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212 HD 130 Speaker impedance switch

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John O'Donnell (john)
Username: john

Registered: 01-2008
Posted on Friday, January 11, 2008 - 08:23 pm:   

On the rear panel of a Music Man 212HD 130 there are two speaker jacks, the panel reads that these are connected in series. There is also a switch for speaker impedance with a 4 ohm and 8 ohm setting.
I am reasoning that the two speakers contained in this unit are 8 ohms each and they appear to be wired parallel. Thus the load of the two speakers is 4 ohms. Therefore, with the internal speakers plugged in, I keep the impedance switch in the 4 ohm position. Is this correct? Also I assume that since the panel says the jacks are connected in series that if I chose to add an external speaker cabinet I should chose one with a 4ohm load. I would plug the external cabinet into the 2nd speaker jack and keep the internal speakers plugged in. Than I would have two 4 ohm loads in series for a total of 8 ohms. Thus I would switch the speaker impedance to 8 ohms. Is this correct?
Giorgio (Italy) (giorgio)
Username: giorgio

Registered: 07-2007
Posted on Saturday, January 12, 2008 - 02:50 am:   

If the total impedance of internal speakers is 4 Ohm and the external speakers impedance is 4 Ohms, yes you're right, you've got to sum their impedances.