Attic Room - would you pick "a," "b," "c," or "d?"

[Mojo Jr]

Hello all,

I'm in the process of acoustically treating a new mix/project room in an existing space, and I'm finally at the acoustic measurement stage.

I'm familiar with how to place the mic in a rectangular shaped room to get the truest baseline of a room's acoustics, (place a speaker on the floor in one corner of the room, and place the measurement mic in the diagonal ceiling corner).

Currently, however, I'm working with a loft space (see attachments), where the side vertical walls rise to a height of only 73cm (28"), and then they begin to slope upwards, terminating in a narrow strip of "ceiling." Basically, forming the letter "A" with a flat top 49cm (19.29") wide along the length of the room from front to back. (see attached graphics for room dimensions).

Getting measurements in a space like this is new territory for me, and I'm wondering which corner I should consider the "ceiling" corner (i.e. the corner formed where the vertical walls begin their upward slope, or, where the sloping walls meet the 49cm strip at the top of the room). I've marked each candidate with letters on the attached photos (A, B, C, and D) to represent possible "ceiling" interpretations.

Where should I place the measurement mic in this scenario. Which of these locations do you feel would yield the best (most trustworthy) acoustic baseline for the space? Basically... where would you place your mic?

One more thing I should add... I'm using, as a measurement mic, an AKG C 460 B, with the CK 61 ULS capsule. Unfortunately, I don't have a capsule with an omni pattern with me. Will the 61's pattern be fine? Is there any special consideration (such as pointing the mic in a certain direction relative to the sound source)?

Thanks in advance for your assistance.

[Soundman2020]

Hi there "Mojo Jr", and welcome!

Each of those locations will give you a different perspective on the room, since each of them will show you a different set of room modes. "A" and "B" will be similar to each other, and "C" and "D" will also be similar to each other, but different from A and B. So you might as well do both "A" and "C" for example, provided that you will be able to get your mic back to those specific locations, in the exact same place, once your room treatment is in place.

However, you didn't way what the purpose of the room is, so you might well be measuring in the wrong place! Measuring at diagonally opposite corners, as you are doing, will give you a lot of information about modal response, but it won't tell you anything at all about SBIR, RT, IR or anything else at other points in the room. If this is going to be a control room, then you also need to set up your speakers exactly where they will be when the room is finished, and the mic exactly where your head will be while mixing, and take another set of readings like that: one with just the left speaker turned on, one with just the right speaker on, and one with both speakers on.

I don't have a capsule with an omni pattern with me.

Then you have a big problem! Acoustic measurements really do need to be done with an omni mic, since you want to capture the response coming to that point from ALL sides, equally. If you use a mic with any other polar pattern, then you are totally ignoring sound coming from some directions, and misrepresenting sound coming form other directions. It has to be omni. And it also has to have flat response, or if the response isn't flat then you need the calibration file for that mic, which shows how it differs from flat.

- Stuart -

[Mojo Jr]

If this is going to be a control room, then you also need to set up your speakers exactly where they will be when the room is finished, and the mic exactly where your head will be while mixing, and take another set of readings like that: one with just the left speaker turned on, one with just the right speaker on, and one with both speakers on.

Hi Stuart, and thank you for your reply. Sorry for not mentioning what the room will be used for.

It'll mainly be used for mixing acoustic-based folk-rock music and downtempo electronic music for film and TV. So definitely the control room scenario. It'll also be used as a project studio for the many songwriting projects I work on with other artists, so I'm hoping to be able to squeeze in a small vocal booth somewhere into the design of it. I'm hoping to keep everything as "modular" as possible since the room is already finished and I feel it would be prudent not to make any changes to the actual construction of the room. I'm hoping there's a way to make the walls temporary like giant slat resonators, but in the shape of entire, temporary walls (with doors) instead of just boxes. More on this in a moment.

With regard to where to place the listening position for the room, I haven't yet worked that out. As you can see, there is a wall of windows in front, which I would love to keep unobstructed if possible. I love John Sayers' design methods, and I've seen him creatively place recording rooms into spaces in ways that I, (and others), would have never considered. So I know there are probably a ton of different ways this can be addressed (many different possible solutions). I'm open to any and all suggestions.

I've attached a couple of SketchUp drawings with one of the ideas I have based on John's designs. They illustrate what I was mentioning about the walls. I'm hoping there's a way to make those additions non-permanent. Any and all comments are certainly welcome.

I probably should mention (after mentioning my admiration of John Sayers' designs), I have a pair of Mackie HR824 MKII monitors, so soffit mounting may be out of the question. I really love these monitors, but they may not be able to be used in conjunction with John Sayers' design concepts. Please correct me if I'm wrong on that. I'd love to be able to incorporate some of John's design ideas and still have free-standing direct fields in the room.

Now that you know my plans, do you feel I should maybe redirect my focus toward figuring out my control room layout instead of concentrating on the room's overall acoustic signature?

Acoustic measurements really do need to be done with an omni mic

After reading your post quote above, I remembered I do have a measurement mic in my collection. It came with my ARC room correction software. I'm hoping it will have a flat enough response to do any measurement tasks. If not, I'll need to add another mic to the collection (probably a Berhinger ECM8000 or something comparable).

Thanks again for your reply. I'm thinking this discussion may eventually end up being more suited to the studio design forum.

- VJ -