John Sayers' Recording Studio Design Forum Archive

Hi all,

I live in the inner west of Sydney.

I have a building in my back yard that I have been working from for a few years doing demos, some rehearsal, (during office hours) and generally as a creative work space.

I have been planning and wanting to do some sound isolation (and later some acoustic treatment of the internal room) for some time, and now having worked out of there and realising that i don’t need to go to massive extremes, I have a plan and some questions that I’d love any feedback on.

BUDGET:
Budget is about $25,000. This needs to include air conditioning etc. I’m not especially handy, so would be paying people to do this.

DETAILS:

The building is 52 m2.

It’s double brick (no air gap.)

4 windows that are old and loose fitting.

1 solid core door, ill fitting, no door jam.

Corrugated iron roof, with some foil backed light insulation, and exposed roof beams.

concrete slab floor, not connected to any other buildings.

As it is, with absolutely no work done, there is a drop of approximately 20db when measuring loud music inside the shed, and about 3 meters outside the door (which is the distance to the nearest other dwelling).

So from drums measuring at 100db when I’m standing in the middle of the room, to 80db when I’m standing outside the shed.

I’m not looking to attempt huge levels of sound isolation. In 3 years I’ve never had any neighbours complain, and it is rare that I’m recording or rehearsing very loudly for long periods of time.

I also don’t want to over- capitalise my property or spend money foolishly.

That being said, I want to improve things as best I can in a rational way.

CEILING:
The roof/ceiling is the biggest problem.

A structural engineer has advised me to reinforce the roof, and on doing so, told me that it would support a suspended ceiling of 2 x 16mm fyrcheck, with insulation on top.

According to CSR red book and general research that would give an Rw + Ctr of about 43.

WALLS:
with the Rw + Ctr rating of the ceiling in mind, I don’t want to go overboard with the walls.

From research I understand that double brick has an Rw + Ctr rating equal to or greater than 50.

I was initially planning to build an internal timber stud frame 100mm off the bricks, insulation and 1 layer of 16mm fyrchek.

However, I understand that will give an Rw + Ctr of about 54, and since the rating for the roof/ceiling is significantly lower than that, i wonder if double brick and a rating of around 50 is sufficient?

I would probably add a layer of 10mm plasterboard on furring channels on the walls, both for aesthetic appearance and also to generally ensure a pretty airtight room.

WINDOWS/DOOR:
Windows would be double glazed with 2 layers of 10.38mm laminated glass with 100mm air gap.

Door would be 2 x solid core doors, one opening out and one in, with heavy duty door seal/jam and about 6 cm air gap.

my understanding is that the Rw + Ctr rating for those would be between 40 - 44 approximately.

FLOOR:
probably just leave as concrete slab.


QUESTIONS:

a) do you agree that it is pointless trying to achieve wall/door/window Rw+Ctr ratings much higher than the maximum i can achieve with the ceiling?

b) do you agree that double brick, with plasterboard (but no air gap) would achieve the rating i proposed above?

c) I think that would be an average rating of about Rw+ Ctr of approximately 45 for my room.

Accepting that I’m not trying to achieve huge levels of sound isolation, would you agree that the above scenario would still offer a vast improvement on what I have now?

My understanding is that sound not exceeding 45db residential areas is acceptable. (according to the Environmental protection agency)

In general, I’d really appreciate any feedback in case I’m not thinking about this correctly.

I can afford to frame up the walls etc, but I don’t want to spend dumb money on something that has a large weaker area in the ceiling that I can’t improve upon…I’d rather buy more instruments with anything left over.

Thanks so much in advance
JP

Hi JP, and welcome!

Your basic plan seems to be OK, but you seem to be making a few assumptions that aren't completely correct.

there is a drop of approximately 20db when measuring loud music inside the shed, and about 3 meters outside the door (which is the distance to the nearest other dwelling). ... So from drums measuring at 100db when I’m standing in the middle of the room, to 80db when I’m standing outside the shed.

You should be measuring at a distance of one meter, not three meters. That's the "standard" way of measuring sound levels. At 3m, you already have a little bit of air attenuation, so you aren't getting a true reading of the isolation that your structure is producing.

Also, "drums measuring at 100db" is pretty quiet! Most acoustic drum kits played normally will typically give about 110 dBC at a distance of 1 m (where you should be measuring), and can easily hit 115 dBC or even approach 120 dBC when played hard and fast. If you only measured 100 for acoustic drums, I'd suspect that you are not measuring correctly, or that there is something wrong with your sound level meter. What brand/model sound level meter do you have? The cheap Chinese things are pretty useless: basically just toys. How did you set up the meter when you took the measurements? (In other words, which weighting curve and response time did you use?)

It would be a good idea to do those measurements again, using a good quality meter that has been recently, and is set up correctly. I'm betting you'll see levels of around 110 dBC inside, and likely around 90 outside. Measure in several places around the building, at 1m and also at other distances, to get an idea of what the levels are really like, and where the weak points lie in the existing building.

