To achieve a high quality mix, it is important to have an accurate pair of monitor speakers that are housed in an adequate listening environment.
Loud Speaker System
Loudspeakers convert electrical energy from an amplifier into sound. In most loudspeakers, an alternating current flows into a coil of wire, which is fixed inside a magnet. The signal produces a changing magnetic field inside the coil, which moves the cone forwards and backwards in response to the alternating current. This then causes the attached cone to vibrate, hence a sound wave is produced. If an alternating current with a frequency of 1000 Hz is passed through the magnet then the cone will move backwards and forwards 1000 times every second.
A loudspeaker system should accurately reproduce sound that spans from 20 Hz to 20 kHz as this is the frequency range that humans hear (audio spectrum). However, because of effects such as resonance, a single loudspeaker is rarely used to cover a wide range of frequencies; instead, a number of specialized drivers are employed that are split by a crossover. The crossover network divides the signal up into different frequency ranges.
The crossover sends each separate frequency range to its corresponding speaker as needed, for example, the lower frequencies are sent to a 15” bass driver.
- The subwoofer speaker reproduces sound in the low frequency range, normally between 20Hz and 250Hz.
- The mid-range speaker reproduces sound in the mid-range frequency range from 250 to 4000Hz. It is also known as a squawker.
- The tweeter speaker reproduces sound in the high frequency range, normally above 5kHz. Tweeters are useful for high frequencies because the small moving part has very little inertia.
The more you listen to a set of speakers, the easier it is to learn their strengths and weaknesses.
Remember that hi-fi systems are not suitable for monitoring work because they are specifically tailored to make pre-recorded music sound good and not to present it accurately. Many hi-fi systems contain built in equalizers to add punch and sparkle to a sound. Monitors attempt to reproduce sounds that are not modified.
Active and Passive
- Passive monitors require an external amplifier to be powered. When matching an amplifier to the speakers, it is important that they are able to handle the power required to drive the speakers in a system efficiently. Passive speakers are less popular than their active counterparts.
- Active monitors are a self-contained speaker and amplifier configuration in which the characteristics of the amplifier and speakers are optimally matched. They do not need outside amplification; all they need is a line output from an amp.
Active monitors are the most popular design in today’s professional studios due to their high quality, compact design and lack of need for an external amplifier.
Setup and Type
Monitor speakers may sound different depending on the location they are in. Two different rooms can have a huge effect on the frequency balance and stereo field of the sound being produced by a pair of monitors. For this reason it is important to understand basic positioning to minimise extreme sound variations.
When positioning monitors, they need to be as far apart as the distance from the listening position, forming an equilateral triangle. If the monitors are too close together the stereo field will become smeared. In contrast, if they are positioned too far apart the sound will lose its focus point or ‘sweet spot’.
The cones of the speakers should be angled inwards towards the head of the listener at around head height. The tweeters should be positioned slightly above/in-line with the ear. Each monitor’s volume needs to be at exactly equal loudness to preserve a balanced mix. Check the level faders and display meters before starting a mix.
Most speaker cabinets work best if they are a little way from the wall. Try and avoid putting speakers close to corners as this will lead to unpredictable bass responses and standing waves.
Near-field monitors are a popular choice in both professional and home studios as they provide the listener with a greater proportion of direct sound compared with the sound reflected from the room. Near field need to be listened to at relatively close positions (1-2m).
Many monitor speakers struggle to give an exact representation of a sound wave due to poor room design and nonlinearities that exist in a speaker’s systems frequency response. It's a good idea to listen to a pair of monitors before you buy them.
Monitor speakers are generally designed with an output that produces a minimal bass response. Unless the room is acoustically designed to handle it, a higher bass response will be unpredictable, leading to standing waves and inaccurate sounding mixers.
Two-way speakers are the most common type. Ideally the bass driver should be at least 8 inches in diameter. Around 90W is deemed acceptable for most monitoring environments. Good quality speaker cable should be used. When choosing a set of monitors, it is important to pick a set that transmit an even frequency balance as possible.
If monitors are wired out of phase one will move in the opposite direction to the other causing phasing. Speakers out of phase usually sound as if the signals image is appearing from beyond the boundaries of the cones and often sounds bass thin. Monitors in phase have all cones moving in the same direction and the signal image appears to originate from the mid-point between the speakers.
It is vital that the speakers are in phase during the mixing process. Check the wires at the back of the speakers to make sure all polarities are the same.
When mixing, it is best to vary the level over time. Listening at a higher volume (not too loud!) will allow the bass to be more audible; where as listening at a moderate volume will allow to check for overall balance. For long periods of time, mixing at a moderate volume is best used, usually between 70-80dB SPL.
It is important to remember that the Fletcher Munson curves will have a direct effect on the frequency balance of a mix.
Although higher levels can be exciting, they should be avoided for long periods of time as ear fatigue may occur. The longer the human ear is exposed to loud music the less responsive it becomes. The most obvious effect of this is when the high frequencies seem to diminish over time. To compensate for this when in a mix, you will keep adding higher frequency content. The result is when returning to the mix at a later stage the mix sounds far too bright. The way to combat ear fatigue is to work at low volumes and have frequent short breaks every hour. It is easy to spend 8 hours mixing a track to a stage where the perspective has sub-consciously changed.
Exposure to high volume levels can cause permanent ear damage/
Having a number of monitoring references is an important part of achieving a great mix. Other places to listen include a stereo HI FI system, car and other acoustic environment.
Always refer to a CD/high quality sound file that you are trying to sound like during the mixing process. This will help to keep your mix on track and sounding professional.
An addition to the ears for checking the frequencies present in a sound is a spectral analyser. The spectral analyser gives a visual display to the frequencies present in a sound. Such devices can help with equalization allowing for an engineer to see offending/prominent frequencies.