John Sayers' Recording Studio Design Forum Archive

I'm not currently building a studio right now but just trying to gain as much knowledge as I can for future use. I have been thinking a lot lately on the issue of flat/straight versus angled walls and ceilings. Specifically the following...

On so many designs I notice that there are angled ceilings. These ceilings appear to be false ceilings with cloth covering bass trap hangers. So the first question is,

1) Is the actual (hard surface) ceiling of the room just a flat/level ceiling with the angled false ceiling below it? Also, I can't seem to find what angle is best for a control room false ceiling of this type.

2) To take this discussion a bit further, I have also noticed that many control rooms have angled side walls. The best I have been able to tell, 6 degrees is the standard angle for these walls. Is this correct or can the angle be varied to greater/lesser effect?

To sum all of this up, is it best to build each room of a studio with basically square/rectangle hard surface walls to ideal dimensions as far as modes and then build in the angles with false walls, traps and absorption? Or are there some uses for hard surface angled walls that have no absorption? I understand that hard surface angled walls would help with certain standing wave issues, but I'm not sure how they factor into most peoples designs. For Mass-Air-Mass designs, you need the two hard surface walls for sure, but do they need to be angled, or do you create the angles with the false walls, traps, absorbers, etc?

It seem for all the studios I've followed in various threads on this site, that a lot of information is imparted about the surface treatments, but not what is behind those treatments as far as the "Mass" part of the wall and the angles that may be beneficial or not.

Thanks for any info you can lend to this discussion that rages in my head...

Rainmaker

Aloha,

Here are a couple of helpful links -
http://www.saecollege.de/reference_material/index.html

Home Recording Studio: Build it Like the Pros (Paperback) by Rod Gervais
http://www.johnlsayers.com/phpBB2/viewtopic.php?t=5670

Hope this helps,

Aloha

Hello Kendale,

Thanks so much for your post. I indeed have read the SAE site and also own a copy of Rod's book. In fact, I just spent two hours reading it yet again tonight. However, I guess what I'm missing and what I couldn't find in either of the references you mentioned above is more information on room dimensions. When I talked about the hard-surfaced walls behind false walls, I'm not talking about isolation techniques... I'm wondering more specifically on room dimensions/angles
to minimize modal issues.

I have read and understand some of the desired room ratios, but where I get very confused quickly is when it comes to rooms with angled walls and ceilings. It seems most of the talk and writing I have seen on the issue of room dimensions and modes has been regarding rectangular rooms. But as you look around this wonderful forum at many of the studios being built, almost all have these wonderfully crafted rooms with various angled walls & ceilings. What I'm really trying to dig into is how to really calculate these types of rooms for ideal dimensions/angles and then how to apply the rectangular charted room mode information to them... In other words, the persuit of that elusive, perfectly dimensioned control room.

Thanks for the help,
Rainmaker

rainmaker wrote:In other words, the pursuit of that elusive, perfectly dimensioned control room.

you and everyone else...

that said, what are your room dimensions currently?

I don't currently have room dimensions. I am planning on building a studio in the future from the ground up. But only after I am satisfied with the design. So I am trying to fully understand some of these issues before I start construction. Since I have no restrictions, I am free to build it however it needs to be.

The main issue that boggles my mind is this...

Let's say that I have created a control room using the ideal dimensions from this Sepmeyer ratio, 1: 1.14: 1.39. So starting out with 12' ceilings that would give me 13.68 wide, 16.68 deep and I would sit 6.33 feet back from front wall using the 38% rule. But here's what's unclear to me; all of that is assuming I have a rectangle room.

What happens when I splay the side walls? The whole ideal width of 13.68 feet is then thrown out the window. Or do I make the ideal dimensions occur at the axis of the listening position? So as the side walls splayed out, they would start out narrower at the front of the room and be exactly at 13.68 where my ears are and then continue to get wider towards the back of the room? Where I'm confused is that with splayed/angled walls/ceilings, there is only one spot that would actually be the "ideal" dimension.

