As some of you know getting your system to sound just right can be a pain in the butt. No bass, too much bass, echo, thin sounding and shrill, muddy, poopy diaper. etc.

I'm hoping I can start a discussion that will let everyone ask questions and chime in with how they solved issues in their room which may help others. I would like your help in interpreting results and making decisions that will impact the acoustics of my HT room eventually. I don't know what I am doing in practice, but have read enough to guess the theory behind what is happening, why, and what to try first.

I can start by recommending first off if you wanna get consistent feedback with what your tweaks are doing to your system you really need to get over that hurdle of measuring your room with software. I know right. Lame, boring, pedantic, tedious etc. But in the end very fast, repeatable and rewarding.

I use the Audio Tools App by Studio 6 Digital. It is inexpensive and works well on my ipad. It has pre-calibrated mic corrections for i devices and bypasses the onboard audio filters in the OS. I get most use out of the included measurement tools. The SPL, RTA plots, FFT plots, RT60 measures and ETC plots are very handy. The ETC plot requires the purchase of the LARSA plugin for an additional fee and is not essential to see trends in frequency response in a room. There are also many included audio calculators and a handy curve overlay function that lets you quickly guestimate NCB levels, STC, Transmission loss etc. Dont worry it's easier than it seems.

For test material I have found using the included pink noise generator helpful, but that tethers me to the equipment with a signal cable. I invested in the Stereophile Editors Choice disc for $10 and it has many helpful test tracks and reference material including a very nice piano piece. Of all the test tracks the dual mono pink noise track is the most used. Any full bandwidth dual mono pink noise test track will do and there are many available free for download.



I'm just cutting my teeth at all of this, but a couple of beers with my father in law and the wife being away got my courage up enough to unbox my 2 sealed subs and tinker in my listening room. It helps when someone is urging you on with a grin on their face. The goal was to determine where my 2ch system was performing compared to a desktop powered M2 setup we both had some experience with. My system was coming up really short in the bass dept. as "Peg" by Steely Dan demonstrated.

The room is setup width wise in a 11' x 18.5' x 8' room. The speakers are setup symmetrically from the sidewalls\centerline of the room and the listening chair puts my listening position about 1' off the back wall. The room has been modestly treated with broadband 2x4 absorbers on the front wall and a hanging tapestry behind the listening chair on a tapestry rod 3" or so off the wall. These treatments were deployed to tackle the flutter issues the room had and reduce the overall RT60 to a measured overall 0.4s. The low frequencies falling off faster at 0.35s and the upper mids at 0.45s. The result is a room that sounds live but still clear and focused. I'm not allowed to treat further.

Here is the basic setup.





Using the pink noise test we measured a response from both speakers at the listening position. This was the before subs measurement. We used RTA at 1/3 octaves because it is easier to read from far away, is easier to spot trends and I knew this was more an exercise in experimentation rather than a lasting setup. A 1/12th octave FFT plot is a much more accurate way of measuring response and finding high Q issues. However, these are often red herrings that lead to tweaking problems that do not matter outside of sound tests.

Before subwoofers added response at MLP. This measurement was taken later with the subs turned off after all the levels were set.



We can see the response rolls off sharply just before 60hz. The peak centered on 50ish hz is due to the proximity of the back wall to the listening position. These are modal issues I really can't do anything about without some serious bass trapping. The effect seems to be a heavier thwack on bass drums and upright bass tracks. Luckily it doesn't seem to be an issue for muddying sound in my room.

We added the subs. One at first at the right side and then the other. They are just inside of the 1/3 mark from the sidewalls my speaker stands occupy. I had been talking them up quite a bit as we were building the basement together and he was disappointed when the first one was set up. It took a bit of messing around with dials, but I thought I had it. We listened to a few tracks and he was still convinced his powered M2s provided an overall more rounded and smooth listening experience.... I was a little miffed and quickly flew down the stairs to retrieve the other sub (afterall, the M2s are under $600!). I had it set up and matched the dials to the other in the hope the low frequencies would now blend better into the minimonitors. The result was a little fatter bassline than before, so I turned each sub's gain down about an "hour" or so on the dial.

With the subs integrated the front of the room took on a different feel altogether. Why is WAF an issue I wonder?



