John Sayers' Recording Studio Design Forum Archive

A couple quick questions regarding my next design...

I was reading a post that "knightfly" made on this thread about air gaps in iso walls...

The more space you can leave between the outer and inner mass leaf, the better your iso, especially in the bass region - 8" is good, 12" is about the max before it doesn't help much. Generally, use as much space as you can up to 12", and fill with insulation.

My design currently shows a 15" air gap between the double drywall of the inner walls (room to room)...is this wasting space considering knightfly's post? Should I bring this back down to 12"?

One other question...I'm trying to figure out how much space I need behind/around the monitors in the soffits (so between the back/sides of the monitors and the drywall isolation wall)...from what I can tell in all my research it seems like the more space the better since it allows for extra insulation etc. and therefore more mass. I'm trying to balance this out while also pulling the listening position closer to the front of the room...I'm tempted to go with something like a 70º or 75º intersect point so that I can keep the glass width that I have, pull the mix position forward, and keep enough space behind/around the monitors in the soffit (it also helps eliminate one of the shorter first reflection points)...does this sound reasonable? Is there a standard for space behind/around the monitors in a soffit design?

Also, Stuart I've done some quick calculations after pulling the mix position forward (almost 2') and it looks like with the shortest first reflection path I have a 17ms time delay between the initial signal reaching the ears and the first reflection reaching the ears. That may be the most I can get out of this room but I figure that's pretty good! BTW I added an extra 6" to the bottom and side of the control room since I had the space to spare in accordance with the 5' to property line code...the extra half a foot helped get that 17ms. I'll post a more detailed analysis and drawing soon...

Thanks!
Trevor

My design currently shows a 15" air gap between the double drywall of the inner walls (room to room)...is this wasting space considering knightfly's post? Should I bring this back down to 12"?

Yeah, 15" is overkill, assuming that you have plenty of mass on each leaf. The relationship is not linear: isolation drops off very fast for gaps smaller than about 4", increases well up to about 8", less so up to about 10", and even less after about 12": the curve gets flatter and flatter. So you could probably bring that down to 12", or maybe even 10", depending on how much isolation you need, and what frequency you need it at.

One other question...I'm trying to figure out how much space I need behind/around the monitors in the soffits (so between the back/sides of the monitors and the drywall isolation wall)...from what I can tell in all my research it seems like the more space the better since it allows for extra insulation etc. and therefore more mass.

More space is useful, but it isn't lie or death. The insulation inside the soffit cavity is just there to provide some damping, not really for isolation, and the mass isn't too important: You can use that cavity as your "insulation dump", for all the offcuts of insulation from the rest of the build, as well as anything else similar: dirty laundry, old blankets, or whatever else!

So you don't absolutely need a lot of space in there. What matters with the soffit is mostly the size, mass, and rigidity of the baffle itself (front panel of the soffit, the one with the hole in the middle that the speaker pokes through). That's the critical factor.

... does this sound reasonable?

That would probably be fine.

and it looks like with the shortest first reflection path I have a 17ms time delay between the initial signal reaching the ears and the first reflection reaching the ears.

Sounds good to me!

I added an extra 6" to the bottom and side of the control room since I had the space to spare in accordance with the 5' to property line code

talk to your neighbor, and see if you can move the property line another couple of feet!!! That would give you the extra 3 ms.... (Just kidding! 17 ms is fine.)

the extra half a foot helped get that 17ms.

Great! So now you just have to figure enough absorption/diffusion to bring the level down 20 dB, and you'll be home free!

This is starting to sound really good (no pun intended!).

- Stuart -

That clears up a lot!! Good to know it's starting to "sound" good lol.. Thanks Stuart!

So here is my new attempt for the layout...guess I'm calling this one 11.1

List of adaptations (and a few..ok a LOT of questions):

-I reduced the air gap between the inner walls from 15" to 12" (this gave me an extra 3" at the top of the control room so I pushed out the right wall another 3" to compensate for symmetry...this also increased the time for the first reflection to 17.45ms woohoo haha)

-The line of sight between the control room and live room is now slightly more "on-axis" with the top left corner of the live room. This was another positive result of reducing the air gap. It pulled the glass over and up to the right a bit. Can't complain about that.

