HRV A/C undone

[tez]

My maiden real post, after many years sitting on the sidelines, envious of watching some great rooms go up.
I've had finalised room plans for a couple of years, now almost ready to build.
As has often been said, the air is the last, but not at all the least, part. I've given it little bits here and there, but now confronted with reality and choices, as well as budget.
A topic that I’m really a fish out of water in, but I’ve tried to get most of it sorted.

My post is to see if the dots are joined in HVAC design, and a check as to what I’ve planned for the rest of the system.

My “hobby” PostProduction/Listening room has been designed by a pro, so I can’t show all plans or precise measurements for analysing, but that shouldn’t be critical considering the issue is HVAC. Drawings are close, and sorry, I’m way too old to go through learning Sketchup for a single project, so CAD plan and elevations it is.

The essentials, approx. 9m x 6m x 4m, with a T Grid drop ceiling at 3m. A great size, and very close to Sepmyer 1:1.6:2.3
Location is rural, only neighbour is 80m away, and often quiet enough to hear the koalas fart. Gets pretty noisy with 120km/h winds sometimes.

As isolation isn’t an issue, single wall, lightweight steel frame and a skillion ( monopitch ) corrugated steel roof. Main issue with this is the truss system getting in the way of ducts, with 500mm at the high side, 300mm mid span and stuff all on the low side. As it’s a bushfire area, cladding is MgO Magnesium Oxide Board, and a 25mm air gap ( sealed all around ) of 25mm EPS Battens.
Internally MgO and 16mm Fire Rated Plasterboard. Due to extreme local costs, no GG or CLD. BTW. The MgO sheets are 24mm thick in shiplap fixing.

Due to the minimum roof space, I want to get the majority of the ducting done while it's just a frame, once the roofing is on, and before the ceiling sheets go up. Access will be from the outside, up a ladder then an access hatch.

I’m not about to detail why this has taken over 3 years, but there’s been many and varied setbacks, some of which have caused delays, others drained the budget, even eating up the contingency reserve.

HVAC.
No windows, so 2 years ago I had an Engineer work out details for a fresh air supply to Code. Engineer got paid twice the price of the $350 fan, an a flex duct sketch.
Lots of looking into ducting, then AC and HRV made me realise more design work was needed, but the lowest quote was $4,000.
Besides the fresh air fan, I’ve decided to include HRV, and also A/C.

I’ve relied a lot on what is in forums, but I confess to “sensory overload” and age related defects sometimes doing my head in. I’ve gone as far as I can.

I discovered a unit that provides fresh air, and at the same time, HRV. http://www.titon.co.uk range is MHRV Titon. Model that suits my room
TitonHRV 1.25QPlus

Original Fan spec required 50l/s @ 80Pa - based on 4 people in the room
Titon HRV has continuously variable fan speed, but 50l/s @ 150Pa - but highest speed.
The noise figures are in the Acoustic Results table. Most of the time there’ll only be one in the room, so approx 15l/s and fan speed 2.

The HVR can use 100mm or 125mm duct. For now, I chose 100mm as 125mm is hard to get, and as 25mm Duct Liner will be fitted, 100mm results in 150mm Rigid Metal Ducting. No luck finding 175mm if 125 internal was picked.

I think I read that smaller duct is OK as long as it only gets to the silencer boxes.
The sketch plan shows Supply duct first with a 90º bend into a Y and angles to get to the Silencers, which need another 90º to go down into Silencers.
2 ducts would halve the velocity, and again with the Silencers, if I read that properly.
50l/s with 100mm gets 6m/s . end goal is hopefully the magic 100fpm = .5m/s though 1m/s is OK for my purpose.
I assume the Y split halves the velocity, so that each input port on the silencers should be 3m/s ?
Jumping to the other side of the Silencer, at 50l/s with 1m/s my Duct sizer App says 250mm diameter, so 300mm with 25mm liner.

The roof space won’t allow larger ducts, due to the monopitch/monoslope/skillion and multiple truss members.
As it severely restricts silencer placement, and as there is a 900mm “plenum” drop from structural ceiling to T-grid, it looks like a lot of space to come up with the best dimensions.
That’s where, if the earlier setup is OK, I think I need help.

Input of 100mm duct = .008m2 Output 250mm = .05m2 (rounded)
If I got this right, the Silencer needs a cross section area of .05m2. Nominal starting point = 500m x 100mm or 200mm x 250mm
( metric makes some calcs easier )
Considering the other “rule” that there should be a long length of straight duct from silencer to diffuser, and there’s only 900mm maximum, the questions begin to multiply.
Should the Silencer be thin and wide, and if so, what the thinnest ratio or dimension to use.
If the output is 250mm dia, should that be the minimum height.
To maintain the isolation of the ceiling, the silencer walls will be nearly 50mm ( 2 inches )
How many baffles, open to suggestions., and plenty of ceiling space available.
In the sketch, I’ve shown the Silencer “reversing’ under the incoming duct to add another turn into the system.
It also places the output roughly where I think the diffusers might best be placed.

If a 250mm duct is workable, and the short duct to diffuser as well, then my next problem, and the one I least understand, is working out diffusors and return air grilles.
No Nailor option here, but a few recommended options down below, if they are suitable.

Again, uneducated guess in providing only one large eggrcrate grille for return air, but totally unsure if the silencer should be different to the supply units.
I’ve run a single return duct around the high side in the roof space. Still a 100mm inner, if that’s not an issue.

A/C was sized at 5Kw cooling, and I picked the lowest noise spec, a Mitsubishi split system, and plan to position up around 2.4m on a side will between the supply and return vents, unless there’s a more scientific method.
If you're Downunder, this is a nice cooling calculator- need to input your Oz city though. Also, each box needs a positive input, so a .1 if you don't have windows. http://www.fairair.com.au/Calculator.Size.aspx
All fixing techniques, eg Isolation hangers, Flex Ducts at joints, complete and total sealing will be used.

comments or critiques ??
100mm from HRV to Silencer ?

Questions.
Would adding a “reverse reducer” , “cone” at the input to each silencer have any benefit on the flow or velocity, as a “smoother” transition than a direct join?

