Building a new studio in an old rustic barn

[sonoftherenegade]

Hello,

I’ve just purchased a home here in southwestern New Hampshire with a detached barn on the property. Working hard to transform the barn into my new studio as all of the recording equipment is currently crammed into the house for temporary storage. Any thoughts or advice on this renovation would be greatly appreciated!

The barn is a 21x21 space with a 16’ tall ceiling at the peak. My plan for the layout is to use this as one large open room, I’ve been working without a control room for quite some time and have become accustomed to that. Eventually I plan to add a small addition on two sides of the building, one for three isolated guitar/ bass amp rooms, and the other for an entryway and storage space.

For the sake of speed, my contractor and I have decided to tackle those additions separately, later on, and just work on getting the main room up and running for now.

In order to stay busy working, I record a lot of different material ranging from classical guitar to full bands, so I am needing to create a quiet space inside the barn and also to keep the sounds of the studio from disturbing the neighborhood. The closest neighbor is about 75 feet away with sparse woods in between. The barn is about 150 feet from the road, which is typically quiet, but I can count on one loud truck with no muffler about every other hour or so. There is a private airport nearby which is usually not a problem, but when the small planes fly overhead occasionally, they can be quite loud. The neighborhood is generally pretty quiet. My last recording space was actually just a few houses down the road, in a basement. I was there for five years and never had a complaint or issue.

So far we have gutted the barn and removed the old floor. Due to some challenges with pouring a concrete foundation and floor, we have decided instead to use the existing sonnet tubes and hired an engineer to design a wooden structure for the floor, which we can then pour lightweight concrete on top of. I've attached the picture of his plans.

1701-Jaffrey-frame.jpg

Currently, the walls are just the exterior barn boards with exposed studs and beams on the inside. Our thought is to fill these spaces with rigid foam to seal the wall and make a vapor barrier. We’ve installed the rafter mate foam in the ceiling to provide venting. The engineer has called for plywood sheathing on top of the rigid foam in two of the corner walls for structural support.

I thought we would then leave a 5” space before creating the interior wall and that we would fill that space with regular lightweight insulation. The plans for the interior wall is to use metal studs with resilient channel. On the channel we would hang two staggered layers of drywall with green glue in between. This plan would apply to the ceiling as well, although we may have to attach the metal studs to the existing barn structure for support somehow, I’m not quite sure about that yet.

My budget is $25,000 USD, although some has already been spent for the engineer and having a new electrical service run to the barn. That budget also includes money I will need for lighting and electrical wiring.

Some questions I have are, ‘Do my plans for the walls need more layers?’ Should I be looking into another drywall layer somewhere or some sort of mass loaded vinyl layer?

Also, there is an issue with the rafter ties that support the roof. As you can see in the engineer's picture, there are two sets. Originally, the rafter ties were right where the roof rafters meet the top plate of the walls. We removed those and installed new 2x8s, those are the ones up high on the picture, which was to be the location of the new ceiling. We did before and after measurements, they are holding the roof very well, but the inspector and engineer both said that they have to be lower and so those are the second rafter ties that you see in the engineer's picture, which have not yet been installed.

My problem is that I really wanted to have that extra ceiling height. We’ve discussed using the higher boards for the actual ceiling and having the lower boards be exposed in the room. Which is fine with me aesthetically, but does having those boards exposed in the room sort of ‘short circuit’ all the work of having a de-coupled interior wall? Will they just be carrying the outside vibrations right into the room and vice-versa?

Thanks for taking the time to read, any help is appreciated! I’ve attached a couple pics of the barn as it stands now.

IMG_1870.jpg

IMG_1871.jpg

IMG_1872.jpg

[Soundman2020]

HI there " sonoftherenegade", and Welcome!

OK, several things about your build that need a comment.

First, before anything else, you need to define how much isolation you need, in terms of decibels, not in in subjective, relative terms. You can't plug in the comment "not disturb the neighbors" to the equations! You need real numbers. So you'll need to get a sound level meter, make some suitable noise, and measure.

Plain and simple: If you don't have that number, then you have no idea where you are going, and will never actually get there. It's all just guess work and assumptions without a goal.

So that's the first order of business: define your isolation. Only then can we tell you if what you are doing is enough, or not, or too much.

