Early Reflections Can Disrupt Good Imaging

[AudiocRaver]

This is something I have been working with for quite a while. Early reflections can have a BIG effect on imaging.

Some will advise that dissipation on the front wall improves spaciousness and has little or no effect on imaging directly. I disagree.

What is your opinion and what experience do you have to back it up?

 

[Leonard Caillouet]

My experience is similar to yours, Wayne.

 

[Todd Anderson]

I would guess room size comes into play.... I have absorption at the first reflection points and it helped to clean up imaging in my HT room. I do wonder, however, what kind of effect something with reflection/absorption would have. GIK sells modified panels...

 

[1_sufferin_mind]

In a small (13Lx8Wx8H) room, I've found that treating 1st reflection points for the mains helps imaging the most, but treating 2nd reflection points makes noticeable, worthy improvements. Seemingly buried details are brought out of the mix, eliminating strain and making them easier to hear. Details start to call attention to themselves, instead of requiring your attention. My mixed absorption/diffusion "panels" also have an effect, though they're placed behind the mains along the front wall. Half of their circumference acts as a HF/MF diffuser, while the other half acts as an absorber for same. In my experience, rotating (or aiming) these special "panels" varies the amount of air, presence, and recording venue space.

 

[tesseract]

Some will advise that dissipation on the front wall improves spaciousness and has little or no effect on imaging directly. I disagree.

What method of dissipation? Absorption or diffraction depends on the type of loudspeaker, the room and listening position. I cannot imagine a scenario where correctly treating the front wall would have a downside. Even placing the equipment rack to the side or rear of the room can have an effect. Many cover the TV with a blanket.

According to Floyd E. Toole, first reflections are beneficial, necessary, even. To what degree, again, depends upon the room. In a smaller room where the side walls and listener are very close to the loudspeaker, bare wall reflections could be useful. In a medium sized room, diffusion could work best. In a large room with listeners placed far away from the loudspeakers, absorption could help preserve the original wavefront from the relatively enormous delay coming from the side walls, which can cause confusion for our ear/brain mechanism.

 

[Leonard Caillouet]

My struggle has always been getting the right balance between reflections from the wall behind the speakers and the side walls. Most systems just cannot accommodate moving the speakers out enough to get the timing of the front reflections far enough from the direct sound to do anything but garbage up the image. Add a display and really mess it up.

 

[1_sufferin_mind]

And it's not just acoustic treatment that matters. Different speaker types also affect the balance of direct to reflected sound. For instance, early sidewall reflections are much less pronounced for electrostatic speakers than direct-radiating types because they're directivity pattern is like a figure-8. People aren't likely to change speakers just to control imaging and spaciousness.

 

[AudiocRaver]

I would guess room size comes into play.... I have absorption at the first reflection points and it helped to clean up imaging in my HT room. I do wonder, however, what kind of effect something with reflection/absorption would have. GIK sells modified panels...

My experience indicates that it takes very little reflection energy to disrupt imaging, if that energy comes from a direction away from the line from ear to speaker to wall. If the reflected energy comes from that that line, imaging is protected and even enhanced if the timing of the reflections is well matched. Panels that mix reflection and diffusion materials should be set (aimed) so reflected energy is not reflected toward the LP.

In a small (13Lx8Wx8H) room, I've found that treating 1st reflection points for the mains helps imaging the most, but treating 2nd reflection points makes noticeable, worthy improvements. Seemingly buried details are brought out of the mix, eliminating strain and making them easier to hear. Details start to call attention to themselves, instead of requiring your attention. My mixed absorption/diffusion "panels" also have an effect, though they're placed behind the mains along the front wall. Half of their circumference acts as a HF/MF diffuser, while the other half acts as an absorber for same. In my experience, rotating (or aiming) these special "panels" varies the amount of air, presence, and recording venue space.

I like the sound of your approach. Your description of the way a track's detail is enhanced by a good SS&I (soundstage and imaging) is very perceptive and accurate.

 

[NBPK402]

When I move...we will have an interesting room to deal with as the walls will all be coming Concrete or clay brick. From what I have heard this is going to be a problem for the bass, but not the mids, and highs...any ideas on this? The next build will not be a all out room in a room, but our will use acoustic panels for first reflections, and bass traps. I am taking all my first reflection panels with me for the new place when we move, and also some bundles of Roxul R60, and R80. I am hoping to also have a room big enough for Diffusers too. We haven't picked our new house yet, but hopefully will be in our new house by early fall. I realize this is just about first reflections, and hope I can get some feedback on what to expect with solid walls like we will have.

 

[NBPK402]

When we built our current HT...we found that the front wall being given absorptive treatment, along with the first reflection panels made a HUGE difference in Soundstage, and spaciousness.

 

[AudiocRaver]

Yes, you often hear it said that a lot of spaciousness can come from the front wall being left partly reflective, but all I can hear from that is poor imaging. Get your spaciousness elsewhere, later reflections, mainly from the rear of the room.

It's a jungle out there. Preserve, protect, enhance, and defend your SS&I!

