screw 2 2x2's to the vertical edges of it with a notch sawn out of the inner sides.  Get some thin plywood that you can bend and flex it to slide into the 2 notches.  Fill behind with absorbtion.  That will leave you a semi-circle (or flatter depending on how wide the plywood is and how much it bends).  Make these tall enough to sit on the floor and extend the full height of the speaker.

This won't give you the same space and time domain even scattering as a QRD/well diffusor but it will at least give you an idea if this is going to work to expand the soundstage somewhat to determine if it's something you want to pursue.

Bryan

[ebag4]

Great Bryan, I will give it a try.  You are recommending 2, one behind each speaker, correct?  Do you recommend a specific width?  Thanks for the direction.

Best,
Ed

[bpape]

Yes - 1 behind each speaker.  Width, hard to say.  I'd shoot for probably 2' total width and use somewhere around 2'6" wide to bend into it.   We don't want the slits in the sid perpendicular to the wall - we want them at 45 degrees at the most.

Again, these are going to be very crude and more of a simple scatterer rather than a tuned diffusor but it will give you an idea anyway.

Bryan

[nodiak]

Hi Ed,
I use polys like Bryan described in my room to help with high freq. echoes/reflections. They work great for me in the rear area of the room on side walls, along with diy skylines on rear wall.
I can recommend using 1/8" masonite as it's easy to bend and cheap. Mine are 32"w x 42"h and masonite is ~5" at peak of bend (this was extrapolated from a 48" wide design that recommended 8-10" peak of curve, I drew it out and measured for 32" width). They could have more curve maybe but work for slap echoes and some (not all) shrillness. Easy to test effectiveness.
Since mine were going up on the walls I made the back of the 1/8" masonite (32 x 42 for mine), then did the side strips of 2" x 2" ripping inside edges at  ~ 60 degree angle, glued them to vertical edges as bryan described. Curved piece slips in and stays put. I forgot how much wider the curved piece needed to be, just a few inches tho.
Am interested in how it works behind your OB's. I've done absorption behind OB's with some 5.5" cotton bass trap material I got from Bryan and liked it. My corners behind speakers use this 5.5" material like you have your rockwool, works very well. My room is half assed I mean halfway done. Just ordered some 2" 6lb rockwool for ceiling and 1st reflection (which I should've done "1st" like those guys said...)
Don 

[ebag4]

Thanks Don, the masonite sounds like a good tip, "easy and cheap" just the way I like it  .

[bpape]

The masonite will work fine as long as you stuff the back fully with something to damp it.  The characteristics that make it easy to bend also make it resonate easily - which over an open cavity might not be too pleasant.  Stuff it full and you should be fine. 

Bryan

[youngho]

Let me start by saying that I know very little about acoustics. I just read a little.

However, it seems to me that you have treated your room for direct radiating speakers, but the open baffle creates a dipolar radiation pattern, which interacts differently with the room.

In the picture but not the diagram, your speakers look awfully close to the rear wall, but this may be due to relative lack of depth of field in the photo. As you know, the speakers can be closer to the side wall than the rear wall, due to the nulls produced by dipoles. I wonder if you might consider making sure the speakers are at least 4' forward from the real wall and sitting closer to them for nearfield listening.

Here (http://www.linkwitzlab.com/rooms.htm#D), Siegfried Linkwitz argues for diffusion on the wall behind dipolar speakers, as well as the side walls at the reflection point. The sidewall absorption that you have may contribute to the relatively narrow soundstage that you note. GiK makes inexpensive diffusers, RealTraps makes combination diffusers/absorbers (though you may want to focus on diffusion for the front), and a company called Core advertises variable depth well absorbers on Audiogon (also available from Auralex under the SpaceArray product line). Of course, there are also the quadratic diffusors like the RPG QRD diffusor line or the Primacoustic Razor Blade.

If you're looking for something less expensive, on Audio Asylum, in the planar speakers board, many Magnepan users have reported good results with placing ficus plants behind their Maggies. It's worth trying. The front of the room looks a little stark.

If you pursue this line of thought, you might move all the absorption to the back of the room.

Happy listening,

Young-Ho

[ebag4]

Thanks Bryan, I will be certain to stuff them thouroughly if I end up with Masonite. 

Youngho, the speakers are actually about 3.5 feet out from the back wall.  These are not the first OBs I have had in this room, they are different from what I had previously.

I no longer needed the largish podium/equipment stand between the speakers so I have removed it and replaced it with the granite slab that was sitting on top, the slab is now sitting on 4 brass carpet spikes with a block of wood between the spikes and the granite.  I don't know why but this seems to have made a positive impact on the soundstage depth and air, I also went ahead and moved the speakers out to 4' from the back wall and they are currently sitting a little over 2' from the side walls.  I still plan on trying th diffuser mock-ups.

Thanks,
Ed

[nodiak]

Ed, the masonite is non-pretty, maybe some inexpensive doorskins could be found ~ same price?
Don

[youngho]

Ed, sorry, I was wrong about the photograph, and I didn't realize that you were familiar with open baffle radiation patterns. I had interpreted your placement of absorption as coming from a background with direct radiators, but like I said, a greater mind than mine would argue strongly against the way you've placed the absorption. According to Linkwitz, placement of speakers at least 3' from the rear wall separates reflected sound by at least 6 ms from direct sound, so pulling them further still from the rear wall may help increase what he calls "sense of space," which I think is analogous to depth of soundstage. Reflections with spectral content significantly different from the direct signal will adversely affect listener perception of stereo information, and most absorption will result in varying absorption at different frequencies, undermining the advantages of the dipolar radiation pattern. He advocates for the importance of lateral reflections, and I mentioned the sidewall absorption's effects.

You might consider looking at F. Alton Everest's "Master Handbook of Acoustics," which notes that the dimensions of the polycylindrical diffusor should be comparable to the wavelengths being diffused, hence "diffusing elements [should] be characterized by randomness" in order to diffuse different frequencies in a similar manner. If all the polys are the same depth, then you will end up with diffraction grating, rather than true diffusion.

There's a wealth of information in Linkwitz's website and Everest's book, so I'll bow out at that.

Best of luck, and happy listening,

Young-Ho

[nodiak]

youngho, thanks for the paragraph on F. Alton Everest's thinking. All my poly's are the same, must be some "diffraction grating". I'll look into making different sizes.
Don   

[youngho]

Nodiak,

http://www.acoustics.salford.ac.uk/feschools/waves/diffract4.htm

[ebag4]

Is it possible to place  a thin plywood on the face of corner bass absorbtion (creating crude polys) and maintain the effectiveness of the absorbtion?  I am considering doing this in addition to other diffusion behind the speakers.  Would this give me mid/high diffusion and bass absorbtion in the same package?

Thanks,
Ed

[nodiak]

Hi Ed, I've been thinking of using the curved panels or curved slats in front of the corner traps for that purpose too. I may be getting things too dead in here, not sure.
This is interesting -
http://www.sensusaudio.com/daad.html
"Click here to get bored, I mean to read more" about halfway down page.
Also on some of the sites about studio acoustics there were corner traps with reflective slats and curved helmholtz resonators. But I've lost the links from a computer break down.
Don

[ebag4]

Very cool, thanks for the link Don.  I am saving the "read more" for later, perhaps right before bed!