We re-listened to the material we were juggling around and decided it wasn't right at all. The bass was thick and slow. It was not boomy, but seemed to hang in the room too long and hide the detail in the recordings. This was all setup by ear at this point. I decided to break out the ipad and was prepared for the "jeez, really?!" But he was eager to get the system up to snuff. He was still riding high on his M2 performance afterall, and wanted to see just where this system was "better" -as I talk about audio all too frequently....

We returned to the pink noise test and set the levels of the sub gain to closely blend into the monitors. But something was wrong. The bass was now thicker and louder than before. "Peg" was now "PEG!" It dawned on me I had been testing with a graph response readout in dBA instead of dBC.... dBA is a better measure for frequencies in the speech range and is often associated with general SPL readings in industry guidelines. Its range is not appropriate to set subwoofer frequencies. Doh! I quickly changed the program settings, re-ran the pink noise test and we returned to "Peg." Much, much better.

Here is the response at the MLP after tweaking the low pass and gain settings with the help of real time meaurements.



The bass still measures ~5db fat, but in the room it blends perfectly with the mini monitors and provides a pleasing warm sound. We finished up our beers and he went home to leave me to listen to the Pink Floyd's "The Wall" for the first time ever. I know, I know. I'm not old like you guys. I don't need to hear "Peg" for a while now...

Things I learned from this experiment.

1. Setting things by ear is a great way to start, but you will only ever reach ideal settings by fluke or by using a lot of time.

2. Knowing where your system starts is a better way of knowing where improvements can be made.

3. Having a second listener is an excellent way to prove your perceived results are real, and to keep you humble when you muck up.

4. Axiom makes good speakers.... Now I have someone to remind me of that constantly.

I will follow up with a plot from the M2 desktop system for a point of reference later. It will be interesting to see just how his setup has influenced his listening preferences. He loves his speakers.

Serenity -- Very nice. Thanks for the recommendation for the measurement app. I'd been wondering if anyone had advise on that front, actually.

I'm tempted to move the right sub around to smooth out that null (or try) and get a flatter response. But I don't know if that is possible. But hey, we can measure and see. This is just a temp setup afterall.

To get that response the subs are running at about 25% of their possible gain.

Here is an interesting discussion on Youtube about room acoustics. Obviously the guy is promoting his own company, but I thought there was some good info too. It is long though - about an hour.

https://www.youtube.com/watch?v=raAyF5ksbkk

Anthony, from the video, is a great resource though. Yes, he obviously has some biases towards his company's offerings, but his advice is generally pretty sound (pun intended).

Anthony Grimani, Ethan Winer and Scott Wilkinson are voices my wife now recognizes. Sunday morning "church of research" on the oppo.

Does anyone here have any experience with diffusion? DIY or otherwise. I'm finding a lot of conflicting info online. I'm trying to figure out if polycylindrical diffusers need to be a certain dimension/depth the be useful from midrancge frequencies upwards.

I have been following this website with interest. Seems like the more I read on this subject the more I learn how much I don't know.

http://arqen.com/sound-diffusers/faq/?aw...amp;omhide=true

I have been left wondering about diffusers, base traps, and absorption panels.

In laying out a room, with too many variables it makes me wonder how would you know what, where and how many? You have your reflection points, but getting rid of them will effect the sound stage and bring your lively Axiom speakers to sound like a studio. But too much and you loose the definition of what you want to hear in garble.

I hear about these base traps, but do I need one in each corner of the room, or can I put one into a corner where I have some protruding piping that I'd like to hide anyway?

if you diffuse a wall, does it need to be the back wall? Or if you did a side wall, would it be negative if you didn't do the opposite wall too?

That is before you start throwing back into the mix, optimal speaker placement as that might change as soon as you hang your room treatment up. The room starts spinning and it's time to get off.

Matt, there are guidelines for what and where. The unknowns are how many and how much (thickness/frequency coverage etc.)

It really depends on the room material/furnishings (sabin/absorbtion calc.) and dimensions (volume) and intended use. These determine the rooms target RT60. In practice I have found the biggest initial payoff was treating front corners with bass traps and treating first reflection points with broadband absorbtion. BUT all of these guidelines you will find online only apply to a normal rectangular room. Any absortion you put anywhere is supposed to lower the RT60, so the initial treatments have a double payoff.

