4ohm or 8ohm

[CalEliteCoach]

I bought a used SWR Goliath III (4x10) cab about 2 years ago. I use a SWR 750x head to run it. I would like to add another Goliath III, but I don't know if mine is 4ohm or 8ohm. Does this matter? Is there a way to tell without removing the speaker to check?

 

[dincz]

Yes, it matters. From the 750x manual:
"Important: The minimum total impedance when operating the 750x is 2.6 ohms. This means you can safely use: a) A single 8 ohm cabinet b) A single 4 ohm cabinet c) Two 8 ohm cabinets (total: 4 ohms) d) One 8 ohm cabinet and one 4 ohm cabinet (total: 2.6 ohms) ** e) Three 8 ohm cabinets (total: 2.6 ohms) ** **Running the amplifier constantly at 2.6 ohms, while technically acceptable, will cause the amp to run hotter than usual, and will cause heat-related wear on components sooner than normal."

You can measure the cab's resistance - usually around 3/4 of its impedance value - with a multimeter. An 8 ohm cab will read ~6 ohms and a 4 ohm cab ~3 ohms.

 

[CalEliteCoach]

Yes, it matters. From the 750x manual:
"Important: The minimum total impedance when operating the 750x is 2.6 ohms. This means you can safely use: a) A single 8 ohm cabinet b) A single 4 ohm cabinet c) Two 8 ohm cabinets (total: 4 ohms) d) One 8 ohm cabinet and one 4 ohm cabinet (total: 2.6 ohms) ** e) Three 8 ohm cabinets (total: 2.6 ohms) ** **Running the amplifier constantly at 2.6 ohms, while technically acceptable, will cause the amp to run hotter than usual, and will cause heat-related wear on components sooner than normal."

You can measure the cab's resistance - usually around 3/4 of its impedance value - with a multimeter. An 8 ohm cab will read ~6 ohms and a 4 ohm cab ~3 ohms.

Thank you for your reply. I'll check on it soon.