Slotted CMU - Painting it or not?

[gabrielaudio]

Hi dear community!

I have been here for several years, reading posts and getting useful information from this amazing forum.

But, now it's the first time that I need some help, since I couldn't find this information. I hope that somebody can give me a hand with this

We have a studio that was designed by a well known acoustic engineer and since the budget was low and the idea was to record live music, he decided to build a dead recording room, using
- Walls: SOUNDBLOX (or sonicbloc), that it's basically a CMU with slots that work as a Helmholtz resonator (I attach 2 pdf's).

- Ceiling: it has Celenit (https://www.celenit.com/en-UK/celenit-l ... 2abe25.php) + airgap + PKB2, and it absorbs also low frequencies.
- Floor: wood.

The size of the room is 50m2 approx:
Height: 410 cm
Length: 980 cm
Width: 528 cm

We have 3 problems
- Flutter echo between parallel walls (we will install some diffusers).
- The room is a bit too dead. It's a 50m2 and the RT60 is 200-300ms (except for the very low end). For live recordings is great, but we want to be more flexible and having a room with more "character".
- The CMU blocks are unpainted and uncovered, so the room doesn't look good.

Waterfall

RT60



We would like to have a more "wet" or "live" sounding room, more suited for recording drums and acoustic instruments, so we are thinking about painting it. But I don't know the consequences of that.

I have checked different sources and I don't have a clear idea of it. Some absorption coefficients of CMU show very little difference between painted and unpainted CMU walls, and others such the opposite...

Some say that painting a porous Concrete (like the CMU) would have catastrophic consequences (extremely reflective walls and way less low-mid absorption). I am specially concerned about the low-mid thing, since the reflection in high-mids or high freqs is easy to treat (diffusion, for example).

Check the differences between this one



VS

this one



In this last one, porous concrete has really low low-mid and bass freqs absorption. In the first one, the opposite...

I can understand that this kind of CMU (Slotted) absorbs mainly using a Helmholtz principle (the slots) and that painting its surface won't be so dramatic. Of course we want to have a more live/wet room but without creating more muddiness because of a bad decission...

QUESTION!!

a) Does anyone have experience painting this kind of CMU? Which data should I trust?
b) Is it a good idea to paint these walls (without covering the slots) or the acoustics of the room will change dramatically and we will have serious issues?
c) What would you do to make the room look nicer and more "live/wet"?

Thank you for your time...it's the first time I can't find anything related to this topic of painting CMU (or porous concrete) so any help would be extremely appreciated

Best!

[Soundman2020]

Hi there "gabrielaudio", and Welcome! Or rather: welcome to active participation (since you've been a member for many years! )

That's a nice sized room, by the way. Very good dimensions. It looks pretty good too. However, I'm a little surprised that you are getting decay times as low as 200-300ms. That's way too short for a live room that size. Maybe you could upload your REW files some place that we can access them, to take a look. Also, how did you do those REW tests? Specifically, where did you have the mic and speaker?

OK, on to CMU's. First point: in the second set of data you show, you are looking at the wrong line: you should be looking at "breeze block", not "porous concrete". That's not the same at all. CMU's / breeze block / cinder blocks, Besser brick / is not made from porous concrete: it's a different mix that includes some type of ash or slag or other material, that gives it rather different characteristics than true concrete.

The problem with building the entire room from those blocks is that all of your walls are tuned to the exact same frequencies. The entire wall surface has the exact same acoustic characteristics, all over, everywhere. There's no variation. According to the PDFs, the absorption peak for those blocks is at about 125 Hz, and to be very honest, that isn't usually a highly problematic frequency band. Most rooms need absorption much lower than that, at least an octave lower, maybe as much as two octaves. Your own REW data is showing strong resonance at around 35 Hz and 45 Hz, which is not being treated by the walls. The lowest one is very likely either your 0.1.0 axial mode, predicted to be at 32.6 Hz, or your 2.0.0 axial mode, which is predicted to be at 35.1 Hz- The second one is probably your 0.0.1 axial mode, which is predicted to be at 42.0 Hz. There's also some signs of your 3.0.0 axial mode, at 52.7 Hz. None od those are being damped sufficiently, and from looking at the data, I suspect that you you have little or no treatment on the ceiling. I'd need to see the full MDAT file to draw better conclusions: a couple of low-res graphs doesn't show enough to be useful.

