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The juggling game of studio design, where you have to keep 197 balls in the air at all times... and they are all different sizes and different weights! 
And you have to do that while riding a unicycle, backwards, on ice.... blindfolded... Sometimes, it really does feel like this:
- crazy-juggler-11-ENH-BIG2.jpg (60.91 KiB) Viewed 37365 times
- crazy-juggler-11-ENH-BIG2.jpg (60.91 KiB) Viewed 37365 times
OK, a few more twists that you could take into account as you work through the process of coming up with the perfect room design: If you need more mass in a thinner package, then consider fiber-cement board. The density is a bit more than twice that of drywall, so you can have the same mass in a thinner panel. Drywall density is around 680 kg/m3, fiber-cement around 1550 kg/m3. MLV is around 1800 kg/m3, if you really want to spend a LOT of money to get mass in a thin package (MLV is really expensive: I rarely use it for isolation but I do use it in other parts of studios...). Other crazy things: Aluminium sheeting is around 2750 kg/m3 (so a sheet 3mm thick has the same mass (surface density) as 12mm drywall). Steel plate is around 7850 kg/m3 (thus, 2mm thick steel plate has the same mass as 23mm thick drywall... As you note, lead sheeting it about 12,000 kg/m3, so 1mm of lead is about the same as nearly 18mm of drywall. (And for the insanely extreme, exotic, and impossible end of the scale: gold is around 19,300 kg/m3, and platinum is around 21,500 kg/m3. So gold leaf just half a mm thick has the same mass as 14mm of drywall, and a sheet of platinum 1mm thick is the same as roughly 32mm of drywall....
)So, considering those, maybe you can come up with some combinations of materials that would allow you to get the right thickness for good symmetry while still retaining the right mass (surface density).
Next up: Why bother?
For all those folks following this thread (and there are lots of them! Your thread has nearly 4,000 views right now, Jennifer...
), what Jennifer is proposing might seem to be silly, crazy, overkill, since she already has a successful studio that is producing great mixes, and making money for her (click on the link in her signature or profile...), so you might be wondering why she would want to change that?Answer: The better your room is, the better your mixes are, and the more effortless it is to mix well. She will be able to to produce even better mixes, will take less time to to do it, and will be less fatigued at the end of the day. That's the basic reason here. She has a good studio, and she wants to make it a great studio. In commercial terms, that means faster turn-around on jobs (thus, more jobs per month = more $$$ per month), as well as improved reputation: folks who use her studio will want to go back for more, and will also tell their friends and colleagues about this fantastic place where its just so easy to track, and the vibe is great, and the results are outstanding, etc. And they won't mind paying more for that. People do actually appreciate quality!
So, she's investing in making her place even better: better isolation between rooms, higher precision in the mix, more accurate acosutic response, flatter, better, smoother... easier to hear defects in the music, and fix it. Better mix translation. Etc.
Thus, her concern about a few mm of "asymmetry" in the room. Some people might think that a few mm here or there won't make any difference, but it will. If you take a look at the science of psycho-acoustics, you'll see why.
Psycho-acoustics deals with the way we humans perceive sound, rather than with the way the sound actually is, physically, in the air. Ears do not work the same way microphones do: a good mic captures the actual pressure changes in the air very accurately, and turns that into precise voltage fluctuations, but ears do not work like that. Our ears are amazing devices that do many things all at once to give your brain the perception of sound, but they do it in a manner that is very different from a mic... and some of that can cause your ears to "lie" to you: so you perceive sound differently than it really is.
