New Music Room in UK south

[Soundman2020]

I have a rough plan for my control room now which I thought I would run by you guys. Maybe there are some important aspects I have missed or things that can be improved at this stage (before I start cutting the wood!). I would love to have any feedback that you can give me. I have never built an entire room before and I am a little worried at the prospect.

... as you should be! You are starting with the control room, which is the most critical, and the most difficult of all. It's the hardest one to do!

It is just the inside leaf, made with 2 x 12.5mm plasterboard.

16mm would be better...

The R side wall is ‘inside out’ with the studs on the inside ( to maximise space).

Good idea, but if you do the left and right walls differently, then you won't have an acoustically symmetrical room.... I would do BOTH side walls the same.

width - 325cm length - 413 cm height 285 cm (or maybe a few cm more to allow for a different flooring to be laid later on). This conforms to ratio 1 : 1.14 : 1.39

It's unusual to have it higher than it is wide, but acoustically the ratio is still valid. I would suggest that you hang a good sized cloud above the desk/speaker area, hard-backed, and angled.

listening spot is at 38% (148cm from front wall)

38% is just a recommended starting point.... not necessarily the best position. There are many other factors that might lead a designer to move away from 38%.

floor - is concrete. It will be sealed and painted ( later ).

ceiling - I plan a couple of largish clouds over the listening area, maybe some more absorption further back if required after testing.

Right. As above: make them hard-backed, and angled.

ventilation - a fan and silencer box located at G (outside the interior door) sucks the air out (from L) . There is a 2nd door outside this that leads to the outside world.
Fresh air comes in at C, near the air conditioning. Silencer box in roof void.

Silencer "box"? singular? Only one? You will have two ducts, one bringing fresh air in, the other take stale air out. Each of those ducts passes through two leaves (inner-leaf and outer-leaf). Therefore you will need four silencer boxes, not just one.

air conditioning - mini split located at B.

Personally, I would put it at "K". It's no fun to have cold air spraying on your face all the time, plus your ears are more sensitive to noise in front of you, then to noise behind you. I generally try to have the fresh air come in at the back of the room, directly into the mini-split unit, where it can be cooled and dehumidified immediately, and then exhaust the stale air out at the front of the room. So the net air flow is form the back of the room towards the front.

A - soffit mounted speakers. Probably some hangers above and below. I still need to work out the exact measurements and design but this is a working estimate.

Soffit mounting is excellent, but yes, you have a LOT of work to do on the soffit design!

B - wall between speakers with 10cm rock wool. Air condoning duct higher up.

Or maybe a window into the live room, so you an see what is going on in there without ending up with a twisted neck? I would seriously re-consider the entire layout, and rotate the CR so it faces the LR. If you don't you'll be remembering my advice for the rest of your life, and wishing you had taken it... (on the other hand, your physiotherapist will love you! He'll make lots of money from your regular visits, to straighten out your neck, and soothe your aching back....)

D (and N) - lots of rock wool here to destroy first reflections.

... on the other hand, if you design your room following the RFZ principle (also CID and NER), then there wouldn't be any first reflections for you to worry about!

E is a window to the outdoors. F is a window into the live room. Exact specs not decided yet but 2 layers of laminate glass for each, maybe 10mm and 12mm.

Don't guess! Do the math... It's not hard to figure out...

H is the door(s) to the live room (2nd door will be on the next wall). Each door will be around 70kg, made with 18mm mdf and 4x2 timber (probably).

What's the 4x2 for? You cannot have hollow studio doors, if that's what you were planning.

K - rear wall to have maybe covered with 20cm rock wool and/or some hangers.

No bass trapping? You will DEFINITELY need bass trapping in your corners. That goes without saying. Which is a REALLY good reason to re-arrange your layout so that there are no doors in room corners. Corners are prime, expensive, valuable real estate for treatment: the best place in the house! Putting a door in a corner is somewhat akin to designing a beachfront town with the garbage dump on the beach, and the houses down in the bottom of the ravine... It makes no sense. Put the houses on the beachfront, and the garbage dump in the ravine. Put the bass traps in the corners, and the doors in the unused parts of the wall.

Any thoughts guys?

The most basic concept is OK, but the overall layout of the facility is poor, and there is a lot of room for improvement...

- Stuart -

[Beeboss]

Hi Stuart, and many thanks for your reply. Very helpful - every time I think I have decided on something you make me revisit and question all the decisions which is very healthy.

I would seriously re-consider the entire layout, and rotate the CR so it faces the LR. If you don't you'll be remembering my advice for the rest of your life, and wishing you had taken it...  (on the other hand, your physiotherapist will love you! He'll make lots of money from your regular visits, to straighten out your neck, and soothe your aching back....)

