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post #1 of 73 Old 08-22-2011, 07:46 PM - Thread Starter
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I have a dedicated Home Theatre room of dimensions 19 ft (length) x 14ft (width) x 9ft (height). I have a 110 inch projector screen with a 5.1 Elac (German brand) speaker system powered by an Onkyo 605 receiver and my HTPC. My walls and ceiling are concrete and has not been acoustically treated yet.

I am not happy with the sound clarity of my speakers. I believe that my speakers are generally "soft" in nature and not as bright or punchy as I would expect it to be, though the volume output is quite good. Also, dialogues are not as clear as I wish it to be. I saw a similar 5.1 setup at a friend's place who also has untreated walls but has Energy speakers paired with a Marantz receiver. I was quite impressed with the quality of the speakers, especially the brightness, sharpness and "punch".

I consulted with a acoustic specialist who, while acknowledging that my speakers were "decent but not as good as Energy" recommended that I should treat my ceiling and side walls first. He recommended acoustic panels for the full wall width and height, and ceiling panels for only first reflection areas. He also recomended a carpet for the floor and leaving the front and rear walls untreated to create some reverb and avoid full dampening.

Here are my questions:

1. The acoustic treatment is very expensive (taking into account installation and finish quality) and costs around $2000. Am I better off investing this kind of money on new speakers rather than on the room treatment? After all, my friend has a similar setup and his speakers sounded good without any acoustic treatment.

2. Is the suggested treatment correct? I read the forums and most have recommended that only first reflection points need to be treated, not the entire side walls or ceilings. However, this specialist says that its better to treat the entire side walls and instead leave the front and rear walls untreated. Going by the forum recommendations would significantly bring down the cost for me, though the finish may not be as good as sporadic panels would be seen here and there (first reflection points only).

Suggestions on how I should proceed will be most welcome. I don't want to spend a bomb on room treatment and then discover that my speakers weren't "good enough" to begin with!


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post #2 of 73 Old 08-22-2011, 10:13 PM
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Originally Posted by contentedbloke View Post

my friend has a similar setup and his speakers sounded good without any acoustic treatment

this specialist says that its better to treat the entire side walls and instead leave the front and rear walls untreated

No surprise about your friend's set-up. Some recent research points to the opposite of what the "specialist" told you. Download the following AES paper by Floyd Toole and go to the 22nd page of the pdf (page marked 472), start reading from the part 9.2.1 Above the Transition Frequency.

Personally, I would at least get a thick rug for the floor between your listening position and the speakers, as well as some treatment for the front and back walls. Rather than absorb the side-wall first reflections, I would try breaking them up with some furniture (bookshelves, etc). Finally, try pointing the three front speakers at the listening position, both horizontally and vertically, so you're listening more on-axis.

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post #3 of 73 Old 08-23-2011, 06:36 AM
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Originally Posted by contentedbloke View Post
recommended that I should treat my ceiling and side walls first. He recommended acoustic panels for the full wall width and height, and ceiling panels for only first reflection areas. He also recomended a carpet for the floor and leaving the front and rear walls untreated to create some reverb and avoid full dampening.
there is no such thing as a 'reverberant-space' in small acoustical spaces - hence why RT60 is meaningless, as is thinking your space will create 'reverb'.

to avoid "full dampening" - try not covering entire boundaries/surfaces with absorbent material - unless the goal is indeed to create a dead room.

there are multiple issues in the specular region (energy that functinos and can be modeled like 'rays') regarding small acoustical spaces:

1) summation of reflections + original signal at the listening position ... constructive and destructive interference creating 'comb-filtering' effect in the specular frequency domain. specular reflections combine in-phase and out-of-phase to create many peaks and nulls.