Strangely enough, you seem to have another resonant peak at around 125 Hz, which is surprising if the walls are all tuned to 125 Hz! That could be your 7.0.0 axial at 123 Hz, or your 0.0.3 axial at 126 Hz. The fact that these stand out so clearly indicates that you do not have enough low frequency treatment in the room. The fact that the decay times roll off steeply in the high end, suggest that you have too much absorption in the high end.

My guess would be that the room sounds rather dull, and somewhat "muddy", perhaps even a little "boomy". Perhaps sort of "heavy" or "oppressive". Acoustically "dark". Clearly, you are not happy with the sound at all, as you have added polys, absorbers, and curtains to try to help fix the issues. My guess is, that's not helping a lot either!

Now, on to your question. Will painting the walls change the acoustics? Yes! Definitely. It will brighten things up quite a bit, and it will not affect the absorption in the low end. However, it still wont not give you what you are looking for, because the lack of highs is only part of the problem. It's going to take more than just a coat of paint to fix your room. I would suggest doing a more complete analysis of the issues, with a series of carefully targeted REW tests at specific locations, to get a better picture of how the room is really behaving, then design specific treatment devices for specific locations, to produce the result you are looking for.

One more thing:

Flutter echo between parallel walls (we will install some diffusers).

I wouldn't do that. Diffusers in a live room can be used for good artistic effects, yes, but they can also cause more problems than they solve. Especially numeric-sequence diffusers. Rather, I would suggest the approach above: carefully analyze the room with REW, using targeted positioning, then design specific devices for specific problems at specific locations, tuned and located carefully. Good rooms don't just happen from randomly chosen and placed treatment. Good rooms only happen by design.

- Stuart -

[gabrielaudio]

Hi Stuart!

Wow first, thank you so much for such a great message . Your advice is really helpful! Since I discovered this community I never stopped learning, just navigating through posts is GOLD

That's a nice sized room, by the way. Very good dimensions. It looks pretty good too. However, I'm a little surprised that you are getting decay times as low as 200-300ms. That's way too short for a live room that size. Maybe you could upload your REW files some place that we can access them, to take a look. Also, how did you do those REW tests? Specifically, where did you have the mic and speaker?

Yeah, it is too short and that's one of the reasons we are not happy with the sound of it. 2 days ago I did new measurements with REW and I attached them here. The previous ones were done in the same way but I wanted to repeat the process just changing corners.

Speaker in the floor in one corner, measurement microphone in the opposite one (diagonal) at 3 meters high approx. Apogee Duet calibrated with REW too. In addition, I did extra measurements: speaker where we usually record drums and the microphone in 3 different positions (where we place different kinds of room microphones). Two of them opened and closer to the corners, one of them more or less in the middle of the room (X axis) but closer to the Left wall (Y axis).

These new measurements were done without Acoustic Panels, without people in the room and with the curtain folded. And there's already a little bit of improvement

The problem with building the entire room from those blocks is that all of your walls are tuned to the exact same frequencies. The entire wall surface has the exact same acoustic characteristics, all over, everywhere. There's no variation.

That was the design of the acoustic engineer who did it. Who knows...I was not here back then so I don't know. And my friend, the studio owner, didn't know anything about acoustics.

According to the PDFs, the absorption peak for those blocks is at about 125 Hz, and to be very honest, that isn't usually a highly problematic frequency band.

Strangely enough, you seem to have another resonant peak at around 125 Hz, which is surprising if the walls are all tuned to 125 Hz! That could be your 7.0.0 axial at 123 Hz, or your 0.0.3 axial at 126 Hz.

The previous CMU reference was wrong. I just attached now a PDF of the most probable one that they used in the design. Also because it fits with what I see in the new REW measurements.

