John Sayers' Recording Studio Design Forum Archive

You seem to not be getting the point I was making: You need to measure the cross sectional area in SEVERAL places, and make sure that it remains reasonably constant throughout. There can be changes, yes, but you don't want to create bottle-necks where you force a very high speed and very low pressure through a small cross-section, then have it widen out to a much larger area, forcing the air to slow down and suddenly increasing the pressure. That large change only needs to happen in a couple of spots, not frequently throughout. Every time you have a large change in pressure and velocity, there is energy loss, which implies a higher static pressure, and a larger fan.

- Stuart -

Okay, I see. I guess that's where I'm confused as though it may not be clear in my design, the width and height throughout my pathway is indeed constant.

So, providing I have a cross sectional area that is at least double (ideally, even more) the cross sectional area of my ducting, then a design like this (a 'y' split') could work?

If yes, then I'll do the following next:

- Spec a HRV that provides the right amount of fresh air at the correct velocity
- Size the duct work accordingly
- Size the silencer boxes to at least double the cross sectional area of the ducting
- Find registers rated below NC20

Paul

- Stuart -

- Spec a HRV that provides the right amount of fresh air at the correct velocity

This means calculating your systems static pressure. Check the sticky at the top of the design forum I started. There has been some great info posted there. I hope to find some time to post more helpful stuff in that thread.

Greg

Gregwor wrote:

- Spec a HRV that provides the right amount of fresh air at the correct velocity

This means calculating your systems static pressure. Check the sticky at the top of the design forum I started. There has been some great info posted there. I hope to find some time to post more helpful stuff in that thread.

Greg

I just noticed that thread, it's very informative, thanks for sharing it!

I found this written by Rod Gervais:

"Fresh air supply systems have to do with the number of people in the room - not the volume of the room.

Picture it this way to get your head around the concept:

In a room that was 6' wide - by 6' deep - with 8' high ceilings you could comfortably put 1 person (perhaps 2 if they really REALLY liked each other ).......... that wouldn't suddenly change simply because those ceilings were 40' instead of 8'.

15cfm per person would be a minimum fresh air supply.........

So figure out the maximum number of people that will be in the room - and derive the volume by multiplying the total by 15 (or 20 if you want a little buffer)

Once you know the volume of air you need - you need to then choose a fan capable of providing that volume........

When it comes to choosing the fan don't let yourself be fooled into thinking that a computer fan can provide that air.......... I don't say this to imply you would - simply a comment because I see a lot of people who believe they will....... thus I mention it just as an aside.

Whatever fan you choose will have specifications (available) that not only tell you the volume of air they provide - but also the velocity that air is going to be traveling as it leaves the fan......... and everything is about the combination of those 2 elements when it comes to figuring this out.

As a general rule - I would not concern myself (if I were you) about trying to calculate friction loss in the duct work (friction loss doesn't really come into play until after the first 100 of straight duct - or combination of straight duct/elbows that equal 100 of straight duct due to additional losses in those elbows)

I would also avoid (like the plague) using any of the flex duct products for long runs..... in the case of flex duct friction loss does come into play much quicker than rigid duct systems - you'll always do better with rigid duct.

OK - so you know your fan size - and you've figured out the duct size you can use to make it from point "A" (which is the fan) to point "B" (your inlet location in the room) - and the corresponding size/location for the outlet in the room (point "C") back to the outside world (point "D")

That would be the total duct length you have to consider for the fan.

OK - so you know the fan size - you know the volume - you sized the duct (so you know the velocity) and now you want to get the air into/out of the room.

As far as location goes - as long as you have at least 4' between the inlet/outlet for the system I would not worry about short cycling the air - note that if you are forced to put the isolation boxes side by side you can deal with that vertically.

Determining the size of your boxes is not that difficult........ you want to get the volume of air into the room while decreasing velocity to less than 300fpm, if you have the room 100fpm is a great target goal.

You should use at least 3 baffles inside of the iso-box - these force the air to turn corners which blocks outside noise from making it's way through the box..

The last piece of the puzzle is the grille - I always specify grilles manufactured by Nailor Industries - they are a bit pricy - but you have a ton of testing done on their products from the perspective of acoustics....... and you can then choose exactly the right grille/louver for your velocity (in a perfect world pick a louver with an NC-0 rating - but never a rating higher than NC-20)

However as long as the manufacturer can provide with you with test data any manufacture's grilles should work just as well.........

