Attic Shaped Studio

#46

Here are more before and after transmission loss curves from room 1 to various others. All off the riser this time.

I didn't do a "before" sweep for room 2, no idea why! It's unfortunate as the improvement there was very significant;

The landing is a disaster in terms of sound transmission from room 1;

In particular look at these holes in the TL curve at 31 and 49Hz. The wall might as well not be there at these frequencies! I wonder if the door and/or the glass bricks in that wall might be part of this problem;

As the landing leads to the stairwell and most other rooms in the house it would seem likely that improving the transmission loss from room 1 to there would generate significant gains in most other rooms too. I have some ideas about improving this, more to follow in the next post.

Cheers,
Jennifer

#47

Room 1 is where I mix and record most things, including drums. Room 2 is used less frequently and usually only for quieter instruments, so reducing sound transmission from there is not as big a priority as room 1.

We've established that transmission loss from Room 1 to the landing is poor and has significant low frequency "leaks". This accurately describes ear observations for what is audible from room 1 in the living room two floors below. Most things aren't audible - mixing at 85 dB is way below the threshold for example - but the following are;

The measurements imply that plugging the holes in the low end and improving overall sound isolation from room 1 to the landing would help this and also reduce sound transmission to the rest of the house in general.

The wall from room 1 to the landing is the one with the glass bricks and door;

As a standard 4x2 stud wall with 12.5mm plasterboard on either side it's the weakest boundary out of room 1. At least it has insulation in it!

- Room 1 floor is a 22mm subfloor with 18mm glued down real wood tongue and groove covering. The cavity below this is 220mm deep with insulation. Ceiling below that is a single layer of plasterboard. It's actually doing a pretty good job of isolating sound to the rooms below, far better than the room 1 / landing wall.
- The short walls from room 1 to the eaves are 12.5mm plasterboard, but presumably the large cavity (now with more insulation) between that and the equivalent short walls on the landing and other rooms helps with sound attenuation.
- Room 1 sloping ceiling is a single layer of plasterboard with 100mm insulation slabs on top of it. On top of the insulation is a layer of something like MDF, then a 2" gap, then OSB, then the roof tiles. At the point this assembly joins the eaves most of the insulation ends have a wooden "cap" on them. Presumably this assembly is doing a bit more than a single layer of plasterboard would.

It would seem logical that bringing the weak wall closer to the standard of these others would be a big help. Here are my thoughts;

1) Beef up the door Rod Gervais style. The existing door is ceramic core FD30 fire rated, mass per area of 27kg/m2. Adding 18mm MDF will add about 12 kg/m2. A layer of code 3 lead between them would add 15kg/m2. Adding both will double door mass and allow multiple perimeter seals. The door jamb is specifically for a fire door, is over 32mm thick and is tough as old boots; presumably ok with the extra mass if I use sturdier hinges.

2) Install a plug for the glass bricks.

3) Add a layer or two of 15mm thick plasterboard to the room 1 side of the wall and also the short walls at either end. I have enough green glue left over from the riser build for two layers :-)

My hope is that these will address the low frequency holes and give a bit more isolation. A realistic prediction? Comments welcome!

Cheers,
Jennifer

#48

endorka wrote:Source of the post As a standard 4x2 stud wall with 12.5mm plasterboard on either side it's the weakest boundary out of room 1. At least it has insulation in it!

How much are you prepared to do to improve isolation here? If you need a reasonalbe improvement, then your plan of adding an extra layer (pr two!) of drywall with Green Glue compound would help somewhat, especially with with the low end. Going further: you could take off the existing drywall, seal up all gaps and edges with caulk all around inside, put up isolation clips (eg: Genie clips, RSIC clips, etc.), put hat-channel in those, stuff the cavity with insulation, then put on two layers of 16mm drywall, with Green Glue compound.

That's a bit more drastic, yes, but if you need a large improvement, that might be the way to go.... as far as the wall itself is concerned...

endorka wrote:Source of the post The existing door is ceramic core FD30 fire rated, mass per area of 27kg/m2. Adding 18mm MDF will add about 12 kg/m2. A layer of code 3 lead between them would add 15kg/m2. Adding both will double door mass and allow multiple perimeter seals. The door jamb is specifically for a fire door, is over 32mm thick and is tough as old boots; presumably ok with the extra mass if I use sturdier hinges.