2) smaller perceived 'space' with early reflections. the arrival time of these early reflections dictate to the brain how large or small the space is. if you are in a bathroom, with your eyes closed, when you speak you'll hear the reflections off the boundaries very quickly as the distance is small - and your brain will perceive this as being in a small room (even with your eyes closed, you can tell how small of a room you are in). now, put yourself into a large space (movie theater, concert hall), and when you speak, it takes a much longer time for the first reflections to reach your ears - increasing the perceived space of the room. by delaying (in time) when the first reflections in your room reach your ear (with respect to the original signal), you are increasing the perceived size of the room. also, if you are listening to music (a recording), and your early reflections arrive earlier in time then the room the music was recorded in, then your room is masking its sound on top of the recording, versus you reproducing the recording space in total before your listening space has a chance to impose. eg, if you are listening to a recording from a concert hall in your small room, your room is going to mask the sound and the early reflections will dictate to your brain that you are indeed in a small space versus being immersed into the room the recording was produced in. it's all about the time-domain.

3) imaging issues as off-axis energy from the left speaker will reflect off the right wall and enter the right ear.



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1. The acoustic treatment is very expensive (taking into account installation and finish quality) and costs around $2000. Am I better off investing this kind of money on new speakers rather than on the room treatment? After all, my friend has a similar setup and his speakers sounded good without any acoustic treatment.
that is a lot of money and you could do DIY room treatments for much less, considerably. but bear in mind as with any 'service', you're paying for more than just the materials (eg., you're paying for the service, experience, etc). $2k is a lot of money when DIY treatments are

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Is the suggested treatment correct? I read the forums and most have recommended that only first reflection points need to be treated, not the entire side walls or ceilings. However, this specialist says that its better to treat the entire side walls and instead leave the front and rear walls untreated. Going by the forum recommendations would significantly bring down the cost for me, though the finish may not be as good as sporadic panels would be seen here and there (first reflection points only).
it really depends on the size of the listening position (how many seats, rows, etc). if it's a single listening position, then you want to be surgical with your treatments (absorption). if you have an entire row, sometimes it is easier to treat a large surface - but i dont see any reason why an entire boundary would need to be treated. another issue with regards to covering entire boundaries with absorption is people generally apply too thin absorption which exists merely to soak the HF content out of the room while the lower and mid specular content continues to exist - creating a muddy sounding room. (and this is irrespective of LF modal issues - an entirely different issue and set of solutions altogether).

ideally, one would use redirection (splayed walls; geometry) to redirect the early reflections away from the listening position towards the rear of the room where they can be diffused and used as a termination - a laterally arriving diffused sound-field for envelopment...but this generally is difficult to do regarding real estate, and absorption is generally used as an easier solution to attenuating early reflections.
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post #4 of 73 Old 08-23-2011, 01:24 PM
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Originally Posted by sdurani View Post

Finally, try pointing the three front speakers at the listening position, both horizontally and vertically, so you're listening more on-axis.



You know, all too often we overlook the obvious.

I'm not referring to this contributor by any means,..... but I see so many system pics, proudly posted by contributers, and I clearly see entirely too many of them ignore the basics,..ie, some degree of room symmetry, axial listening, adjacent surface VER/diffraction, boundary effects/BSC,....then some of them rail on and on wrt different cabling etc.


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post #5 of 73 Old 08-23-2011, 06:02 PM
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Originally Posted by contentedbloke View Post
I have a dedicated Home Theatre room of dimensions 19 ft (length) x 14ft (width) x 9ft (height). I have a 110 inch projector screen with a 5.1 Elac (German brand) speaker system powered by an Onkyo 605 receiver and my HTPC. My walls and ceiling are concrete and has not been acoustically treated yet.

I am not happy with the sound clarity of my speakers. I believe that my speakers are generally "soft" in nature and not as bright or punchy as I would expect it to be, though the volume output is quite good. Also, dialogues are not as clear as I wish it to be. I saw a similar 5.1 setup at a friend's place who also has untreated walls but has Energy speakers paired with a Marantz receiver. I was quite impressed with the quality of the speakers, especially the brightness, sharpness and "punch".

I consulted with a acoustic specialist who, while acknowledging that my speakers were "decent but not as good as Energy" recommended that I should treat my ceiling and side walls first. He recommended acoustic panels for the full wall width and height, and ceiling panels for only first reflection areas. He also recomended a carpet for the floor and leaving the front and rear walls untreated to create some reverb and avoid full dampening.