I have been thinking about this but I can’t seem to make it work in my mind. If I change the orientation of the CR so the mix position faces the window into the live room then the depth of that room would then be only 325 cm which is not really enough for soffit mounted speakers a desk with a chair and a sofa behind that. Not to mention the window (to outside) would then be directly behind the mix position where there should really be some serious absorption. And then there is the problem of the door into the live room which has has to go on the same wall as the speakers, and inevitably that would mess up the symmetry big time.

It's unusual to have it higher than it is wide, but acoustically the ratio is still valid. I would suggest that you hang a good sized cloud above the desk/speaker area, hard-backed, and angled.

The width is 325cm and the height is 285 cm. Length is 413cm (in my ‘stiff neck’ orientation that is). I definitely will do a cloud like that.

Silencer "box"? singular? Only one? You will have two ducts, one bringing fresh air in, the other take stale air out. Each of those ducts passes through two leaves (inner-leaf and outer-leaf). Therefore you will need four silencer boxes, not just one.

Definitely at least 1 (big) silencer for the send and another for the return. I don’t know if I need 2 on each leg, maybe I do. How can I tell? What would be the isolation improvement of having 2 rather than 1?

Personally, I would put it [the mini split] at "K". It's no fun to have cold air spraying on your face all the time, plus your ears are more sensitive to noise in front of you, then to noise behind you. I generally try to have the fresh air come in at the back of the room, directly into the mini-split unit, where it can be cooled and dehumidified immediately, and then exhaust the stale air out at the front of the room. So the net air flow is form the back of the room towards the front.

I can see the sense of this. I am not sure I can achieve it but I will look into it. The issues are that the outside unit would have to sit on the roof which could cause vibrational problems. Also it would then be directly outside my bedroom window and my girlfriend may not be too keen on that!. Also the ventilation fan has to be located at G (because that is the only accessible space that is in between the inside and outside leaf) and so the stale air would have to pass through and extra 4m of duct which is not particularly desirable. Also I was going to turn over the entire rear wall to bass trapping so I am not sure where I could mount the inside A/C unit. I will ask the A/C guy about where it is possible to mount the outside unit for a start.

if you design your room following the RFZ principle (also CID and NER), then there wouldn't be any first reflections for you to worry about! 

Maybe that is a good idea but I have no idea what is involved to do that. I don’t have a budget for a studio designer so unless I can work it out there is no chance for this style of design. I will look into it now and see how far I can get. Any suggestions? Is the idea to angle the front side walls so the reflections are deflected past the mix position? If so I don’t think I can do this as the placement of the load bearing walls has already been fixed now.
Also the room is already small, I don’t want to lose more space.

You cannot have hollow studio doors, if that's what you were planning.

I was thinking about filling the hollows with rock wool or maybe celotex or even some plasterboard (depending how heavy the doors are getting).

No bass trapping? You will DEFINITELY need bass trapping in your corners. That goes without saying. Which is a REALLY good reason to re-arrange your layout so that there are no doors in room corners. Corners are prime, expensive, valuable real estate for treatment: the best place in the house! Putting a door in a corner is somewhat akin to designing a beachfront town with the garbage dump on the beach, and the houses down in the bottom of the ravine... It makes no sense. Put the houses on the beachfront, and the garbage dump in the ravine. Put the bass traps in the corners, and the doors in the unused parts of the wall.

Unfortunately there are no unused parts of the wall for me to put the doors. I may be able to move the door an additional 30cm further along the wall (further from the corner) but that would mean that either the window is 30cm smaller or that the window moves forward past the mix position by 30cm, neither of which are very desirable. Maybe I can compromise a little here.
But definitely I want as much bass trapping as possible! I was thinking there is quite a bit of room back there, enough for a floor to ceiling corner treatment at M and above door height I can have at least an area of about 1m x 75cm x 3m for hangers and/or additional trapping, and on top of that the whole remaining rear wall can have 20cm of rock wool (or more).
Any ideas on a better approach to this?

cheers
David

[Beeboss]

Digging a big hole now, it looks small but 1.5m x 1.5m x 1.5m is hard work on my poor back

[Beeboss]

next job is to fill hole with this lot, 4 tonnes of it

[Beeboss]

in other news i have been building some silencers

[Soundman2020]

Whoaaaa! Hang on there! What are those plastic bag things inside your silencers? That is NOT duct liner! Use only the right materials here: this is important. Get some proper duct liner.


