John Sayers' Recording Studio Design Forum Archive

Dear planners, builders, enthusiasts,

I hope you can answer a question for the studio I am building.

First, it is going to be my 5.1 mixing, and music and voice recording room, 35m2, 2,6m high. Somebody here in Cologne/Germany is helping me to plan the studio, it is going well so far.
Now I am about to install the HVAC / ventilation system / heat exchanger, that I luckily got very cheap. It is able to move 600m3/h (with heat exchange!), although I will never have it run more than 50%.

I am building it all by myself, so I cant afford a HVAC planner. The way the studio is planned, there is gonna be a huge bass absorber in the front, and one in the back. All around the absorbers I leave a 10cm air gap in every direction, so air can float around them, because most of the walls are outer walls.

The to-air pipe goes all along from left to right behind the back absorber, with air outlets every meter, so the air will evenly spread behind the back absorber.
The exhaust air is going to be led out all along from left to right behind the front absorber, right under the ceiling.

My question is: Which height is best for the pipe behind the back absorber? Should I put it on the floor, so the air stream is diagonal? Or in the middle at 1.20m high? or under the ceiling as well, so the slightly colder air will fall down?

thank you alot in advance,
best
Marcus

My question is: Which height is best for the pipe behind the back absorber? Should I put it on the floor, so the air stream is diagonal? Or in the middle at 1.20m high? or under the ceiling as well, so the slightly colder air will fall down?

Your registers/diffusers will have tech documents that show how they throw. Build according to that.

Greg

Somebody here in Cologne/Germany is helping me to plan the studio, it is going well so far. ... I am building it all by myself, so I cant afford a HVAC planner.

HVAC design is a very, very large and very important part of studio design: Your studio designer should be doing all of the HVAC design as well! They go together. You can't have a good studio design until you know where the HVAC will be! The HVAC takes up a LOT of space (especially the silencer boxes), and that normally affects the room shape and size, in one way or another. It's really important that the HVAC and actual studio should be done together.

The way the studio is planned, there is gonna be a huge bass absorber in the front, and one in the back.

That's backwards! What design concept are you following? It sounds rather strange. The REAR wall of the studio is always the one that gives you the most trouble, so that's where you need your "huge bass traps". I normally use the entire rear wall for bass control, in my designs. For example, see here: thread about Steve's control room in New Orleans Note the rear wall treatment. And this one as well: the corner control room thread In both of those, the rear wall is the key to getting the results you see. And in both of those, the front wall is mostly reflective. There's bass trapping in the front walls too, yes, but most of it is at the back.

The to-air pipe goes all along from left to right behind the back absorber, with air outlets every meter, so the air will evenly spread behind the back absorber.

That's a little confusing! You said you had not done any HVAC design yet, but you have already decided where to put the supply duct? Where is the silencer box for the supply air duct? And your plan is going to cause problems with air noise, because you have a long straight duct with perpendicular outlets directly into the room. Those will cause turbulent flow in the ducts and he registers, which causes air noise. What is the air velocity at the registers? And the total flow rate for the room) What size ducts are you using?

The exhaust air is going to be led out all along from left to right behind the front absorber, right under the ceiling.

Here too: Where is the silencer box going to be? What is the surface area of the return (exhaust) registers, and of the duct? What is the air velocity at the registers? And what is the static pressure of the complete system? You need to know all that to make decisions about the design.

My question is: Which height is best for the pipe behind the back absorber? Should I put it on the floor, so the air stream is diagonal? Or in the middle at 1.20m high? or under the ceiling as well, so the slightly colder air will fall down?

With most of my studio designs, I bring in the supply are through the rear of the room, at ceiling height, at very low speed and high rate, and directed either from the rear center towards the rear corners, ro the other way around: from the rear corners towards the rear center. All of that takes place inside the rear bass trap, so the airflow actually permeates though the entire rear wall treatment. I then usually have two or more registers at the front of the room, on the ceiling, directly above the speaker soffits or the cloud. This setup gives good flow through the room, an good mixing of air.

