Room Acoustics for Mastering Suites

[Gomez]

Ok, here's one for the mastering wizards.

I'm pretty confused about this topic.

Let me see if I got it right:

1: you don't want "control room" (supposedly ideal RT60 @ 500 m.secs) acoustics (but I don't remember why) in a mastering suite.

2: You don't want to master in a space that resembles, lets say a "living room" either.

I know quite a bit about the difference between mastering gear (as in monitors etc.) but got no idea about acoustics for mastering suites.

I'd appreciate some comments and help.

... and please forgive my ignorance

[Gomez]

Drowning in the void... Help!

[Ethan Winer]

Gomez,

> I'm pretty confused about this topic. <

It's not nearly as complex as many would have you believe. There are two main goals for any room where the accurate playback of music is needed:

1. As much bass trapping as you can manage in the corners.

2. Treatment of first reflections on the side walls and ceiling.

Other than that it's a matter of taste, though some standards still apply. For example, you don't want too much or too little ambience. But in most rooms if you get points 1 and 2 right you're 90 percent there.

--Ethan

[Gomez]

Thanks so much! No one seems very interested on this thread...

What you say make a lot of sense.

Now, do foam bass traps actually work well (like Auralex etc.) ???

I can't imagine those thingies sucking out a 50Hz wave... do they actually work?

Thanks a lot Ethan!

Gomez

[Brad Blackwood]

Actually, Ethan nailed it, IMO. Trap the LF and insure 1st order reflections are tamed and you are golden - a good room is a good room. This is your bible, afaic...

[Ethan Winer]

Gomez,

> No one seems very interested on this thread. <

Unfortunately, acoustics always takes a back seat to gear lust, when it should be the other way around.

> do foam bass traps actually work well (like Auralex etc.) ??? <

I own a company that sells bass traps and other acoustic products, so it's probably not fair for me to comment. But if you follow the link under my name below you'll find a lot of useful information.

--Ethan

[Ethan Winer]

Brad,

> Trap the LF and insure 1st order reflections are tamed and you are golden <

Yeah, I've been arguing with some guys recently in a home theater forum over the "benefit" of treating the entire front wall, and all the side walls, plus carpet of course, and trying to explain that so much absorption is not necessary and just sucks all the life out of the room.

--Ethan

[faeflora]

Ethan's Real Traps do really work real well. I have 8 real traps, 3 mini traps (thin kind) and 4 mondo traps in my room and not only do they help w/ mixing/playback, but it's now also a great sounding room for tracking.

[Bob Olhsson]

A major difference between many dedicated mastering facilities and most studios is that there is no need for an acoustically isolated performance space and control room unless it's a multi-room facility. This obliviates the need for heavy walls and the extreme trapping needed to tame the problems heavy walls create in the low-end.

[Ethan Winer]

Bob,

Yes, great point. Walls that are rigid and massive create more problems at low frequencies than thinner walls that can pass bass through and absorb a little on their own. Many people don't realize that acoustic isolation and acoustic quality inside the room are competing goals.

--Ethan

[lucey]

Originally Posted by Gomez

Now, do foam bass traps actually work well (like Auralex etc.) ???

I can't imagine those thingies sucking out a 50Hz wave... do they actually work?

Thanks a lot Ethan!

Gomez

No they dont work. They murk.

Mondo traps and mini traps are both great.

Get 2 Mondos for the front corners (or 4 for all 4 vertical corners) and 2-4 Minis for other wall-to-wall joints, 2 HFMicros for the 1st relflection side walls, and some diffusors on the front wall.

If the room is bigger than a shoebox, that will get you VERY close.

[Bob Ross]

Originally Posted by Ethan Winer

I've been arguing with some guys recently in a home theater forum over the "benefit" of treating the entire front wall, and all the side walls, plus carpet of course, and trying to explain that so much absorption is not necessary and just sucks all the life out of the room.

Are you familiar with David Moulton's ideas on room design? Based on several articles of his that were published in Recording Magazine a few years back, it would seem he's quite enamored of making the entire front wall (the one w/ the speakers that you stare at when you're sitting at the console) absorbent.

[Ethan Winer]

Bob,

> Are you familiar with David Moulton's ideas on room design? <

As I understand it, the concept of avoiding early reflections and mixing / listening in a "reflection-free zone" (RFZ) is an offshoot of David's earlier work. When the entire front half of a room is treated with absorption, clarity and imaging are greatly improved. But then, over time, studio designers learned that you can get the same benefit by treating only a few specific places.

A friend of mine who's a pro studio designer - which I am not! - tells me the goal these days is to retain as much liveness as possible while still avoiding all early reflections. In purpose-built mix rooms the side walls can be angled 30 degrees or more to direct the initial reflections to the rear of the room. In smaller rooms and home studios where having severely angled walls is not an option, absorption is used at those specific places. That's how my home studio and home theater are treated. Plenty of bass trapping, with just enough mid/high frequency absorption to avoid early reflections but no more.

Again, this is just my understanding of the evolution from LEDE to RFZ rooms, and is subject to the usual disclaimers. If anyone has anything further to offer I'd love to hear it and learn more.

--Ethan

[insomnio]

Ethan:
What do you think about diffusors? I've seen many rooms with diffusors on the rear wall. Are they good for the front, the rear, or not at all?.

