Basic Measurement for Better Bass
In order to get the transition between your subwoofer and your main speakers close to perfect, you need measurement gear. Measurement makes your sub setup faster and more accurate. Instead of listening to bass lines to gauge the evenness of your bass response, you just run a quick measurement and get a precise result.
The process is simple. Use audio-spectrum-analyzer software that runs on your computer or smartphone. Set up a test microphone (or hold your smartphone) in your listening position. Play the appropriate test tone and you'll see the level of each frequency of sound onscreen.
The idea is to get each bass frequency at roughly the same level. Run the test, then adjust your subwoofer position, crossover frequency, etc., and then run the test again. Repeat until you get the flattest response.
Since I last wrote about audio measurement, I've been evaluating some analyzers that weren't in the original article. One is Room EQ Wizard, a Windows PC application available free from hometheatershack.com. REW combines several functions, including a sweep analyzer that measures your system response with a swept bass tone. You'll need a microphone to use with it; you can use the popular Behringer ECM-8000 with a USB mike pre, or connect the output jack of an SPL meter straight into your computer.
You can also get spectrum-analysis apps for your smartphone. To measure subs, you need an app with at least 1/6th-octave resolution. For the iPhone, there's Studio Six Digital's AudioTools, while my favorite Android apps are AudioTool ($6.50) and RTA Pro ($5.68). AudioTool is more versatile; it includes a signal generator. With RTA Pro, you'll have to play pink noise through your system to run a measurement. If you don't have pink noise on a test disc somewhere, it (along with other tones) is available free at brentbutterworth.com/tech.