Here are my questions:

1. The acoustic treatment is very expensive (taking into account installation and finish quality) and costs around $2000. Am I better off investing this kind of money on new speakers rather than on the room treatment? After all, my friend has a similar setup and his speakers sounded good without any acoustic treatment.

2. Is the suggested treatment correct? I read the forums and most have recommended that only first reflection points need to be treated, not the entire side walls or ceilings. However, this specialist says that its better to treat the entire side walls and instead leave the front and rear walls untreated. Going by the forum recommendations would significantly bring down the cost for me, though the finish may not be as good as sporadic panels would be seen here and there (first reflection points only).

Suggestions on how I should proceed will be most welcome. I don't want to spend a bomb on room treatment and then discover that my speakers weren't "good enough" to begin with!
Sound like you could benefit from a little education. Try reading Dr Floyd Toole's book which can be bought at amazon.com for around $35. It'll be the best $35 you invested into your room and will equip you with the do's and don'ts of room treatments which should help you decide if better speakers are the way to go or room treatments.

Personally, I found my expensive system sounded God awful in an untreated room. With the same equipment in a well treated room the sonic dividends are huge! I would hazard to guess that after reading Toole's book that you might consider (i)adding bass traps to all four floor-to-ceiling corners, (ii)treating your back wall and front wall as reflected sound from them does more harm than good compared to side walls and ceiling reflections, and then experiment with side wall 1st reflection point options of (a)bare reflective wall, (b)diffusion, or (c)absorption. There are pro's and con's to each of the three treatments at the sidewall and ceiling 1st reflection points and to a large degree personal taste dictates.

By the way, you can build lots of bass traps and diffusers for less than $2,000. I bought a 12foot long by 48" diameter Sonotube for around $300 and cut it into 5 hemi-cylindrical (poly) diffusers that double as bass traps when fiberglass was added to the inside cavity. Cover with speaker cloth or Guildford of Maine cloth of your choosing or even better glue a wooden veneer over it and stain it like I did. You might have money left over for a pair of subwoofers, and a parametric EQ to get the bass right afterwards . . .

Good luck and let us know how it goes.
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post #6 of 73 Old 08-24-2011, 09:25 AM
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^^^^ What these guys said.

I would expect that most people would hear far more improvment in their system by spending $2k on treating their rooms than they would by spending an extra $2k (or more) on their speakers.

Even mediocre speakers in a good room will (almost always) sound better than good equipment in a poor room.

My $0.02........

There are no stupid questions. Stupid answers are a whole other story...........
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post #7 of 73 Old 08-24-2011, 11:19 AM
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Im re-doing my HT room adding more treatments to where Im moving the screen. You can save lots of $$$ by doing it yourself.

I just spent $500 yesterday the products you could use to improve your room 100% from what it is today. I purchased the following from acoustimac.com

1. DIY EZ-WRAP ACOUSTIC FABRIC (PRE-MADE WRAPS) 48"x24"x6"

2. MINERAL WOOL 1260 (6 lbs/ft) 48"x24"x2" MNW1260


The also sell the frames if you want them. The wraps are actually a very good quality fabric and I have owned 4 of them for several years already. The only problem is that right now they are out of every color accept red

To start.....

Treat the wall behind your speakers and beside your speakers (maybe 6 panels spread along the wall). Build thicker 4" or 6" pannels to absorb lower frequencies.

You can do this in steps, you can measure/hear the improvements as you improve the room.

If you are going to have 2 rows then you could also create a bass trap out of your 2nd row riser. Im doing that right now, I will use 12 MINERAL WOOL 1260 panels (4 sections 3 panels each = 6" thick, with 2" air gap, riser will be a total of 8" high).

btw, the other suggestestions are awesome too...Chairs, thick carpet, bookcases all help in any room. Finding sonotube (I Have 8 feet of 24" sonotube left over) is a great way to have bass absorption plus differaction.

There is a thread on the DIY forum where a member EricH was going to try and offer DIY flatpacks for building diffusors but he is really, really busy with other audio projects. That would be another great low cost addition considering diffusers seem to run $500 each for high quality ones

I almost forgot....Always treat the room. Even high quality speakers will sound like crap in crap rooms IMO!!! You can always upgrade the speakers later and you will already have a treated room.