Second, you have nearly 450 square feet of area to deal with, and a budget of 25k. Doing the math says that you are planning to spend no more than US$ 56 per square foot, yet you are doing a major refurbishing job, including structural modifications to both the floor and roof. I would say that you are falling short on your budget. You made no mention of HVAC, which could easily eat up a quarter of your budget all by itself, and no mention of acoustic treatment, furniture, of finishing. You also didn't mention windows and doors, which are always take a sizeable chunk of money to do, if you need good isolation. I suspect that you'll need to re-think your budget.

I’ve been working without a control room for quite some time and have become accustomed to that.

I'd like to hear more about how you did that in your current setup. I'd also suggest that you should look at ITU BS.1116-2 and EBU TECH-3276, to see how your current setup and your planned new setup fits in with those. You also didn't mention the purpose of your studio, so you might be fine with that if it is just basically a hobby space for you and some buddies to get together, jam a bit, and make some tracks to entertain friends and family. But if your intention is to make this into a viable commercial facility that turns out good quality albums to compete on the market, even on the indie market, then you might want to reconsider this aspect.

so I am needing to create a quiet space inside the barn and also to keep the sounds of the studio from disturbing the neighborhood. The closest neighbor is about 75 feet away with sparse woods in between. The barn is about 150 feet from the road, which is typically quiet, but I can count on one loud truck with no muffler about every other hour or so. There is a private airport nearby which is usually not a problem, but when the small planes fly overhead occasionally, they can be quite loud.

From what you say, it's clear that typical house type isolation is just not going to cut it for your place: you will need substantially more isolation than that. The question is "how much"? See above....

we have decided instead to use the existing sonnet tubes and hired an engineer to design a wooden structure for the floor, which we can then pour lightweight concrete on top of. I've attached the picture of his plans.

Is this going to he the only floor, or will you be floating another slab on top of this to get the actual isolation that you need? A single leaf light-weight concrete slab that is elevated above ground level is not going to provide good isolation, especially for things like drums, bass cabs, and similar.

Our thought is to fill these spaces with rigid foam to seal the wall and make a vapor barrier.

Yes. Or no. It it depends greatly on the type of rigid insulation you use there. If it is open-cell, then it would probably be OK, but if it is closed-cell, then that would be a big mistake. Closed-cell foam has practically no use in acoustics, because it has no useful acoustic properties at all. Since the microscopic cells are closed and sealed, sound waves cannot be affected by them as they travel through. That type of foam is good thermally, but useless acoustically. Use only insulation that works acoustically and is also good thermally. On a tight budget, that usually limits you to plain old fiberglass and mineral wool insulation types. Those are excellent, both thermally and acoustically. But not just any old insulation: you need to make sure that you get the right density: For this application, that would be 2 PCF density if you use fiberglass, or 3 PCF if you use mineral wool. Those provide the optimal acoustic conditions for wall insulation in an MSM system.

The engineer has called for plywood sheathing on top of the rigid foam in two of the corner walls for structural support.

Check if he will allow you to switch to OSB instead of plywood: it is similar structurally, but less expensive, and also more dense (which is good acoustically).

Another thing here: Before you put any foam anywhere, you MUST decide on the amount of isolation that you will need! It might be necessary to add additional mass to the outer leaf in order to get that, and the only way to do that is to "beef up" the outer leaf between the studs. You'd have to take the insulation out in order to do that, then put it back in again.

You also mentioned that you want to use the rigid foam as a vapor barrier, but that would be a mistake. Where you live, it gets cold, obviously (snow!), so you CANNOT have a vapor barrier that touches your outer-leaf surface. If you did, any moisture ih the air would condense on that vapor barrier up against the cold surface, where it will then create nasty problems such as mold, fungus and wood rot. The vapor barrier ALWAYS goes up against the warmer surface of the wall cavity, which is the inner-leaf in your case. And you can never have more than one vapor barrier inside a wall. You want only one, and it must be up against the inner surface.

I thought we would then leave a 5” space before creating the interior wall and that we would fill that space with regular lightweight insulation.

When you say ' a 5" space ', are you talking about a five inch gap between the framing of the existing outer leaf and the framing of the new inner-leaf? Or are you talking about a total 5 inches of air space between leaves? If the former, then why 5"? Assuming that your inner-leaf walls will be conventionally framed, that would give you a twelve inch air gap, which is fantastic for isolation but does take up a lot of floor area. You could probably get good isolation with a smaller gap. On the other hand, if you are talking about framing your inner-leaf walls inside-out, then you could in deed get just 5" of air space, but that might not be enough. Depending on how much isolation you need, and the frequencies you need it at, the MSM resonance might be to high with just a 5" gap.