Your own REW data is showing strong resonance at around 35 Hz and 45 Hz, which is not being treated by the walls. The lowest one is very likely either your 0.1.0 axial mode, predicted to be at 32.6 Hz, or your 2.0.0 axial mode, which is predicted to be at 35.1 Hz- The second one is probably your 0.0.1 axial mode, which is predicted to be at 42.0 Hz. There's also some signs of your 3.0.0 axial mode, at 52.7 Hz. None od those are being damped sufficiently, and from looking at the data, I suspect that you you have little or no treatment on the ceiling. I'd need to see the full MDAT file to draw better conclusions: a couple of low-res graphs doesn't show enough to be useful.

You are completely right. The ceiling I don't know exactly how it works. I'm asking for photos now. What I know it has Celenit + 30 - 40 cm air gap + Mass Loaded Vinyl (or similar) glued to the ceiling. It is made following this:

M. Newell retained the original suspended plasterboard ceiling and replaced the original acoustic treatment with :
a 60 mm layer of 80kg/m3 open cell polyurethane foam called Arkobel glued to the walls and ceiling,
a 35 mm layer of lightly compressed wood shavings mixed with cement called Celenit glued to the Arkobel.
According to Newell the Celenit glued to the foam acts as a highly damped panel absorber that deals well with the mid-bass frequencies and users were very happy with the results.

Flutter echo between parallel walls (we will install some diffusers).

I wouldn't do that. Diffusers in a live room can be used for good artistic effects, yes, but they can also cause more problems than they solve. Especially numeric-sequence diffusers. Rather, I would suggest the approach above: carefully analyze the room with REW, using targeted positioning, then design specific devices for specific problems at specific locations, tuned and located carefully. Good rooms don't just happen from randomly chosen and placed treatment. Good rooms only happen by design.

And you are completely right again

[DanDan]

That first set of absorption figures says 0.44 at 250Hz for unpainted concrete, and similar in other octave bands.
This is not credible to me.
Painting bricks will of course increase HF reflection, probably sonically quite a bit.
As flutter echo is predominantly HF, this would become much much worse.

I see some curved ply, are they Polys? Good. Large areas of angled wood, curved or straight will kill flutter echo and can also add useful LF absorption.
Your room is vast, you lucky duck!
Also I suspect it sounds very good. Your ambience may be short but I'll bet it has no very early reflections when you move away from the walls. Awesome.
Suggested treatment solution.
Install very large strips of wood or plasterboard. For now let's imagine 4 or 8 feet wide, floor to ceiling, or full width of wall. Back to that in a mo-town. Angle them say at least 15 degrees.
They angles can be 'sawtooth' or V shaped like a lot of John's work here. Or curved. Vertical or Horizontal.
Directly opposite to any of these you can simply paint those bricks.

Here's a pic of Hitsville, home of MoTown. Alternately angled strips of ply and ceiling tile. The idea was for all the musicians to be able to hear each other while avoiding too much mic spill.
I can't quite follow how that might work as ears and microphones are often the same height or close, but certainly no flutter and probably still quite lively. Let's not forget four feet of treatment hidden behind those strips though.

the-recording-studio.jpg

DD

[gabrielaudio]

Hi DanDan,

Thank you for your message!

Yeah, I like that approach. Just need to know how to build it properly, but for sure doable. But anyway as Stuart said, we have issues in the LF area so we need to look into a solution that tries to solve each of the acoustic issues we are experiencing...probably we would just need to ask and pay for a specific design, who knows.

That first set of absorption figures says 0.44 at 250Hz for unpainted concrete, and similar in other octave bands.
This is not credible to me.

Yeah right?

Your room is vast, you lucky duck!
Also I suspect it sounds very good. Your ambience may be short but I'll bet it has no very early reflections when you move away from the walls. Awesome.
Suggested treatment solution.

Thanks! The room is great in size, that's true. Of course it sounds better than my previous room (20 sqm) but it doesn't sound as it should in a room like this. Too much comb filtering due to the flutter echo and too much dullness due to amount of HF treatment (ceiling, which has celenit...which is really absorptive at HF) and the lack of LW treatment. The room is not in balance and it sounds dull. So, in conclusion, to my ears it doesn't sound good and that's why I want to improve it.

spectogram_cornertocorner.jpg

See that drop in 250 Hz? This is the Slotted CMU effect...I think


By the way, this post is turning into a "Design" thing. Should we move it to Studio Design maybe?

