The rear port on a bass reflex speaker design is there to increase the bass response of the speaker. These ports are usually tuned to a frequency that compliments the overall tonality of the speaker.
Simple Changes that Increase Bass
Ideally a rear ported speaker should be at least 1 to 2 inches off the wall. Speakers create sound by moving air. The port on the speaker creates sound in the same way as when you blow in to an empty or partially empty bottle. If the speaker is against the wall or the back of a bookshelf, then you're keeping the air from coming out, as well as the sound. Blocking the port will also add additional air pressure against the inside of the cabinet,changing the way the main driver will sound. Not good.
Experiment with Speaker Placement for Optimum Bass
As we mentioned, keeping the speaker away from the wall will change the sound. Moving it different distances from the wall will also change the sound. Play with it until you get the sound that works best for you. It is also recommended that:
- Each speaker is at an equal distance form the wall
- The wall is material is the same for each speaker
- The speakers are at the same height
Corner placement of a speaker can have undesirable consequences and is best avoided if possible. If you must put a speaker in a corner be sure to play with the placement till you get an acceptable sound.