windows in pre-build stage

Hi all and thanks for a good resource. I am looking at building a new house with a detached garage with a studio in the garage. Location looks like it will be southern Spain at the moment if that means anything. The dimensions I am working on looks like 5500mm x 3500mm for the production and a sound booth that is 3750x3500 (not the best I know but I want to cram in a metal drumset in there). The height is 2880mm (I will expand on this later). Now I got two main questions, the main issue is the window issue. I have read plenty of do:s and don't:s when it comes to studio design, but I have not really gotten a good answer about windows. My first plan was to skip all windows on the building in question because of simplicity and accoustics, but when I thought about staying for hours and hours inside a building with no windows it sort of got to me. So, I am now looking at putting two 900x900mm windows on either the far side (opposite to the monitors), or on the far end but on the right side of the building, giving an assymetrical aspect of the room. Question here is: is it worth it? Should I put smaller windows in or will it be bad no matter how I do it? Is it better to have the windows in the direction of the sound or assymetrical (is it like plauge or cholera?). Second question: how important is the symmetry of the ceiling? The roof will probably be a hip roof with a ceiling height of 2880mm on the right side of the monitors, but on the other side of the room with no inner ceiling the height would be 3944mm. Now I COULD put in a flat inner ceiling in that room to make it more symmetrical, but the advantage of not having that would be more space in the room (given this is southern Spain and can get pretty hot). I would rather have an inner roof that follows the curvature of the roof allowing more air circulation. Any comments or suggestions are highly appreciated.

I have made some changes in the dimensions but the main idea remains the same. I have decided to solve the asymmetry of the roof with a floating inner ceiling, so that should not be an issue. The question remains about the windows, I have added both eastern and southern windows in this design. Question is, which ones are the worst? The eastern ones or the southern ones?

Jon, Welcome! What is your concern with the windows specifically? Is there an issue with outside noise coming in or inside noise going out? Or are you worried mostly about acoustics? For me personally, I can't recall a studio I have worked in that DID have windows! So maybe I am used to it but it never really bothers me. That being said, If i had the option I probably would enjoy it! On another note, if you are building new construction why not toy with the idea of non-rectangular rooms? From what I know (which isn't a lot) you can achieve some really great sounding rooms with a non-traditional design. Cheers Ralph

Hi Jon, and welcome to the forum! :)

Question here is: is it worth it? Should I put smaller windows in or will it be bad no matter how I do it? Is it better to have the windows in the direction of the sound or assymetrical

Windows on the side walls would not be a problem, provided they are not at your first reflection points, but windows on the back wall are out, unfortunately. You need that entire back wall for acoustic treatment: superchunk style bass traps in the corners, and thick absorption over the rest of the all is the normal way of doing it. So as long as you can find positions on the side walls that are not first reflection points, you could certainly put windows there. It could be one big window, or several smaller windows, as you prefer. But when deciding on the size of the windows, do make sure that you leave enough blank wall area left over to be able to provide the right amount of acoustic treatment later.

Second question: how important is the symmetry of the ceiling?

Side-to-side symmetry is critical. The front of the room needs to be perfectly symmetrical: If you cut the room down the middle, the left half should be a mirror image of the right half, and that applies to the floor, walls, and ceiling, as well as the desk and anything else in the front of the room. Behind the mix position it is not so critical, but still a good idea if you can.

I would rather have an inner roof that follows the curvature of the roof allowing more air circulation.

Air circulation is a different issue: That's what your HVAC system is for. HVAC is usually the part of the room that first-time studio builders forget about at the beginning, but having a good HVAC system is every bit as important as having good speakers. More important, in fact: Having no speakers in the room won't kill, but having no HVAC actually could kill you, very literally: Dead, as in not alive. No life. Not breathing. Building a well isolated studio means that you are sealing yourself in a totally air-tight box, with double hermetic seals all around: No way at all for air to get in or out. You can't stay alive for very long if you don't have air... So HVAC is not a luxury for a studio: it is an absolute necessity. You MUST have a system that brings in fresh air from the outside world, and exhausts stale air to the outside world (that's the "V" part of HVAC), and you must also have a system that can heat, cool, and dehumidify the air inside the room, as needed (That's the "H" and "AC" parts). And you have to do all that using correctly calculated, dimensioned, and positioned ducts, fans, registers and silencer boxes, so that air is moved through the room correctly. That's how you get your air circulation right, not just by angling the ceiling.

I have decided to solve the asymmetry of the roof with a floating inner ceiling, so that should not be an issue.

Yes it will be an issue! Adding another ceiling (in addition to your outer-leaf and inner-leaf) will mean that you have a 3-leaf ceiling, which will have worse isolation at low frequencies than the equivalent two-leaf ceiling. The best plan is to make your inner-leaf ceiling flat, then hang a hard-backed cloud below that help with first reflections, flutter echo, and even modal resonance, to a certain extent. A couple of extra comments: As Ralph said, angling your inner-leaf walls and ceiling can give you excellent acoustic (and aesthetic) advantages over a plain rectangular room. There's a studio design concept called "RFZ" (for "Reflection Free Zone") where you use the wall and ceiling angles to force all of the first reflections away from the mix position, sending them to the rear wall where they get absorbed and/or diffused by suitable acoustic treatment. If you follow that concept, you can have the very best sounding room possible. It makes construction a bit harder (to build the angled parts) but the result is well worth it. Also, I'd REALLY suggest that you start using SketchUp for your studio design: It's a full 3D modelling package with some non-conventional methods for modeling that make it a breeze to do complex things. Much easier that AutoCad in many senses, after you get the hang of it. The best part of the deal, is that the basic version is free! - Stuart -

Thanks for the input, I appriciate it greatly.

Side-to-side symmetry is critical. The front of the room needs to be perfectly symmetrical: If you cut the room down the middle, the left half should be a mirror image of the right half, and that applies to the floor, walls, and ceiling, as well as the desk and anything else in the front of the room. Behind the mix position it is not so critical, but still a good idea if you can.

Myeah, but this can be done somewhat by adding symmetry with plates and foam, right?

Air circulation is a different issue: That's what your HVAC system is for. HVAC is usually the part of the room that first-time studio builders forget about at the beginning, but having a good HVAC system is every bit as important as having good speakers. More important, in fact: Having no speakers in the room won't kill, but having no HVAC actually could kill you, very literally: Dead, as in not alive. No life. Not breathing. Building a well isolated studio means that you are sealing yourself in a totally air-tight box, with double hermetic seals all around: No way at all for air to get in or out. You can't stay alive for very long if you don't have air... So HVAC is not a luxury for a studio: it is an absolute necessity. You MUST have a system that brings in fresh air from the outside world, and exhausts stale air to the outside world (that's the "V" part of HVAC), and you must also have a system that can heat, cool, and dehumidify the air inside the room, as needed (That's the "H" and "AC" parts).