For example, if your ear hears the direct sound from a speaker but there's also a reflection that sends a "copy" of that direct sound to your ears with a small delay (because it took a longer route), then that can fool your ears into hearing something that isn't really true. If the reflection is strong and the delay is short (less than about 30ms), your ears do not hear that reflection as a separate sound: rather, it hears a smeared interference pattern between the two sounds, and your ears/brain interpret that interference pattern to mean that the sound came from a different direction (neither from the speaker nor from the spot where the reflection occurred), and also that the frequency response was different from what it really was: this is because your ear itself creates similar interference patterns inside your ear canal, for the very purpose of trying to identify which direction the sound is coming from. That's the real purpose of all those ugly folds, wrinkles, and twists on your pinna (the fleshy thing that sticks out to the side of your head, that most people just call an "ear"). Those folds and wrinkles and bends and angles have a purpose: to create interference patterns inside your ear canal, which the rest of your ear and brain then use to figure out where the sound came from.
Thus, if you are standing out in the jungle and a lion roars, this system is pretty good at identifying where that came from and how close it was, so you can turn the exact opposite way and start running like crazy.. away from the lion! You want this to be accurate, because running the wrong way would not be a good thing... if your ear told you the lion was in behind you when it is really in front of you, then that would not be a good thing, as you'd end up running towards the lion...
So your ear works very well out out in the open, where there are no reflections to mess things up, and you get to live for another day... But inside a room, there are reflective surfaces around, and those can send reflections back to your ears, that create other interference patterns inside your ears... so your ears can tell you the wrong thing! You can hear the sound as coming from a different direction. Your ear has no way of knowing if that interference pattern was produced by the ugly wrinkles in your ear lobe, or by a strong reflection that arrived after a delay: it just recognizes that particular interference pattern as meaning "the sound came from there, not here".Fortunately, inside a studio, your life does not depend on this: there are no lions to eat you (at least, I hope you don't keep lions in your studio!). But it does mean that you can't pan and mix as well as you'd like, because you are not hearing the way things really are: the reflections are fooling your brain.
Worse still, because of the way this happens inside your ears, those interference patterns reduce the intensity of some frequencies and increase the intensity of others, so you are also not hearing the right frequency balance.
When you are out in the jungle and this happens for real, your brain "knows" about the different frequency response for each and every angle that a sound might arrive at your ears, and it compensates, telling you that the frequencies were actually at the right intensities even though they were not, because it "understands" that each angle has a different response. But when that happens in the room from a reflection, your brain has no way of determining that it was a reflection! It assumes that this is a direction clue coming from the folds of your pinna... Therefore, it tries to "compensate" for a frequency problem that does not really exist, and tells you that the levels of the frequencies were difference from what they really are.... Long story short: a strong reflection messes with your brain, and it thinks that it is hearing sound coming from another direction (not the real one) and with another frequency balance (not the real one).
So what happens when you have a whole bunch of less strong reflections, all arriving at slightly different times and levels? Since your brain can't make head nor tail of that mess, it just tells you that the sound is "broader", "wider", or more "spacious", coming from all around you, rather than from a specific direction. And since the frequency balance is also all messed up impossibly, your brain tells you that the sound is "warmer", more "mellow", and more "pleasant". (I guess that sort of calms you down a bit if there are dozens of lions roaring all around you, so you are more tranquil as you consider the inevitability of your impending demise... ).
So, this is where some studio designers go wrong (even professional ones), as they think it is a good idea to have a warmer, more pleasant, more enveloping "spacious" sound that feels nice, when you are mixing... so they try to create that, with many low-level early reflections... but that is actually very wrong! Because it "colors" the sound! That's fine for an audiophile listening room, or a home theater, or even for a concert hall: those early reflections give the music "depth" and "width" and "ambiance".... but you do NOT want that in a control room! Control rooms must sound "accurate", not sound "nice". This often gets confused in control room design: people think that the room should make the music sound good, but it most definitely should not! It should make the music sound exactly the way it really does sound. Control rooms need to be "clinical". Surgical. Pristine. They must NEVER change the sound in any way, because the entire purpose of a control room is so you can hear the ix accurately, precisely as it really is. If the control room acoustics change that, so that bad music already sounds good, then you have a problem. In a control room, bad music must sound bad: no covering it up to sound "nice" or "warm" or "spacious". The control room should just "tell it like it is", warts and all.
