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 flat 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 really want in studio monitors or headphones boils down to two key elements. First, we desire a speaker that produces a wide range of frequencies accurately with a wide dynamic range. Second, we desire a monitor system that is enjoyable to listen to for long periods of time. We need a monitor system that is both accurate and fun. Let’s first take a look at the accuracy part.

Flat Sound Is…

Let’s define flat sound to mean that any sound played through a monitor system sounds exactly like the original source. That is a difficult, if not impossible task for any monitor system. For example, if you listen to a violin in a room, the intensity and timbre of the instrument sounds different at any listening position in the room. So who is to say what does the actual source even sound like? Now let’s just assume that we want to accurately reproduce the sound of a stereo pair of microphones that captured a musical performance. That should be relatively easy.  Compare the size of the microphone diaphragms to the size of typical speaker components. Obviously, there is not a simple one-to-one relationship between the device that captured the recording (microphone) and the playback device (speaker). So, we can see how the translation from source to monitor is a difficult journey, but we still desire accurate monitors that can reproduce all the frequencies and timbres we need to hear, so let’s define accuracy.

Spec Speak

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 reproduce 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 or horns is relatively simple. Accurate bass reproduction, on the other hand, requires much higher power, large physical devices and sometimes 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 can boast the ability to reproduce frequencies from below 20 Hz to above 20 kHz. Studio monitors without high-powered subwoofers, or very large woofers, 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 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 the 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 spec of 20 Hz to 20 kHz looks good, unless it is more correctly shown as 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. How much sound is produced for a given input level. Higher sensitivity numbers mean the monitor will play louder with a given input signal. Written as dB SPL 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 (30 ohms) will play loudly with a portable music player, like a phone. Higher impedance headphones (250 ohm) 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 a 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 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 flat(-ish) frequency response over total width of frequency response, so I would rather have a monitor that produces 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 area, some manufacturers provide specs that look like “± 1¾ dB from 60Hz to 19kHz and down 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, but 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. Most of these factors come down to personal preference and relate to the design and manufacture of a specific device. Ported speakers sound different than sealed boxes. Open back headphones sound different than closed-back headphones. Different 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 metal dome tweeters, but again that difference is not shown by their frequency response graph. Speaker personality and timbre must be considered along with frequency response to truly judge the type of impression a specific monitor produces.

The House Curve

After all this info about flat frequency response, some people, like hip-hop producers, may simply prefer lots of bass in their monitor system because it feels good! We make music because we enjoy the emotion, the fun, and the mood. Creating sound is our passion and our vice, not scientific experiment. Once you’ve chosen a monitor whose frequency response and personality you get along with, don’t be afraid to play with the overall tone 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 a productive or 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

Sonarworks software provides target curves to simulate a typical domestic listening environment and also an X-Curve environment. The domestic playback curve provides an opportunity to audition what a typical home stereo is likely to sound like, while the X-Curve simulates the sound of a movie theater playback system. Sonarworks intends these playback curves to be applied after your listening environment is corrected to be flat. That is, once your system is known to be flat, you change the target curve (house curve) to simulate a specific playback environment.

Flat Sound

I prefer to say accurate, or flat sound is a good starting point and then fine-tune the sound to your liking. Every studio monitor, by way of its physical design and production trade-offs has its own sonic personality, but studio monitors tend to be more accurate, trustworthy and more durable than home stereo models. Try many different monitors, observe what your peers and heroes use, and at the end of the day, trust your gut. Of course, don’t forget to acoustically treat your 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 Sonarworks Reference software allows the user to create a flat sound and then apply a custom house curve via its built-in bass boost and tilt equalizers. Flat sound ultimately describes a certain accuracy that will translate to other systems, but remember to always keep things enjoyable and productive.