How do I?

 

Diagnose a problem with a passive speaker cabinet.

 

So, for some reason, your PA speaker suddenly doesn’t sound right. Before you start spending money on solving a problem, it’s imperative that you identify exactly what the problem is. Countless people have come to us over the years ready to buy an expensive replacement part that they thought they needed only to find, on investigation, that the problem lay in a completely different area.

 

In a typical full-range speaker enclosure, there are three main components; the low-frequency driver, the high-frequency driver and the crossover network, which is a circuit board whose job it is to direct the correct frequencies to the correct driver.

 

If the speaker sounds ‘woolly’: dull, with no high frequencies - as if you’re speaking with your hand covering your mouth, you’ve probably blown the high-frequency driver. If it sounds ‘tinny’: no bass to the sound, then you’ve probably blown the low frequency driver. But it’s very important to confirm the diagnosis as other factors could cause these problems.

 

You’ll need…

                            A fresh 9-volt battery,                                                     A battery clip.

 

                                                                       

 

 

 

 

 

 

 

 

…and a short cable with the relevant speaker connector on one end with the other end stripped.

 

 

 

 

 

 

 

 

 

 

The principle here is that a 9-volt battery sends a typical voltage to a cabinet or driver which causes it to make a clicking sound; so it’s an easy way to check what’s working and what isn’t. Just because a driver is working, it doesn’t necessarily mean it’s working properly, but it’s a good starting point.

 

Firstly let’s see which drivers are working in the cabinet.

 

Connect your bare-ended speaker cable to the speaker input and repeatedly touch the battery terminals to the red & black wires on the bare end of the cable – you can hold the black wire in place permanently and just ‘make’ the circuit with the red…and it’s good to connect red to the positive battery terminal and black to the negative, observing the correct ‘polarity’.

 

What can you hear? If you put your ear to each driver, you should be able to tell which ones are reacting to the battery voltage and which ones aren’t. If all drivers are making a clicking sound then your problem is unlikely to be with the speaker cabinet so you need to look elsewhere in your system. If one or more of the drivers is silent, then it’s time to investigate further.

 

You now need to get access to the actual drivers in the speaker enclosure so you have to work out how to take it apart. The method for this varies from model to model but is usually quite obvious. Important: make a note of any connections that you have to remove so that they go back together correctly. Snap a picture with your phone if it’s easier.

 

Once you have the suspect driver out of the cabinet, or simply have access to its connection terminals touch the battery terminals to the positive and negative connections of the driver – use the battery clip if you need to. If the driver is silent then you’ve found the problem so congratulations!

 

Low-frequency drivers usually have to be replaced completely, although some can be re-coned by the manufacturer, and Peavey Black Widow and Scorpion drivers have field-replaceable ‘baskets’ which are easily fitted. Don’t bother replacing a speaker with anything other than the recommended one – it’s a waste of time and money.

 

High-frequency drivers have ‘diaphragms’ that can be replaced quite easily. These vary from driver to driver but it’s imperative that they get replaced with the correct part. Many diaphragms look the same and will even appear to fit OK but they will break really quickly and you will have wasted your money.

 

If all drivers appear to be working but the original fault is still there then the problem is with the crossover circuitry. This will need to be repaired by a service engineer. It’s not likely to be a ridiculously expensive repair but ask for an estimate before proceeding just in case.