John Sayers' Recording Studio Design Forum Archive

Greetings, I am a return member of the forum, and like many have benefited from the guidance of those more knowledgeable about the practice of studio design. Unfortunately my plans have remained in the virtual world. Somewhat captured by Sketchup, with no real physical form. It’s about time to produce wood, hammer and nails, and I would once again greatly appreciate the advice of those more experienced in the science/art of recording studio design.

Because it has been a while since I have posted to the site, it would seem only appropriate to restate my design goals and parameters.

Location: This will be a basement studio in Northeast Ohio.

Building: The basement area where the studio will be constructed is approximately 1,000 sq ft. (30ft x 34ft). Floor to ceiling (unfinished) is 9ft. There is a kitchen, bathroom and break area in the other side of the basement that will be accessible from the studio. That area is finished except for the ceiling which will be completed after the studio is finished. The electrical panel and HVAC are in that area as well. There are two entries to the basement, one from upstairs, and one from the Garage. The Garage entrance will be the main through-way to the studio.

Design: The existing studio design consists of a control room, an Iso room and a live room. I have purposely divided the construction into two phases so that I can work on upcoming projects after phase one is complete. Phase one consists of the control room and the adjacent Iso room. I have worked with various members of the forum to come to the current Sketchup plans. The rear of the control room will not be flat as shown in the current plans. It will have splayed false walls with slats and bass trapping.

Pertinent Skills: I am an avid wood worker and have a well equipped shop which currently occupies part of the phase two area. This equipment will be moved to a Garage shop (currently under construction). I have basic skills in residential wiring, stud wall construction and drywall hanging/finishing. I am also very comfortable with the Sketchup software where most of the design has taken place.

Budget: I have approximately $12,000.00 budgeted for the building project. Flooring for the entire project has been purchased over the last few years, and will not come out of the existing budget. My goal is to complete phase one in the next 8 months.

Studio Usage: The purpose of the studio is primarily for recording Christian music of all genres. Isolation requirements are mostly to keep the recording clean, and not as much for isolation to the remainder of the house, with the exception of the control room which I anticipate will be used during times my family would like to be sleeping.

Below are a few diagrams depicting the studio layout.

My first question relates to the control room. The existing plans will produce a “finished” control room with the length of 15’ 6” and width of 13’ 5”. The ceiling as you can see from the plans has two heights due to working around HVAC ducts. The two heights are 8’ 1” and 8’ 8”. I found out recently that I can extend the length of the control room by as much as 18”. I would like to have that extra depth if possible. My concern has to do with modal qualities. Below are three outputs from Modecalc (15' 6", 16' 6" and 17ft length control room). My limited understanding of the desired Modecalc output leads me to believe that extending the room to the prefered length may produce a room with much more acoustic challenges than the smaller room. It appears to me that the smaller room produces more evenly spaced resonant frequencies, which from what I understand (from Ethan Winers web site) is a good thing.

Like most of us here on the forum we like to have as big a control room as possible without sacrificing the quality of design. The room will have false splayed walls with slats installed at the sides and rear of the control room and appropriate absorptive materials. I realize this affects the modal properties as well.

Am I over analyzing this? Should I be worrying so much about the calculations since there will be splayed walls, clouds, rear diffusion and absorption etc, or should I stay with the smaller room? I am very interested in opinions of the forum members here. Please let me know if I have not provided enough detail for a proper response. Thank you.

Joe

Well, I picked up lumber this week to begin wall construction of the control room. The Ceiling joists will span the width of the control room (13.5 feet) and rest on the outside walls. The joists will support the two layers of 5/8 ceiling drywall, and any cloud materials. I was going to purchase 2x8s for the joists, but after running the calculations, I believe that 2x6s will work just fine.

I used the Joist Span Calculator at this site: http://www.awc.org/calculators/span/cal ... cstyle.asp

I used the following parameters as input to the Joist Span Calculator
4.62 lb per sq ft (weight of two layers of 5/8 drywall)
Hem-fir (Typical wood sold at Lowes in the US, Northeast)
Number 2 grade
10lb per sq ft Live Load (There really is no live load, but the calculator would not let me specify "0")
5 lb per sq ft dead load (Actual dead load is really 4.62 lb. Five was the lowest value on the calculator)
16in On Center (My joist spacing)

The calculator says I can span 14' 5" with a 2x6 and 19ft with a 2x8

Since there is really no live load, this seems to be a very conservative number. However, I do not do this for a living. I want to make sure I am not missing something.

