DIY rockwool acoustic panels

[RobC]

The big moment will come, aka. a bit of coustic treatment.

I kind of want both sound proofing and absorbtion.

I mainly want such panels on window and door areas.

On their own, windows and the door will be properly sealed, so no sound can easily flow.

I plan to make a frame around the windows, using carpenter wood (used for the roof normally). Then I add a window and door sealing strip, for extra sound proofing. I would somehow attach the DIY acoustic panel to that frame. Point is that it perfectly fits.
Question is: how could I tightly place a DIY panel against the wood frame? (It should be easy to put on and to take off, and the panel should squeeze against the frame and sealing between them.

Another question is the back of the panel. See, I have this thin type of wood, used on the bottom of a bed. I could add that to the back of the panel. Then I have an extra thin layer of isolation, and I won't need to add any cloth/textile to the back of the panel (needed because of the rockwool). But I'm not sure if that would help with sound proofing, or if it makes things worse. Maybe it's better if the back of the panel is open, too? Maybe it absorbs sound coming from outside - while adding the thin layer of wood would prevent absorbtion, and even would increase noise from outside, cause it would bounce around between the window and the back of the panel?

I welcome any help!

Btw, I can get 10 cm thick rockwool (no 15 cm available, sadly). It's 28 kg / m³, I think.

[motuscott]

Fiberglass can be an itchy nightmare, continuously sheds glass particles if not hermetically sealed, especially if you're moving panels in and out of place. There's an alternative made out of recycled blue jeans, more expensive no doubt.

[RobC]

Fiberglass can be an itchy nightmare, continuously sheds glass particles if not hermetically sealed, especially if you're moving panels in and out of place. There's an alternative made out of recycled blue jeans, more expensive no doubt.

I've heard of that - apparently, rockwool is a lot easier on the skin. That said, I do plan to cover them in fabric. They say the easiest way is to buy some basic bedsheets and work with that.
I can only work with what's available here, I'm afraid.

I also plan to just put a few plain rockwool slabs inside fabric (and properly sew them up - maybe even use hot glue), because I have two openings on my windows, and I can put the slabs between them, for even more sound proofing.

Alas, I still need to figure out how to attach panels to wood frames.

[selig]

Fiberglass can be an itchy nightmare, continuously sheds glass particles if not hermetically sealed, especially if you're moving panels in and out of place. There's an alternative made out of recycled blue jeans, more expensive no doubt.

I've heard of that - apparently, rockwool is a lot easier on the skin. That said, I do plan to cover them in fabric. They say the easiest way is to buy some basic bedsheets and work with that.
I can only work with what's available here, I'm afraid.

I also plan to just put a few plain rockwool slabs inside fabric (and properly sew them up - maybe even use hot glue), because I have two openings on my windows, and I can put the slabs between them, for even more sound proofing.

Alas, I still need to figure out how to attach panels to wood frames.

Sheets are typically the opposite of acoustic transparent materials, with higher thread counts that will block much of the sound from coming into the trap. They reflect many of the very frequencies you’re trying to absorb with all that rockwool. You need to wrap the rockwool to be sure, you just don’t want to waste that money on the absorbtion only to block/reflect much of the sound before it ever gets to the rockwool. You basically want something similar to what is used on speaker grills - same concept, let the sound through!

Plenty to read online about this, many suggest the lowest thread count if using sheets, the ‘breath test’ (not scientific), or using burlap if you can’t afford the ‘real deal’. Not sure how much difference it will make because there are a lot of variables - but if I’m going to build panels I’m not going to risk working against myself by cheeping out on the fabric.

[crimsonwarlock]

I suggest looking around this YT-channel for a while: https://www.youtube.com/@AcousticsInsider

[RobC]

I've heard of that - apparently, rockwool is a lot easier on the skin. That said, I do plan to cover them in fabric. They say the easiest way is to buy some basic bedsheets and work with that.
I can only work with what's available here, I'm afraid.

I also plan to just put a few plain rockwool slabs inside fabric (and properly sew them up - maybe even use hot glue), because I have two openings on my windows, and I can put the slabs between them, for even more sound proofing.

Alas, I still need to figure out how to attach panels to wood frames.

Sheets are typically the opposite of acoustic transparent materials, with higher thread counts that will block much of the sound from coming into the trap. They reflect many of the very frequencies you’re trying to absorb with all that rockwool. You need to wrap the rockwool to be sure, you just don’t want to waste that money on the absorbtion only to block/reflect much of the sound before it ever gets to the rockwool. You basically want something similar to what is used on speaker grills - same concept, let the sound through!