---

The issues are that the outside unit would have to sit on the roof which could cause vibrational problems.

why? I don't understand why the compressor would have to go in a different location. Just put it in the same place it would have gone, and get an extension kit for it if the included pipe bundle won't go that far.

the ventilation fan has to be located at G (because that is the only accessible space that is in between the inside and outside leaf)

Why do you want your fan INSIDE the MSM cavity? And how would you get access to that anyway? If you have your fan in the cavity, then it is not isolated... You will likely here it inside the room....

so the stale air would have to pass through and extra 4m of duct which is not particularly desirable.

Why is that not desirable? The longer the duct, the less noise gets to the other end.... Long ducts are a GOOD thing, not a bad thing. The only downside is that very long ducts will increase your static pressure slightly, but if that happens you can either switch to a larger duct for some of the run, or get a fan that can handle the higher static pressure...

I was going to turn over the entire rear wall to bass trapping so I am not sure where I could mount the inside A/C unit.

On brackets bolted to the wall.... or leave a small area on the rear wall without insulation for the unit. It won't affect your acoustics much, and the diffusion you'd get from it might even be a good thing for the room.

I will ask the A/C guy about where it is possible to mount the outside unit for a start.

That can go anywhere you want, as long as it is within reach of the longest extension kit. I have had to use two extension kits sometimes, for very long runs. The manual for the unit will tell you what the maximum permissible length is for the coolant pipes.... as long as your run is less than that, you are fine.

Is the idea to angle the front side walls so the reflections are deflected past the mix position?

Correct.

If so I don’t think I can do this as the placement of the load bearing walls has already been fixed now.

The walls you need for this are not load-bearing. They are extensions of the soffit front baffle.

I was thinking about filling the hollows with rock wool or maybe celotex

That would still be a hollow door. "Hollow" does not mean "air": it means "not wood". Anything that is no solid wood all the way through is a hollow door, and will not give you much isolation.

depending how heavy the doors are getting

They will be heavy. VERY heavy. They MUST be heavy. If they are not heavy, they won't isolate. What stops sound is mass.




- Stuart -

[Beeboss]

Hi Stuart and thank you for your comments

Whoaaaa! Hang on there! What are those plastic bag things inside your silencers? That is NOT duct liner! Use only the right materials here: this is important. Get some proper duct liner.

What is wrong with well covered rock wool? There are builds documented here have used it and it is recommended by some experts as well.

This build was particularly inspiring …
http://www.johnlsayers.com/phpBB2/viewt ... &start=255
scroll down to sunday march 9 2008 to see rock wool duct liner

The main trouble is that here in the UK duct liner is hard to come by and very very expensive. I need about 2m2 for each silencer and so, even if I have only 6 silencers, in total that comes to about £360 just for the foam duct liner!!! That is more than I am spending on 3 fans!!! I am on a tight budget and can’t stretch to luxury foam.

I have wrapped up the rock wool with 3 layers of garden frost fleece which seems to have done the job nicely.

I don't understand why the compressor would have to go in a different location. Just put it in the same place it would have gone, and get an extension kit for it if the included pipe bundle won't go that far.

Ok it may be possible then if they can extend to around 10m, I will ask my a/c guy about it. I didn’t realize that much extension was possible.
However if I have the indoor blower at the back of the room it will be DIRECTLY above the rear seating area (and there is no spare space to move the sofa forward even a metre). At least at the front of the room the mix position will be a couple of metres away from the blower and won’t be directly underneath it. I can’t decide about this.

Why do you want your fan INSIDE the MSM cavity? And how would you get access to that anyway? If you have your fan in the cavity, then it is not isolated... You will likely here it inside the room....

Where else would the fan go? I don’t want the fan inside the control room! And I don’t want the fan outside in the open air and rain so that leaves in between the outer and inner leaves as the only remaining place. The fan is very quiet luckily (if the manufacturers specs are to be believed). I have left 40cm between the external and internal door to allow for access to the fan, just enough to be able to remove it, clean filters etc. I was planning on fixing it to the outside leaf only and having lots of rock wool around it (not actually touching it obviously). Maybe I could build it a little box if necessary. If this is a bad idea what would be your recommendation for fan placement?

Long ducts are a GOOD thing, not a bad thing. The only downside is that very long ducts will increase your static pressure slightly, but if that happens you can either switch to a larger duct for some of the run, or get a fan that can handle the higher static pressure...

The fan manufacturers suggest that a run of no longer than 5m is used. I am guessing that the longer the run the more weight of air has to be moved and it seems counterproductive to have a longer run than necessary if that means having to get a bigger louder more expensive fan to do it. With this in mind I am aiming for maximum runs of just a few metres.

The walls you need for this are not load-bearing. They are extensions of the soffit front baffle.

I am not really understanding this. What is the advantage of having side walls as an extension of the front soffit baffle rather than using that space for extra absorption inside the room? In a small room don’t I need as much trapping as I can get?

