What makes a good driver

[pipo]

Hi

There's a lot of info on the www about DIY Hifi
What makes a good driver?
They offer a lot of brands, all claiming there the best.
For example a 8" bass driver from scan-speak about $120
One from dayton $50, Is the Scan better for it's more expensive?

Whats this stuff with Qts, Qms Qes vas etc.
I know Vas has something to to with the "volume" of your cabinet, but is the V max, the ideal, or what?
What if a driver has Qts 0.38, is it better than one Qts .45?
And then what about the other Q -'s?
What if i see a design with a very expensive driver, let's say to expensive for me , what can i do to exchange this with another brand, to let it sound approximately the same?
Can some-one please explain, and get me out of my misery???

greetings
marcel
holland

 

[GRollins]

pipo,
What makes a good driver?
Whew! Ask an easier question, next time.
This could easily take up about ten threads worth of writing, but I'll try to give an overview.
As for Vas, etc. Those are the Thiele-Small parameters. Boiled down to its essence, a correctly designed T-S enclosure will give you flatter response in the smallest possible enclosure. You are free to put a driver in any sized enclose that you want, but the response will be somewhat less than optimal.
There are things that aren't covered by the T-S parameters, though, and that is where life gets interesting. Drivers distort the sound in various ways, the two most prominent being cone breakup, where the cone doesn't move as a perfect piston, and the fact that a cone has mass, which keeps it from starting to move when the signal tells it to or stopping when the signal stops.
Unfortunately, the things you do to make one of those distortions decrease tend to make the other increase. For example, if you make a cone stiffer in order to make it behave more like a perfect piston, you will increase the mass, which makes it less responsive to the signal. The cost of better drivers is due to better materials and more of them in order to try to balance conflicting needs.
Note that there are many other problems with drivers. A basket (the metal frame of a driver) can flex under load, giving rise to cast baskets on the better drivers. Another oddity that has received little attention so far is the signal to noise ratio of the driver itself. Any mechanical system makes noise, and drivers are not immune to adding small amounts of noise to the music.
Etc., etc., etc....
You can't cheat Mother Nature, but sometimes you can seduce her into giving her a bit of what you want. Like any date, you'd better take along a thick wallet if you want to show her a good time.

Grey