Are your home studio acoustics killing your mix?

The mixdown is one of the most crucial stages in song’s journey, and one of the most overlooked problem areas for home and project studios are the acoustics found in the mixing room.

The mixdown of any given song is one of the most crucial parts in song’s journey from concept to finished recording. The audio mix is when the sonic image is finalized and where all the musical material from the multi-track recording sessions is condensed into a two-track, stereo audio file.

Even if you are mixing a song produced “inside the box” with software such as GarageBand, Ableton Live or FL Studio – using loops, plug-in instruments, and pre-recorded vocals – the mix is still critical. While the audio elements in such programs are pristine, their sonic relationship in the context of the song relies heavily on the audio engineer’s mixing judgments.

Simply put, the best sounding tracks can end up a mess if the mixdown doesn’t go well.

When it comes to recording and mixing your music, most of us agonize over which software plug-ins to buy or what microphones and preamps we can afford. While these elements are important, it’s also crucial to understand and assess the acoustic properties of the room in which you will make your most critical audio production decisions during mixdown.

Indeed, one of the most overlooked problem areas for home and project studios are the acoustics found in the mixing room itself. With that in mind, we spoke with the team at Acoustics First, one of the leading providers of sound treatment materials to the music and media industries.

A great mix begins with a well-thought out, acoustically balanced room. Here are some simple, affordable steps you can take to improve your mixes by improving the acoustics of your home studio.

Sound waves

To understand how the room we are sitting in can affect the sounds we hear, it’s helpful to understand a few facts about sound waves. Sound waves move out from the source in all directions, like the beam of a flashlight, and travel at a speed of 343.2 m/s (metres per second) – or roughly 1,130 feet per second.

When a sound wave encounters a hard, reflective surface, it bounces off and continues on its way, redirected. There are seven characteristics that can be used to describe a sound wave. They are:

1. Frequency, the number of completed cycles per second (measured in Hertz or Hz for short).
2. Amplitude, the amount of air pressure displacement or loudness.
3. Wavelength, the total distance travelled to complete a single cycle.
4. Velocity, the speed at which the wave is traveling.
5. Phase, the wave’s starting point in terms of 360º.
6. Envelope, the shape of the wave’s progression over time.
7. Harmonic content, the mathematical relationship of overtones above (and below) the fundamental frequency.

During a mixdown, sound reflecting off the walls, ceiling, and floor can easily affect all these sound wave characteristics, causing the mixing engineer to make inaccurate judgments and consequently emphasize or de-emphasize specific frequency bands directly related to the imperfections of the room itself. Instead of a flat frequency response – an accurate representation of the sound waves – acoustic anomalies often color the overall mix in an inadequately treated mix room.

A typical result of such a problem could be a final mix in which the low frequencies are overpowering the other frequencies – or an absence of low end in the mix. Such an issue is often the result of anomalies in the room’s acoustics that mislead you during the mixing process, causing you to overcompensate and add too much or too little of a specific frequency.

Acoustical design

So, how can we figure out if the acoustics in our home studio are working for us or against us? The art and science of acoustical design can remedy many of the problems caused by sound generation in an enclosed space.

To explore the finer points of room acoustics, we called up Nick Colleran and Joe Horner at Acoustics First in Richmond, VA. Nick began his music career recording himself in a home studio, progressing to professional studios, and eventually being signed by Clive Davis to a deal with CBS Records in the late ’60s. The band’s singer was drafted, and Nick gave up performing to open a professional studio, Alpha Audio. Joe came in one night to record vibraphone on a track and stayed on for the next 17 years as Alpha’s principal music engineer.

Nick asserts that “Joe and I first learned acoustics with a hammer and saw, moving walls until our mixes worked.” Of course, major construction to your home studio isn’t usually an option, so we asked for suggestions for cost effective acoustic room treatments to help attain a more accurate and detailed mixing environment for the DIY musician.

Acoustic treatments for walls, ceilings, and floors

First, the physical shape of the room is important. “You want to avoid having all equal room dimensions,” says Joe , which means the classic 8’ x 8’ x 8’ spare bedroom in your apartment or home is not the ideal choice for your mix room. Instead, a room with a differential between its length and width is much better to work with.

“If this isn’t possible, then this is one instance where sound diffusers work well,” says Nick. “They don’t take the life out of the room, but they help reduce the intensity of reflected sound waves, making them weaker and harder to distinguish – like acoustical crowd control, dispersing rather than eliminating sound. It is like spreading peanut butter around on a piece of bread. You can’t swallow a lump of it, but you can have a nice sandwich if you spread it out. Sound works the same way.

“Diffusers like the pyramid shaped ones or the block shaped ones you always see in professional studios can fix anomalies at 125 Hz or 250 Hz, depending on their exact shape, because they are flexing membranes.”

Here’s a link to a short video demonstrating how sound diffusers work.

If you want to convert a room – one that’s nearly square in shape – to build a small post-production mixing studio, where do you start?

“First up, if you are able to change the room’s dimensions, then I would make the room deeper than it is wide so you would have some depth behind you.” Nick advises. “Deaden and trap the front of the room as best as you can, all the way up to where your ears are when you sit down to mix, so whatever you’re hearing first is from the speakers. You want to ensure there’s no interference or coloration from a first reflection off the walls, ceiling, or console reaching your ears before the sound coming out of your studio monitor speakers gets to them.”