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post #8 of 73 Old 08-24-2011, 11:28 AM
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Originally Posted by sdurani View Post

No surprise about your friend's set-up. Some recent research points to the opposite of what the "specialist" told you. Download the following AES paper by Floyd Toole and go to the 22nd page of the pdf (page marked 472), start reading from the part 9.2.1 Above the Transition Frequency.


AES link broken...did you mean this?

Loudspeakers and Rooms for Sound Reproduction—A Scientific Review
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post #9 of 73 Old 08-24-2011, 11:48 AM
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AES link broken...did you mean this?

Loudspeakers and Rooms for Sound ReproductionA Scientific Review

Thanx, fixed the link (to the actual paper, not the AES order page).

Sanjay
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post #10 of 73 Old 08-24-2011, 11:58 AM
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2. Is the suggested treatment correct? I read the forums and most have recommended that only first reflection points need to be treated, not the entire side walls or ceilings. However, this specialist says that its better to treat the entire side walls and instead leave the front and rear walls untreated. Going by the forum recommendations would significantly bring down the cost for me, though the finish may not be as good as sporadic panels would be seen here and there (first reflection points only).

Suggestions on how I should proceed will be most welcome. I don't want to spend a bomb on room treatment and then discover that my speakers weren't "good enough" to begin with!


I forgot to answer this specific question. You should treat the wall behind and beside the speakers because that is where the speaker creates WORST response. 2 or 4" OC703 or 2" Mineral Wool (the one I posted) will absorb those soundwaves for you getting rid of their nasty response. You do not have OB designs (Open baffle) so there is no reason to want any refection from the 180deg speaker sound wave let the wall treatments behind the speaker absorb it. You would be surprised how many people create nulls from their speaker placement and untreated front walls.

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post #11 of 73 Old 08-24-2011, 12:33 PM
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I forgot to answer this specific question. You should treat the wall behind and beside the speakers because that is where the speaker creates WORST response. 2 or 4" OC703 or 2" Mineral Wool (the one I posted) will absorb those soundwaves for you getting rid of their nasty response. You do not have OB designs (Open baffle) so there is no reason to want any refection from the 180deg speaker sound wave let the wall treatments behind the speaker absorb it. You would be surprised how many people create nulls from their speaker placement and untreated front walls.

you may wish to make the distinction whether the treatment is for LF modal issues or specular issues. approach and material requirements can be drastically different.

eg, in your quote, you reference the wall behind and besides the speaker - where omni-directional LF reflections may occur, but im not sure how effective 2-4" mineral wool would be due to the requirement for LF absorption for this specific issue.
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post #12 of 73 Old 08-25-2011, 12:09 AM - Thread Starter
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Thanks for the amazing responses guys! I started off by treating the floor by laying a thick carpet and my god - what an improvement! What used to sound kinda hollow and dull has suddenly become rich and tight! I will continue this incremental treatment approach and next use a couple of acoustic panels of 2ft x 4ft on each side wall to see how the sound quality improves.

However, I'm not sure how to treat the front wall as I am planning a fixed frame cinema scope screen for my projector which will be fixed to my bare concrete wall. An acoustic panel will mean a minimum 2" projection from the bare wall which will interfere with the frame and also stand out sorely from the rest of the wall.

Also, the AES paper says that "Reflections from central portions of the front and back walls have the least positive contributions". If my center channel is at 2ft height from the floor and my front L+R floorstanding speakers are around 4 ft height, at what height should the panels be for the rear wall?


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post #13 of 73 Old 08-25-2011, 12:35 AM
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Also, the AES paper says that "Reflections from central portions of the front and back walls have the least positive contributions". If my center channel is at 2ft height from the floor and my front L+R floorstanding speakers are around 4 ft height, at what height should the panels be for the rear wall?

I would start with a 4'x4' square of absorbtion (no less than 4" thick) directly behind the listening position, centered vertically around ear height, and work my way out horizontally (maybe up to 8' wide to see if that helps) and vertically (a couple feet up).