-I added a sliding door between the control room and iso booth.

-I also added a 6º angle to the sliding doors/walls. For some reason this looks very awkward to me and I can't figure out what I may have done wrong. I know 6º is not much (is it even enough?), but with those 2x6 studs it appears to be very steep. Is it possible to angle the glass without angling the walls? I'm losing a decent bit of space in the booth by splaying the walls like that.

-I went with a 76º intersection point at the mix position (38º speaker angles just seemed more realistic than 37.5º).

-The front of the baffles turned out to be 4' 5 1/8" wide. I just extended them all the way to the drywall around where the glass framing would start...is that ok? Glenn's drawing (as well as my past few drawings) showed some kind of extension between the soffits in front of the glass...is it critical to join the two baffles (L and R) across the top and bottom of the glass like that?

-There is about 5' 6" between the front wall and the listening position (given the intersection point is 18" behind the engineer's head, per Glenn's advice)...does this seem about right or do I need more space there? I do plan on buying a console/desk somewhere down the road...

-I read that the monitors should be positioned at a point that is 2/5's the size of the baffle width (rather than centered in the baffle)...is this referring to where the center of the monitor should be, or the side of the monitor? Wasn't really sure what to do there...

-After ray tracing out to 55º on both sides of the left monitor, the only path that is a first-reflection "problem" is the one that basically hits straight off the right wall and reflects back to the right ear. This is the path that I calculated having a distance of 25' 11 3/16" from which I subtracted the direct path from speaker to ear which was 6' 3 7/16" which gave me a difference of 19' 7 3/4". I turned that into decimal form (19.64583333') and divided it by the speed of sound (1126ft/sec) which gave me .017447 seconds. I multiplied that by 1000 to get the milliseconds and as I already stated earlier that turned out to be 17.447ms. Whew that was a lot of numbers...anybody out there wanna check my math?? (granted this is dependent upon whether that little circle is accurate to the size of a human skull...of which I did not measure)

-Does it matter that one of the 55º rays from the left speaker bounces off of the right baffle before heading towards the right wall (and obviously vice-a-verse)?

-Ok I think this is my last question for now. Do you think the door going into the control room has enough space on the right side for proper/substantial framing? Stuart I know you recommended against the superdoor but I want to keep my options open. I will be getting into more of the detailed budget pretty soon and if a superdoor ends up being cheaper than double doors, I might go that route. I just want to make sure I'm allowing for this possibility if it were to be a money saver. I've provided an image of the section I'm referring to.

And finally...I'm sorry for such a long post! I just had a lot of things I wanted to cover. And again thank you thank you thank you for everyone's help...I would definitely be ramming my head against walls by now if it weren't for you guys. And Stuart... you tha man!!!

Cheers
Trevor

Hey Stuart I think this might answer one of my questions from above...

Also, it's a myth that you must splay the glass for acoustic reasons: there are no acoustic reasons why you would want to splay your windows.

I saw where you said this to one of the members on the forum (shayneallen) who is also building a studio here in Nashville...

Anyways does that "myth" then also apply to sliding doors? Could I keep them parallel so that I wouldn't unnecessarily waste space (in the booth) that could be used for bass traps, resonators, etc?

Thanks as always
Trevor

Anyways does that "myth" then also apply to sliding doors?

Yup!

Could I keep them parallel so that I wouldn't unnecessarily waste space (in the booth) that could be used for bass traps, resonators, etc?

Yup!

(Who said that I can't give short, concise answers? )


- Stuart -

Haha thanks Stuart!! I'll re-post my drawing with the parallel walls...

But before I do...did you see any other "red flags" in layout 11.1 (as far as the floorplan is concerned)? I realize that some of the stuff in the control room can be tweaked for awhile without affecting the outer shell (monitor angles etc). I'm just wanting to finalize the floor plan so my builder and I can start working toward the goal of designing the outer shell...I just want to make sure I have it perfect before any major plans are drawn up/concrete is poured etc.

I'm going to start researching HVAC systems in more detail to figure out how we could go about it with this type of floorplan...

Let me know what you think!

