Design of control room for project/home studio asymmetry..

I did that, but only to 75 db, I think I read that number somewhere

85 dB is the "standard" calibration point (if there is such a thing!) At least, that's what modern cinema speakers are calibrated for. It's also the recommended listening level for control rooms, and figures prominently in ITU and EBU documents. You could use 75 dB, if your room was really, really well isolated with an NR curve below about 25. But that is unlikely to be the case. The reason is simply that the impulse response measurement (on which all the others are based) needs to have a good, clean decay on it for at least about 30-35 dB below the initial level, in order for all the rest of the time-domain readings to be valid. If you start at 75 dB, then you need a noise floor below about 40 dB. If not, then the quiet end of the decay gets lost in the noise: Not just the ambient room noise: mic noise, pre-amp noise, digitizing noise, the noise you yourself make in the room, the noise made by the equipment you use to measure, HVAC noise, etc. 1/2 dB there, 1 dB here... They all add up. But if you start at 85 dB, or even higher (wear hearing protection, of course), then the software can "see" a good decay from that point until well above the noise floor, so the time domain readings are a lot more accurate.

OK, so lets say 10cm to give room to the rear port bass, and maybe 10 cm for additional absorption, so somewhat around 20 cm should be ok?

Yup! :) The "mush" on your graphs in the low end is most likely due the untreated room itself. I guess it sounds a bit "boomy" in there right now? That should change once you start putting the treatment in place. But don't expect astounding results: the room is small and has a strange shape, so it won't be perfect. There are physical limitation about what can be accomplished in there. But it sure can be a lot better than it is now! - Stuart -

OK, REW suggested to calibrate the software to a spl meter at 75 db, but the actual measurements should be done louder ^^

Soundman2020 wrote:

But don't expect astounding results

I expect it to be at least better than last time, when I treated without any measuring, just hoping for the best ;-) And I expect to learn a lot in the process, so I can use this knowledge when I build a "real" room somewhere else in maybe 5 years or so... 8) :mrgreen: I did some new measurements, I hope these are more usable? I also have a desktop tilt, for compensating reflections by desks, etc., working around 160 hz. I activated it on some measurements (see graphs). The response between 100 and 200 hz seems to be a little bit more flat this way. But strangely, the highs seem to roll of a little stronger with the switch engaged :?

Something just doesn't look right on those waterfall plots: They decay seems to be linear, which is really hard to explain! I suspect that there is something not being done right. It's also hard to explain why you would be getting 500ms RT-60 times at 8 KHz. Please can you post the actual data file from REW, so I can download it and take a closer look. - Stuart -

:? This really seems to be wrong.... please try to download the file here: https://www.dropbox.com/s/26udpbml4u9x95x/Erste%20Messungen%2016.11.2012.k.mdat Thanks for your help, Stuart!!!

Yeah, there's definitely something wrong: the impulse response graph is showing that your ambient level is about 100 decibels below the impulse level, which is VERY hard to believe! There's no way that your room has a noise floor that low, and there's no way that those Genelecs are producing such extreme levels as to account for this. REW is also showing straight-line linear decay across the entire spectrum, which is just as hard to believe, especially when the RT-60 graph shows the exact same time for 100 Hz and 2 kHz. The only thing that looks reasonable is the simple frequency response curve. Everything else is strange. Did you do the calibration procedure for REW? Are you sure that you kept the mic and speaker in exactly the same position in the room for all of the measurements? I'd suggest that you carefully check your signal path, mic, cables, interface, routing and everything else. - Stuart -

Soundman2020 wrote:

Did you do the calibration procedure for REW? Are you sure that you kept the mic and speaker in exactly the same position in the room for all of the measurements?

Yes :( I will try to find out whats wrong, and hopefully have a correct measurement until Thursday evening

Hi :D I hope you´re doing allright? I havn´t been able to come back to this site for quite a long time. I was busy with moving to another house and I also had some concerts with some *** hard music to learn and play.... But now I finally have time to come back to my room design. Well, everything is, as it was before. I tried to make a new measurement, here is the file https://www.dropbox.com/s/ynfl0psqnllww ... rrect.mdat I tried using my MOTU interface this time, does this look more reasonable? I will make more measurements these days, I think this time i was a little more away from the wall than last time. ^^ What do you think? Peter

does this look more reasonable?

