The 412L came with 8 ohm speakers from the factory, most likely wired series-parallel for a cabinet impedance of 8 ohms. If you wire 16 ohms speakers the same way, the cabinet impedance will be 16 ohms. If you wire all 16 ohm speakers in parallel, the cabinet impedance will be 4 ohms. A 4 ohm cabinet would be preferable if you were going to use a single cabinet with a Beta Lead. If you want to use two cabinets, the amp needs to be happy with a 2 ohm load. A 70's Sunn Model T or Coliseum. Some Concert amps are rated for 2 ohms but many people think it is not safe.