Acoustic Panel Placement for Mixing

Posted by on Nov 14, 2012 in Production, Recording | No Comments

A couple of posts ago I embarked upon an acoustic journey that I really had no hope of doing justice, but I figured I would try anyway.  I’ve got some great feedback and as we move forward I’ll attempt to be more technical when I can, this will probably articles to have a bit more focus – everybody wins.  Welcome now… to part 3… Acoustic Panel Placement for Mixing…

Acoustic Panel Placement for Mix Focused Environments

The first thing to note is this – there’s a fundamental difference between an environment that is prepped for mixing and environments prepared for recording.  As a result of this understanding we will focus specifically on methods of placement as they relate to one making decisions within the mix.   When it comes to the mix environment everything really boiled down to three questions:  Where/how do i put bass traps?  Whats the optimal place for mid-high frequency absorption?  What do I do with my extra panels?  But first, why does the context of the space matter?

Mix Environment

Let’s talk about why a mix environment and a recording environment are different in terms of our treatment goals.  This was first laid out to me by a user on reddit who described it as such:

For tracking/recording: it’s subjective so the types of treatment, their effectiveness across a given bandwidth, how they modify the indirect signal, their placement, etc the source/receive placements, are all subjective to the user’s tastes to achieve a particular sound – so there’s not much to argue there as it is user based criteria – although recommendations can be given for treatments based on what the user is trying to achieve…

For mixing: you want to maintain accuracy such that the early-arriving indirect high-gain specular reflections do not skew the intelligibility, localization, and imaging of the direct signal – which allows you to make critical mixing decisions without the bounded acoustical space masking itself on the signal.

SSL_Console_CloserLook_Recording-1054x589

mmmm… mixing

The complete text of this actually goes on for a while but I wanted to summarize what i thought was important.  What’s this all mean, anyway?  The first bullet pointed out by the reddit user indicates the importance of the human experience as it relates to recording.  The ever present saying “garbage in/garbage out” saying comes to mind, you can certainly tell when something is good can’t you?  For a recording, if an engineer thinks its gold who are we to argue?  The engineer’s experience with the sound in the room will win in the case of recording assuming of course, that they want the sound of the room in the recording.

This is not the case for a mix environment.  In terms of the mix you may be granted the most opportunity should you remove the room as much as possible from the recording.  The second statement provided by the reddit user  seems simple to me although my breakdown might offend some readers who were hoping for something more technical:  we don’t want the room factoring into our mix decisions, so we remove it.  Seems simple enough right?

A note on symmetry…

whoa…

It might go without saying but the position of your workstation in the room matters.  Consider the sound panorama.  You want to create a clear balanced spread of the instruments in your mix.  This means for an accurate representation of what is in your music, it helps a lot if the room treats both sides of your music the same way.  Place your workstation and your monitors in a symmetrical fashion if at all possible.  Don’t believe me?  Just try your monitors in different configurations that are not symmetrical.  Do it, I dare you.

 

The Room and Winer’s rules

Now that that’s out of the way, let’s consider our room.  The dimensions of the roof are important here.  There’s no one solution that will effectively treat all room shapes.  With any room we do the best we can.  For our purposes we’ll use a squarish room where we have one entrance and then 3 walls.  We’ll look at how one would determine where both traps and high-mid absorption would go in a room like this.  From that point you’ll need to apply those techniques to your room keeping in mind that, if you are like me, you’ll have extra features in the room offering you additional acoustic challenges – every surface sounds different.

I think Ethan Winer summarizes the best; here’s the short version according to him:

  • Broadband (not tuned) bass traps in as many corners as you can manage, including the wall-ceiling corners.
  • Mid/high frequency absorption at the first reflection points on the side walls and ceiling.
  • Some additional amount of mid/high absorption on any large areas of bare parallel surfaces, such as opposing walls or the ceiling if the floor is reflective.

Bass Traps

I touched briefly on bass traps on a previous post but we didn’t go too deep.  In short, whatever your bass traps are – the corners are where you experience the most win.  The reason corners are the best place for traps is that solution is the easiest answer to tell people with the simplest explanation; that is, the most bang for your buck.  If you’re on a budget, like everyone, chances are you’ll only be able to handle a handful of the corners and you’ll use the thickest owens-corning material you’ve got for your trap.