[Soundman2020]

I checked your new data, and the decay times are actually longer than you thought:

Gabriel--REW--RT--actual-times-01.jpg

More like 500 - 600 ms, so not as bad as you thought. As I mentioned yesterday, it would be surprising if that room had decay times of around 200 ms. Fortunately, that't not the case. Of course, it will be different for every location of speaker and mic, but since that graph is from a typical setup that you use, it's useful.

However, even though the times are longer than you feared, they are still rather uneven, and rather unpleasant I would guess.

The previous CMU reference was wrong. I just attached now a PDF of the most probable one that they used in the design. Also because it fits with what I see in the new REW measurements.

So peak absorption at around 250 Hz? Yup, that makes sense, and is a better match for the REW data: Here's the decay curves from all three of your tests, overlaid on each other:

Gabriel--REW--RT-all-three.png

You can see the large dip at around 250 Hz. In fact, that's the shortest decay time in the entire spectrum, at around 230 ms. I'm not surprised it sounds "off" to you. That's often about where the snare's fundamentals sit.... How do your snares sound in that room? Good "snap" but a little dull on the low end "thump"? On the other hand, all three of those curves show much longer times around 80 Hz and lower, so the boom of the kick should be well present... maybe TOO present?

There's also the overall rise in decay times around 700 Hz, everywhere.


Here's all three frequency response curves, overlaid:

Gabriel--REW--FR-all-three--20-300.png

There's lots of variation, of course, since you had your mic and speakers in very different locations, but there's still a clear underlying trend: Peak energy around 80 Hz everywhere, for example, along with the subdued 250 Hz region, and a general rise below 100 Hz.

Too much comb filtering due to the flutter echo and too much dullness due to amount of HF treatment (ceiling, which has celenit...which is really absorptive at HF) and the lack of LW treatment. The room is not in balance and it sounds dull. So, in conclusion, to my ears it doesn't sound good and that's why I want to improve it.

Yup. That's what I'm seeing in the REW data too. And if YOU are not happy with it, then it needs fixing! It's that simple... No matter who designed the room, or who says that it is actually fantastic... the real issue is that it's YOUR room, so it has to sound the way YOU want it to sound. Not the way other people want it to sound.

You are completely right. The ceiling I don't know exactly how it works. I'm asking for photos now. What I know it has Celenit + 30 - 40 cm air gap + Mass Loaded Vinyl (or similar) glued to the ceiling. It is made following this:

So the ceiling is basically dead? Just absorption up there? That's not the way I treat tracking rooms or performance spaces. It's important to have some life coming back from above... as long as its not overdone. So, you might want to liven up that ceiling some, with reflective panels hung at fairly steep angles. Curved panels would be preferable to flat ones, but a mix of both would be even better.

See that drop in 250 Hz? This is the Slotted CMU effect...

Oh yes, very much! You could reduce that by plugging the slots on many of the blocks. That would return a lot of the low-mid energy to the room. There's several ways you could plug them, but a simple one would be to just cut some wood strips to the right size, and press-fit them into place. There's several strategies you could follow when doing that as well: for example, just plug up 20% of the slots, evenly spread out across the wall.... or plug up all of them on one half of the wall, none on the other half, to get very distinctive "ends" to your room, one end being warmer, the other boomier. Or maybe do a variation on that, sort of "blending" that along the length of the wall, with almost all the holes plugged at one end in the first 20cm of the wall, then slight fewer in the next 20cm, fewer still in the following 20cm, etc, until there's practically no plugs in the final 20cm. Or maybe split it vertically, not horizontally... Many options open to you there. You could even have a box of plugs in the corner, then add/remove plugs as needed to "tune" that range...

That first set of absorption figures says 0.44 at 250Hz for unpainted concrete, and similar in other octave bands.
This is not credible to me.