Does reversing the silencer box, effectively a U turn with 2 x 90º turns, add too much static pressure or other effect?

How thick or thin should the silencer box be. This will impact on how much large duct will fit between output down to Supply Diffusor.

Best size of Diffusor, presuming ii’s limited by the size of the large supply ducting. 600 x 600 to fit in Ceiling Grid sounds good, but is it right?

Are duct lengths ok, or can they be shortened at all?
Roof cowls and duct for supply and exhaust under 1m each.

Ducting. besides the regular rigid metal duct, I’ve located ( for the 150mm ) a Split Seam duct, that allows sections to be shipped within each other, saving on freight costs. Any issues in using that ?

The question to catch all, what have I missed?


Budget, a lot of other issues means that there isn’t much left. Maybe $3k for HRV($1.6k), duct and Diffusors. A/C has been bought.

HVACschematic.pdf

Bradflo 4 way sound selection.pdf

Bradflo egg crate sound selection.pdf

[Soundman2020]

Hi Tez. Welcome!

My “hobby” PostProduction/Listening room has been designed by a pro,

Great! But you probably should have gotten him to include the HVAC design in there too: it's always a good idea to integrate as much as possible, so it all works together.

So, first question: What level of isolation did your designer make the room for? Your HVAC system needs to be designed to the same or greater level of isolation. Putting in HVAC means chopping enormous holes in the walls or ceiling, which of courses trashes all of your isolation, so the "thing" that you put in that hole must, logically, restore the same amount of isolation. So before anyone here can check your HVAC design, we'd need to know the level of isolation that the room is designed for, so that your HVAC system is kept at the same level.

so I can’t show all plans or precise measurements for analysing, but that shouldn’t be critical considering the issue is HVAC.

No problem, probably, but we do need to know the design figure for isolation, and that certainly isn't a trade secret!

I’m way too old to go through learning Sketchup for a single project, so CAD plan and elevations it is.

OK; but please do check out the preamble to the "rules for posting"...

9m x 6m x 4m, with a T Grid drop ceiling at 3m. A great size, and very close to Sepmyer 1:1.6:2.3

Ummm Sorry, but 9m x 6m x 4m is NOT close to Sepmeyer 1. That's a ratio of 1 : 1.5 : 2.25. It is close to Louden's fourth-best ratio, but far from Sepmeyer's. That's still a reasonably good ratio, though, so no problem. It's also a nice large room. Good possibilities.

with a T Grid drop ceiling at 3m.

Drop ceiling? In a studio control room? That's unusual... I thought you said it was designed by a professional studio designer?

I'm also assuming that the partial CAD drawings you provided are very much not to scale, and very much incomplete on purpose, because they don't make a lot of sense acoustically as shown. It looks like it is supposed to be an RFZ room, but the proportions and geometry are wrong, and the soffits are incomplete... And the isolation system is not shown at all, so either you have no isolation, or you left it off the drawings on purpose. But we will need to see some of the details of the ceiling isolation, to figure out how to help you locate your HVAC ducts, silencers, registers, etc.

As isolation isn’t an issue, ... Gets pretty noisy with 120km/h winds sometimes.

I'm having a hard time correlating those two statements! They contradict each other... Rural locations also have issues like rain, thunder, hail, animals, machinery, aircraft flying over, etc. All of those will be absolutely audible in your studio if you don't have isolation.

corrugated steel roof.

See above. I assume it rains occasionally in Victoria?

I want to get the majority of the ducting done while it's just a frame, once the roofing is on,

Smart move. get as much as you can in before you start building the actual inner-leaf.

2 years ago I had an Engineer work out details for a fresh air supply to Code. ... Original Fan spec required 50l/s

Are you SURE about that? Minimum specs for most places around the world are about 4 room changes per hour. Your room has a volume of 216 m3, which is 216,000 liters, so you need to move roughly 800,000 liters per hour to achieve that. A fan that moves 50 l/s is only going to move 180,000 l per hour.... That's way short of where it should be, for a big room like that. Such a tiny fan is only going to move about 25% of what you need. Maybe you misread the engineer's specs, and it was supposed to be 500 l/s? That's a little too big, but more believable. Or maybe there's a leading digit missing, and it was supposed to be 150 l/s?

Most of the time there’ll only be one in the room, so approx 15l/s

No. Ventilation is determined firstly by the volume of the room, regardless of how few people are in it. Cooling and dehumidifying loads depend on the number of people, yes, but the minimum ventilation rate is determined by the room volume alone. If there will be a lot of people in there, then the rate will need to increase, but it won't even decrease below the minimum. 15 l/s for a room with a volume of 180,000 l is only 0.3 changes per hour: less than one tenth of the normal minimum recommendation.

Are you SURE that those rates comply with code where you live? They sound very much on the low side...

For now, I chose 100mm as 125mm is hard to get, and as 25mm Duct Liner will be fitted, 100mm results in 150mm Rigid Metal Ducting.

Ummmm... I'm not following your math here: If you have 100 mm duct, and you line it with 25mm duct liner, then the internal diameter is now down to 50mm. Because you subtracted 25mm on each side. 100 -25 -25 = 50. ... Your math seems to be faulty here. If you want an ID of 100mm, you'd need an OD of 150mm. Or maybe I'm just misunderstanding what you said, and that's what you meant anyway?

I think I read that smaller duct is OK as long as it only gets to the silencer boxes.

As long as the air flow velocity is something reasonable, and the static pressure / air flow resistance are reasonable.

If you can't find the right size round duct, then you could always switch to rectangular duct.: If space is limited, that helps there too, as you can have a very wide but not high section, and still get good flow. However, do take into account that the friction losses on rectangular duct are higher than for round duct, so you need a larger cross section that you think...

50l/s with 100mm gets 6m/s . end goal is hopefully the magic 100fpm = .5m/s

So you need to slow down the speed by a factor of 1200%, in the few inches where the duct transitions to the silencer? Good luck with that! Major turbulence going on there, huge changes in pressure.... I doubt very much you'll be able to make that work.

Jumping to the other side of the Silencer

Whoa! Hang on! You missed the critical part: what happens INSIDE the silencer? How do speeds and pressures change? How much of an impedance mismatch will that introduce? What is the insertion loss you are looking for?