Assuming you weren’t on a budget or just had an insatiable curiosity – there is quite a bit to know when it comes to bass traps which include handling tri-corners in a special way as well as just adding more owens-corning 705 to your walls.  Panel spacing will also affect how low frequencies are absorbed.  Plenty of forum posts on the net will claim that ‘one can never have too much lf absorption” but again, if you are anything like me, it will come down to that budget.  In summary?  Trap your corners, but read on should you want to know what you are talking about.

When it came to my studio I could afford to treat four corners so I had long panels made twice as thick as my other panels.  These panels used 4″ rockwool and were 7 feet tall or so.  With the frames these weigh about 25 lbs so they are securable to a wall.  Ultimately you do want some space behind them, space behind a panel can almost double its affect on lower frequencies.  Treat as many corners as you can and if you can afford more of the thicker material you can get into hanging up thicker panels in efforts to eat more low frequency sound.

Remember – this isn’t going to be perfect but it might help manage some of your low frequency based room issues.  There’s a lot more to know, be sure to check out the related reading at the end of the post.

 

A note on treating bass in a room

I found this particularly interesting so I’ll just quote this (Thanks Ethan Winer):

Although it may seem counter-intuitive, adding bass traps to a room usually increases the amount of bass produced by loudspeakers and musical instruments. When the cancellations caused by reflections are reduced, the most noticeable effect is increasing the bass level and making the low frequency response more uniform.

I.e. the mangling of acoustic interference in the room may mean that some waves that would otherwise cancel are not and voila, more bass.

Mid-High Frequency Absorption – First Reflection Point

The next thing I learned in my quest to figure out where to put these panels was that I wanted to place absorption at the first reflection points.  Seems easy enough, but what are they?

Reflection Points

Just what is a reflection point?  I think this forum post summed it up quite nicely:

First reflection is the point on the sidewalls, ceiling, front wall (wall behind speakers) and rear wall of your listening space where the sound waves from the speakers will make their first reflections off a hard, reflective surface before they reach your ears

That means that these particular waves of sound are going to be the first to clash with the lovely and pristine sounds coming from your monitors.  Now its important to keep in mind, these aren’t the only reflections the sound will make.  It will bounce all over the place but the first reflection point does offer the strongest contender to the sound you need to hear with a short enough travel time to cause a problem.

Given that, the next item on our to do list is figure out how to locate them so we can place our panels on them.  There will be reflection points on the walls, the ceiling, and my rear.  Finding them is pretty simple, also from the forum post I mentioned above:

Walls – The Mirror Method – Sit in your listening position and move a mirror along the wall until you can see the reflection of the speaker.

Ceiling – Draw an imaginary line between the listening position and the speaker, stand at the mid-way point between the two, look up at the ceiling directly above that spot and that is where you want to locate the middle of your panel.

 

Where’s everything else go?

If at this point you manage to have more panels at your disposal there are other places you can choose to add coverage. Both behind the monitors (the front wall) and the wall behind you (the rear wall) can benefit from absorption or diffusers.

 

Our room with Panels

Let’s do our first run of panels and bass traps for our ‘ideal’ bedroom studio. As I was about to draw this I got the brilliant idea to find one on the net, here’s one from an SOS article on room treatment.

Basic panel and bass trap placement from SOS Magazine

 

As you can see SOS agrees with everything I’ve said here (and they better, I learn just like everyone else does.. reading!).  Now in a real room you probably won’t get so lucky, you’ll have windows, doors, closets, ‘features’ of the house, all kinds of stuff will get in the way of our perfectly laid out little plan.  You have to do the best with what you’ve got.  Where you can change the room around, do it – but plenty of folks can’t do all that much.  At least when it comes to the simple hanging of panels, its as damaging as hanging a painting in your house, much different than knocking down that weird shaped wall.

In my room I’ve got two windows of different sizes, a closet, a door, shelves, and to top it all off the room is an oddly shaped pentagon.  I did my best 😉

 

Studio Laminar v4

I chose to lay the workstation out along the ‘odd wall’ in efforts to make best use of the space of the room which was my primary concern. Then you’ll notice that I’ve got both shelves and a window in my reflection point space. There are other panels about the room, and of course, the panel hanging from the ceiling.

 

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