If you love two-channel audio and want some extended bottom end but are reluctant to add a subwoofer, fear not because it can be done successfully. Unfortunately using the "by ear" method involves a lot of trial and error and in the end you are not completely sure you have the smoothest, most blended, most extended response your subwoofer / system is capable of. Using a laptop, some RTA software (e.g. TrueRTA) a quality microphone and preamp and a full spectrum pink noise test CD you can take the guess work out of the process. Total cost for software, CD, mic and mic preamp was about $200.00. Not outrageous considering the investment in your system. For proper subwoofer integration, the subwoofer you select will need the following features- Level control. Continuous phase control (0-180 degrees). Polarity / phase switch (normal / inverted). Crossover frequency control. Most subwoofers have those features. Many do not have the continuous phase adjustment. This one happens to be critical for smooth integration. I would not recommend a subwoofer without this feature. In my case I have the KEF LS50 speakers and integrated a JL Audio d110 subwoofer. Step 1) Measure your speakers without subwoofer. Put the test CD in the player and play the full spectrum pink noise track (put it on repeat). Adjust the volume to where you listen most. Put the microphone at your listening spot as close to center / ear level as possible. The top of your couch / chair is fine. The first pic below is the response of my system without subwoofer. The natural roll-off frequency (crossover) is 80Hz. This gives a good subwoofer crossover frequency starting point. Step 2) Turn on the sub with these default settings- Level control- half volume. Continuous phase - 0 degrees Polarity - inverted or 180 degrees out of phase (based on experience this is the default setting) Crossover- set at the approximate roll-off frequency of your measured system. In this case- 80 Hz. Step 3) Measure the sub at high output- With the pink noise CD playing and the RTA software running, adjust the subwoofer volume until it is high enough in level to exceed the response of the main speakers. You want it higher so you can measure the actual subwoofer roll-off / crossover frequency. Adjust the crossover control lower / or higher until the roll-off frequency matches that of your speakers. Step 4) Fine tune the sub level. Adjust the level control until it now matches or blends with that of your main speakers. I would recommend the subwoofer be no more than 2-db greater than the level of the speakers at the crossover frequency. Step 5) Fine tune the crossover at normal level. Once the sub level is matched to the speaker output, adjust the crossover slightly ONLY if there are any large peaks or valleys in the response as measured. You want to adjust the crossover slightly up and down to even out the response as flat as possible. If it isn't perfect, don't worry there is another step. Step 6) Fine tune the continuous phase control. If there are peaks/ valleys in the response, adjust the continuous phase dial and measure the response at 1/4 turn. 1/2 turn, 3/4 turn and full turn. Note the position where the response was smoothest. In my case there were still large peaks and valleys until I adjusted the continuous phase to just before the halfway point. Once you find the best position, adjust one more time up and down from your previous best and measure again. Step 7) Road test. Listen to a variety of music and see how it sounds. At this point the only recommended adjustment to make is the level control. In my case the sub was just a little too strong. Adjust the level in fine increments until the level is blended. In my case, plus 2db was perfect as shown in the second picture. The third picture shows final system response. Nearly flat down to 20Hz and measurements are true to the ear test, the system sounds deep yet proper, totally integrated and seamless. The subwoofer plays musical notes and works in perfect harmony with the main speakers with zero localization queues of the subwoofer as the source of the sound. I have tried to do this by ear with many mobile and home systems and have never achieved the level of success you can get by using the RTA software process. I'd be happy to walk anyone through the process in more detail or answer any questions.