John Sayers' Recording Studio Design Forum Archive

Hi guys!

I have a rec room that I am very happy with. However, the area in front of the main window (approximately 2,5- 3 sqm big) is sounding thin because of bass cancellations (I think?) from the concrete wall at the other side of the room. Can you suggest treatment for this? It would be the concrete wall (behind the drums) that needs treatment I reckon?

Also I am getting some flutter between the main window and the concrete wall that needs to be fixed.

The sidewalls are very lively and bright, which can be nice, but I am sometimes hearing a delay-ish sound (in just a couple of spots in the room) when clapping between them even though they are mirrored. Could some treatment on one of these walls control this a bit?

Some info:

This is a concrete building.

The ceiling, which is concrete, is originally 3.35 meters, but is now 3 meters as it's stuffed with fluffy fiberglass (glava). The ceiling in the drum area is probably around 40 cm lower as it is stuffed with even more (around 80 cm) fluffy fiberglass.

- The sidewalls are 20 degree angled plywood panels with around 15 cm lightweight fiberglass. Behind the angled plywood panels is 10 cm more lightweight fiberglass and then concrete. Then more isolation and then the concrete outer wall.

- The wall with the main window is of concrete, but the big grey area (you see it on the picture taken from behind the drumkit) is made of owens corning 703 (3 cm), fiberglass (7 cm), Dacron and fabric.

- The back wall (behind the drums) is pure concrete, painted black.

- The booths (the grey constructions with the small windows) are covered with 3 cm Owens Corning 703, 7 cm fluffy fiberglass and Dacron.

- The two pillars are covered with 3 cm Owens Corning 703, 7 cm fluffy fiberglass.

I must say, the area where the drums are usually set up sounds amazing with regards to close mics, overhead mics etc. Punchy, lot's of controled thump etc. It's just that the middle of the room is a bit thin sounding when one place instruments in the "drum area".

I've attached pictures of the room and also a picture with the dimensions.

Hope you've got some ideas for me!

Hey guys.

Just letting you know that we've done some measurements with REW (mini dsp mic and a KRK speaker)

I wasn't able to add the REW files here (because of the size I reckon?) so I'm copying a WeTransfer link here so that you can have a look at it if you feel like.

https://we.tl/5lcIH12aI4

Christer

Just letting you know that we've done some measurements with REW (mini dsp mic and a KRK speaker)

Excellent! I'm glad you bumped your thread as well, since I had it in my list of "threads to answer soon", but I think I skipped it!

How did you have your mic and speaker set up for that? (Locations in the room)

That's a nice looking room, by the way. Very modern.

the area in front of the main window (approximately 2,5- 3 sqm big) is sounding thin because of bass cancellations (I think?) from the concrete wall at the other side of the room. Can you suggest treatment for this? It would be the concrete wall (behind the drums) that needs treatment I reckon?

Also I am getting some flutter between the main window and the concrete wall that needs to be fixed.

Since you have the impression that the concrete wall is responsible for both issues, there's a simple test we can do to see if that really is the case, or not.

Well, in theory it is simple! Put several large pieces of thick fiberglass or mineral wool insulation up against the concrete wall, and see if the problems go away, or are at least reduces. You will need wool at least 15cm thick, and you need to cover as much of that wall as you can.

That's not the final treatment! It's just to confirm that the wall really is the problem. If it is, then I have some ideas for how you could treat that without damaging the sound in the rest of the room, but you really should confirm first.

The sidewalls are very lively and bright, which can be nice, but I am sometimes hearing a delay-ish sound (in just a couple of spots in the room) when clapping between them even though they are mirrored. Could some treatment on one of these walls control this a bit?

Yes, definitely. But considering that you like the overall sound of the room, and the "liveliness" of those walls, the answer is NOT to put absorption panels on the walls. That would work, yes, but it would change the sound of the rest of the room, and take away the "brightness" of those walls.

The ceiling, which is concrete, is originally 3.35 meters, but is now 3 meters as it's stuffed with fluffy fiberglass (glava). The ceiling in the drum area is probably around 40 cm lower as it is stuffed with even more (around 80 cm) fluffy fiberglass.

Great info! That means that the ceiling is very probably NOT the problem here.

