# Control Room Project



## ejbragg (Dec 13, 2009)

*Summary of dimensions:*

I have built the studio controls into an octagon shaped room. Each wall is approximately 9 feet wide. The console is facing (and is close to) one wall. From the control position, on each (45 degree) wall on either side of the console is an entry - entry to the main hall is to my left, entry to the rear outdoor deck is to my right. On the left (perpendicular) wall is a large, tall bookshelf that practically takes up the entire wall. All other walls are bare, aside from a 4 ft x 4 ft window in the center of each wall.

The room depth is about 21 feet, front to rear, side to side, and across the diagonals. The ceiling follows the roof line, which is a 10/12 pitch. The ceiling over each wall starts at 10 ft. In the center, it is approximatly 18 ft at the (fairly sharp) peak. (A ceiling fan hangs down from the center at about 10 ft overhead.)

There is an audible room mode in the center of the room from this peak - you can hear it as you speak.

From the control position, facing the console, there is a baby grand on the right wall (opposite the book case), and a couch is along the rear wall. There are a couple more chairs in the center, plus some keyboards to my right.

As you may have guessed, this room is to couple as an acoustic tracking room, so control room acoustics cannot be perfect, but I believe the room is large enough to work around the problems in shape. Area is about 390 sq ft; volume is approx 5980 cu. ft. Both entrance doors are outdoor - type, heavy glass patio doors.


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## ejbragg (Dec 13, 2009)

Bryan, I'd first like to address the comment about the treatment of the wall between the console and the wall. My monitors will be centered about 22 inches from the wall (or whatever is on that wall behind them). One of my concerns is the standing waves caused by the monitor proximity to that wall, especially in the low end. Because I cannot now build cabinets into that wall for monitoring, I am looking for a way to flatten the low end reinforcement. Absorbtive material seems like the best answer, and it would seem to me that thicker is better. So why thinner here?


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## bpape (Sep 14, 2006)

It's not that thinner is better, it's that thinner is sufficient (and less costly) in that particular location which will free up budget for other treatments.

I'm going to be spotty in my posting for the next week or so. I'm on a long overdue vacation with my wife. Sitting on my balcony right now in Cabo San Lucas looking out over the Sea of Cortez (and a few lovely young ladies in their beachwear) 

I promised the wife I wouldn't be on more than an hour or so a day checking emails and the forums but I will get back to you.

Bryan


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## ejbragg (Dec 13, 2009)

I'm sorry you're chained to that drudging environment, man. :sn:

So, i gather that since I still have about 40 rolls of thick insulation and numerous 2X4s, then it won't actually _hurt_ to go with 4", eh?

I'm more intrigued about your concernes about the subwoofer location. From the little bit of info I've read, as most people think that low frequencies go around everything so much that it doesn't matter where the subwoofer is placed in the room. Supposedly, the argument is that it does matter quite a bit, and that centered between the studio monitors provides a better balance than having an offset.


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## bpape (Sep 14, 2006)

That's a very common misconception. While bass is non-directional (it radiates spherically in 3 dimensions) the location of the source of the sphere can make a HUGE difference in frequency response (corner placement usually being the worst place).

Sub placement and seating placement are 2 of the most critical things to get right in terms of smooth frequency response.

Bryan


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## ejbragg (Dec 13, 2009)

So what would be the ideal position in this case? Note that I have no room on the floor anywhere except under the console. To place it on the wall would be an awkward aethetic move, the way I laid the room out. However, I do have some ceiling space available (refer above for the description).


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## bpape (Sep 14, 2006)

Well, the octagon shaped room isn't all that great unfortunately. Now we have 4 pair of parallel surfaces instead of 2 pair - and they're all the same dimensions which means that the modes will build up all in the same frequency ranges. Under the console will cause all kinds of other issues from cavity resonances unless you can keep the console away from the wall a decent amount to stop it from acting to close off the cavity under the console.

The ceiling is an interesting idea but not sure you'd have much luck integrating to the mains very well. 

Overall, probably the easiest thing to do is to put the sub in your chair at the seating position and crawl along the floor to find the smoothest response and try to make that work the best you can. Hard to believe that with a room that size, the only place you can use is under the console.

Bryan


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## ejbragg (Dec 13, 2009)

I'm not sure I completely understand what you mean about the crawling along the floor part, but...

I agree with you on the setbacks for the room shape. The octagon shape has its limitations, being a cross between a square and a circle. Directly behind the console (on the opposite wall) is a trap door which leads down to the drum room. The couch sets over the door during mixing sessions, and is moved forward for access during tracking sessions. So the center line down the middle of the room is pretty much off limits due to traffic.