But you do have to get the flow rates and flow velocities correct, and you also have to take care with the design of the silencer boxes to make sure they can handle the right amount oaf air flow while blocking sound from getting in and out.

- Stuart -

Stuart, thank you so much for taking the time!

Somebody here in Cologne/Germany is helping me to plan the studio, it is going well so far. ... I am building it all by myself, so I cant afford a HVAC planner.

HVAC design is a very, very large and very important part of studio design: Your studio designer should be doing all of the HVAC design as well! They go together. You can't have a good studio design until you know where the HVAC will be! The HVAC takes up a LOT of space (especially the silencer boxes), and that normally affects the room shape and size, in one way or another. It's really important that the HVAC and actual studio should be done together.

Yes, I know... I just haven't got the money to let him get his HVAC partner on board. And as I allready have the heat exchange/ventilation unit, and his rough opinion where to have the air in/out in general, I'm trying on my own!
the silencers will be in the next room, right after the duct exits the studio room (blue wall), and lead into the ventilation unit. the ducts go through the wall right into the front and rear absorber (like you explained), see pic attached.

The way the studio is planned, there is gonna be a huge bass absorber in the front, and one in the back.

That's backwards! What design concept are you following? It sounds rather strange. The REAR wall of the studio is always the one that gives you the most trouble, so that's where you need your "huge bass traps". I normally use the entire rear wall for bass control, in my designs. For example, see here: thread about Steve's control room in New Orleans Note the rear wall treatment. And this one as well: the corner control room thread In both of those, the rear wall is the key to getting the results you see. And in both of those, the front wall is mostly reflective. There's bass trapping in the front walls too, yes, but most of it is at the back.

sorry, my fault (I'm not native): the huge absorber is the back one!
thanks for the links!

The to-air pipe goes all along from left to right behind the back absorber, with air outlets every meter, so the air will evenly spread behind the back absorber.

That's a little confusing! You said you had not done any HVAC design yet, but you have already decided where to put the supply duct? Where is the silencer box for the supply air duct? And your plan is going to cause problems with air noise, because you have a long straight duct with perpendicular outlets directly into the room. Those will cause turbulent flow in the ducts and he registers, which causes air noise. What is the air velocity at the registers? And the total flow rate for the room) What size ducts are you using?

well, I don't know yet which outlets I should use. thanks for pointing out the "long straight duct" problem. Do you recommend any kind of outlets or an alternative?

the duct is diameter 16, total flow rate is 0-400m3/h, which is way too much for the room. I can switch it off for quiet recordings or set it to maybe 50m3/h without hearing it (have to test it) or set it to 50% or even 100% when I am taking a break.

I could go from diameter 16 to 20, once the ducts enter the absorbers, to reduce velocity, does that help?
anything else you could recommend?

The exhaust air is going to be led out all along from left to right behind the front absorber, right under the ceiling.

Here too: Where is the silencer box going to be? What is the surface area of the return (exhaust) registers, and of the duct? What is the air velocity at the registers? And what is the static pressure of the complete system? You need to know all that to make decisions about the design.

I haven't planned surface area, or velocities, or pressure... I am trying to build it as good as possible, and in the end I will see how high I can set the ventilation unit until I hear wind noise.
I know it is not ideal, but I don't know how else to do it! Well I try now!

My question is: Which height is best for the pipe behind the back absorber? Should I put it on the floor, so the air stream is diagonal? Or in the middle at 1.20m high? or under the ceiling as well, so the slightly colder air will fall down?

With most of my studio designs, I bring in the supply are through the rear of the room, at ceiling height, at very low speed and high rate, and directed either from the rear center towards the rear corners, ro the other way around: from the rear corners towards the rear center. All of that takes place inside the rear bass trap, so the airflow actually permeates though the entire rear wall treatment. I then usually have two or more registers at the front of the room, on the ceiling, directly above the speaker soffits or the cloud. This setup gives good flow through the room, an good mixing of air.

that is interesting!
the absorbers will be made out of loose polyester fleece, would that material be fine for permeation?