Before I pick up the joists, I would really like to hear what some others have experienced.

Anyone out there have any opinions on the matter? Am I on the right track with the joists? Is there something else I should know? I would greatly appreciate any input. Thank you.

Joe

5 lb per sq ft dead load (Actual dead load is really 4.62 lb. Five was the lowest value on the calculator)

Well, not really... dead load also includes the weight of the joists themselves, nails, mud, tape, caulk, baker rod, the insulation that will be resting on top, the insulation that will be hanging below, the clouds, lights, cables, cloth, paint, and everything else that is supported by the joists. So it's a lot more than you are allowing for!

Also, fire-rated 5/8" drywall is about 2.5lb/ft2, so two layers is at least 5lb/ft2, not the 4.62 you mentioned.

So your dead load is probably more like 7 or 8. Call it 10, to be safe. And that's assuming your cloud doesn't need to be very large and hard backed: that would add considerable dead load, plus some live load if it happens to swing on its chains...

Dead load means the entire constant, fixed, stable load that does not change over time, after the structure is complete. Live load includes loads due to everything else, apart from dead load, which mainly means temporary, short-term, moving loads: building movement, vibration, impact, momentum, etc. Notice: "vibration". When you are pumping 110 dB of sound around that room, the drywall up there is vibrating, big time: that is live load. Open or close the doors, and you are applying pressure to the ceiling: That is live load (since the room is sealed air-tight, opening the door changes the air pressure in the room, which applies forces to the ceiling). Etc. Even wind pressure and seismic events can cause live loading.

So you do have live load up there, as well as dead load. The live load is not zero, even though it seems to be at first glance.

I'd seriously consider going with 2x8: Even though some types of 2x6 might be OK, with 2x8 you'll get less deflection, meaning the structure is stiffer, and therefore better at isolating frequencies below MSM resonance.


Also, I noticed that you are using a room mode calculator that only considers axial modes: that's a mistake. Axial modes are only a part of the total modal behavior of the room. You should only use calculators that consider all three types: axial, tangential and oblique. I'd switch to a better one, and re-test your numbers, playing around with them to see if you can optimize the dimensions. You did mention that you are not sure if this is worthwhile, since your room will have treatment, slot walls, etc.: Yes, it still is worthwhile. Treatment does not count when considering room ratios: only the hard surfaces of the inner-leaf counts. So for get your absorption, diffusion, slot walls and all the rest. Only consider the actual inner-leaf surfaces, plus the soffits. Yes, the soffits are angled, but the effect is not that great, so just figure the average length of the room, and use that in the calculators. The results will not be accurate, but they will still give you a general ball-park idea of how you are doing. You don't need to go crazy here, optimizing down the last micron: just get close to a good ratio, within a inch or two, and you'll be fine. But do make sure you use a calculator that takes into account ALL of the room modes, not just the axial ones!



- Stuart -

Stuart

Thank you for taking the time to provide such a detailed response. Your explanation of the various factors contributing to live and dead loads was very informative. I now understand why I should use 2x8s instead of 2x6s. I really appreciate that kind of guidance.

I will look for a better room mode calculator as you suggested. One that include calculations for axial, tangential and oblique modes. If I understood you correctly, I should take the average room height and not just one or the other. I have two room heights (8' 8" and 8' 1"). As far as walls go, I have been ignoring the splayed areas and treating it as a rectangular room when calculating room modes. So I think I am OK there.

Time to start tweaking and finalizing the control room layout.

Thank you Stuart

Joe

I will look for a better room mode calculator as you suggested.

Try the one at Bob Golds' place:

http://www.bobgolds.com/Mode/RoomModes.htm

That one analyzes things every which way, and gives you a stack of useful info. Maybe more than you need! But it's very good.

If I understood you correctly, I should take the average room height and not just one or the other.

Exactly. Same for the room length: it isn't constant, since the soffits are angled. So just average that.