The entire purpose of a control room is so that you can hear the speakers, only the speakers, and nothing but the speakers... and that you can hear them cleanly, accurately, with raw surgical precision. You are suppose to hear exactly what is on the track, not a warm, fuzzy, nice, happy, spacious version of it: you WANT to hear reality, exactly as it is... because that's what you need to hear, in order to mix correctly! You create the warmth and the spaciousness in the mix, not in the room. That's your job as a mix engineer: to take those clinically sterilized individual tracks, and mix them all so they sound pleasant, good, broad, mellow, and happy. But you cannot do that if the room itself already sounds pleasant, good, broad, mellow, and happy!!!! Because you won't know which part of that is in the room, and which part you are creating in your mix.
Thus, modern control room design philosophies aim to totally eliminate those strong early reflections, and only allow diffuse, delayed, low level reflections that arrive at your ears with delays greater than about 20 ms, so they don't mess up your brains ability to clearly hear the sound.
The entire basic philosophy of a control room is that it must tell you the cold, ugly, harsh truth: it must allow you to hear your tracks exactly as they are, in all their ugly glory, "warts and all"..., So you can then start working to get rid of those warts, and make it sound good. If you mix sounds good in a room that tells the pristine truth, then it will also sound good in any other room that DOES add its own character to the sound. ie, your mixes will "translate". On the flip side of the coin, if you mix in a bad room to make the track sound good, then you have undoubtedly compensate for the deficiencies of the room, in the mix. So when you play it in another room, then those compensations will be acutely audible, and your mix will not translate. That's what I do when I'm designing a control room: endevour to make it as neutral, transparent, and accurate as it can be.
Getting back to Jennifer: she wants her mixes to translate better so she doesn't have to work as hard to make them sound good in OTHER rooms: she wants fewer trips out to the car, living room, bedroom, i-phone, etc. to check how it sounds elsewhere. Because with an accurate room, she already knows that if it sounds good in there, it will sound even better elsewhere.
(Sorry for hijacking your thread, Jennifer, to rant about why accuracy is so important in a control room, and why you are doing what you are doing! But I thought it was a good opportunity to bring that up, in case some of your followers were wondering about your sanity...)
Soooo.... yes, it is important to get the room as symmetrical as you possibly can, because your ears are symmetrical! Your left ear needs to be able to hear the same acosutic "signature" of the room as your right ear, so you can hear both the sound stage and the frequency balance equally accurately with both ears, and make good mix decisions to produce mixes that are not "skewed" to one side or the other.
But millimeters? Is it really necessary worry about a few mm here or there? Do you really need to have the speakers within a couple of mm of being symmetric?
YES!
Think of it this way: the wavelength for a sound wave with a frequency of 1 kHz is about 34 cm. At 10 kHz it is 34mm. At 20 kHz (the upper limit of human hearing), it is just 17mm. So if the sound arriving at one of your ears is offset by, say, 34mm, then that's a an entire two wavelengths! at the high end, and one complete wave at 10 KHz! In other words, the left speaker is 720° out of phase with the right speaker for the higher of those two, and 360! for the lower... And for all other frequencies, it will be out of phase by differing amounts that depend only on the frequency... which implies that, where the difference is 180°, you wont hear that frequency at all, since it will cancel itself out... Ooops!
So there's a phasing issue here, which affects different frequencies in different ways... and messes up your perception of sound.
There's also the issue of those darned early-reflections again: if your speakers are not symmetrically laid out, the early reflections won't be symmetrical either, so one ear will get a different set than the other ear.. thus skewing your perception in other ways...
Conclusion: symmetry is critical, and the better you can get it, the easier it will be to mix accurately, producing clean mixes that sound great everywhere, and translate well.
