[tinkerphile]

I've been giving a lot of thought to how to best go about planning an entire room acoustic treatment.  One of the factors I'm wrestling with is calculating where optimal absorption and diffusion should be placed.  While I get the general philosophy (at least I think I do) - I've been reading several sources and talking with some guys, I do not yet understand the method to arrive at the best placement.  Generally, I am leaning toward the following for a dedicated 2-channel listening room:  Approach: LFZ, front half of rectangular room (12 W x 22 L x 9 H); Floor to ceiling absorption, including significant corner traps.  Some persons differ with beginning with the LFZ approach, as I understand it. So many articles and discussions are geared toward the studio thing, but it seems to apply very well with a listening room application.  I realize that even in the LFZ front-half, there needs to be some diffusion. I'm guessing front wall, center area plus first reflection points (as my loudspeakers baffle/front are 30" from the front wall).  Rear-half of room, will need corner traps, rear wall absorption floor to ceiling, and I'm guessing diffusion at the center of rear wall approximately 6 feet wide by ? inches high. 

I'm concerned that I won't have the proper absorption/diffusion combination at the first reflection points; there must be a general theory of application here, but I haven't found it despite all the resources I've read.  Nor have I found a best design for an effective multi-purpose treatment at this particular area.  Next, I'm concerned to understand the proper method of a step-by-step approach for a solid plan for this approach (that I think I should take) to reach my goals.  Hopefully I've made it mostly clear what I'm attempting to accomplish and what my situation is (?).  Plus, I'm hoping this discussion is something that a lot of others would profit from. 

[Dieterle Tool]

What type of speakers are you using (acoustic suspension or bass reflex, dipole, open baffle)? Any subs?

Not sure what LFZ is? Just from your description above, it sounds like a lot of treatment. I agree with diffusing the first reflections, absorbing the wall behind the speakers but how much depends on type of speaker. Add diffusor back there with rear firing speakers but use sparingly. Thick corner traps are a good idea but not sure floor to ceiling is necessary.

As far as side wall diffusion, a lot of folks use a (foam like) product designed specifically for this but if esthetics are an issue, I recommend some wood, art panels at least 24" x 36" in size. I have never included absorbing panels at this location.

And, using REW (room eq wizard) software and a miniDSP, USB microphone will help you balance the treatments. Keep you from over doing it.

Not sure if this helps, hopefully some of the resident experts will chime in for you.

-Dieter

[JLM]

Yeah, what is LFZ?

You have a well shaped and decently sized room.  Treatments are at best bandaids for a poorly shaped/sized room.  That is most of the battle.  Insulating the room is the next.  Have you set up your system in the room yet?  If so what are your complaints?  Reading Floyd Toole's "Sound Reproduction" 3rd edition you'll learn that all rooms have severe (up to 30 dB) bass peaks/dips and that the best way to solve them is with the use of multiple subwoofers carefully place around the room.  Look up Duke LeJeune (AudioKinesis here at Audio Circle in the manufacturer's child circles).  He's very helpful and into speaker/room interaction.

After setting up the subs the following step should be to analyze the room via REW or Dirac to see what anomalies exist, then make corrections and decide if you like the changes.  Note that this is strictly a testing stage, as digital room correction should only be used as the icing on the cake.  Once you've decided how much correction is needed and at what frequencies go shopping for treatments. 

A classic treatment method is LEDE (Live End, Dead End) where the speaker end of the room is fully treated with absorptive material and the opposite end is left bare.  Another  method is the treat first reflection points (walls/ceiling spots where a mirror would reflect an image of the speaker at the listening position) with absorptive material.  A suggested hybrid would be to use either of the above with side wall diffusion if monopole speakers are used or behind the speakers if dipoles are used. 

Diffusor design is based on proper variation and depth of pockets.  Those nasty laws of physics will limit how far down the frequency range diffusors of varying depths will be effective (7 inch depth = 1100 Hz).  So diffusion is only a mid/high frequency treatment.  And to be effective must be constructed of sonically opaque materials like painted wood, not the thin plastic or open cell foam often sold.  Here's a good link for DIY diffusors:

http://www.pmerecords.com/Diffusor.cfm

The proper balance between absorption/diffusion must be done on a case by case basis.  What are the room finishes?  The harder (glass, plaster, masonry) the more absorption should be used.