Much better, Peter! It is making perfect sense now, and the actual readings match the modal predictions very closely (using Bob Golds' calculator). This is good! I wasn't expecting such a good match, due to the strange shape of the room, but it is good news, as it helps to understand the issues, and what to do about them. First, I just want to confirm that you currently have no treatment in the room, correct? If you do have something, then what is it, and where is it? Anyway, the good news is that it looks like the room can be treated to get it sounding a lot better. First, you have some very early reflections that need to be killed: I'm pretty sure they must be coming off the angled ceiling in front of you, since that is the only thing close enough to cause such short delays (under 1 ms). So put some soft absorption on that angled section, right above and behind the speakers. Probably 5cm thickness 80cm wide would be enough. Next, you are getting early reflections from something with a path length of about 3.8 m: the only thing that fits that is the side walls, so you also need thick absorption there: put a large thick panel (at least 10cm) spaced 5cm to 10 cm away from the wall, at the first reflection points. Make those panels big: about 1.2m wide and floor to ceiling. Next, you have early reflections coming of something with a path length of about 7.5m. My guess is the rear wall, so you need thick absorption there too: once again, at least 10 cm, spaced 10 to 15cm away from the wall. That should also be floor to ceiling, and very wide: about 2.4 m would be good. You could also tilt that forwards a bit, so it is further from the wall at the top, and closer at the bottom. Finally, you have some big modal issues, and the low frequency decay time is too long, s you need lots of bass trapping: Use the rear vertical corners of the room. Build a large superchunk bass trap in each corner, about 90 cm across the front diagonal face, and 60 cm or so along each wall. Also do something similar on the two side walls, above the door and above the window. Try that, then take another measurement with REW, and post those results here. There should be a decent change, I expect. It probably won't be a huge change, but should certainly be noticeable. - Stuart -

:D

Soundman2020 wrote:

First, I just want to confirm that you currently have no treatment in the room, correct? If you do have something, then what is it, and where is it?

I only have my couch and the electric piano in there that you can see on the picture. I guess they don´t really matter about the lo freq response. But the piano has to go anyway, so I will put it out and measure again.

Soundman2020 wrote:

So put some soft absorption on that angled section, right above and behind the speakers. Probably 5cm thickness 80cm wide would be enough.

I´m not sure about the "soft" and "hard" absorption people use. The only product I know in German is Rockwool, but it should do the job, right?

Soundman2020 wrote:

You could also tilt that forwards a bit, so it is further from the wall at the top, and closer at the bottom.

Sounds like a very good idea, I can get deeper frequencies without having to put the couch to far away from the wall :mrgreen:

Soundman2020 wrote:

Finally, you have some big modal issues, and the low frequency decay time is too long, s you need lots of bass trapping: Use the rear vertical corners of the room.

I have the door and the window there. Problem for superchunck. Maybe the front corners? The corners behind the speakers? I have lots of free space there for a lot of Rockwool. And I could probably use the corners over the door and window. And the horizontal corner at the ceiling from door to window. What about a Cloud? Would also be nice for putting some light in there. And some kind of slat resonators? Maybe my room ist too small for them? Thanks for your fast reply and analysis of the room! Peter

The only product I know in German is Rockwool, but it should do the job, right?

Rockwool is fine, but see if you can find different types and densities, and also see if you can find fiberglass insulation. I would suggest using a lighter, fluffier type in that angled part, due to the high angle of incidence of the sound waves. There are sure to be different types of insulation. Take a look around a few local large hardware stores / building supply stores, such as Home Depot, or Lowes, or whatever the equivalent is where you live, and see what they have to offer. Note down the density, and your impression of how "fluffy" or "hard" each type is, take some photos, and post the results here so we can help you choose the best type for each area of your room.

I have the door and the window there. Problem for superchunck.

Is there any bare wall at all bet ween the door and the rear wall? Even if you can't make it 45° diagonal, you can still angle it as much as possible and make it as deep as possible: It's a very small room, so it will need lots of bass trapping, and you'll need to use as many corners as you can for that.

The corners behind the speakers? I have lots of free space there for a lot of Rockwool.

Yes! Absolutely! Use those corners too.

And I could probably use the corners over the door and window.

Yes!

And the horizontal corner at the ceiling from door to window.

Yes!

What about a Cloud? Would also be nice for putting some light in there.

I was thinking of a cloud too, and that could be very useful, but do the first round of treatment as above, then test, so we can get a better idea of how to do the cloud.

And some kind of slat resonators? Maybe my room ist too small for them?

They would be great, but you don't have much wall area where you could put them, unfortunately. They would be a good idea for your room, but I can't see any place they can fit in! - Stuart -

Soundman2020 wrote:

Is there any bare wall at all bet ween the door and the rear wall? Even if you can't make it 45° diagonal, you can still angle it as much as possible and make it as deep as possible: It's a very small room, so it will need lots of bass trapping, and you'll need to use as many corners as you can for that.

There ist about 16cm. of Wallspace. If I do that, should I do the opposite corner (next the window) the same way for symmetry, or just go for as much bass trapping as possible? Or maybe just two panels, one on the door, the other on the wall?

There ist about 16cm. of Wallspace.

That's better than nothing! You could either make a triangular "wedge" in that corner, 16cm deep at the door frame narrowing to 10 cm about 60cm away from the door, or just do a vertical panel 60cm wide and 10cm deep, angled across the corner. The second option would be easier, and probably just as effective.

If I do that, should I do the opposite corner (next the window) the same way for symmetry, or just go for as much bass trapping as possible?

As much as possible. In the rear of the room, and especially for bass trapping, symmetry is not that important. So do the other side as large as you can: for example, about 90 cm across the front face, which means it will be about 60cm along each wall.