Doors are always weak points: especially the seals. Beefing up a door will improve isolation, yes, but perhaps not as much as you'd like: doubling the surface density will get you an increase of maybe 5 dB, realistically (6 in theory). Improving the seals can get you anywhere from just 1 or 2 dB to maybe 10 dB or more, depending on how bad the situation was, and how well you do it.

That said, beefing up a door with high mass is more than just adding on some dense layers: as you mentioned, there's also things like hinges to think about: you'll probably need to replace the existing hinges with heavy-duty hinges, and also add a couple of extra ones: I always use at least 5 hinges on a medium studio door, and 6 (or more) is also common for heavy ones. When you think that a good door might weigh 120 kg, and each hinge only has four screws in it, the typical 3-hinge arrangement means that each screw is supporting 10 kg just in vertical weight, but the screws in the top hinge are also supporting the "leveraged load", of the entire door weight trying to pull them straight out of the jamb, where the bottom hinge is the fulcrum and the width of the door is the lever arm with the full weight of the door on it.... well, there's a hell of a lot of force on those screws, as you can imagine! It's a good idea to put a couple of hinges close together up near the top of the door, a couple more spread a little further part around the middle, and the last one (or two) down towards the bottom, spread even further apart. And use extra-long screws, to resist the high "pull-out" forces

Plus, it's not just the door, jamb, and hinges: all of that is attached to a stud frame inside the wall, which was likely originally only intended for a typical house door. Even though that might be able to take the vertical weight of a studio door, there are also some rather major forces that it wasn't designed for, trying to twist it out of shape: And as you open and close the door, you move those forces around, swinging them through 90°: With the door open, you have that same "leveraged load" trying to tip the wall over towards you: It won't actually tip the wall over, of course, but it certainly can bend the framing a little. Over time, the door will sag, twist, warp, bend... and end up not sealing properly, and probably binding against the threshold and the jambs.

The solution is to beef up the framing. Here's how I often do the framing for studio doors:

There's two king studs on each side, plus a jack stud on each side under the header, then outboard of that there are additional noggins that help transfer some of the load to adjacent studs, and also provide extra rigidity. Not visible here, is the "backer" that runs up behind the three studs on each side, inside the cavity. That might be just a strip of 19mm OSB or plywood, or better still is a 2x6 turned sideways. That thickens the support column, and provides extra rigidity and strength for when the door is open. If you look at Tom's thread, you can see how we did that for his isolation wall.

The final part of that, is to then use OSB or plywood as the first layer of sheathing on that part of the wall, then put the drywall over that for the final layer: both OSB and plywood are very good with sheer loading, so the add extra structural integrity, strength and rigidity to the whole "sandwich" of stuff that is holding up the door, and keeping it straight and true.

Here's a couple of examples from actual studios built by clients:

How serious you have to get with that depends on how heavy your door is, but anything over about 50 kg or so needs some extra care. And if you are getting up around 100 kg or more, then it's time to get very serious.

Then there's seals: For typical home studio doors, I suggest two complete full-perimeter seals, and for high isolation three complete seals. By "full-perimeter" I mean that there is a continuous rubber seal that runs completely around the door, unbroken: header, threshold, and both sides. No gaps. Yes, there can be joints in the seals (such as where the vertical side seals meet the horizontal threshold seal), but when the door is closed they must all be pressed together properly, so there are no cracks. For example: if you have a drop-down seal embedded in the bottom edge of the door, then that must not only seal tight against the threshold when it drops into place as the door closes, but it also needs to seal against the rubber running up the sides. Small gaps and cracks can leak a lot of sound.

If you're framing very rigidly, and are certain that your framing won't budge, sag, twist, etc, and the door is mounted with "overkill" heavy duty hinges, then it's OK to just use fixed rubber seals glued to the jambs. But if there's a chance that things could sag or shift over time, then it's better use adjustable seals, such as those made by Zero International. Those allow you to simply pull off a small dust-cap, insert a screwdriver, and adjust the seal for a tight fit, any time you notice that it isn't sealing well. They aren't cheap, but that's the best solution if things might move out of plumb and square over time. It sure beats modifying the jambs to compensate for the load shift!

A realistic prediction? Comments welcome!

If you do "all of the above", then you could maybe get as much as 10 dB improvement in isolation, maybe even a little more. If you can only do some of it, then likely around 4 to 6 dB improvement. In perspective: 4 dB is noticeable, 6 dB is very much noticeable, and 10 dB reduces it the level by about half, subjectively.

