Cabinet Testing

• 1). Remove the back plate of the guitar cabinet with the screwdriver to reveal the internal speakers and wiring. Remove the input jack from the back plate with the crescent wrench, if necessary, to avoid damaging the cabinet's wiring.
  
  
• 2). Test the cabinet's impedance with the multimeter. Set the multimeter to its lowest resistance reading mode, and place one test lead onto the input jack's tip lug and the other lead onto the input jack's sleeve lug. The meter's reading indicates the cabinet's impedance, which typically is between 4 and 16 ohms.
  
  
• 3). Remove the internal wiring by either unclipping the leads from the speakers or unsoldering the leads with a low-wattage soldering iron and electrical solder.
  
  
• 4). Test each speaker's individual resistance with the multimeter. Record each speaker's resistance with a marker on the the back of each speaker.
  
  

Rewiring a Four-speaker Cabinet

• 1). Connect the positive lug with the negative lug of one pair of speakers with the low-wattage soldering iron, electrical solder, wire strippers, wire clippers and heavy-gauge hookup wire. Repeat the connection for the remaining two speakers. This creates two pairs of speakers that are wired in series.
  
  
• 2). Connect the tip lug from the input jack to both open positive lugs on two speakers. This connects the two series pairs of speakers in parallel.
  
  
• 3). Connect the input jack's sleeve lug to the remaining open negative lugs on two speakers. This completes the parallel connection of both pairs of series speakers.
  
  
• 4). Measure the cabinet's impedance with the multimeter at the input jack's tip and sleeve lugs. A series/parallel connection creates an impedance that matches each speaker. Two speakers connected in series adds their resistances together, and the two pairs connected in parallel divide these resistances. For example: Four 8-ohm speakers connect in series, creating two pairs of 16-ohm speakers, which are then divided by their parallel connection, resulting in a guitar cab with an impedance of 8 ohms.
  
  
• 5). Repeat the steps for a cabinet wired in series by connecting the input jack's tip lug to one speaker's positive lug. Connect that speaker's negative lug to the next available positive lug. Repeat until all four speakers are connected in series. Connect the last speaker's negative lug to the input jack's sleeve lug. Test with the multimeter. In this arrangement, each speaker's resistance is added. If all four speakers are rated at 8 ohms, a series connection results in a 32-ohm cabinet.
  
  
• 6). Repeat the steps for a cabinet wired in parallel by connecting the input jack's tip lug to the positive lugs on each speaker. Connect the input jack's sleeve lug to each speaker's negative lug. In this arrangement, each speaker's resistance is divided by the number of speakers. If all four speakers are rated at 8 ohms, this results in a 2-ohm cabinet.