Home Theater Hacks

Hack #49. Choose the Right Subwoofer

Buying a subwoofer involves a lot of knowledge about enclosures, wattage, and drivers: get the scoop on all of these in this hack.

So, now that you've got the basics of subwoofers [Hack #48] in your head, there is still an important question to answer: "What should I buy?" This hack will give you some insight on what to look for; sometimes it's more than just raw power or how cool the enclosure looks.

Displacement

When it comes to high-output subs, there simply is no replacement for displacement. What is meant by displacement? Displacement is the volume of air the driver can displace. Take the effective radiating surface of the driver (usually abbreviated in driver specs as Sd) and multiply it by the distance the driver can linearly move its cone (usually listed as the driver's Xmax). This determines the volume of a cylinder that will be mapped out by the cone's full range of motion. This is the Vd, or volume displacement, of a driver. The higher the volume of air that the driver can displace, the better.

Table 6-1 supplies the approximate Sd values of the most common subwoofer driver sizes.

Table 6-1. Sd based on driver size

Driver Size (inches)	Sd (square centimeters)
8	225
10	325
12	475
15	775
18	1,150

As you can see, a 10-inch driver would have to move more than three times as far as an 18-inch driver to displace the same amount of air. Generally, bigger drivers can move more air. However, if the smaller driver can move more ...