John Sayers' Recording Studio Design Forum Archive

Hi all,
This is my first post so I'm a little nervous about getting it right and following all the rules. Forgive me if I mess up.

I'm getting set to build a studio in Country Victoria (Australia).
It will be on my property and stand alone from the main house.
I'll be getting the foundation, external walls and the roof built as part of the build of my new home and will be doing the rest myself with the help of my Father In Law (who is a builder).
I'm looking at a 14mx9m foundation and a wall height of 2.8m
I want to fit a Control Room, Live Room and 2 ISO booths into this space.
My priorities will be:
a) a Live room that can help me achieve beautiful BIG drum sounds (most of what I will be recording will be of the Heavy Rock variety)
b) a well balanced, flat, clean Control Room

I've been reading the forum and various other sources for a while and I'm learning to use Sketchup.
I also did some university study on acoustics many moons ago ('90-'93) but to be honest most of it is a distant memory so I'm really relearning most of it as I go.
I had a look at http://www.bobgolds.com/Mode/RoomModes.htm
and played with some ratios for my control room based on what I understand should give me a reason starting point.
The CR dimensions I came up with are these:
H: 2.80m; W: 4.58m; L: 5.50m
I am however struggling a little to interpret that data so any help in that area would be hugely appreciated.
Am I on the right track with these dimensions?

Noise in a quiet neighborhood is obviously going to be a challenge. I'll looking at needing to take a 115+dB drummer inside my LR down to somewhere around 40dB at my fence line (roughly 3m from the studio wall). Here is my wall construction plan (see Wall Structure pic below):
Leaf1: rendered ext wall (270mm) either Double Brick or Bessa Bricks filled with concrete w/ a 150mm gap filled with insulation.
Leaf2: 2x16mm Plasterboard (green glued) on reversed stud wall with insulation and speaker cloth cover.
Do you think this is a good plan or do I need more 'beef'?
Any ideas about whether there is a significant difference between Dble Brick and Bessa w/ concrete in terms of isolation? So on to the CR layout (see Control Room Pic below). I am thinking of large sliding glass doors (3 standard door widths) on both the north (leading to LR) and south side (leading outside). I hoped this solution would give me a good view into the LR and bring in some light from outside. I have positioned the doors so as to allow for a couch at the back of the room and also so as not to encroach on proposed absorption for first reflections (assuming a listening point at the 38% the length of the room). In terms of isolation I guess I will need 2 lots of doors on each side and some thick glass.
I suppose the question is how thick is thick?
And more importantly is this a reasonable solution or am I asking for trouble here?

As for speaker placement. I have drawn in guidelines using an equilateral triangle from the listening point.
Any suggestions about soffit vs stands for this room. I like the idea of soffit but I am struggling to see how it would work in this room.
Do I have to set them back in the existing wall?
OR
Bring the wall out further to accommodate them?
OR
Leave the space between the speakers as is and bring the outer sides out in order to create an angle for the speakers?
If either of the later is the case would that mean I'd need to recalculate my room dimension for Room Modes?

Lastly (for now haha!) I am wondering about placing small windows in the back wall of the control room so as to have a line of sight into the 2 ISO booths. Do you see this posing a problem acoustically? Thanks in advance for any help and thanks so much also for all the existing info on this forum. What an incredible resource to have. You guys rock!

Hope I've been clear enough with my questions. Be gentle

Tim

Hi there Tim, and welcome to the forum!

This is my first post so I'm a little nervous about getting it right and following all the rules. Forgive me if I mess up

IT looks like you ticked all the boxes perfectly!

I'm looking at a 14mx9m foundation and a wall height of 2.8m
I want to fit a Control Room, Live Room and 2 ISO booths into this space.
My priorities will be:
a) a Live room that can help me achieve beautiful BIG drum sounds (most of what I will be recording will be of the Heavy Rock variety)

The height is fine for the control room and iso booths, but if you could go higher for the live room, that would help with your goal of "beautiful BIG drum sounds". Drums sound better in fairly large spaces, especially if you plan to have overhead mics on them, so the rule here is "the higher, the better". If you could figure out how to get more headroom there, that would be great. For example, how about digging a bit deeper where the LR will go, and having a step (or two) down? That would keep your roof line the same while still giving you more headroom.

If not, then 2.8m is OK, but more would be better.

The CR dimensions I came up with are these:
H: 2.80m; W: 4.58m; L: 5.50m

That's a nice large CR, so it bodes well for meeting your goals. However, a couple of comments on that:

1) You say the wall height will be 2.8 m, so it's hard to see how the finished ceiling height can also be 2.8m, while also attaining high isolation! You will lose a fair chunk off of that 2.8m for the isolation system of your ceiling, probably around 15 to 20 cm, maybe more. Even if you went with "interleaved" joists, or with an "inside-out" ceiling, you'd still be losing at least 5 cm, so I can't see how you would end up with 2.8 m for your finished inner-leaf ceiling height.