Options for that type of treatment could include two-inch thick acoustical fiberglass; some bridged, flat-panel corner bass traps; or perhaps a cloud above, angled upward so you are not getting reflections from the ceiling as the sound leaves the speakers. The goal is to have the room sonically expand as the sound waves move back from the speakers.

“Once the sound passes your ears, you want to spread it around as much as possible,” Joe adds. ”One good way to do that is by using polycylindrical traps in the back of the room, which will make the room sound even deeper.”

In regard to floor coverings, Nick explains that “Carpeting is fine at the front of the room, up until the chair. From there back you can have hardwood flooring. You want to hear the direct sound coming out of the speakers un-interfered with, initially.

“After it passes your head, if you have diffusion behind you, it will make the room feel bigger because you won’t be able to audibly locate the position of the back wall. With these kinds of treatments, the room is more likely to work well acoustically, and as a result, a good set of two-way speakers will do just fine to give you accurate reproduction.”

All about the bass

Concerning the issues we mentioned earlier regarding bass being too loud or too soft in home mixes, Nick explains that, “What happens is the shape of the room itself may cancel certain bass frequencies. If a wall is half a wavelength away from the sound source, this ‘target’ wall reflects the wave, which combines with the incoming half-wave, to produce a null. It is a zero-sum game that cannot be corrected with an equalizer.”

This phenomenon, often referred to as a room’s “resonances,” can result in peaks or dips at certain low frequencies. What this means is that what you hear in your room, with respect to bass energy, is significantly different from what is actually in the track. In essence, what you hear is not what you get. Here’s a video that demonstrates the room cancellation phenomenon that can occur in an untreated room.

The glossary of acoustic terms on the Acoustics First website explains that low frequencies are particularly difficult to absorb due to their long wavelengths. Bass traps are designed and constructed to absorb these longer waves and control unwanted room resonances.

In terms of acoustics, the absorption of sound occurs when sound energy is attenuated (lessened, reduced). Thus, when a broadband absorber that extends to lower frequencies is called a bass trap, that’s imprecise. “The term ‘bass trap’ is counterintuitive,” says Joe, “since these devices really eliminate low frequency room cancellations, allowing bass to be heard accurately.”

So bass absorption, which can be accomplished a number of ways, will help reduce the impact of low frequency room resonances and spread out any anomalies over a wider frequency range, thereby minimizing bass coloration.

Nick adds, “Once you open the room up so the waves are free to roam, the bass does not then get canceled out.” This is a very important point as much of today’s popular music heavily emphasizes thumping bass frequencies.

Symmetry matters

A final important consideration is room symmetry. “When sitting at your mixing desk, look left and then look right,” says Joe. “You should see approximately the same thing on both sides. The symmetry, both mechanically (materials used) and physically (dimensional), needs to be identical. For instance, if you’re sitting in a room and you have an open hallway on your right-hand side and a flat wall two-feet away from your mix position to your left, you will never get a balanced stereo mix.”

“Even if your mixing desk is placed symmetrically centered within the room, the walls on both sides need to be of the same material,” Nick adds. “For example, drywall flexes and absorbs low-end, unlike a hard solid brick wall. With different wall surfaces there is a compliant difference resulting in a frequency response difference in comparison from left to right.”

Optimize your speakers

Make sure your speakers are on the same plane, facing you, level with your ears. Do not place them on different shelves at different heights. Ideally, the mixing position should be the tip of an isosceles triangle with the left and right speaker positions being the other two corners. Depending on the speakers you have, how your speakers are placed will directly determine what you hear at the mixing position.

If you are using a passive monitoring system, with a separate power amplifier, make sure the speakers are wired in-phase. A simple test to see if your speakers are in-phase is to switch the monitor output of your mixer from stereo to mono. If the collapsed mono mix image causes you to lose bass response as a result of phase cancellation, you will need to switch the wiring polarity on one of the sides. (This is rarely a problem with active or powered monitors.)

Make sure the cabling from your mixer to your power amp or powered speakers is balanced (three conductor XLR) and identical in specification, quality. and length. Cable mismatch may cause amplitude and frequency differences within the stereo image.

Finally, eliminate any external noise sources such as fans, buzzing of florescent lighting, noisy appliances nearby, pumps, or any other device that creates an audible noise floor.

The final mix

If you already have a home studio mixing room, take inventory and see which of these tips you can employ to create a better sounding mix room. If you are thinking about putting in a mixing room at home, look into the basic investment needed to arrive at a good sounding room and then see what type of budget for gear and software you can afford. In the end, the musical results will be much more accurate and translate better to the real world.

Acoustics First is an acoustical product and design firm that offers affordable solutions for home and project recording musicians. They offer consultation via e-mail for studio design projects.

Keith Hatschek is a regular contributor to the Disc Makers Blog and directs the Music Management Program at University of the Pacific. He has also written two music industry books, How to Get a Job in the Music Industry, which just came out in its third edition, and The Golden Moment: Recording Secrets from the Pros.

Jeff Crawford is a recording engineer and producer with more than 30 years industry experience. He also teaches music technology at Pacific.

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