I understand that, but I come from a place (scandinavia) where AC is considered unnatural and somewhat unhealthy even, and after having lived in places like Florida I have a strong distaste of the reliance on it except for taking out the edge of the heat. I cannot stand living in the airflow of a strong AC unit, I need passive circulation that comes from having plenty of airspace (i.e. I do not want to breath the air straight out of the unit which often is the case in places like the US). In addition to the energy cost from running it it also adds sound which I am not certain how to solve. I know there are ductless systems but I do not know how effective they are and how quiet they are when they run at full power (unless of course you trust the manufacturer). The main house building I am constructing has plenty of passive cooling and heating systems installed so it sort of breaks the purpose if I do not use it in this building too.

And you have to do all that using correctly calculated, dimensioned, and positioned ducts, fans, registers and silencer boxes, so that air is moved through the room correctly. That's how you get your air circulation right, not just by angling the ceiling.

If I would use ducts, what material should I use in the ducts? My father uses plastic on his boat which I imagine resonates less than metal.

Yes it will be an issue! Adding another ceiling (in addition to your outer-leaf and inner-leaf) will mean that you have a 3-leaf ceiling, which will have worse isolation at low frequencies than the equivalent two-leaf ceiling. The best plan is to make your inner-leaf ceiling flat, then hang a hard-backed cloud below that help with first reflections, flutter echo, and even modal resonance, to a certain extent.

That was sort of the plan but I am not following the logic here, what would be the difference between a floating ceiling with a catcher behind it and a solid ceiling with a catcher behind? It seems like most people build catch screens with a loose fabric at the end in order for the sound to continue before it bounces back rather than having the foam on a solid plate?

As Ralph said, angling your inner-leaf walls and ceiling can give you excellent acoustic (and aesthetic) advantages over a plain rectangular room.

It is space concerns and monetary costs. I do not need state of the art accoustics and I will have to get a loan approved to build the house. A non-rectangular room seems to need at least twice as much space in that particular area (I need the two car garage to remain intact as I expect to have more than two cars and the southern sun to waste everything not under the carport roof) so it seems like a waste of money if I can solve the angles with screens and foam.

Also, I'd REALLY suggest that you start using SketchUp for your studio design: It's a full 3D modelling package with some non-conventional methods for modeling that make it a breeze to do complex things. Much easier that AutoCad in many senses, after you get the hang of it. The best part of the deal, is that the basic version is free!

I have tried it but I am fluent in Autocad and I have all my macros set up in it. What makes it better is that I can use it for civil engineering stuff too quite easily, like TIN rectangulation for ground straight from the building site. If I have to use Civil 3D for the site I might aswell use it for the architecture. Maybe they have added that stuff to Sketchup too but after I have learned Autocad I do not see the point.

Myeah, but this can be done somewhat by adding symmetry with plates and foam, right?

Not really, no. The actual shape of the inner leaf itself must be symmetrical, since that is what sound waves "see". The hard, solid, massive, boundary surfaces of the room are what matter for things like modal response, critical frequency, ratios, and things like that. Yes, you can reflect higher frequencies with panels, but not low frequencies. Any wave whose wavelength is larger than the panel will simply not be affected by it. Sound waves only react to objects that are substantially larger than they are, so you'd need panels 17m high and 17m wide to be able to affect the full audio spectrum...

I understand that, but ...

I see a lot of arguments there why you don't want to install an HVAC system, but you seem to have missed the most important part of why you need one: "Having no speakers in the room won't kill, but having no HVAC actually could kill you, very literally: Dead, as in not alive. No life. Not breathing."I'm not sure how well you would be able to make music in your room, if you are dead from asphyxiation! :) Besides, you are talking about "air conditioning" but I am talking about "HVAC", which is another thing entirely.

I cannot stand living in the airflow of a strong AC unit,

Can you stand being dead? :) Besides, nobody said anything about any airflow that you can feel from a strong AC unit. In a studio, if you can feel the air flow so much that it bothers you, then there is something badly wrong with the way the system was designed and built! What I said was that you need enough air to keep you alive. The volume of airflow is carefully calculated according to international standards, and the speed at which it flows (which is very different from the volume of airflow...) is carefully set by the normal parameters used for studios: Very, very slow airflow, in order to not make any noise. No faster than 300 fpm, maximum, and preferably no faster than 100 fpm. It seems to me that you are raising arguments why you don't want it, before even finding out if your arguments are valid or not!

I need passive circulation that comes from having plenty of airspace

Then you are going to need a room that is about 10 to 15 times as big as what you are planning, so it can hold enough oxygen and moisture during a normal day's work. There won't be much passive circulation at all in a room as small as yours. There will be some convection going on, yes, but there will be zero cooling, and zero dehumidifying, and zero oxygen added, and er CO2 removed, all of which are critical. There will not be any passive cooling at all, since the room has to be extremely well sealed and insulated. The thermal mass of the walls will be very high, and they will be covered with multiple layers of excellent thermal insulation, so there is nothing that can keep them cool. I'm not sure how you will deal with the humidity issue, if you don't have an HVAC system in there: Maybe you could spread large amounts of Silica Gel all over the floor each time you go in, then sweep it up and bake it for a when hours when you leave, ready for the next session? Probably around 20 or 30 kg of silica gel should be enough, I would think. If you spread it over enough area, it should be able to control the humidity a bit.

In addition to the energy cost from running it

A few cents per hour, maybe. About the same cost as running your audio gear, in terms of electrical power consumption. Why would that be an issue?

it also adds sound which I am not certain how to solve

It does not add any sound: the fan is outside the room, far away at the other end of your ducts, and on the other side of your silencer box. You won't hear it at all. A good mini-split produces about 30 dBA in operation, or maybe a bit more, and even less if you duct it or place it a silencer box. And as I said above, the noise from airflow is inaudible, since the air speeds are kept so low that they make no appreciable noise.

I am not certain how to solve

You are not certain how to build a studio either, which is why you are here on the forum! :) That's what the forum is all about. Just like you can learn how to build your studio here, you can also learn how to build your HVAC system here. There are many examples on the forum of people who have done that, and they show in detail how they did it, and how the calculated it, and then tell you how it worked out in the end. (And the good part of it is, they are all still alive! Not one of them died inside their studios, due to lack of oxygen, or CO2 poisoning....)