Plenty to read online about this, many suggest the lowest thread count if using sheets, the ‘breath test’ (not scientific), or using burlap if you can’t afford the ‘real deal’. Not sure how much difference it will make because there are a lot of variables - but if I’m going to build panels I’m not going to risk working against myself by cheeping out on the fabric.

I saw a youtube video, where the DIY panel maker used bedsheet. I had no clue where to get fabric, let alone the fabric's name, the proper definition, what to search for. So I thought, it's actually more expensive that I got two bedsheets, since it's a finished product.

Now I looked up low thread count. Apparently it's called linen. Measured in g/m². The lowest I found, is 115-120g/m2. It's expensive, but sill doable.

So I ask, is that the real deal? Is it called linen?

[RobC]

I suggest looking around this YT-channel for a while: https://www.youtube.com/@AcousticsInsider

All I need to know is whether to leave the back of acoustic panels open, with fabric on? Or should I buy sound isolating panels (common in offices for example), and put that on the back for better isolation?

And that should I put rockwool in fabric between two windows, or an isolation slab?

I will look around, but the channel is full of gaslighting titles.
If I know something, I just type the info out on here, too.

[RobC]

Okay, so basically, even if I stack 2 slabs of the rockwool available here, which would be 20 cm thick, with a 20 cm airgap behind it, would barely do an ~80% absorbtion down to 200 Hz. That would cost about 200 USD/EUR for DIY 3 panels.
A good thing I didn't throw out my gobo shield for my microphone.
I mean, sure, I could go to a corner, place 2 panels behind and next to me, and one above me, and the microphone with the shield in front of me, (with me facing towards the center of the room), but eh, that is far from a proper amount of absorbtion for a male voice.

And I still don't have isolation. I tops found some foam type slab that's available here.

Maybe it's time to stop dreaming.

[crimsonwarlock]

Okay, so basically, even if I stack 2 slabs of the rockwool available here, which would be 20 cm thick, with a 20 cm airgap behind it, would barely do an ~80% absorbtion down to 200 Hz. That would cost about 200 USD/EUR for DIY 3 panels.

Any level of absorption will have a positive effect. My panels are 10 cm deep, with a 3 cm air-gap behind them. I have a total of 14 panels, and two additional full height panels that are just 8 cm deep. The resulting acoustics are very nice. You can check my 'studio build' to see the pictures and the resulting SonarWorks measurements. The total cost for all these panels together was around 300–350 euros.

As for sound-proofing (isolation), indeed stop dreaming. To get anything useful in that regard, you need massive walls (as in, lots of mass) and/or air-gaps between walls (like a room within a room). We're talking serious construction work for that.

EDIT: just so you don't have to search for it: viewtopic.php?f=5&t=7530733

[mcatalao]

Sheets are typically the opposite of acoustic transparent materials, with higher thread counts that will block much of the sound from coming into the trap. They reflect many of the very frequencies you’re trying to absorb with all that rockwool. You need to wrap the rockwool to be sure, you just don’t want to waste that money on the absorbtion only to block/reflect much of the sound before it ever gets to the rockwool. You basically want something similar to what is used on speaker grills - same concept, let the sound through!

Plenty to read online about this, many suggest the lowest thread count if using sheets, the ‘breath test’ (not scientific), or using burlap if you can’t afford the ‘real deal’. Not sure how much difference it will make because there are a lot of variables - but if I’m going to build panels I’m not going to risk working against myself by cheeping out on the fabric.

When i built my traps, a friend of mine that understood a bit about that, said i shold get a tissue that allowed air to pass if you blow it near the moth, but with some pressure. Too thick would reduce apsortion, less thick would allow the rockwool to leave. I used a thick burlap tissue, tightening the Rockwool. It's a whool like matherial, sufficiently tight to allow even air to pass but a lot less rockwool material. I think i bought it on the curtains section. I have my bass traps in the studio more than 10 years and had no trouble breeding or whatsoever. The back tissue is a bit more thick, like a felter.

[crimsonwarlock]

I think i bought it on the curtains section.

