Results of my Acoustical Room Treatment

Discussion in 'Audio Hardware' started by ToTo Man, Oct 29, 2013.

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  1. ToTo Man

    ToTo Man the band not the dog Thread Starter

    Scotland, UK.


    Until recently I had not given consideration to acoustical room treatment, as I was naively under the impression that loudspeakers had by far the greatest influence on a system’s sound. My opinion on this has been emphatically changed, as I have found myself on a very steep learning curve the past few weeks! I therefore thought it would be helpful to share my results in case others are considering pursuing a similar route with regards to room treatment.


    When I recently removed the dominating wardrobe and stack of unused loudspeakers from my room in an attempt to create a more symmetrical and spacious listening environment, the quality of the acoustics took an absolute nose-dive. Obviously the excess furniture clutter was doing an effective job at keeping the sound relatively tight and well balanced, as after its removal the room became unbearably boomy, echoey and smeary. I was absolutely devastated by the change for the worse, but was determined not to revert to the former layout. After much online research I contacted GIK Acoustics for advice on how to treat my room with acoustical products to restore its previous sonic character, and after an extremely helpful consultation I placed an order for a few of their absorption panels. Regretfully I did not take any in-room acoustical measurements prior to removing all of the excess furniture clutter, however I have documented each stage since, from the room being completely absent of treatments through to its current treated state.

    The Room:

    The listening room is a standard cuboid-shaped space of dimensions 13’7” long by 12’5” wide by 10’8” high. It features a single bay window behind the listening position (but offset to one side). All four walls are parallel (or as parallel as to be expected from a Victorian build!), and are plaster over stone construction. It has a suspended wooden floor that has been sheeted with plywood and carpeted with underlay, and a flat ceiling of traditional lathe and plaster construction. The system is located centrally on the long wall (opposite the window), and thus plays across the shorter room dimension. The loudspeakers are positioned 5’4” apart, 4’1” from the side walls, and 2” from the front wall (all measurements taken from front edge of loudspeaker cabinet and on tweeter axis). The loudspeakers are mildly toed-in and are a parallel distance of 7’5” from the listening spot (7’10” if measured diagonally). The listening spot is central and 3’ from the rear wall.

    The System:

    Source: Digital lossless library of mixed resolutions (16/44 through 24/192).
    Transport: Mac Mini using Audirvana/iTunes.
    DAC: Schiit Bifrost asynchronous 32/192 USB.
    Amplification: Yamaha CR-1000 Natural Sound Stereo Receiver.
    Loudspeakers: Tannoy Lancaster Monitor Gold 15” LSU/HF/15/8 (w/upgraded crossovers, wiring and cabinets).
    Cabling: Digital Interconnect (Basic 1m Belkin USB 2.0 cable); Analogue Interconnects (1m Van Damme XKE instrument cable with NYS373 REAN phono plugs); Loudspeaker Cable (Van Damme Studio Blue 2x2.5mm).

    The Treatments:

    I have only included some of the purchased treatments in the results and analyses that follow; namely the GIK 244 Broadband Bass Trap (a 2’ x 4’ x 4” panel typically used to treat the first reflection points), and the GIK Tri-Trap (a 2’ x 4’ x 16.5” wedge bass trap used to treat the room corners). I also purchased the GIK Monster Bass Trap (a 2’ x 4’ x 6.5” broadband panel typically used to treat the lowest frequencies) to specifically address my room’s peaks and nulls at the lower end of the scale, however I have yet to find a location in which this product reliably alleviates these issues. I have also still to install EPS diffusor panels, thus the room is by no means the finished article yet.


    The Measuring Equipment:

    Mic: Behringer ECM8000.
    Mic Pre-amp & ADC (analog-to-digital converter): Apogee Duet FireWire 24/96.
    Software: Room EQ Wizard.

    The Results:

    Key for all graphs:
    Red = untreated room.
    Blue = four 244 panels at first reflection points (two per side wall).
    Green = four 244 panels at first reflection points (two per side wall) and four Tri-Traps (one per corner).
    Yellow = four 244 panels at first reflection points (two per side wall) and eight Tri-Traps (two per corner).

    (N.B. I have many more results recorded as I repeated the tests by varying the listening position forwards and backwards a few inches from my usual spot. It would however be superfluous to upload all of the results, and in fact the general picture does not change significantly, so for the purposes of this write-up I am focusing on a single listening position, 36” from the rear wall.)




    Analyses & Discussion:

    The objective is to obtain as uniformly flat a frequency response and RT60/waterfall as possible, and to reduce the RT60/waterfall to an acceptable target reverberation time, given the inherent practical limitations of the room and the system.