It's for porous concrete BLOCK (ie, cinder block), not porous concrete. Different animals. Other sources agree with that, including the second chart. Also these:
http://www.acoustic.ua/st/web_absorption_data_eng.pdf
https://www.engineeringtoolbox.com/acco ... -d_68.html
http://www.sengpielaudio.com/calculator-RT60Coeff.htm

... and many others. It's not uncommon for such materials to have fairly good absorption. But that's not the same as ordinary porous concrete, which is pretty darn lousy at absorbing!

Too much comb filtering due to the flutter echo

Yup I see it. Very "zingy", especially from about 3 kHz upwards, all the wya to about 10 kHz. Not nice at all! Pays havoc with your cymbals, I would expect. It's very evident in the "front of drums" test, but also visible in the others. It's associated with your room width, as far as I can tell. You could deal with that by putting absorbers on the side walls (tall, not too wide, spaced randomly, and "checker-boarded" across the room), but the room is already on the dull side and that would make them even more dull. Personally, if that were my room, I'd go with several John Sayers style tuned slotted wedges: tuned low, and also maybe a little around 600 Hz, but built wide and tall enough to help recover some of your missing 250 Hz, as well as your high end. That would be my plan for the side walls. Combine that with the tilted/curved panels hung from the ceiling, and maybe plugging some slots, then see how it goes. But first, do the targeted tests I mentioned before. And also decide if you want the room to sound the same all over, or to be "zoned", so there are different areas with slightly different sounds to them, which you can use creatively for different instruments...



- Stuart -

[gabrielaudio]

Hi Stuart!

Thanks again for your reply, very useful! Thanks for your good tips and good analysis of the situation. If you ever come here you will enjoy a good "pulpo a la gallega" and zamburiñas

More like 500 - 600 ms, so not as bad as you thought. As I mentioned yesterday, it would be surprising if that room had decay times of around 200 ms. Fortunately, that't not the case. Of course, it will be different for every location of speaker and mic, but since that graph is from a typical setup that you use, it's useful.

Yeah, after removing the curved panels and the GOBOs it improved, for sure! But even though...too dead for us.

You can see the large dip at around 250 Hz. In fact, that's the shortest decay time in the entire spectrum, at around 230 ms. I'm not surprised it sounds "off" to you. That's often about where the snare's fundamentals sit.... How do your snares sound in that room? Good "snap" but a little dull on the low end "thump"? On the other hand, all three of those curves show much longer times around 80 Hz and lower, so the boom of the kick should be well present... maybe TOO present?

When we record snares we have snap but no "density", and of course "dull" as you said.
In the room microphones the kick is TOO present for sure.

We want to have a live room where the drum sound is balanced, representing the drum kit correctly and with enough "room sound" to create more depth and character in our mixes (avoiding room reverb plugins). I think our room has good dimensions for it, but we'll need to treat it carefully. We are also thinking on creating a chamber room since we have an area in the warehouse with a long reverb (but this would be just an experiment).

So the ceiling is basically dead? Just absorption up there? That's not the way I treat tracking rooms or performance spaces. It's important to have some life coming back from above... as long as its not overdone. So, you might want to liven up that ceiling some, with reflective panels hung at fairly steep angles. Curved panels would be preferable to flat ones, but a mix of both would be even better.

Here there are some photos of the ceiling acoustic treatment:

ceiling with insulation, airgap and celenit.jpg

ceiling insulation 2.png

ceiling insulation.png

ceiling.jpg

So, the ceiling acoustic treatment has Celenit + airgap + insulation (acustisol or pkb2)...and then 1 layer of drywall + insulation (acustisol or pkb2) + wood panels.
The idea of the acoustic engineer was to let the bass freqs leave the room through the ceiling, and that's why the ceiling is so weak on soundproofing compared to the concrete walls.

What I also know is that the Celenit is highly HF absorptive, and that's not making us a favour. Glad to see that you don't treat tracking rooms like this because it doesn't work at all

So yeah, I think we will try your idea of reflective panels just hanging beneath the Celenit. Good tip! I guess just we'll need to try and test which angles work best for a specific recording area (REW...our dear friend).