That would still be a hollow door. "Hollow" does not mean "air": it means "not wood". Anything that is no solid wood all the way through is a hollow door, and will not give you much isolation.

I saw this hollow door idea on the SOS website …

http://www.soundonsound.com/sos/mar98/a ... ofing.html

They say to “build your own doors, from two layers of thick ply or chipboard, leaving a gap between the two layers of ply and using Rockwool or fibreglass to fill it. This will help to deaden any vibration of the panels and also absorb a proportion of the sound trying to radiate from one panel to the other.”

So I suppose then that this isn’t really a very good idea. Maybe I can still make a 4x2 frame around the perimeter of the door and fit one sheet of mdf (or external grade ply) over that for one side (overlapping it round the edges) and then use 2 more sheets of mdf cut slightly smaller to go inside the 4 x2 perimeter from the other side. Same weight (75kg ish) and no hollows. Just pondering to myself here really...

So many things to consider, it is all getting a bit much for my small brain. Thank for your help Stuart.

Cheers
David

[Soundman2020]

Where else would the fan go?

On the far end of the exhaust duct. As far away as possible from the room, and definitely not inside the MSM cavity of the wall. If you put it in the cavity, you'd have to break a hole in the wall each time the fan needed servicing, cleaning or replacing.

And I don’t want the fan outside in the open air and rain

Why not? That's the best place for it, actually.

so that leaves in between the outer and inner leaves as the only remaining place.

... meaning the fan would not be isolated from either the interior of the studio, nor the exterior. It would be audible in both...

The fan is very quiet luckily (if the manufacturers specs are to be believed).

I believe in Santa Clause! Take those numbers with a grain of salt: they are measured under ideal conditions, not real-world conditions.

If this is a bad idea what would be your recommendation for fan placement?

Use a proper HVAC extraction fan that is designed for the specific purpose of being used outdoors at the end of a long run of HVAC duct, and get one that is matched to the parameters of your studio. It must be able to move the required voume of air (cubic feet per minute) at the required velocity (feet per minutes) in the size of duct that you will be using, and when working against the static pressure that your HVAC system will create. You cannot just throw any fan from Home Depot in there, and hope it will work. Get the right fan for the job. Just as you would never consider using an SM58 inside a kick drum, or a U47 for recording interviews out in the street, so too you should not consider a fan that is not matched to the purpose for which you are using it.

The fan manufacturers suggest that a run of no longer than 5m is used.

Then you DEFINITELY have the wrong fan! That one is probably mean for a bathroom, kitchen, or laundry, NOT a proper HVAC system. To start with, one meant for an HVAC system would not tell you how long the duct can be;: it would tell you what static pressure range it can handle, and would have a graph that shows the flow rate vs. static pressure.

Send that fan back and get a real one.

I am guessing that the longer the run the more weight of air has to be moved and it seems counterproductive to have a longer run than necessary if that means having to get a bigger louder more expensive fan to do it.

It's not about the weight of the air that has to be moved, but rather about the static pressure created by your duct system. And the correct fan fill probably be quieter, since it will be the correct one for the job, not a re-purposed household extractor fan.

With this in mind I am aiming for maximum runs of just a few metres.

Then you are aiming for little to no isolation. Sorry to be harsh, but that's the way it is. You can only get substantial isolation if your ducts are long enough, and have enough turns in them, and are lined, and incorporate silencer boxes at all penetrations through leaves.

I am not really understanding this. What is the advantage of having side walls as an extension of the front soffit baffle rather than using that space for extra absorption inside the room?

Because you seem to be designing an RFZ room, and the basic principle of an RFZ room is that all first-order reflections are directed past the listening position, to the rear of the room, where they are absorbed and/or diffused. A true RFZ-style room does not attempt to absorb first reflections very much: it attempts to reflect them at the correct angle.

In a small room don’t I need as much trapping as I can get?

Yes yo9u do, but that can go INSIDE the angled section, with large openings at the bottom and/or top to allow sound to enter. I normally use hangers inside those spaces, but even stuffing them full of insulation can be very effective. But for RFZ-style rooms, the front is a solid, massive, rigid surface, whose purpose is to re-direct direct sound from the speakers, past the listening position.

They say to “build your own doors, from two layers of thick ply or chipboard, leaving a gap between the two layers of ply and using Rockwool or fibreglass to fill it. This will help to deaden any vibration of the panels and also absorb a proportion of the sound trying to radiate from one panel to the other.