I know there are ductless systems but I do not know how effective they are and how quiet they are when they run at full power (unless of course you trust the manufacturer)

They are just as quiet as the manufacturers claim, if you buy from a reputable manufacturer. In the range 30 to 40 dBA, roughly. Some are even quieter. And if you cannot find one quiet enough for your needs, then do your HVAC system using the "exchange chamber" concept. Or if you don't like that concept, then do it with a fully ducted system where the AHU is outside of the studio shell. That way, the entire HVAC system can be totally silent.

The main house building I am constructing has plenty of passive cooling and heating systems installed so it sort of breaks the purpose if I do not use it in this building too.

Think of it this way: You will be working inside a plastic bag that is perfectly sealed, then placed inside another plastic bag that is also perfectly sealed. There is no way for air to get in our out. Now please explain how "passive cooling" is going to get oxygen into your lungs and keep you alive? How is "passive heating" going to get the accumulated carbon dioxide out of the room so that it does not kill you?

If I would use ducts, what material should I use in the ducts? My father uses plastic on his boat which I imagine resonates less than metal.

There are many options for ducts, but metal is the most common (and the cheapest). Flex duct is another option, or you could build your ducts from duct-board. You could even make ducts from wood, if you wanted to. I wouldn't use plastic, though. All ducts must be lined on the inside with duct liner, which prevents resonance.

That was sort of the plan but I am not following the logic here, what would be the difference between a floating ceiling with a catcher behind it and a solid ceiling with a catcher behind? It seems like most people build catch screens with a loose fabric at the end in order for the sound to continue before it bounces back rather than having the foam on a solid plate?

I'm not sure what you mean by "catcher" in that sense. Maybe you could draw a couple of diagrams, to explain what you are saying? The point I was making is that if you have a third ceiling, in addition to your outer-leaf and inner-leaf ceiling, then you have a 3-leaf system. The resonant frequencies of a 3-leaf system are always higher than those of the equivalent 2-leaf system, so therefore the isolation you would get from that is WORSE than it would be if you just built a normal 2-leaf system. For a two leaf system, there is only one fundamental resonant frequency (MSM resonance), but for a three-leaf there are two fundamentals, and they are both always much higher than the resonance of the 2-leaf system, all other factors being equal.

A non-rectangular room seems to need at least twice as much space in that particular area

It shouldn't need that much! You only need to angle the front section of the room (as far back as the mix position), and the space you "lose" like that can then be used for things like your HVAC ducting and your silencer boxes. If you don't angle your walls, then those either have to go inside the room (taking up space there) or outside the room (taking up space there). They are big.

so it seems like a waste of money if I can solve the angles with screens and foam.

Screens and foam do not reflect sound: they absorb some of it. So you can't use them to redirect sound in other directions, which is what you need to do. Screens and foam also do not change the shape of the room, and thus have no effect on modal frequencies. They might help slightly to damp some modal reverberation, but they won't help to correct the frequency spread.

If I have to use Civil 3D for the site I might aswell use it for the architecture. Maybe they have added that stuff to Sketchup too but after I have learned Autocad I do not see the point.

Well, the point is that not many people here on the forum use AutoCad, so you won't be able to get much help from us if you don't post your models in SketchUp format! The Pro version of SketchUp can read .dwg files and other formats too, and it can also export those same file formats, so you would still be able to generate your plans in AutoCad, if you wanted to. SketchUp also makes it very easy to visualize all aspects of your studio in 3D, very simply and clearly. - Stuart -

Soundman2020 wrote:

Not really, no. The actual shape of the inner leaf itself must be symmetrical, since that is what sound waves "see". The hard, solid, massive, boundary surfaces of the room are what matter for things like modal response, critical frequency, ratios, and things like that. Yes, you can reflect higher frequencies with panels, but not low frequencies.

I understand, but I was thinking of 30 mm MDF-boards with foam behind, like the picture attachent. Of course the asymmetry ABOVE will affect the sound resonance a bit, but the roof is not in the direction of the speakers, right?

I see a lot of arguments there why you don't want to install an HVAC system, but you seem to have missed the most important part of why you need one: "Having no speakers in the room won't kill, but having no HVAC actually could kill you, very literally: Dead, as in not alive. No life. Not breathing."I'm not sure how well you would be able to make music in your room, if you are dead from asphyxiation! :)

I am talking about a passive cooling circulation system on top of the AC unit, it does not mean I am not going to have an AC unit, just that I do not need the "V8-turbo" system. I want to reduce the reliance on the ducts to remove noise aswell as unpleasantness of cold drafts and the other problems that comes with small spaces.

It seems to me that you are raising arguments why you don't want it, before even finding out if your arguments are valid or not!

No, I have lived both with and without AC and I are familiar of many passive cooling systems that can reduce the temperature below 20C/ 75F without the use of electricity. I have studied both architecture and and passive cooling systems and think I am capable of constructing a sufficient system for this building.

Then you are going to need a room that is about 10 to 15 times as big as what you are planning, so it can hold enough oxygen and moisture during a normal day's work.

No. Read up on passive circulation systems of the types used in India and the middle east on small buildings.

There won't be much passive circulation at all in a room as small as yours. There will be some convection going on, yes, but there will be zero cooling, and zero dehumidifying, and zero oxygen added, and er CO2 removed, all of which are critical. There will not be any passive cooling at all, since the room has to be extremely well sealed and insulated. The thermal mass of the walls will be very high, and they will be covered with multiple layers of excellent thermal insulation, so there is nothing that can keep them cool.

I am not following you here at all. Why would it be zero ventilation?

I'm not sure how you will deal with the humidity issue, if you don't have an HVAC system in there: Maybe you could spread large amounts of Silica Gel all over the floor each time you go in, then sweep it up and bake it for a when hours when you leave, ready for the next session? Probably around 20 or 30 kg of silica gel should be enough, I would think. If you spread it over enough area, it should be able to control the humidity a bit.

Again I think you misunderstand the point in using passive circulation. If you read up on middle eastern architecture I think you get the main picture. You know they have built studios in the middle east before the advent of airconditioners?

A few cents per hour, maybe. About the same cost as running your audio gear, in terms of electrical power consumption. Why would that be an issue?

That's the point. If I do not build passive cooling I would have to run the AC unit 24/7 in order not to ruin the electronic equipment in the room, which in southern spain would end up to thousands of dollars per year. By implementing passive cooling I can run the same temperature at a fraction of the cost. Seems like a no brainer for a home studio.

It does not add any sound: the fan is outside the room, far away at the other end of your ducts, and on the other side of your silencer box. You won't hear it at all. A good mini-split produces about 30 dBA in operation, or maybe a bit more, and even less if you duct it or place it a silencer box. And as I said above, the noise from airflow is inaudible, since the air speeds are kept so low that they make no appreciable noise.

