Choosing the right room size — this applies to you too
Part 3 — Designing and building a DIY home recording studio
The whole story — part 1, part 2, part 3, part 4, part 5, part 6, part 7, part 8, part 9, part 10, part 11, part 12, part 13, part 14, part 15, part 16, part 17, part 18, part 19, part 20, part 21, part 22, part 23, part 24, part 25
Just when I thought I had it solved
This all gets a little heady, but choosing the right dimensions for a music studio is one of the most important things you could do and I ran into a huge brick wall (figuratively speaking), trying to calculate room behavior of a non-symetrical space. Well, it was all symmetrical except the back wall, but because of the shape I had some decisions to make that I couldn’t make on my own. I needed help, so I called in and hired my friend and studio designer Aaron Merrill. I’ve included Aaron’s cool room layout suggestion for me at the end of this post.
Ugly room modes and nodes and how to avoid them
So, one of the coolest things I’ve learned over the years about acoustics is that symmetrical rectangular rooms cause frequencies to behave in very predictable ways. Small changes to size, shape have a big impact on what frequencies become overly excited and which ones will seem to almost completely disappear. Getting the shape and size of a room to be just right — so it doesn’t interfere with the balance of the sound coming from your speakers — relies on a whole bunch of theory, experience and educated guessing…and then with as much confidence as you can muster, you jump in and start throwing a bunch of money into construction hoping the calculations and predictions are correct. But no worries. If you miscalculate or if you are trying to use an existing room that just doesn’t want to play nicely, there are more than enough companies creating products to help reduce the negative mode effects your room is causing.
Now, to be clear, a mode gives the perception there is more bass coming out of the speakers than there really is. That means if you mix a song based on the frequency spectrum you think you hear (because why wouldn’t you), and modes (created by the room) are providing false boosts in certain frequencies, you won’t be mixing enough actual bass in your song and your song will actually sound quite anemic when played back in an environment that isn’t creating the same modes. So, without those extra resonance boosts being created by the room, what you will now hear — in the new environment — is only what was actually there all along. In a rectangular room, we can fairly easily calculate what these frequencies are and how much louder the frequencies will be perceived and where they occur in the room. In a non-rectangular room it is basically becomes a bunch of guessing and ultimately just having to build it and try it out and see what we are dealing with.
Just when you thought dealing with modes was a challenge, there is an evil twin called Nodes. Nodes are physical locations in your room where, for lack of a better way to explain it, there are basically little black hole areas where it certain frequencies behave opposite of modes and will seem to disappear no matter how loud you boost the level. Literally if you place your head in those listening positions, it will sound like frequencies are missing that are actually really still there. All you have to do is move your head a couple inches to the left or right or up or down and they are back. Now, imagine you are mixing the same song, but now you are sitting in a node. Now you will think there isn’t enough bass in the mix so you will keep adding and adding with little results. Now when you go to that new listening environment where there isn’t a node at your listening position, you notice you are about knocking everyone over with WAY too much bass content. Where did that come from all of a sudden you wonder. I am tired of the nightmare of trying to guess where my mix should be because I’m compensating for modes and nodes. I want this space to have flat/accurate response.
It actually becomes fairly easy to tell if a song was mixed in a room suffering from modes or nodes in the mix position. In fact, thank goodness for mastering engineers and their rooms that are extremely neutral which allows them to reshape the EQ of a song mixed in a poor mixing environment to correct for too much or too little bass.
I love free tools!
So, to properly account for and calculate for all three forms of waves occurring in a room (Axial, Tangential and Oblique) it really does require an acoustician…or, a calculator produced by an acoustician. Luckily there are some really smart and generous individuals who were kind enough to make and share some very elaborate mode calculators . An online search using key words “mode calculator” will bring up several results, but be warned they are not all created equally. Years ago I ran across the Bob Gold’s mode calculator which combines various methods/approaches of figuring modes and creates results based on the combination of approaches. It is very cool and has a permanent place in my toolbox. I am happy/unhappy to say it has been quite correct in calculating (rubbing in), just how bad my last several rooms were.