The plans for the interior wall is to use metal studs with resilient channel.

Why? You implied that you are going to build separate stud framing for your inner walls, not attached to your outer leaf, and therefore those walls would already be fully decoupled: Why would you then need to decouple them a second time with RC? Decoupled is decoupled. There is no benefit to decoupling something that is already decoupled. Save yourself some money, and skip the RC. As long as your inner-leaf wall really is properly decoupled, then there's no need for the RC.

we would hang two staggered layers of drywall with green glue in between.

Do yourself a big favor, and substitute OSB for the first layer (on the studs). So you would have studs-OSB-GG-drywall. The density of OSB is only slightly less than drywall, but it has much high structural strength (especially in sheer), and also provides a nailing surface around the entire room: you would not need to hunt for studs in order to hang your acoustic treatment, or your electrical raceways. It will only increase your costs slightly, but you already saved a lot of mony by not using RC, so the net increase is likely zero. Or less!

This plan would apply to the ceiling as well, although we may have to attach the metal studs to the existing barn structure for support somehow, I’m not quite sure about that yet.

Why? Is there something wrong with the metal framing in your area, that prevents you from using it for ceilings? Is there some type of code issue? Is there a problem with spans and loads? Are you ware that if you attach your inner-leaf ceiling directly to your outer-leaf joists, you totally trash your isolation ?

My budget is $25,000 USD, although some has already been spent for the engineer and having a new electrical service run to the barn. That budget also includes money I will need for lighting and electrical wiring

As I already mentioned, you should probably take a look at that budget again. You made no mention of HVAC yet, which will cost a significant amount, as this is a studio.

Some questions I have are, ‘Do my plans for the walls need more layers?’

You are asking "Is my piece of string long enough?", but you have not yet told us what you want to use the string for! You are asking us if your plan will provide enough isolation, but you have not yet told us who much isolation you need. So the answer here is just a question mark. Nobody can answer that question until you provide the information that we need to answer it. Your plan might be just fine, it might be ay insufficient, or it might be overkill. There's no way of knowing until you define the number. In effect, you are embarking on a journey but you don't know where you are going yet, or even why you are going there!

Should I be looking into another drywall layer somewhere or some sort of mass loaded vinyl layer?

Why MLV? You don't have enough money to use MLV on your walls: you would very literally have to add another zero on the end of your budget if you wanted to do that. MLV is about fourteen times more expensive than drywall, to get the same mass. It's a wonderful product! .... if you happen to be in the business of selling it. For they buyer, it's not so wonderful. Think of it this way: the equations in physics that define how well a barrier will stop sound are based on mass. The more mass you have, the better isolation you have. But there's no place to insert the price tag into those equations. Sound waves really don't care how much you pay for your mass. The are not elitist, they won't be impressed if you forked over huge wads of money to get that mass: they can't even read the price tags anyway! All they see is the mass itself, and they react to that. So unless you want to make a huge increase in your budget, forget MLV. It does have some uses in acoustics, such as for limp membrane devices, and for isolating round objects like pipes and ducts, which would be really hard to do any other way, and also for putting a lot of mass into a thin space. But using MLV to add mass to a wall is pretty pointless.¡a dn very expensive exercise. Yes, it works, because mass is mass, but Wow! is it ever an expensive way of getting isolation!

Originally, the rafter ties were right where the roof rafters meet the top plate of the walls. We removed those and installed new 2x8s, those are the ones up high on the picture, which was to be the location of the new ceiling. We did before and after measurements

You removed structural members form the roof, then re-positioned them BEFORE consulting a structural engineer? You are a brave man! And lucky.... What "measurements" are you referring to? Are you saying that you somehow measured the stresses and tensions created by the roof on the walls, and determined that your raised ties were doing the job of keeping those in check? If not, then what "measurements" are you talking about?

they are holding the roof very well,

That is not the purpose of those ties. They are not there to "hold the roof" at all! They are there to prevent the loads on the roof from spreading the wall tops apart, and causing structural failure, which would bring the entire building crashing down on your head.

but the inspector and engineer both said that they have to be lower

Smart people, those two! They actually do understand the purpose of those collar ties, and they also know that the wind load and snow load and other live loads would have crushed your walls sooner or later.

those are the second rafter ties that you see in the engineer's picture, which have not yet been installed.