Yep, I got the cloth for my panels from the curtains section at IKEA

[selig]

Sheets are typically the opposite of acoustic transparent materials, with higher thread counts that will block much of the sound from coming into the trap. They reflect many of the very frequencies you’re trying to absorb with all that rockwool. You need to wrap the rockwool to be sure, you just don’t want to waste that money on the absorbtion only to block/reflect much of the sound before it ever gets to the rockwool. You basically want something similar to what is used on speaker grills - same concept, let the sound through!

Plenty to read online about this, many suggest the lowest thread count if using sheets, the ‘breath test’ (not scientific), or using burlap if you can’t afford the ‘real deal’. Not sure how much difference it will make because there are a lot of variables - but if I’m going to build panels I’m not going to risk working against myself by cheeping out on the fabric.

When i built my traps, a friend of mine that understood a bit about that, said i shold get a tissue that allowed air to pass if you blow it near the moth, but with some pressure. Too thick would reduce apsortion, less thick would allow the rockwool to leave. I used a thick burlap tissue, tightening the Rockwool. It's a whool like matherial, sufficiently tight to allow even air to pass but a lot less rockwool material. I think i bought it on the curtains section. I have my bass traps in the studio more than 10 years and had no trouble breeding or whatsoever. The back tissue is a bit more thick, like a felter.

The 'breath test' is so vague I tend to stick with the known sources such as GIK. All my studio panels are from GIK, but they also sell all the raw materials for the DIY'er.
It's $12/yard for the basic fabric, which is 65" wide (by 36") which is more than enough for a typical 2x4 panel. The cheapest flat sheets I found with a quick search, which are too high a thread count for this application, are about $10 for 65x100" which can make two panels. So if you find 'twin' sheets for $24 you'd be spending as much as you would getting the "good stuff" which is guaranteed to work. Just my 2 cents…

https://www.gikacoustics.com/product/st ... -the-yard/

[mcatalao]

The 'breath test' is so vague I tend to stick with the known sources such as GIK. All my studio panels are from GIK, but they also sell all the raw materials for the DIY'er.
It's $12/yard for the basic fabric, which is 65" wide (by 36") which is more than enough for a typical 2x4 panel. The cheapest flat sheets I found with a quick search, which are too high a thread count for this application, are about $10 for 65x100" which can make two panels. So if you find 'twin' sheets for $24 you'd be spending as much as you would getting the "good stuff" which is guaranteed to work. Just my 2 cents…

https://www.gikacoustics.com/product/st ... -the-yard/

Ah didn't know they sold the tissue appart! Good to know, i'm planning to build two more floor to ceiling traps and 4 traps for first and second reflections.

Actually GIK acoustics was an active user of one of the forums I had some discussions about my bass traps, almost half a life ago. They were super friendly, they didn't ship to EU at the time so i went all in with the DYI route, but they were quite active on that forum and helped a lot at that time. They were SUPER helpfull and Ethan Winer aswell - asmf i "robbed" a lot of ideas from one of his schematics for broadband traps.

IMHO, It's better to have a less than ideal solution than no solution at all and when you're tight, you have to compromise. A lot of stuff in my studio are compromises. The 3xBCF2000 with a hyper cooked remote file is a poor man's 24 fader controller, and it works! My mixing desk is a mixer QuickLock desk with a wood top that i bought 2nd hand, again... half a life ago. And so on. I don't cut corners on some stuff (mics, instruments, computer, monitors, etc), but on other stuff I was forced to improvise a little because a full studio with GIK would be brohibitive (specially 17 years ago).

Necessity is the mother of invention!

But i digress.

That being said, if i was doing audio as my main occupation, probably all my acoustics stuff would be GIK as they now have a EU/UK store and it's a lot easier to get their stuff.

[mcatalao]

I think i bought it on the curtains section.

Yep, I got the cloth for my panels from the curtains section at IKEA

Right????? It works! You need more "whooly" fabric than soft tissues. The good thing is that rockwook is way less aggressive than fiberglass. But you still don't want that flying on the studio.

[mcatalao]

All I need to know is whether to leave the back of acoustic panels open, with fabric on? Or should I buy sound isolating panels (common in offices for example), and put that on the back for better isolation?

Nooooooo.... Man you are better off with no Acoustic panels than with a serious lung problem. You need to cover the front and the back of the panel with fabric that doesn't allow the rockwool to degrade. And get solid sheets not the whooly stuff, so high density sheets is the best way to go.