RT60 used to be the only characteristic in planning/evaluating a rooms acoustic performance. Since then relections and our spatial/timing perception have become a focus in planning a space.

Both our rooms are constructed on resilient channel, and I have an optimistic outlook about bass response. Our walls should already be hugely useful in taming bass reverb. They should absorb and re-emit bass at a shifted frequency, hopefully helping with modal issues as well. Dunno yet.

One a side note, I found a recipe for building polys that many seem to have built and are happy with. I should mention the polys I'm building are for between the 1st and 2nd absorbtion points and were chosen because of their look more than their diffusion properties. They will appear as colums in the finished room.

https://www.gearslutz.com/board/attachme...poly-panels.pdf

To answer your dilemma, you set your speakers, treat room, then tweak your positions if need be. It's really not as hyper dynamic as it seems. The speaker response direct/off axis doesn't change, just reflections. Since your mains are omni directional I'm not sure treating the front wall is a good idea with anything but diffusion (if at all.) I have seen pics of a few dipole setups with large diffusers on the front wall but I'm not sure if it was done as a matter of performance rather than indulgence.

Alan would be best to comment on what to do there.

I could not eliminate the peak/null at around 60hz in my test room by moving subs around. I tried several locations. The response didn't change enough to warrant more graph pics. -just a differing level of nullness by a few db or so. The dual setup pictured was the best response overall. What was interesting is how the bass hump changed shape as I moved things around. It seemed to remain broadest at the 1/3 locations and become more peaky as I moved away.

My seating location must move to improve things I would say. Not worth it to smooth a 7db null. In content I couldn't ever reliably tell a null that size was present anyway. But it was an interesting test.

"We only started "fixing" rooms when we started measuring rooms." - Floyd Toole

I've been following the acoustical treatment thread over at AVS for a few years and it is, honestly, VERY complicated when throwing everything into the mix. There are definitely guidelines that help to tame every room, but getting those to be optimal is difficult for the DIYer. That is why a number of people focus just on the "biggest bang for your buck" approach while doing the most simple application of treatments that they can. That is just absorption. Corner bass traps are large absorption pieces, front wall treatments are pretty much just really tall/wide absorption pieces, and then stopping the first reflection points with absorption panels, and you get (my made up number) 80% there. WAY better than nothing in the room, but still room for improvement. Then the old 80/20 rule kicks in...

You can spend 20% of your time/money/effort to get 80% of the desired result, but to get that last 20% of the desired result, will cost you 80% of your effort. In other words, to get any further will take 4 times the time/money/effort than the other pieces. That has a lot to do with getting it right and not just slapping things up, and getting it right really takes someone that knows what they are doing (money), and for the diffusion panels it takes more money to buy them, or time and effort to make them.

I have my entire front wall treated (behind my screen and false wall). Floor to ceiling bass traps, and then 3.5" of absorption everywhere else on that wall. I have a thick carpet and pad (counts towards high frequency absorption more so than a thick rug on a hard floor), and I have 6 large (24"x48") acoustical (absorption) panels on my walls - 3 on each wall, plus an extra thick 24"x48" panel on my back wall above my rear seats. I didn't want to make the rear wall completely dead like the front as most advise that you have a dead-live setup with the front wall dead (absorption) and the rear wall live (reflective or maybe diffusion) but I was able to really get some good taming of lower frequencies when I added that 5.5" thick panel to the back wall.

I've been in a home theater that was fully tested and designed by an expert acoustician, and it was absolutely amazing, but that room cost $800 for the room analysis and acoustical plan (actually cheap, but because the expert had the homeowner take the measurements with equipment that they shipped him to save on flying the expert out to Iowa), and then they worked up a ton of DIY acoustical panels specifically designed for his room. It took the guy about a month, he said, of working every night after work and a bit on weekends to get all of those done (again, lots of time). It was a small price to pay for him though. I mean, he put in a separate $15,000 or so HVAC unit just for his home theater so that he could pump in cold air in winter when the rest of the house was getting heat, and so that in summer, the rest of the house wasn't an ice box just to keep the theater cool.

For more info on it, and even a 21 minute video done by the acoustician in post #5, go here (16 minutes 40 seconds into the video shows the left side wall with the fabric panels removed and the many, but not all, DIY treatments that were designed specifically for that room):

The Savoy Theater


In that same post (#5) it shows the slides that David (the homeowner) used for the get together that I was at. There are some slides showing the plans for the acoustical treatments as well as general construction.

