# Looking to make THIN first reflection point panels!



## swatkins (Nov 26, 2013)

I just spent some time marking out reflection points for my two rows of seating and I have 6 different points I need to cover. I also want to make this room look very nice and I think having panels hanging 4 inches off the surface of the wall is going to look weird and in one place, around a door, almost impossible. 

What is the thinnest absorption material I can use and still expect the panel to perform well? 

I would love to keep the panels 1 1/2" to 2" thick.


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## hjones4841 (Jan 21, 2009)

Most of our members use 4" for first reflection absorption; that is what I use and it works well. The problem with thinner material is that it will not absorb midrange frequencies very well, and that is where our ears will hear the reflected sound best. You may want to check out these:

http://www.gikacoustics.com/product/gik-artpanel-acoustic-panels/

or these:

http://www.gikacoustics.com/product/gik-acoustics-242-acoustic-panel/

GIK panels are well made and look really nice. Great customer service as well; bpape works with them and can be found in this forum. He was a big help when I treated my room 4 years ago.

Bass traps have to be thicker to work well, so let us know if you plan on adding them and our members will chime in with recommendations. Again, GIK is a great place to buy if you don't want to DIY them.


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## bpape (Sep 14, 2006)

Did you mark reflections for all 3 speakers to all seats? I would think you'd have a lot more points that that. For example if you have 2 rows of 3 (6 seats), you'd have 18 points to cover.

4" will do a very good job. 2" is pushing but you can get by with it if necessary. 4" will go lower and do a better job on upper bass/lower midrange phase related issues from the reflections.


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## swatkins (Nov 26, 2013)

bpape said:


> Did you mark reflections for all 3 speakers to all seats? I would think you'd have a lot more points that that. For example if you have 2 rows of 3 (6 seats), you'd have 18 points to cover.
> 
> 4" will do a very good job. 2" is pushing but you can get by with it if necessary. 4" will go lower and do a better job on upper bass/lower midrange phase related issues from the reflections.


I only had help for 10 minutes so i just marked the center seat in both rows.. But from what i can see the other points follow the same pattern and to make the decor of the room "right" I need to go back to my original plan of covering the whole wall. up to 44", with sound panels. 

I can also place full corner bass traps in all corners and see how much of the back wall will need to be paneled. 

My mic arrived and I have been trying to slog my way through REW so I will have the tools to measure as soon as I figure out why i can't set the mic levels in REW 

I had planed on placing a 3/4" piece wood strip on the wall in a Block panel pattern and then making frames and covering them with GOM to cover either painted sheetrock, cotton batting or absorbent material as needed. If I make the frames 2" thick that would allow for a absorbent panel 2 3/4" thick and not be as noticeable. 

I was looking for a semi ridged material that can be used for the main panel and then , if necessary, placing a piece of ACOUSTI-BOARD™ ULTRA Soundproofing Backer  , or something simular, behind the 2 inch material. Then if needed i could always use my new CNC routing table ( or table saw) to cut lines, grid patterns or even cube shape patterns into the face of the sound backer to break up the front surface of the material so sound waves are further absorbed, or trapped in that area, and just not reflected back out. If this is feasible it would result in a 2 3/4 panel that could fit into my recessed space.

All my reading has also directed my attention to the ceiling. I don't know how common it is to treat the ceiling but if necessary I can make something neat looking for up there.


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## phazewolf (Feb 5, 2012)

My friend for side wall reflection points marked the wall where they issues were and cut away the drywall from those spots. Then he placed a 2" panel over the holes and with that plus the insulation in the walls it made for a over all deeper panel. 

To me it seemed crazy but he really liked how it sounded. If I recalled he later used art panels and it had a nice look it it.


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## swatkins (Nov 26, 2013)

In my case I would have to remove 16' of double 5/8 rock with green glue to expose the cavities at all the points I need to treat.  If I can't come up with a thin solution I could always build a wall in front of the side walls, it would be a lot easier than trying to reinstall the drywall inside those cavities


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## phazewolf (Feb 5, 2012)

Yes I was not saying it was a fun way to deal with it and to be honest I never measured to see how well it worked. 

Personally I would use 4" art panels and dress them up to look like movie poster boxes and even use lights like the do at a theater to make them into a focal point of the room. 

Why hide something you can't when you can call ones eyes to it and use it to not only show off your space but make it sound great.


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## swatkins (Nov 26, 2013)

If it was not for my left side wall, where the entrance door is located, I would not worry about it so much.. A major part of that door area is going to need panels along with the back of the door. To open the door flat against the wall is very nice now but will soon be impossible even with 2 inch thick panels. I am even toying with rebuilding my door with the sound panel inserted into the door cavity.


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## bpape (Sep 14, 2006)

Or possibly swap the door to open out.


