Drivers frequency range

[qguy]

What makes 12 inch sub able to do 20 hz ? I reckon size is not a factor as a some 10 inch (or even 8 ???) can do 20hz too. What limits a similar size 12 inch woofer to say 35 hz ? is it the cone material ? surround ? spider ? coil ? magnet size /weight ?

[just a guy]

Any driver can do 20 hz, even the tiniest tweeter - they just won't be able to do it loud.

Drivers used for low frequency reproduction are chosen based on how they will be used. For example, when used in infinite baffle, large xmax and qts of .5 - .9 is most desireable (unless you plan to use extensive eq). OTOH, a horn sub (which will be huge if tuned to 20 hz) does not require either of these things per se. It all depends on the application.

[Rademakers]

Size is a factor to some extend. To get a respectable level at 20 Hz you want a large volume displacement (Xmax x Sd). A 10" will have to move 4 times as much as a 18" for the same Vd.

In general design you also want to have a low Fs (free air resonance), preferable at or below the lowest frequency you want to reproduce. You can have a 18" with a Fs of 50 Hz and a 12" with an Fs of 18 Hz, so size doesn't have to say anything, it's in the T/S-parameters. Only really small drivers will have trouble getting a low Fs because of their size.

In horn loaded applications you can get a driver to reproduce safely below it's Fs, because of the air load in the horn. IOn certain tapped horns you can even get away with a Fs, one octave above the lowest frequency to be reproduced.

The lower the Qts, the higher the response will start to drop down towards the fs. A highish Qts driver will have an easier time going flat down towards it's fs.

Regards Johan

[qguy]

what determines a drivers Fs ?

[GM]

Its moving mass and compliance:

Fs = [(1/Pi)/2]*{[1000/(Mms*Cms)]^0.5}

where:

Mms is in grams and Cms is in mm/N

GM