Input of 100mm duct = .008m2 Output 250mm = .05m2 (rounded)
If I got this right, the Silencer needs a cross section area of .05m2. Nominal starting point = 500m x 100mm or 200mm x 250mm
( metric makes some calcs easier )

True, so let's do it in cm and cm2, which is even easier than mm.
Your 100mm duct has a cross section of about 78cm2. Therefore the interior cross section of the silencer should be AT LEAST 160 cm2, so it will have to measure about 16cm x 10cm on the inside, plus duct liner. It can be bigger, of course, but not smaller. Also, where did you get the number "Output 250mm = .05m2"? 25cm round duct has a cross section of about 490cm2, which is only about 600% increase in area, compared to 10cm duct. So if you had air coming in at your screaming 6m/s, it would be coming out at 1m/2, which is still twice your target speed of 0.5 m/s.

Should the Silencer be thin and wide, and if so, what the thinnest ratio or dimension to use.

It can be thinner and wider, yes, but don't overdo it! The general recommendation is keep the aspect ratio lower than 1:4.

If the output is 250mm dia, should that be the minimum height.

Nope. It's not about heights, widths and diameters, but about cross sectional area. You want the cross sectional area to increase by the same ratio as the decrease you need in speed. So if you are starting with a cross section of 78cm, and you need to reduce the speed by 1200%, then you need to end up with a cross section of 78 x 12 = 936 cm2, so if you had square duct, it would need to be 30cm x 30cm. Or if it was rectangular, it could be something like 45cm x 20cm, which is a reasonable ratio. That's the final inside dimensions, of course: you still need to add the duct liner to that, to get to the actual size of the metal duct itself.

So, when you have decided on what your duct sizes will be at the entry and exit to the silencer box, you can figure out what size to make the box itself (one again, allowing for the thickness of the duct liner inside, plus the thickness of the wood).

To maintain the isolation of the ceiling, the silencer walls will be nearly 50mm ( 2 inches )

How did you figure that? You never told us what the isolation for the ceiling is in the first place!

How many baffles, open to suggestions., and plenty of ceiling space available.

How much isolation do you need? At what frequencies? In other words, what insertion loss are you aiming for?

then my next problem, and the one I least understand, is working out diffusors and return air grilles.

The open area of the register (grill) needs to be at least the same as the interior cross section of the duct that feeds it. so for example, if your final duct has an area of 500 cm2, then the open area of the register needs to be at least 500cm2. Assuming that you can find a register with an open area of 70% (the vanes only take up 30%)m then you'd need a register with an area of about 700cm. So something like 35cm x 20cm would be about right, in this hypothetical case.

The return air side has to be the same as the supply side, or ideally a bit larger. So your return air registers would be identical to the supply registers, the return silencer box would be identical to the supply silencer, and the return ducts would be identical to the supply ducts.

A/C was sized at 5Kw cooling,

Based on what sensible heat load and what latent heat load?

and I picked the lowest noise spec, a Mitsubishi split system, and plan to position up around 2.4m on a side will between the supply and return vents, unless there’s a more scientific method.

That should be about right. Get it a bit higher if you can (your ceiling is at 4m), so it gets a good gulp of the warm humid air up there.

Would adding a “reverse reducer” , “cone” at the input to each silencer have any benefit on the flow or velocity, as a “smoother” transition than a direct join?

Yes, definitely! But having larger ducts througout would be an even better idea. Keep them all as large as you can.

Does reversing the silencer box, effectively a U turn with 2 x 90º turns, add too much static pressure or other effect?

the baffles provide multiple 90° turns inside the box, so you don't really need any more outside. Each turn creates turbulence = noise = flow resistance.

I'd suggest working through your assumptions and calculations again. I'm not sure that you started off with the right assumptions at all, regarding flow rates and flow velocities. Your math from there on through seems to be about right, but the assumptions you started with don't.

I'm also wondering why you are going to all the trouble of large ducts, silencer boxes, large registers, etc. when you only have a drop ceiling over your CR, and all of the noise will be audible through that anyway! What is the point? especially when you say that isolation isn't even an issue to start with...


- Stuart -

[tez]

Hi Tez. Welcome!

My “hobby” PostProduction/Listening room has been designed by a pro,

Great! But you probably should have gotten him to include the HVAC design in there too: it's always a good idea to integrate as much as possible, so it all works together.

My guy prefers to use specialist HVAC qualified engineers. I know some designers do both.

So, first question: What level of isolation did your designer make the room for? Your HVAC system needs to be designed to the same or greater level of isolation. Putting in HVAC means chopping enormous holes in the walls or ceiling, which of courses trashes all of your isolation, so the "thing" that you put in that hole must, logically, restore the same amount of isolation. So before anyone here can check your HVAC design, we'd need to know the level of isolation that the room is designed for, so that your HVAC system is kept at the same level.

I am missing that info, as it was done a while ago. Leq here is generally around 40 A wtd. I think I recollect 54db isolation. Walls are sheet 24kg/m2 outer, 25mm air gap, 90mm steel frame with R2 earthwool & inside 16mm FR plaster and 24mm 24kg/m2 sheet. Ceiling is 2 x 24mm sheets + 16mm plaster = 61kg/m2

so I can’t show all plans or precise measurements for analysing, but that shouldn’t be critical considering the issue is HVAC.

No problem, probably, but we do need to know the design figure for isolation, and that certainly isn't a trade secret!

looking for a calculator to help.

I’m way too old to go through learning Sketchup for a single project, so CAD plan and elevations it is.

OK; but please do check out the preamble to the "rules for posting"...

9m x 6m x 4m, with a T Grid drop ceiling at 3m. A great size, and very close to Sepmyer 1:1.6:2.3

Ummm Sorry, but 9m x 6m x 4m is NOT close to Sepmeyer 1. That's a ratio of 1 : 1.5 : 2.25. It is close to Louden's fourth-best ratio, but far from Sepmeyer's. That's still a reasonably good ratio, though, so no problem. It's also a nice large room. Good possibilities.

