Pro Audio Files

5 Things You Need to Know about Room Acoustics

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Microphones are great. High end preamps and compressors are awesome. Fancy monitors with perfect response are imperative for a mix and make the whole process much more enjoyable. But none of that really helps if your room doesn’t sound good.

The room is indeed the front end of your signal chain.

But how much does your room really impact the sound? I mean how much difference can an untreated vs. treated room really make?

Well, put it this way: when I first got into my new space, if I swept a sine wave up to 103Hz it completely vanished. As in no sound. Kind of hard to figure out if the bass is right when +/- 103Hz is sharply attenuating and 103Hz literally is inaudible.

Because it doesn’t matter how much I boost or cut there, I just simply couldn’t hear that tone without moving to a different place in the room! And these kinds of problems were showing up all up and down the frequency spectrum.

To make matters worse, the room opens directly into a hallway, giving me a 1.5 second sound tail. In other words, everything sounded like it had a short room reverb return on it! Kind of made it difficult to piece together what kind of spacial processing I needed to do in the mix.

So I hired an acoustics specialist (actually I hired two, but one didn’t work out so well) and we figured out a game plan to fix things up.

What I needed was something that was:

A) Affordable

B) Temporary (since I’m currently renting)

My goal wasn’t perfect acoustics, but rather, something that could make the space work well enough that I could at least somewhat gauge what I was doing.

Here are 5 things I learned about treating a room on a budget.

1. In a Small Room You Need Absorption

Problem numero uno in my room is that it is small. About 13′ x 14.5′ x 8.5′.

I actually thought that was a decently sized space until I realized it wasn’t.

Based on those measurements it turned out I needed about 200 to 250 square feet of absorption! With about 700 square feet of surface area (including the floor), that means I need to cover around a third of the room in absorption.

Turns out, this isn’t uncommon. This would shorten the room decay within the room to about 0.2 second, and a heavy 18 ounce velour curtain hung in the opening would adequately decouple the room from the hallway. The absorption would also help even out the frequency response of the room.

2. Not All Absorption Is Created Equal

The next immediate question is: what do I use for absorption?

The three main contenders were: Rigid Fiberglass, Roxul (mineral wool), or Cotton Insulation.

All three have comparable absorption properties at equal thickness.

Regardless of what you choose you are going to want about 4″ thick panels. The trick is to mount your absorption with an air gap between the material and the wall.

The reason is that this form of absorption is based on velocity — it is the movement of air through the material that converts one kinetic energy (movement of air molecules) to another (heat) as the little fibers in the material provide resistance.

What it all means is that there needs to be air moving for the absorption to work. Right at the wall is where the sound reflects. Reflection is a process where kinetic energy turns to potential energy and then back to kinetic — in other words, at the surface of the wall, there is no air movement! Putting absorption there negates its full potential.

Then of course there’s the question of Auralex. Auralex panels are effective for frequencies above 500Hz, but do very little for lower tones. It’s also very expensive relative to insulation.

While Auralex can be useful, I wouldn’t rely on it much. Wrap some insulation in a breathable fabric and you’ll be better off.

3. Position Is Key

One of the complexities of treating a room is that the effect of the room changes based on where the monitors are placed — and where you are placed relative to the monitors.

Certain areas of the room are going to be guaranteed issues.

The dead center of the room will be a problem if you are sitting there. You’ll find the biggest nulls in that spot. Likewise, you’re going to get a lot of anomalies if you are sitting right up against a wall (and it will hard to get in and out of the chair).

The general rule of thumb is to be 1/3 of the room’s length away from the wall. This generality usually works out. However, in order to get your imaging right, you will still want to be along the center axis between two of the walls. You’ll be in a strong null, but you’ll also have equal coloration from the walls and be equidistant between the speakers.

So, halfway between two walls along one axis, 1/3 of the way away from one of the walls along the other axis. Then there’s the issue of placing the monitors.

Generally speaking the same rule of thumb applies for speaker position as it does for listening position — however, you might not have enough space in your room to pull that off.

One solution can be to have the speakers flat up against a wall. There are two things to consider when doing this: First, you need closed-back monitors. Open back monitors rely on the rear port to accurately work, particularly in the low end. Putting a solid surface up against that port will change the frequency response.

Second, you are sticking the monitors at the highest point of potential energy, which means the room modes are going to be strongest. The benefit, however, is that you have one less wall surface to worry about for all but the lowest frequencies.

In my room, I currently have my monitors flat against the wall. The peaks and dips in the lows are a bit exaggerated, but the room decay is significantly less and the higher frequencies are more accurate, so it seems to be the better choice… for now. That may change.

4. Don’t Forget The Small Details

Little things are easy to gloss over: Decoupling your speakers from the speaker stands. Placing your work desk and computer in a way where you don’t have early reflections bouncing directly into your ears. Having storm windows installed to block outside noise, being ear level with the speakers and being equal distance between them.

All these small things can make a pretty big difference.

5. Keep a Pair of Headphones Handy

The truth is, even with a lot of money invested into treatment you’re still going to have issues in small rooms.

A pair of trustworthy headphones can help bridge the translation gap. Headphones are rarely perfect as far as monitoring goes, but a good pair will give you a decent representation of the sound without the room factoring into the equation.

Navigating room treatment is tricky. Acoustics is a complex and involved science and requires a great deal of specialization to truly grasp.

However, with a little hands on effort and some know-how you can make your small room adequate for serious projects. It’s always an ongoing quest!

Share your experiences below — believe me, I’m all ears!

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Matthew Weiss

Matthew Weiss

Matthew Weiss is a Grammy nominated and Spellemann Award winning audio engineer from Philadelphia. Matthew has mixed songs for Snoop, Sonny Digital, Gorilla Zoe, Uri Caine, Dizzee Rascal, Arrested Development, 9th Wonder, !llmind & more. Get in touch: Weiss-Sound.com.
  • Cody Blase Skully

    Branching off this, I know of some very nifty software you should check out if you’re tuning (or re-tuning) your room

    Mac: http://supermegaultragroovy.com/products/FuzzMeasure/

    PC: http://www.roomeqwizard.com/

    Great article! Thank you

  • Andre Ryabchenkov

    Great article Matt! I just treated my room not long ago. Long, tedious and a bit costly process but worth every penny. I used Rockwool on the walls and also in the corners for poor-man’s bass traps. The result is phenomenal. I will take the frequency measurement soon to see what happens

  • Mikael Ebrima Mbenga

    Excellent article! I was just planning to do this type of treatment and this answered a lot of my questions. Thank you for the great work you guys do over at the Pro Audio Files!!

  • joe

    Velour curtain won’t do anything for LF which is a major contributor to room coupling

  • Paco Muro Croket

    could you please add a comment on the over use of absortion pannels? I have heard that too many can “kill the room”, when using for example way more than in your example.

  • Paco Muro Croket

    Another detail: In my home studio I already use rockwool pannels well covered with bed sheets, but in between I first added a layer of the common transparent kitchen foil, to avoid smells. Does that have a major effect on the performance of the pannel? wold it resonate of reflect when it is too tight?

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