Studio diary: practicing the basics!

Hi there! After a 2-year acoustic break, here I am again building a new control room. With this one, I'm trying to practice the basics that I've learnt here, which I would roughly summarize like this: - make good measurements (SketchUp helps a lot) - build as many basstraps as possible - think of every aspect before building (electricity, ventilation, lighting, etc.) - make measurements and fine-tune from there The room is 4.33 x 4.19 x 2.92 meters - which is almost a square - aouch! The ceiling is difficult, as well: long rounded holes. There is also a window that is not centered and warm water tubes under the ceiling. Not an easy starting point. I've decided to keep as much space/volume as possible and make it as functional as possible, on top of balancing the acoustic at least decently. First SketchUp draft:Then I went for basstraps like these:

Then, reading on this forum that a solid concrete floor is a good starting point, I had a concrete floor made by professionals. So, first step was to remove the carpet and the tiled floor. Then, the concrete floor. Please note the ceiling's profile.

Then, we mounted a wood/rockwool/wood wall. 3cm MDF - 5 cm Typ3 rockwool - 3cm MDF. And a door. From the outside:From the inside: From the inside, with wood structure to support the rockwool:

pask74 wrote:

The room is 4.33 x 4.19 x 2.92 meters - which is almost a square - aouch!

ouch is right. that's going to be a tough room to get under control. I had a look at your sketchup plans and they don't appear to show enough details to comment on the rest of the build. The idea for the bass traps looks correct, but again, not a lot of detail in the plan. It looks like you've got the right idea with your floor and the wall/door you've put up, but it's probably a good idea to do some calculations on room modes before you do any more of the build to see if there's a way of addressing the modal issues. good luck and

pask74 wrote:

- think of every aspect before building (electricity, ventilation, lighting, etc.)

If you're able to, do a sketchup of the complete build before you pick up the hammer again. That way, you or someone on the forum will hopefully point out any flaws before you have anything actually built. This could save you a lot of time ad expense. good luck :D -------- edit: I didn't see your other thread in design. Looks like you've ticked a lot of the right boxes over there and have got some input from Stuart which will help you out enormously :D

Yes - I actually haven't done all the things I recommend on doing ;-) In this case, SketchUp-ing the whole thing. With this project, I have quite a few constraints, including a window, water ducts, that strange ceiling and the need for useable space! So, I decided to go for the basics and evolve from there. The main use of this space will be a Vocal Coaching School, so no need for immediate perfection anyways. But - yes - I'm aware that I may run into some problems that I won't be able to tackle once the building is completed.

Here is the first SketchUp draft, but all corner traps aren't mirroring actual reality...

Some progress... Ceiling - rockwool: - installation of wooden slats to attach plastic leaf/cloth to: - plastic leaf and cloth:

Walls - new wall completed (outside): - from the inside:

Side walls and ceiling bass traps: - structure: - light switch prep: - side wall and ceiling bass trap:

Back superchunk: - rockwool: - plastic: - cloth:

Front right basstrap: - structure: - rockwool: - cloth: It's amazing how the high mids and highs are preserved when using a plastic leaf under the cloth! This time, I've used 80micron thick plastic leaf. For the other space, I had used (I guess) 200 micron, which gave some unwanted "clicky" effect in the room. 80micron seems to be better but I'll reserve my judgement for the day we'll start measuring for good.

First measurements. The last bass trap is not yet built, some cloth is missing, no slats yet, speaker and mic are not in their final place, etc., so this is just a first impression.

Please post the actual MDAT file: it's hard to figure out anything from just one waterfall plot that shows practically the entire spectrum... :) - Stuart -

Hi Stuart, I tried to post the mdat file but the forum wouldn't accept this format, I'm afraid...

OK - so I've tried again to attach an .mdat file without success and its zip version weights too much, so here are jpegs.

Am I right to be mostly concerned by those dips in the lows and low-mids? I've put thin plastic under the cloth everywhere, is this the reason for those lively high-mids and highs?

A noob question I probably should have asked first ;-) : is it ok to measure with a mono speaker aligned with the measurement microphone?

I just made 2 measurements: One without the plastic sheet on the front left basstrap One with it. It seems that the 3k-9k range is slightly affected by this change (RT lenghtens). What do the specialists say? Is that a bad thing that the upper mids and highs are a bit more lively than the mids and low-mids?

I tried to post the mdat file but the forum wouldn't accept this format, I'm afraid...