The second thing that confuses me is where do you measure from? Example: let's say I build 12' ceiling with three layers of drywall on the ceiling, then I frame in an angled false ceiling a couple feet down and hang bass trap hangers and put cloth over that. I now have two different ceiling heights; one is the "solid" ceiling at 12' with the drywall, the second is the false angled ceiling that you see that's lower (maybe even an additional cloud hanging down further than that). So which one is the actual "ideal" measurement taken from? I would assume it would be from floor to ceiling drywall, ignoring the acoustic treatments in between. The same would be asked of the side walls, because some side walls are false walls with acoustic treatment in front and the hard-surfaced wall behind them some distance.

So this is what I think is correct (please correct me if I'm wrong). Ideal room dimensions using ratios from Sepmeyer and Louden should be measured from one hard/solid surface to another, ignoring any acoustic treatment in between. Also, if there are angled walls/ceilings, make the ideal dimension occur at the axis of the listening position.

That's where I'm at right now. I would appreciate any help or correction in my thought process if I'm wrong.

Thanks,
Rainmaker.

Bumping this one to the top - I'm very curious about this one as well!

rainmaker wrote: Ideal room dimensions using ratios from Sepmeyer and Louden should be measured from one hard/solid surface to another, ignoring any acoustic treatment in between.

Correct!

Also, if there are angled walls/ceilings, make the ideal dimension occur at the axis of the listening position.

The norm is to use the average of the distance. Room modes deal with wavelengths so long that the entire walls act as one unit. that is each wall is homogenous as far as modes are concerned.

Keep asking. The more you know the better studio will be.

Twisted, but not splayed,
Andre

I spent some time reading different links on this great forum & Rod's book & several others. But couldn't find answers to some questions. So, I'll appreciate much if someone can explain in details the following :

- If

Ideal room dimensions using ratios from Sepmeyer and Louden should be measured from one hard/solid surface to another, ignoring any acoustic treatment in between

does that mean the acoustic treatment won't change room modes & will act only as separation to isolate rooms from each other?

- Rainmaker's question regarding wall angles has not been replied. It would be nice to give us more infos on horizontal & vertical wall angles. I've noticed vertical angles in some studios. What are the advantages and what would be the benefits if i angle my inner walls?

- Same for the false CR sealing, what would be the usual angle?

Cheers.

FPR wrote: - If

Ideal room dimensions using ratios from Sepmeyer and Louden should be measured from one hard/solid surface to another, ignoring any acoustic treatment in between

does that mean the acoustic treatment won't change room modes & will act only as separation to isolate rooms from each other?

What we normally refer to as acoustic treatment is not effective at the frequencies of the lowest room modes. That is why we refer to the hard surfaces.

- Rainmaker's question regarding wall angles has not been replied. It would be nice to give us more infos on horizontal & vertical wall angles.

Which question was not answered? To the best of reading ability looking over the thread, all questions were answered. My guess is not clearly though.

Splaying surfaces is a complex subject. For further reading, read this thread.

Keep asking!

Andre

Thanks Andre,
that page was on this forum & i haven't found it!

I think one simple sentence resumes most of all i wanted to know : "Rectangular is more predictible"

Cheers.

Hello,

I know this thread is old, but I have few questions relative to this topic, on which I can't find any answer :

I've read here that "Ideal room dimensions using ratios from Sepmeyer and Louden should be measured from one hard/solid surface to another, ignoring any acoustic treatment in between.../... so we refer to the hard surfaces."

Right, but supposing we already have a rectangle hard surface [8m long, 5m large, 3m to 2,10m height) made of 20 cm width cinderblocks, and on those walls we plan to create 16 cm of fiberglass for walls thermal insulation with plasterboard on it (standard is 13mm in Europe), and even 28 cm for ceiling thermal isolation (typical thicks where I live). And inside all of this "thermal" structure, we create the "studio" walls with wooden structure, with high fiberglass thickness inside walls, wooden diffusors, walls with angles, and so on...
On which surface should we refer ?

