Speaker with built in attenuator

[mayfly]

Check this out from Eminence.  A speaker with a knob on the back that you use to turn it down:

http://www.eminence.com/speakers/speaker-detail/?model=Reignmaker

From what I understand - it's simply mechanical.  Turning the knob moves the magnet in and out of the voice coil, thus changing the flux density - and therefor efficiency - of the speaker.  All this without changing the voice coil or introducing attenuators or the like.

That's pretty nifty IMHO.

 

[Cagey]

They've been around for a year or two now. Haven't heard one in real life yet, but there are a lot of demos on YouTube. Of course, you can't appreciate what they're doing because of all the compression, but it's interesting that they don't change tone much when they are attenuated.

 

[Super Turbo Deluxe Custom]

I'm curious, for you engineer types, would using an electromagnet in the speaker to strengthen or weaken the magnetic field be feasible?  Other than being absurdly expensive, prone to failure, unnecessarily heavy, possible electrical interference, and just plain silly, I can't think of any drawbacks.
:icon_jokercolor:

 

[Cagey]

Yeah, it would work, and it's been done. It just means adding a power supply to generate the DC needed. One company that does it is called "Fluxtone". Not sure if anyone else does it.