John Sayers' Recording Studio Design Forum Archive

Hello professionals and fellow amateurs!

Starting the process of converting my living room into a control room.

I’ve done a lot of pre-reading, and I’m still working through two books (Master Handbook of Acoustics and Acoustic Absorbers and Diffusers by Cox), but I now know enough to realize that I’ve only scratched the surface! Would love help sanity checking my work and proposed plan to treat this room. Very much open to any and all suggestions.

Dimensions: Room is far from perfect but it’s what I got. Photo with dimensions (apologies for scale!)

[edit: see updated diagram in later post]

As you can see dimensions are non-rectangular, so calculators are unfortunately not helpful here.

Measurements were taken with room completely bare, save the speakers, mic stand, and cables / power brick. The rolloff at 10k is to be expected when using mic vertically (per the calibration file that came with the mic from Cross Spectrum).

[edit: see updated measurements in later post]

Materials: wood floors, drywall walls/ceiling. Wooden slats over the glass windows covering a substantial chunk of the left wall, plus a small built in AC unit beneath the windows and a large metal heating vent on the right. The floor in the kitchen area is tile.

Loudness: Isolation is practically non existent. I can hear pretty much anything that happens outside, the floor vibrates when my neighbor walks up to the steps to the adjoining apartment or inside their apartment with heavy shoes on, etc. Given that anything beyond putting up full length floor standing treatments isn’t feasible (2nd floor rental), I’m prepared to abandon isolation efforts and restrict loud use of the room to times when it’s quiet outside / my neighbor isn’t around.

Goals: My primary output is song demos, which are ultimately re-recorded, so 100% mastering accuracy is not necessary, nor possible given the room and logistical constraints. I would like to get the room sounding as accurate as possible to cut down on the amount of time I spend cross-checking across different reference sources before I send a mix out.

A secondary goal is to create a nice environment for tracking a drum set, but I’m prioritizing the control aspect and will handle the live part only if it appears feasible down the line. In the event that it is not, I have a second room I can use (unfortunately small, cuboid, and also my bedroom, which is why it isn’t my first choice).

Budget: Willing to spend 2-3k, but hoping to be under that if I can help it. Generally good with my hands and planning on DIYing as much as I can to stretch the budget.

Questions:

(1) Does anyone see anything glaring from the REW data that suggests I should abandon all hope of treating the room and continue my trial and error multiple-source mixing techniques? The frequency response actually looks better than I was expecting, but I am entirely open to the possibility that I don’t know what I’m looking at.

(2) I decided to pretend there was a full length wall between the kitchen and living room and use general rectangular principles to guide my experimentation. After multiple measurements in that general area (+/-12 inches) I found this classic 67.5" sided equilateral triangle with the speakers equidistant from the side walls and aimed at 30 degrees 12 inches behind the mic produced the least/lowest peaks on the REW freq response graph.

I understand FR doesn’t tell us everything, and I don’t have access to calculated modes to check against, so are there other positions I should be considering and graphs I should learn how to interpret to suggest other listening positions I should evaluate?

(2b) Should I be considering creating some sort of "false wall" to separate off the kitchen from the living room? (On wheels so I could roll it out of the way when not in use). I was thinking the extra length would help with the low end, but is having a rectangular room more desirable?

(3) Is there potential to differentiate between modes and things like SBIR by comparing graphs taken with different speaker positions and listening positions? I imagine some manipulation and comparison of measurements will tell me this, but I don’t have enough of a grip on the material to know how or what yet. My asking this is because I’m motivated by a desire to completely understand the room’s every nook and cranny and how it reflects in the measurement in order to design treatment. Is this level of specificity overkill/impossible?

(4) If at all possible I’d like to avoid / cut down on exposed fiberglass/substitute use in my treatments (someone with sensitive lungs spends a lot of time in the room and I’ve seen them cough in its presence before). I understand this is going to make treating the low end harder, and creating or buying sealed/ tuned traps is going to be difficult and/or expensive, but I’m up to it if folks think it’s possible. Or is my situation too out of control to be dealt with with anything other than a lot of mass absorption?