If you look at most manufacturers they would have you fill the room with treatments which would certainly over dampen the room.  Recommend contacting GIK (here at Audio Circle).  They sell effective absorption panels at reasonable prices.

Once you have the room treated, then repeat the REW/Dirac process to fine tune. 

[tinkerphile]

Thank you DT and JLM for the advice - very much appreciated. 

Sorry about the LFZ … cerebral flatulence: I had my mind so preoccupied with LEDE that when I had intended to type RFZ, I borrowed the letter L.  So, yeah, I had meant RFZ.  And in reality, I had considered my approach would have to be LEDE/RFZ. 

Room is painted drywall.   Loudspeakers are DeVore O'96's.

I'll get in touch with the contact you suggested here on AC.  And, thank you also for the link provided.

Another individual suggested a particular microphone which is more than adequate for a reasonable cost, and I'll familiarize myself with REW, as you suggest I will need to have.

I will not be able to afford the acoustic treatment, so I am stuck with DIY for the most part. 

RE multiple subs - - That's one of the most interesting approaches I've seen.  Those would also have to be DIY.  I'll take a look at the cost over at GR Research's site.   I already have one of his large center channel speakers and really like it, and for the money you can't beat it. 

[JLM]

RFZ = Reflection Free Zone.  In other words use of absorption panels at the points in the room where a mirror would show the speaker from the listening position (first reflection points).  LEDE is the "overkill" version of RFZ. 

Every room has bass peaks/dips (some up to 30 dB!).  Humans are very adaptable and the untrained ear is conditioned to ignore them.  Multiple subs (3 or 4) carefully placed around the room is the best solution, but not cheap.  Diffusion only works at higher frequencies due to the depth of the panel versus the size of the sound wave.  Diffusion has been recommended for the wall behind dipole speakers to enhance midrange/treble performance.  Absorption can help but only if the right material is used (look for test data).  Run away from open cell foam.  Owens-Corning 703, high density fiberglass, is the best and is used by GIK (a sponsor here on Audio Circle).  Rockwool is the fall back material.

Is the room insulated?  How much outside noise is there (from other occupants, furnace, wind, traffic, etc.)?  If possible add insulation in wall/ceiling/especially windows.  Avoid thru wall electrical boxes and recessed can light fixtures.  Wrap ductwork with deadening material or replace with lined flexible fiberglass ductwork.  Install an exterior insulated fiberglass door with weather seals.  All this can drop the noise floor by 20 dB!

Suggest setting up the room (after you've insulated) to see how you like it.  Second measure the room.  REW (Room Eq Wizard) is free but you'll have to buy the microphone (which should be calibrated).  Third add the subwoofers to help with bass peaks/dips, setting them by ear.  Fourth add the treatments to address midrange/treble issues, again by ear - not by eye.  Lastly remeasure the room and make any needed corrections.  Most recommend only applying room correction to the frequencies below 500 Hz as above that you'll be changing the sound of your speakers (which is assumed that you bought them because you like how they sound).  Don't boost narrow dips which can't be heard and suck power, causing amps to clip that can destroy speakers.

Digital or EQ room correction tries to cheat the laws of physics.  According to Earl Geddes, a well respected acoustician, it's best to solve physical problems by physical means (room size/shape, subwoofers, absorption, diffusion).  Room correction provides ideal sound but only at a single location, by taking from or adding to other locations in the room, creating very unnatural effects like squeezing on a balloon.  So only apply as icing on the cake.  Realize that subwoofers, absorption, diffusion, and room correction are only bandaids to fix a poor room and your room shape/size is already good.

Make sure that any DIY absorbers are wrapped in acoustically transparent material to keep harmful particles encased.  Suggest starting out with just a few absorbers and play it by ear. 

Note that DIY subs is a very tough way to save money as so much of the cost goes into the driver which manufacturers buy at bulk discounts.  SVS SB-1000 is a good small sealed sub at $500 apiece.  Rythmik L-12 is a better small sealed sub with servo control added at $569 apiece ($539 when bought in multiples).  Sealed subs are recommended for audio for their tighter sound and slower roll off into deep bass frequencies (which natural room reinforcement compensates for).