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## Babak (Mar 20, 2009)

Hi 

Why do you want to use absorbers?
Does your RT60 or RT30 measurement show that you need to reduce certain frequencies in your room response? 

I would rather use diffusors to weaken the negative effect reflections and maintain their positive effect on spaciousness. 

Using absorbers to reduce reflections could reduce spaciousness and make the resulting image flat. 

Cheers 
Babak


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## swatkins (Nov 26, 2013)

Good idea but not possible because it would then block another door. I am working through learning REW so I should have some measurements soon...


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## swatkins (Nov 26, 2013)

Babak said:


> Hi
> 
> Why do you want to use absorbers?
> Does your RT60 or RT30 measurement show that you need to reduce certain frequencies in your room response?
> ...


I really have no idea on what the room needs now, just going off what other people say to do about reflection points.... I will soon have some room measurements and then we can see what I really need


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## Babak (Mar 20, 2009)

Hi



swatkins said:


> I really have no idea on what the room needs now, just going off what other people say to do about reflection points.... I will soon have some room measurements and then we can see what I really need


People do a lot of different things about reflections.
Unfortunately there is a lot of folklore about that sometimes leading to totally dampened room where everything sounds dead and flat.

I would recommend some reading, for example as a start (you can stick to the topics applicable tio 2-channel stereo)

*Audio, Science in the Service of Art *By Dr. Floyd E. Toole, Vice President Acoustical Engineering, Harman International Industries, Inc.
http://www.harman.com/EN-US/OurCompany/Innovation/Documents/White Papers/AudioScience.pdf


*Part One: How Many Loudspeakers? What Kind? Where?*
By Dr. Floyd E. Toole, Vice President Acoustical Engineering, Harman International Industries, Inc. 
http://www.harman.com/EN-US/OurCompany/Innovation/Documents/White Papers/LoudspeakersandRoomsPt1.pdf

*Part Two: Making a Good Loudspeaker – Imaging, Space and Great Sound in Rooms*
By Dr. Floyd E. Toole, Vice President Acoustical Engineering, Harman International Industries, Inc. 
http://www.harman.com/EN-US/OurCompany/Innovation/Documents/White Papers/LoudspeakersandRoomsPt2.pdf

*Part Three: Getting the Bass Right*
By Dr. Floyd E. Toole, Vice President Acoustical Engineering, Harman International Industries, Inc. 
http://www.harman.com/EN-US/OurCompany/Innovation/Documents/White Papers/LoudspeakersandRoomsPt3.pdf


And of yourse Floyd Toole's excellent book:
*Sound Reproduction: The Acoustics and Psychoacoustics of Loudspeakers and Rooms*
http://www.amazon.com/Sound-Reprodu...F8&qid=1393053503&sr=1-1&keywords=floyd+toole

Depending on the listener's preferences (more direct sound for Rock/Pop/Electronics fans or more enveloping sound for Jazz and classics afficionados) one can deal with rooms and reflections several ways.
The book helps to understand how to achiebe whoch results.

Cheers
Babak


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## bpape (Sep 14, 2006)

There are well defined targets for both the decay time and specific reflections that should be addressed. In home theater, the room will be a bit more damped than in a 2 channel situation since there ar multiple speakers to create the 3 dimensional soundstage where in 2 channel you try to use the room to help you somewhat.


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## swatkins (Nov 26, 2013)

I have been reading a lot, mostly about REW, and trying to come up with a basic understanding of room acoustics. Frankly there is so much information, so many differing points of view and so many "experts with a keyboard" that I find myself just going around in circles. 

Check me out on my understanding so far and please help me with a few questions.. 

From my reading I think I'm trying to achieve a room that has a "slight" amount of "sound bounce". If I go too far and cover all the walls with panels I will make the room too dead sounding by absorbing all the reflecting or "bouncing" sound. I'm not too sure why or how the room is improved by letting a small amount of sound bounce around by not covering the top half of my side walls. 

By reducing the first reflection points with absorption pads I make the sound from the speaker "cleaner" or not muddied by delayed sound reaching my ears after the direct sound does. In order to achieve this goal some people advocate covering the bottom of my side walls with 44 inch high absorption panels and leaving the top parts of the walls untreated.. (that was my plan before I found this Forum  ) Some say just placing a 4 inch thick panel at the first reflection point is enough... Which is best??? 

I should cover the entire screen wall to absorb any sound not coming from the speakers. What I don't know is why... I can see where delayed sounds would muddy the sound from the speakers but what I can also see where a little "background" sound would help blend in the sound stage and make the mains and center disappear. 

Same goes for the back wall... 