Should we take account of plasterboard "thermic" wall for the ratios ? for 13mm ? And for 2x13mm (doubled-glued) plasterboard thickness ? Or definately the hardest and heaviest ones made of cinderblocks ?
Will the "thermal" plasterboard walls acting as an interesting low frequency absorber ? Or should we drill plasterboard a bit to tune the LF absorbing effect and potentially enhance this effect (but closing the holes with thin plastic to ensure air proofing) ? How to calculate the number of holes to each m2 and their diameter ??

Is it also conceivable to flush mount speakers inside the third wall (acoustic wall) made locally of plasterboard + 40 cm fiberglass inside + plasterboard ? / or even with OSB if better (oriented strand board) + fiberglass inside + OSB ?

Thanks for your advices in advance,

Best regards,

Fred

Nobody comments...Too old thread to ask new questions here ?

Nobody comments...Too old thread to ask new questions here ?

There is an announcement at the top of the forum about what to do to assure getting as many responses as possible.
The announcement leads to this post (click here). Actually, several people, who are experts on this forum, will most likely not reply if you don't do what is written in that post. Many others who are very helpful, will most likely not reply out of respect for the moderators' wishes.

You ask a question early on a Sunday morning, and when you didn't get an answer by Sunday evening you want to know why? Seriously? When you don't even want to read and follow the forum rules?

There's only a few people here who could answer your question, and all of us are volunteers. Nobody pays us to provide answers here. We just do it because we feel like helping. We all have family lives outside of the forum, and many of us take Sunday as a day of rest. If we all happen to be busy, sometimes it can take days for one of us to reply to a thread... and you get upset when you don't get an answer in a few hours???

---

we already have a rectangle hard surface [8m long, 5m large, 3m to 2,10m height)

To start with, that isn't a rectangle. The height changes. So you cannot use standard room mode calculators for that, and normal room ratios do not apply. Room ratios and mode calculations are only accurate for rooms that really are rectangular. The example you give is not. All axial mode calculations in the X.0.0 sense will be incorrect, as will all tangential modes in the X.X.0 and X.0.X senses, as well as all oblique modes.

with plasterboard on it ... And inside all of this... we create the "studio" walls with wooden structure, ...inside walls, ... walls with angles,

What you are describing is not clear, but that sounds like a 3-leaf wall at least, and possibly a 4-leaf wall, so you would get rather poor low frequency isolation from that. It would be much better (and cheaper) to build it the way studios are normally built: using only a fully decoupled 2-leaf MSM isolation wall that has sufficient air gap and surface density to attain the desired level of isolation at the desired frequencies.

On which surface should we refer ?

If you only built it with a single layer of thin, low mass 13mm drywall (plasterboard) then both leaves would play a role, and you'd have two sets of modal frequencies in the very low end, at least up to the point where the MSM system is actually doing it's job. Above 1.414 times the MSM resonant frequency, all of the modes would be related only to the inner leaf. Below that, they would be related to the outer leaf.

But if you built the wall correctly, as a proper studio wall, then all of the modes would only be related to the inner leaf.

Should we take account of plasterboard "thermic" wall for the ratios ? for 13mm ? And for 2x13mm (doubled-glued) plasterboard thickness ? Or definately the hardest and heaviest ones made of cinderblocks ?

Use the equations for isolation to determine which modes would be related to each. But once again, if you build the wall properly, as a normal studio wall, then the modes will only be relative to the inner-leaf, as explained above.

Will the "thermal" plasterboard walls acting as an interesting low frequency absorber ?

If you build it as a membrane trap, then yes it would. But if you build it as a proper studio wall, tuned correctly, then no, it would not.

Or should we drill plasterboard a bit

Why would you want to drill holes in an MSM isolation wall? That would destroy the isolation completely, and turn your entire wall into a perf panel resonator. I have no idea why anyone would do that. It makes no sense at all.

(but closing the holes with thin plastic

That makes even LESS sense!!! If you create a tuned perf-panel resonator by drilling holes in a panel, then seal up the holes again, you kill the tuning! The air slug has to be able to move inside the hole neck in order to resonate. Sealing the hole prevents that. So all you have is a useless wall that is not a resonator and is also not an isolator: it serves no purpose at all.

How to calculate the number of holes to each m2 and their diameter ??