It is not the noise from the airflow that bothers me, it is the noise from the duct itself. It may be true that 30 dBA is inaudible in the studio but if it is possible to reduce it more by using a plastic duct or a ductless system I think it is worth it.

Think of it this way: You will be working inside a plastic bag that is perfectly sealed, then placed inside another plastic bag that is also perfectly sealed. There is no way for air to get in our out. Now please explain how "passive cooling" is going to get oxygen into your lungs and keep you alive? How is "passive heating" going to get the accumulated carbon dioxide out of the room so that it does not kill you?

Why does it have to be sealed? And what is the difference regarding ventilation between having a passive cooling system and a HVAC system with or without an AC unit? Where does the isolation come in play? And who says I am not going to have an HVAC system but you anyway? I wrote I am not going to rely on it for 100% of the cooling, but it does not mean I am not having an HVAC system.

I wouldn't use plastic, though.

...because?

I'm not sure what you mean by "catcher" in that sense.

I will post my latest design later (see the front attachment). The "catcher" would be a frame with glass fibre foam or accoustic foam that can be put between the MDF-ceiling boards and the outer roof (catches low frequencies by reducing their available space of resonance).

Screens and foam do not reflect sound: they absorb some of it. So you can't use them to redirect sound in other directions, which is what you need to do. Screens and foam also do not change the shape of the room, and thus have no effect on modal frequencies. They might help slightly to damp some modal reverberation, but they won't help to correct the frequency spread.

I understand that, but I have a hard time thinking a thick MDF-board should have noticably lower stamina than the buildings I have used as studios in the past. What are we talking about anyway for a studio this size, 1 semitones in the low frequency spectrum?

The Pro version of SketchUp can read .dwg files and other formats too, and it can also export those same file formats, so you would still be able to generate your plans in AutoCad, if you wanted to. SketchUp also makes it very easy to visualize all aspects of your studio in 3D, very simply and clearly.

Allright, thanks I will look into it.

I understand, but I was thinking of 30 mm MDF-boards with foam behind, like the picture attachent.

30mm thick is excellent, as that gives it plenty of mass and also makes it quite stiff (rigid). However, it's the length and width that matter, regarding what frequencies it can handle. For example, if you hang a board from your ceiling, and the board measures 1m by 1m, it would only really have an effect on frequencies above 340 Hz. That's not much use for modal issues, which are generally in the region under 200 Hz, with the worst under 100 Hz, for typical home studios. To deal with frequencies under 100Hz, your panel would have to measure about 3.5m by 3.5m.

Of course the asymmetry ABOVE will affect the sound resonance a bit, but the roof is not in the direction of the speakers, right?

No, but the modal response is. Room modes terminate in the corners of the room, so the place where all modes are triggered (and can be treated best) is in the room corners. The BEST corners are the "tricorners", where three surfaces meet: wall-wall-ceiling or wall-wall-floor. Second best is corners where two surfaces meet. Modal response has nothing to do with which direction the speakers are facing, since low frequency sound is not directional at all. For wavelengths longer than the lowest mode, things are even worse: the entire room is "pumping" down there, sort of inflating and deflating, since the pressure variations must affect all surfaces equally at frequencies lower than the lowest mode. So regardless of which way the speakers are pointing, you will always have modal issues in the room corners, and they will be at the same level, since they are opposite ends of the same standing wave. So for example if your lowest axial mode is 60 Hz, then the level of that mode measured in any room corner at the front and rear walls would be exactly the same.

No. Read up on passive circulation systems of the types used in India and the middle east on small buildings.

:) How do they manage to get air through the air-tight seals? You seem to be entirely missing the point here that your studio is equivalent to a sealed plastic bag inside another sealed plastic bag, and each of those is wrapped in several layers of very thick insulation. So my question is: how do you plan to get the excess heat out through those multiple layers of insulation, and how do you plan to get air through the sealed leaves, if you don't have a proper HVAC system, specially designed for a studio?

I am not following you here at all. Why would it be zero ventilation?

Zero ventilation because acoustic isolation requires two complete hermetically sealed "shells" around your room Those are called the "outer-leaf" and the "inner-leaf". The outer leaf is often the exterior wall of the building, and the inner-leaf is the surface you see when you stand inside the finished room, before installing any acoustic treatment. BOTH of those leaves are totally sealed, air-tight. They have to be, or you don't have isolation. Even a small crack under a door or around a window is unacceptable for studio isolation. If air can get through from one side of a leaf to the other, then so can sound. So EACH leaf is fully sealed. This is NOT the way houses, offices, schools, and shops are built. They are never built fully sealed, so that air can seep in and out through all the numerous gaps, cracks, and openings. But a studio MUST be sealed: if not, there is no soundproofing. To make it even more complicated, we are talking about TWO complete hermetic seals, not just one. Each leaf is sealed independently, and completely: no air can get in or out. Unless, of course, you install proper ducting, silencer boxes and fans to force the air in and out. Added to that, is the issue of the insulation: Each leaf has very thick acoustic insulation around it, such as mineral wool, fiberglass, or even cellulose. That same stuff is also really, really good thermal insulation: it prevents heat going in and out. Yes, you could use very large areas of glass exposed to the outside world to get heat into to the room during daylight hours, and allow heat to escape at night, but that is not a realistic solution for studios, mainly due to cost: the amount of glass area you need is quite large, and the type of thick laminated glass you need is very expensive, especially when you take into account that for each window you need TWO panes of glass: one in the inner-leaf, the other in the outer-leaf. Only studio owners with deep pockets can afford that amount of glass. Not to mention the fact that you can't have large percentages of your studio walls made of glass, since you need that same wall area for acoustic treatment...

Again I think you misunderstand the point in using passive circulation. If you read up on middle eastern architecture I think you get the main picture. You know they have built studios in the middle east before the advent of airconditioners?

Sure, but they had little to no isolation... or they were massively expensive to build. You cannot bypass the laws of physics.

That's the point. If I do not build passive cooling I would have to run the AC unit 24/7 in order not to ruin the electronic equipment in the room,

To be very honest, I'd be much more worried about my own health than my equipment, in a studio with no HVAC! :)

It is not the noise from the airflow that bothers me, it is the noise from the duct itself.

