What do we really want?
Choosing new studio monitors or headphones seems to be a very straightforward process. At the heart of the issue, we basically need a monitor system with accurate sound. How much can I afford? What product has the best specifications for my budget? Easy enough. Is it really that easy? We should all suspect that the answer is not that simple. When choosing the best headphones or monitors many factors come into play that seem to have little to do with specifications or even price.
What we require of our studio monitors and headphones boils down to two key elements. First, we need a speaker that accurately reproduces a wide range of frequencies with a wide dynamic range. Second, we desire a monitor system that is enjoyable to listen to for long periods of time. In short, a monitor system that is both accurate and fun. Let’s first take a look at the accuracy part.
Flat Sound Is…
We can define flat sound from speakers to mean that any source that is played through a monitor system sounds identical to the original source. That is a difficult, if not impossible task for any monitor system. Speakers need to reproduce the sound produced by acoustic and electronic sources and captured in so many different ways. The translation from source to monitor is a difficult journey, but we expect monitors to accurately reproduce all the frequencies and timbres we need to hear, so let’s define accuracy. Speakers, like every acoustic sound source, interact with the room they are in, so the sound they produce is modified by the acoustics of their environment. For this article, we will ignore room acoustics and look specifically at speaker and headphone characteristics. In other articles, we tackle acoustic and electronic treatments that tame the acoustic characteristics of rooms and headphones.
There are many specifications that manufacturers use to describe the performance of monitors and headphones, some of which describe their accuracy and some of which simply describe their physical or electrical attributes. (See sidebar) For this discussion, the most important specification relating to flat sound is frequency response. We basically need our monitors to faithfully reproduce all the frequencies that humans can hear–from 20 Hz up to 20 kHz. In reality, it is extremely expensive and complicated for a monitor speaker to cover this wide range, so we settle for a reasonable range that covers the music or sound that we mostly need to focus on. For instance, string instruments from double bass up to violins, cover from a low of about 40 Hz to as high as 17 kHz. For hip-hop or electronic music with synth sub-basses or even for pipe organs and concert bass drums, the lowest frequencies may extend slightly below 20 Hz. We can assume that most monitors produce adequate high frequencies because the power requirements and physical manufacturing of high-frequency tweeters and horns are relatively simple. Accurate bass reproduction, on the other hand, requires much higher power, large physical devices, and often some very sophisticated tricks of physics.
Headphones will almost always beat studio monitors in their ability to affordably reproduce bass frequencies and even modestly priced headphones boast the ability to reproduce frequencies from below 20 Hz to above 20 kHz. Studio monitors without subwoofers, rarely produce much below 40 Hz, with many affordable models rolling off around 70 Hz. Therefore, we simply have to buy the speakers or phones with the widest frequency response for the price we can afford. Well, maybe that’s not really the whole story…
Monitor manufacturers often boast about their monitor’s capabilities in a way that hides the flaws of their true frequency response by leaving out the data that doesn’t look so good. The more respectable manufacturers don’t simply show a frequency response range, but they also mention the amount of tolerance, or variability, throughout that range. For instance, a specification of 20 Hz to 20 kHz looks good, unless it really means 20 Hz to 20 kHz (± 6dB). That plus or minus number tells you that perhaps 1 kHz is 6 dB above the average response and 100 Hz is 6 dB below the average response. That gives us a 12 dB window of accuracy at any frequency. Not so good. Be wary of any frequency specification that does not mention the range of tolerance.
Basic Monitor Specifications
Sensitivity: Useful for headphones or passive monitors. A measurement of a speaker’s efficiency that describes how much sound is produced for a given input level. Higher sensitivity numbers mean the monitors will play louder with a given input signal. Written as dB SPL, it describes the output for a given input, like 90dB/1milliwatt. Doubling the power (mW) will increase the loudness by 3 dB.
Impedance: Impedance, a measurement of electrical resistance in ohms (Ω). For headphones, low impedance phones (< 80 Ohms) will play loudly with a portable music player, like a phone. Higher impedance headphones (> 80 Ohms) are more appropriate with professional headphone amplifiers and studio equipment.
Frequency Response: A monitor’s ability to produce sounds from low bass to high treble, in Hertz. Usually, this spec is accompanied by tolerance in decibels, like 20 Hz to 20 kHz (± 3 dB). Ideal human hearing covers 20 Hz to 20 kHz.