Do the math: Let's say you followed their advice to the extreme, and used two layers of 3/4" plywood (density around 550 kg/m3) with a 1" gap between them. The MSM resonant frequency of such a door would be 115 Hz. It would not isolated at all until 161 Hz. ti would isolate reasonably above 231 Hz, and would isolate well starting at about 350 Hz.. Check that against the musical scales of most instruments and human vocals too... At best, it would give you around 35 dB of isolation, which is about the same as a typical un-insulated house wall (2x4 studs with 1/2" drywall on each side).

On the other hand, building a proper studio door as a pair of back-to-back 2.5" thick solid doors with a 4" gap between them, would get you around 50 dB of isolation, starting at 46 Hz...

So many things to consider, it is all getting a bit much for my small brain. Thank for your help Stuart.

I'm not sure if you have Rod's book, but if not then I'd highly recommend that you buy it and work through it. He speaks about all of the problems you are facing, and shows you how to deal with them...



- Stuart -

[Beeboss]

Apologies for late reply, I have been away travelling for a couple of months. Now I am back the whole HVAC thing is really beginning to hurt my head. I had the expert round today and he thought my fan and baffle design would kind of work but the problem he explained to me was that if I was bringing in sufficient air the mini splits would have to be working full out all the time to be able to make the inside temperature comfortable (if the temperature outside was either quite hot or quite cold). His solution was to install a heat exchanger located outside that would recover the heat/cold efficiently and supply air through an 6” pipe with a T off for each room. Another 6” pipe would take out the stale air.
I can see the point of it - without a heat exchanger I would effectively be dumping around 300m3 of heated/cooled air outside each hour which is an expensive waste, and not to mention problematic to be blowing cold air in the room in winter etc.
The noise attenuation he was suggesting didn’t seem like it would work that well (off the shelf cross talk attenuators) but the system would work (he said) with homemade baffles (of a different size that the ones I made already-grrr). Also it would cost £3800 not including noise attenuators (or the 3 mini splits which cost another £4700!!).

I was wondering if it would be better if I was to go for this heat exchanger system to have one big air conditioning unit that could supply the whole studio in one go rather than a mini split for each room? Would that be more cost effective? I guess it would be a little less independently controllable but with the air being shared between the rooms anyway I don’t know if there is much point in independent split units.

Also I am wondering if there is anything else I have overlooked or not considered? Or if there is another cheaper more efficient method? This is getting very expensive very fast.

I'm not sure if you have Rod's book, but if not then I'd highly recommend that you buy it and work through it. He speaks about all of the problems you are facing, and shows you how to deal with them...

Yes I read it but there is nothing specific enough about the ventilation system design - no mention of baffles at each wall penetration, no mention of baffle design, and I don’t see anything about locating fans outside either. I have read that chapter closely and still have no idea what is the most viable way to go about designing the ventilation. I am taking this bit seriously …

“Re-work is always a lot more expensive than doing it right the first time. So save your money, keep your sanity, and plan for this now. “

building a proper studio door as a pair of back-to-back 2.5" thick solid doors with a 4" gap between them, would get you around 50 dB of isolation, starting at 46 Hz...

OK, solid doors it is, as heavy as I can manage. Thanks for pointing me in the right direction.

cheers, David

[Soundman2020]

Now I am back the whole HVAC thing is really beginning to hurt my head.

Then you are definitely on the right track!

he explained to me was that if I was bringing in sufficient air the mini splits would have to be working full out all the time to be able to make the inside temperature comfortable (if the temperature outside was either quite hot or quite cold). His solution was to install a heat exchanger located outside that would recover the heat/cold efficiently and supply air through an 6” pipe with a T off for each room. Another 6” pipe would take out the stale air.

Yep. That's a good way of doing it.

The noise attenuation he was suggesting didn’t seem like it would work that well (off the shelf cross talk attenuators)

Right. Those are not meant for high levels of isolation: They are good at blocking fan noise, and voice-range noises, but not for loud, bass-heavy music.

but the system would work (he said) with homemade baffles (of a different size that the ones I made already-grrr).

How big are yours, and how big did he suggest you make them?

if it would be better if I was to go for this heat exchanger system to have one big air conditioning unit that could supply the whole studio in one go rather than a mini split for each room? Would that be more cost effective?

Very likely, yes. With that arrangement, you can recirculate some of the air, and you only need to run the make-up air through the HRV. It would also be quieter, as you would have the AHU completely outside of the isolated area. So fan noise and the other sounds that mini-splits make would be totally gone.

You might also find that a single AHU would be less expensive to buy and install than individual mini-splits. The installation costs can be substantial, and you'd only need to pay for one installation, not two...

I guess it would be a little less independently controllable

Not really: you can have motorized dampers to control the flow to each room separately, and a system controller to run them, as well as controlling the AHU, HRV and other aspects of the system. You could get fancy and have thermostats in each room, as well as humidity sensors and even CO2 sensors if you want, all feeding back to the controller that would then decide how much make-up air you need, how fast to run the AHU, and how much air to move into each room, all automatically.