Rockwool is not a cancer harzard material, but it still has very small particles that in contact with your lungs will manage to hurt it to some degree. So you want to be sure it doesn't get in contact with air, moisture or water.

Be safe! Cover it on the front and back!

[mcatalao]

All I need to know is whether to leave the back of acoustic panels open, with fabric on? Or should I buy sound isolating panels (common in offices for example), and put that on the back for better isolation?

Nooooooo.... Man you are better off with no Acoustic panels than with a serious lung problem. You need to cover the front and the back of the panel with fabric that doesn't allow the rockwool to degrade. And get solid sheets not the whooly stuff, so high density sheets is the best way to go.

Rockwool is not a cancer harzard material, but it still has very small particles that in contact with your lungs will manage to hurt it to some degree. So you want to be sure it doesn't get in contact with air, moisture or water.

Be safe! Cover it on the front and back!

I meant you nee simething whooly tgat doesnt allow the rockwool to degrade. Not too solid not too opened. Curtain burlap for example is a good option.

[RobC]

Okay, so basically, even if I stack 2 slabs of the rockwool available here, which would be 20 cm thick, with a 20 cm airgap behind it, would barely do an ~80% absorbtion down to 200 Hz. That would cost about 200 USD/EUR for DIY 3 panels.

Any level of absorption will have a positive effect. My panels are 10 cm deep, with a 3 cm air-gap behind them. I have a total of 14 panels, and two additional full height panels that are just 8 cm deep. The resulting acoustics are very nice. You can check my 'studio build' to see the pictures and the resulting SonarWorks measurements. The total cost for all these panels together was around 300–350 euros.

As for sound-proofing (isolation), indeed stop dreaming. To get anything useful in that regard, you need massive walls (as in, lots of mass) and/or air-gaps between walls (like a room within a room). We're talking serious construction work for that.

EDIT: just so you don't have to search for it: viewtopic.php?f=5&t=7530733

I want to be able to make a fully professional vocal recording. The room size is ideal for it.
I don't want to invest into expensive rockwool, low-thread linen, and wood, just to have tamed highs with boomy lows. So, of course it's all frustrating and disappointing.

As for this house, I think it's constructed with air gaps. It's usually dead-silent. It's also built well above ground, up to a meter. The problem is with the window and door area. Like I said, a year ago, simple sponges between two window doors made a huge difference.
I simply asked if between the windows, if I put rockwool, if that would help? Maybe sheets are enough for covering those, since in that area, it would be used for sound proofing.

As for my absorbers, those would get covered in linen.

[RobC]

When i built my traps, a friend of mine that understood a bit about that, said i shold get a tissue that allowed air to pass if you blow it near the moth, but with some pressure. Too thick would reduce apsortion, less thick would allow the rockwool to leave. I used a thick burlap tissue, tightening the Rockwool. It's a whool like matherial, sufficiently tight to allow even air to pass but a lot less rockwool material. I think i bought it on the curtains section. I have my bass traps in the studio more than 10 years and had no trouble breeding or whatsoever. The back tissue is a bit more thick, like a felter.

The 'breath test' is so vague I tend to stick with the known sources such as GIK. All my studio panels are from GIK, but they also sell all the raw materials for the DIY'er.
It's $12/yard for the basic fabric, which is 65" wide (by 36") which is more than enough for a typical 2x4 panel. The cheapest flat sheets I found with a quick search, which are too high a thread count for this application, are about $10 for 65x100" which can make two panels. So if you find 'twin' sheets for $24 you'd be spending as much as you would getting the "good stuff" which is guaranteed to work. Just my 2 cents…

https://www.gikacoustics.com/product/st ... -the-yard/

About 1m² linen goes for about the equivalent of 16 USD in Hungary. (3-4 work hours on minimum wage for example.)

[RobC]

All I need to know is whether to leave the back of acoustic panels open, with fabric on? Or should I buy sound isolating panels (common in offices for example), and put that on the back for better isolation?

Nooooooo.... Man you are better off with no Acoustic panels than with a serious lung problem. You need to cover the front and the back of the panel with fabric that doesn't allow the rockwool to degrade. And get solid sheets not the whooly stuff, so high density sheets is the best way to go.

Rockwool is not a cancer harzard material, but it still has very small particles that in contact with your lungs will manage to hurt it to some degree. So you want to be sure it doesn't get in contact with air, moisture or water.

Be safe! Cover it on the front and back!