Insomnio

[Bob Olhsson]

Dave, as you may know, had a career as a recording engineer at Columbia Records before he went back and got his engineering degree. Based on our experience back in the dinasour age of studio design, we both have serious questions about the whole "kill the early reflections" concept. When it comes to mix translation, the colorations introduced by attempting to kill the early reflections seem to create more problems than they solve in the "real world."

Early reflections, as you know, fuse with the direct sound. For this reason, any early reflection colorations, especially low frequencies that aren't effectively killed are going to be very misleading. He uses diffusers that are designed to compliment the off-axis response of the speakers to break up early reflections.

Dave and Manny did an imaging demonstration using their ultra-wide dispersion speakers in a bare-walled/bare floored hotel room that pulls the rug right out from under most people's room treatment concepts.

[7rojo7]

I've had to face particular problems that make LEDE and RFZ impractical for my space which is small and has 90cm stone walls. I found a concept in a magazine and later researched some on internet, which is exactly what Bob Olssen is describing, I believe it was called High Early Reflection Model. I've seen some Variation of this in some of the Storyk-Walters' designs in NY
I have a 35 sq meter space divided in 3 parts by triple pane glass walls and doors, 1 control room and 2 "semi" isolation spaces for tracking acoustic sound sources. I opted for semi isolation between the spaces, favoring the visual contact between musicians, being that it would be impossible to make perfect isolation anyway.
I came up with a mix of all that I'd seen used in studios that I'd worked in and all that I'd researched for this project.
Since isolation from the outside was already complete I had to think of a way to absorb or "vent" the bass. Since one lateral wall is glass panels and doors of different dimensions some bass trapping and absorption was occuring, I trapped all the 90° (actually some were more acute than 90°) angles in the CR (18sqm) with permanent constructions. Because I'm in a building that was built on top of an annex of a roman temple (I have couple of 1000 year old bared curtain wall stones in view) in the 16th century, the angles and proportions of the walls are somewhat distorted, so I had to re-square the room without taking up any space. I did this by making the angle killers of different sizes and starting their construction from 1 meter 40cm from the ground leaving space for studio furniture, studio furniture itself does some work but in a rather imprecise manner. All the wall to ceiling angles are killed at 50° as are the wall to wall angles. The listening area is symetrical without taking space from the moving around area. On the surface of the bass traps there are mounted diffusors which are made of wood of varous thicknesses which has been cut in curves in a way to diffuse 3rd, 5th, 7th and 11th harmonics of the length of the floor to ceiling. These are also mounted on a part of the ceiling directly over the main listening area (calculating the dimension of the width of the room) which houses an air conditioning fan unit which also acts as a bass trap which actually "vents" bass outside.
The back wall and ceilings were constructed as panel absorbers. By using various spacing of the studs on which was hung lead backed sheetrock covered later by cork, it created different resonant frequencies. The back wall was originally stone, by putting a light wall up in front of it with this widely spaced studs technique I gained a little more absorption. Between the phenomenom of the glass, the air conditioning chamber above the listening area, the back wall, killing the corners with vented bass traps (they're more like huge helmholtz resonators) and the prime number harmonic diffusion this very small CR has just the problem of room nodes, which I don't know how to cure easily any way, but it's a small problem.
Everyone who hears my room is astounded, I'm designing a room for someone else and they asked me if it would sound as good as mine and I said better, because at his place we're floating everything and using an inside out light wall varying widely spaced stud constructions inside everywhere and we have space for some poly cylindrical panels and some wobbly absorbers in the ceiling above the HERM diffusors.

Some very cheap methods of room treatment which I use in my tracking spaces.
I have these 2x4 foot and 4x6 foot Hemp rugs hung from the ceiling a few inches from the wall behind which I've sown some panels of rigid fiberglass, I have 10 feet worth of glass doors and walls that divide a stone room, you could imagine the problem, this practically eliminates it.
You could hang something like these across the corners and along the back wall. If your space is small I'd investigate some kind of diffusor panels (even egg crates sprayed with some kind of "hard" paint, you can use both side for variation) close to the inital reflection areas in back of the speakers if they're not soffit mounted on the ceiling and walls close to the speakers, as Bob Olssen pointed out, some have better results with this method. Or if you have more than a 12 ms slap from behind (the Haas effect) (get out your calculator) put them in the corners behind you in front of the bass traps (they're called Haas kickers) too. Cork is a good material for mid absorption, min. 1 " thick
Diffraction has a Psychoacoustic effect, your brain doesn't recognize the highly diffracted reflection as such nor the lack of it as with absorption (which may sound unnarural to the brain). This effect is not measureable in a scientific physical way thus some may not give it creedance.

[Ethan Winer]

Insomnio,

> What do you think about diffusors? <

I think they're great if you have a large enough room. Even in a smaller room they can be useful. But - and this is the big one - good diffusors are expensive to buy (or complicated to build), and the cheap / simple types are useless. All the cheap diffusors I've heard sounded to me worse than a plain flat wall.

> I've seen many rooms with diffusors on the rear wall. Are they good for the front, the rear, or not at all? <

My friend, studio designer Wes Lachot, always puts those deep RPG "well" diffusors on the rear wall. But again, these are rooms where the rear wall is 10 to 15 feet or more behind the mix position. I see no advantage to putting diffusion on the front wall because loudspeakers aren't pointing there.

--Ethan