Need some help for living room acoustic treatment - Page 2

^^^^^^^

I just read your attempt at starting a thread pertaining to room acoustics. I'm sorry but it completely changed the subject of this thread for me. You Sir are something else!

I'll just say this, most of the audio websites I frequent, fortunately, have members who work in the "acoustic industry". These members work and study residential audio and manufacturer and distribute products that actually make a difference in the specific environments they were intended, our homes. These products tame the many negative aspects that occur when one turns on a stereo in a room. Fortunately these acoustic professionals contribute and give advice without concern to whoever asks on these audio websites. As has been the case with this thread.

I am not sure what this emotional response is about. Marty/you asked the relationship between density of fiberglass and its effectiveness. I pointed you to a specific post that had the answer not based on anecdotal data, but research from top experts in the industry:

Dr. Toole has 40 years of experience in the field of sound reproduction in rooms. He is heavily published in this field and needs no one to defend him. No, he is not in "acoustic industry." That is good. Because he is not motivated to sell you acoustic products. He is trying to teach you the science and then you can decide what to do about it. If you want a voice from that industry, that is also there in the above quote in the form of Dr. D'Antonio, who is the founder of largest acoustic product company (RPG) and with more published research papers in the area than all the people in this thread combined and then some.

What about me sharing the above info got you to post what you post? Are you saying you rather have members like Marty not hear what the top industry researchers say? Just because they choose to not be a member here???

We are fortunate to have individuals post on this site that have real world experience in residential acoustics. It appears you have taken up home integration as a hobby and I find that interesting. You have a very excited mind. I hope I didn't offend you in anyway that wasn't my intention.

Here are some of my questions that I need some help with. I have had two different people tell me two different things, so I would like to get some more opinions on it.


1. So do all of you guys believe that lower density insulation is the best?

2. What about with fluffy insulation, is lower density still the best with it?

3. Also with regards to the fluffy stuff, should it be compressed, or not?

4. If the fluffy stuff should be compressed, then how much should it be compressed?

5. Also, if going with the fluffy stuff, what brand/model/density/R-value should I look into?

I will let Ethan answer your questions.


However you have Amirm, quoting Dr. Tool, quoting D'Antonio which is confusing. The quote he is borrowing refers to controlling reflections with a single density material. I would ask Amirm to please explain the difference between reflection points and absorbing low frequencies. And to provide specifications on the low density material he is recommending.

If costs, space and appearance are not issues, then yes.

Of course, costs, space and appearance are almost always important.

If by fluffy insulation you mean insulation that is put in walls and ceilings to trap heat, then in general its density is too low for an efficient absorber design.

For best results, obtain insulation that has the desired density without being compressed any further. If you try to compress fluffy sheets, you may get uneven density. Besides, trade pricing of absorbing material tends to follow weight. Denser material can be used in thinner thicknesses (within limits) and the weight and therefore the price tends to remain the same.

If you experiment with the porous absorber spread sheet that I posted a link to, you will find that for any given thickness and configuration of absorbing material, there is an optimal density that gives the best results.

One general rule might be that the thinner the absorber, the denser the absorbing material needs to be.

We are usually constrained as to the thickness of the absorber as we don't want it sticking way out of the wall or ceiling! Therefore the optimal absorbing material may be thinner and denser.

No, you heard two opposite answers. Ethan gave you measurements he made that said higher density is better. I post reasoning from top industry people that says the answer is the opposite. The reference Arny gave you proves the same thing I said but requires material science knowledge to use and verify in this case.

The physics of this can be complicated to explain but let me say it at very high level. A "porous" absorber like we are talking about works by having the air particles enter it and then due to friction of the fibers get converted into heat and with it, give you the absorption you are after. For this to work the best, you want no resistance to particles wanting to go inside it otherwise they reflect back and you get no absorption. Once inside, you want to have higher resistance for the energy to dissipate. To optimize the former, you want the "impedance" (its resistance to flow) to be the same as air in your room. Anything higher will cause an "impedance mismatch" and cause some of the sound energy to reflect. As I noted, what is reflected will not be in the absorber so therefore by definition cannot be converted to heat/absorbed.

The other poster said we should listen to people in acoustic industry and not me (even though I gave him industry people quote, not my own). So here is one: http://www.readyacoustics.com/index.php?main_page=faq_info&fcPath=13_4&faqs_id=36

"Yes, but I have read that higher density acoustic insulation (like OC705) is better for low-end absorption.
That’s simply not true.