2) the ratio isn't that good. if you look part way down the page on Bob's calculator, on the right, you'll see a section of text under the heading "Computed Information:" Part of that is a set of three BBC critical tests. You are failing one of those tests, because "ratio3 = ratio1 * 2". In other words, your length is almost exactly twice your height, or within 5% of each other. If you check the list of modal resonance frequencies, you'll see this:

61.5 hz 20.4% 5.6 : 2.8 : 1.4 (0,0,1 Axial)
62.6 hz 1.7% 5.5 : 2.75 : 1.38 (2,0,0 Axial)

And also this:

123.0 hz 2.1% 2.8 : 1.4 : 0.7 (0,0,2 Axial)
125.2 hz 1.7% 2.75 : 1.38 : 0.69 (4,0,0 Axial)

In other words, those two modes, and all of their harmonics, will line up nearly perfectly, so basically when an instrument plays those notes (or close to them), BOTH modes will potentially be triggered, doubling your problem. One mode could also easily decay in to the other, causing strange things to happen. If you follow Wes Lachot's philosophy, then you should also aim for musical relationships between fundamental modal frequencies, which also implies that you should try to get the modes aligned with actual notes. That just makes sense, actually: if not, then as the instrument note itself dies away, the related mode can die away at a slightly different frequency, thus creating strange BFO effects.

So you would need to change your dimensions a bit. For example, making them 5.55 long, 4.16 wide and 2.62 high improves things considerably, as that hits B's, E's, G#'s, D's and C's with your first few modes, and also improves the modal spread. Plus, it passes all three "BBC Critical" tests, and also brings your inner-leaf ceiling height down to a feasible level. But you could probably find other good ratios by playing around a bit. Here's another calculator that you might find useful, as it displays things in a slightly different way, and also "auralizes" the modes, so you can actually hear what they sound like: http://amroc.andymel.eu/

I'll looking at needing to take a 115+dB drummer inside my LR down to somewhere around 40dB at my fence line (roughly 3m from the studio wall).

That's a pretty tall order! 75 dB of isolation ain't easy to accomplish. OK, so let's allow for that 3m distance to help you a little, and say that you need 70 dB of isolation at the standard 1m distance from the wall (theoretically, that would decay to 72dB at 2m and 69dB at 4m). So, 70 dB.... Hmmmm and a lot of that in the low end (drums). Hmmm.... You sure do have your work cut out for you! It is do-able, but not easy. What you need: mass (huge amount of it!) damping (oodles) and air space (truck loads).

On the plus side, you are starting out with Besser brick, which is reasonable mass, and good down to reasonably low frequencies. But nowhere near what you are aiming for. You did mention filling them with concrete, but I would also suggest filling them with sand: Sand will help with damping, to a certain extent, and also has plenty of mass: around 1800 kg/m3, which is pretty close to concrete. So assuming standard besser blocks (190mm thick), you'd be looking at a surface density of around 380 kg/m2, which implies around 48 dB of isolation overall, maybe 50 if you are lucky. Still far short of the 70 you need. That would fall to about 30 dB of isolation at 30 Hz, which is not bad, but still not as good as you need.

Clearly mass law alone is not going to provide what you need (it never does!). But you already knew that, and added an inner-leaf of 2x16mm drywall over a 150mm air gap, for a true MSM system. Theory says that the combination will give you an MSM resonant frequency of about 22 Hz, and your wall will isolate well above 43 Hz, with total isolation estimated at about 67 dB (I'm developing an "isolation estimator" spreadsheet right now, but it isn't ready for public consumption yet as it makes a lot of questionable assumptions. But FWIW, that's what it predicts for your wall). Adding one more layer of drywall and increasing your air gap to 180mm would get you to 69 dB (according to my spreadsheet), but in reality probably a bit more. I would also stucco (plaster) the outside surface of that wall, and seal the inside surface with masonry sealer (or even just paint), to improve the isolation that extra bit. Or even plaster the inner surface as well: extra mass plus good seal: that would get you a touch over 70 dB, I reckon.

So from that point of view, you'd be good to go. Theoretically...

However, at high levels of isolation such as that, you are getting close to the flanking limit for your concrete floor, especially considering that drums are involved (impact noise as well as airborne noise), so you might want to consider pouring the floor of the control room as a separate isolated slab. Since you are building from the ground up, that does not increase cost or complexity much at all: it just involves a bit more concrete for the monolithic footer for that slab, and a bit more work in keeping it separate, but no big deal. You would then build your inner-leaf walls on top of that slab, totally isolating the inner-leaf from the outer leaf.