Oh yes, very much! You could reduce that by plugging the slots on many of the blocks. That would return a lot of the low-mid energy to the room. There's several ways you could plug them, but a simple one would be to just cut some wood strips to the right size, and press-fit them into place. There's several strategies you could follow when doing that as well: for example, just plug up 20% of the slots, evenly spread out across the wall.... or plug up all of them on one half of the wall, none on the other half, to get very distinctive "ends" to your room, one end being warmer, the other boomier. Or maybe do a variation on that, sort of "blending" that along the length of the wall, with almost all the holes plugged at one end in the first 20cm of the wall, then slight fewer in the next 20cm, fewer still in the following 20cm, etc, until there's practically no plugs in the final 20cm. Or maybe split it vertically, not horizontally... Many options open to you there. You could even have a box of plugs in the corner, then add/remove plugs as needed to "tune" that range...

That's a great idea! Never thought about it

The good thing is we can do infinite amount of measurements and just trying and checking what works best. So definitely we will cover some of the slots as you suggested.

Yup I see it. Very "zingy", especially from about 3 kHz upwards, all the wya to about 10 kHz. Not nice at all! Pays havoc with your cymbals, I would expect. It's very evident in the "front of drums" test, but also visible in the others. It's associated with your room width, as far as I can tell. You could deal with that by putting absorbers on the side walls (tall, not too wide, spaced randomly, and "checker-boarded" across the room), but the room is already on the dull side and that would make them even more dull. Personally, if that were my room, I'd go with several John Sayers style tuned slotted wedges: tuned low, and also maybe a little around 600 Hz, but built wide and tall enough to help recover some of your missing 250 Hz, as well as your high end. That would be my plan for the side walls. Combine that with the tilted/curved panels hung from the ceiling, and maybe plugging some slots, then see how it goes. But first, do the targeted tests I mentioned before. And also decide if you want the room to sound the same all over, or to be "zoned", so there are different areas with slightly different sounds to them, which you can use creatively for different instruments...

Yes...not nice at all We need to solve that flutter echo urgently without making the room more dull. I like your idea of the slotted wedges. I know those but I can't find any info about how to calculate the slots, size, etc, to tune it to the right freqs.

You mean this right?

slotted wedge.jpg

It looks good but I searched on the forum and I couldn't find anything. No clue about how to design it and build it for now. Is there any public and published information about these slotted wedges from Sayers?

[Soundman2020]

Thanks for those photos! It's a lot more clear now, why your room sounds so "off". A rather strange way of designing and building a room, for sure...

the ceiling acoustic treatment has Celenit + airgap + insulation (acustisol or pkb2)...and then 1 layer of drywall + insulation (acustisol or pkb2) + wood panels.

I'm not at all surprised that your ceiling isolation is poor, when it could be good, and that it sounds lousy, when it could sound great. In fact, I suspect that some of your resonant issues might be coming from your ceiling.

The idea of the acoustic engineer was to let the bass freqs leave the room through the ceiling, and that's why the ceiling is so weak on soundproofing compared to the concrete walls.

Indeed! ... I hate to say this, but it looks like that plan wasn't too successful...

What I also know is that the Celenit is highly HF absorptive, and that's not making us a favour.

VERY true!

Fortunately, your room is fixable. I guess the real question here is: How far are you prepared to go to fix ALL of it? Do you just want to do the minimal to get it usable, or do you really want to re-work the whole room to get it great? There's many things you can do for the first option, to get it usable, but most of them are just to fight the problems create by the room itself. If you were willing to invest a lot more time (and money), then you could fix the underlying problems too (so you don't have to fight them), and have a better room. That's your call, of course: If you need to make money with the room soon, and can't spare the down-time or budget to do major surgery, then it's understandable that you'd just want to take the firsts option.

So yeah, I think we will try your idea of reflective panels just hanging beneath the Celenit. Good tip! I guess just we'll need to try and test which angles work best

There's a basic layout and overall design that I use for that with my clients. It can be refined for individual cases, as needed, but the basis works for most rooms.

That's a great idea! Never thought about it ... The good thing is we can do infinite amount of measurements and just trying and checking what works best. So definitely we will cover some of the slots as you suggested.