The common misconception that higher density acoustic insulation makes for better low frequency absorbers arises from a fundamental misunderstanding of how the physics of porous acoustic absorption works in the real world [as opposed to the world of internet chat forums]. "

He then provides the same explanation I gave above plus these set of measurements:



The numbers you see are coefficients of absorption. The higher the numbers, the more it absorbs sound at that frequency. At 500 Hz for example with a 4 inch panel against the wall, 703 has an absorption coefficient of 1.24 vs 1.17 for 705. So higher density resulted in less performance. The difference is not huge though so if all you can get is 705, and you know the material will enhance the sound in your room not make it worse, go ahead and use it.

Note that as I said, at some point this equation reverses where you have too little resistances inside the absorber and hence effectiveness goes down. This is not an issue with respect to 703 and 705 material that are far denser than this threshold.
The problem you have with lose material is how to contain it and build a structure out of it. If you put fabric, plastic or whatever in front of it, you again create an impedance mismatch and at some frequency, the sound starts to reflect instead of going into the material. When it does, then it acts more like an equalizer, filtering/absorbing some frequencies more than others. If you have a well designed speaker that had pretty even off-axis (side-ways) response, you just screwed that up by modifying the spectrum that comes back from the absorber. So while there are products of this sort in the market, you have to be careful in using them.
Per above you want to have less "compression" than more. Also note that the relationship between density and resistivity flow is not always as I explained. If you change material from the ones we are talking about, you are on your own researching what that is .

So stay with the common 703/705 material. It has a good balance between acoustic and structural aspects.

Answering the other posters comments, you do not want to use these materials as your main means of controlling low frequencies. Porous absorbers work best when the particles are moving fast by them. When the wave hits the walls, the air particles obviously are not moving anymore so there is nothing to absorb. If you move the panel further inside the room, then it starts to work better at low frequencies that have their highest velocity there. The above table does not go low enough to show this. Here is a simulation based on the (useful) spreadsheet link Arny provided to you that does demonstrate this effect:



As you see the low frequency absorption improves when you add 4 inches of air behind 4 inches of porous material. The reason for that is what I just explained: you are placing the absorber where particle velocity is the highest.

Note that even with this technique, you are still not getting a lot of absorption at low frequencies. The simulation even stops at 62 Hz. You would need to use a lot of these panels to make a dent in low frequency absorption. This is why you want to use other techniques first to reduce the impact of the problem first (see my article on Low Frequency Optimization: http://www.madronadigital.com/Library/BassOptimization.html). Using those techniques, you may not need any absorbers for low frequencies. But if you do, then you don't need as much of it.

Above low frequencies, you *really* need to be careful to not run off with "forum wisdom" or companies selling products as that can be lead you astray, resulting in worse sound in your room, not better (see my other article on Perceptual Aspects of Room Reflections http://www.madronadigital.com/Library/RoomReflections.html. Best use of such solution, if you have an otherwise bare room, is to control the later reflections that linger in the room which is a different animal than first/early reflections. Rooms need to be not too live, not too dead.

As you can see, there is a lot of complexity here and what seems intuitive often is not what the science says.

It depends on the thickness, as Arny mentioned. With thinner material, like 1 or 2 inches, higher density is definitely better. Once you get to 8-12 inches thick low density works very well and for less cost.

Yes, but as related to my answer above. If you have room for 12 inches of insulation, I'd leave it at the full 12 inches.

I'll also mention one of my favorite sayings: "Empirical evidence trumps theory every time." The graphs in my Density Report are from actual measurements, not the result of simulation calculators or gut feelings.

One of the problems with simulations - and even lab tests - is they don't take other factors into account. For example, FRK type rigid fiberglass three or four inches thick mounted straddling a corner can vibrate as a unit and increase absorption at bass frequencies. This doesn't occur in most lab tests where the materials are typically placed on a cement floor. There are other such issues I can explain if anyone cares.

--Ethan

Looks like a good plan to start with. Those should help alot.

Save yourself some trouble and get one of these new USB based measurement mics, http://www.avsforum.com/t/1442623/new-mic-option-from-the-good-folks-at-minidsp.

I've already got the mobile pre and a calibrated behringer 8000, but if not I'd save some $ and cable hassle.


Sent from my 32GB iPhone4 using Tapatalk

Boomy bass is most likely a couple of sub 100hz room modes. Acoustic treatment unless you use A LOT does little down there. Best options are multiple subs and/or EQ. Personally I'd EQ in your situation.