Avoid cheap grilles with no data - they will most probably be very noisy

A cheap grille forms an added barrier to air flow - a bottle neck if you will - and (as such) that can be a point of introducing noise - which is what you have been trying to avoid all along with proper sizing and baffle design.......

I hope this helped,

Rod"

So he's saying it's best to work out the required air supply based on the amount of people that'll likely be in the room(s), but I noticed in your previous reply you mentioned working it out based on the 30% minimum.

If I worked it out using the amount of people then if I said there is going to be 10 people then it would be:

10 x 15cfm = 150cfm

If I worked out using the 30% minium fresh for my room volume with 6 air changes per hour then it would be:

23.92 x 19.57 x 11 x 6 = 30,895.55

30,895.55 / 60 = 514.93

30% of 514.93 = 154.48cfm

So, very similar numbers. I just want to check with you that I have done that all right, and therefore I need to spec a fan/HRV that can provide that amount of cfm?

In the UK we use the metric system and I am only see specs in m3/h, things like this:

Extract Air Performance:
Boost – 100 m3/hour
Trickle – 30 m3/hour

Intake Air Performance:
Boost – 100 m3/hour
Trickle – 30 m3/hour

which means I need to convert my cfm to m3/h:

154.48cfm x 60 = 9268.8

9268.8 = 262.46 m3/h

Have I worked that out correctly?


Paul

Looks good!

Greg

Hi again guys,

I would appreciate some help regarding the triple leaf effect. I have read the threads on here as well as the Wyle paper and though I understand some of it, I am not clever enough to understand the more complex maths.

My thinking is related to my build; as I am building my studio in stages, starting with the inner inside out leaf of the control room, my plan is to construct the outer leaf as well as all the other rooms at a later stage when I have the money and time to do so.

That has complicated things for many reasons, but it means I need to be extra vigilant (don't we all) right now while in the planning stage.

Now to my question: I know that putting a dividing wall in between a double wall assembly is generally not a good idea if you want maximum low frequency isolation, as it splits the air gap up into smaller cavities, changing the frequency at which the wall assembly isolates down to etc etc... so in layman's terms, a triple leaf wall assembly constructed of the same materials with the same overall thickness as the equivalent double wall assembly would perform worse at low frequencies than the double wall assembly.

But what if after constructing a double wall assembly, with a nice big air gap, and which isolates effectively as required all the way down you then construct another wall in front of it with another big air gap and extra materials? In other words, the new triple leaf assembly's initial air gap would be the same as the original double wall assembly, but with another added air gap and more mass on the other side.

Why am I asking this?

I was wondering if I could build my control room fully isolated now, and then at a later date add on the live room and other rooms without needing to demolish the one wall in question. The wall that I'd need to demolish would be supporting the outer leaf roof, and so it would not be a simple task. I would build my outer leaf with concrete blocks, and my inner leaf is timber frame.

If it is not a good idea to use this triple wall then I will just have to make do with a single leaf structure for the time being, but if it either a) improves isolation or b) performs as good a double wall, then it would be a nice way to go for me.

I have attached some drawings of what I had in mind with some calculations:
Marked in red is the triple wall in question. Control room to the left, live room to the right. My original floor plan does not have this assembly, there are only two decoupled walls. Concentrating just on the control room, if I built a concrete block wall all the way around the inner timber leaf, then for the time being that room would be completely isolated, then I could add on and extend with the other rooms later.

This triple leaf design would maintain the exact same air gap between the first and second leaves, but introduces a third leaf. This means it takes up more space, which eats in to the side of my live room. The ceilings for the control room and live rooms would be supported on the inner leaves of each room and the roof the whole building would be supported on the outer block walls as well as this middle concrete block wall.

The double wall option would be like this:
The triple wall option would be like this:
And here's the calculations separately for both the control room side of the triple leaf assembly, and the live room side of the assembly:

Control Room Side Live Room Side And here's the data for just the double leaf option: I can calculate the wall assemblies for a double leaf properly, but I do not know how to calculate for a triple leaf assembly properly, maybe someone much cleverer than me can calculate it for me based on the info I've given here?