After I started really trying to understand reflected sound and a rooms shape and surfaces, I started looking up at the ceiling and wondering what the I should do up there. After all the sound bounces off of that smooth surface and reaches my ears, right? I "think" I need to hang a really large panel ( 4' x 12") at the first reflection point of the main and center speakers. So what about the reflection points of the 4 surround speakers? If I start covering them all do I risk making a dead sounding room?

I now have REW setup and can make measurements... Now my problem is "reading" the graphs and figuring out what needs to be done. There is tons of information on making the graphs but information on reading them is pretty sparse. Last night I found some really old threads on another forum that gave me hope and a few clues on reading the graphs.. Does anyone know of any comprehensive graph reading resources? 


And just to keep this post on topic  A question on the thin panels... 

IF I was able to figure out a way to hide some of the thickness of the panel just how high and low on the wall should the panels be mounted. I have a 9' ceiling height and the bottom of my surround speaker is at 7'. From looking at the marks on the wall, where I mapped out the first reflection points from the seats, I am going to need to cover almost 12 feet of wall... Other sites have recommended 44 inches high... What say you? 

Thanks for any help
Steve


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## swatkins (Nov 26, 2013)

Babak said:


> Hi
> 
> 
> 
> ...


Thanks,, I'll go check them out now


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## fokakis1 (Feb 29, 2012)

swatkins said:


> I have been reading a lot, mostly about REW, and trying to come up with a basic understanding of room acoustics. Frankly there is so much information, so many differing points of view and so many "experts with a keyboard" that I find myself just going around in circles.
> 
> Check me out on my understanding so far and please help me with a few questions..
> 
> ...


You have good questions. I can't answer all specifically, but I can give you a simple summary that has helped me achieve good results without over thinking or overdoing it.

Treat as many first reflection points from your front speakers as you can, then treat the rest of the room holistically until you have about 20% of the room's boundaries covered in absorption and 15% in diffusion.


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## bpape (Sep 14, 2006)

Treating the front wall is to address surround reflections messing up the front soundstage. The front you want a well defined soundstage. In the rear you want something less defined, and more diffuse (no necessarily diffusion) to better create an ambient surround field(water in a cave, footsteps in a castle, etc) unless it is a hard pan where you want to define a specific channel location. 

Specific percentages of absorption vs diffusion might give a decent starting point in some rooms but every room is different. For instance, a 15x20 room with a hard floor and only 2 chairs and 2 people would require much more absorption to get to the target decay time than a carpeted room with 7 seats and 4 people. You MUST take into account what the room itself, the furnishings, and the people are doing to the room acousitcs.

Diffusion is something that can be used but has restrictions. Pending the thickness of the diffusion there is a minimum distance that any listening positions need to be spaced. This is based on wavelength of the lowest frequency that the diffuser will scatter effectively. Sitting closer than that puts in in a place where diffusion has not yet had a chance to scatter sufficiently and that has a lot of phase related nasties going on. Most theaters with 2 rows, that only leaves high on the walls to help with slap and flutter echo. The rest is too close to seating.


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## fokakis1 (Feb 29, 2012)

bpape said:


> Specific percentages of absorption vs diffusion might give a decent starting point in some rooms but every room is different. For instance, a 15x20 room with a hard floor and only 2 chairs and 2 people would require much more absorption to get to the target decay time than a carpeted room with 7 seats and 4 people. You MUST take into account what the room itself, the furnishings, and the people are doing...


Good point. The percentages I mentioned include carpet, curtains, bookshelves, etc.


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## bpape (Sep 14, 2006)

and walls, wall construction, floor type, windows, that all also are going to add in some way to how the room reacts. I assume that's in the etc.


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## Gordoj (Feb 24, 2014)

bpape said:


> Diffusion is something that can be used but has restrictions. Pending the thickness of the diffusion there is a minimum distance that any listening positions need to be spaced. This is based on wavelength of the lowest frequency that the diffuser will scatter effectively. Sitting closer than that puts in in a place where diffusion has not yet had a chance to scatter sufficiently and that has a lot of phase related nasties going on. Most theaters with 2 rows, that only leaves high on the walls to help with slap and flutter echo. The rest is too close to seating.


And to add to what is being said, a listener would want to be placed around 3 wave lengths from the diffusor in order to not have the phase and comb filtering problems as stated above. So, since most diffusors for this type of room would have a lower limit in the 300 to 500HZ range that would mean that you would want the listening position approximately 3m from the diffusor (in the ideal world).....

Gordo


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## bpape (Sep 14, 2006)

Agreed. In the real world, you're out of 90% of the problems at 4-5'.


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## swatkins (Nov 26, 2013)

Ah! So another important thing to consider is how far the waves are traveling! I was thinking that even after the sound wave leaves an absorption panel, located at the first reflection point, it still had enough energy to travel to a second reflection point and so on and so on... where it could combine with other sound waves to either produce a null or intensify. 