- The sidewalls are 20 degree angled plywood panels with around 15 cm lightweight fiberglass.

How thick is the plywood? How is it mounted? I'm wondering if what you are hearing might be some type of vibration in the plywood...

Hope you've got some ideas for me!

My guess is the concrete wall. That test with the insulation panels will confirm it. There are other ways of confirming it too, using REW, but time consuming for both of us, and I don't have a lot of spare time right now. I'm working on several studios at once, and my paying customers have first priority, obviously! So let's try the easy way, with those insulation panels first. If we can't confirm it that way, then I'll tell you how to it the slow way, but it will take a while before I'll be able to analyze the data and get back to you.

I have downloaded your MDAT files, and I'll take a quick look at them, but I need to know where in the room you had the mic and speaker for each test. Mark it in the diagram you drew.

Edited to add: I looked at your REW data, and it is noisy: Where you in the room when you did those tests? You should be outside the room when the actual test runs. Use the "Start delay" feature of REW to do that. Set it so you have enough time to get out of the room completely and close the door, plus another few seconds extra to allow for things to calm down inside.

Also, set ""sweeps" to at least 2, to improve the signal-to-noise ratio.





- Stuart -

Hey Stuart!

Thanks for answering.

Appreciate it a lot!

As you can see in the REW files, the speaker and the mic was moved around quite a bit and categorized in the REW files. Each measurement in the REW files is described. "speaker 2m from the concrete wall", "Mic 1m from the rear wall" etc. But maybe it's better to draw the positions on a picture and add that to this post?

We'll do some new measurements without being in the room. Thought we where quiet, but not quiet enough it seems!

We'll put up thick fiberglass against the concrete wall and do more measurements with this added.

As for the sidewalls, the plywood is maybe 25mm thick. I'll add a couple of pictures of the build. What the pictures don't show is us adding lot's of lightweight fiberglass to the frames/ traps themselves directly behind the plywood. The angle is 9 degrees by the way. Also the panels are mirrored between the two sides of the room. If that makes sense?

Thanks for doing this. I know you're a busy man!

Hi again Stuart!

Just measured the room again.

Should be less noise as we where out of the room on every measurement. We did hear that the speaker enclosure resonated a bit on a couple of frequencies, so maybe that was some part of the issue. Turned the levels down a bit on these measurements so now it should be fine.

We didn't have too much lightweight fiberglass left, but added what we had and did a new round of REW tests. With and without the fiberglass. All measurements are clearly described in the REW file. I've also added three pictures showing how the speaker was positioned, the microphone etc. All this in a new WeTransfer link, which is here:

The .mdat measurement files are split up in 2. The "mid room" file contains measures where the mic is set up in the center of the room, between the control room window and the concrete wall at the other side of the room. The "corner" file contains measures where the mic is positioned in the main corners of the room.

https://we.tl/2WBA2Ze8ij

Talk soon!

I've been looking at your new data, and there's something that's just not right about it. It does not seem to be valid, and not what I'd expect from that room. There's a lot of noise in the signal still, and it doesn't make a lot of sense.

Are you CERTAIN that you calibrated REW correctly?

Are you CERTAIN that you set up and ran the tests at 86 dBC? And you checked that with a hand-held sound level meter (on "C" and "slow")? And you calibrated REW to the same level?

The graphs do not show that.

Are you CERTAIN that there was nothing else noisy in the room while the tests were running? Did you have the HVAC system turned off?

Did you set the "Sweeps" setting to something greater than 1? It should be 2 or 3.

That data is just too noisy to be much use.

Also, there's not much point in moving the speaker and mic to several random points in the room like that. We need things set up simply and repeatably. Find the location in the room where you notice the problem most, as you are walking around. Set up the mic at that location, pointing towards the black wall but angled upwards at about 60°. Set the speaker on a chair about 2m away from the mic, towards the direction of the black wall, and facing the mic. Make sure that you have all of your gain structure set correctly for the entire signal chain, and that there is no EQ applied anywhere (completely flat), and also no dynamics.

Now calibrate REW to 86 dBC, using your hand-held sound level meter.

Run one single test like that WITHOUT the insulation in the room, then another test WITH the insulation in the room. Send me that file.


- Stuart -