Paul

Cool to see you're finding the calculator useful! I was wanting to make a three leaf version of it sometime. I actually started on it, but it's much more daunting than a two leaf and I'd rather spend any free time I have with my wife and kids. . . I know.... I'm selfish!

Anyway, I fully understand your dilemma and as much as I appreciate your efforts and desire for killer isolation, if appears with your concrete leaf, you're going to be limited by flanking in your slab. I mean, the values the calculator put out are theoretical assuming your floor is able to provide that level of isolation as well. Also, HVAC insertion loss. Having said that, I can confidently say that your three leaf system will be fine for what you're doing. If you didn't have concrete, it'd be a different story.

Greg

Gregwor wrote:Cool to see you're finding the calculator useful! I was wanting to make a three leaf version of it sometime. I actually started on it, but it's much more daunting than a two leaf and I'd rather spend any free time I have with my wife and kids. . . I know.... I'm selfish!

Incredibly selfish... how dare you

Anyway, I fully understand your dilemma and as much as I appreciate your efforts and desire for killer isolation, if appears with your concrete leaf, you're going to be limited by flanking in your slab. I mean, the values the calculator put out are theoretical assuming your floor is able to provide that level of isolation as well. Also, HVAC insertion loss. Having said that, I can confidently say that your three leaf system will be fine for what you're doing. If you didn't have concrete, it'd be a different story.

Thanks Greg, that's very good to know. I wonder, could I even expect better isolation with the concrete leaf in the middle?

For what it's worth, the plan is for each leaf to be built on its own leaf. So for that middle wall between the control and live room there would be three fully decoupled slabs. The middle one would be the same one used for my outer leaf running all the way round the perimeter of the entire building.

Paul

For what it's worth, the plan is for each leaf to be built on its own leaf. So for that middle wall between the control and live room there would be three fully decoupled slabs. The middle one would be the same one used for my outer leaf running all the way round the perimeter of the entire building.

I bet you meant to say that each leaf will be built on it's own slab.. ??

If so, that's awesome and will certainly improve your isolation.

Greg

Gregwor wrote:

For what it's worth, the plan is for each leaf to be built on its own leaf. So for that middle wall between the control and live room there would be three fully decoupled slabs. The middle one would be the same one used for my outer leaf running all the way round the perimeter of the entire building.

I bet you meant to say that each leaf will be built on it's own slab.. ??

If so, that's awesome and will certainly improve your isolation.

Greg

Whoops! Yes, that's exactly what I meant to say, sorry for the typo.

Great, thanks for your reassurance. Now back to HVAC...

What kind of ducting are you using Greg? Are you using rigid or flex duct?

Paul

What kind of ducting are you using Greg? Are you using rigid or flex duct?

Sheet metal except between a two of the silencer boxes I plan to use flex duct. That will be like 4 feet or so.

For between all of my other silencers, I'll join the MDF sleeves using a product from this company:

http://www.durodyne.com/connector.php

Greg

Just a quick question: Has anyone ever used this product?

https://www.insulationshop.co/british_g ... _19mm.html

19mm thick, 15kg/m2 surface density and in 2' wide sheets. The price is also not bad.

Thoughts?

Just a quick question: Has anyone ever used this product?

https://www.insulationshop.co/british_g ... _19mm.html

19mm thick, 15kg/m2 surface density and in 2' wide sheets. The price is also not bad.

Thoughts?

It looks like good stuff!

Greg

Gregwor wrote:

Just a quick question: Has anyone ever used this product?

https://www.insulationshop.co/british_g ... _19mm.html

19mm thick, 15kg/m2 surface density and in 2' wide sheets. The price is also not bad.

Thoughts?

It looks like good stuff!

Greg

Excellent! The plan is to use a layer of this then a layer of 12.5mm 8kg/m2. Both of these layers will go over the 18mm OSB I have up already, so the total surface density will be around 34kg/m2. According to your calculator this is what will be needed (in conjunction with a 6” airspace and then concrete blocks) to isolate all the way down to the low lows with a tl in the 60s.

One thing I was thinking about Greg, is the flex element of panels. Is there any realistic way of either being able to predict what effect that has on increasing TL or compensating for it?

Paul