Cheers
Trevor

I found the post from John that I mentioned yesterday:

http://www.johnlsayers.com/phpBB2/viewt ... ors#p99679

"...it's not necessary to angle sliding glass doors. I used to think it was but I don't angle them now."

So there's your permission slip to not angle that bit!

But before I do...did you see any other "red flags" in layout 11.1 (as far as the floorplan is concerned)?

Yeah, it's terrible! Red flags all over! Do it again!
Naah, just kidding: it looks pretty good. Time to flesh it out in 3D, I'd say, and start figuring basic treatment.

I just want to make sure I have it perfect before any major plans are drawn up/concrete is poured etc.

Regarding concrete pouring: have you considered embedding your electrical and signal cable conduits in the concrete? Makes it a hell of a lot easier to cable things up afterwards... Cheap and easy to do now, hard and expensive to do later... Just a thought...


- Stuart -

Great to know I've got John's approval! (BTW I think your link is broken)

In regards to running cables in the concrete...I had thought about this awhile ago but since we aren't pouring all new concrete I figured we wouldn't be able to (refer to the concrete diagram on page four). For reference though, I've drawn dotted lines to represent where the new concrete will be in relation to the floorplan (as seen below in layout 11.2). Everything to the right and below the two dotted lines will be new concrete but the upper left segment is already fixed. Can I just run my cables through the studs/air gap around the walls to the positions I want the wall plates in each room?

Here is the layout with some modifications:

-Changed it back to the parallel sliding doors...it makes the booth so much nicer!

-I mirrored/reversed the way the door opens out from the bathroom...it seemed more logical/better to enter on the side opposite the front door.

That's about it really...the only thing I am really contemplating now in regards to the layout is the angle on the front of the booth...it's currently a 14º angle upward from the corner of the control room. I think it's pretty much the best compromise in terms of sight lines and space. Seem okay?

Onward!
Trevor

After talking to my Dad earlier, he made me realize it would probably be worthwhile to go ahead and incorporate conduits in the new concrete to the live room, booth, and maybe even the bathroom (this was my idea in case I ever wanted to throw a panel in there down the road for an extra "semi" iso booth). We wouldn't be able to put them in the most ideal positions in the live room...but at least there would be some type of channel to send a line through after the build is finished if we ever needed to. We would still have to run a couple snakes through the wall cavities to reach spots in the live room that I consider more "ideal". Does this sound like a good idea? It's more of a precautionary, might-as-well-do-it-while-you-can sort of thing...

Anyways, thanks for pointing that out Stuart...let me know what you think about it and I'll draw up a conduit/cable routing diagram to see what would work best.

Trevor

(BTW I think your link is broken)

Damn! Don't know how I managed to do that. But I fixed it now. Thanks!

Can I just run my cables through the studs/air gap around the walls to the positions I want the wall plates in each room?

You can, yes, but if you have the opportunity to put some of them in the slab, it makes it easier. However, you should only have ONE penetration into each room, and distribute from that point to all the plugs, boxes, lights, switches, etc. It's not a good idea to have multiple penetrations, as each one is a potential breech of your isolation. That's why we normally recommend using all surface-mount ducts and boxes inside each room. Minimize penetrations as much as possible.

-Changed it back to the parallel sliding doors...it makes the booth so much nicer!

Yup! You could do some angled slot walls in there, better acoustics.

it's currently a 14º angle upward from the corner of the control room. I think it's pretty much the best compromise in terms of sight lines and space. Seem okay?

Looks good to me. Seems like you have pretty decent sight lines in all directions.

- Stuart -

Hey Stuart...for some reason I'm not quite sure what you mean by this...

That's why we normally recommend using all surface-mount ducts and boxes inside each room.

Thanks for the quick reply though. This week I am going to meet with my builder to show him the final floorplan. We should be able to get a better idea of how the outer shell will be built at which point I can proceed with working on the HVAC design, electrical, etc. I do have a couple quick questions for you whenever you get the chance...

-I began working on the 3D model but since I have not shopped around for doors and whatnot, I feel like I'm wasting my time by drawing in "temporary" details. Wouldn't it make more sense to go ahead and shop around so I can determine exactly what I will be installing before I get into the messy details of SU? (It seems like the superdoor at the entrance and the beefed up bathroom door might be cheaper just to build ourselves...but not the sliding doors or double doors into the CR)

-In a "room within room" structure such as what I am preparing to build, where is the most typical path for HVAC ducts? In between the framing of the outer roof and inner ceiling? Or perhaps in the space created by the trusses on the outer roof? I am going to continue my research in this area, but I just wanted to make sure that I was on track...at least a little bit.