(5) Am I giving up too easily on the prospect of insulating from outside noise? Can I get the room fairly quiet without building a room within a room? Less concerned with cutting down vibrations, but for example I’m pretty sure the mic was picking up the crickets singing outside while I was measuring this evening…

(6) My next steps were going to be to continue to read, learn how to interpret the various REW graphs, and develop a robust understanding of what is happening in the empty room, using the books mentioned above. Will I find what I’m looking for or are there other sources I should be looking into?

Thanks much for all your time. Looking forward to your comments and to updating with my progress!

Hi there "spinstonchurchill", and Welcome!

Would love help sanity checking

Well, you are planning to build your own studio, so that certainly makes you insane like the rest of us who build studios, so "check" for that!

Photo with dimensions

I'm not sure I understand that at all!!! I can't figure out where the walls, doors and windows are. The only solid line on there is between your are and the kitchen, which I presume is a wall, but later you asked if you should build a wall there, so I guess it is NOT a wall!

Please do a more complete, clearer diagram. Preferably in SketchUp.

As you can see dimensions are non-rectangular,

That's the trouble: I can't see that,since I can't even figure out where the room is! Is it the dashed lines? The solid lines? Some other lines?

The rolloff at 10k is to be expected when using mic vertically

Yes, but your roll-off starts at about 5 kHz, and does not follow the normal logarithmic rolloff that one would expect. Something else is happening there: Is the floor carpeted? Drapes/curtains? What speakers did you use? What mic (brand, model)?

A secondary goal is to create a nice environment for tracking a drum set,

You said that you can't really isolate the room at all, and that it's a rented apartment, so I'd say that recording drums is out of the question. Your neighbors would probably object, strenuously...

so are there other positions I should be considering and graphs I should learn how to interpret to suggest other listening positions I should evaluate?

Your listening position and speaker geometry is not correct. They way you have it now will not work. You have no symmetry, your speakers are far away from the front wall, your head is close to the rear wall, and a few other things too.

It seems like the only place where you can get symmetry (which is absolutely critical for a control room), is by rotating your setup 90° and pushing it up to the top olf your diagram, so that your speakers are tight up against the "window with wood slat covers". I'm assuming that the solid line to the left of that are and the dashed line to the right really are walls: If not, then that won't work either.

I can't tell you more than that, since I don't know how long that wall is, since it is not marked on the diagram. Hopefully with your next diagram, and some actual photos of the room, it will be more clear and I can give you more complete instructions on how to proceed.

(1) Does anyone see anything glaring from the REW data that suggests I should abandon all hope of treating the room

It's going to need a ton of bass trapping! But that's normal for a small room. Some of the modes are crystal clear: 40 Hz, 74Hz, 85 Hz, 93 Hz, 113 Hz, 141 Hz, 162 Hz, etc. The overall decay time is well over one second (around 1150 - 1200 ms), and you have decay issues all the way up the spectrum to about 5 kHz. So it will need lots of treatment to make it neutral.

The frequency response actually looks better than I was expecting, but I am entirely open to the possibility that I don’t know what I’m looking at.

Not so good. Here's the low-end response, with the range from 40 Hz to 200 Hz highlighted:
As you can see, there's swings of more than 34 dB, meaning +/- 17 dB. International specs for critical listening rooms call for no more than +/- 3 dB. In the real world, mediocre to good studios get +/- 5 dBb, and for a home studio +/-9 dB would be good. But 17 dB: not so much...

Even if we take a more lenient part of the spectrum, from 80 Hz to 8 kHz, it's till not so good:
That's +/-12 dB. Still not very good.

Should I be considering creating some sort of "false wall" to separate off the kitchen from the living room?

If it is "false" then it isn't a "wall" Not much use. So if that solid line on your diagram is not a wall, then what is it?

I was thinking the extra length would help with the low end,

Unless the wall is complete, reaching ceiling to floor and side to side, sealed, and massive, then low end sound would pretty much ignore it, since it would be very small compared to the wavelengths: It would have some useful effect on modes, yes, but it won't be the solution you are looking for.

(3) Is there potential to differentiate between modes and things like SBIR by comparing graphs taken with different speaker positions and listening positions?