Put those in as soon as you possibly can. You do not want to leave unrestrained lateral forces pushing out your walls for very long.

Here's a quick test: accurately measure the distance between opposite wall plates at the very end of the room, where the end walls are keeping all that in check, then measure again at the center of the room, where there is not restraint. I'm betting that there will be a substantial difference in those distances already, and it will only grow with time.

My problem is that I really wanted to have that extra ceiling height. We’ve discussed using the higher boards for the actual ceiling and having the lower boards be exposed in the room. Which is fine with me aesthetically, but does having those boards exposed in the room sort of ‘short circuit’ all the work of having a de-coupled interior wall? Will they just be carrying the outside vibrations right into the room and vice-versa?

Exactly. Doing that would trash your isolation, as you would have multiple flanking paths between your leaves. You cannot allow even a single nail to connect between the two leaves, let alone a few dozen 2x8's! A single nail will already harm your isolation very noticeably, so imagine what a 2x8 will do. Then multiply that by the number fof 2x8s....

If you need to convince yourself of this, then go find an old-fashioned tuning fork: the type musicians used to use before electronic tuners were invented. Tap that on something solid, then hold it up in the air a couple of feet away from your face. That's how much sound will be transferred from leaf to leaf in a properly decoupled wall. Now tap it again then set the bottom end of the fork down firmly on the surface of a table: that's how much sound will be transferred between leaves if there is just one nail connecting them. 'Nuf said.

Unfortunately, your ceiling height is limited by the height of those collar ties on your trusses. With careful design of your ceiling, you can get your final inner-leaf acoustic ceiling height to within about an inch of those collar ties, but that's it.

There's a long shot here: Ask your engineer if he would allow you to move those collar ties up a bit more if you also sister your trusses. In other words, to each of the existing rafters, bolt and/or nail an identical rafter right nest to it: that's the "sister". So your rafters end up as 4x8s, instead of 2x8's. With a bit of luck, that might provide enough additional resistance to bending to allow you another few inches of height for the collar ties. Maybe not: only your structural engineer can say for sure, but it would be worth asking him. Another option might be to halve the spacing: Insert an additional truss midway between each pair of existing trusses.

Those are the only two options that would conceivably allow you to raise the collar ties, but the difference in height might not be worth the effort and expense. The engineer can tell you how much higher you'd be able to move the collar ties, then you'll have to decide if it is worth it or not.

By the way, you are missing out on one key issue here: you cannot use your roof as the outer leaf, since it is ventilated. You will need to put plywood, OSB, MDF or drywall on the trusses to create the actual acoustic leaf. Yes, that will create a three-leaf ceiling, but you ave no choice, and you can compensate for that. So you do need to tell your engineer that you will be putting a ceiling directly on those trusses: he needs to know that, to include the weight of that ceiling in his calculations of where the collar ties have to go, and also check the total roof loading meets specs.


- Stuart -

[sonoftherenegade]

Thanks so much for your response and for all of this information Stuart! This has already really helped me out in my planning.

I'd like to hear more about how you did that in your current setup.

I know that it is often frowned upon or considered crazy to have the control area in the open space with the live room. But as I said, I’ve been working this way for a while now, I really enjoy the communication flow with the artists when we are in the same room. Of course I will have to acoustically treat the control area a little differently than the recording area of the room, but that’s something I’ll be experimenting with.

So you'll need to get a sound level meter, make some suitable noise, and measure.

I will work on this this afternoon!

Is this going to he the only floor, or will you be floating another slab on top of this to get the actual isolation that you need?

Well this was going to be the only floor, but I am reconsidering that now after your comments. I spoke with the engineer about possibly adding a second floating style floor on top of the slab. He said that it shouldn’t be a problem weight wise if I used wood. I’m looking into the Kinetics roll out isolation material for wood floors.

That type of foam is good thermally, but useless acoustically. Use only insulation that works acoustically and is also good thermally. On a tight budget, that usually limits you to plain old fiberglass and mineral wool insulation types.

Part of the purpose of filling these spaces with the rigid foam is that the exterior boards of the barn are not tight, in some cases you can see daylight. I thought the foam board would at least seal those gaps in order to act as the outer leaf. After your comments I am rethinking this and considering filling these spaces with OSB board to both seal the wall and also add mass to the outer leaf.