Oh, and to accomplish this, he lost something like 2 feet of space for each side wall and the rear wall, the front screen is something like 4 feet from the actual real wall.

I'd like to throw in my two cents on this topic:

After being in this business for over 18 years now, and being a lifelong "audiophile", I have set up hundreds of systems in all types of rooms. I have been involved in and present for the evaluation of numerous new room builds, ranging from simple to extremely complex in terms of acoustic treatment. Based on this wide range of information, these are the rules I live by and recommend to customers:

1. If you are building a new construction room or home and have the option, the most important thing you can do is to build the room following "golden ratio" dimensions.

2. If you are building a new room from the ground up and think that lossey channels, staggered studs, double drywall, etc. will result in a "better" sounding room you might be disappointed by the results. I would suggest actually finding a room built in this manner and doing some listening.

3. There is nothing wrong with adding room treatments to an existing room, but don't think you will be able to make a "bad" speaker into a "good" one.

4. Whatever room treatments you think you need, make sure that they can be easily added and removed. In most cases I have found that proper placement combined with the addition of simple items such as area rugs, drapes, and a bookcase or two can fix the majority of issues in a typical room...assuming you are starting with a "good" speaker.

5. Always trust your ears over whatever your measurement system might be showing you. If it sounds good, it is good, regardless of what the measurements tell you.

Thanks,

Andrew

Hey Andrew, thanks for your advice. Can you say if HT use is different than music listening rooms in terms of acoustics in your experience? It would be great to have more input from you as this rolls along. Can you elaborate on how sound isolation construction strategies can make a room sound bad?

Would be great to have a speaker designer give their impressions as this thread evolves into something hopefully useful to someone.

Videos like this are what convinced me to take the plunge and actively "correct" my room to let the soundtrack/music shine through. This is for demonstration only. I would never go this far......

It isn't that room isolation will make things sound bad, per se, but they are for soundproofing, which is different than acoustical treatments.

I will say this. Soundproofing (ok, nothing will truly be "sound proof" unless you bury yourself in a concrete bunker underground and have no door to escape) can help with sound quality though, but not like you think. It is a nice improvement from preventing outside sound from contaminating your room's audio performance. Most people focus on keeping sound IN their room, but dropping the audio level of their "sound floor" by blocking exterior noise helps too. Just keep in mind that without treatments inside the room itself, it won't really matter. That is what, I believe, Andrew is getting at.


Think of it this way. Lets say that you have a great sounding audio system in your car. It obviously sounds better than some cheap-o system in another car. Maybe it is tuned better, has better components, etc, but if you put the windows down (no more "soundproofing" then the audio is completely contaminated with ambient and wind noise and neither will sound great.

Same with audio speakers and gear, and the same with a room. A well treated room can sound bad if you hear the HVAC running next door, or a TV on an adjacent wall.

Any single piece will effect the other. Bad vs good speakers and gear (#1 priority), treated vs. untreated room (should be #2 priority), and isolated vs. non-isolated room (#3 most important, unless you live by train tracks or some other loud environment).

That's exactly what I thought and expected. I just wasn't sure if Andrew meant the use of soundproof strategies was detrimental in some way. I chose to do it so my furnace and laundry nearby wouldn't be a bother.

I found a great white paper article c/o Nyal Mellor at acoustic frontiers. Thought it would be good to share it:

http://www.acousticfrontiers.com/wp-content/uploads/2011/10/acoustic_measurement_standards.pdf

It focuses on the evaluation criteria and measurement principles in creating a reference 2ch system/room.

Ok, so here is a bit of a before after (and after part 2) summary. It looks like in this room the "ideal" front wall sub location is somewhere between 1/3 and 1/4 to center of driver from sidewall length. I was not able to test on exactly 1/3 or 1/4 because this footprint is occupied by the speaker stands. I would love to hear peoples input on where their R/L speakers landed in their room. Same general 1/4-1/3 footprint perhaps? I am confident we can assume somewhere in this general region would work well for subs in this room.

No subs. Baseline measurement.