The fact that you are only getting 20 dB from a double-brick wall indicates that you have major issues with the roof, doors, windows and ventilation system. A double brick all by itself should be giving you better than 40 dB.

A structural engineer has advised me to reinforce the roof, and on doing so, told me that it would support a suspended ceiling of 2 x 16mm fyrcheck, with insulation on top.

Sounds like a good plan! And if you are going to do that much work on the roof, how about also replacing the tin with plywood, and putting asphalt shingles on top? Much better isolation and much less resonance, rattling, and thermal noise issues.

According to CSR red book and general research that would give an Rw + Ctr of about 43.

According to mass law, two sheets of 16mm drywall will give you about 33 dB of isolation, in the real world. The equation is very simple: Tl = 14.5 Log (M * 0.205) + 23, where "M" is the surface density of the barrier. A single sheet of 16mm drywall has a surface density of about 12kg/m2. So 2 sheets together as a single leaf has about 24 kg/m2: Do the math. The insulation above, and the tin roof above that, will add very slightly to that, but not much. Certain not another ten dB. Maybe 2 or 3, tops. I'm not sure where you found that 43 estimate, but it is very much on the high side for a single-leaf barrier made from two layers of 16mm drywall.

From research I understand that double brick has an Rw + Ctr rating equal to or greater than 50.

Using the same equation, and taking the typical density of brick (2300 kg/m3), and assuming that you have two standard bricks side-by-side (110mm each, total 220mm), then your surface density is about 500 mg/m2, and the equation gives you an answer of about 52 dB. So yes, that assumption is pretty close: your double brick wall should be giving you about 52 dB of isolation exactly as it is right now. Which is why your measurement of only a tiny fraction of that (just 20 dB) shows that you have very major problems with the rest of the structure. You are getting just 1/1000th of the isolation that you should be getting for a single-leaf brick wall...

I was initially planning to build an internal timber stud frame 100mm off the bricks, insulation and 1 layer of 16mm fyrchek

You could do that, yes, but you say that you don't need very high levels, and you should be getting over 50 already, so you'd probably be better off concentrating on the things that aren't isolating right now, rather then the things that are!

However, I understand that will give an Rw + Ctr of about 54,

Correct, but maybe a bit higher. The combination 2-leaf MSM wall with double-layer brick as the outer leaf and a single layer of 16mm drywall as the inner leaf, with an empty 10cm air gap, will indeed give you about 54 dB. But I'm curious about that: You seem to be implying that you'd attach your 100mm studs directly to the brick, which implies only a coupled two-leaf wall, which actually decreases your isolation considerably. It would likely be less than the brick alone like that, due to the coupled MSM effect at low frequencies. If you were to fully decouple the inner frame by even a very small amount, say an extra 2cm (ie, by leaving a 2cm gap between the brick wall and the wood frame) your total air gap would be 12 cm, not 10, and also filling the air gap with suitable insulation, you'd get all the benefits of a fully-coupled fully-damped 2-leaf MSM wall: your isolation would then be north of 60 dB, with luck.

and since the rating for the roof/ceiling is significantly lower than that, i wonder if double brick and a rating of around 50 is sufficient?

50 dB is pretty decent isolation for a home studio, so you could leave your walls as just plain brick. But then you'd have the problem of how to attach your two doors to that, and your windows, and still get them to act as proper MSM systems... with only a single leaf wall to attach them to, you can't make them into decoupled systems, so you would be severely limited in how much isolation you'd get from them.

I would probably add a layer of 10mm plasterboard on furring channels on the walls, both for aesthetic appearance and also to generally ensure a pretty airtight room

Bad idea. Thin drywall over a thin air gap will give a large reduction in isolation. Assuming you get a 1cm air gap between your brick wall and your drywall, your overall isolation would drop to about 44 dB. The reason is simple: the MSM resonant frequency of that system would bye way up in the low end of the mid range, at around 214 Hz, meaning your wall would only isolate decently above about 430 Hz... But if you build it the way I suggested with the stud frame (12cm total gap, insulation filled, 2x16mm), the MSM resonant frequency would be way down around 26 Hz, meaning that your wall would isolate decently above 52 Hz, with overall isolation of about 60 dB. That's a huge difference! It isolates fifty times better, and goes down two entire octaves lower.

Windows would be double glazed with 2 layers of 10.38mm laminated glass with 100mm air gap.

So you are talking about a total of two laminated panes, each made from two layers of 5mm glass with an acoustic interlayer, with a large air gap? That would work, yes, but to get the same isolation as the wall assembly, you'd need to increase the air gap to about 22 cm: That shouldn't be a problem, since your brickwork is already 20cm thick, and allowing for the stud+gap, you get a total available depth of 34cm. Allowing for frames, you should have no problems at all getting at least 25cm distance between your two panes But just to clarify: you would NOT use ready-made double-glazed units: you would put one frame with one single pane in the outer leaf (the brick wall), and another frame with the second pane in it, in the inner-leaf (the stud framed wall with two layers of drywall on the room side.

Door would be 2 x solid core doors, one opening out and one in, with heavy duty door seal/jam and about 6 cm air gap.