BTW, since others have mentioned DIY panels, can you get rigid fiberglass or rockwool insulation in Chennai?

Sanjay
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post #14 of 73 Old 08-25-2011, 03:15 AM - Thread Starter
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I would start with a 4'x4' square of absorbtion (no less than 4" thick) directly behind the listening position, centered vertically around ear height, and work my way out horizontally (maybe up to 8' wide to see if that helps) and vertically (a couple feet up).

BTW, since others have mentioned DIY panels, can you get rigid fiberglass or rockwool insulation in Chennai?

Directly behind the listening position? Do you mean the front wall (behind the speakers) or the rear wall (behind the seating)? We get fiber wool, glasswool and poly fiber filling in Chennai. There's an accoustics company called Anutone which has a huge range of products, which is what I'm planning to use.


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post #15 of 73 Old 08-25-2011, 03:29 AM
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Not all treatments can be DIY'ed combination tools such as RPG's BAD panels or Quest AI perfsorbers are pretty nifty and cant really be done DIY.

I echo the comments above regarding Toole's book and a little education. If you're really confused or not sure this is a pretty good service to get it right.

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Not all treatments can be DIY'ed combination tools such as RPG's BAD panels or Quest AI perfsorbers are pretty nifty and cant really be done DIY.



http://www.component.se/forum/index....0&#entry145270

http://www.component.se/forum/index....1&#entry150191
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post #17 of 73 Old 08-25-2011, 08:29 AM - Thread Starter
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Guys, can you guide me on how to treat the front wall? Should I place the acoustic panels behind the centre channel and at what height?


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post #18 of 73 Old 08-25-2011, 09:50 AM
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Guys, can you guide me on how to treat the front wall? Should ?

what are you looking to solve?

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Should I place the acoustic panels behind the centre channel and at what height?

what energy is being emitted directly behind the center channel that requires attention?
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post #19 of 73 Old 08-25-2011, 10:00 AM - Thread Starter
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what energy is being emitted directly behind the center channel that requires attention?

I have no idea! I was just referring to the AES paper and the views of other member s on this thread.


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post #20 of 73 Old 08-25-2011, 11:42 AM
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you may wish to make the distinction whether the treatment is for LF modal issues or specular issues. approach and material requirements can be drastically different.

eg, in your quote, you reference the wall behind and besides the speaker - where omni-directional LF reflections may occur, but im not sure how effective 2-4" mineral wool would be due to the requirement for LF absorption for this specific issue.

My post has everything to do with > 100Hz.

This is not rocket sceince. EVERY speaker creates a soundwave at even 180deg), this means there is a soundwave travelling out from the back of the speaker and hitting the wall behind it. Everything above 500Hz can be absorb when having >= 2", therefore removing that off axis response created by the speaker.

We have been in this discussion already.

Modal issues (below 300Hz in most rooms) is another topic. 100Hz can be addressed with thick (> 6" ) bass traps and also by using mulitple subwoofers or bass bins even running up to 300Hz placed near the main speakers but firing off in a different direction.

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post #21 of 73 Old 08-25-2011, 11:45 AM
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what energy is being emitted directly behind the center channel that requires attention?

Again, speakers create a soundwave 360deg. You can either worry about it or not worry about it. How do you think nulls around 140Hz are created from main speakers placed 2 feet from the wall?? Its because of the rear wave created by that speaker.


If you have measurement equipment you can put the mic behind the speaker and measure the 180deg off axis response of that speaker. You gate the measurement out to 2 or 4ms (Depending on room, speaker placement during measurement) to remove any reflections.

I have never seen a good off axis response from any speaker @ 180deg. I will go further to say that 90deg off axis response are generally horrible too. Also if the speaker has no directivity control you can include 60deg off axis response.

I want to control any off axis response that does not match that of the on axis response. Of course I build speakers that have controlled directivity out nicely to atleast 60 deg so I have less concern about inaccuracies off axis.

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post #22 of 73 Old 08-25-2011, 11:51 AM
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Guys, can you guide me on how to treat the front wall? Should I place the acoustic panels behind the centre channel and at what height?

How big is the front wall ?? EDIT, you posted 14 feet.