Quick real-life story: about a year ago, I was approached by a small studio owner in the UK who had built his studio with some help from an "acoustician" friend... but he found he could not produce decent mixes in there at all! He hired me to fix that. I got him to analyze the room using REW (like this: How to calibrate and use REW to test and tune your room acoustics), and the data he sent me was really really ugly! Symmetry was way off, frequency response was all over the place, terrible early reflections, etc. So I re-designed the front end of his studio for him: mostly just improving symmetry, clarity, "tightness", and eliminating the early reflections (plus some stuff that needed doing on the rear wall). He built that, and then we started some precision tuning of his room, but that got sidelined after a while and we didn't complete it back then (mostly my fault...
) ... however, recently he send me a message that I'd like to quote, but removing identifying information: "I have just finished an album for a nine piece [genre] band, recorded live with just a few overdubs. I tentatively sent the first mixes out to all having mixed them unattended by the band. All nine have come back with "sounds awesome" and not a single change to be made. This is unheard of in my world!! ... What's changed ? ... It's down to the control room that you designed for me last year. Thank you so much Stuart I couldn't be happier.". That's a partial quote of what he wrote, selecting the pertinent bits. This is a very clear demonstration of why this stuff matters. Before, he could not mix at all in that room. Now he can produce mixes that translate perfectly and come back from his clients with zero edit requests! He did not change any gear in his studio: same mics, same speakers, same effects boxes, same DAW, same plugins. The ONLY thing that he changed, was the room acoustics. He's a member of the forum, and we are currently working on even higher precision tuning for his room, but I'm not going to identify him or his studio (unless he wants to pop in and tell his story.... that's up to him). The point I'm trying to make, is that this stuff IS important! It can very literally make or break a studio, as in this case. Just getting the front end symmetry precise, reducing early reflections, and cleaning up the overall acoustic response, can make a world of difference. (This is not an isolated case: it happens all the time. I just chose this one since it happened a few weeks ago, and is very relevant to what Jennifer is doing).So: Jennifer is on the right track here, for sure! The case above was making a bad room good, and Jennifer is making a good room better. After she is done, I reckon we'll see similar messages from here!
[THREAD HIJACK MODE = "OFF"]
You can deal with the first-reflection point to a certain extent with treatment, but of course eliminating it would be better. But the asymmetric baffles on the soffits is a different thing: that's big: they do need to be symmetrical, or the frequency response won't be the same. Try to get them as symmetric as you can.This created a problem for soffit design demonstrated by a draft design below. The first reflection point of the listening positing hits the door. Of course the soffit face on the left will be wider than the right, creating an asymmetrical response.
That's fine! 4mm is pretty darn good.With the Genie clips and furring channel installed with just the original 12.5mm plasterboard layer, this is pretty much corrected. The door has been beefed up with ~41mm of MDF, almost doubling its mass and keeping it flush with the moved plasterboard. This means that first reflection point and soffit symmetry is within 4mm, not bad at all;
Use two layers of 6mm fiber-cement board: total thickness only 12mm, for the same mass as about 27mm of drywall...for when we add another layer of 16mm plasterboard to the left wall the soffit asymmetry returns, now a 12mm difference.
Probably not too much of a deal for the first reflection points, but for the soffits, I would try to keep it tighter. A good goal would be to have the actual faces of the two soffits identical (in mirror image, of course), and also have them set up symmetrically i the room (speaker axes equidistant from side walls, mirror-imaged around the room center line), and to compensate for any gaps with miniature "wings" between each soffit and its associated side wall, where the "wing" is basically just a thin gap stuffed with insulation and a fabric front face: so "soft wing, not hard". It won't be entirely symmetric, but it's one of those many juggle balls: sometimes you have t compromise, and a "skinny soft wing" would be the least serious compromise.If this asymmetry is significant,
Once again, sorry for the slightly off-topic rants that were not really pertinent at all to your questions, and which I'm pretty sure you already knew about anyway! That was mostly for the folks following your thread.. but maybe a little too much!
I do get carried way, occasionally 
Sorry!- Stuart -
