Post-Production Studio Design

[1430591]

I am building a new post-production studio and would appreciate some advice about the shape of the room.

The studio will be a free-standing construction within a larger room, and will be double-shelled. At the moment I'm working on the dimensions of the inner shell to try and achieve an optimum acoustic environment.

I have been following the following principles so far:
– listening distance to speakers is 1.4m (optimum distance for my speakers – Genelec 8340s)
– speakers are 5cm from wall, and I have allowed an additional 7cm for absorbent behind them.
– listening position is 38% into the room.
- front sides are angled at 8.5 degrees, back corners cut a minimum of 45 degrees.
– I have kept the number of sides/angles to 8 to cut down on construction complexity.

I have arrived at two options:

A – sides entirely splayed, and slightly larger volume space
B – some of sides parallel and smaller angle at back corners

In both cases the front part of the room will be treated with absorbent. The rear wall will be treated with diffusers. I should also add that I haven't forgotten about the room height, and am planning on angling the ceiling also.

I can't make the structure any wider due to the space constraints. This has caused me to cut the sides higher up in Option A, leading to the large (20 degree) angle.

My questions are:

(1) I'm trying to get a reflection free zone around the listening position. What are the important angles (leaving the speaker) that I need to look out for? I've tried various angles with these models and don't seem to be reflecting onto the listening position.
(2) Is there a limit on how much you should cut the rear angles? In all the models I see, this is usually more modest than, for example, in my option A.
(3) Is there anything else about either of these designs that strikes you as problematic?

Many thanks in advance for your insights.

Ben

[Soundman2020]

Hi Ben, and Welcome!

The studio will be a free-standing construction within a larger room, and will be double-shelled.

If you did that, then you would have a three-leaf system, which is potentially bad for low frequency isolation. You should aim to have only two leaves: the fist leaf is the existing outer "larger room", and the second leaf is the actual inner-leaf of the room itself. If that would create the situation where there is a very large gap between the two leaves on one (or more) sides of the room (more than about a meter or so), then you'll need to build an extra leaf to closer off that part.

At the moment I'm working on the dimensions of the inner shell to try and achieve an optimum acoustic environment.

Your diagrams do not show the inner shell: they show the final visible surfaces of the room after all the treatment is in place, which is a very different thing.

If you were to build your inner leaf using either of those designs, you would end up with pretty bad acoustics: To start with, you would have no place to put your bass traps! And without bass traps, any small room will be no use as a mixing / mastering environment.

– listening distance to speakers is 1.4m (optimum distance for my speakers – Genelec 8340s)

I'm not sure how you arrived at that figure. I could not find anything similar in the Genelec documentation. The distance from the speakers to your ears is not set like that in any case: It is set by the room dimensions and the room treatment mostly, not much by the speakers. In some rooms it is very feasible that 1.4m could be beyond the critical distance. In other rooms, that might be too close. It is impossible to say what the "optimum" listening distance is without knowing anything about the room.

– speakers are 5cm from wall, and I have allowed an additional 7cm for absorbent behind them.

Why those numbers? Just leave a 10cm gap, and put 10cm of suitable insulation in it. The rear corner of the speaker can touch the front face of the insulation, if necessary.

– listening position is 38% into the room.

38% is only a rough guideline. It is not written in stone, and there is nothing magic about it. It's just a theoretical good point. You can vary that widely, if needed, from about 30% to about 45%.

- front sides are angled at 8.5 degrees, back corners cut a minimum of 45 degrees.

Why those angles? What's the theory behind that? And as I mentioned above, if you cut off the rear corners of your room, you will have no place to put the bass trapping that you will very much need. If you cut of the front curners of the room, the same applies, plus you will not be able to soffit-mount your speakers, which is arguably the best single thing you can do to improve acoustics.

– I have kept the number of sides/angles to 8 to cut down on construction complexity.

... this making it impossible to predict the actual room response at low frequencies, using the simple tools that are available, but don't work for rooms with more than 4 sides....

– I have kept the number of sides/angles to 8 to cut down on construction complexity.

If you were to make it 4 sides, then you'd cut down construction complexity even more! In fact, you'd minimize construction complexity like that.

Why do you want 8 sides when 4 is better acoustically, better for simplifying construction, and better for simplifying prediction?

I have arrived at two options:

A – sides entirely splayed, and slightly larger volume space
B – some of sides parallel and smaller angle at back corners

I would suggest "Option C": Three sets of parallel faces (simple rectangle), and don't angle the back at all! That's the best layout, from all points of view.

In both cases the front part of the room will be treated with absorbent.

Why would you do that? You cannot create a full RFZ using absorption, and killing the front of the room is a concept that has long since been abandoned. Especially if you soffit-mount your speakers.

The rear wall will be treated with diffusers.

Why would you do that? The room is small! Therefore it needs massive bass trapping on the rear wall. And it is too small to be able to use numeric-based diffusers.

I should also add that I haven't forgotten about the room height, and am planning on angling the ceiling also.

Why? For what reason? How much? Are you aware that angling the ceiling greatly increases construction complexity, and makes prediction using simple tools impossible?

I can't make the structure any wider due to the space constraints

Then make it as wide as you can, WITHOUT the angles.

(1) I'm trying to get a reflection free zone around the listening position.

You are not achieving that, for many reasons. In both of your diagrams, you clearly do have first-order reflections arriving directly at the mix position. Also, since you are not soffit-mounting your speakers, you'll find it practically impossible to achieve a reflection free zone.

What are the important angles (leaving the speaker)

You can't leave out the speaker! The important angles are based on the speaker! And the angles for the speakers are based on the room. You are showing your angles at 30°, fixed, but there's no need for that: it's a myth. You can vary the angles as needed to get the speakers and the mix position in the correct places.

I've tried various angles with these models and don't seem to be reflecting onto the listening position.

You definitely do have reflection paths to the listening position, in both cases.

(2) Is there a limit on how much you should cut the rear angles?

Yes: The limit is that you should never cut them at all! If you do, you remove the best location in the room for bass traps.

In all the models I see, this is usually more modest than, for example, in my option A.

Which models are you referring to? Please post a couple of links, so we can see the rooms you are talking about, where the rear corners have been "cut off".

(3) Is there anything else about either of these designs that strikes you as problematic?

Yes: 1) the room corners are cut off, thus removing the best location for bass traps, 2) Reflections are getting to the mix position, 3) The speakers are not soffit-mounted, 4) The geometry (speaker position and angles, listening position) is not optimal.

- Stuart -

[1430591]

Thanks very much for these comments – very helpful.