Generally a 2'x4' panel (several of them) placed on the wall with small gaps between them will improve your in room response. To determine roughly how many you need you just need to divide your distance by 2 feet.

EDIT I would say 6 4" panels would be great with 6" panels placed in the corners (diagonally) so thats 18 2" acoustical panels (Mineral wool or OC703), which is 3 packages ( they come in packages of 6) and are about $70each + shipping.

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post #23 of 73 Old 08-25-2011, 12:25 PM
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Again, speakers create a soundwave 360deg. You can either worry about it or not worry about it. How do you think nulls around 140Hz are created from main speakers placed 2 feet from the wall?? Its because of the rear wave created by that speaker.

what you're referring to is SBIR.
in your original response (to which i replied), you stated:

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You should treat the wall behind and beside the speakers because that is where the speaker creates WORST response. 2 or 4" OC703 or 2" Mineral Wool (the one I posted) will absorb those soundwaves for you getting rid of their nasty response.

i didn't agree that 2" or even 4" would cure SBIR issues. specular issues, sure...but SBIR is a LF issue which will require LF absorption. and i replied with the statement:
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you may wish to make the distinction whether the treatment is for LF modal issues or specular issues. approach and material requirements can be drastically different.



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If you have measurement equipment you can put the mic behind the speaker and measure the 180deg off axis response of that speaker. You gate the measurement out to 2 or 4ms (Depending on room, speaker placement during measurement) to remove any reflections.

hopefully the speaker mfg would provide polar responses
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post #24 of 73 Old 08-25-2011, 12:28 PM
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Originally Posted by penngray View Post

EDIT I would say 6 4" panels would be great with 6" panels placed in the corners (diagonally) so thats 18 2" acoustical panels (Mineral wool or OC703), which is 3 packages ( they come in packages of 6) and are about $70each + shipping.

very thick traps of lower GFR material (cheap, pink fluffy insulation) will be far more effective at LF absorption than 6" mineral wool/OC703 if one doesn't have real estate constraints.


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Generally a 2'x4' panel (several of them) placed on the wall with small gaps between them will improve your in room response. To determine roughly how many you need you just need to divide your distance by 2 feet.

placed where, exactly? improve the room response in what region (specular or modal)? shouldn't he have actual identified issues before proceeding with treatments to address said issues?
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Im pretty sure the OP is looking for real life solutions from those who have done similar DIY treatments. If you have a real life solution (like a real custom HT room with real treatments) to post then Im sure he will welcome it.

I have already posted about placement, I have posted what it absorbs (direct off axis sound waves). The OP can choose to do what he wants if he wants to discuss theories then he can. Im pretty much done with a lot of theories, If it was me I would only care about who is buying/building and doing.

After years of banter over many, many audio topics I have concluded that any theory without practical experience now tells me not enough $$$/work.

I want $$$/work more less theory

Maybe you are posting that my suggestion does nothing for his room?? Is that what you are trying to post?

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Maybe you are posting that my suggestion does nothing for his room?? Is that what you are trying to post?

your recommendation for 2-4" mineral wool for LF absorption of SBIR issues - i disagree with, yes. i added my input that cheap, pink fluffy insulation will be a far more effective porous LF absorber than OC703/mineralwool, given that he does not have real estate constraints.

i also think your recommendation for: "Generally a 2'x4' panel (several of them) placed on the wall with small gaps between them will improve your in room response.", is confusing - as it does not say what the panels are to address (what specific issues, so he knows why he is placing them) or where specifically on a boundary they should be placed.

and saying that it will "do nothing for his room" is just a strawman. treatments should be chosen based on specific issues one is looking to address - not blind applications of random treatments.
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post #27 of 73 Old 08-25-2011, 01:44 PM
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Originally Posted by localhost127 View Post

your recommendation for 2-4" mineral wool for LF absorption of SBIR issues - i disagree with, yes. i added my input that cheap, pink fluffy insulation will be a far more effective porous LF absorber than OC703/mineralwool, given that he does not have real estate constraints.

Do you have measurements to back up that opinion? 4" will absorb down to 100Hz (100%). That is all that is needed.