Right, but you should do that as a balanced approach: fix the walls as part of the overall design for fixing the entire room. It would be good to come up with a strategy: an overall plan for how you want the room to sound when it is done. Then design the treatment for each part of the room that would make it perform that way, as a whole. It's usually not a good idea to "patch" bits and pieces of the room individually, but rather to design it to be balanced. You are already fighting the room itself: don't end up fighting yourself too!

We need to solve that flutter echo urgently without making the room more dull. I like your idea of the slotted wedges. I know those but I can't find any info about how to calculate the slots, size, etc, to tune it to the right freqs. It looks good but I searched on the forum and I couldn't find anything. No clue about how to design it and build it for now. Is there any public and published information about these slotted wedges from Sayers?

Ahh, well, yes... Hmmm.... Those wedges are an original John Sayers design concept, and I'm pretty sure he doesn't share the design secrets in public, so you probably won't find much published about that!

However, I did figure out a few things about them myself a few years ago, and I have used the same concept in several rooms that I have treated (always giving the credit to John, of course, since it was his idea originally!). But out of respect for John, I don't publish anything about mine either! I just design them for my clients, and they build them, and they work.

That said, it's certainly possible to figure out the basic principles and design your own, by yourself, if you have a good understanding of acoustics. There are several principles involved at ones in those things, which is why they are so great. You would need to do some extensive "trial and error" testing, making several of them with slightly different designs, test them, take them apart, re-build a bit different, re-test, etc. You would eventually get a good design like that. It might take some time, though, but it is possible.

You mean this right?

Exactly! That's the general concept, but the practical implementation is different for each room.

Here's one I did for one of my clients, where I adapted it into a "variable acoustic" device for a small isolation room / vocal room:

Variable-acoustic-01--panels--construction--half-open-SML.jpg

Variable-acoustic-02--panels--construction--fully-open--SML-ENH.JPG

Variable-acoustic-03--partly-completed--SML-ENH.jpg

Variable-acoustic-04--room--completed--SML-ENH.jpg

You can see the central wedge in there, and there are two "wing" modules that swing over that. They modify the response of the wedge as they close over it, while also uncovering two additional panels behind where they were "parked". This has a noticeable effect on the overall decay times in the room, changing different parts of the spectrum differently. Here's the actual results from that device, with the wings open to various angles:

variable-acoustic-05--acoustic-rt60-plots-all-positions-t20.jpg

As you can see, as the panels are moved the decay times increase in high-mids, but decrease in the low end: with the panels full open, the decay is about 180 ms at 120 Hz., but that increases to nearly 350ms with the panels closed. And at the same time, at 2 kHz, the decay is about 380 ms with the panels closed, but drops down to around 280 with them open. In other words, you can make the room dry and boomy at one extreme, or bright and warm at the other.... or you can get a more neutral sound by opening them part way.

It might be an idea to do something similar for your room: have variable panels that you can open/close/flip/rotate/ etc, in some way or other, to modify the sound of the room, as needed for different situations. Tracking drums is rather different tan tracking vocals, for example! And tracking a rock band is very much different from tracking a string quartet. If you want to make your place flexible, so you can offer services to a broader range of musicians, producers and engineers (and also charge more... ), then it might be worthwhile doing a bit extra, to make your room variable. I've done that in a few rooms, and the clients seem to really like the results. It gives them far more creative options, for tracking.

Thanks again for your reply, very useful! Thanks for your good tips and good analysis of the situation. If you ever come here you will enjoy a good "pulpo a la gallega" and zamburiñas

Sounds fascinating! I guess that the "pulpo a la gallega" is some type of pork dish? Yummy! Or is it the other type of pulpo, from the ocean, with 8 legs? Either way, sounds great! I have no idea what the zamburiñas are, but I'd love to try them anyway! If I'm ever in your part of the world, I'll be sure to drop by and take you up on your offer! I'll bring a bottle of Pisco Sour, and a good Chilean Cabernet Sauvignon, to accompany the meal...


- Stuart -

[gabrielaudio]

Thanks for those photos! It's a lot more clear now, why your room sounds so "off". A rather strange way of designing and building a room, for sure...