Ok, so it looks like I will have to splurge on the OC703 as opposed to the regular pink fluffy stuff. I live in a very rural part of the country and none of the local stores, including the Home Depot or Lowes (about 30 min away), seem to have anything except the fluffy stuff. So with that being said, I will have to order the OC703 or OC705, both of which are a lot more expensive than the pink fluffy stuff. I will most likely stack 2 layers of the 2 inch OC703 for a total of four inches made in to 4 foot by 4 foot panels that will be placed on the ceilings and rear walls. I will use a 4 inch air gap between the panels on both the rear walls and the ceiling. I still haven't decided on whether or not I want to treat my side or front walls. I know that, normally, the best thing to do would be to measure first, then treat the room based on the measurements, but the problem with that is the fact that my mains are bipolar Def Techs, and thus, are made to bounce the sound off of the front and side walls, and would likely be a huge mess for measuring.

That's a valid point, real world applications have changed a lot over the years with room correction software and the ever increasing use of sub/s, not to mention the use of more speakers in general.
You're not going to run into very many systems now not using any one or more of those. So even if you don't get the room treatments perfect as you'd strive to in lab conditions, you've got other tools & conditions in the real world.

Gistum, what's that narrow room on the left of your couch? If you can access it, and it's basically empty it might be a great location for an inexpensive but effective infinite baflle sub....

It is most likely real! If you have done nothing to deal with bass response in your room, it is likely all over the place. The peaks not only increase the level of that frequency but also make the notes last longer. The electronic techniques the few of us have been talking about fix the problem in both domain, even though some claim only acoustic products do. That simply is not the case. For the proof, and a mini tutorial on how to use REW correctly to analyze this problem, click on the first link in this google search:

https://www.google.com/search?q=site%3Awhatsbestforum.com+Acoustic+Measurements%3A+Understanding+Time+and+Frequency&rlz=1C1SNNT_enUS374US375&oq=site%3Awhatsbestforum.com+Acoustic+Measurements%3A+Understanding+Time+and+Frequency&aqs=chrome.0.57j58.5654&sugexp=chrome,mod=8&sourceid=chrome&ie=UTF-8

There, you see real measurements and step by step equalization that reduced both frequency response variations and time doing "ringing" as the effect you are talking about is called.

I can't emphasize enough the need to first reduce the impact of these issues electronically+subs. Ask anyone who builds high-end theaters and these techniques are absolutely standard practice. Somehow in these forums the message gets lost and confused, with all the focus put on fiberglass as the means of getting better sound in a room. If anyone claims to fix these problems with insulation material alone, ask them to post a picture of how much it took in a real residential room and what the response was at the end. You will likely find an uneven response and tons of panels. There is just no reason to turn part of a home that is not a dedicate theater into such chambers.

I have read the early reviews and seems like a very cost effective solution. For the price and simplicity of use, it is very worth it.

I am not sure why adding a sub is out of the question for you and your wife. The addition of a subwoofer is paramount to what you're trying to accomplish.

Many quality manufacturers build in wall subwoofers, I found this Velodyne model online with a cost of $430, I know you live in Europe but an in-wall will be easy to find.


http://velodyne.com/sc-600-iw-in-wall.html

what's comical is neither arny nor amirm even understood porous absorber design (eg, "flow-resistivity") or were even aware of a porous absorber calculator until i presented it to them.

glad you guys are finally starting to "catch-up", but your understanding still shows some fallacies


it's cute how you guys rush to catch-up on a topic only to regurgitate it here and then make an attempt to present yourselves as "experts" on the subject.


oh, dear -- and how this guy used to argue me relentlessly on the subject of acoustical treatments and design - and now he's basically presenting the same information that he was in contention with when i provided it some considerable time ago.

thanks for the laugh; you still have some gaping holes in your commentary regarding the subject - but you're making progress, amirm.

i now look forward to some new "articles" by you relaying your newly found information/understanding on what has already been well known and well understood for some considerable time in the field.

the "huge mess" here is the ignorance of the previous commentators in failing to explicitly define the proper types of design (and subsequent materials and placement) dependent on how they are to be used (eg, what specific acoustical problem they are being procured to solve). they attempt to lump all types of absorbers together as if one type or one design etc is sufficient for indirect specular reflection control and subsequent modal issues. nevermind the fact they are attempting to use reverberation chamber methods/absorption coefficients (eg, random-incidence diffused field) when we most certainly do not have that type of acoustical behavior in our residential spaces.

to dumb this down as simply as possible:

--- utilize 4" OC703 (or equiv 4pcf mineral wool) w/ 4" air-gap for indirect specular reflection attenuation down to lower schroeder cut-off (~250-300hz - typical of home residential sized rooms). this is based on Delaney, Bazely, and Miki models (and subsequent modifications, as they satisfy all of the various mods to it). if your design requirements for the room's total specular response calls for attenuating of early arriving, high-gain, sparse, indirect specular reflections - then you would place these at areas as identified via the Envelope Time Curve (ETC) response. if you do not have a measurement platform, then you can blindly place these by utilizing a mirror (where angle of incidence = angle of reflection for wavelengths that are SMALL with respect to boundary size).