That would take care of things down below (the slab) and to the sides (the walls) ... but what about up above? Isolation is an "all or nothing" proposition, requiring that you maintain the same surface density of each leaf around the complete building shell. Since your outer-leaf walls and floor are basically thick concrete, you'd have to do the same to the roof to complete the outer shell. So that implies that the roof over your studio will be flat concrete slab. That's the only way to get the level of isolation you are talking about, at reasonable cost.

Isolation is only as good as the weakest link. If you build your walls and floor to 70 dB, but your roof is only good for 40 db, then your total isolation is 40 dB. Period. And of course, whatever gets out through the roof will be just as audible for your neighbors as it if went out through the walls: Especially low frequencies, which are not directional.

So your roof is going to need to have the same surface density as your wall and floor, if you want 70 dB of isolation.

OK, so assuming you already have that resolved, and your entire MSM system will be done to the same 70 dB level all around (walls, floor and roof), the next issue is doors / windows. Getting 70 dB for walls is relatively easy, compared with getting 70 dB for doors, since doors have to open! Your doors will need to be extremely massive, and extremely well sealed. I would suggest triple rabbeted seals on all doors, all around all the perimeters, and I would also suggest using a pair of Rod Gervais style "superdoors" back to back. You will need to heavily beef up the framing for those doors too, of course, to support the huge weight. Hanging a couple of hundred kg on ordinary frames is going to bend them substantially, and perhaps break them, considering the moment arm. Heavy duty hinges are also needed, of course. With a couple of those doors and a sufficiently large air gap between them, you should be able to get in the general ball-park of 70 dB, but it will require careful work and good precision with the seals.

Then come windows: Thick laminated glass is your only option, but you probably already knew that.

And finally, the least-considered but most important aspect of studio isolation: HVAC. After you have built your two perfectly sealed, perfectly decoupled, extremely massive leaves, you then have to chop huge holes in them to get your HVAC ducts through! So you are going to need silencer boxes ("baffle boxes") on all penetrations where a duct goes through a leaf, and they will also have to be massively built, in order to retain the level of isolation you are talking about.

So overall what you propose to do can be achieved, but it does require careful design, careful planning, and careful construction. It also requires a pretty big budget. You didn't mention how much you plan to spend here, but at a rough estimate, from what I understand of Australian building costs, I would estimate somewhere north of $100,000.

I am thinking of large sliding glass doors (3 standard door widths) on both the north (leading to LR) and south side (leading outside).

Sliding glass doors are really nice in studios, and for the path from LR to CR that's certainly a good option.

However, from the CR to outside? I don't think that is on. There's no way you'll get 70 dB from a pair of sliding glass doors. 50 dB maybe, with luck, but 70 dB is a hundred times harder (100 times the sound intensity). I would suggest no doors at all on that wall: Maybe a window, of you want natural light, but no doors.

In terms of isolation I guess I will need 2 lots of doors on each side and some thick glass. I suppose the question is how thick is thick?

Right. Thick glass. How thick? Thick enough to maintain the same surface density as the rest of the wall. So for your inner leaf: Drywall weighs about 12kg/m2, three layers will be about 36 kg/m2, glass is about 2500 kg/m3, so to get 36 kg/m2 you would need a thickness of about 15mm thick, so probably a 7+8 laminate would work fine for that, or 8+8 to be safe.

For your outer leaf: your besser brick wall is coming in at about 380 kg/m2, so to maintain that you'd need about 15 cm thick. Yes, that does say 15 centimeters, not 15 millimeters. So your best bet for that if you want natural light and high levels of isolation, would be glass bricks. Solid ones. If you wanted to go with normal glass, then you might have to go to a three-leaf system with two leaves on the besser brick wall, using say 12+12 mm laminate on the middle leaf and 10+10 on the outer leaf, then maybe 9+9 0n the inner leaf (drywall). I didn't do the calculations on that, and I might be over-estimating a bit, but it's probably not far off from what you would actually need.

From the above, you can see why I said that sliding glass doors are out of the question, for 70 dB of isolation to the outside world.

As for speaker placement. I have drawn in guidelines using an equilateral triangle from the listening point.

Right, but you have the triangle apex incorrect, in what is actually a very common misconception: Your ears are on the SIDE of your head, not the FRONT, so if you want the acoustic axes of the speakers aimed at your ears, then the apex of the triangle actually has to be located a distance behind your head, not inside your head. The normal recommendation is that the axes intercept about 20 to 60 cm behind your head. That means you have to move your speakers further apart, or reduce the toe-in angle a bit, or both.