That's why I keep on talking about silencer boxes. You must have a silencer box on each wall penetration, and it greatly attenuates any duct-borne sound. That's also why I mentioned that the ducts must be lined with duct liner. If you don't know what that is or what purpose it accomplishes, then search the forum for the term "duct liner". Here are a few examples of the type of silencer box you need for a typical home studio: viewtopic.php?f=2&t=15430&start=45 viewtopic.php?f=2&t=1929&start=74 viewtopic.php?t=8425&start=2 viewtopic.php?f=1&t=11542&start=5 viewtopic.php?f=2&t=9761&start=0 viewtopic.php?f=2&t=11485&start=98 viewtopic.php?f=2&t=11508&start=157 viewtopic.php?f=2&t=13821 viewtopic.php?f=1&t=15378&start=44 viewtopic.php?f=2&t=18202&start=16 They work on the basis of several principles, but the main ones are impedance mismatch at the entrance and exit (and to a lesser extent around each baffle plate), as well as the fact that sound travels well in straight lines, but not so well around corners, while air can easily get around corners. There is also acoustic absorption going on in the duct liner, and at each baffle, as well as things like edge diffraction, and even mass law has a part to play here. They are VERY effective at blocking sound in ducts. That's not the only way of making them: they can also be made using the same principles as gun silencers or car exhaust silencers, with perforated panels and meshes, and expansion chambers, and suchlike, but this is the easiest and least expensive way of making them for home studios.

It may be true that 30 dBA is inaudible in the studio but if it is possible to reduce it more by using a plastic duct or a ductless system I think it is worth it.

You should probably check your local building code and fire code to find out if that is even allowed. In the USA, this is the situation: "Using PVC for ductwork is NOT recommended. The flame spread and smoke developed for PVC piping does not meet the ASTM E84 guidelines of a flame spread index of less than 25 and a smoke-developed index of less than 50 which is specifically prohibited in plenums." It can be used for underground ducting, provided that it is fully encased in concrete and does not carry hot air, but it cannot be used for general ducting in ceiling plenums or wall cavities, due to the high fire danger. That's the situation for PVC. Other plastics might be different, but you'd have to check exactly what is and is not allowed in your country. I heard that you guys have very strict fire codes, though, so you might find that only metal and fiberglass ducts are allowed, or other non-flammable materials.

Why does it have to be sealed?

Because it is a studio, and needs to be isolated, acoustically. "Soundproofed". The very fact of soundproofing your room means that the room must be sealed. No seal = no soundproofing.

And what is the difference regarding ventilation between having a passive cooling system and a HVAC system

You seem to be confusing the two issues. Cooling is one thing, and ventilation is an entirely different, separate, and unrelated thing. Cooling is related to removing excess heat and humidity from the room, period. That's all. Ventilation is related to bringing in enough oxygen so that you can stay alive, and removing the same amount of stale air that is overloaded with carbon dioxide and other gasses that you exhale as you breathe. These are two very different things, and both of them need to be addresses. That's what the letters stand for in HVAC: H=Heating, V=Ventilation, AC=Air Conditioning. They can be combined into one single system, and they sometimes are for larger studios, but they can also be totally separate systems, and that's usually the case with smaller studios: There is a ducted system for ventilation, and a separate air-conditioner unit that controls temperature and humidity. And they are all carefully designed such that they provide the correct amount of air movement at the correct speed, and the correct amount of cooling (sensible heat removal) and dehumidifying (latent heat removal).

I am not going to rely on it for 100% of the cooling, but it does not mean I am not having an HVAC system.

That's good! I'm glad I managed to convince you. :thu:

Where does the isolation come in play?

It's a recoding studio, so therefore it is isolated. Recording studios are loud inside, and that sound has to be stopped for both legal reasons, and also for simply keeping family and neighbors happy. It's a recording studio, so sounds on the outside have to be stopped from getting in. You do not want the sounds of wind, rain, hail, thunder, people talking, phones ringing, the radio, TV, the dog barking next door, cars going past in the street, the toilet flushing, the vacuum cleaner and all the other typical sounds, getting into your recordings, or bothering you while you try to concentrate on a complicated mix. That's the entire reason for building a studio! It needs to be isolated from the outside world so that you can work in peace and quiet, without anyone bothering you with their sounds, and without you bothering anyone else with your sounds. If you don't have isolation, then you don't have much of a useful studio!

I wouldn't use plastic, though.

...because?

Fire, for one. Most plastics are flammable, and therefore dangerous. Health, for another: Many plastics release chemical odors and gasses into the air. Static for another: most plastics build up static charges as air flows over them, which means that the air in your room will end up statically charged. Cost is another issue: plastic piping big enough for studio HVAC work would be VERY expensive. I'm not even sure where you would find such huge pipes: You'd probably have to call suppliers of industrial equipment fo find large enough pipes. Weight is another issue: plastic pipes that big would be much heavier than ordinary metal HVAC duct. And building code could be a major issue: if your local code does not specifically state that you can use the exact type and size of plastic pipe for HVAC in human occupied spaces, then you can't use it. I have no idea what the building code in your country says, but where I live, it isn't allowed. Here, plastic pipe can only be used for water, and for electrical conduit.

The "catcher" would be a frame with glass fibre foam or accoustic foam that can be put between the MDF-ceiling boards and the outer roof (catches low frequencies by reducing their available space of resonance).

Sorry, but that just doesn't make sense. Anything you put between your inner leaf and outer leaf becomes part of the MSM resonant system, which governs isolation, not treatment. Treatment has to go inside the room, not in the resonant cavity between your inner and outer leaves. You absolutely must fill that cavity with insulation anyway: its the damping for the MSM system, so there won't be any room for "catchers" in there anyway. Even of there was, it would have little effect on the room, other than what the entire MSM wall system has as a whole. The normal way of managing modal issues, is with deep broadband absorption in the corners, or tuned devices placed at very specific locations in the room. The normal way of dealing with first reflections is with absorption placed at the correct points on the wall and ceiling. The normal way of creating room symmetry is by placing the inner-leaf walls and ceiling correctly when they are built, so that the room is symmetrical about the front-back vertical plane. Things placed outside the isolation shell have no effect on things inside the room, unless the room is very, very poorly isolated.

I understand that, but I have a hard time thinking a thick MDF-board should have noticably lower stamina than the buildings I have used as studios in the past. What are we talking about anyway for a studio this size, 1 semitones in the low frequency spectrum?

All of your modal issues will be in the range 20 Hz to about 200Hz or so, maybe up to 300 Hz, if the room is very small. Modes are a direct consequence of the dimensions of the room, and there is nothing you can do to change that. There is no treatment that will destroy a mode. All you an do is damp modes sufficiently that their decay times are within ITU / EBU specs. You can change the frequency of modes (to a certain extent) by placing a very large, very massive, very rigid panel in the right location and at the right angle inside the room, but not outside. The normal way of doing that is with a hard-backed cloud hung from the ceiling on chains, and placed at a suitable angle.

Attachments: File comment: inner (left front view)

There's a mistake on that diagram: the inner-leaf ceiling does not meet the inner-leaf walls, and therefore there is no isolation. You should fix that. - Stuart -

Soundman2020 wrote:

:)How do they manage to get air through the air-tight seals? You seem to be entirely missing the point here that your studio is equivalent to a sealed plastic bag inside another sealed plastic bag, and each of those is wrapped in several layers of very thick insulation.

