Blog Forums DIY Speakers and Subwoofers Argh!!! Choosing Drivers Reply To: RE: Argh!!! Choosing Drivers

#12699
tvor-ceasar
Moderator

This is a highly personalized part of the hobby. Some want to only look at the highest of the high end, some are open to the mid priced stuff, some look to find a real bargain or diamond in the rough, and others are looking to see if they can at least make costume jewelry out of canine feces.

There are a couple of ways to go, but really, you should start with assessing the equipment you will be hooking the speakers to (amp power/ohm capability), the room size (LxW) or nearfield / desktop use, and overall general acceptable size of the speaker for it’s intended placement, so you can get a rough idea of internal volume you have to work with. 

Obviously, the amp’s power needs to be considered when choosing a driver. Too low of a driver power rating and you run the risk of frying the voice coil. So keep that in mind, and especially for the lower frequency drivers.

The bigger the room, the more SPL you’ll need to fill it, so higher sensitivity or higher power handling. Nearfield and desktop don’t generally need as much power or sensitivity.

Overall maximum size will be important when doing rough calcs to see if a bass or midbass driver will be able to be used in that box. Try to stay a bit flexible here.

Now that you have a few key parameters, you can go to a site like Parts Express and dial them in to narrow the search. Remember to give yourself a range to look for, otherwise you might miss that one driver that would possibly be “the one.”

For me, I end up with several QBasic windows open and my old programs running to help narrow down the choices. The absolute minimum you need for both sealed and ported is Fo/Fs, Qts, and Vas. Transmission Line uses Driver Diameter (equivalent if not a round driver) and Fo/Fs. I can run a calc in less than 10 seconds to see if it’s worth considering. Then I can download the full info and files for something like WinISD to run a better analysis.

For crossover info, you’ll need to look at the resonant frequency of the driver that will be the next in line (up frequency), double it, and see if the driver below it will work with it.

So say you have a woofer that goes from 30-2000Hz, a mid-range that goes from 800-6000Hz, and a tweeter that goes from 2400-22000Hz.

As you can see, 800×2=1600Hz. This “fits” within the 2000Hz limit, but you may want to consider a mid-range that goes a little lower to better fit the overlap. Now the tweeter at 2400×2=4800Hz, so you are fairly good there, but may still consider a tweeter with a slightly lower Fs. Ultimately, you’d need to chase down the graphs, FRD and ZMA files to put in a XOver software, just to make sure, but this will give you a starting point.

Don’t forget to keep an eye on the SPL ratings. They are easiest to compare when they are of the same impedance and designation, like 1W/1M or 2.83V/1M. If you have questions about this, please ask. I’ve gone over it a few times, but I don’t mind doing so again. Mixing differing impedances makes it harder to easily match levels and tends to make the XOver design more complicated, though it can be done. 

The more you do it, the better you’ll become. And maybe, just maybe, you’ll find that jewell you never knew you were looking for.


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