Tomas's room

Finally decided to do accoustic treatment form my poor room that is located in a block building on second floor. As I have neighbours, I do mixing at fairly low levels - normally at 80-85 dB SPL C. also real soft at night 60dB, and rarely checking how it is loud at 95dB. I use KRK RP 8 monitors and KRK RP 10S subwoofer. http://www.krksys.com/v3/rokit.asp I plan to use semi-rigid rockwool panels 1000x600x100 mm and 150mm. (3'3"x2'x4" and 6" thick), having 50kg/m3 density (3pcf). They are made by Rockwool poland and are claimed to be extremely good accoustic absorbers (big label on package even says "Enjoy the silence"). I already got 4 bales of these (each containing 5 4" panels). And droppen in my room randomly. It improved mode absorbtion quite a lot as attached graphs show. I peform all measurements using quite basic SPL meter at C mode, it has output from it's omni microphone, that I capture to pc using TASCAM FW1884. It's response range is limited 31.5Hz-8kHz, but it's the only omni I have got, and suits my low end needs. Below is the plan (both US and metric), first picture is top view showing wall absorbers - I will make two studiotips super chunk type of traps at front corners, by cutting each panel along diagonal into two. Then I would hang 2 absorbers on each side wall. 4" and 6" thick. Basically these are made by two panels each so they have dimensions 3'3"x4' each). Second picture displays vertical cut of a room. I'd place two same type of chunk absorbers in corners by the ceiling, also few 6" panels could hang from the ceiling (one being at reflection point, and others to keep modes in place (width and height of a room are quite similar, so I need heavier absorbtion at these dimensions than on room length). The last picture shows the ceiling absorber layout from the top. Also current subwoofer and monitor placement is shown. Subwoofer is lifted from floor to have cone center at 18inches, monitors are on table cones 35" from floor. Walls are concrete, covered with paper (forgot correct term), the thin wall could be gypsum or something, there is small room behind, but this wall triggers the modes so I think further apartament plan is irrelevant. Question 1 is whether this amound of absorbtion is appropriate? Won't the room be too dead, and would the modes and standing waves be treated with smaller amounts of absorbtion. Question 2. Do I need additional types of absorbers/diffusers, or can all be fixed with rockwool. Question 3. back wall treatment, should there be anything? Question 4. I don't expect an answer to this one, as I did not enough homework for it - where should I place my monitors. I was playing a lot with sub placement, but with all these modes I found that I want to place it at mode canceling points. Hopefully correct accoustic treatment will allow placing it in more neutral places. Almost forgot to tell - I mainly record guitar and bass with DI, or tube preamp. Modes did not allow using guitar amp for usefull recording. In future I might use microphone for guitar recording. I also record vocals (mostly quite close miked to get dry, then add impulse based reverb to that). So question 5 would be asking for idean on vocal recording in this room - will it be usefull? In any case I will be proceeding with my plan so if anyone sees I'm doing nonsenses please stop me before I spoil to much material and time :) And thanks for these forums with lot's of useful info.

The measurements of sound with omni mic placed in very corner. (first is treated with 4 bales of rockwool, second is empty).

Tomas - you've left out the most important wall - the rear wall!! (bottom of drawing) you must treat this wall as it efffects all the rear reflections. cheers john

yes, I thought so:

Question 3. back wall treatment, should there be anything?

But should I put absorbers there or some diffusers? I'm aware that there are diffusers available and even DIY ones, and from what I understood they are usually placed on a rear wall (and sometimes on other places). Maybe most important question for diffusion is whether my room is just too small to provide usefull reverb?

knightfly wrote:

Generally, diffusion is best kept at least 10-12 feet from your ears; otherwise, there's a strong chance of getting specular reflections from the individual elements since there hasn't been enough distance for the individual reflections to "mix" - If you don't have really high ceilings, an absorbent "cloud" is usually a better overhead treatment.

I will also have a human heihgt 2' wide bookshelf, and some low drawers somewhere in my room. Maybe placing them at back wall and making 2 GOBO type of absorbers to block the back area. But I'm still afraid that the room will be too dead. But maybe controlled dead is better than chaotic reverberant. Another option is to put 4" or 6" rockwool panels on as much of the back wall as needed behind the book shelves (which would act as some sorf of diffuser). Is it so that mid/hi diffusers can be placed on top of LF absorbers - modes are handled, but room is not dead. Also for front wall (window) early reflections, I think I will put smaller absorbers behind monitors that will block signal being sent to front wall at all, rather than do some complex removable absorbtion on windows. I will post updated picture in evening (our time).

