Monitor speakers - grilles?

[musicman691]

Just ordered a pair of JBL LSR308's from B&H (currently priced at $149 which is $100 off per unit). These are replacing the Yamaha MSP5's I've had for ages and am passing down to my wife for our (actually hers) Mac Mini replacing a pair of mini Bose speakers. She asked me a question I couldn't quite answer and that was: 'I get why studio monitors don't have grille cloth as who needs them to look pretty in a studio but the Yamaha's have a metallic grille over the woofer and just about every other monitor speaker I see has none (the LSR308's for example)'.

Other than for protection on the Yamaha's is there a technical reason most monitors don't have some kind of grille over the speakers? Diffraction of the sound maybe? I could understand that for tweeters & midranges but woofers?

edit for additional:
This is not just an academic question but also a practical one aside from the 'why' part. I have a cat that likes to roam about on things and there's been many a time I've seen him (Phelps because he loves water) up on my Motif 7, the bench that I use, etc. Can't really lock him out otherwise he'll just sit at the door and meow.

[cwsand]

I think it's more an aesthetic choice and/or there for protection. The 2030's didn't originally have anything over the tweeter, until (I'm assuming) they were getting tons of returns for damage to or dents in the tweeter's foil. In my case, it happened when I was measuring the speaker height and my tape measure tapped it and dented it in. The newer ones all have a protective grille over it, thankfully!

[BScout]

Case by case basis: some speakers it is strictly protection, some it is for aesthetic reasons, some it has to do with diffraction (boundary edges, ripple effect of high frequencies.)

Whatever the case, if the speaker has a grille, it should be left on as the speaker was most likely tuned for the effects of the grille being in place. I see a lot of speakers with grilles removed by "amateur" users (being kind here) because they are trying to replicate the look of some pro control room they've seen.

As for the MP5, as a small nearfield, it looks like protection for where it'll likely be positioned (close to the user where errant movements could spell disaster.) And the tweeter also has some protection though not a grille (the boundary guard over it). Small Genelecs have the same kind of grille over the woofer but as you get bigger, they aren't there.