 

[NBPK402]

Yes, you often hear it said that a lot of spaciousness can come from the front wall being left partly reflective, but all I can hear from that is poor imaging. Get your spaciousness elsewhere, later reflections, mainly from the rear of the room.

It's a jungle out there. Preserve, protect, enhance, and defend your SS&I!

On our next build I anticipate having good the front wall be covered with 2" of Roxul ( only to the height of to screen unless the whole wall is needed which I hope not with as high as my ceilings will be). I want to try a mix of diffusion and absorption toward the back of the room too.

 

[Mark Seaton]

On our next build I anticipate having good the front wall be covered with 2" of Roulette ( only to the height of to screen unless the whole wall is needed which I hope not with as high as my ceilings will be). I want to try a mix of diffusion and absorption toward the back of the room too.

Lots of 2" thick absorption (might you have meant Roxull/rockwool?) on too much surface will have as many detrimental effects as positive. Thickness and wide bandwidth effect is key. I strongly recommend looking into some of the fabric track options on the market to greatly open up your options. If you want to add significant absorption, consider 4-6" of thickness at important areas of the front wall, especially inside and behind the main speakers, and definitely behind/around the center channel if this is a home theater setup. I also would prefer to balance this type of absorption with more thick treatment at the rear wall as well. If you really want to go all out, I'd suggest reaching out to Nyal Mellor of Acoustic Frontiers who is also in the N Calif. area. He can work up a complete acoustic plan and is one of the more flexible designers I've come across in working within a wide range of budgets and expectations.

Control of or enhancement of early lateral reflections are an interesting bit to experiment with giving trade offs of different subjective qualities, but we should also remember that you really can't possibly have too much control of a room's acoustics below 250Hz, so don't let the considerations of the higher frequencies leave you overlooking the very important bass range.

 

[NBPK402]

Lots of 2" thick absorption (might you have meant Roxull/rockwool?) on too much surface will have as many detrimental effects as positive. Thickness and wide bandwidth effect is key. I strongly recommend looking into some of the fabric track options on the market to greatly open up your options. If you want to add significant absorption, consider 4-6" of thickness at important areas of the front wall, especially inside and behind the main speakers, and definitely behind/around the center channel if this is a home theater setup. I also would prefer to balance this type of absorption with more thick treatment at the rear wall as well. If you really want to go all out, I'd suggest reaching out to Nyal Mellor of Acoustic Frontiers who is also in the N Calif. area. He can work up a complete acoustic plan and is one of the more flexible designers I've come across in working within a wide range of budgets and expectations.

Control of or enhancement of early lateral reflections are an interesting bit to experiment with giving trade offs of different subjective qualities, but we should also remember that you really can't possibly have too much control of a room's acoustics below 250Hz, so don't let the considerations of the higher frequencies leave you overlooking the very important bass range.

Thanks Mark. On our current setup we did the whole from the wall with 2" of Roxul, and then used 4" of Roxul for 1st reflections. For the rear wall we used 9" of Roxul for a bass traps with a thin rubber membrane on the front of the Roxul to prevent too much high frequency absorption. The current setup us a room within a room. The new setup will be all clay brick ( including the ceiling), with concrete floors.

Do you have any experience with a room like I am building this time by chance? I ask this because some people say it is the best to start with, and others say it is bad unless you do a room in a room build.

Tia,
Ron

 

[phillihp23]

I found bass traps in the front corners, subs are on either side of center speaker, and acoustic panels to the left and right of the front row seating greatly increased the clarity and cleanness of audio in my HT. I also placed two hanging panels down the center of the ceiling between the screen and front row seating, my ceiling peaks in the middle. I noticed a clear difference. I am a believer in proper treatment of first reflection points now, I was skeptical prior. Used Gik panels, they were real helpful in determining placement. The sound was scattered and muddy before. After treatment I could turn the volume higher without it being loud and obnoxious. Now when turned up it is still clear and defined. I used to set it at 60 now I often set it at 70....unless there is a lot of bass in which case I have to turn it down a bit lest my four svs subs rattle the room.

 

[NBPK402]

I found bass traps in the front corners, subs are on either side of center speaker, and acoustic panels to the left and right of the front row seating greatly increased the clarity and cleanness of audio in my HT. I also placed two hanging panels down the center of the ceiling between the screen and front row seating, my ceiling peaks in the middle. I noticed a clear difference. I am a believer in proper treatment of first reflection points now, I was skeptical prior. Used Gik panels, they were real helpful in determining placement. The sound was scattered and muddy before. After treatment I could turn the volume higher without it being loud and obnoxious. Now when turned up it is still clear and defined. I used to set it at 60 now I often set it at 70....unless there is a lot of bass in which case I have to turn it down a bit lest my four svs subs rattle the room.

I had a similar experience with my panels...which I consulted with GIK for placement. When you said hanging panels...did you mean hanging from the ceiling lengthwise or did you mean hanging them parallel to the ceiling?