CAVEAT! Doing this means that the results are NOT accurate! As soon as you angle one wall in a room, then ratios are no longer 100% meaningful. True ratios only apply to perfect rectangles, and so does the math used in these calculators

However, if the angles are not too great, then averaging the dimensions can still give you a rough idea of how things will be, which is all you need anyway. Once the place is built, then you will need to measure the actual response, and design the treatment based on that. You have to do that anyway, even in a perfect rectangle, since reality in acoustics never works out exactly as predicted. So the treatment will be based, in part, on the predictions, but also in the other part on actual measurements of real room response.

As far as walls go, I have been ignoring the splayed areas and treating it as a rectangular room when calculating room modes.

That's fine, as long as there are no solid, sealed surfaces on the walls at angles. Slot walls and absorption don't count, but panel resonators do, for example, and so do some types of diffuser... I don't see those in your design, though, so probably you are fine wit the side walls. So it's just the front-back and up-down that you need to average.


- Stuart -

"I used the following parameters as input to the Joist Span Calculator
4.62 lb per sq ft (weight of two layers of 5/8 drywall)
Hem-fir (Typical wood sold at Lowes in the US, Northeast)
Number 2 grade
10lb per sq ft Live Load (There really is no live load, but the calculator would not let me specify "0")
5 lb per sq ft dead load (Actual dead load is really 4.62 lb. Five was the lowest value on the calculator)
16in On Center (My joist spacing)"

Hem-fir is either Hemlock OR Fir and that would be the only reason you could theoretically span as far as the table you are using suggests, and even that should be used with caution.

If this is part of the interior framing of a double wall assembly then certainly there is no live load imposed. But as Stuart has pointed out, the dead load is the combined weight of everything involved in that particular build. As it would stand with a double wall assembly, the dead load is what ever the weight is of everything that weighs directly on the interior side of the assembly.

So while a live load would never be imposed on this interior side of the assembly the deadload could be smaller since the loading material in question is of a smaller amount.

The deadload is an overall number used to understand the entire structures ability to support the weight the live load and the potential seismic events plus the seasonal events will impose on the structure.

It does not apply as neatly to a double wall assembly when you consider the interior side of the assembly.

Well, I went back to the drawing board on the control room and determined the maximum dimensions for that space. The control can be up to 13’5’ x 17’ x 8’ 5” (finished). Since those dimensions do not correlate with one of the recommended ratios, it is necessary to calculate a good ratio that will fit in that space.

Going mostly by the graph output and the recommended ratios of Bob Golds room mode calculator, I came to 16’ x 12’ 6”. I’ve posted a picture of the graph reflecting those values. The ratio is “1 : 1.48 : 1.9”. The closest recommended ration is “1 : 1.4 : 1.9”. Interestingly, the recommended ratio did not yield as smooth a graph as the “1 : 1.48 : 1.9”.

I have added a diagram that shows my current construction approach as it relates to drywall and placement of sound treatment. The room will be completely dry-walled before the soffits and the splayed walls are built. Five feet of the front of the room is a flat surface with a window looking on to the adjacent Iso room. The right wall of the control room contains a large window as well (visible in earlier pictures posted).

It was mentioned that I should “average” the room length to account for the soffits. This brings me to a few questions:

1) If I average the length of the room to account for the soffits, doesn’t that mean I will have to make the room longer to maintain the ratio?

2) Lastly. I am not sure how to “average” the soffits. It was easy for the ceiling heights. There are only two. The soffits seem a little more challenging, as they are reflecting to different areas of the control room. Is there a good post that explains how this is done?

I’ve started searching but have not found clear instructions as of yet. I will keep looking.

Thank you all for your guidance thus far.

Joe

PICKING A ROOM DIMINSION:
The vast majority of folks attempting to develop a well isolated acoustically correct room will stumble on a few phrases that often make the process of moving forward difficult.

One of these phrases will be “room ratios”. Why even consider the dimensions of a room and how it relates to sound? Since it does relate to sound, the idea is that these ratios are very important when in fact, as important as they are, it is simply a small aspect of the build.

The rooms size and shape will determine the modes (wave length and frequency associated with your rooms dimensions). Small rooms are known to have issues with low frequency since a small room will accumulate longer low frequency waves that will overlap if they cannot locate an exit from the room. This always presents a challenge to overcome without some understanding of what you are up against.