And you miss the basic assumption point regarding this studio: it is built in a rural area on the bottom floor, with two seperate rooms: one for production and one for recording. Hence, if I play the drums it will not affect the closest neighbour even without any insulation. Secondly, a passive circulation system can be isolated just like any HVAC system.

So my question is: how do you plan to get the excess heat out through those multiple layers of insulation, and how do you plan to get air through the sealed leaves, if you don't have a proper HVAC system, specially designed for a studio?

Who says I am not going to have a proper HVAC system? I am adding a passive circulation system ON TOP of the HVAC calculation, understand? Having passive circulation is not like having an extra engine with a seperate axis on the car, it is like having an extra cylinder.

Zero ventilation because acoustic isolation requires two complete hermetically sealed "shells" around your room Those are called the "outer-leaf" and the "inner-leaf". The outer leaf is often the exterior wall of the building, and the inner-leaf is the surface you see when you stand inside the finished room, before installing any acoustic treatment. BOTH of those leaves are totally sealed, air-tight.

I am thinking only adding complete isolation to the recording room. OTW I would never have added a window in the first place.

To be very honest, I'd be much more worried about my own health than my equipment, in a studio with no HVAC! :)

I really do not understand why you keep repeating this, I assume this is something that is common in beginner-threads. To make it clear: I understand HVAC-systems more than the average homebuilder: I have lived in both sub-polar regions aswell as the tropics and have experience from everything in between.

You should probably check your local building code and fire code to find out if that is even allowed. In the USA, this is the situation: "Using PVC for ductwork is NOT recommended. The flame spread and smoke developed for PVC piping does not meet the ASTM E84 guidelines of a flame spread index of less than 25 and a smoke-developed index of less than 50 which is specifically prohibited in plenums."

Yeah of course, but there has to be inflammable plastics too, something like: http://www.tedpella.com/company_html/pl ... erties.htm

That's good! I'm glad I managed to convince you. :thu:

You did not, you misunderstood me from start.

t's a recoding studio, so therefore it is isolated. Recording studios are loud inside, and that sound has to be stopped for both legal reasons, and also for simply keeping family and neighbors happy. It's a recording studio, so sounds on the outside have to be stopped from getting in. You do not want the sounds of wind, rain, hail, thunder, people talking, phones ringing, the radio, TV, the dog barking next door, cars going past in the street, the toilet flushing, the vacuum cleaner and all the other typical sounds, getting into your recordings, or bothering you while you try to concentrate on a complicated mix. That's the entire reason for building a studio! It needs to be isolated from the outside world so that you can work in peace and quiet, without anyone bothering you with their sounds, and without you bothering anyone else with your sounds. If you don't have isolation, then you don't have much of a useful studio!

That is why I keep the two rooms seperated. The recording room can be more isolated with less cost both on isolation and running costs.

Sorry, but that just doesn't make sense. Anything you put between your inner leaf and outer leaf becomes part of the MSM resonant system, which governs isolation, not treatment. Treatment has to go inside the room, not in the resonant cavity between your inner and outer leaves. You absolutely must fill that cavity with insulation anyway: its the damping for the MSM system, so there won't be any room for "catchers" in there anyway. Even of there was, it would have little effect on the room, other than what the entire MSM wall system has as a whole.

Can you elaborate on this, because this is like exactly the opposite of the theory behind building foam screens with loose bottom ends?

Things placed outside the isolation shell have no effect on things inside the room, unless the room is very, very poorly isolated.

I have a really hard time understanding that... low frequencies transplant themselves through objects, no?

File comment: inner (left front view)

There's a mistake on that diagram: the inner-leaf ceiling does not meet the inner-leaf walls, and therefore there is no isolation. You should fix that. [/quote] It's a design feature, not a bug. I have not thought through the actual construction detail that supports the MDF:s yet as I am not certain I will use it. If I were to go ahead with that design I would probably put a rafter or similar on top and then some sort of consoles in the walls that I could attach the MDF:s easily.

I have a really hard time understanding that... low frequencies transplant themselves through objects, no?

OK, it seems you have a very, very basic misunderstanding of how acoustic isolation works. The very best I can do here is to recommend this paper, which is probably explains the whole concept the best of all that I've seen: https://app.box.com/shared/jcaoavdc8g It's very old (from 1973) but lays the foundations for understanding how isolation works. Once you understand that, I'm sure you'll understand the entire issue with what you are proposing. There also seems to be a very basic misunderstanding of acoustics in general, so I'd suggest this book: "Master Handbook of Acoustics" by F. Alton Everest. That's sort of the Bible for acoustics, and is meant for people who know nothing or very little about acoustics. The good thing about that book, as compared to the Wyle report, is that it does not use mathematics very much, and instead explains acoustics with examples, diagrams, graphs and tables that are very easy to understand. Those two will probably give you the foundation that you need in order to understand both acoustics and isolation, and to see why the things you are proposing will not work in the way you imagine they will. Acoustics is actually very non-intuitive, and many, many people do have a hard time grasping the way sound waves actually behave since sound does not actually work the way we naturally tend to assume it works. We can't see or touch sound waves, and we hear them in only one single location: the ears, so we never really perceive how they move through the air, and how they interact with different types of objects, to it does take a while of studying the subject until you grasp the basics. Most people need to first "un-learn" what they think they know about sound, then re-learn how it actually works.

And you miss the basic assumption point regarding this studio: it is built in a rural area on the bottom floor, with two seperate rooms: one for production and one for recording.

So you are saying that you do not need any isolation at all? Then why are you even building a studio? If you don't need isolation, then you can just set up your equipment and instruments in pretty much any room with a decent ratio and good symmetry. If you don't need any isolation, then there simply is no point at all to building walls around the room. In fact, it would be better to completely remove those walls, and have no hard boundaries around the room at all.

Hence, if I play the drums it will not affect the closest neighbour even without any insulation.

And you are not concerned about outside noises spoiling your recording sessions? None of the following sounds occur where you live?: Wind, rain, hail, thunder, aircraft flying over, helicopters, trains, cars, trucks, dogs barking, other animal noises, phones ringing, people talking, radio playing, TV, washing machine, vacuum cleaner, water running, toilet flushing, footsteps, and all the other hundreds of noises that occur in houses? If you really can honestly say that you don't mind those sounds getting into your recordings, and they don't bother you at all when trying to concentrate on a delicate mix, then I guess you would be fine with no isolation at all. But that's not the case for most people. The vast majority of studio builders, everywhere in the world, do need isolation.

