Alesis M1Active MKII User Manual - Page 22

Speaker Installation PLUGGING THE PORTS TO ADJUST FOR ROOM ACOUSTICS The low frequency response of the M1 Active Mk2s can be custom tailored by plugging the ports. If the speakers must be placed less than one foot from a front wall, or if they are too close to a corner, then the bass may become exaggerated and inaccurate. The rules of thumb for these situations are as follows: a) less than 1 foot from a front wall but away from any corner: plug one port b) less than 1 foot from a front wall and a corner: plug both ports The "plug" can be wad of cloth to completely block the port(s) or a more porous material like fiberfill which will give less bass attenuation. The bass output of the M1 Active Mk2 is thus easily variable depending on in-room positioning and/or personal preference. If the M1 Active Mk2s are to be used in a system with a subwoofer, the proper blend of the two systems is critical if low-bass accuracy is to be maintained. Here again, your ear is your most important piece of test equipment. If the subwoofer (such as the Alesis Point One) or preamplifier has 80Hz high-pass filters built-in for connection to the other amplifiers, then no port plugging is necessary. The proper match will have already been taken care of electronically. In the absence of an 80Hz high-pass filter feeding the M1 Active Mk2s, you'll need to experiment with various degrees of port plugging to minimize the cancellations and nodes that can occur from bass sources placed several feet apart in a room. In practice we've found that a single port plugged with cloth is usually the best compromise. See Figure 5 below. It shows the approximate bass attenuation that can be expected with one port plugged. 24 M1 Active Reference Manual