Grills ON or Grills OFF?

With my Signature S2s, I prefer to listen with the grills on. Even though the highs are ever so slightly rolled off (which, with this speaker is not necessarily a bad thing), the dispersion and the ability of the speakers to disappear is better. Plus, I like the protection factor. How do you conduct your listening sessions, and why?
IMO it depends on the speakers first; and to lesser mesurable effect, the gear driivng them.

I used to have Totem Forests and Arros (even bi-amped) .... taking the speaker grilles off was strongly preferred.

Now with a new premium integrated amp and cdp (REGA Osiris and Rega ISIS valve) married up to my new REGA R9 speakers, leaving the speaker grills on has no effect and you get the dust et al protection to boot.
Without; I could see how attenuating the high might be a benefit in some cases but I can't see how the grills could improve imaging. As to disappearing; well , with the grills you can't see the drivers so I guess you could say they "disappeared".
Grills on because I dont' want my 8 year old son to be curious about the drivers. I've never heard my speaks with the grills off.
Just about always grills off.

Infinity RS1b-off
Never heard speakers that sound better with grills on.
I once owned a pair of Krell Resolution 3s, that had stretchy "string" grills. I discovered, with the help of a spectrum analyzer, that the speakers response was flatter in my listening room with the grills on. Go figure.
When the listening session begins, the grill covers come off. When the listening session ends, the grill covers go back on. It's a habit that I've gotten myself into, just like turning equipment on and off.
I leave the grills on my Revel F-32's. I can't hear the slightest difference either way.
Magnepan grills on, as taking them off is major surgery, and then the speakers look really ugly. So grills on for me.
(When I have had speakers with removable grills, it was always grills off.)
Off why would you want them on muffle the sound!!
Off, since the speaker makers do all their testing and design that way.
Grills are one of the greatest banes of the audio industry. Case in point, I heard the Goldenear Triton speaker recently, what a disapppointment; the plastic grill and grill cloth are major impediments to performance. Just terrible decision in terms of sonics. It was one of the reasons I chose to not review it. I can hardly imagine a worse decision in terms of sound than to put plastic framework and fabric over drivers.

I have never heard a speaker sound superior with a grill on. If it does, then you have a problem elsewhere in your rig that you are masking with the grill, imo.

It's gotten to the point where speakers like Vandersteen I now consider significantly compromised due to the grill material messing with the wave coming off the drivers. :(
I think Paradigm makes thier speakers to sound best with grills on.My Studio 100s v.2 used to sound best with grills on.I would say ,what sounds best to you is correct.
Depends upon the speakers.
I have owned three speakers that would either require major surgery to remove the grills or were designed to be listened with the grill in place. The Mirage M760 were designed to be listened to with the grill on. Same for the rest of that series. The Mirage M5si grill sock could probably be removed but they probably wouldn't look so hot with it removed. Same is true for the rest of the M and Msi series. The Intuitive Design Summits are voiced with the grills in place and are purposely very difficult to remove. In general, I prefer to listen with the grills off. But as Onhwy61 states, it depends on the speakers.
It really depends on the speakers. When I had Dyn original C1's the soundstage really collapsed with the grills on. When I upgraded to the C1 Signature the soundstage doesn't collapse but if you 'squint' you can hear the highs get ever so slightly roll off. Me personally I like the grills off more for looks. OTOH when my grandkids come over the grills are ON.
My current speakers are designed w/o grills. Prior to that my Dynaudios and Vienna Acoustics sounded best with the grills 'OFF'. Grills should only be used for shipping to protect the drivers from packing mishaps or young children.
I can honestly say that I don't notice any difference in SQ between grills on or grills off. But, having said that, I prefer grills off. However, I notice that i'm indifferent when using my system for movies. However, for whatever reason, when listening to music I much prefer the grills off. Just seem to enjoy the listening session more when I'm looking at the actual speakers.
What's a grill?
You know, one of those things you cook on at tailgate parties.
It depends if the grill was an after thought by the designer or if like on Vandersteens it was part of the design. It is not the shear Fabric we hear but the diffraction caused by most grill frames. Vandersteen speaakers use the grill and frames to smooth the transistion from the driver edges and the enclosure.
Without them large peaks and dips + - 6 DB can be heard and measured. If in dought call the manufacture and ask if the speakers were designed with the grills on or off. Look at the pictures of show reports and see if the manufactures showed with them or without.
My Salon's only have a grill on the lower four drivers, the mid and high frequency drivers are up high and have no grills, seems like the best of both worlds.
Grills ON. . . Grills OFF. . .Grills ON. . . Grills OFF. . .Grills ON. . . Grills OFF. . .sounds like a line of dialogue from Karate Kid Part I (the original version).
Grills are like bras. No need for them unless children are around.
Depends on the speakers. Thiel CS 2's use the grills as part of the design.
On, because with the grilles off, they're ugly. I'll gladly sacrifice that last 10th of reproductive quality so that I'm not looking at a speaker thinking, "Boy, that's ugly."
grills off when listening, grills on when the system is not on
On my new BOSE 901's I got in 2011 my speakers sound better with the grills off. You know I set back hear all these people on the forums complain about the top end and bottom end performance with these 901's made in the past.

Well, BOSE was listening because with new BOSE 901's I have NO complaints AT ALL with the top end and bottom end performance with my new 901's and my room is not small at 18 by 24 !

Looking at the speaker driver cones, the voice coil wires have a clear coat coating over them because you can see the solder they put on the voice coil wires.

Maybe they did this to get more top end and bottom end performance out of these speaker drivers in these new 901's because I have NO complaints with these new 901's !!..
It's always SOMETHING!!!
Dynaudio recommends grills off on their speakers so grills off
Grilles on when not in use. They are naked when in use.