Thanks!
Trevor

What I meant by that was that the normal way of installing switches, outlets and lights, in normal houses, offices etc. (not studios) is to cut a rectangular hole in the drywall for each one, poke an electrical box through the hole, connect up the cables, then attach a switch plate, outlet plate or light fitting plate, as needed. But with a studio you cannot do that: each such hole would drastically degrade your isolation: You CANNOT make holes in your drywall anywhere. So your only option is to use surface-mount boxes that go on top of the drywall, sticking out from the surface and NOT going through it. So there is no penetration of the drywall. Of course, this means that the entire box is visible, so you need to use boxes that are specifically designed for surface mounting. It also means that the wiring between boxes also cannot penetrate the wall, and must be done on the surface of the wall, where it will also be visible. So once again, you use structured surface-mount ducts for your wiring, that attach to the wall surface. It can look quite attractive if done correctly. There are several manufacturers who make this kind of surface-mount electrical hardware: I have used both Legrand and Kalop, but there are others. I'm not sure what you can get in your area, but look around and I'm sure you'll find something suitable.

If you are doing inside-out walls then this is not so much of a problem as for "normal" walls, but even with inside-out it makes things easier and neater to use a structured system and proper surface-mount hardware.

You can still cut all those huge holes in your wall if you want, and do things the conventional way, but then you have to take great care to seal around the back of each box with putty pads, using enough to replace the mass and seal that you lost with the hole, and creating many more headaches for yourself than you need!

On the 3D model: Doors come in several standard sizes, so it's an easy thing to just create the rough openings in your framing to be the correct size for the nearest standard door, even if you don't put in the detailed door yet. So for example, if you had sketched in a door that was 31-1/8" wide, then change that into a standard 32" door, and do the framing accordingly for the rough opening for a normal 32" door. Don't forget that the doors will be VERY heavy by the time you have modified them correctly, so normal practice is to have three studs on each side of the rough opening.

The best place for HVAC ducts is wherever they will fit! You'll need silencers each time they pass through a leaf, and the silencers also take up a lot of room, so take that into account.

- Stuart -

Ahh that makes much more sense now!! I had planned on just cutting holes in the drywall and using putty pads to seal, but now I realize I've seen exactly what you are describing in many of the construction threads...just now putting two and two together . Definitely seems like a much safer route, isolation wise. One question on this though...from what I've seen of surface mounted mic panels, there is one small hole in the drywall that allows the snake through...but from what I can tell by your post, there should be NO holes at all...I guess I'm confused as to how there can be absolutely no holes in the drywall and still allow for the cables to run into each room...does the penetration happen through the floor where the conduits in the concrete empty out? And then the snake is run around the room via a wall surface mount if other panels are required in the same room? Am I thinking about this correctly?

That's also good to know about the doors! I figured that was the case...but since I'm no home builder (or anything close to it), I had no idea what those standard sizes were. And yes I will definitely account for the weight of the doors! Since I'm using 2x6 studs, is it still necessary for three on each side of the framing?

In regards to the HVAC, I have been getting into more detailed research... wow I must say it is pretty overwhelming! I have so many calculations ahead of me! But after the meeting with my builder today he told me that if I figure out the specs for what I need (BTU output, fresh air needs, conditioning, volume/velocity of circulation, etc) then he can let his HVAC guy direct me towards the best type of unit that will accomplish my needs. Basically it will save money if I do all of that work myself. These calculations will also allow me to figure out how big the ducts need to be in order to achieve the proper velocity coming out of the vents (I read that should be 100-300fpm maximum in Rod's book). Knowing the size will then allow me to properly design the trusses to accommodate both the silencer boxes and ducts within the roof/ceiling structure. One question on this...I read somewhere that the silencer boxes need to be accessible even after the build is complete...does this mean I have to make soffits so that each silencer box actually resides within the inner leaf (double drywall)? Or can there be some kind of access door to the attic space (which poses another potential isolation breech)?