When I said that, I meant to cover the back with wood, and the front with fabric. By now, the absorbers in the room will have a wood frame with rockwool in them, and then covered with linen.

For the "cloud" absorber, I will probably use wall brackets.
But the absorbers that go on the wall, is another question, especially if I want up to 20 cm air gap.
How do you put those up?

[mcatalao]

When I said that, I meant to cover the back with wood, and the front with fabric. By now, the absorbers in the room will have a wood frame with rockwool in them, and then covered with linen.

For the "cloud" absorber, I will probably use wall brackets.
But the absorbers that go on the wall, is another question, especially if I want up to 20 cm air gap.
How do you put those up?

My absorbers are not in the wall, they are floor to ceiling and i have feet under them. So i don't have them in the wall. And the other reflection points, now have a foam product from a Brand called RPS. Not a perfect solution too. But those are the ones i plan to make new broadbands.

For broadbands (the ones with 70 cm to 1 meter high you usually see on studios) they usually are not too far from the wall, they're right on top of it. However, since i believe a gap from the wall is still usefull, if/when i build these, I'm planning to leave a 10 cm gap. To achieve that ill build a 20 cm frame instead of just the size of the rockwool plaque. So if the rockwool plaque is 7 cm high, i'll make a 17 cm frame, if it is 10, ill make a 20 cm frame and so on.

Does that make sense?

Cheers,
MC

[RobC]

When I said that, I meant to cover the back with wood, and the front with fabric. By now, the absorbers in the room will have a wood frame with rockwool in them, and then covered with linen.

For the "cloud" absorber, I will probably use wall brackets.
But the absorbers that go on the wall, is another question, especially if I want up to 20 cm air gap.
How do you put those up?

My absorbers are not in the wall, they are floor to ceiling and i have feet under them. So i don't have them in the wall. And the other reflection points, now have a foam product from a Brand called RPS. Not a perfect solution too. But those are the ones i plan to make new broadbands.

For broadbands (the ones with 70 cm to 1 meter high you usually see on studios) they usually are not too far from the wall, they're right on top of it. However, since i believe a gap from the wall is still usefull, if/when i build these, I'm planning to leave a 10 cm gap. To achieve that ill build a 20 cm frame instead of just the size of the rockwool plaque. So if the rockwool plaque is 7 cm high, i'll make a 17 cm frame, if it is 10, ill make a 20 cm frame and so on.

Does that make sense?

Cheers,
MC

I just need good acoustics for professional vocal recording, so I need to have good response down to ~100 Hz. Though I really should do a proper measurement of my own voice.
Maybe I should just build legs for my planned absorbers, too. Then I can move them around, or put in storage. Seems like a flexible solution. Fairly easy to build, even out of wood, and I have plenty wood material for that.

[selig]

Nooooooo.... Man you are better off with no Acoustic panels than with a serious lung problem. You need to cover the front and the back of the panel with fabric that doesn't allow the rockwool to degrade. And get solid sheets not the whooly stuff, so high density sheets is the best way to go.

Rockwool is not a cancer harzard material, but it still has very small particles that in contact with your lungs will manage to hurt it to some degree. So you want to be sure it doesn't get in contact with air, moisture or water.

Be safe! Cover it on the front and back!

When I said that, I meant to cover the back with wood, and the front with fabric. By now, the absorbers in the room will have a wood frame with rockwool in them, and then covered with linen.

For the "cloud" absorber, I will probably use wall brackets.
But the absorbers that go on the wall, is another question, especially if I want up to 20 cm air gap.
How do you put those up?

What design are you following that has wood on the back, I've never seen that before…

I've been recently reading more folks saying air gap is very minimal improvement. I mounted my panels against the wall, but they have a few inches gap between the back of the rockwool/fabric and the wall (the frame extends further back than the materials inside the frame). So they have a bit of gap built in. For my ceiling I use the same panels but they simply straddle the exposed ceiling joists in my current studio which was a huge improvement over trying to attach them to a concrete ceiling at the previous place (NYC condo tiny studio).

As for how I put them up, I was going to go with a French cleat but my carpenter simply mounted them on two screws and it's been fantastic. As simple as possible, but not simpler FTW (Einstein).

[selig]

My absorbers are not in the wall, they are floor to ceiling and i have feet under them. So i don't have them in the wall. And the other reflection points, now have a foam product from a Brand called RPS. Not a perfect solution too. But those are the ones i plan to make new broadbands.