OK, it's nicely in Bolt, EBU and IEC, near a Salford, and most likely good enough for tired degenerating old ears.

with a T Grid drop ceiling at 3m.

Drop ceiling? In a studio control room? That's unusual... I thought you said it was designed by a professional studio designer?

Might be a language translation error. Hard (shell) ceiling at 4m, this is a grid of acoustic tiles the Nc of 1 from memory. plus 300mm insulation on top. Front of room is soft as well.

I'm also assuming that the partial CAD drawings you provided are very much not to scale, and very much incomplete on purpose, because they don't make a lot of sense acoustically as shown. It looks like it is supposed to be an RFZ room, but the proportions and geometry are wrong, and the soffits are incomplete...

you're right, on tweaked and distorted to protect the payer and payee.

And the isolation system is not shown at all, so either you have no isolation, or you left it off the drawings on purpose. But we will need to see some of the details of the ceiling isolation, to figure out how to help you locate your HVAC ducts, silencers, registers, etc.

Budget blown out due to many other factors, but as I noted, it's quiet enough to hear koalas farting, so only a single wall, but hoping the 60kg/m2 does enough.

As isolation isn’t an issue, ... Gets pretty noisy with 120km/h winds sometimes.

I'm having a hard time correlating those two statements! They contradict each other... Rural locations also have issues like rain, thunder, hail, animals, machinery, aircraft flying over, etc. All of those will be absolutely audible in your studio if you don't have isolation.

If the iso is a failure, I'll just have to pick my days for listening. There are only about 6 flights per day past here on the NZ route, and the only way you'd normally notice them is the vapour trail.

corrugated steel roof.

See above. I assume it rains occasionally in Victoria?

1100mm pa. Below the colorbond corro is foil/25mm insulation ( Anticon ) and above shell ceiling is 300 earthwool

I want to get the majority of the ducting done while it's just a frame, once the roofing is on,

Smart move. get as much as you can in before you start building the actual inner-leaf.

soundman 10 tez 1

2 years ago I had an Engineer work out details for a fresh air supply to Code. ... Original Fan spec required 50l/s

Are you SURE about that? Minimum spec for most places around the world is about 4 room changes per hour. Your room has a volume of 216 m3, which is 216,000 liters, so you need to move roughly 800,000 liters per hour to achieve that. A fan that moves 50 l/s is only going to move 180,000 l per hour.... That's way short of where it should be, for a big room like that. Such a tiny fan is only going to move about 25% of what you need. Maybe you misread the engineer's specs, and it was supposed to be 500 l/s? That's a little too big, but more believable. Or maybe there's a leading digit missing, and it was supposed to be 150 l/s?

did re-check .. The comps were done to AS1668.2, and from memory, these only take into account the Floor Area, and not the room volume.

Most of the time there’ll only be one in the room, so approx 15l/s

No. Ventilation is determined firstly by the volume of the room, regardless of how few people are in it. Cooling and dehumidifying loads depend on the number of people, yes, but the minimum ventilation rate is determined by the room volume alone. If there will be a lot of people in there, then the rate will need to increase, but it won't even decrease below the minimum. 15 l/s for a room with a volume of 180,000 l is only 0.3 changes per hour: less than one tenth of the normal minimum recommendation.

Are you SURE that those rates comply with code where you live? They sound very much on the low side...

For now, I chose 100mm as 125mm is hard to get, and as 25mm Duct Liner will be fitted, 100mm results in 150mm Rigid Metal Ducting.

Ummmm... I'm not following your math here: If you have 100 mm duct, and you line it with 25mm duct liner, then the internal diameter is now down to 50mm. Because you subtracted 25mm on each side. 100 -25 -25 = 50. ... Your math seems to be faulty here. If you want an ID of 100mm, you'd need an OD of 150mm. Or maybe I'm just misunderstanding what you said, and that's what you meant anyway?

Maybe my poor description. I always meant 100 ID as that is what the Titon HVR/Fan can do. (ok, 125 as well, but not a common sizing here, so expensive) Plus, 2 x 25mm liner = 150mm Duct. agreed.. my bad word selection. ( and if I wanted 125mm duct -inner- with liner that would have meant 175mm duct - custom made )

I think I read that smaller duct is OK as long as it only gets to the silencer boxes.

As long as the air flow velocity is something reasonable, and the static pressure / air flow resistance are reasonable.

My maths is c- rap. hope the fan chart describes an OK solution.

If you can't find the right size round duct, then you could always switch to rectangular duct.:

150mm duct is easy enough. The reason I note the Split Seam option is to save on freight if it's suitable.

If space is limited, that helps there too, as you can have a very wide but not high section, and still get good flow. However, do take into account that the friction losses on rectangular duct are higher than for round duct, so you need a larger cross section that you think...

rectangular all seems to be custom, at custom cost too! And more maths!!

50l/s with 100mm gets 6m/s . end goal is hopefully the magic 100fpm = .5m/s

So you need to slow down the speed by a factor of 1200%, in the few inches where the duct transitions to the silencer? Good luck with that! Major turbulence going on there, huge changes in pressure.... I doubt very much you'll be able to make that work.

Could be the reason I come to the experts on my knees, requesting a miracle solution.
If I forgo the Nirvana principle of 100fpm, for Rod's maximum of 300fpm, then metrically it's 1.5m/s ( my level of maths ) and 6/1.5=4 ce'st n'est pas Are we getting into the realm of practical and considering there's no microphones, just ears listening.

Jumping to the other side of the Silencer

Whoa! Hang on! You missed the critical part: what happens INSIDE the silencer? How do speeds and pressures change? How much of an impedance mismatch will that introduce? What is the insertion loss you are looking for?

Whoa'd. nope, This place deliberately left vacant, as was my brain. I read, and re-read so many threads on this till my "ears were ringing", but didn't find a definitive step by step guide, not even a pay per view one.
Yes, lots of info on various builds, but not enough for me to join the dots.