- Stuart -

#49

That is amazing information, thank you. 10dB improvement in isolation will totally do the job, allowing me to crank the monitors to check the kick and bass, and record amplified guitars with substantial low end without these being heard in room 5. So a couple of extra layers of drywall and green glue will do the trick. I'll incorporate this into the HVAC design, with sleeves and silencer walls of appropriate thickness.

For the door I'll figure out what sort of stud framing is currently in place and augment it accordingly. All makes total sense now - the hinges are spaced closer together near the top of our exterior doors, I've always wondered why!

Cheers!
Jennifer

#50

That is amazing information, thank you.

10dB improvement in isolation will totally do the job,

I should clarify: 10 dB is probably towards the limit, and would need "all of the above". ie, take off existing drywall, beef up framing for heavy door, seal wall interior well, add clips + hat channel, good insulation, then old drywall on again plus two layers of new drywall, with GG, plus heavy door, plus at least two seals. All together that could give you maybe 10 dB improvement, give or take. I don't want to get your hopes up that you'd get that much easily! Lots to do, and carefully... But knowing how meticulous you are with everything, I'm pretty sure that 10 dB is within range!

One thing I forget to mention about heavy doors: forget about trying to close them by hand! That's a lot of moving mass: a lot of inertia, and you don't want that slamming into your jambs and seals all the time. That will quickly put things out of whack. You also do NOT want to have a finger in the way when there's many dozens of KG of mass moving around, with a sharp edge on it! :shock:

Instead, get yourself a heavy-duty automatic door closer, of the right capacity for the weight of your door. Allow that to close the door, and adjust it so that it slows down the close rate for the last few cm, then applies pressure when the door is fully closed, to get the seals pressed together snugly. That way, you don't even need a latch on the door, so no penetrations through the door for a lock-set. Just a pull handle on the outside, and a push plate on the inside. Let the closer do the job of closing it slowly and gently, then applying pressure.

I'll incorporate this into the HVAC design, with sleeves and silencer walls of appropriate thickness.

If you want, post your design for that here when you have it done, for checking... Have you figured your flow rates and velocities yet, and your static pressures, and duct diameters, all the other fun stuff?

All makes total sense now - the hinges are spaced closer together near the top of our exterior doors, I've always wondered why!

Yup! Moment arms are important to consider... heavy weights hanging out there on the far edge of the door slab, a meter away, with a fulcrum lower down, can put a fair bit of pull-out pressure on those screws.

- Stuart -

#51

Soundman2020 wrote:Source of the post
That is amazing information, thank you.

10dB improvement in isolation will totally do the job,
I should clarify: 10 dB is probably towards the limit, and would need "all of the above". ie, take off existing drywall, beef up framing for heavy door, seal wall interior well, add clips + hat channel, good insulation, then old drywall on again plus two layers of new drywall, with GG, plus heavy door, plus at least two seals. All together that could give you maybe 10 dB improvement, give or take. I don't want to get your hopes up that you'd get that much easily! Lots to do, and carefully... But knowing how meticulous you are with everything, I'm pretty sure that 10 dB is within range!

Right, now I get it! I hadn't realised the old drywall can be removed and put back on again, I had assumed it would be destroyed by removing. But a quick search reveals otherwise. I think it is installed with screws so should be even easier to remove than nails.

One thing I forget to mention about heavy doors: forget about trying to close them by hand! That's a lot of moving mass: a lot of inertia, and you don't want that slamming into your jambs and seals all the time. That will quickly put things out of whack. You also do NOT want to have a finger in the way when there's many dozens of KG of mass moving around, with a sharp edge on it! Instead, get yourself a heavy-duty automatic door closer, of the right capacity for the weight of your door. Allow that to close the door, and adjust it so that it slows down the close rate for the last few cm, then applies pressure when the door is fully closed, to get the seals pressed together snugly. That way, you don't even need a latch on the door, so no penetrations through the door for a lock-set. Just a pull handle on the outside, and a push plate on the inside. Let the closer do the job of closing it slowly and gently, then applying pressure.

I've been planning to use a DORMA TS 83 Door Closer for this purpose. It can cope with the weight and has a "backcheck" that slows the door for the last part of closing. Expensive but nice

https://www.dormakaba.com/gb-en/solutio ... -83-266910

I'll incorporate this into the HVAC design, with sleeves and silencer walls of appropriate thickness.
If you want, post your design for that here when you have it done, for checking... Have you figured your flow rates and velocities yet, and your static pressures, and duct diameters, all the other fun stuff?

