What separates a good subwoofer from a bad one, aside from frequency range?

[EPC]

I'm shopping around for a sub and there is a huge range in price but not much on what the real difference is...
I know Genelec have a special porting system and JBL have port stuff going on, but the rest seems pretty standard.
And advice?

 

[Katji]

Major influence on price is the cost of the driver and then the cost of the [integrated] amplifier [and DSP.]

 

[escape2]

You did not mention if the sub is going to be for movies/home theater or for music. For music only, you may be better off with a sealed sub, in which case the whole "port stuff" doesn't apply.

Having a good/powerful amp is important to better control the driver.

Some companies have their own tricks such as direct servo from Rythmik that claims to better control driver movement.

DSP technologies, as @Katji mentioned, also help achieve a smoother frequency response.

If this is for music duty, some subs also have built-in high pass filters to remove low frequencies from your main L/R speakers.

 

[Jdunk54nl]

Low frequency extension, cabinet resonances, power handling, amp size, looks, dsp and software for that.

All get better with price increase, obviously diminishing returns, which seem to be about the $600-$1000 range. After that you aren’t getting a whole lot more.

 

[Bombadil]

JL Audio Fathoms are expensive, but if you don't have room eq from other sources, the 18 band equalizer in the Fathoms will take care of the most important part of room correction (the lower frequencies). They also have balanced inputs/outputs which for me have eliminated hums that were present with RCA cables. Their amplifiers are exceptionally powerful and build quality is superb. I've owned many brands and I wish I had just started with Fathoms, would have saved a lot of $.