How good is good?
In reality, a tolerance of ± 2dB or even ± 3dB over the entire frequency range is acceptable, as long as the overall frequency response curve doesn’t dip up and down like a picket fence. Small variations in frequency response over wide frequency ranges are easily smoothed over by our brain and even a perfectly flat response from a monitor will not be perfectly flat by the time it reaches our ears For my money, when reading specs I value a relatively flat frequency response over the total width of frequency response. I would trust a monitor specification that states 50 Hz to 18 kHz (± 2 dB) than a monitor that simply states 35 Hz to 25 kHz with no mention of tolerance.
Since bass is really the most difficult range to produce, some manufacturers provide specs that look like “± 1¾ dB from 60Hz to 19kHz and -10 dB at 40 Hz.” This spec tells us not that only is the frequency response extremely flat for most of the range, but also describes how the bass rolls off down to 40 Hz, where it is still present, but at a lower level. So, choose a frequency response that you feel covers the range you need, stated with an accuracy that you feel secure about.
The rest of the story
Ok, we know how to interpret frequency response specs, and we know what flat sound is. Now we get to the part of what do you actually want to listen to all day long for inspiration, comfort, appropriate volume, and, of course, accuracy. The design and manufacturing of speakers and headphones create different personalities that you can’t determine simply by reading their frequency response or power handling specs. Ported speakers sound different than sealed boxes. Open-back headphones sound different than closed-back headphones. Crossover frequencies and driver sizes affect midrange phase response, which colors the sound in a way that a frequency chart will not explain. Ribbon tweeters sound different than hard or soft dome tweeters, but again their differences are not described by their frequency response graph. So, the personality of a particular speaker may appeal to you and provide a more natural or comfortable listening experience.
The House Curve
Even though we need accurate (flat) monitors to produce music that translates well to the rest of the world’s playback systems, some producers, like hip-hop producers, may prefer to work on monitor systems that are bass-heavy because it feels good and simulates the environment of a club or auto sound system! Creating sound is our passion and our vice, not a scientific experiment, so we need to enjoy the process and the environment. Once you’ve chosen a monitor whose frequency response and personality you get along with, don’t be afraid to play slightly with the frequency balance of the speaker. The overall treble vs. bass response is often referred to as the “house curve” of the monitor system. Most monitors allow you to slightly customize the low, mid, and high frequencies of the monitor. These onboard equalizers help with accuracy and room correction, but may also be tuned for your personal taste. Once again, flat sound represents a sort of accuracy, but flat sound may not be the most enjoyable way to work.
If one should choose to incorporate a house curve into their monitor setup, it becomes more likely that mixes and masters will not accurately translate to the outside world. Therefore, if you enjoy working on a monitor system with hyped bass, you must be aware that outside your room the mix will have less or possibly uneven bass. Mixers who regularly use the same mastering engineers come to trust that their mastering engineer will correct this type of problem, but if you master on a hyped system, the potential for poor translation increases.
Simulated Target Curves
SoundID Reference software provides customizable target curves and built-in translation curves. The translation curves simulate typical listening systems, like mobile phones, studio monitors, TV speakers, and car stereos. The customizable target curve allows the user to start with a flat monitor response and then add a custom parametric EQ to create a house curve. For instance, I have one pair of headphones that feels slightly aggressive in the midrange even with the SoundID correction curve. For this pair of ‘phones, I add a slight midrange dip that makes the headphones sound more natural to my ear and they still translate very well (and predictably) to other playback systems.
The core idea is that flat sound is an important starting point. Flat sound in your studio or headphones will ensure that your music will play back predictably on most other playback systems out in the world. Every studio monitor, because of its physical design and manufacturing trade-offs has its own sonic personality, but studio monitors tend to be more accurate, trustworthy, and more durable than home stereo speakers. You should audition many different monitors, observe what your peers and heroes use, and at the end of the day, trust your gut with what sounds natural and comfortable to you.
Of course, don’t forget to acoustically treat your room. Great speakers will only sound great in a well-treated room and even modest speakers can sound excellent in a well-treated room. Experiment with creating your own house curve so that you enjoy listening in your own environment, but be aware of potential translation problems! Remember that SoundID Reference software allows you to start with a flat response and then you can slightly modify that sound with a custom target (house) curve. Flat sound ultimately describes an accuracy that will translate to other systems, but remember to always keep things enjoyable and productive.
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