Thank you, you can count on it! The design is nearly finished, calculations done and seem plausible. I just have to figure out the exact models of supply and return grilles and plenum boxes so I can account for the static pressure added by them.

Cheers,
Jennifer

#52

endorka wrote:Source of the post I just have to figure out the exact models of supply and return grilles and plenum boxes so I can account for the static pressure added by them.

Right! For the registers, don-t forget to take into account the "open area" vs. the actual face area. Registers have fins, grills, vanes, or whatever that take up part of the frontal area... sometimes a substantial part. So, for example, you might have a 10" x 8" register, which would seem to have 80 in2 cross sectional area, but all of the vanes and stuff could take up 25% of that, leaving you with only 60 in2 of actual frontal area... And if the vanes are movable (to direct the air flow in certain directions), then that opens and closes them even more... in some registers, you can adjust the vanes to completely block off the air flow, which of course reduces the area to 0 in2.

Just some more things to take into account! Just when you thought there was light at the end of the tunnel...

Also, if you can find them (not easy to do), some registers are specifically designed to be "low noise". The vanes and interior surfaces are designed especially to minimize resistance to air flow, and keep it moving smoothly, creating as little turbulence as possible, and maximizing open area. Get those, if you can find them, and if they are suitably sized.

- Stuart -

#53

Rod Gervais recommends Nailor grilles because they are low noise. I don't know whether that means all Nailor grilles are or just specific ones.

#54

Finding the good stuff has been something of an adventure, especially as I have no prior experience of this sort of thing. My plan is to do my best, but also design the system such that the grilles can be replaced relatively easily if they are too noisy or what have you. In our favour at least is that where I could find noise figures for specific air velocities going through certain grilles, the noise is very low (or even "unmeasureable") for some of those at less than 300 ft/m.

The closest to Nailor I could find in the UK were Advanced Air, "A member of the Nailor Industries International group";

https://www.advancedair.co.uk/products/ ... nd-louvres

Cheers,
Jennifer

#55

Jennifer, what I did in my last studio was to not use grilles at all. Here (top photo) is the duct delivering fresh air over the top of the AC and the stale air exit duct (second photo) has two entry points without grilles, half hidden behind the cloud. So far my plan is to do the same in my new place. Where Stuart could helpfully advise is whether grilles serve any practical purpose in a studio other than how they look. I think grilles are fitted to plenums, not to the duct, and a plenum usually looks like a box with an inlet for the duct and it holds the grille for the outlet. As the plenum is bigger than the duct, maybe the slowing down of the air speed in the plenum keeps the air noise quieter than my method. I don't know so I am not suggesting you copy me; just be aware that no grille works but it may not be the best method. I need to learn more about this.

#56

Starlight, I'm no expert, but I think part of the purpose of diffusers is to guide airflow in certain directions. You can get ones that direct it down, or to the left or right, swirl it about or what have you. There are ones that make use of the "Coanada Effect" which causes the air flow to "stick" to a surface such as a ceiling and run along it. All potentially useful in keeping direct airflow away from areas you don't want it, e.g. microphones.

There are also ones that can open and close to varying degrees to manage the flow rate, but as we both seem to have units dedicated to one room I don't know if this is of much use in our applications. I expect having a grille in place is also useful to stop creatures crawling in there too.

In truth, figuring all this out in advance when I don't have a clue what airflow at 300 f/m actually feels like has been part of the difficulty. I've no idea if placement will get into microphones or make unwelcome drafts for people. So it is very, very reassuring to read your post about being able to use just the ducts. Although it might not be the most efficient way, it means I can try some temporary setups at first for the ductwork inside the room and see how they work out before committing. Especially important as the silencer sleeves will enter the room behind the proposed soffit location, and I'll not be building the soffits until later. The rest of the system will be properly worked out, of course!

Cheers,
Jennifer

#57

Starlight wrote:Source of the postI think grilles are fitted to plenums, not to the duct, and a plenum usually looks like a box with an inlet for the duct and it holds the grille for the outlet. As the plenum is bigger than the duct, maybe the slowing down of the air speed in the plenum keeps the air noise quieter than my method

Indeed so. I followed Rod Gervais guidelines in this, that the cross section of the silencer coming in to the room is at least twice the area of the cross section going to "outside". The duct is the same cross sectional area as the "outside" in my design, so only 1/2 of what it should be. I suppose this means the air is moving at twice the velocity when coming out of a duct instead of proper sized register, and noise I believe increases exponentially with velocity, bad news! I should be able to rig up a plenum and test diffuser that can be moved with ease though I reckon.

