The Basics
First and foremost, it’s important to establish that a car is not and will never be a reference environment. Think of a recording studio and a picture should readily come to mind: you have a bassist rolling a joint, a guitarist tuning down to drop C, [Editor’s Note: not to be confused with dropsy – JT] but more importantly, excellent soundproofing, low ambient noise levels and freedom to place monitor-grade loudspeakers wherever is best. In a car, your music is competing with road noise, wind noise and powertrain noise, and speakers can only be packaged in so many locations. After all, you can’t really hang a 6.5-inch speaker from the A-pillar, nor can you really place a speaker beyond the perimeter of the interior. Another car audio issue is material reflection. Look around the interior of your car and you’ll likely find glass, plastics, foam and textile. Glass is flat and extremely rigid, so it reflects sound very well. On the opposite end of the spectrum is the foam in your seats which absorbs sound reflection. As a general rule, sound reflection reduces clarity. Perhaps most importantly, very few car audio systems offer a true Hi-Fi experience with flat frequency response. In fact, every sound system is engineered with a sound signature in mind. Objective clarity is rarely ever the goal.
Warming Things Up
Let’s go back to the concept of noise. The roar of the wind over bodywork, the rush of the road and the slap of a car’s tires often emit low-frequency noise. Let’s look at road noise specifically. The University of Auburn did some really cool noise testing of various paved surfaces and published this awesome graph of tire noise on open graded friction courses. Notice how road noise peaks between 400 and 800 Hz. That’s right in the meat of the low mid-range, around where keys 47 through 59 or G4 through G5 on a piano sit. As for tire noise, the Acoustical Society of America found an important number of resonant modes in the 170 to 650 Hz range. Of equal importance is a pilot coast-down test by the US Government that saw significant tire noise in the 200 to 500 Hz range, right where a vast number of guitar notes sit. Perhaps more importantly, humans are really bad at perceiving low frequencies compared to higher frequencies. Our perception of loudness starts rolling off below 1,000 Hz, or 1 kHz. To combat tire and road noise and help bring bass to life, sound engineers can slightly boost low-end frequencies. A slight boost in the low to lower midrange is called a warm sound signature and while it’s fun to listen to and masks road noise, it does impact clarity. The further low frequencies are boosted, the more they tend to blend together on most audio systems. Go really far, and you end up with a dark audio signature which is basically bass soup. A great example of this process in action is in the current Nissan Sentra’s mid-range six-speaker audio system. It’s a fairly basic system with paper-cone woofers and all the heavy lifting done by the head unit’s digital signal processing and integrated amplifier. It’s not super powerful, nor made of the highest-end materials, but Nissan’s sound engineers likely still wanted it to be punchier than the stereos in most competitors. As a result, it’s quite a warm audio system, with fairly drowned-out bass. When playing modern music with electronic production like Kanye West’s I Am A God, 808s and kick drums start blending together and there’s a definite loss in mid-range clarity. That’s before you find the little digital icon marked Bass Enhancer. Tap that and the audio system goes from warm to dark, with kick drums growing as subtle as a shovel to the back of the head. Now the kicks and 808s sound nearly one and the same, vocals feel slightly drowned and synths really have to fight to be heard. Yep, welcome to speaker distortion. Not the most fun place to be, especially with the likelihood of frying gear. Disable bass enhancement and you’re left with a stereo that’s more fun than similar six-speaker systems in the Toyota Corolla and Kia Forte, at the expense of some clarity.
Flying The V
One trick often used in audio is a colored V-shaped sound signature. What do I mean by that? Well, first let’s talk about bright sound signatures that feature slight treble boosts. When a sound signature is set up for a slight treble boost, great for bringing out detail between say, 3 kHz and 10 kHz. The sort of space where violins, cymbals, upper-range synths and higher piano keys like G7, A7 and B7 exist. Studio techs often like a bright sound signature for mixing because it readily reveals imperfections. When you pair the treble boost of a bright sound signature with the slight bass boost of a warm sound signature, you create a V-shaped sound signature that offers bright yet punchy sound. In terms of the science behind a V-shaped sound signature, it helps a great deal to look at equal-loudness curves. Each line on this chart represents the sound pressure levels that humans perceive as a constant loudness from steady-state tones. The lower the line dips, the more perceptive humans are to tones at that point on the line. As I mentioned before, human perception of loudness rolls off below 1 kHz, so boosting bass helps add some punch to music. But what about that 3 kHz to 10 kHz range? Why boost it when human perception of loudness peaks at 3 kHz? Well, it’s largely a matter of staging. In pretty much every car, the tweeters are placed in front of the driver. When sound is coming from in front of a human, it has to go around the human’s head and bounce off the outer ear, so narrow frequencies above 1 kHz or so can seem a touch faint. Punch those up, and everything sounds just that little bit crisper. Plenty of audio engineers set mass-market systems up with V-shaped sound signatures, from Beats headphones to car audio systems. Why? Because it’s the most colorful sound signature and humans like colored sound signatures. V-shaped sound signatures imbue most popular music with such a sense of fun that most people prefer their sound to that of a flat sound signature. It’s definitely not the cleanest sound out there, but a V-shaped sound signature or equalizer profile can put a little sparkle on even a slightly crappy stereo.