I could try to do it that way: 1 register inside or almost behind the rear absorber, that blows to the corners, and 1 register in the front of the rear absorber.

But you do have to get the flow rates and flow velocities correct, and you also have to take care with the design of the silencer boxes to make sure they can handle the right amount oaf air flow while blocking sound from getting in and out.

allright, I try to wrap my head around that now!

thank you so much!

Yes, I know... I just haven't got the money to let him get his HVAC partner on board. And as I allready have the heat exchange/ventilation unit, and his rough opinion where to have the air in/out in general, I'm trying on my own!

Doing it on your own is fine... as long as you know what you are doing! If you can't afford the money to hire someone to do it, then you MUST take the time to learn how to do it yourself.

You are obviously investing a lot of money in building this studio: Think about that: Do you really want to invest all that money, and then find out that you can't use your studio because the HAVC system is too noisy, or does not supply enough fresh air, or is not dehumidifying correctly, and you now have mold (fungus) growing on your walls?

This investment is too important to take shortcuts. I would really urge you to take the time to study everything you need to know about studio HVAC; which is VERY different from the typical HVAC installation in an ordinary house, shop, office, school or something like that. Studios are very, very different, and the HVAC system s very very different. You need to spend the time to do the math, and calculate everything correctly.

the silencers will be in the next room,

Then they won't work! The silencers MUST be at the exact point where the duct goes through the wall, into the room. The wall is what creates your isolation that stops sound getting in and out. If you cut a hole in the wall to put the duct through, then you have destroyed the isolation: Sound will now get in and out very easily. This is the purpose of the silencer box: it aloows the air to get through, but prevents the sound from getting through. If you have the silencer box outside the room, then a piece of duct connecting to the room, that simply will not work: the sound will just radiate out through the duct. The silencer box MUST be located at the wall itself, and it has a thick, heavy "sleeve" on it that penetrates the wall.

Here are examples of silencer boxes that forum members have built:

http://www.johnlsayers.com/phpBB2/viewt ... 0&start=45
http://www.johnlsayers.com/phpBB2/viewt ... 9&start=74
http://www.johnlsayers.com/phpBB2/viewt ... 42&start=5
http://www.johnlsayers.com/phpBB2/viewt ... 61&start=0
http://www.johnlsayers.com/phpBB2/viewt ... 5&start=98
http://www.johnlsayers.com/phpBB2/viewt ... &start=157
http://www.johnlsayers.com/phpBB2/viewt ... =2&t=13821
http://www.johnlsayers.com/phpBB2/viewt ... 8&start=44
http://www.johnlsayers.com/phpBB2/viewt ... 2&start=16

But don't try to copy those! The silencer box MUST have the correct dimensions for YOUR hvac system, not the dimensions for someone else s HVAC. The internal dimensions of the silencer have to be correct, or it won't work properly.

sorry, my fault (I'm not native): the huge absorber is the back one!

well, I don't know yet which outlets I should use. thanks for pointing out the "long straight duct" problem. Do you recommend any kind of outlets or an alternative?

Your HVAC registers must be the correct size! If they are too small, then the air flow will be too fast, and it will create turbulence, and noise. So you need to calculate the CORRECT air flow rate for your room, then you use that rate, along with the correct air flow velocity for your room, and that will tell you what size registers you need. It will also tell you what size ducts you need, and how big the silencer boxes have to be.

You MUST do the math here! You can't just guess...

the duct is diameter 16,

16 what? Inches? Centimeters?

total flow rate is 0-400m3/h, which is way too much for the room.

I'm not so sure about that. That's about enough for a small room, but yours looks to be quite big. What are the dimensions of your room?

I can switch it off for quiet recordings

No you can't. You might think you can, but you can't. That doesn't work.

or set it to maybe 50m3/h without hearing it

If you have designed your isolation walls correctly, and you build your silencer boxes correctly, then you will not hear the air flow nor the AHU at all, inside the studio. That's part of what the silencer box does: it blocks the noise coming in through the ducts, and some of that noise is coming from the AHU. A properly designed and built silencer box will remove all of the noise.