Input of 100mm duct = .008m2 Output 250mm = .05m2 (rounded)
If I got this right, the Silencer needs a cross section area of .05m2. Nominal starting point = 500m x 100mm or 200mm x 250mm
( metric makes some calcs easier )

True, so let's do it in cm and cm2, which is even easier than mm.
Your 100mm duct has a cross section of about 78cm2. Therefore the interior cross section of the silencer should be AT LEAST 160 cm2, so it will have to measure about 16cm x 10cm on the inside, plus duct liner. It can be bigger, of course, but not smaller. Also, where did you get the number "Output 250mm = .05m2"? 25cm round duct has a cross section of about 490cm2, which is only about 600% increase in area, compared to 10cm duct. So if you had air coming in at your screaming 6m/s, it would be coming out at 1m/2, which is still twice your target speed of 0.5 m/s.

I'm a true believer in rational compromise, if it is adaptable to the situation, as per a little earlier where 1.5m/s (300fpm) is sometimes OK for at least one guru in the field.
I've lived through 63 years of compromise, what's a few extra feet per minute going to cost.

Should the Silencer be thin and wide, and if so, what the thinnest ratio or dimension to use.

It can be thinner and wider, yes, but don't overdo it! The general recommendation is keep the aspect ratio lower than 1:4.

BINGO a perfect 10 score..

If the output is 250mm dia, should that be the minimum height.

Nope. It's not about heights, widths and diameters, but about cross sectional area. You want the cross sectional area to increase by the same ratio as the decrease you need in speed. So if you are starting with a cross section of 78cm, and you need to reduce the speed by 1200%, then you need to end up with a cross section of 78 x 12 = 936 cm2, so if you had square duct, it would need to be 30cm x 30cm. Or if it was rectangular, it could be something like 45cm x 20cm, which is a reasonable ratio. That's the final inside dimensions, of course: you still need to add the duct liner to that, to get to the actual size of the metal duct itself.

that's the step by step I can now understand.

So, when you have decided on what your duct sizes will be at the entry and exit to the silencer box, you can figure out what size to make the box itself (one again, allowing for the thickness of the duct liner inside, plus the thickness of the wood).

ditto

To maintain the isolation of the ceiling, the silencer walls will be nearly 50mm ( 2 inches )

How did you figure that? You never told us what the isolation for the ceiling is in the first place!

E&OE.. I did spec the walls,, forgot to look up! same 2 x 24mm sheets MgO - 48kg/m2 + 16 Fyrechek (12.55kg/m2 ) = 60kg/m2 ceiling
BTW no Green Glue. local cost considering the diving dollar makes it cheaper to add plaster.

How many baffles, open to suggestions., and plenty of ceiling space available.

How much isolation do you need? At what frequencies? In other words, what insertion loss are you aiming for?

match the walls, once I find or compute it.

then my next problem, and the one I least understand, is working out diffusors and return air grilles.

The open area of the register (grill) needs to be at least the same as the interior cross section of the duct that feeds it. So for example, if your final duct has an area of 500 cm2, then the open area of the register needs to be at least 500cm2. Assuming that you can find a register with an open area of 70% (the vanes only take up 30%) then you'd need a register with an area of about 700cm. So something like 35cm x 20cm would be about right, in this hypothetical case.

I think that's covered in the bradflo attachment, though I can't work out the NC curve optimum sizing.

The return air side has to be the same as the supply side, or ideally a bit larger. So your return air registers would be identical to the supply registers, the return silencer box would be identical to the supply silencer, and the return ducts would be identical to the supply ducts.

that looks straightforward even for me

A/C was sized at 5Kw cooling,

Based on what sensible heat load and what latent heat load?

I just used the referenced airah website calculator. The gear going in is minimal, Adam S-3 P-33s, MacPro, OPPO player and a Preamp.

and I picked the lowest noise spec, a Mitsubishi split system, and plan to position up around 2.4m on a side will between the supply and return vents, unless there’s a more scientific method.

That should be about right. Get it a bit higher if you can (your ceiling is at 4m), so it gets a good gulp of the warm humid air up there.

Would adding a “reverse reducer” , “cone” at the input to each silencer have any benefit on the flow or velocity, as a “smoother” transition than a direct join?

Yes, definitely! But having larger ducts througout would be an even better idea. Keep them all as large as you can.

Does reversing the silencer box, effectively a U turn with 2 x 90º turns, add too much static pressure or other effect?

the baffles provide multiple 90° turns inside the box, so you don't really need any more outside. Each turn creates turbulence = noise = flow resistance.

all good.

I'd suggest working through your assumptions and calculations again. I'm not sure that you started off with the right assumptions at all, regarding flow rates and flow velocities. Your math from there on through seems to be about right, but the assumptions you started with don't.

OK. PM sent as Engineered. I hope he got it right,, if not, lots of recalculation coming up.

I'm also wondering why you are going to all the trouble of large ducts, silencer boxes, large registers, etc. when you only have a drop ceiling over your CR, and all of the noise will be audible through that anyway! What is the point? especially when you say that isolation isn't even an issue to start with...

Language translation problem possibly, but definitely a solid ceiling at 4m, tiles at 3.1 so a "plenum" for silencers.

Way more analysis than I thought Stuart, magic work...

[tez]

A couple of clarifier, missed in first reply.

For now, I chose 100mm as 125mm is hard to get, and as 25mm Duct Liner will be fitted, 100mm results in 150mm Rigid Metal Ducting.

Ummmm... I'm not following your math here: If you have 100 mm duct, and you line it with 25mm duct liner, then the internal diameter is now down to 50mm. Because you subtracted 25mm on each side. 100 -25 -25 = 50. ... Your math seems to be faulty here. If you want an ID of 100mm, you'd need an OD of 150mm. Or maybe I'm just misunderstanding what you said, and that's what you meant anyway?

We both said exactly the same thing, just differently. I was trying to differentiate the ID duct of 100mm for calculations, to the 150mm lined duct for installations.

Also, where did you get the number "Output 250mm = .05m2"? 25cm round duct has a cross section of about 490cm2, which is only about 600% increase in area, compared to 10cm duct. So if you had air coming in at your screaming 6m/s, it would be coming out at 1m/2, which is still twice your target speed of 0.5 m/s.

I did round to .05m2 for simplicity, not thinking it a huge jump from .490m2.
The following 600% calcs were based on what I thought would happen by using 2 Supply side Silencers, thought it read it somewhere...
and now, I'd be ok with terminal velocity of 1.5m/s.