The baby grand is near the trap door, actually, along the side wall, but pushed toward the back. There is certainly room under this instrument, and in the space between it and the trap door (1 - 2 ft). My only concern is the lop-sided placement.


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## bpape (Sep 14, 2006)

Literally, get on your hands and knees and crawl on the floor and listen to the bass. All you're doing is swapping your ears for the sub (which is why it sits in your chair). When you find the place with the best bass, place the sub there (within your restrictions). Being off center is not at all a bad thing for sub positioning provided the xover point is 80Hz or lower.

Bryan


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## ejbragg (Dec 13, 2009)

I see. Interesting. So you're basing the position, in a sense, to the location from the listener. I like this approach. But what about the differences in the distance between the wall and the subwoofer? The listening position is about 5.5 ... maybe 6 feet from the wall. The subwoofer could be, depending upon the position chosen, anywhere between 1 - 4.5 feet. Won't this also have a bearing on the subwoofer's response? Or are you suggesting that the wavelength is so long that it won't make much of a difference?


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## bpape (Sep 14, 2006)

Actually, it's a distance from boundaries and a distance from the speakers. During that exercise, you're simply swapping speaker and listener to get a rough feel for how things are interacting. It's not a perfect way but in an odd room, it will get you close.

Bryan


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## fractile (Mar 15, 2009)

I've been thinking about this since I have a single sub in this room I'm working on. My room is dimensionally pretty much symmetrical, yet acoustically like a matrix transform, due to door placements.

From what I recall in theory 1/3 space is better than 1/2. Bryan was mentioning listening to where the sub sounds the best from. I recently rotated this room 90 degrees, but before, the node was right inside the front door; nowhere to put a bass bin. I don't know where it is now, since the change and added acoustic treats.

Anyway, I tend to be sensitive to low frequency directivity, but I was thinking to try aiming the sub across the middle from the side, to possibly achieve balance. I mean if the sub is left, point it 90 degrees right. I haven't got to that test yet, still have some amps to rack and speakers are next.

Ultimately I guess 2 subs might be best (or 4). I heard a surround test of 20 to 20kHz at AES. A sub goes down to about 8Hz. My Rhythmik is rated to 10. More than the Earth shaking I relate it with what I call harmonic completion, why we have electronics doing 100kHz and speakers 30; to get an octave extra outside.


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## ejbragg (Dec 13, 2009)

I have not actually picked up my subwoofer, and am still doing some research. Wondering what your input is, Bryan - or anyone else, for that matter - on the Tannoy models... I have not made a hard decision to purchase a Tannoy subwoofer, but want to seriously include their models, since my promaries are made by the same company. Here's what I have found, and am looking for suggestions for which might be the best choice for my particular set-up and needs. But I am also interested in any alternative suggestions...

My potential jobs include, in order of most predominant project types:
1. Stereo mixing - music (from heavy metal to orchestral).
2. Audio for video (stereo music, voice-overs, foley, and other sound FX)
3. 5.1 surround audio for video (rare for now)

Here's the Tannoy line-up:
First 3 models: variance and sensitivity are not listed on main page....
TS8: 200WRMS 8" driver - low freq: 32Hz, 2nd ordr low pass: 50 - 150 Hz @-6dB; volume = 0.45 ft^3
TS10: 300WRMS 10" driver - low freq: 29Hz, 2nd ordr low pass: 50 - 150 Hz @-6dB; volume = 0.60 ft^3
TS12: 500WRMS 12" driver - low freq: 26Hz, 2nd ordr low pass: 50 - 150 Hz @-6dB; volume = 0.78 ft^3
TS112iDP: 750W (pk?) 12" driver - freq range: 25 - 150 Hz +/- 3 dB; volume = 22 liter (theoretical claim)
TS212iDP: 1500W (pk?) 12" driver - freq range: 25 - 150 Hz +/- 3 dB; volume - 45 liter (theoretical claim)

More tech info available here. Note that I don't mix at high levels, and rarely do I even listen to the mix at high levels. I am very interested in extended bass, but I'm just not sure how low I need to go. My present monitors go out to 45 Hz fairly flatly before rolling off, so I'm already a little spoiled.