Also,
I have yet to see an install with pink fluffy insulation so please point me to references. Fluffy insulation has horrible Absorption Coefficients

You should use this as your reference..
http://www.bobgolds.com/AbsorptionCoefficients.htm, check out that "fluffy" stuff...I guess if you had 14 foot wall, 10 feet deep it might be worth something and it might start working

btw, I have posted many times in many threads that 10Hz to 300Hz takes more then just some panels on walls so Im not sure why you keep posting thinking Im giving a perfect solution for 10Hz to 300Hz. Im posting that 300Hz to 15KHz and above matters too and when we remove the bad off axis response from the room we have a more accurate/more detailed listening experience.



Quote:



i also think your recommendation for: "Generally a 2'x4' panel (several of them) placed on the wall with small gaps between them will improve your in room response.", is confusing - as it does not say what the panels are to address (what specific issues, so he knows why he is placing them) or where specifically on a boundary they should be placed.

and saying that it will "do nothing for his room" is just a strawman. treatments should be chosen based on specific issues one is looking to address - not blind applications of random treatments.

Either you have real proof, real room, real experience or you argue from the strawman position which I already know you are.

Until you post an exact $500 solution then my solution like 100+ others on here stands as a viable solution with measurement improvements backing them up. You just need to spend a little time going through 100+ HT builds to see the differences it makes.

I know the differences even from speaker design/measurements because I use 2'x4' 4" panels around my speakers when I measure them to remove any room issues. The impulse is much cleaner out past 4ms and that is all that is important.

Real life solutions are all about breaking it all down to what fundamentally matters and when we can Improve the speaker impulse measurement and we will have a better sounding room.

I guess we could banter theory until the cows come home but lets get to real life application/solutions. I will ask you this.....IF you had $500 for room treatments what would you do??

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post #28 of 73 Old 08-25-2011, 02:15 PM
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Originally Posted by penngray View Post

Do you have measurements to back up that opinion? 4" will absorb down to 100Hz (100%). That is all that is needed.

im specifically stating that 4" will not be sufficient to handle LF modal issues (below 100hz) as you originally stated. you stated 2-4" would be sufficient. please take a moment to read my posts or simply use the quote feature for clarity.

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Originally Posted by penngray View Post

Also,
I have yet to see an install with pink fluffy insulation so please point me to references. Fluffy insulation has horrible Absorption Coefficients

do you understand how to build an effective porous absorber (for LF modal issues/absorption)?


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Originally Posted by penngray View Post

You should use this as your reference..
http://www.bobgolds.com/AbsorptionCoefficients.htm, check out that "fluffy" stuff...I guess if you had 14 foot wall, 10 feet deep it might be worth something and it might start working

it helps to have an understanding of how porous insulation 'absorbs', (eg based on particle velocity, as it is a velocity-based absorber) - and why we need thick traps or large air-gaps to bring the insulation away from the boundary (where velocity is zero and pressure is maximum), and towards areas of high particle velocity such that the absorber will be more effective.

within the specular region, the wavelengths are relatively short and have much less energy than LF - hence we can get away with a few inches of rigid fibgerglass (or another relatively high GFR material) to fully attenuate a specular reflection.

for the LF modal region, the wavelengths are much longer and as such, porous absorption in not very effective when the insulation is spaced close to the boundary where particle velocity is approaching a minimum. hence, the absorber will become more effective (and at lower frequencies) as the insulation is spaced away from the boundary towards areas of high particle velocity. this is generally done by using thicker material or providing an air-gap for the panel. however, since this is porous insulation, the thicker the trap the lower gas-flow-resistivity material you will want to use.

if you continue stacking dense, rigid fiberglass panels together, eventually the porous holes will be unpenetrable and the 'absorber' will function like a reflector.

one can build more effective porous LF absorbers with thick traps of cheap, pink fluffy attic insulation than with thinner (4-6") panels of rigid fiberglass such as OC703 or equivalent GFR mineral wool.

the thicker the trap, the more effective it will be. as you make thicker and thicker traps, you need to use a lower GFR material.