Back to munch on more.

[Soundman2020]

I am missing that info, as it was done a while ago. Leq here is generally around 40 A wtd.

Leq tells you about background noise (ambient noise), long-term, averaged over many seconds. "A" weighting means it is ignoring low frequencies. That's not a very useful measurement for designing a studio! It should be "C" weighting, "slow" response, with peak hold. And it should be measured at typical noisy times of day, since we are talking about blocking sound coming in to your studio.

I think I recollect 54db isolation.

That's a nice goal to have, but you will not be getting that from the construction you described so far! Maybe you'll get about one tenth of that, if you are lucky, but I'm not convinced it would even be that good. You haven't provided all the details I'd need to calculate accurately, but I'd guess that you'd get in the region sf 40 dB isolation, form what you have said.

Ceiling is 2 x 24mm sheets + 16mm plaster = 61kg/m2

... which will get you about 38 dB, according to empirical mass law. The metal roof beyond is irrelevant here, since all it does is act as a sounding board for things like rain and hail, and provides practically no isolation at all for most other sounds.

looking for a calculator to help.

figuring isolation is a lot more complicated than a simple calculator can help you with!

For single-leaf construction, you have mass law:
TL(dB)= 20log(W) + 20log(f) -47.2
Where:
M is the surface density of the panel,
f is the frequency

Or the simplified empirical version:
TL = 14.5 log (M * 0.205) + 23 dB

When you get two 2-leaf walls, then you need a different equation:

msm-2-leaf-equation.jpg

For three-leaf walls, it is even more interesting:

TRIPLE-LEAF-EQUATION.jpg

Beyond that, it gets complicated.

The above is just the basics: there are many other factors to consider in addition. It's not so easy to come up with a number... No simple calculator can do that... which is why you are having a hard tome finding one! _) I've been working on developing a spreadsheet to predict isolation for typical studio walls. I'm on version 34 of that spreadsheet right now, and I've been going for 4 years... When it's done, I'll let you know... Right now it is reasonably reliable, to within maybe 5 or 6 dB either way, but that's still not much use practically, and I'm having trouble getting it ti draw graphs that are meaningful to non-exports, taking into account things like the Fletcher-Munson curves, and NC curves, and things like that...

OK, it's nicely in Bolt, EBU and IEC,

Yep. but it's far from Sepmeyer, which is what you said initially! There's nothing terribly wrong with that ratio, and I know where the error came from in thinking it was Sepmeyer, but it isn't.

and most likely good enough for tired degenerating old ears.

Well, the age of the ears isn't a factor in determining if a room is good or not! Even "aged ears" won't be happy in a lousy room! Ratios are all about modal response: if a room has bad modal response, and has not bee treated for that, then it will sound bad to everyone, regardless of age. The boominess, ringing, and low end artifacts will still be there. In fact, "aged ears" will notice them more than "young ears", since age-related hearing loss is mostly in the high end of the spectrum, so the low end is more important to older ears...

Might be a language translation error. Hard (shell) ceiling at 4m, this is a grid of acoustic tiles

It's not a language error: What you describe really is a drop ceiling with "acoustic" tiles. A framework of thin metal angle sections, hung from the roof above on wires, and with light-weight "acoustic" tiles sitting in the framework. It is very common in offices, shops, schools, etc. But not in studios! Those "acoustic" tiles are not meant for studio acoustics. They are meant for office acoustics: They are designed to reduce the annoying mid-range sounds of people talking, phones ringing, photocopiers running, computers, printers, and all the common sounds of people working.

But they don't do what you want in your studio! That's why you almost never see "acoustic" tiles used in studios. Those tiles are not what a studio needs. They will allow all of the noise created by your HVAC system to get into your room...

Also, if you were talking about your room ratio here, then the drop ceiling is irrelevant: room ratio is about low frequencies, and all measurements are to the rigid, massive boundary of the room.

Front of room is soft as well.

True LEDE design??? Modern studio design has long since moved away from true LEDE. That was a concept that was tried in the 70's, but found to not be very good: it is fatiguing and unnatural. Modern design concepts have taken the good parts of LEDE, left out the bad parts, and moved in a different direction. CID, ES, RFZ, NER and others are where we are at currently. I'm not aware of any major studios still being designed with LEDE as the basis. The "bad part" that is now left out is the dead front end...

you're right, on tweaked and distorted to protect the payer and payee

Fair enough.

so only a single wall, but hoping the 60kg/m2 does enough.

single leaf (or fully coupled 2-leaf) are limited by mass law. See the equation for that above. Basically, it says you need enormously huge amounts of mass to get good isolation with single-leaf. In order to get your 54 dB of isolation from mass law alone, you'd need a surface density of about 700kg/m2 all around the room (walls, floor, ceiling, windows, doors, ...). The volumetric density of reinforced concrete is roughly 2000 kg/m3 (give or take a bit), so if you made the entire studio from single-leaf concrete, you could get that level of isolation with walls about 35cm thick. Or you could do it with about 58 layers of standard 16mm drywall...

Single-leaf is not your friend... Mass law is not your friend...

There are only about 6 flights per day past here on the NZ route, and the only way you'd normally notice them is the vapour trail.

Are you considering sympathetic resonance? I live a few blocks away from a big hospital. They have a helipad on the roof, and an emergency response helicopter ambulance is always sitting up there, ready to go when needed. When they start that thing up for a medevac flight (which happens many times per week), they warm it up with the engine idling for several minutes before take-off, and if I'm outside in my garden or in the street, I can barely hear it. It's a quiet chopper. It sounds like a bus or truck idling, distantly. But if I go into some rooms inside my house, it is deafening! Because the resonant frequency of those rooms just happens to coincide with the engine idling frequency of that chopper. The same can happen to you, once your room is built if it isn't isolated properly: you might well find that your room happens to have a natural resonance that coincides with the distant jets...

1100mm pa.

(rain). So about 21 per week? In other words, it happens regularly?