 

[phillihp23]

I had a similar experience with my panels...which I consulted with GIK for placement. When you said hanging panels...did you mean hanging from the ceiling lengthwise or did you mean hanging them parallel to the ceiling?

Parallel to the ceiling they are rectangle
so the short ends abut. Hung them on chains and hook from corners of panels as the peak runs down the middle behind the panels. I have some pictures in the Finshed HT thread, Mjolnir Theater.

 

[NBPK402]

Parallel to the ceiling they are rectangle
so the short ends abut. Hung them on chains and hook from corners of panels as the peak runs down the middle behind the panels. I have some pictures in the Finshed HT thread, Mjolnir Theater.

I remember seeing panels hanging from the ceiling from chains years ago in audio room setups and always wondered how they worked , but you're are hung like mine are except I used hooks and O rings to hang mine.

 

[AudiocRaver]

Lots of 2" thick absorption (might you have meant Roxull/rockwool?) on too much surface will have as many detrimental effects as positive. Thickness and wide bandwidth effect is key. I strongly recommend looking into some of the fabric track options on the market to greatly open up your options. If you want to add significant absorption, consider 4-6" of thickness at important areas of the front wall, especially inside and behind the main speakers, and definitely behind/around the center channel if this is a home theater setup. I also would prefer to balance this type of absorption with more thick treatment at the rear wall as well. If you really want to go all out, I'd suggest reaching out to Nyal Mellor of Acoustic Frontiers who is also in the N Calif. area. He can work up a complete acoustic plan and is one of the more flexible designers I've come across in working within a wide range of budgets and expectations.

Control of or enhancement of early lateral reflections are an interesting bit to experiment with giving trade offs of different subjective qualities, but we should also remember that you really can't possibly have too much control of a room's acoustics below 250Hz, so don't let the considerations of the higher frequencies leave you overlooking the very important bass range.

Without realizing it, I have been doing pretty much what Mark suggested on my front wall. I have no screen mounted there yet (that was the next step before the plumber came along and made me gut the room), and the front wall was basically covered with about a foot thick of material: 1 layer on the wall plus a layer in a GIK DIY 2x4 panel plus 2 layers of Knauf ECOSE that come with the GIK panels. The thought at the time was to deaden the LF along with HF, not really to eliminate the modes, but to make them die super fast for TIGHT bass and a rocking clean soundstage.

The Visio screen was to be mounted above the treatment, above ear level, basically. That's right, sports fans, some of us are so particular about our sound that the video gets mounted ABOVE the sound absorption. Crazy, I know.

 

[NBPK402]

Without realizing it, I have been doing pretty much what Mark suggested on my front wall. I have no screen mounted there yet (that was the next step before the plumber came along and made me gut the room), and the front wall was basically covered with about a foot thick of material: 1 layer on the wall plus a layer in a GIK DIY 2x4 panel plus 2 layers of Knauf ECOSE that come with the GIK panels. The thought at the time was to deaden the LF along with HF, not really to eliminate the modes, but to make them die super fast for TIGHT bass and a rocking clean soundstage.

The Visio screen was to be mounted above the treatment, above ear level, basically. That's right, sports fans, some of us are so particular about our sound that the video gets mounted ABOVE the sound absorption. Crazy, I know.

Did you do the whole wall floor to ceiling, or just to the height of the top of the speakers?

 

[AudiocRaver]

Just up to 4 foot height.

 

[NBPK402]

Just up to 4 foot height.

Thanks, that will make my setup much easier to do too then...my current setup we went floor to ceiling, but pt the new room would not be fun doing a 15' tall absorption, plus cosmetically this room will not be a fabric wall room.

 

[AudiocRaver]

I think going up to LP head height, or 4 feet high, might satisfy you.

 

[Chris A]

And it's not just acoustic treatment that matters. Different speaker types also affect the balance of direct to reflected sound.

Yes...and controlled directivity loudspeakers (i.e., fully horn loaded) even more so. The issue that I see with most loudspeakers used today is that their coverage angles change with frequency. If this is the case, then you have a very large problem with early reflections changing the timbre of the sound, and at lower frequencies--affecting speech intelligibility quite strongly. The "clarity" plots that Mulcahy added to REW a while back unfortunately isn't a very good measure of this. I recommend this presentation to learn more about this little understood area affecting many HT enthusiasts: http://www.davidgriesinger.com/ICA2013/What is Clarity4.pptx


Chris

 

[AudiocRaver]

Yes...and controlled directivity loudspeakers (i.e., fully horn loaded) even more so. The issue that I see with most loudspeakers used today is that their coverage angles change with frequency. If this is the case, then you have a very large problem with early reflections changing the timbre of the sound, and at lower frequencies--affecting speech intelligibility quite strongly. The "clarity" plots that Mulcahy added to REW a while back unfortunately isn't a very good measure of this. I recommend this presentation to learn more about this little understood area affecting many HT enthusiasts: http://www.davidgriesinger.com/ICA2013/What is Clarity4.pptx


Chris

Well spoken, Chris, very good point.