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Originally Posted by penngray View Post

btw, I have posted many times in many threads that 10Hz to 300Hz takes more then just some panels on walls so Im not sure why you keep posting thinking Im giving a perfect solution for 10Hz to 300Hz. Im posting that 300Hz to 15KHz and above matters too and when we remove the bad off axis response from the room we have a more accurate/more detailed listening experience.

please stop putting words in my mouth.
if you actually read what i've written, i noted a difference of opinion in regards to your claim that 2-4" mineral wool/OC703 would be sufficient for SBIR issues.


Quote:
Originally Posted by penngray View Post

Im posting that 300Hz to 15KHz and above matters too and when we remove the bad off axis response from the room we have a more accurate/more detailed listening experience.

right - but that "bad" off-axis response/energy is specular - as such, it's modeled like light (which is why we use the 'mirror-trick' to identify reflection points). this was my disagreement with you when you commented to simply place the absorbers on the wall (without any distinct clarification on precisely where with respect to the listening position).


Quote:
Originally Posted by penngray View Post

Either you have real proof, real room, real experience or you argue from the strawman position which I already know you are.

and either you understand how porous absorption works and how to build effective absorbers, or you dont..


Quote:
Originally Posted by penngray View Post

Until you post an exact $500 solution then my solution like 100+ others on here stands as a viable solution with measurement improvements backing them up. You just need to spend a little time going through 100+ HT builds to see the differences it makes.

my recommendations above for a porous LF bass trap is cheaper and more effective than your recommendation for expensive OC703. save the expensive OC703 for the specular reflection attenuation - but build thicker traps of lower GFR material for the corner bass traps.
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post #29 of 73 Old 08-25-2011, 03:24 PM
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im specifically stating that 4" will not be sufficient to handle LF modal issues (below 100hz) as you originally stated. you stated 2-4" would be sufficient. please take a moment to read my posts or simply use the quote feature for clarity.

Here is a perfect example of why its a pointless discussion with people like yourself (those who do not spend $$$ and time to actually figure it all out). You not only mis-read but you actually ask me to take a moment to read anything you have posted.

Show me where I posted anything about "handling LF modal issues (Below 100Hz)" ??? Besides that major mistake, I still wait for a link proving your theory about fluffy fibreglass....which is CRAP to deal with in the first place. I would never touch it myself but hey you seem to have lots of experience with fibres stuck to your cloths, etc Please feel free to provide links instead of strawman arguements.

You think the OP wants to get a PhD in acoustics but in reality he just wants someone to tell him what to do without spending a fortune. He can still choose read/learn but let him decide that. 99.9% can just follow exactly what others have done. In the world of business there is zero reason to re-work the wheel. Cost effect solutions are found from others doing the dirty work. Example CVS does not need to research locations when Walgreen already did it (and visa versa)


The OP can choose to follow someone with only theory, no HT room and no actually solution or he can follow all the history found on many, many DIY acoustical treatment threads online. Remember just doing something is half the battle. If he wants perfection he has to go the extra mile but that extra mile is exponentially more expensive and time consuming. I say get something basic in and its an improvement period. Simply put...Rooms without any sort of treatments suck period compared to any room with basic DIY treatments.

Quote:


and either you understand how porous absorption works and how to build effective absorbers, or you dont..

So you have no real life experience??


Quote:


right - but that "bad" off-axis response/energy is specular

100% different topic...Im not sure you understand how a speaker radiates sound and how that sound can be absorb. Its easy to see in measurements so please do some measurements.

Im done, the OP will choose, This seems to be going off on silly tangents like the other thread with point by point questions (Sign of strawman debating style, not interested) and your questions are not really valid to what the OP needs. Remember its your room, your money and your time so post those results of using fluffy fibreglass at your convience. I know what I did worked very well for me and my room.

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post #30 of 73 Old 08-25-2011, 03:31 PM
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I still wait for a link proving your theory about fluffy fibreglass....which is CRAP to deal with in the first place. I would never touch it myself but hey you seem to have lots of experience with fibres stuck to your cloths, etc


http://www.whealy.com/acoustics/Porous.html


penngray,
where placed is a porous bass trap (LF absorber) most effective?
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