    Initially I was disappointed to find that the frequency response (Figs. 1A, 1B & 1C) had not flattened out as much as I hoped it would post-treatment, but perhaps I had unrealistic expectations. Of course, it depends on how much “smoothing filter” you apply to the graphs. With 1/48th octave smoothing the post-treatment response still looks horrendous, but with 1/3rd octave smoothing (which is typically what loudspeaker manufacturers quote in their anechoic tests) the response doesn’t look too bad. I am not sure which smoothing filter correlates most closely with what we actually hear, so I have included 1/48th, 1/12th and 1/3rd graphs to give as complete a picture as possible (although I think 1/12th strikes the best compromise between detail and trend).

    Most evident from the frequency response overlays is the positive effect installing the 244 panels at the first reflection points on the side walls had. There was a significant gain in output of mid and especially high frequencies (an average boost of around 6dB), bringing their respective SPLs up closer to those of the low frequencies and thereby creating a flatter response. It is interesting that the installation of absorption treatments had the effect of boosting upper MF and HF output, as I would have intuitively expected the opposite result. This suggests that there must have been significant first reflection cancellation occurring across these frequencies in the untreated room. There was an audible improvement in focus, detail and clarity following installation of the first reflection panels, plus a noticeable difference in tonal character. However the actual audibility of the changes when listening to music was not as significant as the frequency response overlays suggest. I can only assume that this is because there were still long reverberation times (as shown in Figs. 2 and 3B) favouring the upper bass frequencies. As is evident from these two graphs, installation of the first reflection treatments had little impact in neither reducing nor flattening out the room’s ringing below 1kHz, and this mirrored what I heard.

    However, the subsequent installation of a quad set of Tri-Traps (one installed in each corner of the room) did have a significant impact in reducing ringing, and the effect this time was both measurable and audible. As shown in Fig. 2, reverb times reduced on average by 1/3rd to around 500ms, and more importantly flattened out considerably across the audible range above 100Hz (excluding the remaining peak at ~300Hz). [N.B. The observant will notice from the waterfall graphs (Figs. 3A, 3B, 3C & 3D) that there hasn’t been as much improvement below 90Hz, and very little improvement below 50Hz. The dimensions of my room give rise to a fundamental mode of ~42Hz, and frequencies this low are notoriously difficult to treat unless heavy artillery is thrown at them. I have been advised that I would either require Tri-Traps 3’ in width instead of the standard 2’, or Soffit traps (cuboids of size 4’ x 16.5” x 16.5”), and unfortunately due to layout restrictions my room cannot accommodate such massive structures!] This time there was a more noticeable audible improvement in focus, detail, clarity and imaging accuracy following installation of the four Tri-Traps. The sound was tighter and snappier, and dynamics had improved too. The difference in the system’s tonal presentation was also more evident, presumably because the now shorter decay times in the upper bass frequencies were no longer masking the attack of the higher frequencies. Ignoring the potential for anecdotal bias, this was probably the closest my system/room sounded to the way it did before it was cleared of the excess furniture, but now the sound had improved focus.

    The final installation stage was to add another four Tri-Traps (stacking them atop the existing ones), taking the total to eight. This has in my opinion had the biggest audible impact in changing both the tonal presentation of the system and ambience of the room, and by much more than the graphs suggest. In fact, before even playing any music the whole “feel” of the room changed profoundly the instant the final trap went up; it was quite eerie actually! As shown in Fig. 2, reverb times reduced on average by a further 20% to around 400ms. The room sounds much “deader” after this last stage of treatment and, as a result, nuances and cues in favourite tracks that I had never noticed before have now been unmasked for the first time. While this is most definitely a welcome positive, other aspects of the change in sound required more time to accustom to and ultimately appreciate. Initially it seemed that this latest stage of treatment had robbed the music of its ambience a little too much, making it sound too focused and sterile and not as spatially enveloping and emotionally involving. However having now lived with this sound for a few weeks, it has become the “norm” to my ears, and listening to music in less-damped listening rooms now sounds sub-optimal. Tonally, the system sounds markedly more different now than at any stage before. In fact if I was blindfolded I would swear that I was listening to a completely different setup; that is how pronounced the change has been. It now sounds significantly crisper in the upper frequencies, and the previously soothing Tannoy lower mid-range “bloom” seems to have receded and been replaced with a thinner, cleaner, and more piercing upper-MF presence. The closest tonal presentation I can liken it to is that of an outdoor reproduction system that is (presumably) devoid of the usual colourations caused by an indoor listening space. It is indeed as if a blanket of colouration has been lifted from the system, such has been the gain in transparency and clarity. Another major benefactor of the treatment has been the system’s dynamics, which are now simply to die for! I have literally been startled on numerous occasions by the clarity, attack and scale of the crescendoes in favourite tracks that I did not realise had such great SPL range. Last but not least, I have noticed a significant lowering of the system’s/room’s noise floor post-treatment, which makes it possible to listen at lower SPLs than before whilst retaining impressive amounts of resolution.