Read more or less all about diffusion on this site. My room is too small. http://www.johnlsayers.com/phpBB2/viewt ... t=diffuser Conclusion I came to is all I can have with useable freq. response is dead room. And for music enjoyment, pass the signal through room reverb. For mixing I will have to "learn" my new room when it's ready.

Tomas - every room your music is played in will have it's own colouration of the sound due to it's size, height, wall treatment etc etc. The aim of a control room is to provide a neutral, flat response room which is your reference point - without room colouration. Therefore - if it sounds correct in your room it will be correct in other rooms, despite the individual colouration each other room adds. cheers john

Yes, I understand it now. But before I've read in few places how bad deadening is, that you mix too much reverb etc... I did two full height superchunk traps 100x60cm (3'3"x2') at fron t of my room in corners, and thrown in 10 sheets of 4" rocwool (mainly at early reflection points and back wall). Imaging difference is unbelievable, can't I wait till I finish all the treatment. Also it's raw rockwool everywhere and tons of dust. I include LF waterfall for untreated and treated rooms. Microphone is located in corner to reveal modes. Mix position is much smoother. Hopefully first mode (42hz) will stop ringing with back wall treatment. 60Hz is caused by ceiling-floor reflection wich is almost untreated yet. After weekend I'll try playing with listening position and monitor/sub placement, and draw construction plan for ceiling mounting superchunks.

It's a pleasure reading about your acoustic improvements! Andre

Here are my updated plans. If no better ideas by weekend, I'll go to implementation. Traps are basically rockwool with minimal wood for reinforcement. All is wrapped in polyester batting and covered in burlap. Rear wall is made of 2 GOBO traps, which cover possible storage area and creates bigger space behind traps for better LF absorbtion (adjustable). Front corners have 1.5 of "normal corner trap". Ceiling corners are treated with 3 on each side. Any comments on such design? What's the performance of slat resonators compared to solid rockwool corners? Does it make sense to consider in my case?

What's the performance of slat resonators compared to solid rockwool corners?

the difference is that slots are aimed at the low mids only and don't effect the high end which it reflects whereas solid rockwool sucks up all the highs as well. cheers john

So let it be done! I started construction according to plans presented. As my room size can't give usefull reverb without giving too early reflections, everything will be broadband absorbtion. In case I get too dead room (RT60 of highs much smaller than lows), I could correct it by placing plywood panels in front of some of the absorbers, right? But I'd place them not to give me any early reflections. Or is this very weird idea and I should build slat absorbers in such case? Here are some pictures of first days. I know everyone likes pictures more than reading :) Pic1. Carpet removed - glue left. Scratched the glue away with guitar pick, not to damage the floor :shock: Pic2. Caps for corner traps cut. Elecrtic saw is fun. Pic 3. Concept vs. implementation. "Proof of concept" superchunk still in the corner, trap according to my design being erected in front.

Answered my own question. For flat panels I will make them one side absorbent another side reflecting high and mid by covering with panel. Not sure how the material is called (it's 3mm thick): http://www.senukai.lt/katscan/50/50578945.JPG I will have more versatile panels and it's way cheaper than polyester + burlap on both sides. Also I will cover back walls of corner traps with this. So top layer costs will be cut in half :)

Here is first update of my room treatment. Pics in order: Lumber loaded. Poor mans fabric absorbtion test bed. Had to choose what to cover rocwool with. The test winner - soft cotton cloth. Test results. Rockwool (empty). Test results. Cotton tighter weave. Test results. Winner - soft cotton cloth (also good for wrapping babies). Not sure if such test is worth anything, but it sort of confirmed what my intuition was suggesting. Unfortunatelly did not get any material that looks like grill-cloth. So decided to use soft one, that seems to absorb highs better.

