"Fast" and "slow" bass. Know what they mean?

[Looneybomber]

This is a very simplistic explaination. And a video at the bottom...

Everyone's heard these words thrown around and we've all heard subs that sounded fast or slow, and know that we don't want "slow" subs. So what is this fast bass and how do I get it?

Fast or slow are just laymans words for describing transient response.Transient response is time based metric, so to speak, used to tell us how fast a speaker can respond to transitions. But here is what people don't know, transient reponse is frequency response. Here's why...

- If a subwoofer could only play to 50hz (cycles per second) due to it's inherent limitations, the fastest it could react to a transient would be 1/50th of a second. - If a subwoofer could play to 200hz, it could react to a transient in 1/200th of a second.

Makese sense? No? Ok, I'll break it down some more.If a speaker can only play up to 50hz, then it can only move back and forth 50 times/second and no faster. That means it can't react to a transient any faster than 1/50th of a second.

Q. So how do I get fast bass?A. Get a (sub)woofer that can play up into the triple digits; 150hz minimum, but ideally something flat to 250-300hz would be real nice. The key word here is FLAT, because no speaker just stops playing at a certain frequency, it instead tapers off, playing softer...which is useless.

Things that effect a speaker's frequency response are...- It's motor strength (might not be strong enough to move it fast enough)- Moving mass, (more weight = less speed. Duh)- Compliance, - and Inductance. Sure there are other things, but what I really want to touch on is inductance.

A 1st order high pass filter, is an inline capacitor.A 1st order low pass filter, is an inline inductor.

Crossover designers add inductors to prevent high notes from being played by a speaker driver. The size of the inductor and the impedence (ohms) of a speaker driver, determine where the low pass filter becomes effective.

If a subwoofer has a lot of inductance, it will function as an inline inductor, causing the higher notes to be filtered out. If the inductance is high enough and the driver's impedence (ohms) low enough, it will begin filtering as low as 55-65hz, as is the case with many SPL drivers.

Things that increase inductance...- Copper voice coil winding vs Aluminum winding- The more wire used in the voice coil- The material of the pole piece, motor structure, and other things.

Things that reduce inductance...- Shorting rings and sleeves.- The opposit of what's listed above

How to spot this inductance?Look at the Thiele/Small Parameters (TSP)T/S Parameters:FS: 29.0HzQts: 0.22Vas: 390LZ: 8ohmLe: 0.41 mH1WSPL: 98.2dBPe: 1000W continuos

This speaker, with its very low inductance (.41mH) and it's higher impedance (8 ohms) will not be effected until well past 500hz. If it was say, 2 ohms, to have the same ratio of inductance to resistance, it would then need only 0.10mH. So that's another thing to look out for. Sometime

Where subs run into problems is where there's a 4:1 ratio of ohms to mH's or lower. 2:1 is real problematic.

So how do I get a "Fast" sub?- Get one with more than a 4:1 ratio of resistance (ohms) to inductance (mH)- Get one with a strong motor (high BL)- Get one with light moving mass (mms)- Set your crossover high enough so that your quality speaker can sound "fast"

Check out this Youtube video (download original if you can)http://www.youtube.com/watch?v=dUt39wOnRdA

- If you're using a home receiver like I am, set your subwoofer XO to 40 or 50hz (whatever is it's lowest).- Play video- Set XO to 150hz- Repeat video

http://www.youtube.com/watch?v=R6vVv41hSFYI need a better camera and mic to do this. But you can see the 2nd time I play the song (at 150hz XO) the woofer cone is more blurry and the mic distorts a lot more. While it's not impressive in this video, that 15" sure hits it hard.

If you have a quality sub, you will notice the 2nd time you play it with the higher crossover point, it will sound "faster" and hit you "harder". This shows that fast bass is all about transient response which is the same as frequency response.*note* if you didn't hear a difference, you may need to upgrade your sub.
Modified by Looneybomber at 1:57 PM 6/9/2009