Yes, but you only need to move the mic, not the speakers. Once the speaker are in the correct position for that room, then start with the mic in the correct listening position,l and do a series of tests in REW as you move the mic straight back tot he rear wall in increments of 6": Compare the graphs and the difference is obvious. Modes do not change frequency at different points in the room: only the amplitude changes. Since SBIR is directly related to the location of the mic, you will see it happening at different frequencies for each location. Also, modes ring, SBIR does not. SBIR is a purely frequency domain issue, not time domain. Modes are both frequency and time: they decay slowly.

Is this level of specificity overkill/impossible?

Not at all! I do that all the time when I'm tuning a room. Sometimes it's hard to figure out what you are seeing on the graphs, but the worst modal problems and the worst SBIR issues are usually crystal clear, as are early reflections and a couple of other things.

(4) If at all possible I’d like to avoid / cut down on exposed fiberglass/substitute use in my treatments

Possible, to a certain extent.

I understand this is going to make treating the low end harder,

Not really. It will make treating the HIGH end difficult. The usual way of doing what you want is to put plastic across the front of the insulation. Low frequencies (very long wavelengths) don't even "see" the plastic: for them, it simply is not there. But high frequencies (short wavelengths) do "see" it, and they bounce off. If you need to absorb some mids and highs, that will be hard to do if all of your insulation has to be sealed. That rules out slot walls and all other Helmholtz resonators...

Can I get the room fairly quiet without building a room within a room?

Not really, especially on a limited budget. Isolation requires mass and hermetic seals, both of which cost money.

Will I find what I’m looking for or are there other sources I should be looking into?

The best source I know of is this forum. Look through several threads on completed rooms, to see how people went about it, and what mistakes they made, so you can avoid making the same mistakes.


- Stuart -

Soundman2020 wrote:Hi there "spinstonchurchill", and Welcome!

Hopefully with your next diagram, and some actual photos of the room, it will be more clear and I can give you more complete instructions on how to proceed.

[edit: see updated measurement files in later post]

[edit: see updated measurements in later post]

And finally, some photos of the actual room.

1895 is taken in the NE corner of the room. 1896 in the SE. 1897 in the SW (from the kitchen, facing E wall).

Opened some slats for light but I have been testing with them closed for uniformity.

Okay -- finished the Master Handbook of Acoustics and Absorbers and Diffusers and was able to answer many of my questions and realize I made a few (more) measurement errors. Have now remeasured.

Sketchup File

Updated Measurements
To the extent the data looks strange, 2 potential factors: the first is the measurement microphone (spec sheet from CS labs attached to this post). The second is that white object you see in the file -- it's a heating duct with some kind of metal panel inside that resonates like crazy from low frequency vibrations. I'm going to have to figure out how to stop it from moving as best as I can.

As far as the measurements go, am I right in thinking listening position 4 (which corresponds to the speaker/LP orientation denoted by the orange triangle on this photo) looks to be the more promising listening position? The first 3 were from the green triangle wall (window) side.
Also, in the interest of working around my fiberglass limitation so I can broaden the effectiveness of panel/slat absorbers, I've started to search for fibre-less wool-type alternatives with similar absorbent properties. I have come across two potential products. Would be interested to hear peoples' thoughts on these (or others that may be out there!)

(1) Liaver's Reapor, which looks similar in spec to OC 703/705: http://www.liaver.com/fileadmin/user_up ... r_2014.pdf

Have an email out to them to see if they have any US vendors. Shipping is likely going to be prohibitive if there isn't already a network in place, and I don't think there is, but thought I'd try.

(2) Thermacork, which is less appealing (not entirely sure about cell structure or quality of density/gfr measurements, going to be slightly harder to calculate when designing) http://www.amorimisolamentos.com/xms/fi ... 20EIFS.pdf

They rate this around 60kpa and Cox book has an example of a 70kpa absorbent working inside a Hemholtz device, though, so I suppose it's worth a shot if I can't source the Reapor...