Any suggestions about soffit vs stands for this room. I like the idea of soffit but I am struggling to see how it would work in this room.
Do I have to set them back in the existing wall?
OR
Bring the wall out further to accommodate them?

Soffits provide major advantages in practically any room, and IMHO soffiting your speakers is about the single most useful thing you can do to eliminate many of the artifacts associate with having speakers inside a room. In your case, you would build the soffits within the inner-leaf, extending into the room diagonally across the front corners of the room.

If either of the later is the case would that mean I'd need to recalculate my room dimension for Room Modes?

Correct: modal response refers to the massive, rigid, hard, solid reflective inner-leaf boundary of the room, which is the front face of the soffits.

Lastly (for now haha!) I am wondering about placing small windows in the back wall of the control room so as to have a line of sight into the 2 ISO booths. Do you see this posing a problem acoustically?

How about turning your CR around so it faces those booths? That way you have direct sight lines into them... Even better; turn the room to face the LR, with a window into that too, then put the booths on either side of the angled front walls of the CR, also with windows. Best case, all around...

Hope I've been clear enough with my questions. Be gentle

Very good first post! I wish all first-posts were as clear, concise, and well thought out as yours. Good job!


- Stuart -

Well Stuart let me start by saying WOW!!!! Thank you soooo much for your brilliant response.
That Mode Calculator (and your explanation of the musical nature of the room Modes) made everything so much clearer.
I played with the calculator for a while and (of course) your suggestions for dimensional changes were spot on.

The roof was always the part I was most afraid of. I suspected that a good level of isolation was going to come down to the integrity of the roof.
I didn't wanna go there in my first post mainly cos I was interested in seeing your response to the wall design but also because from a structural perspective the roof is much harder for a novice like me to conceive. I have lots of questions

It seems that I will be pushing *bull gunk* (my new favorite substitute word from Adventure Time) up hill trying to achieve a 70dB drop. Especially without a slab roof and I'm skeptical about achieving such an engineering feet.
So, I think its time to lower my expectations slightly as well as rethink some plans.

A word on budget ( SHOULD HAVE MENTIONED THIS IN THE FIRST POST ). I want to get the foundations, exterior walls and roof all in for about $50k if I can (I haven't looked into it yet but I would assume that a concrete roof would be well outside my budget).
As a side note: I'm lucky enough to have a mate who is doing a complete tear down of an old studio and we are negotiating a price for me to take a good chunk of that building material at a heavily discounted price. I am keen to get a solid plan in place for my build so we can work out exactly what I will need and how much of that we can salvage from the old studio.

I was thinking about a Gabled roof initially. Particularly for the LR as a way of maximizing interior space but I live on the coast and high winds would probably count this option out. I think your suggestion of going down to get more head room is probably the most practical (I was considering this in general anyway since 2.4m is the standard wall height in Aust and sinking the slab 400mm might be preferable when attempting to get council approval instead of asking to have an out building that is higher than the main house. Incidentally the main house will be built at ground level with a standard ceiling height. Perhaps I can set down even further. Maybe 800m down for finished ceiling height of 3m in the LR and ISO's. Being coastal I would have to look into the ramifications of doing this. Don't want to have to swim from the LR to the CR

So how to get decent isolation from the roof without putting a dirty big concrete slab up there?
The main house will likely have a Hipped roof and so it would probably be best to have the same on the studio.
Am I correct in thinking that when building a Double Brick or Bessa design (ie. not a Veneer which is the common way in Aust) that the Trusses are supported by the exterior walls and therefore part of the OUTER leaf?
And if I am correct then is it a matter of hanging as much plaster and heavy insulation as the roof can handle?
Do I then need to run joists that are supported by the INNER leaf which intern holds as much plaster and heavy insulation as they can handle while maintaining an air gap between the it and the Trusses above?

While I'm on a roll...back to the original design...
My orig design came about for a few reasons.
1) I chose to orientate the CR sideways as it allowed space to slip the ISO boots up the side and not encroach on the floorspace available for the LR.
2) It also meant that I could have the CR longer than it is wide which means band members sitting on couches at the rear of the room would be as far a way a possible from my work area.
3) I placed the speakers on the wall opposite the ISOs cos I was thinking that soffit speakers set back in the inner leaf might be getting a little close to the action in the booths (they will probs have cranked Marshals blasting in them at various times) and make it more difficult to keep them well isolated.
4) I chose to place sliders between the CR and LR to maximize the view between the two rooms
5) I chose to place sliders in the CR on the wall opposite the LR in the interests of symmetry since I'd read that it was paramount when designing a CR

