Click here to purchase the entire book in PDF format. Disadvantages There's a big hunk of metal (the voice coil) that you're trying to move back and forth. In this case, inertia is not your friend. The more energy you want to emit (you'll need lots in low frequencies) the bigger the coil - the bigger the heavier - the heavier, the harder to move quickly - the harder to move quickly, the more difficult it is to produce high frequencies. The moral: a driver (single coil and diaphragm without an enclosure) can't effectively produce all frequencies for you. It has to be optimized for a specific frequency range. They're heavy because strong permanent magnets weigh a lot. This is especially bad if you're part of a road crew for a rock band. They have funny-looking impedance curves - but we'll talk about that later.