Cheers,
Jennifer

#58

The 300 fpm number is the limit: If you stand in front of a register blowing 300 fpm, you'll feel it. Lower is better. If you want it to be so slow that you can't really perceive the air movement on your skin, then 50-100 fpm is more like it.

What I normally do in control rooms is put that 300 fpm flow down into the hangers at the rear of the room, where it diffuses greatly and comes out through the fabric at the front of that, very much slower. Imperceptible. For live rooms, I use more registers and split the flow among them. And for small booths, I just keep the flow into the silencer slow.

I'm giving away all of my secrets here!

- Stuart -

#59

Cheers Stuart, very useful information indeed thank you. I'll be able to do something similar with the bass traps at the rear of the room.

Jennifer

#60

The more I read about the Genie clips and furring channel you recommended for the left wall in room 1 Stuart, the more I like it. Having studied IR761 they seem to confer many of the benefits of staggered or even double stud walls, and are certainly easier to retrofit. IR761 cites resilient channel, and it would seem that Genie clips + furring channel give further gains whilst being more idiot proof to install. As well as the decoupling, the increase in cavity depth gained using these will help too, even keeping the same mass of drywall layers as before. They'll increase the cavity depth (and depth of the whole wall assembly) by 41mm, increasing the low frequency transmission loss. Standard UK stud walls are 89mm deep, so this will be significant. Adding mass will help even more. Nice.

It also brings me to a wrinkle in the design mentioned earlier in the thread that demonstrates the truth of Avare's signature: "Good studio building is 90% design and 10% construction". Note that currently the short walls and corresponding slopes at the front of the room are different widths, left is 625mm, right is 580mm;

This created a problem for soffit design demonstrated by a draft design below. The first reflection point of the listening positing hits the door. Of course the soffit face on the left will be wider than the right, creating an asymmetrical response.

With the Genie clips and furring channel installed with just the original 12.5mm plasterboard layer, this is pretty much corrected. The door has been beefed up with ~41mm of MDF, almost doubling its mass and keeping it flush with the moved plasterboard. This means that first reflection point and soffit symmetry is within 4mm, not bad at all;

Alas, the good times are short lived, for when we add another layer of 16mm plasterboard to the left wall the soffit asymmetry returns, now a 12mm difference. Adding another layer will make this 28mm. At least the first reflection point remains symmetrical however, as the door thickness has not increased. Mass could be increased with lead if desired, which would not add much thickness.

If this asymmetry is significant, I've been pondering several ways of addressing it, all assuming two additional 16mm plasterboard layers on the left wall;

1) Use Genieclip LB3 instead of RST. This reduces the depth added to the cavity

: pliteq_genieclip_lb3_photo.jpg (20.15 KiB) Viewed 35221 times

: pliteq_genieclip_lb3_photo.jpg (20.15 KiB) Viewed 35221 times

Pros: allows symmetry of soffits, first reflection points and entire room.
Cons: reducing cavity depth will reduce low frequency transmission loss. Genieclip LB3 are a bit more expensive and time consuming to install, and less idiot proof.

2) Also add two additional layers of 16mm drywall to the right wall.
Pros: gives soffit symmetry.
Cons: Expensive and time consuming. The added mass will give little benefit as this is an exterior wall already doing a good job, and pointless next to all that glass. Will reduce width of room at rear by 32mm. Creates first reflection point asymmetry unless 32mm of MDF is added to the door. That would make the door 117mm thick!

3) Use standard Genieclip RSTs. Add the light green coloured ~28mm "kludge" to the right soffit to match the left wall up to where the door starts. It'd be ~200mm long.

Pros: gives soffit and first reflection point symmetry. Costs next to nothing and easy to install. Better drywall cavity depth for improved low frequency transmission loss. Easy to get an exact match for soffit symmetry.
Cons: rear of room beyond door will be asymmetrical. Not a big problem I think as it won't influence the listening position much. Will have some sharp corner transitions in the sound path at the edge of the kludge. I could round them out though, and as this is bordering a first reflection point it will be trivial to conceal the entire kludge behind an acoustic absorption panel.

I'll keep pondering, but inclined towards option 3 at the moment. Comments welcome of course!

Cheers,
Jennifer

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