    The above results underline the importance of a two-pronged approach in the use of absorption products in acoustical room treatment; treatment of early reflection points to restore a flatter in-room frequency response at the listening position, and treatment of room corners to reduce and smooth out reverberation times. The results show that - in my situation at least - both phenomena greatly influence the ability to hear a system’s true resolving capabilities and thus obtain accurate sound reproduction. It is clear from my findings that the facility to control these significantly enriches the listening experience.

    Further Thoughts:

    It is evident - especially from Fig. 1A - that bass nulls still persist post-treatment (e.g. at ~100Hz). Going forward, this is something that will require further investigation and treatment. More generally, it will be interesting to listen to - and measure the effects of - adding diffusion treatments to the room. Finally, it would be good to discover what the optimum or recommended reverberation time actually is for a domestic listening environment for 2-channel HiFi stereo, as this would aid in determining whether the current amount of treatment in my room is adequate. I have searched many online threads but cannot actually find a specific target value, only the recommendation that a room dedicated to Music should possess a longer reverb time than one dedicated to Home Theatre. Speaking of which - and on a final positive note - dialogue through my Plasma TV’s built-in speakers has never sounded better than it does now. It really is a novelty and joy being able to watch telly and no longer need to strain to decipher muddy, unintelligible speech!...


    Your thoughts on any of the above are most welcome.
  2. action pact

    action pact Music Omnivore

    How about WOW!

    A VERY impressive report!
    Mister Charlie and Dave like this.
  3. ToTo Man

    ToTo Man the band not the dog Thread Starter

    Scotland, UK.
    kevintomb likes this.
  4. Bill In WV

    Bill In WV Active Member

    Hurricane, WV
    I concur, very intersting! Nice job.
  5. theron d

    theron d Forum Resident

    Baltimore MD
    Very nice, I'll be writing up something similar for a basement listening room (project). I like the flow of your writeup...
    mindblanking likes this.
  6. Have you tried moving the speakers out further from the rear wall?

    I have Tannoy DMT II 15s and they sound best about 18" from the rear wall in my room. I am also using two GIK Monster Bass traps with great success.
    theron d likes this.
  7. ToTo Man

    ToTo Man the band not the dog Thread Starter

    Scotland, UK.
    I just re-read my post and noticed a typo. I meant to write that the speakers are 2 feet from the front wall to the front edge of the cabinet (or 1 foot if measuring to the rear edge of the cabinet), not two inches! I'd like to try them further out into the room but entering and exiting the room would become rather precarious as the speakers would encroach into the space that the door opens into.
  8. LeeS

    LeeS Blue Note Fan

    Excellent discussion!
    kevintomb likes this.
  9. hvbias

    hvbias Forum Resident

    Great work! Treating my room made my system sound more natural and unforced more than any electronic piece.
  10. HAmmer

    HAmmer Forum Resident

    Milwaukee WI
    It took me a week to read that report but my findings are that it's AWESOME!!! Great Job :righton:
  11. Hipper

    Hipper Forum Resident

    Herts., England
    Thanks for taking the trouble to put that together. I hope others will see and be inspired by it.

    Firstly, GIK sell a targeted absorber that can be used to treat specific frequencies, called Scopus Tuned Membrane Bass Traps. I've not used them.
    I agree with the suggestion of moving your speakers about to alter the bass response if you can. I followed advice here:

    Another suggestion I found beneficial was to move my gear to one side. Previously I had it between, but behind, the speakers. Placing it to the side reduced the higher frequencies by some 3dB for some reason, resulting in the removal of harshness in some vocals, strings and saxophone for example, and allowing more bass to be heard. It was a major improvement well worth the effort.

    I have done something similar to you in the last few months, and ended up using 'The Thirds' positioning and GIK products. This is the result:


    I used Soffit Traps, Monsters, 244s and diffusers. I'm not sure I've got it exactly right yet but I've got depth and width, and it is the depth particularly that offers new insight into the music.

