When a customer brings in PA speakers and complain of no highs, the usual suspect is the horn. Here's one such occurrence where a customer brought in a EV Eliminator. Below is how I tested the EV Eliminator High Frequency Driver. (Horn) Customer knew he had been pushing the system too hard and some unsuspected screaming from excited club goers directly in the mic coupled with the horns had quite a bit of play time on them, they just quit. This is how I determined it was defective before ordering. The important thing to remember is there are numerous situations where an ohm meter comes in handy with music gear. Learning how to use one can really save time in determining where a problem lies in your equipment.
Here's a video I did many years ago. It still holds true today. Speakers are similar but you can have a reading on a speaker and the coil can still be burnt so there's an extra step. Thankfully with diaphragms you can tell right away. Usually if you take it a part the wax/plastic coating shielding the wire coils has melted and it's easily seen when you take the diaphragm out of the magnet.
Make sure you take something like masking tape and something thin like a strong business card to wedge in to the magnet canal. You want to get all the little shavings out, dirt, anything in the little slot that the coil slides in to. A very strong vacuum will get it out usually. Put the new one in, observe polarity with the wires from the speaker cab. (it's always a good idea to mark the wires when you take them off because wires can be the same color sometimes going to the horn)
in this video I'm going to show you how to use an ohmmeter nanometer can come in very handy for musicians and a lot of different situations for instance this is a horn out of the knee the Eliminator cabinet and it's got a bad diaphragm but how do I detect that's the case here's the horn so you recognize it before i go any further horn diaphragm magnetic coming ok here's a flick-on meter and I got it set to homes right there this is an auto ranging I got a pretty low setting and right here as you read out right now that's open or infinity ohms gives you the little whore she right there make sure and you're in gear touch the leads together goes to almost zero ohms so I look at this diaphragm with the warm removed and here's your two leads all it is a coil and a magnet just like a speaker so here's your two ladies doesn't really matter about the polarity just want to see if there's continuity touch like that the meter stays open oh well there it is close contact complete the circuit of the meter but you're not doing it here and move it around make sure you got a good metal connection that tells me that you have a open diagram so you're ready you just order one you doing replace it
I would suggest buying the best one you can afford. Just like music gear, the more you spend the better in the long run. I'm partial to Fluke because like the one in the picture they are very rugged and can take just about anything a demanding musician can throw at it.