I am taking this bit seriously …

OK, solid doors it is, as heavy as I can manage. Thanks for pointing me in the right direction.

You're welcome!

- Stuart -

[Beeboss]

Thanks you for your reply Stuart, very helpful as always.


I got another HVAC guy round and he had another idea so now I have 4 plans and no real clue which to choose, all seem to have some advantages and some disadvantages.

plan A - 3 mini splits (one for each room) and a heat exchanger ventilation system. approx price £9000

plan B - one large unit outside ducted to all the rooms, with dampers and control system.
Unpriced as yet but probably more. HVAC guy is being very slack providing the quote.

plan C - single 14kw standard ducted indoor unit with outdoor compressor, ducted to the 3 rooms
approx price £7000

plan D - 3 x 5kw standard ducted indoor units with 3 external units, independent system for each room. approx price £8000

No idea which of these is best but am learning towards plan D because the systems are independent and should be pretty quiet inside and fairly quiet outside. Would I be making a big mistake to go with plan D?

How big are your [baffle boxes], and how big did he suggest you make them?

The baffle boxes I made are for 100mm pipe whereas Plan D piping is all 200mm (plan A is 150mm pipes). Still I only made 3 baffles and probably will need 12 so I can put them down as practise boxes!. Even these ones are quite big so I am worried that with 12 baffles sized for 200mm pipe I won’t have any space left in the studio for me or anyone else!
It is just possible I may be able to reuse or resize the existing ones with some effort.
The HVAC guy looked at me strangely when I explained my plan to use homemade baffle boxes, I think he thought I was a bit mad - I don’t think he had ever seen anything like my baffles before. He was suggesting I use off the shelf in-line attenuators.

I did a quick calculation for the baffle boxes - would a size of around 100cm x 50 cm x 30cm be adequate as a minimum size (for 200mm inlet/outlet) ? would bigger be better?
Should I use 12mm acoustic duct liner foam (fire retardant) - is that thick enough? or do i need 25mm foam as a minimum?

Cheers
David

[Soundman2020]

plan C - single 14kw standard ducted indoor unit with outdoor compressor, ducted to the 3 rooms
approx price £7000

That sounds like the best option to me, and is the way I would do it. But 7k? Sounds steep!

Any chance you can get that cost down by doing much of the work yourself? Making/modifying silencer boxes is simple (as you already discovered), installing duct-work isn't that hard either. You'd only really need the professional installers to install the hook up the actual AHU and compressor, as that's a specialized task. I can't see how an AHU + compressor + control system can come to 7k! Where I live that would cost no more than 3k max. 14 kw is only 48,000 BTU/H: not a huge system. Here's links to a couple of local HVAC companies where I live that I found with a simple Google search:

http://www.airecenter.cl/index.php/tien ... 0-btu.html

http://www.anwo.cl/aire-acondicionado/e ... c=1279&u=5

Price range: 1.500.000 to 2.000.000 Chilean pesos for that system. Exchange rate is about 650 pesos to the US$, so those things would cost me about US$ 2,000 to US$ 3,000. Add another thousand for installation, and it should be no more than US$ 4,000, or abut £3,000. I can't see why it would be more than twice as much in the UK!

Even these ones are quite big so I am worried that with 12 baffles sized for 200mm pipe I won’t have any space left in the studio for me or anyone else!

Put then in places where people would never be: ceiling cavity, wall cavity, outside, soffits, etc. There's a lot of room to be creative with placing silencer boxes. If you do it carefully, they don't take up any space at all in the actual rooms...

The HVAC guy looked at me strangely when I explained my plan to use homemade baffle boxes, I think he thought I was a bit mad - I don’t think he had ever seen anything like my baffles before. He was suggesting I use off the shelf in-line attenuators.

Yeah, you do need a different HVAC guy! If he has no idea about peculiarities of doing HVAC for studios, then he's not the right guy for you. It's rather different from doing it for a typical house or office!

I did a quick calculation for the baffle boxes - would a size of around 100cm x 50 cm x 30cm be adequate as a minimum size (for 200mm inlet/outlet) ? would bigger be better?

What open area is that (allowing for the duct liner)? What air flow velocity and air flow volume did you use to arrive at that section? How many air changes did you use as the basis? What static pressure did you come up with? And which room are we talking about here? the rooms are rather different isn volume, so they will have very different needs in terms of flow rate.

Bigger is always better: lower air speeds, better isolation (greater impedance mismatch), etc.

Should I use 12mm acoustic duct liner foam (fire retardant) - is that thick enough? or do i need 25mm foam as a minimum?

