How to test a loudspeaker drive head unit

It’s simple to test a drive head unit with a multi-meter or using a 9 volt ‘PP3’ (also known by the code 6LR61) battery.

To test using a multi-meter

Picture showing different types of multi-meter
  • Turn the multi-meter on and set to Continuity/Diode test
  • Briefly touch the two test probes together – you should hear a continuous beep
  • Next disconnect any existing wires from the drive head terminals / connector block and move them aside.
  • Now touch the red probe of the multi-meter to one terminal/wire of the loudspeaker drive head and the black probe to the other terminal/wire. If you hear the same continuous beep there is a complete circuit in the drive head unit, so there’s a good chance it will work.
  • Next set the multi-meter to resistance (Ω) and touch the red and black probes to the same points. A good drive head will have a resistance of between 12Ω and 16Ω.

After testing, reconnect the wires you disconnected earlier.

To test using a 9V battery

Image of a 9 volt PP3, 6LR61 or MN1604 battery

To do this test you need a known-good PP3/6LR61/MN1604 9 volt battery and two short lengths of wire with the insulator stripped back approximately 10mm at each end.

  • Disconnect any existing wires from the loudspeaker drive head terminals / connector block and move aside.
  • Connect one of the short lengths of wire to each of the terminals / connector block of the drive head unit
  • Briefly touch the other end of these wires to the terminals on the battery. A good loudspeaker drive unit will be heard crackling.

After testing, reconnect the wires you removed earlier.

If the drive head appears to be working, trace the wiring back inside the van and repeat the above tests, which will tell you if the wiring is also good.

If the drive head unit failed any of the tests it should be replaced with a new loudspeaker drive head. Unscrew the old head from the end of the horn in an anti-clockwise direction. It may be very tight! If it is seized, seek assistance.

Before fitting a replacement drive head unit, wipe the thread inside the top of the horn with a clean rag to remove any gunge or other debris, then smear a thin film of grease (you can use Petrolgel for this) onto the threads of the horn and new drive head to aid reassembly.