Below the colorbond corro is foil/25mm insulation ( Anticon ) and above shell ceiling is 300 earthwool

That's great thermal insulation, and pretty good acoustic damping for a resonant system, but won't do much to stop sound getting through. That's a common myth. A lot of people think that porous absorption must be great at stopping sound, but in reality that's not how it works. It is great at stopping sound when used as part of an isolation system, but pretty useless by itself. If you have a piece of that lying around some place, tape it across the front of your speaker and play some music, to see just how useless it is at stopping sound...

The comps were done to AS1668.2, and from memory, these only take into account the Floor Area, and not the room volume.

... and there's your problem! Floor area calculations for HVAC sizing assume standard ceiling height of 2.4m. Your ceiling is at 4m...

If you think about this logically, it should be clear. The HVAC system is there to cool the air in the room. ALL of the air in the room. Not just the air that is sitting on the floor. If your ceiling were just 10cm from the floor, then you could cool it in seconds even with a very small unit. If the ceiling were at 50cm, then it would take five times longer too cool it, because there is five times more air in there. Simple logic. If the ceiling were at 100cm, it would take take ten times longer. And of your ceiling is at 4m, then it takes 40 times longer...

HVAC is all about room VOLUME, not about room floor area. Domestic systems are often "rated" for floor area, since the assumption is that the ceiling is at the normal height for a domestic room. But yours is much higher: there is much more air in the room, and it all needs to be treated...

rectangular all seems to be custom, at custom cost too! And more maths!!

Yup! Welcome to the wonderful world of studio design! Where math is the entry ticket, everything interacts with everything, it is all complicated, everything is custom, and the cost is much higher than you ever feared, even in your worst nightmare!

Could be the reason I come to the experts on my knees, requesting a miracle solution.

Well, we can help you out lots within the laws of physics, but for miracles you'll have to chat to the Good Lord himself!
Seriously, there are no "miracle" or "magic" materials or methods in acoustics. Everything has to follow the laws of physics, and those laws aren't too encouraging. So there's a lot that can be done when the laws are understood and put to good use, but there's no way around those darn laws!

for Rod's maximum of 300fpm, then metrically it's 1.5m/s

That's fine. That's a reasonable target speed for your place. I would aim for 1m/s, but if it turns out to be 1.5, then you are still doing fine for your needs. 0.5 would be wonderful, but that implies over-sizing everything greatly. I normally design for 200 fps, and if something isn't spot on in the design or build, and it ends up at 300, that's still acceptable (unless you are building a Foley stage!)

Yes, lots of info on various builds, but not enough for me to join the dots

Hmmm... that's sort of like designing a car where your plans show a fuel pipe coming into the engine bay, the drive shaft leaving, and a big box labeled "magic happens here" in between, to show how fuel becomes mechanical thrust...

You probably need to add a little more detail to your silencer box design!

I did spec the walls,, forgot to look up! same 2 x 24mm sheets MgO - 48kg/m2 + 16 Fyrechek (12.55kg/m2 ) = 60kg/m2 ceiling

Those are surface density specs, not isolation specs. All kilograms are not equal! It all depends how you use them. I ca arrange your 2 sheets of 24mm board in such a way as to provide 35 dB of isolation, or I could arrange them another way and get 50 dB of isolation... It's not just the mass: it's how you use it...

BTW no Green Glue. local cost considering the diving dollar makes it cheaper to add plaster

No problem. GG is nice to have if you can afford it, but it's not the end of the world if you can't.

I just used the referenced airah website calculator. The gear going in is minimal, Adam S-3 P-33s, MacPro, OPPO player and a Preamp

And the people? And the lighting? People also produce humidity: you need to take into account not just sensible heat load but also latent heat load. And also the volume of the room, not just the floor area....

Language translation problem possibly, but definitely a solid ceiling at 4m, tiles at 3.1 so a "plenum" for silencers.

You should think that through a bit more: the acoustic tiles¿ drop ceiling provides about zero acoustic isolation. Nothing at all. So you have your fans, ducts and the silencer itself all located right inside the room, from that point of view. Having the drop ceiling tiles in place, or removing them, is not going to make any real difference to how much of the plenum noise gets into the room below. At best, it might reduce the mid-range noise by a few dB, but that's about it.

The normal way to build a control room is to have a solid, massive, rigid inner-leaf that surrounds the entire room, on all sides (all four walls and also the ceiling), then to put the HVAC ducts and silencers on the other side of that, outside the room. Only the last tiny part of the duct comes through the isolation leaf, and has the register on it. In fact, I normally design the system so that the silencer box itself has a thick wooden sleeve on the end of it that goes through the inner-leaf (decoupled from it), directly to the register.

In other words, if you were to scrap the drop ceiling and replace it with a properly designed inner-leaf ceiling, THEN you would have a good system. But the drop ceiling is useless. It provides no acoustic isolation at all. It is only acoustic treatment and aesthetics, and all it really does is to attenuate the mid range, selectively.

Way more analysis than I thought Stuart, magic work...

- Stuart -

[tez]

Quote:

Could be the reason I come to the experts on my knees, requesting a miracle solution.

Well, we can help you out lots within the laws of physics, but for miracles you'll have to chat to the Good Lord himself!
Seriously, there are no "miracle" or "magic" materials or methods in acoustics. Everything has to follow the laws of physics, and those laws aren't too encouraging. So there's a lot that can be done when the laws are understood and put to good use, but there's no way around those darn laws!

Well, I went searching for miracles and/or magic this last week, but HE/SHE didn't respond. I though I might try Quantum Acoustics.
but, went back through numerous threads seeking the Holy Grail.

I think I've got a little better understanding of the HVR/HVAC setup, and have considered your comments on Isolation of which more further down.

On the air side of things, a few items to be noted that conflict in some way.
1. "normal" calculations for air are based on the room's volume, so roughly 220m3. At 4 changes p/hr = 880m3.
2. The Engineering Comps and Calcs, done to Australian Standards, are based on floor area, = 180m3 or 50l/s
3. While 50l/s may not work for real studios, it should be fine for 99% of the time as I will be the only occupant.
4. The other benefit of this is that the costs can be kept as low as possible.
5. Target velocity should be suitable if set at 1.5m/s

I hope have got more of this sorted out compared to the last effort.. but am ready for corrections.