Test 1. Subs inside speakers just larger than a 1/3 from sidewall measurement. (by a few inches)


Test 2. Subs outside speakers just smaller than a 1/4 from sidewall measurement. (by a few inches) I was messing around with louder tests so the the graph Y axis is taller but the range is still in 10 db intervals. Notice the gross low frequency output is higher as they move closer to the corners.


I will do a similar test in the HT eventually to determine where an "ideal" front wall placement outcome exists, but I can hypothesize from this test 1/3 and 1/4 placement is a fantastic place to start.

In this room, with the bookshelf speakers, the measured overall system response is better with the subs located outside of the speakers near 1/4 width. My overall listening preference is with the subs just inside of the speakers as they seem to blend better and decay faster somehow near 1/3 width. A tighter sound. Perhaps this is due to less reinforcement from the corners as the subs move from the 1/4 to 1/3 position.

The Subs lateral move was about 16" for this test. The net sub change from test 2 to test 3 was widening ~32" The difference in output and timing was not subtle.

I learned a couple of things from part 2 of this test:

1. A better measured result does not always mean a superior listening experience.

2. Our ability to hear subtle changes in bass output or nulls is not very good at all. An SPL meter should be used to help set the sub volume where possible. In this test, with 2 listeners, the bass was initially set far too hot before measuring. Almost 10db!

As promised a while ago, here is the measured response of the powered M2s at my father in laws place. This is NOT the same response you will have, nor is it telling of the M2s anechoic response. His speakers are located extreme nearfield in a computer setup, and nested inside the walls of a wrting desk. Not an ideal setup, but it still sounds pretty good.

Where did my speakers land? Smack dab 1/3 of the way into my room. Freakin' amazing acoustics. Speakers completely disappear. I can't imagine how much better it could sound with better bookshelves, real stands and that coffee table out of the way.

Mojo's second dojo

Awesome! Great pics. Handsome panels, there.

I've thought about using the 1/3 dimension for my towers...thinking its a rarity that all the seats are used.
I might pull the seats out of the room and focus on the two lazyboys again. I can always place the kids chairs back in the room after.
There is seating for 8 atm (4 adults size seats 4 children size), getting back to tweakville would really make my winter.
Its all about me, and"can it be any better with what I have?".

Another tinkerer!

If you havent done the measure, laser, toe-in match its a great "wow" improvement.

Laser all the way. Save so much time and stress'n over knicking/scratching etc.

I love lasers! (insert Doctor Evil joke)

Here's how I do mine fer those interested. Probably easier ways but this is consistent and I can take notes on how each position performs with great accuracy (and repeatable if I want to change back. -Abort mission)

I put a scale behind the listening position on the centerline of the room. Scale gets larger off centerline so right and left channels can be set without moving scale around. To set the scale, I measure from zero point to each sidewall and make sure the measurements are equidistant.



Then I plunk a line laser atop the speaker and shoot towards the listening position along the centerline of the speaker cabinet. You can see an example of the laser reading in the scale photo. I match the toe in like this during setup. I take notes and change the toe in a couple inches at a time until it sounds like the singer is locked in place dead center and the phantom image is as loud as the hard left and right panned sounds. I use the Barenaked Ladies album "Gordon" to do it and the songs Yoko Ono, Brian Wilson and Box Set for testing. Centered vocals and busy percussion are good tracks to test with I find. Centered vocals for phantom image and busy percussion for timing cues\smearing. Yoko Ono gets annoying, but there is a great right/left/phantom singer setup that makes sensing balance a little easier. Toe in too much and phantom is too strong, too little and other singers are louder. Toe in also affects treble balance, so it's good to listen to female vocals as well to sense if they are getting too nasally or sibilant. I use "Cults" self titled album, as she is already on the verge of being too nasal. The tracks You Know What I Mean and Oh My God are good ones. Love Madeline's vocals. I want to make sure I'm not shifting them any further.

Some people use mono recordings to do this, but I found that it is too hard to get a balance between phantom and left\right sound level when only a phantom image is present. Not sure if you are close to good stereo\phantom balance? Use headphones to check the track without the room involved.

Yes, I have speaker setup OCD.

As i am a fan of measurements and occasionally obsessive about probes and temperatures and thick meats, i will read through this thread when i have time.
One thing i have yet to do is take a frequency response of my own setup and room.
Maybe one day if i ever buy a laptop...though first i should maybe consider a cell phone...don't have one of those either.