Welcome To The Stage
Now it’s time to get into the really fun stuff – staging. So what is staging? It’s basically the position and direction of sound in a room. Through millennia of evolution, mammals like humans have gained excellent ability at picking out what direction a sound is coming from. Well, excellent on a horizontal plane, at least. See, humans really aren’t great at approximating vertical sound positioning. In a 2003 study of auditory spatial resolution in horizontal, vertical and diagonal planes published in the Journal of the Acoustical Society of America, researchers at the Vanderbilt University Medical Center found that only 30 percent of subjects had a minimum audible angle of less than 10 degrees on a vertical plane. While this isn’t great in a survival scenario, it’s just fine in an audio staging setting. See, there isn’t significant sound missing from above us in a room, but because most cars don’t have a center driving position, it’s extremely rare for drivers to be in the sweet spot where left and right speakers are equidistant. This prevents stereo sound from having a truly immersive feel, so vehicle audio engineers are often turning to surround sound to make things sound fuller. There’s just one problem. Most songs are two-channel recordings. How the hell do you turn two audio channels into five or seven? Well, you kind of have to cheat by using signal processing to add reverb, mess with time alignment to delay sound from speakers close to the driver, implement a variety of low-pass, high-pass and bandpass filters to shuffle frequencies around to various speakers in the cabin, and run digital reconstruction to try and eke the most out of compressed audio. Is it immersive? In most cases, absolutely. The trouble is that a certain level of clarity is sacrificed over a simple two-channel or 2.1-channel (the 0.1 is a subwoofer) setup. Isolated vocals can sound distant, bass can be muddied and two rhythm guitarists can simply blend together. While some modern tracks like Chief Keef’s Faneto and SOPHIE’s Ponyboy do well in a surround sound environment, sparse tracks like Feist’s 1234 and guitar-heavy tracks like Arctic Monkeys’ Fluorescent Adolescent can seem really dampened and distant. Granted, there are a handful of cars where surround sound processing works. The on-stage mode in the Genesis GV80’s top-spec Lexicon audio system is thunderous yet still reasonably clear, while surround sound on the Lexus LS 460’s Mark Levinson system does a good job at sending kicks, 808s, synths and hi-hats to different speakers in an attempt to sound fuller without sacrificing too much in the way of clarity. However, every premium audio system I’ve tested has been crisper and cleaner with surround sound processing switched off. My all-time favorite, the Bowers & Wilkins system available in the current Volvo XC90, sounds absolutely spectacular in studio mode. The much-vaunted Gothenburg Concert Hall mode? It’s really more of a gimmick, heavy on the reverb and not particularly crisp. So now you know three techniques that automakers use to trick you into thinking that their audio systems are better than they actually are. Is it bad to enjoy any of them? Hell no! I’ve run V-shaped equalizer settings in almost every car I’ve owned, and I adore the sheer thunder of the Toyota Prius Prime’s available dark, bombastic JBL audio system. Reference environments and neutral sound signatures are great for analytical critique but as I previously said, a car isn’t a reference environment, nor is it a space typically suited for a neutral sound signature. Having a car audio system with a fun sound signature is totally cool, but it’s worth recognizing that clarity is sacrificed in the process. Now go out there, have fun, and try boosting bass and treble by just a tick or two in your daily driver to hear what a difference sound signature makes. Lead photo credit: Volvo I’m looking at you, Porsche. Your Bose systems aren’t that great but your customers pay too dollar to get out of the purgatory of your base audio equipment. I can’t … even. There are a few cars I’ve driven with Mark Levinson and Harmon Kardon stereo systems. Mostly Lexuses and Kias. And every time there are no mids. It’s all a very crushed high-end, and a deafening level of bass. Tuning the equalizer does nothing, turning off the faux staging does nothing, disabling software levelling does nothing. Listening to a nu-metal song, prog metal, or hard rock? You can’t hear the vocalist, and the guitars get smashed into noise. Listening to trance or new era drum and bass? Good luck hearing the high hats, claps, snares, and lead synths. Listening to jazz, jazz fusion, or acid jazz? All you’ll hear is the tail end of the crash cymbal in the high end, and all the woodwinds will be a wall of noise behind the brass section. Listening to old school hip-hop? Hope you hate everyone in a five mile radius of your car, because the bass is going to shatter windows and give cats and birds heart attacks.