The important point of decay has not been emphasized enough in the articles and threads I have been reading... Well at least not emphasized enough for a novice like myself


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## Gordoj (Feb 24, 2014)

swatkins said:


> Ah! So another important thing to consider is how far the waves are traveling! I was thinking that even after the sound wave leaves an absorption panel, located at the first reflection point, it still had enough energy to travel to a second reflection point and so on and so on... where it could combine with other sound waves to either produce a null or intensify. The important point of decay has not been emphasized enough in the articles and threads I have been reading... Well at least not emphasized enough for a novice like myself


Well, yes and no. What we were referring to above was the distance a listener should be from a diffusor. A diffusor as it scatters the wave, has an impact on the wave both in time and phase. So, in order to hear a cohesive "sound" back from the diffusor you need to be located at a distance that allows the full bandwidth to form. Much like listening to a speaker, the closer your get to the speaker the less full bandwidth you hear and more pin pointed to one driver and the more anomalies from phase and time are heard. 

I assume the decay you are referring to is the reverb time or RT of a room? In many critical listening environments of small rooms, the RT 60 wants to be in the .3 to .4 range (still not agreed on by many). However, that decay time would be an even dispersed sound field that many small rooms do not have due to the issues that are being addressed in this series of posts.

Gordo


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## swatkins (Nov 26, 2013)

Babak said:


> Hi
> 
> 
> 
> ...


Just wanted to thank you again Babak.. I just finished reading the online papers you linked to and found some interesting tidbits  One section made me feel a lot better about the size of my room. I designed the size more with seating and distance away from the side walls, along with how much I could afford instead of thinking about how the sound would fill the room... Looks like my shape and size is not going to be too difficult to correct.. Thanks for the great reading!


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## swatkins (Nov 26, 2013)

Gordoj said:


> Well, yes and no. What we were referring to above was the distance a listener should be from a diffusor.
> Gordo


I see. A diffuser needs space for the waves to, well diffuse  Sort of the rational I used when leaving a wider aisle between my side surrounds and the seating. 



Gordoj said:


> However, that decay time would be an even dispersed sound field that many small rooms do not have due to the issues that are being addressed in this series of posts.
> 
> Gordo


 I keep thinking that I might be able to improve the effectiveness of my thin first reflection point panel by using a diffuser behind the material.. I was thinking that I could use 1 1/2" thick rigid fiberglass air conditioning duct board placed over a 1/2 inch drop in acoustic ceiling panels. I was thinking that cutting irregular grooves in the panel would turn it into a mini diffuser / trap and further scatter the sound waves as they exit through the rigid fiberglass..

Would that help the decay times?


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## swatkins (Nov 26, 2013)

bpape said:


> Specific percentages of absorption vs diffusion might give a decent starting point in some rooms but every room is different. For instance, a 15x20 room with a hard floor and only 2 chairs and 2 people would require much more absorption to get to the target decay time than a carpeted room with 7 seats and 4 people. You MUST take into account what the room itself, the furnishings, and the people are doing to the room acousitcs.


 I understand what your are saying about the room and furnishings  While I was reading a thought flashed into my head about treating my back wall. 

My back wall is 8.5 feet high and 19' wide. I am placing a 8' wide by 30" desk in the middle so that would leave 5.5 feet on each side. 

I was thinking I should place a panel on the desk front, screen facing, surface to absorb sound behind the front row seating and then placing a 48" tall by 12' wide panel on the back wall itself. I keep reading about bass traps for corners and if I find I also need those I can place two full height traps in each back corner thus covering most of the back wall and everything near ear level. Would that be a reasonable plan?


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## bpape (Sep 14, 2006)

Diffusion behind an absorber will do nothing - especially a thin diffuser behind a thin absorber. The point of a diffuser is to scatter without removing energy. Thin diffuser will only do upper mid and high frequencies which will already be absorbed.

I would not do a 4x12' thin panel behind you. You need something thicker pending your distance to it, where you have cancellations from that wall, etc.


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## Gordoj (Feb 24, 2014)

bpape said:


> Diffusion behind an absorber will do nothing - especially a thin diffuser behind a thin absorber. The point of a diffuser is to scatter without removing energy. Thin diffuser will only do upper mid and high frequencies which will already be absorbed. I would not do a 4x12' thin panel behind you. You need something thicker pending your distance to it, where you have cancellations from that wall, etc.


Indeed swatkins. You would be better off to increase the thickness of the panel to improve the midrange absorption and be done. If you really want diffusion then products such as the QRD, etc would be in order. 

You can get diffusion with absorption but the absorption happens behind the diffusion and is specific to a lower midrange target area. One of these type products is called a Binary Amplitude Diffsorber (BAD Panel) and when applied correctly can work quite well to absorb the midrange and lower midrange while diffusing the upper midrange and HF.

Gordo


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