Nope. 6cm gap between your doors is waaaay to small. Here too you need two frames (not one). One frame/door in each leaf, and once again, AT LEAST 20cm air gap between them. More if possible.

my understanding is that the Rw + Ctr rating for those would be between 40 - 44 approximately.

Not the way you originally described it, but if done correctly, yes. "Correctly" assumes at least two full perimeter seals on each door, and a huge amount of mass in the doors (at least 30 kg/m2, hopefully much more).

FLOOR: probably just leave as concrete slab.

a) do you agree that it is pointless trying to achieve wall/door/window Rw+Ctr ratings much higher than the maximum i can achieve with the ceiling?

Right. So that's where you need to concentrate all your efforts. The ceiling / roof combination is by far your weakest link, so putting most of your effort into that would be the smart thing to do.

b) do you agree that double brick, with plasterboard (but no air gap) would achieve the rating i proposed above?

Nope!

c) I think that would be an average rating of about Rw+ Ctr of approximately 45 for my room.

Probably, if you do it right. But there's one thing you haven't mentioned that is rather important: HVAC! Since your walls will be sealed absolutely air-tight- you do need to have a ventilation system to bring in fresh air and remove stale air, and that needs to be designed to provide the same level as the rest of the building. You can't just poke a few holes in the wall to ventilate it!

My understanding is that sound not exceeding 45db residential areas is acceptable.

It's usually lower than that, and usually tied to the time of day. 45 might be fine during the day, but often it is lower at night, maybe 40 dBA or even 35 dBA (which is basically impossible to achieve anyway...).

Plus, different cities have different ways of measuring it: sometimes it is at the property line, at a fixed height above the ground, other times it is at the location of the complaining party. You really should check what it is in YOUR area: check with your local municipality.

Assuming that 45 dB is what you are allowed, and assuming typical 110 dB drums, that means you'd need 65 dB of isolation, total. Assuming your wall is 4m away from your neighbor's wall, you'd need about 55 dB of isolation from your building, to be safe (the other 10 would come form the distance). Of course, if drums is your biggest concern, then you should concentrate on low frequency isolation, not just overall isolation.

I’d rather buy more instruments with anything left over.

Don't forget to allow for treatment inside the room! the very fact of isolating it will make it sound worse inside, acoustically. Basically, isolation stops the sound from getting out: which implies that if it didn't go out, then it must have stayed in! So now you have all that sound that could not exit, bouncing around inside the room and making it sound awful. Your RT-60 time will go way up, so you need treatment in there to control that, and get it sounding good again.

- Stuart -

Hi Soundman, thanks for the reply and feedback, very much appreciated.

On reading your response, I fully realise that the ceiling, doors, windows are the biggest problem.

On your advice of NOT adding a coupled layer of gyprock to the walls, and just leaving it as brick, this would save me money that i can allocate to ensuring the ceiling, doors and windows are the best they can be to my requirements.

With this in mind, I have the following questions, and again, I appreciate the feedback.

1) Weakest point is the ceiling.
at the moment it looks like this, but the central beam will be replaced with LVLs and the whole structure reinforced: If I were to lay ceiling insulation in between the EXISTING roof joists, and then fix a layer 10mm plasterboard to the EXISTING roof joists, (meaning i'd be filling up any air gap between the existing tin/sarking and the new layer of Gyp with insulation) would that create one decent Leaf? OR would that actually be two leaf's, even though the air gap would be stuffed with insulation?

If i then did the suspended ceiling with 2x16mm fyrchek below the above suggestion, would this create a good 2 leaf system, OR would my modification of the original roof actually create a 3 leaf system which i'd obviously want to avoid?

In your opinion would that creation of the extra leaf justify the cost of an extra layer of 10mm plasterboard and insulation?

2)

Soundman2020 wrote:But then you'd have the problem of how to attach your two doors to that, and your windows, and still get them to act as proper MSM systems... with only a single leaf wall to attach them to, you can't make them into decoupled systems, so you would be severely limited in how much isolation you'd get from them.

If I accept that i can't have decoupled window or door systems, i have been exploring windows made of 12.76mm PVB which according to the glazier has a rating of 43.
I have read online on various suppliers websites that the rating ranges from 40 - 45, so 43 seems about right.

** Would adding a layer of 6mm polycarbonate sheeting fixed onto rubber seals over the INTERNAL side of the window frame, as secondary glazing, improve that noticeably?
The air gap between the two layers would be about 15cm.
From reading, an air gap may improve isolation by about 3db, and the polycarb sheeting is hard to find ratings on, but even if the secondary glazing only improved things by 6-8db, that would get it roughly the same as the dbl brick walls.

In regards to DOOR, if i accept single leaf walls, and therefore no option for a double door system, spending extra money on a professionally built acoustic door could be an option? What is your experience with those?

OR, could i achieve a rating of 45-50 from adding mass to a single solid core door, and obviously having a full perimeter seal, as I have seen in various home and semi-pro studios?

OR would building a second frame JUSt for the second door be another option?

Again, i hugely appreciate anyone's thoughts on this.
jp