    I use an equaliser too. Here’s an SPL reading from REW for the left speaker with 1/24 smoothing. The red is with the equaliser bypassed but all treatments in place, the blue with the equaliser.


    The route you and I have chosen is the key to really good listening. Speaker and ear position, room treatment, an equaliser perhaps, using measurements on the way. It's not easy or cheap but it is most definitely worth it.
    JulesDassin, wgb113 and hvbias like this.
  12. DPM

    DPM Forum Resident

    Excellent report, Toto Man.

    I installed GIK panels and traps in my room several years ago, and the improvement was not subtle. As you discovered, the installation of acoustic panels/bass traps makes the room let go of the sound faster--clearing it up to great effect. As of right now my GIK acoustic treatment lineup of panels/bass traps includes only two of the corner units, and your report has me considering stacking two more--one each on top of those already in the rear.

    I also have several of the bigger traps straddling the wall/floor junction behind the listening position. When installed these improved the mid-bass punch.

    My one major bass problem is a dip centered at 42 cycles. Luckily, it is masked by a return to full scale output at 30 cycles, so I don't feel the need to take the extreme measures required to fill it in.

    Regarding that dip in your graph centered at 100 cycles, that may be a floor bounce anomaly. My floor bounce dip is centered at 180 cycles, but it is pretty shallow as these things go. In fact, it doesn't even exist two feet in front of my listening position. Unfortunately, my room layout precludes me moving my couch out into the room that two feet. Oh well.

    Anyway, moving your listening position forward MAY tame that dip. Check it out.

    Also, since you sit fairly close to the rear wall you may want to install an absorption panel on said wall directly behind your head. I did this and the result was a much clearer soundstage. From what I've read a diffuser used at such a close distance won't be as effective.

    Good luck in your continued experiments/adventures in taming the room.
  13. jh901

    jh901 Forum Resident

    My early reflection points have been treated with DIY 9" cylinder bass traps and the corners are treated with 16" DIY bass traps. I also have a "corner tunes" for the back corners. The room feels and sounds different upon entering (with no music playing). Would be nice to get some measurements, but I'm certain that a better room and more acoustical treatment would result in even better results.

    The profound non-gear related discovery for me was in the positioning of the speakers and listening position.

    I do hope that the OP will be motivated to listen to more music and upgrade components. Once the room and listening position have been dealt with to a large degree, then gear upgrades will really pay off. Next up for me should be vibration control, better line conditioning, speaker cables and interconnect upgrades, and some help tweaking positioning and acoustic treatment.
  14. John Moschella

    John Moschella Forum Resident

    Christiansburg, VA
    I'm a big believer in room treatment, but speaker positioning is more important IMO. I have a dedicated listening room and I basically use the rule of thirds where the speakers occupy the central 1/3 of the room. The creates a near-field listening environment. I also have diffusers at the primary sidewall reflection points and use these "corner tunes" things in the upper corners. Those things are amazing.

    Except for bass, you can do a very effective job of speaker positioning and room treatments just by listening.
  15. e630940

    e630940 Well-Known Member

    Last edited: Oct 29, 2013
    Geithals likes this.
  16. ToTo Man

    ToTo Man the band not the dog Thread Starter

    Scotland, UK.
    Yes it could very well be a floor bounce issue as I have tried adding monster panels in various locations in the room and the only location they reduce the null is when placed on the floor in front of the speakers. Bizarrely, when absorption treatment is placed on the wall behind my head the nulls become worse! I've experimented with various listening positions and have measured each position with REW, and as expected each position brings its own set of advantages and disadvantages. For the moment, my 'ears' tell me that 3' from the back wall sounds best taking everything into account. The next step will be experimenting with small changes in loudspeaker positioning, which will be a major physical effort given that the buggers are spiked onto a stack of bricks!!!
  17. I have my Tannoys on Sound Anchor stands with Herbies Big Fat Dots between the stands and speakers and Herbies Gliders under the spikes of the stands. The gliders allow me to easily move the speakers around to experiment with positioning.
  18. Kyhl

    Kyhl formerly known

    Nice job. You really reduced the decay times.

    When you analyze the graphs it might be easier to focus on the bass to low midrange sections, 400hz or 200hz on down. As you can see from your graphs, the rest of the frequencies come along for the ride and improve on their own because you are using broadband traps.

    I found it easier in my room to focus on unsmoothed graphs. They are ugly but they help you nail down which are your problem frequencies.

    Ugly example of my room this evening. You can see that I have some phase issues to deal with yet. I installed a GIK Soffit trap on a ceiling corner over the weekend and finally got around to measuring the changes. It still didn't fix my problems.