In some cases, as in using an existing room in your residence, it may not be possible to move any of the existing walls! So you move forward, knowing that you will have to face this issue down the road, the issue being the existing modes the room might present.




The Golden Ratio:

The golden ratio is an irrational mathematical constant, approximately 1.618.
The golden ratio has fascinated Western intellectuals of diverse interests for at least 2,400 years. According to Mario Livio:
Some of the greatest mathematical minds of all ages, from Pythagoras and Euclid in ancient Greece, through the medieval Italian mathematician Leonardo of Pisa and the Renaissance astronomer Johannes Kepler, to present-day scientific figures such as Oxford physicist Roger Penrose, have spent endless hours over this simple ratio and its properties. But the fascination with the Golden Ratio is not confined just to mathematicians. Biologists, artists, musicians, historians, architects, psychologists, and even mystics have pondered and debated the basis of its ubiquity and appeal. In fact, it is probably fair to say that the Golden Ratio has inspired thinkers of all disciplines like no other number in the history of mathematics
Reference: Golden ratio - Wikipedia, the free encyclopedia

Room dimensions typically start from the ceiling hard boundary. If we use the golden ratio then this will produce a room with dimensions based on the ceiling height, then to the width of the room and next the depth of the room.

With an eight foot tall ceiling, based on the Golden ratio we would use 1: 1.62: 2.62, this would be a room with a ceiling height of 8 foot with a width of 13 feet and a depth of 21 feet! WOW! That is a lot of room which is certainly good for the music to expand but you may not have this kind of floor space or money to build something so large.

Imagine if you were lucky enough to have a ten foot ceiling, the room would be so large as to become too expensive to build.


Optimized Room Ratios:

Room ratios have been around for decades and rooms in general have been designed to be pleasing visually and sonically by many builders/ architects. You only have to look around the building you are in right now to recognize this is not something new, it has been around you all your life you just were not aware of this.

The inclusion of room ratios for an acoustical environment is different in that the ratios used have been tested so that the builder has a better starting place than a typical room ratio that a typical builder might use.

Alton Everest ( Master handbook of Acoustics - 4th Edition) presents 3 of the most widely used ratios developed by L.W. Sepmeyer (1965) and M.M. Louden (1971)



Height Width Length
_______________________________ _________
Sepmeyer A. 1.00 1.14 1.39
B. 1.00 1.28 1.54
C. 1.00 1.60 2.33

Louden A 1.00 1.4 1.9
B 1.00 1.3 1.9
C 1.00 1.5 2.5

It must be noted that when these ratios were being tested a ten foot tall ceiling height was assumed. In some detail, we will find out why this was an important aspect to this particular testing procedure.

Based on Loudens first ratio “A”, 1.00, 1.4, 1.9 with a ten foot tall ceiling this would produce a room with the interior finished ceiling height of 10 feet with a interior finished width of 14 feet and a depth of 19 feet. This room will have a volume of 2,660 cubic feet. Plenty of height for the sound to expand and develop and exceeds the 1500 cubic feet room volume limit determined to be the least amount of volume a quality audio environment should have.

(C.L.S. Gilford, Affiliation: British Broadcasting Corporation,“The Acoustic Design of Talks Studios and Listening Rooms” circa 1979, maintained that a “small” room based on the research done would be a room with a volume of 1500 cubic feet. Further he states “It is shown that a distinctive characteristic is that, because their dimensions are comparable with the wavelength of low-frequency sound, the sound field is characterized by strong simple standing-wave patterns which cannot be eliminated without eliminating the reverberation itself. It is shown also that for the audible effects are confined to those associated with simple axial modes and that, by careful adjustment of dimensions, provision of diffusion and the proper distribution of absorbing material, the worst faults can be avoided. “)

An interesting thing happens when we look deeper into these ratios, when we look at the single components of the room and not the end result.

The speed of sound at sea-level is considered to be 1,130 feet per second and in order to get the fundamental frequency of the height or width or length we have to use the equation F=1,130/2xD.

The height of ten feet using the above equation will produce: 1,130/20=56.5Hz. This is important to know since 56.5 Hz relates to the note A1. It actually falls 1.5Hz past the frequency of 55Hz.