Having said all that the obvious impracticalities you've pointed out for achieving the level of Isolation I want with all this makes it pretty much out of the question.
I am entirely open to changing things around to get a better result in terms of acoustics, isolation and functionality as well as reduce costs of course.
BUT I have a question:
Given that the CR will not be pouring out anywhere near the kind of dB levels of the LR and ISOs (I'm thinking more like 90dB max for any length of time) should I be able to get away with slacker restrictions between the CR and the outside world?
OR
are they effectively the same because the Outer leaf surrounding the CR is not decoupled from the one surrounding the LR and ISOs?
If the later is true could I completely decouple the CR from the other rooms and therefore relax my Isolation requirement a little for that part of the build?

Tim

I know I haven't given you an opportunity to respond to my last post yet. My apologies but a quick question...
Given that my interior wall is to be inside out should I be measuring my room dimensions from the plaster rather than the cloth?

Given that my interior wall is to be inside out should I be measuring my room dimensions from the plaster rather than the cloth?

Correct. All room dimensions are measured to the hard, solid, massive, rigid boundary surface of the room.

- Stuart -

OK excellent! Now I know where I'm measuring from. Good start.
So Speaker Placement is the next thing I am having a crack at.
I've had a read through the Control Room section of The Master Handook Of Acoustics
and had a search around the forum for info on RFZ and although I think I have a handle on the concept I am still a little confused as to how to put it into practice.
Not exactly sure about how to go about working out what the angles need to be.
Perhaps you could point me in the right direction.
Anyway based on a few 'rules of thumb' I've picked up I came up with the layout below for my speaker placement.
* I have not taken into account height and/or forward tilt (if nessasary) yet.

1) Ideal speaker placement is 28% in from each side wall
2) Ideal speaker angle is 30degrees from the front wall
3) Ideal Listening Position 38% up the length of the room.
4) Actual Listening Position adjusted forward to allow for the spacing of the ears

Am I on the right track here or am I missing something?
Assuming the soffits follow the line of the speaker faces and that I want a window between the speakers out to my LR.
How far back should the front panel/window to the LR be?

*NOTE: in the diagram I have only shown the Plasterboard as it is the place where all the measurments are being taken from.

3) Ideal Listening Position 38% up the length of the room.
4) Actual Listening Position adjusted forward to allow for the spacing of the ears

You are sort of contradicting yourself there: The LISTENING position is where your EARS are... For most people, their ears is what they listen with..... In other words, it is your EARS that should be at the 38% mark, then adjust the speaker position/angle/separation to get the triangle correct, so that the acoustic axes pass by your ears, and intersect a distance behind your head.

Also, don't forget that all of the above are just GUIDELINES: nothing is written in stone. They are theoretical good places to start from, but you can adjust as needed. You will not be arrested by the Speaker Triangle Police if your ear location is not exactly 38%, or the angles are not exactly 30°! Way too many people take these starting points waaayyyy too seriously, and attempt to nudge things around by millimeters and fractions of a degree, when it just is no necessary at all. The same rules apply as for room modes: As long as you are reasonably close to a good set of dimensions, then you should be fine People seem to forget that just reaching for the trim pot on the console, or turning your head a bit to look at your mouse, or leaning back in your chair, puts your head way out of whack with all of the above: the distances are now many inches off, and the angels are totally screwed. Yet you can still hear things pretty well...


- Stuart -

OK got it. As N.W.A. said F**k Da (Speaker Triangle) Police!!

So on another note I have redesigned my layout with the new optimized CR dimensions (measured from the rigid walls)
I've resized the ISO rooms to be (what I think are) better dimensions.
As well as doing away with the large windows on each side of the CR I've added an entry which will also include a storage cupboard. The entry hall will remain untreated and I'm anticipating it coming in handy for some ambient micing as well now and then.
The LR basically just takes up the rest of the available space I have so I am yet to deal with it from an acoustic perspective. The CR has the speakers placed where I think they will work well.
The picture below shows 3 ray traces of the angles that helped me understand where first reflections will effect the listening position. If I'm understanding the concept correctly, if I can defuse reflections off the side walls beginning from the edges of the soffits back to the line marked by the yellow ray reflection and defuse reflections of the back wall I should have a relatively reflection free zone inside the blue area.
**I have not considered desk reflections yet and I'm anticipating needing to raise the speakers and tilt the front wall to cope with that. Once I get that sorted I'll look at how to frame up the window through to the LR and what to do about doors.
Am I doin OK so far?

That's looking better!

A few more comments:

Is that glass on the front wall, and also on the soffits? There's no problem with glass on the front wall (I do that all the time), but wrapping it onto the soffits as well might be a big challenge, from the construction point of view. It can be done, but it makes things very complex to build.