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## fractile (Mar 15, 2009)

Your mention of sound for video brings to mind that the LFE channel in theatrical releases is specified down to 8Hz, if I am correct. This was behind my decision to go with a Rhythmik sub, with a -3dB roll-off at 10Hz.
http://www.rythmikaudio.com/products1.html
They have several options, including a DIY version with plans, in case you want to build them into your own cabinetry. There is also the F12G model with a paper coned driver, made by GR Research: http://www.gr-research.com/
Hope this helps a little.


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## Darnstrat (Jan 9, 2010)

ejbragg said:


> *Summary of dimensions:*
> 
> I have built the studio controls into an octagon shaped room.
> 
> ...


I would seriously consider diffuser solutions combined with absorptive panels behind the speakers. Absorptive panels will suck the life out of the room and will only moderate the room mode. Diffuser panels will give the room a better distribution and likely solve your 'hot spot' problems. Of course, it all boils down to what sounds best for your application. But given you have a piano in the room, I'd go with a room with some life to it.

-your results may vary-


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## ejbragg (Dec 13, 2009)

Fractile -

That's an interesting bit of info. A 3 dB dip at 10Hz is rather incredible, especially if the remaining response is relatively flat. Just found the specs, as well. Looking good! A true subwoofer, even for the 12" model! Of course, the 15" specs look even better.

Darnstrat - 

I fully agree with you on the live feel. It goes well with the piano for many projects. I intend to build a cloud over the center of the room - the ceiling is plenty high enough to allow such a device without hindering my "breathing" space. Besides, I don't intend to seal it - sound will be free to travel up the sides. As for the diffusion - I intended in using diffusers around the windows, but hadn't considered using them directly behind the monitors. I'll have to digest that idea for a while. Thanks for the input.


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## bpape (Sep 14, 2006)

Absorbers behind the monitors will help with boundary interaction. I personally prefer diffusion on the ceiling (if high ones) at the reflection points, on the rear half of the side walls, and up high around the perimeter of the room to minimize slap echo. None of those locations are counter to any of the things you want to do in the room.

That said, getting the decay time correct across the band and addressing response anomalies is job 1 in my book. A nice lively room doesn't do much good if you have 2+ second ringing in the 40-80Hz range and +/-15db swings in response - especially since your primary goal is mixing.

Bryan


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## fractile (Mar 15, 2009)

I'm also working on a control/tracking room and I think the only way to have both a control space and a live room is to go with a modular/convertible approach, with removable/sliding acoustic panels, and possibly some of those tubular bass traps that can be moved around.

Any flat surface acts like a mirror, depending on its size and refractive/absorbtive properties, and where two or more flat surfaces join, it will magnify as well (if they're both angled inward/concave). I think the audibility of this will also depend on the output/listening level of the speakers, as a ratio of the output : attenuation of the surfaces. So, If you're listening at 40dB and the attenuation in the reflection is -6dB, the reflection will be more audible than when the output level is 80dB.

Anyway, I got a good view of this room the other day while listening at low/moderate level while lying on the floor with my eyes closed. The source of the sound got transposed toward two reflective surfaces on the side walls, and the one bare corner in the upper back wall became a sound source. I view those as only the most prominent places to deal with; after that I figure the next ones will show up.

A space can be used or appreciated in different ways. A person learns as they go, depending maybe on their technical requirement and experience. One of the more current so-called trends I heard about with control rooms is to have a more tightly controlled front-of-room with a more lively room toward the back, maybe to allow some real-life ambiance to the monitor.

Anyway, I think bpape gave a realistic approach to even out the frequency response in the room as a whole.


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## bpape (Sep 14, 2006)

That's an interesting way to 'look' for reflections and horn effects. Probably pretty effective actually once you take your eyes out of the equation and let your ears do the work.

The next step would be to wander around the room with bass heavy material playing and see where it's building up other than the standard corners, right against boundaries, etc.

Bryan


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## fractile (Mar 15, 2009)

I had a bass resonance in the sharp corner, when the speaker was pointed diagonally into it. I rotated the room so that the back of the room is 1/2 octagon and haven't noticed that node. Maybe I should turn it up more often and see how the modes excite. The low frequencies need some power to get them going and resonant.

ej said the resonance is in the middle of the room; that is at about the 1/2 wavelength of the 45Hz roll-off he said he has on the mains. It's a symmetrical room. I think that subs will change the equation and then some real testing can be done... In other words, I imagine that the mains are coupling into a void that would be filled by subwoofers.
0.02¢


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## ejbragg (Dec 13, 2009)

It's possible that the ceiling is creating a void toward the floor corners; however, from what I've heard, I'm kinda leaning toward the mode being directly in the middle of the room on the floor (on one end), and directly above (on the other end) where the ceiling comes to a point from all sides. It's a tight corner.