Check if he will allow you to switch to OSB instead of plywood: it is similar structurally, but less expensive, and also more dense (which is good acoustically).

Thank you, I did ask and he said that was fine.

When you say ' a 5" space ', are you talking about a five inch gap between the framing of the existing outer leaf and the framing of the new inner-leaf?

Yes, that is what I meant, 5” between the leaves, sorry for the poor wording.

There is no benefit to decoupling something that is already decoupled. Save yourself some money, and skip the RC.

That totally makes sense, thanks for helping me simplify!

Do yourself a big favor, and substitute OSB for the first layer (on the studs).

Both the contractor and I love this idea, thank you!

Are you ware that if you attach your inner-leaf ceiling directly to your outer-leaf joists, you totally trash your isolation ?

You’re right, I don’t know why I was worried about this issue, that shouldn’t be necessary.

You made no mention of HVAC yet, which will cost a significant amount, as this is a studio.

Honestly, I am on a tight budget and am not planning on any complex HVAC. My plan for the heating is to use electric hydronic baseboards which are supposedly efficient and fairly quiet. For the summer I did look into a mini split AC setup, but am considering using a standalone AC unit that could drain with a small hose outside somewhere or even into a container, which I would simply run in between takes. Also can open the front door here and there for air circulation. Not the most professional setup I realize, but trying to keep things simple and inexpensive.

Why MLV? You don't have enough money to use MLV on your walls

Great point! Thinking outside my budget, will rule this one out.

You removed structural members form the roof, then re-positioned them BEFORE consulting a structural engineer?

Well, I made sure to have guidance from the contractor, we proceeded carefully after some planning.

accurately measure the distance between opposite wall plates at the very end of the room

This is the measurement I was talking about. Haven’t checked in the last few days, but for the first several days there was no change at all. I will keep tabs on that though until the lower ties are installed.

Unfortunately, your ceiling height is limited by the height of those collar ties on your trusses

Thanks, I have come to terms with this. I ran the ‘long shot’ ideas by the engineer and he would prefer they stay positioned as they are in his original plan. And so that’s fine! I’ve had to adjust my vision for the space a little, but I think it will still be a decent ceiling height, about 10’ or so. Thank you for your advice and thoughts on this!

You mentioned that with careful planning I could get the ceiling pretty close to those collar ties? I'm wondering if you would be willing to share any ideas about this? Would I need to build an outer leaf above those ties?

It is true, my budget is fairly limited for this project. I can’t afford to make the studio completely perfect, but I do want to get as close as I can, particularly in having a quiet space. It seems to me that I can improve the inside of the room over time with additional acoustic treatment and a knowledge of how the space sounds and works. But I can’t go back and add mass to the outer leaf or anything like that once it’s up and running. So I really appreciate the help and input with this planning, thank you!!

[sonoftherenegade]

I have numbers from some sound meter readings that I've taken today.

Standing just outside the barn with no activity going on outside, the ambient volume is averaging around 42 db[C]

When a car passes by it reads as high as 56 db[C]

My mixing volume range is usually between 74 - 83 db[C]

Some recordings that I do of soft singers and soft acoustic guitar can range between 63 - 74 db[C]

I've never taken a reading from a live band in the studio, usually because I'm running around like crazy trying to make sure everyone's happy and also get a decent recording, but from what I can find, an average rock band might read somewhere around 110 db?

Unfortunately, I cannot really get any data from inside the barn, since the floor has been completely removed and is open to the outside.

[sonoftherenegade]

After more researching I am realizing my naivete when it comes to the HVAC system. Too much heat and humidity was an issue in my last space, I guess I thought that the larger room volume would help with this problem. But I can understand that you need some circulation in an otherwise airtight room and that my space will be too large and humid for any type of indoor, ventless AC unit. And so I have more research and work to do.

[sonoftherenegade]

Hi all,

Well we've been working hard and have finished the framing for the floor today.

IMG_1901 (1).jpg

We are hoping to finish squaring up the old barn walls with the new floor structure and to secure it all in place tomorrow. On top of the floor framing will be a layer of plywood, a thin layer of rigid foam (to prevent the concrete from contacting cold lumber as this floor is up off of grade and resting on sonnet tubes), and then 4" of lightweight concrete.

