How to Use RTA to Tune/EQ A Car Stereo

Car Stereo

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My family is not American (we hail from jolly old England) but I was born and raised in the U.S. And I love America for its many wonderful and inspiring contributions to modern culture. America did not invent the car, but with the Ford Model T, we invented mass car ownership. We did not invent music, but with our unique melting pot of cultures and industrious creative spirit, we shaped modern music more than anyone else. And with our love of individual expression, freedom to blaze trails, and vast expanses of land…

Well, what I’m trying to say is, is there anything more American than blasting your music from your car? There’s even an American cultural movement, Cruising, that involves driving around aimlessly with friends, listening to music and enjoying life. (For further cultural education, watch American Graffiti, George Lucas’s pre-Star-Wars Americana masterpiece.)



Car Culture

Yes, from the AM radios of the early 20th century to the subwoofers of the present, driving to music is a classic and relatable experience that almost anyone has had. You’re going on an adventure, whether you have a specific goal or you just want to drive. You are celebrating your independence and your mobility. You’re alone or with friends or with family. You are getting in touch with yourself, or sharing your favorite places and sounds with friends. And you have your car’s sound system to thank as much as your car itself.

You can enhance this magic by making your car’s sound system sound its best. Whether you have a bougie after-market stereo and speakers, or your car’s default system, you can measure the way the sound is actually happening inside your car, and make adjustments to perfect it. It’s the audio equivalent of using Windex to clear up a smudgy window, and the best part is, you can do it with relatively inexpensive equipment and basic computer skills!

Why Calibrating a Car Stereo is Important

Sound, and the way we experience it, is very complex. After all, sound is really just waves of motion through an environment. The second music leaves a speaker, it starts being distorted and warped as it bounces around its environment in complicated ways. And the human mind has an equally sophisticated ability to process sound and understand it. Meaning, half the time when sound is distorted by our environment, our minds automatically make up for it and fill in the gaps.

So we can “understand” music just fine, even when it’s being created in sub-optimal and low-fidelity ways- like a poorly calibrated stereo, or tinny smart phone speakers. But just because we understand the music, doesn’t mean it’s satisfying. That’s why people spend so much time and money trying to perfect audiophile-level home stereos, or going to concerts and festivals and clubs. We know that nothing compares with flawlessly-executed music. Nothing feels as good as your favorite song, with all the movement and detail and feeling, gripping your soul!

The human ear can understand sounds of frequencies ranging from 20 Hz to 20,000 Hz. Low-frequency sounds are rumbling movement and high-frequencies are delicate details. And great music usually involves sounds across the frequency spectrum, layered together. So, tuning your car’s sound system means you are using your stereo’s equalizer to balance those frequencies against each other. Well-balanced frequencies translates to powerful, clear music, that sounds as close as possible to the artist’s original intention.

Tuning Your Car Stereo

RTA stands for real-time analyzer. Using a microphone and RTA, you will measure how sound is actually being experienced in your car, and compare it to an ideally balanced frequency spectrum. By adjusting your stereo’s equalizer settings, you can bring the stereo closer to a truly ideal sound, compensating for the imperfections in your car’s physical environment.

Gear

Perhaps the most important piece of gear is your reference mic, which is designed for exactly this purpose. Essentially, the mic will act like robot-you, sitting approximately where your head would be in your car, and measuring what you are really hearing. Try the Dayton Audio UMM-6 which is reasonably priced and connects to your laptop via USB for simplicity. While it’s significantly pricier, AudioControl offers a unique alternative in the SA-4100i which uses a lightning cable to connect directly to an iPhone or iPad, bypassing the need for a computer at all.

You will need software like the popular and free REW (Room Equalizer Wizard) if you are using a laptop, or an app like the creatively-named RTA for iOS devices. I would warn you that REW is a bit intimidating, but there are loads of guides online to help you navigate it.

You will also need to play pink noise over your car’s speakers. Pink noise is similar to white noise; they both sound like static to the untrained ear. If you want the technical definitions, white noise has equal energy at every point of the frequency spectrum, and pink noise has higher energy at lower frequencies, lower energy at higher frequencies. This more closely matches the way your ear actually experiences sound. You can download a pink noise file to play on your computer or phone, or you can buy CDs such as this or this to play pink noise.

Some people recommend using a mic stand to hold the mic about 26” above the seat, approximately where your ears would be in the driver’s seat. Other people simply wedged the reference mic in the space between the seat and headrest. Honestly, I’d probably end up doing this myself.

Method

Recommendations vary slightly, but the basic principle is the same. You will be playing pink noise over your car’s sound system, with the reference mic in position. You will monitor the RTA, probably from the back seat so as not to interfere too much. Then you will adjust your stereo’s EQ settings and check again.

Essentially, you want your RTA reading to be smooth. It doesn’t necessarily have to be completely flat, although you might try that and see how it translates to your listening experience. Many people talk about creating RTA readings that match personal preferences such as “warm” and “mellow.” But you will be looking for anomalies in your graph, such as sudden dips or jumps between bars. These are your problem areas that you want to smooth out.

How Deep Do You Go

Some guides recommend just keeping the reference mic in the listening position and testing all speakers at once. Others recommend testing the speakers individually first, and then playing them all together. Some guides even recommend testing your speakers’ tweeters and woofers separately (woofers play low frequencies and tweeters play high frequencies. They meet somewhere in the middle and overlap.)

This all depends on how precise you want to get with your adjustment. It also depends on the capabilities of your stereo. For instance, my own car actually has a very basic factory stereo, and the equalizer only has three bands- bass, mid, and treble. There’s barely any point in tuning a stereo like this, as only very broad changes to the overall tone can be made. But other car stereos have closer to a dozen EQ bands, and much more meaningful adjustments can be made. If you feel like you want to get more technical than this guide allows, some basic googling will lead you to more in-depth guides. But I’ll keep things introductory here.

Fixing Problems

Suppose you are testing your speakers, and you notice that in the lower frequencies, one of your RTA bars is at a significant dip compared to the others surrounding it. This is called a null, and it occurs for physics-related reasons. It means some low-frequency wave is reflecting and canceling itself out. If you were in a music studio or tuning a nice home stereo, I would recommend making a change to your room in order to address this null. But that is not usually an option in cars. Instead, you will have to accept the null, and adjust the rest of your equalizer to flatter it. You will not be able to raise that EQ band to change your RTA reading, because the sound is canceling itself in physical space. But you can lower the surrounding EQ bars to more closely match.

In general, you should lower EQ bars instead of raising. Raising the gain of EQ bars runs the risk of introducing distortion into your system. This is not dangerous or anything, it just doesn’t sound great. If you do want to raise an EQ bar, try not to do it by more than about 3dB.

Conclusion

If you follow these steps successfully, you should notice an appreciable difference in the way music feels in your car. The equipment is pretty minimal, and you don’t have to get extremely technical to make a big difference! Now you’re ready to spin a really deep groove like Green Onions and cruise down the boulevard in style. Trust me, a track like this sounds so rich on a good system, there’s nothing like it. Enjoy!