The picture below shows 3 ray traces of the angles that helped me understand where first reflections will effect the listening position.

Right. That is, indeed, the correct way to ray-trace. And as you discovered, you will have reflections coming off the side walls, getting back to your head. So yes, you need treatment on those points.

If I'm understanding the concept correctly, if I can defuse reflections off the side walls beginning from the edges of the soffits back to the line marked by the yellow ray reflection and defuse reflections of the back wall I should have a relatively reflection free zone inside the blue area.

I wouldn't use diffusion for that: diffusers create "lobing" patterns for the scattered sound, in both the time and frequency domains (and therefore phase domain too), within a radius of about ten feet from the diffuser, and perhaps even further if the diffuser is tuned to lowish frequencies. So you don't want your ears within ten feet of a diffuser. That's why you will frequently see the recommendation here to not use diffusion at all in small rooms, such as typical home studios. It is fine in f the room is big enough, but with small rooms it is usually impossible to have all seating at least ten feet away from diffusers.

Just use absorption in your first reflection points. At least a 4" thickness of OC-703.

Another option, instead of diffusing or absorbing on those wall sections between the soffit and the doors, is to angle those by several degrees, so that the reflections themselves never get to your head: That's the way to do a true RFZ: Angle the side-front wall sections to send all reflections behind your head to the back wall, where you have thick absorption (really thick!) that takes care of them. The concept of RFZ is that no first reflections get back to your ears until at least 20ms after the direct sound got there, and even then they come in at a level of about 20 dB quieter, and more diffuse, as a soft reverberant field. So there's a 20 ms ITDG (Initial Time Delay Gap), followed by the ambient field. That 20/20 rule can be relaxed a bit in small rooms, and 15ms/-15db is still fairly decent.

**I have not considered desk reflections yet and I'm anticipating needing to raise the speakers and tilt the front wall to cope with that.

Think about that carefully! If you raise the speakers up then tilt them down, you now have MORE reflections from your desk / console surface hitting your ears! Try ray tracing both options (no-tilt and tilt), and you'll see what I mean. The best way to minimize reflections off the console surface is to have the speakers as far away from the desk as you can get, so the sound hits at a more glancing angle, and therefore bounces off into your stomach and chest, not your head. That's another good thing about soffit mounting: it does indeed put the speakers as far away as is physically possible. You should be fine, from that point of view. There's a couple of other tricks you can use to minimize desk reflections...

One other comment: I would make your couch a bit smaller, and use the space in the rear corners for superchunk style bass traps. I would also bring it away form the rear wall a bit, and use the space there for deep hangers.


- Stuart -

Is that glass on the front wall, and also on the soffits? There's no problem with glass on the front wall (I do that all the time), but wrapping it onto the soffits as well might be a big challenge, from the construction point of view. It can be done, but it makes things very complex to build.

I tried making the window smaller just to fit in the straight glass but the field of vision into the studio was pretty bad. Massive blind spots on both sides but the left particularly.
I've got a pretty wacky window set up going on with a wider window in the LR but it allows for a 60degree field of vision from the CR chair. I had a chat with my builder and he reckons it can be sorted. As you can see from the pics the white box in the corner is clearly visible. With a little head turning I should be able to see most of the room from that vantage point.

Another option, instead of diffusing or absorbing on those wall sections between the soffit and the doors, is to angle those by several degrees

I had a go at this before I submitted my post with the ray tracing on it and I found it difficult to get the angles to work unless the angled wall started right up against the outside of the speakers. I was under the impression that the speaker would not behave nicely if they were to close to a corner. Is that true?

I've added some 4" absorbers to the side walls.
Just wondering am I correct that the rest of the insulation should just be standard home insulation?
and if so could I replace the standard insulation that is behind the cloth in the side walls (90mm gap) with OC 703?
I was thinking then once the room is built if tests show it needs beefing up I could add a second layer in a frame.

There's a couple of other tricks you can use to minimize desk reflections...

Did some more ray tracing and as you suggested the desk (particularly with the the console on it doesnt seem to pose much of a problem.

I would make your couch a bit smaller, and use the space in the rear corners for superchunk style bass traps. I would also bring it away form the rear wall a bit, and use the space there for deep hangers.

I wanna keep the couch big if at all possible. I know from experience how frustration it can be sitting squashed up with 4 blokes on a couch in someones studio.
Wanna keep things as spacious as possible. Of course if it has to be done it has to be done.
In the pic below I've added 2 x 24" superchunks and just a couple of 4" absorber panels. Not enough I know but ...
a) how deep do the hangers need to be. Any more than about 600mm and things are starting to look seriously cramped.
b) would the hangers need to go right across the back wall with the superchunks set in front of them? OR can I leave the chunks where they are and run the hangers across the back. I'm thinking 600mm wide strips on a 45degree angle would only have to come out 425mm. **the purple lines on the image below. Does that sound acceptable?