BTW. the test "hole" has top cover of rockwool as well which is not visible on photo. And microphone is cardioid so it should get most of the sound from the hole itself not the room. Ok, here are pictures from corner trap construction. Start of assembly. The back walls of the box are connected with on side wall. The other side is only to help assembling this far. It get's removed when rockwool is being placed. Unit filled with rock. That's how the triangles are fit inside. Unit #1 ready. Unit #1 in place. The final result of day 1 really assembling the traps. Last pictures are from saturday evening. By now I have 2 big vertical traps 2 small vertical traps as in the left corner in last picture + 5 of 6 ceiling/wall corner traps. This evening I will make the last corner trap and tomorrow hopefully they will get hung in place. Stay tuned for measurements. Further plans - 8 "FlatTraps" as in original design. "~0dB PC" (top secret project... well if I make it happen I will share experiences here). "SubLift" to give some minimal peace to my neighbours below... and "MonitorStand", to keep my KRK RP8's and LCD in ear (eye) level, and unblock access to FW1884 inputs 4-7. Actually I'm thinking replacing 2 of "FlatTraps" with 6 smaller "MiniFlatTraps" on ceiling, spaced randomly from the ceiling to give some diffusion, and different absorbtion frequencies. Also angling some to fully avoid early reflections if it's left over after absorbtion. And I can't get 6" rockwool, so I will relplace it with 2 sheets 4", making 8" total.

Great thread! Got any more pictures from the final result? Also, what was the product name/id for your rockwool panels? I will order my own rockwool/isover/glava panels in the next day or two (although the Norwegian prices are not as low as the Polish, the products they sell should be similar.. :) - david

"Rockwool rockton". Sorry for no updates for so long. But here you are. Pic1. Corner is attached to the ceiling as can be (hardly) seen from picture #1.Hook is crewed into wall. It has long handmade bold attached on a steel cable loop. This bolt is secured with a nut to the metal corner on the side of the trap. Such construction allows adjusting tension. Pic2. Whole left side ready. Pic3. All 6 traps up. Pic4. Middle section of the ceiling is treated with 6 "bricks" 100cmx60cmx20cm. "Brick" is made of 2 sheets of 4" (10cm) rockwool with plywood back wall. All is wrapped in polyester batting and cloth secured with staples to that back wall. there are 2 1"x1" wood inside running across the trap (attached to the back wall), which have hooks 4 screwed in at the ends and serve as mounting points. Mounting is similar to that of corners, but air gap is left behind the traps to increase LF absorbtion. Pic5. 2 bricks Pic 6. Complete ceiling and corner treatment. Next post will contain waterfall tests of this whole setup.

Here are the test results. Aren't they sweet? Pic1. All the corner treatment - 6 big ones at the top, 2 big+2small in the front. As seen in Pic3 of Update2. Pic2. the ceiling treatment is finished. (as in Pic6 of Update 2). One thing for sure - such treatment really works. Problems are much of smaller scale than when I started. I still have modal issues related to room length 42Hz and harmonics. This should be handled by back wall GOBOs. Side-to-side problems are audible at higher frequencies when you clap, because 2 huge walls untreated, interestingly enough side-to-side mode of ~65Hz is not making much problems, but I will do side wall treatment at least for sake of early reflections. Good luck in your projects, I hope these graphs will keep your faith during early phases :)

Now the short one. Pic1. Rear panel being constructed. I stuffed each of 3 sections with 2 sheets of 4" rockwool. Then polyester and cloth wrap, and finally base on wheels. More construction pictures in next update (about side walls). Pic2. The results with 2 such panels constructed and placed according to design (seen on page1). My interpretation is as follows. Placing rear panels quite far away from rear wall I got great performance (most probably because they are closer to 1/4 of wavelengths of the lows), so quite dramatic cut of 42Hz & 84Hz is seen compared to results with no rear treatment as well as dip at ~145 is much reduced. Now side-to-side modes are exposed and are on my target with side wall treatment, using same construction of traps. Unfortunatelly I can't space them from walls at such distances as ceiling and rear wall treatment, but let's wait for results. My speculation. It seems that amount of untreated space matters more than amount of treated. I mean that having 25% treatment and doubling that up to 50%, won't improve things twice, rather 1/3 of the problems should go, as instead of 75% untreated space you are left with 50%. Therefore most dramatic changes are seen with the last additions to room treatment. My initial worries after bringing 9 bales of rockwool were that if after 9 bales I still have terrible response, bringing another 9 would improve things only as much as initial 9, and then to see some useful improvement I'd need even another 18bales, etc. Thanks god it works just opposite. BTW. With percent I don't mean whole room surface, but percentage of parralel surfaces where none of two walls have treatment. Treating the second wall (floor for example) should give minimal results if one is treated already. Correct me if I'm wrong, although this room is approching it's final trap, hopefully it's not the final room in my life. So I want to learn by this experiment and don't want to make wrong conclusions. Or even worse to make my wrong conclusions lead someone to wrong assumptions when doing their projects.