[Jon L]

After reading many reviews complaining about how the average foam acoustic treatments either don't work that well or have QC issues, I bit the bullet and ordered some Acoustimac DMD panels, which are rock wool based (claimed to be better than Corning) inside wood frames. 

I am very impressed by their build quality, especially for the reasonable prices.  What I didn't realize is how heavy these things are!!  The 4'x2'x4" bass panel alone weights 20 Lbs.
I have changed my mind to just stand them on floor or raise them temporarily with some support under them before I figure out their optimal positions for mounting. 

https://www.acoustimac.com/categories-products

Acoustimac by drjlo2, on Flickr

[tinkerphile]

Thanks for the information.  I took a look at their products via the link you provided.  Since the panel at the right side of your photo appeared to be 4" deep, I searched the linked web site, but found only 2" products.  Also, I didn't find any lab tests on the site.  I suppose one could easily calculate the effectiveness based on the type of insulation used and its thickness. 

As my post indicated, one of the considerations I'm trying to work through is whether absorption, diffusion, or a sophisticated combination of the two is best to use at particular locations, such as first reflection points on side walls or on ceilings, as well as on the rear wall.  I've seen many engineer-designed listening rooms with a combination of low frequency absorption on front walls/corners and diffusion in the center.  So my question remains on of where to place diffusers and the method used to determine placement and the dimensions.  As it stands, for the present time, I'm good with understanding what needs to occur at corners and most of the front wall (except for the diffusion area in question) and at the rear wall in terms of LF mitigation.  But again, in terms of the front half of the room on the ceiling and center of the front wall and rear wall, plus first reflection areas, I'm not sure at all.

[Big Red Machine]

A sophisticated blend of both is best. I personally prefer diffusion at first reflections.

The room is going to dictate a bunch of things you have to try and tackle or work around.

I ended up sitting in a much different location than any online calculator told me to escape a bass null and achieve better sound to my ears.

Here is a cool calculator to do the math for you if you don't have a friend to hold the mirror against the wall and ceiling for you.

http://www.acoustic.ua/forms/calculator4.en.html

[Jon L]

Since the panel at the right side of your photo appeared to be 4" deep, I searched the linked web site, but found only 2" products.  Also, I didn't find any lab tests on the site. 

The 4" panels are found under "Bass Traps."
https://www.acoustimac.com/dmd-bt4000-bass-traps-48x24x4/

Acoustimac4inch by drjlo2, on Flickr

[SoCalWJS]

Experiment!

Try Absorption & Diffusion. Live end/dead end, Dead end/live end. Move speakers around. Measure. Compare.

I've gone to a couple of "Lectures" on Acoustics at various Audio shows and learned quickly there are different Theories ("Opinions" IMHO).

Between the differences in Speakers & Rooms and how they interact, there is no Universal solution.

[mick wolfe]

I agree with SoCalWJS.  When all is said and done, it will still be a trial and error process in most cases/rooms. I started with absorbing panels on the front wall and diffusion devices on the back wall. This is a small room where near field listening ends up being mandatory.  Despite this, some first reflection/side wall absorbing can help in the taming process. Your ear will tell you when you've over damped with absorption, so go slowly in this area. I guess one could say less is more in this case. Lately I've added some diffusion devices to the front wall as well to good effect.  It's also important to note if the speakers used are panel, open baffle or even omni's, front wall diffusion (as opposed to absorption) becomes the better option. 

[mcgsxr]

My listening room is my basement so I had 100% autonomy for placement and approach. 

My DIY traps (3 inch plus hung with a 1-1.5 inch gap) are held in place with 3 of the 50lb rated wall driller drywall screw inserts. 

Works perfectly.  Even with a 15lb cat jumping on and off them.

I wasn’t concerned about holes in the walls.  All will be patched as part of an audio cleanse when the time comes to sell. 

I’d play with leaving them on the floor initially to find the places that work best in your room. 

[tinkerphile]

Thanks Jon, SoCal, others - all very helpful. 

