How low do they go?
Of the 30 here with a figure quoted, most are rated between 55Hz and 130Hz, with a median of 75Hz. 1 of them are quoted at 40Hz or below, which is roughly where a soundtrack's low effects and the bottom of a bass guitar live. Makers measure this differently, so use the figure to rank models rather than as a promise.
What do they cost?
Most sit between $299 and $1,800, with a median of $775 and a full range of $119 to $18,638. Prices are for a pair unless the listing says otherwise. These are the current asking prices we hold, not sale prices, and they move - check the retailer before deciding.
What amplifier do they need?
Sensitivity here is mostly 85.0dB to 93.0dB, median 87.0dB. 17 of the 33 that state a nominal impedance are 8 ohms. Every 3dB of sensitivity is worth as much as doubling the amplifier's power, so a sensitive speaker needs far less amplifier than an insensitive one of the same size. Read the minimum impedance as well: a nominal 8 ohm speaker that dips to 3 ohms is the harder load.
How big are they?
Most are 159mm to 379mm tall, median 219mm, and weigh 2.7kg to 11.1kg, median 4.2kg. Every listing gives height, width and depth in both inches and millimetres, so measure the space before you order rather than after.
How many do I need?
Two for a 5.1 system, four for 7.1. They go to the sides of the seats, slightly behind and a little above ear height, and the rear pair goes behind. They carry effects rather than the main soundtrack, so they can be smaller than the front three - but keeping them in the same range keeps a sound that pans from front to back sounding like one thing.