For broadbands (the ones with 70 cm to 1 meter high you usually see on studios) they usually are not too far from the wall, they're right on top of it. However, since i believe a gap from the wall is still usefull, if/when i build these, I'm planning to leave a 10 cm gap. To achieve that ill build a 20 cm frame instead of just the size of the rockwool plaque. So if the rockwool plaque is 7 cm high, i'll make a 17 cm frame, if it is 10, ill make a 20 cm frame and so on.

Does that make sense?

Cheers,
MC

I just need good acoustics for professional vocal recording, so I need to have good response down to ~100 Hz. Though I really should do a proper measurement of my own voice.
Maybe I should just build legs for my planned absorbers, too. Then I can move them around, or put in storage. Seems like a flexible solution. Fairly easy to build, even out of wood, and I have plenty wood material for that.

I've recorded and seen vocals recorded in any number of "unprofessional" spaces with great success. The biggest factors are dealing with extraneous noises (from outside, mechanicals, etc). If you can get away from walls and the space is at all OK sounding I've been able to get "professional" results every time. I've done records in living rooms, old churches, basements, etc and no one has complained (yet).

That said, the one place I've never been happy with vocals has been in vocal booths, even high end studios. The space is just too small, the walls are too close. Often you track the record with the vocals in the booth, then move the same exact setup out to the studio floor and suddenly there is "the sound". So the idea you just need a dead closet is relative: it may be better than a flutter-echo filled room but only by a little...

[RobC]

When I said that, I meant to cover the back with wood, and the front with fabric. By now, the absorbers in the room will have a wood frame with rockwool in them, and then covered with linen.

For the "cloud" absorber, I will probably use wall brackets.
But the absorbers that go on the wall, is another question, especially if I want up to 20 cm air gap.
How do you put those up?

What design are you following that has wood on the back, I've never seen that before…

I've been recently reading more folks saying air gap is very minimal improvement. I mounted my panels against the wall, but they have a few inches gap between the back of the rockwool/fabric and the wall (the frame extends further back than the materials inside the frame). So they have a bit of gap built in. For my ceiling I use the same panels but they simply straddle the exposed ceiling joists in my current studio which was a huge improvement over trying to attach them to a concrete ceiling at the previous place (NYC condo tiny studio).

As for how I put them up, I was going to go with a French cleat but my carpenter simply mounted them on two screws and it's been fantastic. As simple as possible, but not simpler FTW (Einstein).

I was simply trying to figure out how to cover the back of a panel, and create sound proofing, cause originally, I wanted to put it in front of the windows.

I saw some videos that actually warned against insulation material. So I might pass on those and go for acoustic foam/sponge - even if I need to wash and sun dry those now and then. Or at least blow it out with a compressor and put it under the sun. Or buy new ones every few years.

Anyways, the videos:

[RobC]

I just need good acoustics for professional vocal recording, so I need to have good response down to ~100 Hz. Though I really should do a proper measurement of my own voice.
Maybe I should just build legs for my planned absorbers, too. Then I can move them around, or put in storage. Seems like a flexible solution. Fairly easy to build, even out of wood, and I have plenty wood material for that.

I've recorded and seen vocals recorded in any number of "unprofessional" spaces with great success. The biggest factors are dealing with extraneous noises (from outside, mechanicals, etc). If you can get away from walls and the space is at all OK sounding I've been able to get "professional" results every time. I've done records in living rooms, old churches, basements, etc and no one has complained (yet).

That said, the one place I've never been happy with vocals has been in vocal booths, even high end studios. The space is just too small, the walls are too close. Often you track the record with the vocals in the booth, then move the same exact setup out to the studio floor and suddenly there is "the sound". So the idea you just need a dead closet is relative: it may be better than a flutter-echo filled room but only by a little...

In this room, the center seems to sound best, but that's a bass-dead zone. Wouldn't that kill the low-end of my voice? The gobo I have may help some further. And some treatment in the windows worked well - yet those were just sponges in the past.
I guess a bit of treatment on the closest walls and ceiling to me can't hurt either.

In theory, this somewhat bigger than 2 meter x 3 meter room should be ideal for vocals. At least a few years ago I read that kind of size recommended by an engineer in the music industry. Or is that vocal booth size?
Btw, when I had those sponges I mentioned, the room sounded pleasant. Not dead-dry, but I hear that's not a good sound anyway.