Thanks especially for the Bass Traps reference and the lab test specs.  In terms of Sabins, what would be a near-complete, effective number be? 

How far from the floor is recommended for bass traps (I'm thinking here in terms of front wall and rear wall, not corners, as I doubt the panels from Acousitimac panels would be very effective standing in the corner at 45 degrees)?  My DeVore O'96 bass and tweeter are about 24"- 34" from the floor. 

When I see the cost of very low frequency effective corner traps (e.g., Real Traps, others like that), it's insane...esp. times four corners, to 6 or 8 feet high...like $900 per corner.  So I am trying to find a good DIY set of plans for the perforated resonator trap some folks talk about over at gearslutz as being highly effective when built right.  I saw some old plans Ethan Winer had from back in the day, but they weren't perforated.

I would definitely order some diffusers from Jens Eklund if they would ship to the U.S.  I think I would prefer horizontal only, 1D.

My distance from side wall to listening position at reflection angle is approximately 80" 

In terms of the ceiling, in the area between speakers and listening position, does anyone have an opinion on absorption vs. diffusion?

[Jon L]

When I see the cost of very low frequency effective corner traps (e.g., Real Traps, others like that), it's insane...esp. times four corners, to 6 or 8 feet high...like $900 per corner.

This is how I ended up with Acoustimac.  Most of the other commercial stuff are much more expensive, and most of the cheap stuff (mostly foam) did not look to me like they would absorb enough bass. 
Acoustimac makes beveled versions of bass traps that fit into corners at 45 degrees with space inside.  They even make 6 inch thick version if you need even more bass absorption!

https://www.acoustimac.com/cbt424/
https://www.acoustimac.com/corner-bass-traps-cbt426/

[tinkerphile]

RE: Acoustimac bass traps:  I'm trying to interpret the lab data, in particular the "per unit" numbers (mainly on the corner traps) While I don't understand those per unit specifications in terms of objective absorption, it is reasonable to believe that they are sufficiently effective in the +-100 Hz range.  But it seems the numbers are quite low below 80 Hz. 

On the subject of "target" focused treatment (say, 60 Hz, etc.) given my room dimensions and the predictive models based on that, I will have issues to mitigate at 60 Hz (the corner bass traps may work well for the issues at 90 and 120).  Now, how important that is to treat in terms of its effect on SQ, in relative terms, I don't know.  I'd hate to think I put $30K into my system, treat most of the room for other factors, then neglect something at LF that is causing some serious issues.  Since my present goal is to approach the room treatment from a RFZ/LEDE philosophy, the LF treatment is my first step, together with targeting diffusion at reflection points.

[mick wolfe]

Maybe I'm somewhat out of line here, but it sounds like the cart is getting ahead of the horse.  I've always addressed room issues after a system has been set up in the room. Seems you're anticipating problems that may or may not exist.  The most difficult acoustic issue to correct or manage will indeed be bass.  In this case, it's much easier when one chooses a speaker that is doesn't overload/overpower the room with bass in the first place. Just my approach and as always YMMV.

[tinkerphile]

Hi Mick. Thanks for your input.  No, you're not off base.  All feedback is welcome!

But what made you think my system wasn't already set up in the room?  I've kinda settled on the system location (for now?) My current setup is where I came to after much experimentation, much advice, and a final recommendation from an acoustic engineer.  Doesn't mean I won't experiment some more, though.

I'm not quite sure what to make of the last couple sentences, RE: speakers and room overload, "in this case."  I must be missing something.

[JLM]

Again avoid full range speakers, they're so last American 20th century.  Most of the cost is in lumber and veneer and modern thinking (look through the links in the thread at the top of this circle) and do read Toole's "Sound Reproduction" to learn how speakers behave in-room.  Those full range speakers load the room in exactly the wrong way (reinforcing bass peaks/dips in the direction they're facing).  Midrange/treble is best produced away from walls, bass is best done against walls.  Get away from the big trophy mentality.  Monitor/sub approach is best and eliminates the worry about overpowering the room (which I did in younger years).

