How the SRS1500 actually makes the SRM450 play louder.

The response graphs of the SRM450 and SRS1500 appear to be nearly identical in the lowest octaves (Drawings C1, C2 and C3). If this is so, what's the point of adding a subwoofer? The answer is, if you're only using your SRM450s at low volumes in small spaces, there's probably less need for a subwoofer. But if you're going for serious volume or even modest volume in a large space, the SRS1500 can add a lot of bass.

This is confusing until you understand the basic principle of sound power: It takes increasing amounts of energy to produce lower and lower frequencies. At test reference output, the SRM450 does have almost same low-end response as the SRS1500 subwoofer. But at very high SPLs, most of its power is required to produce bass, which eventually compromises midrange output (D).

When connected to the SRS1500, the subwoofer's crossover reduces the 450's output below 200Hz where the SRS1500 takes over (E1). The substantial savings in energy (shaded area in E2) allows the SRM450 to deliver more volume at higher frequencies. Working together, the SRM450 and SRS1500 combine to produce flat response at much higher volumes (Drawing F).