You might be able to get away with 1/2" (12mm), but 1" would be better.


- Stuart -

[Beeboss]

Hi Stuart and thanks for your reply

Price range: 1.500.000 to 2.000.000 Chilean pesos for that system. Exchange rate is about 650 pesos to the US$, so those things would cost me about US$ 2,000 to US$ 3,000. Add another thousand for installation, and it should be no more than US$ 4,000, or abut £3,000. I can't see why it would be more than twice as much in the UK!

The UK is expensive. This is the unit the HVAC guy is thinking of installing…
http://www.orionairsales.co.uk/mitsubis ... -175-p.asp

Thats £3k just for the unit, not including spigots, ducting, labour, baffle boxes, £1k of duct lining foam, electrics, 20% vat etc. His fee for installing the unit (without vat but including ducting) is £5.2k which doesn’t seem so outrageous.

I think I am going to go for the 3 smaller individual systems (3x FDUM40VF) though for several reasons -
- about 60% of the time (I anticipate) I will just be in one room and will not need the other rooms to be ventilated/heated/cooled all the time.
- individual control over temperature in each room is important
- when one unit breaks and needs to be replaced then the cost will not be so huge.
- the smaller units are significantly quieter which is always good.
- it is only £1k more which is not that significant in comparison with the cost of the whole system.

re baffles …

What open area is that (allowing for the duct liner)? What air flow velocity and air flow volume did you use to arrive at that section? How many air changes did you use as the basis? What static pressure did you come up with? And which room are we talking about here? the rooms are rather different isn volume, so they will have very different needs in terms of flow rate.

I don’t have any calcs for static pressure, air flow, air changes etc, I have left all that to the professionals, I gave up trying to understand it. The system I mentioned above (and also the 3 individual units if I go with that) all have 200mm ducting for the circulating air, so I am guessing I need to build baffles to reflect that. The same for each room.
Probably I would cover these with a few more layers of plasterboard once installed. Does this look approximately right size wise?

cheers
David

[Soundman2020]

- about 60% of the time (I anticipate) I will just be in one room and will not need the other rooms to be ventilated/heated/cooled all the time.

Do you plan to keep any instruments or mics in one of those rooms? Instruments need constant temperature and humidity to sound good. It must be held to the range 45% to 55% all the time. If not, the wood either swells or shrinks with each humidity change, which of course changes the tone. If the swings are reasonably large and frequent enough, the joints and even the wood itself can crack. Condenser mics (and some ribbon mics too) will change their tone as temperature changes.

Imagine trying to track an acoustic guitar with a condenser mic, where both of them have been in the room overnight, with freezing temperatures and high humidity. Then you turn on the HVAC... in a few minutes the humidity drops drastically and the temperature rises drastically... You tune the guitar and start recording, but soon notice that is sounds terrible: the mic tone is changing due to the rising temperatures, and the guitar tone is changing due to the falling humidity.... Good luck with that session! And good luck with getting your guitar re-calibrated every few weeks, because it never seems to sound right...

In other words, if you have prized instruments, and you want them to always sound good and last for a long time, you cannot afford to cut off the HVAC in that room. Ever.

- individual control over temperature in each room is important

I'm not sure why you think that would be a problem with an AHU: that's the job of the system controller. It keeps things the way you want them in each room, individually.

- the smaller units are significantly quieter which is always good.

Ummmmm.... Nope! they are not. they never can be. If you have a mini-split system in each room then you have a FAN AND COIL AND VANE MOTOR inside your room, and probably some relays too. They all make noises, even if it is low level. Apart from anything else, the fan creates turbulent air flow, which is noisy. And it is all right there, in your room. With an AHU, NONE of that is in your room! It is all outside your room, where it cannot be heard at all. The AHU is located at some place where it simply cannot be heard inside the rooms. At all. Nothing. And if the system is designed correctly, the airflow is so slow that you don't hear a thing form the movement of air through the registers.

A proper ducted AHU system is silent. Mini-splits never are, even if they claim to be "quiet". The relays click on and off all the time, the fan runs and changes speed, the vane motor keeps the vanes moving, and the refrigerant moving through the coils can also make a noise. So can the condensate trickling out.

I'm not sure who told you that a mini-split is silent, but he is dead wrong, and has obviously never been inside a well isolated studio where there's a mini-split on the wall: they are annoyingly loud.

I don’t have any calcs for static pressure, air flow, air changes etc, ... Does this look approximately right size wise?

Sorry, can't help you there at all. If you don't give me the numbers, then there's no way that I could know if your silencer box design is correct or not. You'll have to get me those numbers if you want a valid opinion.

all have 200mm ducting for the circulating air, so I am guessing I need to build baffles to reflect that.