(1) Liaver's Reapor, which looks similar in spec to OC 703/705:

Actually, it is not similar at all: if has zero low frequency absorption, which is where OC-703 is excellent. It also shows the absorption characteristics on a graph with a linear scale, not logarithmic... indicating that whoever did the graph has practically no idea at all about acoustics. The graphs shows no data above 3kHz, and the vertical scale on the graph is so highly compressed as to make in unreadable, and pretty useless.

If you are interested in using that stuff, first ask the manufacturer for the full report from the independent test laboratory where the testing was conducted. If they cant (or wont) give you that report, then walk away...

Comparing that stuff with 703, at 125 Hz absorption seems to be about 0.2 versus 0.84 for OC703, which is about 400% higher. At 250 Hz the "stuff" has absorption of around 0.5 versus 1.24 for OC703, and at 500 Hz it shows about 1 versus 1.24 for OC 703. Those are huge, major, enormous differences. That stuff would be terrible for low frequency absorption, probably due to the very, very high density: it is listed at 270 mg/m3, which is about ten times higher than the density of fiberglass that is typically used in acoustics. The only place that stuff would be useful is for an absorber that is designed to ONLY treat mids and highs while NOT absorbing any lows.

(2) Thermacork, which is less appealing from a #s perspective

I didn't see any acoustic data on that web site. All it says is "Excellent soundproofing", which is not very useful at all (especially considering that it uses a term that most acousticians try to avoid...), and "Density: 110 to 120 kg/m3" which is also way too high for good low frequency absorption. It also mentions the term "Perpendicular Face Resistance: declared TR50" which seems to be something that they invented themselves, sin googling that term only leads back that specific manufacturer and its products, so who knows what that means. The units are not related to acoustics in any case, so that is not any use.

(~60kpa gfr)

GFR is not measured in kpa. That's a measurement of pressure. GFR is measured in rayls. In MKS units, 1 rayl is 1 Pa·s·m^−1 (or also 1 N·s·m^−3). Or if you prefer in SI units, kg∙s^−1∙m^−2 (in other words, kg/(s * m^2) ). It is a measure of acoustic impedance, not pressure.

it's probably better than nothing...

I'm not so sure about that!

I'm also wondering if you are chasing after a non-existent problem:

http://www.gearslutz.com/board/bass-tra ... eview.html

I've started to search for fibre-less wool-type alternatives with similar absorbent properties.

If you really, really, really are determined to not use properly manufactured fiberglass panels, then probably your only real alternative us to use more expensive commercially manufactured acoustic foam panels. That will increase the cost, of course, but it you are convinced that natural neutral fiberglass (which is basically just sand) is a health hazard, then your only option is to pay more for a synthetic alternative, made through a chemical process.

- Stuart -

Soundman2020 wrote:specs

Well there goes that! Cox and D'Antonio made it sound like it would be a reasonable substitute. Perhaps they based this assessment more on theoretical properties of the material vs. actual testing. (Like you say, I'm not sure I really trust the testing done so I paid less attention to that.)

I'm also wondering if you are chasing after a non-existent problem:

Trust me, I wish the problem was non existent! Would make my life a lot easier. Unfortunately my SO literally starts hacking within minutes of exposure to FG dust. Whether it's a psychosomatic response or she has the world's most sensitive lungs is unclear, but... unhappy girlfriend definitely is a health hazard. So the goal was to find a material that doesn't require handing her a gas mask every time she's around.

If you really, really, really are determined to not use properly manufactured fiberglass panels, then probably your only real alternative us to use more expensive commercially manufactured acoustic foam panels. That will increase the cost, of course, but it you are convinced that natural neutral fiberglass (which is basically just sand) is a health hazard, then your only option is to pay more for a synthetic alternative, made through a chemical process.

May have to go this route.

Unfortunately my SO literally starts hacking within minutes of exposure to FG dust.

Then don't use fiberglass! Use mineral wool instead. That works very well for acoustic treatment. Density needed is about 50 kg/m3 for the correct GFR (higher than for fiberglass, which is about 30 kg/m3.)