My thinking is this: build a cloud with low frequency absorbers on top, facing the ceiling where that nasty corner is. Because spectral analysis shows a build-up there of 31 Hz, I'll build some absorbers with that low freq in mind. On the underside, I have been considering installing 2-D diffusion, as you have suggested, Bryan.

You guys have given me some more info to digest, thanks.


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## fractile (Mar 15, 2009)

It's an interesting problem. A rough calculation in my head tells me there is about 30 feet from the peak to the center of the floor, with the peak as a projective sound source resonating/coupling with the floor at that wavelength.

In my imagination I suggest running a simulation of what a bass trap at 1/2 that wavelength will do, since you mention putting it in the middle, above the cloud.


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## ejbragg (Dec 13, 2009)

Hey, fractile,

The peak is actually at about 18ft in there. And the ceiling at the outer edges is 10 ft. The octagon is roughly 21 ft in diameter, when measured perpendicular between facing walls. I actually don't have a simulator (I do my computations manually). If you've got one (and some spare time), I'd be interested in seeing what yours comes up with.


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## fractile (Mar 15, 2009)

Ok; I looked at it again and got 18.5' as the half-wave length of 31Hz. I'd mistakenly been looking at the full wave-length, when it is the nodes of the wave that resonate in the space and these nodes are at each end and in the middle of the full wave. Getting my laws of physics straight.

I'm not set up for that simulation, either. Maybe someone around here is. This problem is something to help me comb out my technical proficiency. I was having a little difficulty comprehending why the loudest resonance is at the zero-crossing of the nodes, where the wave is at least amplitude. My best explanation is that this is where the soundwave in the air molecules couples with the boundaries of the room, like the bridge and nut of a guitar; without the guitar you'd barely hear the strings.

My room looks pretty symmetrical, but the doors are like a giant matrix, so I don't worry too much about symmetric placement of the sub; we'll see when I get to that stage of tuning.


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## ejbragg (Dec 13, 2009)

fractile said:


> I was having a little difficulty comprehending why the loudest resonance is at the zero-crossing of the nodes, where the wave is at least amplitude.


Not sure about that, either. Where's Bryan when you need him?

I do remember... this applies to a bass trap - maybe it can be translated into room acoustics ... that at the back end of a quarter wave bass trap, the air velocity is zero - because the air is trapped and has nowhere to go. At the opening of the trap, the air is free to move, and at the target frequency, the velocity is the highest (pressure is the lowest).

In any room, if you're playing a stereo, you'll hear the bass getting louder toward the corners, where they seem to be gathering. My guess is that the hard walls offer resistance to the wave fronts, resisting the air movement, creating high pressure at these frequencies. .... The same principle as the bass trap physics, except there is no effort in open air to "trap" the energy.


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## fractile (Mar 15, 2009)

Well (that's a deep subject ;-) the way it works, i think, as i mensioned, is that the wave couples with the room, like two ends of a string. The dimension of the room couples first at the lowest frequency harmonic with the output of the lowest frequency response of the speaker, if that is in the dimension of the room at 1/2 wavelength, at the nodes . Other harmonics will be less audible by 6dB or whatever.

The low frequencies have the easiest ability to resonate a space, say, because it is fundamental.

On velocity of the wave, if you look at a sine wave, the velocity is maximum increase/decrease around zero; the rate of change. The amplitude is low, yes, but the dynamic transient is greatest.

It helps me to think in physical terms, say, like the air is a 3D string vibrating, and the room has walls that tie the ends of the string and serve as a sounding board to resonate and amplify the sound. This will be at the fundamental resonant dimension frequency of the room and will drop off at 6dB per octave or something. You will hear other echos and reverb at higher frequencies, but these will not resonate as much as that fundamental. That's about what I've gathered from my reading and listening.


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## fractile (Mar 15, 2009)

I should mention that at the corners of a room the dimensional length is greatest and therefore more easily audible as a resonance, due to some law of physics and the fundamental resonant tone of a room (space). The corners do serve to reflect and amplify/regenerate the wave.


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## fractile (Mar 15, 2009)

What I mean is that this will also happen on a sphere with no corners, that the sphere will resonate at its fundamental tone.


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## ejbragg (Dec 13, 2009)

Yes, a sphere is the absolute (theoretical) worst case scenario. Whatever its fundamental diameter, it will be repeated from any direction at its center.

I think the 3D picture you've come up with is handy and easy to remember.


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