My friend, who payed for the design and materials, is not happy at all, even more now after reading your messages and seeing the measuring tests...Whatever...

I'm not at all surprised that your ceiling isolation is poor, when it could be good, and that it sounds lousy, when it could sound great. In fact, I suspect that some of your resonant issues might be coming from your ceiling.

I did some tests and it seems that the ceiling could have a peak absorption rate at...around 250 Hz! And then it would decrease around 600-800 Hz (remember that 700 Hz issue you saw in the REW data?). Besides that, the acustidan + celenit would be 100% absorptive at high freqs so it's just making the room extremelly dead without treating any bass freqs.

Indeed! ... I hate to say this, but it looks like that plan wasn't too successful...

Yeah, I know! Thanks for saying the hard truth . And you didn't see the Control Room yet...it is another kind of nightmare...it has celenit...EVERYWHERE

Fortunately, your room is fixable. I guess the real question here is: How far are you prepared to go to fix ALL of it? Do you just want to do the minimal to get it usable, or do you really want to re-work the whole room to get it great? There's many things you can do for the first option, to get it usable, but most of them are just to fight the problems create by the room itself. If you were willing to invest a lot more time (and money), then you could fix the underlying problems too (so you don't have to fight them), and have a better room. That's your call, of course: If you need to make money with the room soon, and can't spare the down-time or budget to do major surgery, then it's understandable that you'd just want to take the firsts option.

Well, we have max 2 months to fix all the issues, so it's not a lot, since we want to relaunch the studio with better acoustics, better equipment, etc. I don't think we would have time to do major surgery, but at least to make the room "good enough", usable, to work with it, because right now it's just a detrimental tool (taking into account our expectations for a room of this size). Also, as always, budget is limited. We want to have the perfect room but it won't happen now since it would mean investing several thousands of €. So we need to invest step by step: first, solving the most problematic issues, making the room useable, working again...saving money and investing step by step on improving it more and more. So, the perfect solution for us would be just having a Design that we can implement in 2-4 stages.

It might be an idea to do something similar for your room: have variable panels that you can open/close/flip/rotate/ etc, in some way or other, to modify the sound of the room, as needed for different situations. Tracking drums is rather different tan tracking vocals, for example! And tracking a rock band is very much different from tracking a string quartet. If you want to make your place flexible, so you can offer services to a broader range of musicians, producers and engineers (and also charge more... ), then it might be worthwhile doing a bit extra, to make your room variable. I've done that in a few rooms, and the clients seem to really like the results. It gives them far more creative options, for tracking.

It looks really good and I agree with you that having a variable acoustic solution is great! Maybe I will send you a PM to see if we can work together.

What do you think about a zigzag slotted resonator?


These ones are easier to calculate and design, I could even do it myself. PLUS some bass traps in the corners with slotted panel. PLUS some reflective cloud panels as you suggested before. Ideally, creating an area in the room where most of the first reflections are being "reflected" to the furthest walls, so we reduce the amount of early reflections and we increase the late ones, increasing the sense of space and distance between the sounce source and the first and stronger reflections. It wouldn't be easy because the angle of each panel should be perfectly calculated I can imagine.

calcul.png

Does it makes sense to you?

Sounds fascinating! I guess that the "pulpo a la gallega" is some type of pork dish? Yummy! Or is it the other type of pulpo, from the ocean, with 8 legs? Either way, sounds great! I have no idea what the zamburiñas are, but I'd love to try them anyway! If I'm ever in your part of the world, I'll be sure to drop by and take you up on your offer! I'll bring a bottle of Pisco Sour, and a good Chilean Cabernet Sauvignon, to accompany the meal...

Pulpo á feira is called actually:


And Zamburiñas...some of the best seafood here

[Soundman2020]

Hi again! Its been nearly 2 months since this first discussion, and you said you only had 2 months to fix this, so I'm wondering how it is going? Any updates, news on what you did, how it is improving the acoustic response? More tips on seafood cuisine!

I'm intrigued about how this room turned out in the end... if you managed to fix it...


- Stuart -