acoustic foam placement

I've had these suckers up for a while now, and

I'm sure I'm missing a few spots in the room that could use them. In most of the studio pictures I see, whether home-based or pro, there's always

that typical configuration of foam on the wall behind the speakers.

If I understand correctly, the foam is there to tame standing waves, mostly in the high-mids and high frequencies? As for bass control, most articles I've read on the subject advise bass traps on the corners of the wall opposite the monitors, basically behind your back. Foam on the walls apparently doesn't do much for bass control...(still learning)

So I ask, what is the foam behind the monitors actually controling, or taming? Sorry for a seemingly basic question but again, I'm still on the quest to create the best monitoring environment I can in this tempermental room of mine!

Should the foam go pretty high up on the wall or would about a foot above the monitors suffice?

What about the side walls, I've read about the mirror technique but it seems you just look at at where to monitors are facing (from their angles positiion) and place some foam on that spot?

I couldn't thank you enough for some good advice on this one!

I've had these suckers up for a while now, and

I'm sure I'm missing a few spots in the room that could use them. In most of the studio pictures I see, whether home-based or pro, there's always

that typical configuration of foam on the wall behind the speakers.

Honestly acoustic foam is not a great solution for treating the acoustic in a room. While some home-based studios owners decide to use them because they can't afford anything else, you won't see acoustic foam anywhere near a pro studio.

If I understand correctly, the foam is there to tame standing waves, mostly in the high-mids and high frequencies?

No. Standing waves create issues in low frequencies, and foam doesn't do anything for low frequencies, so it can't help at all with standing waves. All it does is suck up high frequencies and dull your room, making it imbalanced, and if anything making low frequency issues even more conspicuous.

As for bass control, most articles I've read on the subject advise bass traps on the corners of the wall opposite the monitors, basically behind your back.

You're right that the single most important device for acoustic treatment in a room is a bass trap. It doesn't really matter in which corners you put your bass traps. Start with the tri-corners (anywhere three surfaces meet), so the four corners of the room, close to the ceiling if your ceiling is more reflective than your floor.

So I ask, what is the foam behind the monitors actually controling, or taming?

I don't believe there's necessarily treatment behind the monitors — let alone foam which is a bad idea to begin with. If you're going to use some sound absorbing treatment like fiberglass for example, I would put it in the path of early reflections. For example you have someone slide a mirror on the back wall behind the monitors while you're sitting at the listening position. When you see the monitors in the mirror, that's an early reflection path. You can do the same for the side walls and the ceiling. Don't forget that you'll also get early reflection issues from your desk, your keyboards, your computer monitor, your mixer... you may not do anything for those and still they'll be there.

What about the side walls, I've read about the mirror technique but it seems you just look at at where to monitors are facing (from their angles positiion) and place some foam on that spot?

No. Keep in mind that if you place absorbing material in positions that aren't in the path of sound somehow coming back to your ears then it doesn't serve any purpose.

Acoustic foam placement:

Sorry, couldn't resist.

Seriously: what David said, although I can't stress the importance of massive corner traps enough.

To make up for my rude comment, here are some constructive tips:

https://www.gikacoustics.com/acoustic-primer/

Acoustic foam placement:

 

Sorry, couldn't resist.

 

Seriously: what David said, although I can't stress the importance of massive corner traps enough.

s#!+ you beat me to it

To the OP:

you won't see foam in pro studios. You'll see them in promotional pics because it speaks well to the crowd, but I've never been to a professional studio that has foam anywhere.

In my studio i have foam (not the pyramid kind) in the air-vent baffles only.

And what was left i used to make the desk softer to the touch.

You won't tame standing waves with foam, it's like trying to tame sea-waves on the beach with your body.

What foam does is it kills the high end reflection which are usually not even problematic, since most of the crap becomes from a muddy low-end and uncontrolled mids - frankly, only using foam will make things worse not better.

Bass trap really needs to trap bass for it to be effective, unfortunately rockwoll and similar only works down to 120Hz, leaving most of the actual bass untouched.

And something I never really considered until i experienced it first-hand, uncontrolled bass can skew midrange, making your monitoring experience worse. (2nd,3rd and 4th order harmonics, intermodulation, blabla, i'm not a physicists)

edit: there is actually a foam with similar density as rockwool and other common acoustic materials which can be used instead, but it gets very expensive.

For my baffles I used 40kg/m3 foam, which is not as dense as some dense rock wool, but much denser than the usual "acoustic foam"