One other update...in our meeting today my builder, Joseph, expressed further concern about the large tree by the foundation. The two major problems are potential root damage to the concrete (over time), as well as the possibility of a bad storm causing the tree to fall either by lightning or wind (that would be a lot to risk for such an expensive structure!). So, I decided to call a tree specialist who is going to meet with me ASAP to assess the situation. We will then come to a decision about whether to cut it down or not... Honestly, I'm not looking forward to seeing this thing go...I'm still hoping for the best but it's not looking good.

Anyways, thanks Stuart for yet another great reply!! I've got plenty to keep me busy in the meantime...

Cheers
Trevor

A couple more updates...

1.) I met with a tree specialist a couple of days ago and he basically informed me that the wisest plan of action would be to take the tree down during the demolition phase of the existing structure (so before we dig and pour the additional concrete). He said if I were to keep the tree, there is a high probability that it would die sometime in the next 5 years due to the soil becoming compacted during construction. This cuts off proper oxygen supply to the roots which leads to all kinds of problems for the tree . This is not to mention the obvious danger of a bad lightning and/or wind storm causing the bone-wrenching reality of walking out to a studio with a caved in roof . So anyways...the beautiful Silver Maple has to come down... (moment of silence)

2.) Now that the tree is no longer an obstacle, I have drawn up two more layouts. The first one (Layout 11.3) is just like 11.2 but has concrete in the upper right corner to square off that notch where the tree would have been. I was able to incorporate a small storage room alongside the bathroom...no angled walls here as I tried to keep it as simple as possible. The second layout, which I'm going ahead and calling Layout 12, is a whole other beast in and of itself. This one has additional concrete extended 2' 9.5" on the entire right side of the structure. This squares off the outer shell (34'2" x 34'2") which accomplishes several things:

- The line of sight between the control room and live room is at the absolute optimum due to being completely on axis from corner to corner.

- Both the booth and live room are a little bit larger (not to mention the shape of the live room feels better all around).

- There is room for a decent size storage/mechanical room between the CR and LR. This would be a huge step up from previous designs but obviously will have a price tag too.

- The bathroom is also a bit larger.


Anyways, let me know what you think of these layouts. I know this just keeps growing bit by bit...however our reasoning behind this is to go ahead aim for the most ideal design, get a quote, and scale back from there if we have to. Our builder wants to help us do this as cheap as possible and isn't looking to make the kind of money he makes on normal home construction. His team will be in the neighborhood for awhile because they keep buying new properties to build on and/or renovate considering it's the perfect "up-and-coming" neighborhood for a good profit margin. So he will not have to make special trips with equipment to get the job done. Fortunately, there's this convenience factor that he is taking into account.

In the meantime I have been reading a lot in the construction threads as I need to learn as much as I can there...ceilings are my new priority as I am probably the most clueless in that area of the build.

Thanks in advance for any input!!
Trevor

So I'm pretty sure I might be nearing the record for "most proposed designs" for a single studio on the forum...that being said, I've got one more for ya!!

Anyways, after increasing the potential size of the foundation to a perfect square (34'2" x 34'2") I realized I needed to rethink other possible layouts, just in case I came across something better than the corner style control room. And by "better" I mean something more suited to my needs, as listed earlier in the thread (large live room, small but workable control room with a RFZ being the priority, etc).

I think I may have found just that...and I'm calling it "Layout 13" **insert dramatic music**

Alright alright so here are the specs and reasons for why this might be a better direction to go in:

-HUGE live room (473sq ft)...a solid 47sq ft increase from the largest corner CR layout (layout 12).
-Complete RFZ in CR with first reflections coming in at 20ms after the direct signal reaching the ears...wooo!!!
-Less square footage in CR (57 sq ft less) which allows for extra space in LR and storage room.
-CR now has a back wall...perfect for hangers/absorption and whatnot (and not just a corner trap).
-One less door is used in this layout as well as less glass at the front of the CR (money saver).
-Drum booth square footage remained the same.

Let me know what you guys think...I personally feel like the benefits of this design far out weigh the negatives. However, I need input to help me either confirm that or set me straight!

Thanks in advance!!
Trevor