--- for LF absorption within the modal region (eg, corner porous bass traps if you are limited to velocity-based absorbers only - where wavelength is LARGE with respect to boundary size), sufficiently thick absorbers (which are required due to the much longer wavelengths of the lower frequencies) are more effective when using materials with lower gas-flow-resistivity (eg, pink fluffy = ~ 5000rays/m). it is imperative that the insulation is LOOSELY filled and UNCOMPRESSED. you can build wooden frames or use orchid/bird netting found at any hardware store to contain the insulation. sound has size - the LF absorbers need to be as physically LARGE as possible as well to restrict the waves from simply diffracting around it. again, this introduces a new problem as installing many large porous absorbers (for LF absorption) in the room will inadvertently attenuating indirect specular reflections within the room as well - which can quickly lead to a highly damped (dead) space. if this is NOT a design goal, then you can wrap the LF absorbers with a reflective material such as 6mil plastic - which will reflect ~500hz+ specular energies back into the room. and even more ideally, you can apply a scattering or diffusive surface to the exterior (outer face) of the LF absorber (MLS, BAD, QRD, PRD, etc)....

a "peak" that is a result of two or more signals combining in-phase (constructively) to provide a higher perceived gain at a particular point in 3space (technically 4space) does NOT imply a resonance (eg, mode/antinode) where that energy would persist ("last") any longer.

you cannot continue to make these overly generalized assumptions in your commentary - it leads to further confusion.

for a "peak" that is a result of a modal resonance within the room, yes - but not all peaks are going to result in "notes lasting longer". since when does basic 3D spatial polar lobing result in increased decay times.




modal ringing (LF decay times) as evident by a CSD/waterfall plot is NOT a time-domain measurement.



"no reason", he states. since when did you have the authority to dictate how to modify a residential room based on a user's design requirements or what they find pleasurable?

yes, ask anyone who builds "high end theaters" and you'll probably find that in the process of something called the "design phase", they actually take into account how to effectively start off on the right foot with regards to LF response. anyone who builds "high end theaters" should hopefully NOT be concerned with installing porous absorbers after the fact - unlike people here who have ALREADY CONSTRUCTED residential rooms.

oh, and you're still seemingly clueless as to the existence of pressure-based resonant absorbers ...which have only been used in professional rooms for decades.


i know it's 2013 now and all, but much of this information is already well known and has been deployed for decades. this is not new.
Edited by localhost127 - 1/3/13 at 3:16am

Acoustic treatment can be pretty. Check my avatar pic and I'm a chick so it's chick approved. I would definitely recommend some heavy drapery for the rear glass doors. Since you're space challenged for a sub, what about an in wall subwoofer? I have 5 subwoofers so , needless to say, I value their importance.

I really hate to see someone senselessly hurting themselves by breaking both arms while trying to pat themselves on the back. ;-)

I will admit that my interchanges on AVS have been beneficial and educational, but it was more in spite of certain poster's obfuscation, lack of people skills and arrogance than it was because of them...

As far as Chris Whealey's porous absorber calculator goes, a little web research will show that Chris, Ethan and I co-posted on the Usenet rec.audio.pro forum a number of years back (ca. 2006) and discussed it then and there:

http://www.audiobanter.com/showthread.php?t=75030

On balance, our alias-protected correspondent does seem to be taking some relevant hits on one of our more refractory local eggspurts who claims business connections to a high end audio store. ;-)
Edited by arnyk - 1/2/13 at 9:31am

I don't know that particular microphone, but I've tested many including some that cost even less:

Comparison of Ten Measuring Microphones

--Ethan

noted and i take back my comment related to you. it was the reference to 'flow-resistivity' that we were in debate many months ago, not the PAC.

although it is comical to see amirm catch on in the older threads, where he started taking screenshots of the PAC without providing reference - and referring to it as "simulations".
Edited by localhost127 - 1/2/13 at 10:30am

If you are a salesman trying to cast an image of yourself as being right to unsuspecting readers, what else would you do?

and that's basically all that needs to be said. all of these attempts at generalizations regarding which density is "better" is utterly meaningless without the context of the other variables that are part of the system - the most important variable being the specific acoustical problem the 'treatment' is being procured to solve.

eg, why are some here discussing "panel" absorbers with respect to LF absorption? panel absorbers are for indirect specular reflection attenuation. the design, placement, approach, etc is different. one user here just stated "You would need to use a lot of these panels to make a dent in low frequency absorption.". of which i would reply, why are you attempting to achieve LF absorption with panel absorbers???