The width of 14 feet using the equation F=1,130/2xD (1,130/2x14(28)) = 40.36Hz which closely correlates to 41.20Hz or E1 on a midi keyboard.

The remaining length measurement 19 feet X 2 = 38 produces 1,130/38=29.74Hz, relates closely to 29.14 (A#0/Bb0)

Using the 8 foot ceiling height and Loudens first ratio produces a room 8 feet tall, 11 feet and a few inches wide and 15 feet and a few inches deep. That is about the size of a typical bedroom or the living room in some homes.

The consideration for having a balanced proportional room is valid and worth the effort to use in any sound related type room. A few things to consider along the way. The measurements that are obtained from the ratios define the interior side of the wall.

In order to use these measurements, you must determine how much and of what thickness your interior sheathing will be. This allows you to step out the placement of the sheetrock or MDF/OSB or whatever combination you may use, in order to establish were the actual framing will be placed on the floor of your build.

[needs graph on this stepping out procedure]

To that end, ratios are not scalable...they cannot be modified and expect the same results: Room Sizing Tutorial | Acoustics, Audio and Video | University of Salford

Brien

Thank you for your input. While your response was informative, it did leave me a little confused. The message seemed somewhat contradictory to previous advice given.

I believe your response was directed towards my comment of not being able to use the entire open space available for my control room. This was because none of the room ratios fit exactly in that space.

I’m hoping I got your general message. If I may summarize: it seems to me you are saying that proper ratios are a good thing, but not absolutely necessary, and issues of room modes can be addressed through other methodologies. In addition, room ratios that were determined with 10ft ceilings are not necessarily transferable to my 8ft plus ceilings.

If that is the case, my desire would be to build the room to fit the space. However, I do not want to sacrifice accuracy of the room. I must admit things seem a little fuzzy for me right now, especially after reading a post from John Sayers stating “once you splay the walls and add angular structures like the soffit mount all the modal stuff goes out the window IMHO”

Brien, please let me know if you think I’m way of base and totally misunderstood your comments. Otherwise, I think I will try to maximize the use of my space. Thank you.

Joe

Hi,

you can also use this room mode calculator. http://amroc.andymel.eu/
There you can change the size of your dimensions with the mouse and see how the mode distribution changes immediately. I used as much space as possible for width and length for my room, and adjusted the height with this applet.

Maybe it helps
Andy

" The message seemed somewhat contradictory to previous advice given."

Not contradictory at all. In respect to rectangular rooms it fits perfectly. When you choose to get outside of that and use canted walls (angled) then it has no effect in respect to testing or treating.

A rectangular room has two pair of parallel walls, has a known distance that can be correlated with frequency, etc. When you splay the walls you cannot do this testing with math and you have to test the site physically due to the change in geometry.

Averaging is a near miss in my experience with these types of set ups.

"I’m hoping I got your general message. If I may summarize: it seems to me you are saying that proper ratios are a good thing, but not absolutely necessary, and issues of room modes can be addressed through other methodologies. In addition, room ratios that were determined with 10ft ceilings are not necessarily transferable to my 8ft plus ceilings."

Exactly. But that we did not build a square room is a great start

Do not get lost in the room ratio thing, it only hurts your head and there is no pain reliever for that.

I believe your response was directed towards my comment of not being able to use the entire open space available for my control room. This was because none of the room ratios fit exactly in that space.

I think that's part of the point that Brien was making: You don't need to nail one of the good ratios down to the nearest 1/64". As long as you are in the ball park of a good ratio, and well away from bad ratios, that's all you really need. Ratios are not the only issue that you need to consider, and if you can get a bit more space into your room by sacrificing a bit on the ratios, then that is worth considering. Ratios are only a major issue when you are close to one of the bad ones.

If I may summarize: it seems to me you are saying that proper ratios are a good thing, but not absolutely necessary,

I agree. It is worth looking at your ratio to see where you are and if you can improve, but otherwise not a big deal.

and issues of room modes can be addressed through other methodologies.

The room will need to be treated in any case, regardless of what your ratio is. Choosing a good ratio does not make the modes go away: they are still there, still just as strong. The only difference is whether they are spread around a bit more evenly, or not so evenly. You STILL have to treat them, regardless, in ANY room, no matter what the ratio is. So it doesn't make much sense to waste a lot of time on ultra-tweaking your room dimensions to get a "perfect" ratio.