MDAT files are too big for the forum. You need to post them on a file-sharing service (eg Dropbox), then post the link here. - Stuart -

OK - fine. Is this GDrive link working? https://drive.google.com/file/d/0B6wx2y ... sp=sharing

Is this GDrive link working?

Yep, that link works fine. However, the data in your MDAT file is suspect. According to that, you did the test at a level of about 140 dB :!: :shock: If that were, true, you'd be dead. Also, the data only goes up to about 15 kHz, and at around 1 kHz the sound dies away normally for around 300 ms, then suddenly comes back up again after about 500 ms! That is impossible. the RT60 shows that the decay time is under 100ms at 300 Hz, but increases drastically to nearly 300 ms at 6kHz: that is pretty hard to explain, unless you have some very large tuned traps in the room. And there's only one test in that file: you said you did two tests, but the MDAT you sent only contains one test. So I suspect something is wrong with your test procedure, or your test equipment. I would start by repeating your calibration procedure again, to make sure that the readings are at least realistic. What mic were you using for that test, where was it located in the room, and what speaker did you use for the tests? - Stuart -

Hi Stuart, thanks for your reply. Here is this morning's measurements: https://drive.google.com/file/d/0B6wx2y ... sp=sharing Test level: it was a bit too loud (the speaker was saturating a bit), but never at 140db as I could stay in the room while the sweeps were playing. I've adjusted it for this test. The lively (high-)mids is one of my concerns, actually. It's something I can even hear just while talking in the room. I've put a plastic sheet under the cloth, as advised by John to preserve the higher frequencies. It actually does but also seems to lenghten the RT of those frequencies quite noticeably. There are no tuned traps whatsoever in the room, unless those cavities in the ceiling (see early pictures on that thread) could be seen as tuned (which I doubt, as they are open)? Am I missing something here?

OK, so I wanted to understand more what this plastic layer is doing to the sound, so I removed the upper half of it on the left wall. Here are the results: https://drive.google.com/file/d/0B6wx2y ... sp=sharing I can clearly see that the highs and high-mids are being shortened - am I right? If so, I may well have to remove at least a good portion of this plastic sheet... (sob). Any other impressions? PS: I checked the levels again and they seem to totally fine. I'm not sure why REW indicates such high SPLs?

I'm not sure why REW indicates such high SPLs?

Did you follow the complete calibration procedure? You have to tell REW what the real level is in the room by measuring it with a good quality hand-held sound level meter (not an iPhone app!) then entering that information into REW. It is part of the calibration. If you don't do that, then REW has no way of knowing what the actual SPL level is, and can only take a wild guess. After you calibrate, you should then run the tests at about 80 dB per individual speaker, so you should be getting about 85 dB with both speakers and the sub all working at once, or about 83 dB if you don't have a sub. What mic and speaker are you using for these tests (make and model), and where is the mic located? Some photos of the room would help greatly to understand what is going on.

I can clearly see that the highs and high-mids are being shortened - am I right?

No. The two tests were done at different levels: the second one is about 5 dB higher than the first, so you cannot validly compare the two. After your system is calibrated, you must ALWAYS do all later tests at exactly the same level, and with the mic in exactly the same position in the room, highly accurately located to within a few mm, every single time. If not, then you cannot compare measurements. I'm still highly skeptical of the data in that REW file: I find it hard to believe that your RT-60 time increases so drastically in the highs, and drops to a minimum in the low mids: that makes no sense. I also find it a bit hard to believe that the speakers are showing almost flat response at 20 kHz. Please increase the upper limit to 30 kHz. next time you measure: I'd love to see how it is doing up there. You'll also need to increase the sampling rate of your sound card to be able to do that, but it will be worthwhile, I think... What are the dimensions of the room? - Stuart -

Hi Stuart, Mic: Behringer measurement microphone (the famous one lots of people seem to use). It's located at 38% of the length of the room from the front wall. Speaker: http://www.psiaudio.com/product/active-monitors/a17-m Preamp: a Neuman-type console from the 90s. Converters: Black Lion Audio modified MOTU HD192 I calibrated the soundcard by recording a loop but did not use the SPL meter, etc. - I need to do it first thing on Monday? Thanks for flagging this out. I have a proper SPL meter in the studio so that shoudn't be a problem. Sorry for this bad start. Now, I can clearly hear those (upper)mids when just talking in the room, so unless it's purely psychological, what I see on the graphs in the mids kind of makes sense with my impressions when in the room. Anyway, let me calibrate REW completely and run new measurements. Currently, I only use 1 speaker, should I go for a stereo setup right away?