I found it difficult to get the angles to work unless the angled wall started right up against the outside of the speakers.

I just noticed that you seem to have your speakers too far apart, and your listening position too far back in the room. Your EARS should be at the 38% mark, NOT the intersection of the acoustic axes, which is what you have now. so move your speakers closer together (and get them out of the middle of the baffles too!), and re-position your desk and chair to get the correct geometry. With your head closer to the front wall, you'll have better sight lines to the other room in any case.

I was under the impression that the speaker would not behave nicely if they were to close to a corner. Is that true?

Right, but that's not really a corner if the side wall is angled enough: it becomes more of a low frequency wave guide, something like a horn, and the angle is what you need to calculate such that the wave interaction (SBIR) is not causing too much of a low frequency dip at that mix position. From that point of view, having the angled wall is better than having the non-angled wall! Plus, the wall won't need to be tight up against the speaker.

Just wondering am I correct that the rest of the insulation should just be standard home insulation?

Normally that is fine. If it is fiberglass then look for stuff with a density of around 30 kg/m3, and if it is mineral wool then it needs to be more like 50 kg/m3. The best stuff is, indeed, OC-703. Almost nothing beats 703.

and if so could I replace the standard insulation that is behind the cloth in the side walls (90mm gap) with OC 703? I was thinking then once the room is built if tests show it needs beefing up I could add a second layer in a frame.

So you are doing inside-out walls? Excellent! You'll probably find that 4" of 703 is more than enough, and will in fact make the room too dead. But that's fine: it gives you the option to add slats to create a slot wall, or perhaps other treatment.

In the pic below I've added 2 x 24" superchunks

Well, you COULD go down to 24" superchunks, but normally you'd want 36" for a room that small.

a) how deep do the hangers need to be. Any more than about 600mm and things are starting to look seriously cramped.

That's fine. You can get hangers into that depth.

b) would the hangers need to go right across the back wall with the superchunks set in front of them? OR can I leave the chunks where they are and run the hangers across the back.

If you go with hangers, you could skip the superchunks, continue the hangers all the way across, and make bigger hangers for those corner areas, then put a panel of 703 in front of them (just behind the fabric) to finish off. That works very well.

And you need to angle the hangers opposite ways, symmetrically. The ones on the left side of the wall face one way, and those on the other side face the other way.

I'm thinking 600mm wide strips on a 45degree angle would only have to come out 425mm. **the purple lines on the image below. Does that sound acceptable?

that should work, yes. Then put 10cm of 703 in front of those too, plus fabric, for a total depth of around 550 mm. That would be really good bass trapping and rear absorption for your room.

- Stuart -

I just noticed that you seem to have your speakers too far apart, and your listening position too far back in the room. Your EARS should be at the 38% mark, NOT the intersection of the acoustic axes, which is what you have now. so move your speakers closer together (and get them out of the middle of the baffles too!), and re-position your desk and chair to get the correct geometry. With your head closer to the front wall, you'll have better sight lines to the other room in any case.

I think you may be referring to an an earlier post with what you've said here. I changed those values based on your suggestions from my original Speaker Placement post.
My listening position is in fact 38% from the front wall.
Granted the desk was a little close to the listening position (fixed that)
The intersection of the acoustic axis is 600mm behind that.
The speakers are at a 60degree angle from the axis.
The speakers are not in the middle of the baffles they are 670mm from the front wall and 770mm from the the side walls.

So from what I understand the only 'rule' I'm not following is that the speakers do not sit 28% from the side walls.
Are you suggesting that I compromise the 60degree speaker angle to get closer to the 28% position?
(note: I'm working on the angled wall. The blue part of the walls shows the sections that still cast reflections to the listening area. I can see how bringing the speakers in will allow me to angle those walls more and reduce the reflections further.

If it is fiberglass then look for stuff with a density of around 30 kg/m3, and if it is mineral wool then it needs to be more like 50 kg/m3. The best stuff is, indeed, OC-703. Almost nothing beats 703.

OK thanks.

You'll probably find that 4" of 703 is more than enough, and will in fact make the room too dead. But that's fine: it gives you the option to add slats to create a slot wall, or perhaps other treatment.

Interesting. I definitely don't wanna suck all the life out of the room. I'd rather add some absorption where necessary rather than over do it and have to compensate. I guess this is one of the advantages of the inside out walls. You get to add that stuff last.

