Cab Impedance

[cwatson]

Cabs are rated at different resistances eg 2 ohm, 4 ohm, 8 ohm. Amps are rated at different output wattages for different impedance ratings. I'm still a little confused about all of this.

 

If I have two 8ohm cabs does that mean My overall impedance is 4 ohms, 8ohms or even 16 ohms?

 

Also, do you buy cabinets with a specific resistance to suit your set up i.e a manufacturer will produce different models of the same cab that can run at 4 ohms or 8 ohms etc or that are switchable. Or does the price of a cab have an effect. eg the more you pay the lower the resistance of the cab due to higher quality components etc?

 

any help will be much appreciated,

 

Chris

[Kindness]

Basic info to get you started:

 

1. Two 8-ohm cabs in parallel is a 4-ohm load. (1/8 + 1/8 = 1/x and x = 4 ohms)

 

2. Selecting the proper impedence of your cabs to suit your system is the best way to approach the situation.

 

3. Impedence does not relate to cabinet quality.

[ToeJamFootball]

 

Basic info to get you started: 1. Two 8-ohm cabs in parallel is a 4-ohm load. (1/8 + 1/8 = 1/x and x = 4 ohms) 2. Selecting the proper impedence of your cabs to suit your system is the best way to approach the situation. 3. Impedence does not relate to cabinet quality.

 

Unles your cab has an impedence of 35784Ohms. Then youd be worried.

[Craig Vecchione]

 

Cabs are rated at different resistances eg 2 ohm, 4 ohm, 8 ohm. Amps are rated at different output wattages for different impedance ratings. I'm still a little confused about all of this. If I have two 8ohm cabs does that mean My overall impedance is 4 ohms, 8ohms or even 16 ohms? Also, do you buy cabinets with a specific resistance to suit your set up i.e a manufacturer will produce different models of the same cab that can run at 4 ohms or 8 ohms etc or that are switchable. Or does the price of a cab have an effect. eg the more you pay the lower the resistance of the cab due to higher quality components etc? any help will be much appreciated, Chris

 

 

Most amps and cabinets are set up so that connecting two cabinets would result in them having a parallel circuit (rather than series). When the cabs have the same impedance, the easy calculation is to halve the impedance of the cabs....hence two 8 ohms cabs in parallel are a 4 ohm total impedance. If the impedances are different (4 and 8 for example) then use:

 

1/(1/R + 1/R + 1/R) = total impedance (Use as many R as there are cabinets)

 

 

The important issues regarding impedance:

 

For solid state amps you usually do not want the speakers to have lower impedance than the amp's rated minimum. If you do this, the current through the circuit will be too high, which will overheat the amp. Sometimes you can get away with it, sometimes the amp will shut down to protect itself, and sometimes the "magic smoke" is emitted.... Don't chance it. It is fine to run a solid state amp without a speaker load. Why would you do this? For instance, a two-channel amp where one channel isn't needed.

 

For tube amps, the impedance should be matched as closely as possible, but slightly lower impedance than minimum is not as much of a problem as with solid state amps. Never run the amp without a speaker load, as this can damage it.