    Adding smothing 1/6 octive smoothing makes it look great, +/- 5dB. Maybe better.

    It is possible to affect the bass frequencies. Here is the waterfall of my first attempt at a large corner bass trap.

    After adding stuffing you can see the reduced ringing down to 20hz.

    I am using one analog PEQ adjustment taking off 10dB at 37hz. Without that the 35-40hz range would continue to ring like the 19hz ringing. Unfortunately, my PEQ only goes down to 20hz so I can't try to tame the 18-20hz range to see if it fixes the 36hz- 40hz problem.
  19. wgb113

    wgb113 Forum Resident

    Chester County, PA
    Bravo to everyone here who has tackled their room! I did it about a year and a half ago and, like many people, kicked myself for not doing it sooner. Your ears, room and speakers account for over 90% of the sound you get. Everything else, if competently designed, has minimal effect.

    Misery_loves.. likes this.
  20. Hipper

    Hipper Forum Resident

    Herts., England
    Some of the signal picked up by the microphone may be noise.

    Here's a waterfall plot of noise only in my room:


    It picks up traffic and other noise from neighbours that I might not hear so that readings in the 40-50Hz area particularly cannot be used.

    Next are two plots from the same measurement of my left speaker.


    You can see the noise continue after the signal has mostly gone. The line at 149Hz is amplifier hum!


    This spectrogram is interesting because it shows the signal generated by REW - at 0ms - and the noise BEFORE the signal was made - the minus figures, the signals below the middle line - and continuing after the generated signal has died down. You can also see the amplifier hum at around 150Hz continuing consistently right through the plot.
  21. jh901

    jh901 Forum Resident

    I'd agree that the sound quality of a system with average electronics with the speakers ideally positioned will likely be better than a system with hi-end electronics and the speakers too close to the walls. I'd also agree that throwing money at a system in a poorly treated room where the speakers and listening position are not going to be ideal is foolish. But suggesting that electronics have such a small impact is simply wrong.

    Once the room and positioning is pretty good, then that opens the door to discovering just how incredible hi-end gear can be. The digital front end alone has a huge impact. Pre-amps, including phono stages, have a huge impact. Even power amps do. I'd suggest borrowing some very highly regarded gear a few steps abover your own. Gotta hear it in your own room though. With your own music and on your own time.
  22. kevintomb

    kevintomb Forum Resident

    I agree with most of what you say, but only differ in regards to how you word things a lot.

    Huge, to me anyways, is reserved for changes like speakers, maybe room acoustics, Speaker positioning etc.

    I have never even remotely considered a pre-amp or amp change, "huge" in difference, but for sure noticable, and often a welcome improvment etc.

    I think I reserve "huge" for things that any average person would hear just walking into a room and listening.
    wgb113 likes this.
  23. soundQman

    soundQman Forum Resident

    Arlington, VA, USA
    Inspiring! I hope to do similar analyses on my room response and treatments in the future.
  24. jh901

    jh901 Forum Resident

    Without debating how dramatic we each define "huge", you might point out that you've never auditioned any of today's hi-end gear in your own (or at least a very familiar) listening space.

    I can guarantee you that the look on my neighbor's face having upgraded CD players suggested "huge". There was nothing subtle or "small" about the sonic improvements. Nor was there jumping from a decent SS pre to an entry level hi-end tube pre. And then from that to a more serious tube pre. Quite dramatic and impressive. The refinement will shock many who are passionate about sound quality, but haven't yet experienced hi-end.
  25. wgb113

    wgb113 Forum Resident

    Chester County, PA
    This is kind of where I'm at as well jh901. Too often on internet forums and in audio magazines the descriptions of something's impact on a system's sound are blown out of proportion - a change from one DAC to another, a different set of tubes, widgets that hold cables off of the ground, a different software solution, etc. Their effect pales in comparison to the quality of your hearing, the accuracy and range of your speakers and how they're positioned in the room, and how you've addressed the room's acoustics to take it out of the equation as much as possible.

    In some ways I think what you may be alluding to is the increased ability to differentiate between changes in the system once a room & speaker system has been optimized to begin with. This allows you to hear how a flawed DAC, set of tubes, widget tweak, etc impacts the sound of your system. Without that solid foundation though it's simply a lot of psychoacoustic bloviating about the latest thing one has acquired. Seeing some of the setups of both fellow hobbyists and respected (or not) reviewers has really opened my eyes as to how credible I hold their opinions on anything audio.

    Last edited: Oct 31, 2013
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