This is a great question.

First, let's take a look at what an IP rating is. An IP rating is a 2 digit number that provide a metric for both mechanical (dust) intrusion and water ingress protection. 

The challenge with IP ratings in loudspeakers is that in most cases, loudspeakers require the movement of air, and the prevention of dust particles entering a loudspeaker cabinet also would likely prevent sound from exiting the cabinet. This is why on many outdoor loudspeakers, you will see ratings like "IPX5" - the "X" meaning that the loudspeaker carries no rating for mechanical (dust) intrusion. 

The purpose of making something meet an IP rating spec is intended prevent sensitive things (like electrical equipment) that do not like water and dust, from receiving contact with significant amounts of water and fine dust.

When we studied the components that make up the DML500, we realized that much of the components are fairly impervious to water and dust - with the exception being the exciter drivers - and those are well shielded from direct water/dust intrusion due to their placement. And in the end, we did not feel that pursuing IP rating was necessary. We had run experiments for several years at venues from outdoor bars to cruise ships, using nothing more than a standard DML500, and it performed remarkably well.

For the final weatherized version, we added UV-resistant powder coating, water-resistant grille cloth, stainless steel hardware, a waterproof dust cap for one of the Speakon panel connectors, and small drain holes to allow condensation to escape - in addition to a few other minor features, and we call it the DML500W. We followed this up with a generous 4-year warranty. 

Introducing the DML500W - Weatherized version!

You can find out more about the DML500w here.