I am thinking only adding complete isolation to the recording room.

Once you understand how isolation works, you'll see why that is impractical for most studios. Yes, you CAN do it like that, but there's no logical reason why you would, if you are building the place from scratch.

I really do not understand why you keep repeating this, I assume this is something that is common in beginner-threads. To make it clear: I understand HVAC-systems more than the average homebuilder:

It's good that you understand HVAC so well, but I'm not actually talking about HVAC. The issue is the ISOLATION of the room, not the HVAC. It is the very fact of suitably isolating a room that creates the need for a properly design HVAC system. The basic issue here is this: with a properly isolated studio, there is no way for air to get into and out of the room, thus there is no passive cooling, nor passive ventilation (they are two different things, as you know). The air inside the room, stays inside the room because it is sealed inside the room. It HAS to be sealed, in order to have isolation. If air cannot move from the interior to the exterior of the room due to the double perfect hermetic barriers, then there is no possibility for passive ventilation. If you do create a duct system, with suitable silencer boxes for maintaining the isolation, then you still need fans, because passive ventilation alone will not be capable of moving enough volume of air to keep the room properly ventilated, according to the usual international air standards that you already know about. Studios need about 6 to 12 room changes per hour: it would be really, really hard to get that much airflow without fans. You would have to create huge temperature differentials somehow, not to mention the size of the ducts and boxes you would need. You would not be able to do it with typical duct sizes, as the static pressure would be too high.

You did not, you misunderstood me from start.

So when you originally rejected HVAC with the following words, you were just joking? :) "I come from a place (scandinavia) where AC is considered unnatural and somewhat unhealthy even, and after having lived in places like Florida I have a strong distaste of the reliance on it except for taking out the edge of the heat. I cannot stand living in the airflow of a strong AC unit, I need passive circulation" When you said that HVAC is unhealthy, that you have a strong distaste for it, and that you "need" passive, that wasn't actually true? Now you are saying that you recognize that you will have to have it, after I explained to you why it is necessary...

OTW I would never have added a window in the first place.

So your original question wasn't actually an option at all? When you asked this below, you didn't actually want an answer, since you never planned to use windows at all? "Now I got two main questions, the main issue is the window issue. ... Question here is: is it worth it? Should I put smaller windows in or will it be bad no matter how I do it? Is it better to have the windows in the direction of the sound or assymetrical (is it like plauge or cholera?). " It's confusing that you first say you want help with windows, then say you never even considered windows in the first place.

Sorry, but that just doesn't make sense. Anything you put between your inner leaf and outer leaf becomes part of the MSM resonant system, which governs isolation, not treatment. Treatment has to go inside the room, not in the resonant cavity between your inner and outer leaves. You absolutely must fill that cavity with insulation anyway: its the damping for the MSM system, so there won't be any room for "catchers" in there anyway. Even of there was, it would have little effect on the room, other than what the entire MSM wall system has as a whole.

Can you elaborate on this, because this is like exactly the opposite of the theory behind building foam screens with loose bottom ends?

The MSM isolation wall is a system, not a collection of individual parts. Each part does not act on it's own: they all act together as a resonant system, governed by this equation: The entire wall resonates at that specific fundamental frequency, and that is the key to isolation. At that frequency, the wall does not isolate at all, and in fact it can not only transmit sound perfectly, but it can also amplify the sound passing through it. However, since it is a tuned system, it acts very much like a tuned electronic "bandpass" circuit: it passes that frequency very well, but it isolates all other frequencies much better than any other method. At 1.414 times the resonant frequency, the wall starts to isolate. At 2 times resonant frequency, it isolates reasonably well, and at three times resonance it isolates very well. Isolation increases very much like a third-order filter, until the critical frequency of the wall, where coincident resonance brings it down again a bit, but the isolation is already so good at that point that the coincidence dip doesn't really matter much in a well-designed wall. So, in order to understand what I said, you have to stop looking at the isolation wall as a group of individual pieces of construction materials, and start seeing it as a resonant system. It isolates because it resonates. If you do something to change the system, such as putting large, massive pieces of wood inside the resonant cavity as you proposed, then you change the resonant characteristics of the system. And since a 2-leaf MSM system is already the optimum arrangement for maximum isolation, anything you do like that actually decreases isolation, because it drives up the fundamental frequency. In fact, placing a third leaf inside a 2-leaf system turns it into a 3-leaf system, which has TWO resonant frequencies, not just one, and both of those are much higher than the frequency for the equivalent two-leaf system. So basically what would happen if you put your sheets of MDF inside the isolation system, is that you would make it isolate worse, and also since the resonant frequency would then be much higher, it would probably interact with the room itself to either amplify those frequencies within the room, or to suck them out drastically, depending on several factors, such as your location within the room, the location of the speakers, whether or not the MSM resonance happens to also coincide with a room mode, etc.

Things placed outside the isolation shell have no effect on things inside the room, unless the room is very, very poorly isolated.

I have a really hard time understanding that... low frequencies transplant themselves through objects, no?

Yes and no, but we are not talking about simple objects here: the wall is a resonant system, and placing things inside it (or even outside it, very close to the outer surface) can modify the resonant behavior of the entire wall system.

There's a mistake on that diagram: the inner-leaf ceiling does not meet the inner-leaf walls, and therefore there is no isolation. You should fix that.

It's a design feature, not a bug.

No, it really is a bug! If the inner-leaf is not a completely sealed system, then you have very poor isolation: your room is now open to the resonant cavity inside the the wall, and all that resonant activity is now returned to the room, instead of being separated from it: Isolation will be lousy, and so will room acoustics. Your modal response also reverts to be a combination of all three systems, but is mostly governed by the outer-leaf now, which is not symmetrical, rather than the inner-leaf or the middle-leaf, so you have probably made matters much worse like that. There's also the additional problem that I haven't mentioned yet: That MDF would also act as a resonant plate, since it is basically just a an undamped resonant panel hanging inside a cavity: It will resonate at it's own frequency, independent of the rest of the system, in addition to being part of the total resonant system. The effects of that resonance are hard to predict, but I'm pretty sure it would not do nice things to the room acoustics...

I have not thought through the actual construction detail that supports the MDF:s yet as I am not certain I will use it. If I were to go ahead with that design I would probably put a rafter or similar on top and then some sort of consoles in the walls that I could attach the MDF:s easily.

