Impedance question for Kustom Defender amp

Marshall

I have an old Kustom Defender 112 50w combo which has its factory 16ohm 50w speaker currently installed. The amp also has an impedance switch next to the 2 speaker out jacks, one of which is connected to the internal speaker. 

Having just picked up a secondhand 12” 25w 8ohm speaker but currently no amp/cab apart from the Kustom that provides a switched impedance speaker out, I am considering temporarily plugging in the new 8ohm speaker into the Kustom’s speaker out, switching the impedance selector to 8ohm and unplugging the Kustom internal 16ohm speaker while I test the secondhand speaker is functioning properly. 

I’m a tad concerned about doing this however as the Kustom user guide states the following regarding the impedance/speaker arrangement:

Impedance Selector: This switch is used to select the appropriate impedance, and is important in achieving the desired results from The Defender. The correct impedance should be selected using the Impedance Selector Switch as follows:

a. Internal speaker only: 16 ohm setting

b. Internal speaker + external 16 ohm speaker: 8 ohm setting

c. Internal speaker + external 8 ohm speaker: 4 ohm setting, although it’s not matched.

Based on this, there’s no scenario to run the amp with the internal speaker disconnected or running an 8ohm speaker by itself out of the speaker out jack.

Any advice would be most appreciated from you amp techs/wizards out there

ICBM

Just set the amp to 4 or 8 ohms and plug in the external cabinet along with the internal one, it will be fine. Impedance matching is far less critical than popular belief, and not really important at all unless the amp is cranked right up.

Marshall

ICBM said:

Just set the amp to 4 or 8 ohms and plug in the external cabinet along with the internal one, it will be fine. Impedance matching is far less critical than popular belief, and not really important at all unless the amp is cranked right up.

 many thanks @ICBM ;