In addition, room ratios that were determined with 10ft ceilings are not necessarily transferable to my 8ft plus ceilings.

They do scale up and down, yes, but the frequencies change, falling at different points on the musical scale. So what sounded good in a 10' room will not sound the same in an 8' room. Even though the modes are still in the same relationship, they are now at different notes on the scale. If you subscribe to Wes Lachot's line of reasoning, then that can mean your room is no longer tuned nicely to a chord, but maybe offset to being sharp or flat. Personally, I'm not convinced that this is something the average home studio builder needs to worry about much, and in most cases he can't anyway, since the room sizes are pretty much dictated by the way the house is built, so I wouldn't go out and jump in front of traffic if I can't tune my room perfectly to a certain major key because my ceiling is only 9' 11-7/8", not 10'. If you catch my drift! Since most house ceilings are only 8', most home studio builders don't have a lot of choice in the matter! You are really lucky to have 9' basement ceilings! Some folks only get 7'-6", and that is REALLY hard to deal with. Yet they still build reasonably good studios.

I must admit things seem a little fuzzy for me right now, especially after reading a post from John Sayers stating “once you splay the walls and add angular structures like the soffit mount all the modal stuff goes out the window IMHO”

Exactly! What both John and Brien are saying there, is the same thing: As soon as you splay one of the walls, the entire room mode relationship falls apart. You still have modes, of course! And big ones. Splaying your walls does NOT make them go away, and John didn't say that. What he DID say, is that when you splay the walls, you can no longer CALCULATE the modes accurately with simple mathematical equations. You now need to resort to very complex methods, computationally intensive, to figure out the modal response of the room. It can be done, but you need FEM/FEA software, and a good operator who knows how to set up the boundary conditions correctly for acoustics, and how to run and interpret the analysis. Not something most home studio builders are able to do, or even need to do.

The room mode calculators you see all over the place, such as the ones you have been using, are for rooms with parallel walls, which make it dead simple to predict how waves will bounce around: the axial modes just go straight back and forth, directly between the walls. But if you angle one wall, then that no longer happens: those axial modes associated with that wall go away, but the tangential and oblique modes are still there, and at only slightly different frequencies than they were for parallel walls.

With splayed walls, a room mode calculator no longer gives you accurate readings. For example, if you splay your side walls, so that they are now ten feet apart at the front and twelve feet apart at the rear, which number do you put into the calculator? 10 or 12?

But you CAN average the dimensions, and still get a rough ball-park analysis, if you know how to read it, and what to ignore / not ignore. For example, once again if you splay your side walls then the axial mode numbers between side walls is no longer valid at all, but the vertical axial modes still are, and so are the front-back axial modes, since those walls are still parallel. All of the tangential modes that only involve the front, back, ceiling and floor are also still valid, and the others won't be far off. And all of the oblique modes won't be accurate either, but they too will be reasonably close. So averaging is still useful, if you take that into account when you look at the results, but not accurate.

And all rooms need to be analyzed with actual acoustic tests in any case, as soon as the structure is complete but before they are treated, to understand not just the modal behavior but also everything else. So if you are going to run the analysis to find out how to treat it, then going crazy about modes and ratios isn't necessary, since you'll have to treat ANYWAY, regardless of what ratio you chose.

That's what both John and Brien were saying: With splayed walls, ordinary calculators are "out the window", since they no longer tell the truth. Especially ones that only tell you about axial modes! Those are questionable to start with, but pretty much useless for splayed walls. If surfaces are splayed in all three dimensions, an axial-only calculator gives you no valid information at all, since there are no axials in such a room.

- Stuart -

If we had a "like" option I would "like" this post Stuart.

Awesome clarity...simple awesome!

Hell...I might make it a sticky...I can do that right?

Thanks for the "virtual like", Brien, and for the kind words! You make me blush!

Hell...I might make it a sticky...I can do that right?

I'm not sure if moderators can do that... I guess we can, but I've never really gone looking for how to do it! Must be a button somewhere...

- Stuart -

Brien and Stuart

Thank you so much for the awesome clarifications! I feel the fog is lifting. Time to put the Aspirin bottle down and move forward. Sure is nice to have you gentlemen around.

Joe