Again insulate the room first.  Lower the noise floor.  Major in majors.  For instance, too many focus on pushing dynamic range of DAC from say 100 dB to 120 dB, yet the room has a 40 dB noise floor, limiting useable dynamic range to 70 dB with most speakers.  In this scenario you're missing 30+ dB of dynamic range.  Insulating the room provides an improved baseline to allow everything else to sound better and be more effective.

Regarding treatment, you can overdo that too.  Too much absorption and the room makes everything sound muted, with highs deadened.  Diffusion helps the room behave as if it larger but only at higher frequencies.  That's based on depth of diffusers used and the size of sound waves (6800 divided by the frequency) will give you the depth of diffuser needed.  Which is why most diffusers only are effective down to roughly 1000 Hz.  Conventional thinking says to treat bass in the corners and reflections at first reflection points (all walls, ceiling, and floor for both speakers to the listening position).  First reflection points can be treated with diffusers or absorbers. 

Speaker choice is a personal matter but will greatly impact what treatments will work best.  Dipoles (including open baffles), bi-poles, and omni-poles have more need for front wall treatment.  Mono-poles (traditional front firing speakers) can be the least room interactive, especially those with controlled directivity design (typically found with large wave guides for the tweeters).  Being less room interactive they tend to sound the same regardless of the room or setup (bass reinforcement of close wall/corner placement aside).

[mick wolfe]

Hi Mick. Thanks for your input.  No, you're not off base.  All feedback is welcome!

But what made you think my system wasn't already set up in the room?  I've kinda settled on the system location (for now?) My current setup is where I came to after much experimentation, much advice, and a final recommendation from an acoustic engineer.  Doesn't mean I won't experiment some more, though.

I'm not quite sure what to make of the last couple sentences, RE: speakers and room overload, "in this case."  I must be missing something.

OK, after glancing at this thread again, I do see mention of Devore O/96's. They should be a very manageable speaker given your room size. My speaker/room interface statement would apply if you were to try to cram the O/96's into an 8' x 10' room. Just simply saying, size the speaker with room volume as a major consideration.

[tinkerphile]

Thanks, Mick.  Your feedback was helpful.  And, like I said, you made a couple of good points and caused me to give a little more consideration to placement.  It also caused me to think about how I would approach treatment and placement in order to keep options open for best final results - in terms of placement and treatment coordination.

In my opening thread post, I could have been more clear/should have been more clear.  I don't want to start a new thread similar to this one, though.  However, some of the feedback I've gotten so far has really made me think about my situation and goals in a different way. Special thanks to JLM for his input and info via PM.

Here is a very simple restatement of my situation for which I'm looking for feedback, ideas, recommendations:

My goal is to fully and effectively treat my present room as a dedicated 2-channel listening room.  I'm setting a budget of $5k, give or take.  This amount assumes some treatments will have to be DIY.  Why? Because highly effective LF corner traps, floor to ceiling, resonator-type(?) focused, are well over $1K per corner.  I can't imagine treating the room effectively can be accomplished without most of each corner being treated, say 70%-95% (though I only have 3 corners - my room is a daylight basement in a tri-level home, where a 4'-wide stair opening occupies a rear wall corner area). 

I am attempting to find corner treatment DIY plans for perforated, focused LF, limited band-width corner units, or something as effective.

I anticipate I'll need about a dozen LF absorption panels on the walls.  I don't know what to do with the ceiling at the front half of the room, but I'm getting there.  I'm also anticipating 1-D diffusers on a portion of the front wall, the rear wall, and perhaps at first reflection points at side walls - though I believe that side wall scheme may sacrifice some needed absorption.

I'm really at the point where I'm considering working with an acoustic consultant who doesn't sell products...a sort of RFP thing...?  There are a couple of pretty capable, honest guys out there who don't sell acoustic products.  I'm not in a big hurry, but I would like to get this done in the next 6-9 months, or so.

I haven't been satisfied this past year or two, when I did one of those popular approaches of sending your room info' to company X, specify a budget, and receive a plan for limited treatment.   I did contact a couple of different companies.

Or, as some helpful guys have suggested - - It's not that complicated: Purchase the mic, use the REW software, read some literature, get some help, and do it yourself - and you'll be surprised how well you succeed...even if only starting with very limited knowledge.