Use the equations for perf-panel.

Is it also conceivable to flush mount speakers inside the third wall

Speakers can (and should) be flush mounted wherever possible, to prevent all the artifacts that are created by having a speaker inside a room. But a properly built studio does not have a "third wall"!! It only has a single wall that is made up from two independent, fully decoupled leaves.

made locally of plasterboard + 40 cm fiberglass inside + plasterboard ? / or even with OSB if better (oriented strand board) + fiberglass inside + OSB ?

Why would OSB be better than drywall? What makes you think that?

- Stuart -

First of all, I really apologize if I seemed a little impatient. This is not what I wanted to express in my sentence, I really thought that this topic could be "frozen" so I should perhaps had better to create another topic. My english is not perfect (I'm french) so maybe I didn't use the right formula to express my thoughts. Whatever I have now read the announcement and rules carefully. Indeed, several things missed !
Noticely I forget to indicate my location, and we have to take account of jetlags (hour shiftings) between countries, for instance France for me, Chile for you ! If I remember well I wrote saturday night (french hour) and had a look in the forum sunday in the evening. Anyway, I really did not wanted to urge or annoy anyone here and all my apologies again if I did it unfortunately. I am conscious that everyone here have families and needs a rest. And more, I am very admirative and grateful for the amount and the degree of intellectual gift that many specialists here give to everyone in this forum. As we say in France, chapeau bas (hat there !) for all.

So thanks a lot for your answers, dear Soundman2020.
And please sorry if you feel that my descriptions lacks of precision, that's also the language barrier.

About my previous questions (to close the subject here) :

Rectangle : I wrote "rectangle" to simplify because I don't know how to express in your language this kind of false rectangle with changing height. I am conscious that I can't use standard mode calculators because of this...But I'm wondering how to calculate them then ! AS far I searched, I did not find such calculator which can take account of inclined roofs.

Let's forget my question about drilling holes and making the 2nd [thermic] wall acting as resonator. My idea was just to tune the wall to the highest peak resonance of the room to absorb it, using the thermal wall at least for one acoustic thing. But this is a bad idea, so forget it, since as I explained before, nowadays we can avoid 3 layers walls if needed. I just thought naively that the vapour barrier could close the holes (for thermic reasons) and won't affect LF tuning, but you're right, this is silly, if we block air leaking, even with thin microporous membrane, tuning will be consequently affected since it would limit the air movement as you explained. Anyway, let's forget it and let's concentrate rather to the other questions, since I won't apply this bad idea.

About the 3 leafs, OK, this is acoustically silly. I guessed it, not to says I knew it in advance, but wanted to know exactly what could be wrong with this, and how.
Your answer is very clear. It would generates

two sets of modal frequencies in the very low end, at least up to the point where the MSM system is actually doing it's job.

I had some other questions but I bumped them into a new topic there :

http://www.johnlsayers.com/phpBB2/viewt ... 82#p138882

I did it because I felt that the subjects are a little off of this topic here.

Thanks again for replies, rejoice very much to read further explainations

I wrote "rectangle" to simplify because I don't know how to express in your language this kind of false rectangle with changing height. I am conscious that I can't use standard mode calculators because of this...But I'm wondering how to calculate them then ! AS far I searched, I did not find such calculator which can take account of inclined roofs.

The only way to do that accurately is by using FEM/FEA type software (Finite Element Modeling / Finite Element Analysis), which is something you'd need to hire an expert operator to do for you. But you don't need to do that! You can estimate the modal response of a room that is close to rectangular, using the standard calculators, using the average dimension for the angled part, and taking into account that the result will be close, but not accurate. The greater the angle, the greater the inaccuracy. If the angle is only small, the it will be very close.

Also, the main effect will be on the axial mode for the surface that is angled: the axial modes for the other surfaces that remain parallel will be correct, and so will the tangential modes related to only those surfaces. The oblique modes will all be affected, of course.

I had some other questions but I bumped them into a new topic there :

OK... I'll reply to that thread when I reach it, but I have a string of several other threads in line first, so it might take a while.

- Stuart -