Or maybe just two panels, one on the door, the other on the wall?

You might need those as well, but let's wait until you have done the basic treatment and measured the results, then see what else needs doing. - Stuart -

Hey Stuart, thanks for your help! Just one more question now: If I do 60cm on both rear corners, and 2,4m in the middle of the rear wall I have 3,6 m. But the wall is only 3,96m long. Maybe I should just do the whole rear wall? Fake wall out of absorption?

You could do that, yes. You could even do a "hanger wall", but that might take up too much space (you need at least 50 cm or so for that). - Stuart -

Hi! I went and checked the home depot stores around. They stopped selling rockwool products and now they only have products from URSA. It is all cheap glasswool for thermo-insulation. I called the guys at ursa, and it seems it is not very suitable for acoustic purpuses. They had only one product with measurement data. Max. thickness is 50 mm and has 0,22 at 125hz. And it was too expensive. Then I called other manufacturers, and found the following data: Rockwool Sonorock (3,72€ per m², 100mm thick) density: ca. 28 - 30 kg/m³ flow resistance/friction loss (dont know the english word) > 6 no absorption data Rockwool fixrock (no prices found) densiy ca. 50 kg/m³, flow resistance > 6 now apsorption data Isover kontur fsp2-035, (10,42€ m²), density: 45 kg/m³, flow resistance > 5 (guy told me its not measured because its normally for thermo, but he said it is the same material as some other that has flow resistance 15) They told me it is just like Isover topdeck dp1 wich has apsorption of 0,71 at 125hz Isover ssp 1/2: (price unknown), density: unknown, flow resistance: >= 11 absorption at 125 hZ (50 mm thic): 0,26 I also found Owens Corning in Germany. Unfortunately they don`t sell mineral wool products in europe... But the guy told me maybe its possible to import it somehow. But should be very expensive, i guess.... What should I go for? Which density and flow resistance is ideal? Owens Corning 703 48kg/m³ looks good, but It´s going hard to find a similar product in germany because they normally don´t measure for sound absorption -_- Maybe rockwool sonorock can do the job? at least the price seems ok^^

Will the rockwool sonorock work for my superchunks and panels? Does anyone have experience with it?

The Sonorock will be fine.

flow resistance/friction loss (dont know the english word) > 6

I'm not sure what they mean there. Gas flow resistivity is measured in Rayls MKS, and the numbers are in five digits for usable acoustic properties. So that cannot be gas flow resistivity, as the number is a few thousand times too small! I guess they must mean something else. - Stuart -

Thanks Stuart :D Well, the people on the phone (at any of the above mentioned brands) also were not really able to explain what it means^^ I will order Sonorock then :D Today I found this: http://www.bhphotovideo.com/c/product/432505-REG/Genelec_8040_450_8040_450B_Flush_Mount_Speaker.html Flushmounting kit for Genelecs. Does it look reasonable? In this document they provide more info about it: link to pdf

Does it look reasonable?

Yep! If that's the speaker you have, and that's the way the manufacturer recommends mounting it, then that's the way to do it. - Stuart -

I just tried to imagine soffitmounting with sketchup. Seems like its impossible to do in my room. Even with a 90° speaker angle it will push my listening position into the middle of the room -_- Or do you see any way I could make it? And if I would do it, the nice corners behind my speakers couldn´t work as superchunk/basstraps, right?

You might be right, with that shape/size room. Not a lot of options! But post your SKP file here anyway, and I'll see if I can figure out something... - Stuart -

That would be so nice of you :D Here is the file: https://www.dropbox.com/s/0xo13922ji11n5k/raum_detail_soffit.skp

Actually, you CAN do it!!! :) http://digistar.cl/sayers-forum/STRANGE ... soffit.avi That's with a 39° angle on your speakers (78° intercept), but you can probably fiddle it to about 35 or 36 if you really want to. But 39° would be fine. That puts your head at about 40% of the room depth, which is also fine. You'll have to fill in the details, of course, and modify your desk a bit to get things to fit, but it is possible to soffit mount!

And if I would do it, the nice corners behind my speakers couldn´t work as superchunk/basstraps, right?

Yes they can, if you follow John's soffit design. You could even do those front corners as floor.to-ceiling hangers, with a solid extension of the front soffit panel and a large opening at floor level. That would work very well, actually... - Stuart -

Hello Sorry to But in on your thread. I was reading it and noticed that, it is best to do tests before adding acoustic control. Can I use any type of speakers to output the sine wave/software, or do I need to use the monitors I intent to use? Cheers Bruce

Can I use any type of speakers to output the sine wave/software, or do I need to use the monitors I intent to use?

The acoustic testing should be done with the best possible speakers you can get hold of, with the flattest response across the entire spectrum. Even if those are not the speakers you will actually use in the room, you still need to test with very good quality, full-range, flat response speakers, in order to get the most accurate results. You also need a good omnidirectional mic with flat response. And you do need to have things set up correctly in the room, in terms of speaker and mix position geometry. - Stuart -