Just got a Whirlwind and was set to order this upgrade, but the inductors are out of stock. Thing is, Amazon is almost out of stock on the speakers... I can guess what will happen if I wait for the inductors to come back in :/ Is there another inductor that would work?

Also, anyone have any insight on using this for a System 9? I've read that Space Shuttle benefits from a boost visa other means, but I like the elegance of this system. Thing is, that era machine only uses one oval speaker in the backbox, and I'm not sure how the onboard amp is spec'd... I can research this later, but figured I would ask if anyone already "knows" one way or another?

OK, just for reference, after a bit of reading, if I understand correctly a quick & dirty rule of thumb would be a lower inductance (mh) value raises the crossover frequency; a higher value lowers the frequency. Which is what I suspected, but confirmation is always good.

According to the chart I found here:

http://www.apicsllc.com/apics/Misc/filter1.html

For the 8ohm Pyramid woofer, a 8mh inductor value yields a 159Hz crossover. Going to 7mh yields 182Hz; going to 9mh yields 141Hz.

My personal preference is not to drown out the backbox speakers as some have reported, so I went with the 7mh value to pass some of the higher frequencies, though overall it sounds like it should still be heavily low-end focused. Guess I'll find out soon enough...!

In general, changing nothing else, you want to match the size (cone diameter and/or mounting flange, for fit), and the impedance rating (in ohms). The impedance is important as that will match the rest of the circuitry - deviating too much can cause poor sound or even damage other components. Usually the impedance is marked on the speaker and easily identified. So just pick a speaker of the right size with a matching ohm value (usually either 8, 6, or 4 ohms), and that's that for a quick safe swap (make sure to keep the + and - terminals correct).

Of course there "can" be other considerations: speakers are also spec'd by efficiency, freq response, power, etc... things get more complicated when you pursue the rabbit hole of "better sound" or even "best theoretically possible replacement"... but if you just want to fix a rattling rip, stick with size and impedance, any new decent speaker shouldn't be much worse than what was there originally.

In general, watts is the rating of power that a speaker can handle. If the original rating is known, try to match if you can. A higher rating is OK... Compared to a lower rating which might get blown out by the original circuitry (amplifier).