I'm also wondering if your girlfriend is allergic to the glass itself (unlikely), or if it is an allergy to one of the binders used in cheap or older fiberglass products, Modern fiberglass uses inert binders that are formaldehyde-free. Also, if you build your bass-traps correctly, there will be no fiberglass exposed to the room at all: it would all be covered with plastic. You could seal them fully air-tight if you wanted.

- Stuart -

Soundman2020 wrote:

Unfortunately my SO literally starts hacking within minutes of exposure to FG dust.

Then don't use fiberglass! Use mineral wool instead. That works very well for acoustic treatment. Density needed is about 50 kg/m3 for the correct GFR (higher than for fiberglass, which is about 30 kg/m3.)

I'm also wondering if your girlfriend is allergic to the glass itself (unlikely), or if it is an allergy to one of the binders used in cheap or older fiberglass products, Modern fiberglass uses inert binders that are formaldehyde-free. Also, if you build your bass-traps correctly, there will be no fiberglass exposed to the room at all: it would all be covered with plastic. You could seal them fully air-tight if you wanted.

- Stuart -

We did a test of Roxul at the hardware store a while back and it had the same effect, which is what lead me ot suspect either fibres or some kind of mental component, but there were more than a few unscientific things about that test (not blind, did it after FG when she had already coughed, etc.) that means it may not be a dead end...

I had read about the plastic membrane sheathing here, but didn't want to gamble on it if there was an alternative. Looks like gambling may be the best approach, though.

As far as air-sealing, the designs that I have seen for absorbers have the porous absorbent exposed in some fashion (through slits or holes or fabric). If I can put plastic wrapped FG/Wool inside, and air seal that will not be a problem at all. I just didn't think I could address the low end problems with something air sealed (trying to grab the 40hz issue, for example, won't that require a design that has an exposed porous absorber?) Am I wrong (as usual) about this? I hope so!

Sorry for all these questions -- frustrates me that I don't yet understand the various functions of all these materials enough to answer them myself. Need another go through the materials.

I had read about the plastic membrane sheathing here, but didn't want to gamble on it if there was an alternative. Looks like gambling may be the best approach, though.

It's not gambling: it's using the principles of acoustics in your favor.

As far as air-sealing, the designs that I have seen for absorbers have the porous absorbent exposed in some fashion (through slits or holes or fabric).

You've probably been looking at slot walls, perf panels, and other forms of Helmholtz resonator. But those aren't bass taps anyway. Superchunks, corner traps, and similar bass traps are what I'm talking about.

I just didn't think I could address the low end problems with something air sealed (trying to grab the 40hz issue, for example, won't that require a design that has an exposed porous absorber?)

If you hold a piece of plastic over your ear, what do you hear? The high end will be muffled to a certain extent, depending on the thickness of the plastic. But you'll still hear the bass thumping through, with no attenuation at all. The thicker the plastic, the more muffled the highs will be, and the further down the scale it will be, into the mid range. But you'd need REALLY thick plastic to affect the lows much.

I don't know if you have ever used industrial ear plugs, the usually orange or yellow foam type that are required in many work places where noise levels are too high, but if you have, you'll notice that even with those things, which are basically just very thick plastic (many millimeters thick), you can still hear deep bass frequencies. No highs at all, almost no mids, some attenuation in the upper part of the low range, but very low frequencies are still audible, even with those foam plugs that are specially designed to stop sound.

Sound waves are affected in different ways by the same object, depending on frequency, mass, surface density, rigidity, etc. Plastic across the front of bass traps is often used to control the absorption of high frequencies precisely because it does not affect lows. Bass traps have to be huge in order to provide enough absorption to do their job on the lows, but that also means the are sucking out way too much of the mids and highs in small rooms. Putting plastic over the absorption reflects the highs back into the room, preventing them from being absorbed by the insulation, but allows the lows right through as though it wasn't even there, to be absorbed by the insulation.

Yes, sometimes it is necessary to cut holes or strips in the plastic, in order to provide some mid and high absorption, and you can "tune" the bass trap to a certain extent like that, but you don't need to do that if you don't want to. You could perfectly well have the plastic fully covering the bass trap, and it would still be effective in the lows. As long as you leave the plastic loose (don't stretch it taught!), it will work fine.


- Stuart -