Thanks for all the hanger advice. All taken on board and processing. I will try a couple of layouts and see what I come up with.

Stuart,
I'd be really interested to see your reaction to my last post.
Particularly with regard to making compromises to the 'rules of thumb'.
I've taken on board your thoughts about the Triangle Police and that these so called 'rules' are just guidelines
but which guidelines should do you think I should follow more closely than others and how much of a stretch is too much?

Here's a couple of scenarios. Which do you think is the preferable one?

1) I maintain the 38% listening position but bring the speakers in closer together.
This would compromising the 60 degree speaker angle and decrease my lines of sight.
BUT it would allow me to get the speakers closer to 28% from the side walls AND enable me to increase the side wall angles for less first reflections.

OR

2) I compromise the 38% listening position and bring it closer to the front wall while also bringing the speakers in closer together.
This would maintain the 60 degree speaker angle and leave the line of sight more or less the same.
This would also get the speakers closer to 28% from the side walls AND also enable me to increase the side wall angles for less first reflections.

OR

(as it is now)
3) I maintain the 38% listening position AND the 60 degree angle by leaving the speakers further apart.
This would compromise the 28% position from the side walls making it more like around 18%.
It would also restrict my ability to angle the walls and decrease first reflection.

OR

4) make a compromise on all fronts so as not to impact any of the tolerances too much?

OR

5) none of the above. Your are over thinking it. Stop being a tool and just build the thing already!

Here's a couple of scenarios. Which do you think is the preferable one?

Hmmmm... tough call! But I think I'd go with #2, and a bit of #4. It's a bit of a juggling act, as you play around with several parameters at once and try to come up with a good compromise. None of the factors is "life and death", yet all of them are important, to some extent.

So it helps to understand what each of them is about:

38% is all about modal response of the room. It is the theoretical point where modal peaks and nulls are at the best compromise. 50% and 25% are bad here, and anywhere in the range of roughly 33% - 43% is "not so bad".

60° speaker angle is all about stereo imaging, sweet spot, and sound stage. If your speakers were not angled at all (0° both facing straight back down the room), then your ears would not be "on axis" to the speakers unless they were right next to each other, slammed together in the middle of the room. However no matter where you go in the "forwards or backwards" sense, the levels of the speakers would match exactly, and so would the phase. There is no point in the room where the two axes intercept. Also, your left ear would "see" the right speaker very well, and vice-versa, at about the same level and arrival time. The same is true as you turn your head side to side. So not too much stereo image there, and almost no width to the sound-stage, but what little imaging there is, is in a broad and deep sweet spot. And great for people sitting on the sofa at the back: they hear almost exactly the same as what you hear. Go to the other extreme, with the speakers on the side walls facing each other across the room and your head in the middle: Now your left ear cannot hear the right speaker at all, and vice-versa, since your head is "shadowing" them crosswise, so you have fantastic sound-stage width. The levels, phase and arrival time match only when your head is perfectly in the middle. Move your head even a fraction left or right, and your ears are hearing very different levels, different phasing, and different flight times. Also, move your head forwards/backwards even a bit, and your ears are off-axis to the speakers. So the sweet spot is very small and narrow, and you basically need your head held by a rigid frame to keep you in it! But the stereo image is amazingly wide and incredibly detailed, sort if like with headphones or ear-buds. And the guy sitting on the sofa hears nothing at all like what you hear: in fact, he hears garbage. The 60° intercept (speakers angled 30°) is a good compromise between those extremes, but basically anywhere from about 45° to 90 intercept is fine. In other words, anywhere between 15° and 45° angles for the speakers. Less that 15° and the end up too close together, less sound-stage but large sweet spot etc. More than 45° and your head starts shadowing, great sound stage but smaller sweet spot, etc.

And finally, speakers at 28% width is the point where, theoretically, there is the least objectionable interaction between the speakers and the side walls, in terms of SBIR, so the least distortion of the frequency response curve, etc.

Oh, and one other: having the speaker in the center of the soffit front baffle is also the worst location from that point of view, as the interference patterns all line up to create peaks and nulls in the response curves. so keeping the speaker offset from the center (both left/right and also top/bottom) as much as possible is a good idea. But here too there is obviously a compromise: if you put the speaker too close to one edge of the baffle, then you lose the very effects you were aiming for with the soffit! Power imbalance correction, minimizing SBIR with the front wall, minimizing comb filtering, phasing issues, etc.

So it's just a matter of trading off what is least important for you, in that room, and maximizing what is most important, while still maintaining a practical, usable, good looking room.

Sorry I can't be more specific! All rooms and goals are different.


- Stuart -