The HVR system also doubles up in providing the fresh air.
Outlet size is 125mm so at 50l/s is 4.1m/s
To locate the HVR to allow ducting to just below the roof, a 90º bend needs to be fitted on the outlet.
Then a "cone" to increase to a 150mm duct (ID) . with lining the OD =200mm
Duct Calc App tells me that this brings the velocity to 2.9m/s, just double the target
Duct Length - can be anything that is most suitable, from 600mm up to 8 metres. I've not found links to what is optimum, though found one stating minimum of 4 x the diameter of the duct. The Return duct will be of similar length.
At the end of the xxm duct will be another 90º bend, short decoupling flex, then attached to a "cone" . This will expand to the same diameter as the outlet, and is intended ( guessed ) to smooth the turbulence of a straight "jump" into the Silencer.
As the output of the Silencer should be double the surface area of the "nominal" input, which for a 150mm duct is 176cm2, the output duct = 352cm2.
This calculates back to a radius of 105.88mm. I hope rounding this to a 200mm dia. is acceptable, but if not, a rectangular duct of the same construction as the Silencer can be built precisely.
Silencer
Construction would likely be 2x18mm walls of MDF. OSB here is usually only 6mm, for bracing board.
Cross Section area is approx 0.362m2 , and the Silencer approx 1m W x .36m H, with extra to be added for the baffles and duct liner.
With these dimensions, and using 200mm ID duct, the Silencer will fit in the roof area above the ceiling, but only just.
I've noted the Silencer designs where the duct into the room is incorporated into the build, which seems to have benefits in regard to being simpler to seal through the ceiling layer(s).
I'm still not sure how long to make the Silencer, but have plenty of room to play with. I don't know what effect on pressure would be though.
I'm considering oversizing the Diffusor, which has a square neck input. This would hopefully "cover" the louvre to open ratio, which doesn't appear in the specs. Size would be 375mm x 375mm input, so a 450mm square opening. If placing this close to the rear of the room, I'd guess a 1 way blanking that directs air towards the front of the room might work. Diffusers look to be a science of their own.
http://www.bradflo.net/bradflo/au/techcatalogue/236.pdf
The A/C split would be on the side wall and mix in with the fresh air.

I realise I haven't done much on pressure, but from the figures I've seen there's not much loss in rigid ducting, only 2 x 90 degree bends, and whatever is in the Silencer, and there's no branching etc, so am hopeful it's not a major factor.

Ducting will be hung with isolators, the only flex at the junction to the Silencer and solid square duct down to the diffuser, sealed through ceiling layer.

That's all I've been able to resolve, and yes a hole or 2 to sort out, though I think I got the airflow velocity sorted at least.

As there's a query on the Isolation of the current setup, TL, Rw, STC etc.... I've done some evaluations regarding alternatives.
Currently it's a single wall, clad each side. This was chosen due to the remote location and because budget is a critical factor.

You'd mentioned having a few tricks to improve the isolation by different ways of doing things.
There are likely better, simpler and cheaper ways but this is what I've considered.
I know Green Glue, but have already dropped that idea due to cost, instead I added 16mm Fire Rated Plasterboard.
I also costed adding Isolation Clips and Furring Channel on the inside, but this was also a bit costly.
I've now down a basic costing for internal steel frame stud, but built on the Sayer's Inside Out method.
At this stage it might just be feasible, though I'd have to "see a sibling" or 2 to fund it for a while.

If I went with this method, it would mean a lot of revision in the internal geometry, another cost factor in design time.
Even with a minimal gap of 50mm and the 24mm + 16mm sheets that's 180mm less overall on L & W.
The walls seem simple, but ceilings look more complex.
A single sheet of 24mm on say 22mm or 16mm channel of the roof trusses looks fine.

But how to make the inner ceiling without losing a lot of space?
The Wall system isn't load bearing, so another option would seem to be an isolated hanging system.
But this seems to involve TCR and Furring Channel grid, so takes space as well.

Given the extras for wall and ceiling as well as full internal re-calculation for acoustics, it's all a bit overwhelming.
So I'm happy to hear of any alternative methods to improve the TL.

EDIT: a new discovery of a less expensive Isolation Clip may see that as a more viable option, and if combined with a 16mm furring channel, wouldn't "intrude" into the internal geometry as much as the I/O wall would. A longer legged version of that clip looks like allowing the inner ceiling to be attached, but isolated from the main roof trusses, but with only a small gap between the top direct fixed sheet and inner lower 2 sheets.

Alternatively I'm out to buy a set of Quantum Headphones.

T.

[tez]

I think I recollect 54db isolation.

That's a nice goal to have, but you will not be getting that from the construction you described so far! Maybe you'll get about one tenth of that, if you are lucky, but I'm not convinced it would even be that good. You haven't provided all the details I'd need to calculate accurately, but I'd guess that you'd get in the region sf 40 dB isolation, form what you have said.

I've now got a figure for isolation, though not TL. STC 58 for walls, based on ir761. p150. It may be even slightly better, as mass is higher than the example construction there.
The ceiling will be less as there's no gap, but an iso system could be used. Rondo looks to have an affordable resilient iso clip and channel system.

Ceiling is 2 x 24mm sheets + 16mm plaster = 61kg/m2

... which will get you about 38 dB, according to empirical mass law. The metal roof beyond is irrelevant here, since all it does is act as a sounding board for things like rain and hail, and provides practically no isolation at all for most other sounds.

The only allowance re the tin roof is that the Anticon foil+insulation will dull the rain noise a bit.

The above is just the basics: there are many other factors to consider in addition. It's not so easy to come up with a number... No simple calculator can do that... which is why you are having a hard tome finding one! _) I've been working on developing a spreadsheet to predict isolation for typical studio walls. I'm on version 34 of that spreadsheet right now, and I've been going for 4 years... When it's done, I'll let you know... Right now it is reasonably reliable, to within maybe 5 or 6 dB either way, but that's still not much use practically, and I'm having trouble getting it ti draw graphs that are meaningful to non-exports, taking into account things like the Fletcher-Munson curves, and NC curves, and things like that

The ir761 of the 21st century.. subscription or pay per view