You would have to damp and decouple that, so you'd need resilient clips or isolation mounts of some type. That would solve the flanking issue with that MDF plate, but even then, you'd still have the 3-leaf resonance issue. I'd suggest one other book to help you understand these things: "Home Recording Studio: Build it Like the Pros", by Rod Gervais. That one deals more with the actual construction issues of how to build MSM resonant walls, and ow to build studios in general. There's also a very good chapter on HVAC systems that you might find interesting. - Stuart -

So you are saying that you do not need any isolation at all? Then why are you even building a studio? If you don't need isolation, then you can just set up your equipment and instruments in pretty much any room with a decent ratio and good symmetry. If you don't need any isolation, then there simply is no point at all to building walls around the room. In fact, it would be better to completely remove those walls, and have no hard boundaries around the room at all.

There are two rooms: one with isolation and one without. The one without isolation is only about symmetry: I do not need to isolate it because I am not going to record any audio in it. If I were to isolate it for the sake of isolation it would cost too much and I would have to run an AC 24/7 etc. It is a home studio and I do not expect to make enough money on my music to pay for the construction cost. Now, this discussion applies in general to both rooms but only certain aspects of it applies to both rooms. Isolation no, resonance yes.

And you are not concerned about outside noises spoiling your recording sessions? None of the following sounds occur where you live?: Wind, rain, hail, thunder, aircraft flying over, helicopters, trains, cars, trucks, dogs barking, other animal noises, phones ringing, people talking, radio playing, TV, washing machine, vacuum cleaner, water running, toilet flushing, footsteps, and all the other hundreds of noises that occur in houses?

If you have more than 500 meters to your closest neighbor then the neighbor is not considered a noise problem on the bottom floor inside a concrete building, no. In a wood building on the second or third floor yeah maybe if they are shooting with machine guns but again, that is why I seperated the studio into two rooms to begin with. I do not need to record audio from the production room and if I did, the combined noise from the computer and the AC would probably go above 40 dB SPL anyway.

Once you understand how isolation works, you'll see why that is impractical for most studios. Yes, you CAN do it like that, but there's no logical reason why you would, if you are building the place from scratch.

Yes there is. There is a big monetary cost involved and I do not expect my music to pay for it. The building is supposed to generate more power though solar input than what it consumes, and if I run an AC unit 24/7, which I would have to if I built the production room isolated, it would be a design breaker. Read: hobby project, not commercial studio.

It HAS to be sealed, in order to have isolation. If air cannot move from the interior to the exterior of the room due to the double perfect hermetic barriers, then there is no possibility for passive ventilation. If you do create a duct system, with suitable silencer boxes for maintaining the isolation, then you still need fans, because passive ventilation alone will not be capable of moving enough volume of air to keep the room properly ventilated, according to the usual international air standards that you already know about. Studios need about 6 to 12 room changes per hour: it would be really, really hard to get that much airflow without fans.

Do you now understand why I do not want to isolate the room with all my electronic gear in it? Having that stuff going every second, every hour, every day, every year when I am not in it, when I am sleeping, when I am at work or when I am on vacation cost a lot of money. In the hottest part of Europe: literally thousands of dollars per year. Limiting the isolation to one room means literally thousands of dollars both in construction costs and running costs. Per year. It is not much of a choice to me, particularly when I do not have the actual mortage loan approved.

So when you originally rejected HVAC with the following words, you were just joking? :) "I come from a place (scandinavia) where AC is considered unnatural and somewhat unhealthy even, and after having lived in places like Florida I have a strong distaste of the reliance on it except for taking out the edge of the heat. I cannot stand living in the airflow of a strong AC unit, I need passive circulation" When you said that HVAC is unhealthy, that you have a strong distaste for it, and that you "need" passive, that wasn't actually true? Now you are saying that you recognize that you will have to have it, after I explained to you why it is necessary...

I clearly wrote AC, not HVAC. You are referring to HVAC. And I never wrote I would not have an AC unit either, I just implied I would not rely on it for 100% of the cooling. So you misunderstood every line yes. Which confunds me, as you earlier implied I was the one confusing AC with HVAC. I seriously do not understand how you interpret my reluctance to sit in a highly airconditioned room to refuse a ventilation system either. I cannot understand how you jump to that conclusion, one does not have anything to do with the other and you wrote that yourself earlier in the thread. I mean... :shock:

So your original question wasn't actually an option at all? When you asked this below, you didn't actually want an answer, since you never planned to use windows at all?

You do assume a lot, don't you? 8) It was a question and I got it answered. But the recording room did not have any planned windows except the window between the recording room and the production room (which is not really a window from my perspective as it can be built from other premises than an outside window). The question was the windows in the production room, which you assumed I was going to isolate with a 2-leaf system. If I had asked about windows in the recording room I would have wrote so.

It's confusing that you first say you want help with windows, then say you never even considered windows in the first place.

Yes, and it is even more confusing when ppl interpret A for B and vice versa. I never wrote that I was going to record in the production room, I should have I guess.

The entire wall resonates at that specific fundamental frequency, and that is the key to isolation. At that frequency, the wall does not isolate at all, and in fact it can not only transmit sound perfectly, but it can also amplify the sound passing through it.

So isolation works like a self-enforcing frequency attenuation? But in a non-isolated room, then we are still talking about resonance, right? And in those situation the areas where I put the bass catchers would be the areas that the lower frequencies were most likely to resonate, correct (given the angled MDF:s and angled outer roof)?

So, in order to understand what I said, you have to stop looking at the isolation wall as a group of individual pieces of construction materials, and start seeing it as a resonant system. It isolates because it resonates. If you do something to change the system, such as putting large, massive pieces of wood inside the resonant cavity as you proposed, then you change the resonant characteristics of the system. And since a 2-leaf MSM system is already the optimum arrangement for maximum isolation, anything you do like that actually decreases isolation, because it drives up the fundamental frequency. In fact, placing a third leaf inside a 2-leaf system turns it into a 3-leaf system, which has TWO resonant frequencies, not just one, and both of those are much higher than the frequency for the equivalent two-leaf system.

I can dig that the plates causes resonance, sure. Tricky problem.

No, it really is a bug! If the inner-leaf is not a completely sealed system, then you have very poor isolation: your room is now open to the resonant cavity inside the the wall, and all that resonant activity is now returned to the room, instead of being separated from it: Isolation will be lousy, and so will room acoustics. Your modal response also reverts to be a combination of all three systems, but is mostly governed by the outer-leaf now, which is not symmetrical, rather than the inner-leaf or the middle-leaf, so you have probably made matters much worse like that.

What you are saying is that there is no way to create even rudimentary symmetry without isolation?

I decided to go for another roof plan. Kind of obvious it should be a gable roof and not a hip roof, do not know why I did not see that :? Straight symmetry between the rooms in terms of ceiling space. Of course the recording room will be smaller when I isolate it but at least the shape is symmetric. Removed some windows, if the remaining window will cause a problem I can always put a movable screen in front of it.