I could go from diameter 16 to 20, once the ducts enter the absorbers, to reduce velocity, does that help

?Yes it does help, you you can't just guess! You need to design your HVAC system so that you have an air flow velocity of no more than 1.5 m/s at the registers, and the correct air flow rate for your room size.

I haven't planned surface area, or velocities, or pressure... I am trying to build it as good as possible,

You can't build anything until it has been planned! There are very simple "rules" for deisgning a studio HVAC system. Everything depends on following those rules. You only need to worry about the air flow rate, the air flow speed, and the static pressure. Those are the three big things that you MUST control, with the ventilation system. The things that you must control with the cooling system are the sensible heat load, and the latent heat load. That's it! If you control those five things correctly, then your studio will be a wonderful place to work in, from the point of view of air movement.

On the other hand, if you just guess and hope, then the HVAC will be a disaster, ans so will the studio: you won't be able to work in there: it will too warm, too cold, to windy, to stuffy, too hot, too cold... and unpleasant. After spending all that money to build it, do you REALLY want to end up with a place that is unpleasant to work in?

and in the end I will see how high I can set the ventilation unit until I hear wind noise.

WRONG! That is exactly the wrong way to do things. Instead, you need to spend the time to CALCULATE what the correct flow rate is for your room, then set the speed of the AHU to that setting, and leave it there. It never changes after that.

I know it is not ideal, but I don't know how else to do it!

If you don't know how to do it, then learn how to do it! It's not that hard.

the absorbers will be made out of loose polyester fleece,

Why? What is the coefficient of absorption for that material? What is the density? Is it able to damp the modal resonances of your room, and also deal with the SBIR artifacts from the rear wall? Is it fireproof?

It seems to me that you are guessing here too. The bass traps at the rear of your room must be DESIGNED to do what YOUR room needs- You can't just pile up a bunch of any old thermal insulation, and hope it will work. You need to make sure that what you are using will actually work, and will do the job that needs to be done.

Personally, I would never do the rear bass trapping like that. I'm a big fan of acoustic hangers. You can see those in both the corner control room thread and Steve's thread, that I linked you to above. And you can see how effective they are, in both cases. Please spend the time to work though those two threads, so you can understand how studio treatment is done. What the process is, and what materials are used.

loose polyester fleece, would that material be fine for permeation?

I have no idea, since you didn't say what the density is, or what the gas flow resistivity is, or what the thickness is... but my guess would be that no, it would not be fine. When I do the method I mentioned to you, the rear bass traps are not solid chunks of insulation: rather, they are hangers, which have empty air spaces between them and there is a breathable fabric panel stretched across the front. Plenty of place for air to flow through.



However, now that you have posted a picture of the actual studio plan, it seems that HVAC is not your only problem. There are many, many problems with the layout that you are showing there, that need fixing. Please don't take this as criticism, but here's a short list of just a few things that I can see in there:

1 ) The side walls are not angled correctly: it will be hard to build that, and it will not be effective.
2 ) The room is too long for the width and height.
3 ) The mix position is way too far forward: it appears to be at the modal peak for all second-order axial and tangential modes.
4 ) It seems that you are trying to do an RFZ design, but you are not doing it correctly
5 ) It seems that you are trying to do a 5.1 room, yet your front surfaces are all reflective! Very bad.
6 ) You show a huge amount of diffuses on the side walls at the rear of the room: that won't work, and it will be VERY expensive to implement
7 ) Even if it would work, you are showing the diffusers set up in a repeating pattern, so therefore you would be creating major lobes of sound intensity: diffusers should never be placed in repeating patterns like that. (You can have alternate diffusers with the inverse QRD layout to overcome the lobing problems, but that still would not make that work).
8 ) The overall acoustic response of that room would be too dead.
9 ) The bass trap issues: I have already mentioned those

And several others. All of those issues need fixing. The room will not work out well at all if you follow that plan.

How much of that have you built already?

- Stuart -