"Guessing" at studio design is always a bad idea. but especially so with HVAC. What you need to do is to check that your silencer boxes will have a large enough cross-sectional area inside, allowing for the duct liner, to ensure that the air flow velocity remains low enough to not cause unwanted noise, while the air flow volume remains high enough to supply the correct amount of air to your room, while also not increasing the static pressure beyond the capability of the fan system.

You can't guess here. You need to be certain that the dimensions are correct for the flow rate and velocity and static pressure...

What is important here is that you need a sudden change in cross-sectional area of at least 200% at the entry point, and possibly the exit point as well. And a few other things too...


- Stuart -

[Beeboss]

Hi Stuart, and thanks for your reply.

I think maybe we are talking at cross purposes a little


“- the smaller units are significantly quieter which is always good.”

Ummmmm.... Nope! they are not. they never can be. If you have a mini-split system in each room then you have a FAN AND COIL AND VANE MOTOR inside your room, and probably some relays too.

I wasn’t comparing a 3 x mini split to a single AHU solution, I was comparing plan C and D - a single 14kw system to 3 x 4kw systems - both indoor ducted systems with an external condenser and an indoor unit (or 3 indoor units) which sit in a mini machine room. I have already given up on plan A, the one with the mini splits, as it doesn’t make any sense. So comparing plan C and D …


Plan C- 1 x FDUM140 single indoor unit ducted to the 3 rooms (with a condenser located outside)
Plan D - 3 x FDUM40VF units - 3 individual indoor units each ducted to their respective rooms (with 3 condensers located outside)

Looking at the specs for these models the sound generated at the indoor unit is ..
plan C - 30/40 dB(A)
plan D - 26/32 dB (min/max)

so the system with 3 units is a tiny bit quieter although this is not that significant as these units will be in a mini machine room outside the sound isolated rooms. I can’t find the figures for the external units offhand but there was more of a difference there, not a really important difference though.



- individual control over temperature in each room is important

I'm not sure why you think that would be a problem with an AHU: that's the job of the system controller. It keeps things the way you want them in each room, individually.

Neither of the systems I have had quotes for include motorised dampers and a control system. I asked my HVAC guy and he said that a single outdoor AHU unit would be ‘significantly’ more expensive, and that is assuming I had somewhere outside to put it, which I don’t. Basically I have had to give up on plan B because I am not rich enough. It may have been ultimately the best system but I need individual control on a budget. There may be some drawbacks of plan D compared to plan B but I don’t know what they are?

What you need to do is to check that your silencer boxes will have a large enough cross-sectional area inside, allowing for the duct liner, to ensure that the air flow velocity remains low enough to not cause unwanted noise, while the air flow volume remains high enough to supply the correct amount of air to your room, while also not increasing the static pressure beyond the capability of the fan system.
You can't guess here. You need to be certain that the dimensions are correct for the flow rate and velocity and static pressure...

I want to be certain but it is difficult as I am not capable of making those calculations. I tried to understand all the the HVAC nitty gritty for some months but realise it is beyond me. I am just a musician! That is why I got a pro HVAC guy to calculate the requirements for the rooms and their occupancy. He has never seen homemade baffles like mine ( that is not surprising) but he did say that as long as the air flow wasn’t restricted at any point less than the 200mm duct then it would not be problem for the fan. As far as sound isolation goes he doesn’t know anything so I have to make my best guess based on nuggets of info I can gain from you and other experts. To be honest it is not going well. Even if I build the baffles according to the size in my last post I need about £1388 of foam duct liner which is completely ridiculous - in the UK the cheapest I can find is around £40 a m2 and I need around 35m2 (2.9 m2 for each baffle, 12 baffles). I don’t have a solution or a way forward on this yet.

If you don't give me the numbers, then there's no way that I could know if your silencer box design is correct or not. You'll have to get me those numbers if you want a valid opinion.

I found the figures, they don’t mean much to me but hopefully they will clarify. Static pressure for the 3 x FDUM40VF units I am considering is 100PA. Max air flow is 10 m3/min, maximum length communication is 30m. From this, knowing the duct size is 200mm, I calculate (quite possibly wrongly!) that the duct velocity will be at maximum 12.5 m/s, although I suspect I will not be using the system at full power very often so it should be a lot less than this most of the time. The units have already been calculated as being right for the rooms based on the ventilation/cooling/heating requirements so I don’t need to get into any further air changes per hour calc. What I don’t know is how (or if) I should adjust the design of the baffles based on these figures?

fuller specs of FDUM40VF here…
http://specsen.com/air-conditioners-mit ... m40zmxvf-/

Any advice on my baffle dimensions or other issues are most welcome.

Cheers, David