I'm still unsure of what to do with the floor beyond that. I've considered completing my room within a room construction and then playing some loud drums and bass inside to see how bad it is and possibly installing the floating floor afterward if necessary. Is that a crazy idea? I know it's a rather backwards process, but is it possible to do?

As for taking the next step with a floating floor, the Kinetics RIM for wood floors seems like an appropriate option since my floor cannot support much additional weight beyond the concrete. Has anyone used this stuff with good results? It's rather expensive (for my small budget), but seems to make up for that in ease of installation? Any thoughts on this or similar products would be greatly appreciated, thanks!

[sonoftherenegade]

Well it’s been a while and I finally had a chance to sweep the floor so I figured it’d be a good time to snap a couple photos and post an update!

The concrete floor has been poured, it’s a 4” slab of a 4000 lb mix. They said the floor came out nice and flat, judging by how well the finishing tools ran across the floor.

The new rafter ties have been installed to the engineer’s specs, with 1/2” osb board fastened on top creating a new celing/ attic floor. r38 insulation was placed on top of the floor in the attic space.

We’ve removed all of the old barn windows and doors and filled the cavities with osb board and 2x4 studs. From the outside it looks a little rough right now, but we’ll get some siding up soon.

All of the barn walls have been filled and sealed with foil faced 1/2” rigid foam and then with r11 insulation. Except for the roof areas leading up to the new ceiling which were filled with r19.

We’ve created a new front entrance with an outswing door. This was done in anticipation of the acoustic inswing door which will be part of the inner leaf. So there will be two doors leading into the main room.

The Kinetic roll out insulation for the floating floor has arrived, you can see it in the pictures as the two large trash bags. Hoping to get that laid out over the weekend.

Once the floating floor is installed we can begin on the inner leaf structure which will be a metal stud frame with osb/ green glue/ drywall on the inside.

For heating, I’ve chosen to go with three electric hydronic baseboard units which should hopefully be more than enough for the space and they are supposedly fairly quiet.

http://www.homedepot.com/p/Cadet-SoftHe ... /100157848

For cooling, I’m looking at a Daikin unit which is also supposedly quiet, although I am thinking I may have to power on/off during recording times, but will place a shutoff switch nearby by the control area for this reason.

https://www.ecomfort.com/Daikin-KN12NMVJU/p65530.html

And for general air circulation, my plan is to manage the entrance door and occasionally open between recording. The near-future plan is to add an addition to the front of the building (where the new front door is) to create an entryway/ storage area/ possible future amp isolation room. The main entrance will eventually be to the side of this addition. My thought is to place a window on the wall of the addition, directly in front of the door into the main room, so that I can open that right up and flood some new air into the room when needed. Not ideal, I realize, but getting up to do things like open the door gives me an excuse to stretch a little bit anyway.

I’ll try to post some pictures of the roll out floor material over the weekend.

I don’t have any specific questions at this time, but definitely welcome any comments or suggestions. Thanks!

[garethmetcalf]

Hi
Looks like an interesting build and great to see the pictures. I'm by no means an expert, but in doing the research for my own build I'm concerned about your plans for air. If you are trying to build a studio that's a room in a room for improved sound isolation you will also end up with a room where no air can get in or out which means you could worst case asphyxiate but at the least be uncomfortable.

As I understand it, you need to create a system with an air inlet and an air outlet that moves enough air for 6 complete air changes in an hour. In order to keep the noise in (and out) you build silencers in both of the inlet and outlet systems, that force the air to change speed dramatically and turn corners, which combine to reduce the noise transmission.

It doesn't cost much except some wood, ducting and a fan but is hugely important.

There's loads of posts about these silencers etc on this most useful forum! sorry I havent linked to any for you.

Good luck with the build!
Gareth

[Soundman2020]

If you are trying to build a studio that's a room in a room for improved sound isolation you will also end up with a room where no air can get in or out which means you could worst case asphyxiate but at the least be uncomfortable.

Yep! Very true....

As I understand it, you need to create a system with an air inlet and an air outlet that moves enough air for 6 complete air changes in an hour. In order to keep the noise in (and out) you build silencers in both of the inlet and outlet systems, that force the air to change speed dramatically and turn corners, which combine to reduce the noise transmission

Perfect! You said in two dozen words what it takes me two thousand to say! Very good summary indeed. Clear, concise, and spot on.

It doesn't cost much except some wood, ducting and a fan but is hugely important.

Yes!

- Stuart -