This is great stuff Tomas - thankyou for sharing. could you please give us the top end graph as well? cheers john

Hi, I was not able to interpret the other graphs, so I might be that I captured wrong graphs with wrong settings Anyway here are some graphs that were captured. they go by 3 - all corner traps (incl ceiling), ceiling bricks added, rear wall added. logarithmic response graph uses 1/12 octave averaging. I also have energy time curves if that's of any help. Hi frequency waterfalls looked like random data to me if using longer gate times, ok with all treatment it seems less random. But still I can't interpret it. Also it does not take ETF to notice that some frequencies still resonate between side walls when clapping. I also did not pay attention too much to these graphs as neither my listening position, nor speaker placement will remain the same, and I believe highs are more position dependant than lows. Anyway I hope tomorrow or over the weekend to finish the treatment and the table - so I could make measurements of real mix position. Both with traps facing soft and hard side, also playing with positioning the traps (angles, distances from the walls etc.). If I'd get some understanding what to look for at high end I could make more educated experiments and measurements. What plots should I prepare and what settings should I use in ETF that would make sense to you (also not to clutter the topic with useless imags)? Also what is at my disposal to correct problems in highs once I identify them? Any reference material? P.S. My graphs end at 10kHz as SPL meters mic is good to some 12kHz only. I only have SM58 & AKG C3000b as other mics (they have superioir hight freq response, but both are cardioids).

It's scary!!! I put ETF in Continuous mode, so it shows changes in LF respose as I move these huge panels. And it feels as I'm rotating gigantic knobs on FreakEQ where it is sort of obeys your hand but in completelly strange way, and all knobs control the same 4-5 frequencies and are interconnected. Exactly the same happens with subwoofer placement. The panels are REFLECTING some lows down to 50Hz. So I can create my own modes, or influence geometry of the room. By sub & panel tweaking I was able to create/recover dip of 20dB!!! I wish I could control this in predictable way. Surprisingly enough, configuration very close to my design (a bit adjusted from what's on the net) works best after 2 hours of playing. At weekend I will allocate more time to play around and capture results. Up to this point I felt like being in control - now panic mode! Luckily enough I have configuration that has quite good low frequency response, otherwise I could shoot myself trying to control this monster. Here is the waterfall of the final setup for this evening.

So here are the shots of my finished mixing room. Pic1. "New" desk. I built quite basic monitor lift, to hold all my 3 monitors at ear (eye) level. Pic2. Same. Pic3. Side walls are treated with 2 big panels each. It's also the biggest "big picture" I can get with my mobile phone through doorway :) Note that right GOBO is removed to be able to take this picture. Pic4. GOBO & side wall treatment. 2 such moveable walls are used to treat the back wall. General storage are is behind. And now you can congratulate me, as I've created myself new problem - 600Hz hole (a terrible one) caused by comb filtering from my desk. Reflection points are right next to corners of my control surface. I'm thinking about creating two L shaped mdf panels that will run from the top desk to the bottom at an angle that will cause no reflection at listening position. They would be removeable. Another questionable idea is to create 2 vertical "separator panels" extending form top desk mounts. So that reflections are not allowed to propagate to center, but are "rereflected" to side walls and absorbed there. Question 1. What would you suggest for desk-reflection treatment? Question 2. Do I need some front window treatment? It has horizontal blinds that should reflect/diffuse higher frequencies to top, and hopefully window itself is not reflecting so much mid/low? Subjective listening gives very clear stereo image and depth perception. Records containing natural space (jazz) sound bit scary - as the room does not end with the window, but rather a studio is located in front and all musicians are gathered right next to you. First time experience in my life where recorded space sounded so immersive. Also really funny listening to my mixes that revealed only modest A/B difference from originals before :) Frequency domain is acceptable in some cases, but time domain is totally off. I spent ~1 month after my day-job (excluding weekends that were used for other hobbies) or ~80 hours building this all. 21 bale - 6 cubic meters (300 kg) of rockwool was used, as well as quite some polyester batting, covering cloth and lumber. No animals (except huge population of some very very tiny bugs that invaded my kitchen) got injured. Very rough numbers: rockwool 200 eur poly+cloth 150 eur wood 100 eur fixing elements 50 eur. So total budget being about 500eur.