About 6 months ago I stumbled across a new calculator by Amcoustics called amroc which is quite a bit more visual and is highly interactive — in how it displays the mode results compared to the Bob Gold’s calculator. They both have their own strengths though, so I’ve been using both quite heavily recently.
The Conundrum
So, remember when I said rectangular rooms have predictable behavior. Well, apparently non symmetrical rooms don’t. After hitting the books pretty hard and running numerous room dimension calculations it occurred to me that the space includes an alcove/walk in closet/storage room area in the back with a framed wall/doorway that is apparently resting on 12" x 2' of cement foundation footings. Odd place it seems for a load bearing wall, directly under a walk in closet, but oh well.
Anyway, I have an option to replace the closet doorway wall using two laminated beams (LVL’s) and slide the wall forward towards the mixing position which would give me that parallel back wall I’m needing for the room to become symmetrical. If I did this it would create a larger version of the room in the back which would work nicely, except that moving the wall where I suggested would make the smaller room a square. If you want to see a mode calculator light up like a Christmas tree, plug in the dimensions for a square room. Ok, I’ll do it for you. Here’s what the small room would have looked like in terms of mode issues if I went with the option to move the wall to create a parallel back wall to the studio and create a nice square vocal booth. I’m sure that barrage of built up/overly excited modes would have just sounded fantastic in any recording I would have done using that room.
Well, so after spending too much brain power trying to figure out how to use that little alcove room and reshape it into something non-square, it occurred to me that I needed to calculate the modes using my new option of a rectangular room — as a result of having a parallel back wall. Sadly, the results were not what I was hoping for at all. It was at that moment that I realized that calculating a non-symmetrical room was beyond my current tool kit. Time to call Aaron for some help to figure this out and see if any good dimensions were possible for this space.
My meeting with Aaron
I always appreciate speaking with someone who knows what they are talking about. I had created a list of about 20 questions for Aaron that I was going to rapid fire at him, but really, it came down mostly to knowing if there was anything I could do in my space to get good modal response. Even stating that I really didn’t even need the small room in the back for anything if I needed to use that for something else. Aaron was very quick in making a few good suggestions based on my first proposed layout of the room, but then he turned the conversation to “what if you did this….” Now things started to get exciting. Aaron suggested that if I really didn’t need that little room for anything specific, I should slide the couch to the right, away from center, and push it into the alcove a bit so the front of the couch lines up flush with the other half of the back wall (as pictured below).
Then I could just make a nice little client area over there with some nice lights above etc. Then, step 2 would be to create a wall-to-wall/ceiling-to-floor, framed, acoustically transparent fabric wall which would be mounted directly behind the couch. Then, that entire cavity behind the new screened wall — all the way back to the rear foundation wall — would be filled with fibrous absorptive material like fiberglass. The magic about this approach is now I can still take advantage of the added dimension/volume the alcove provides for the room for my desperately needed extra volumetric room length, but I now have a space which lets me put enough fibrous material to effectively turn that cavity into one huge 6' x 8' x 8.5' bass trap. Plus the added bonus of now having the horrible 1/4 wave cancellation issues that occur when someone sits directly in front of a wall, because really, it in fact isn’t a wall. It’s just a screen separating the room from the absorptive material which has now become a HUGE bass trap. It occurs to me it is a large enough bass trap I probably need to give it a name or something.
The dimensions listed above in the very first picture represent my new proposed space using Aaron’s ideas. I was elated to see how smooth the room now behaves in terms of mode response. And how cool that a large majority of my bass trapping needs are met. Although I will still build bass traps for the other back wall corner and both front corners as well as using the large cloud system above me as additional hidden bass trapping. I think this is going to work! It occurs to me that the other benefits of making that room a bass trap is I just eliminated a lot of sound proofing material, flooring, lighting etc that would have gone into that room, had I made it an isolation room etc.
