How grills affect?

According to Joseph D'Appolito ( and i quote ): "The grille is there only for cosmetic effect and to protect the drivers from prying fingers. The perfect grille is still the Holy Grail of speaker design". The article that he stated this in shows the performance of a speaker with and without the grille on. With the grille off, the response is very flat overall and almost resembles a perfectly straight line across the band. Simply adding the grille caused an increased variation of +1 and -3 dB's. That's a variance of 4 dB's total and a graph that looks choppy as can be above 1.5 Khz.

With that in mind, I have yet to see a grille that didn't:

1) create upper midrange / high frequency irregularities. This is due to what is known as "diffraction" and "nearfield reflections".

2) soften and slow high frequency transients. This is due to non-linear absorption characteristics, with higher absorption taking place as frequency rises.

Some grille's are obviously worse than others, depending on the materials used and their support structures. Since there is no such thing as "acoustically transparent" material, all grille's will alter the sound to some ( usually quite measurable ) extent. It is up to the end user to decide whether or not the grille's are beneficial or detrimental to performance within the confines of their system and personal preferences.

Since we are on the subject, metal "cages", "screens" or "lenses" over tweeters or mids can also create massive ringing and glare. I have yet to hear a speaker that didn't sound smoother after the "cage" was removed. Obviously, this WILL affect their radiation patterns also. Whether or not you want to do this with "little ones" around may be a different story though.

As far as i know, the folks that have done the most research in terms of grille effects were Acoustic Research ( AR ) and John Dunlavy. They both came out with very similar findings and designs at about the same time ( late 70's ).

Personally, i typically like to leave the grille's off when listening. If a recording is very bright, glaring or forward, putting the grille's back on can help tame this, but typically with other noticeable side effects. As such, i typically just deal with it. Sean
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From the Thiel 1.5 manual:

"The grille on the CS1.5 is designed as an integral part of the system to reduce unwanted diffraction effects. Therefore, it must remain in place for proper operation. If you do need to remove the grille, pull the bottom of the grille frame away from the speaker an inch or so and then pull the top of the grille forward to remove it."

I have no speaker design knowledge but clearly Jim Thiel sees reason for the grilles. Not sure what that means though.

I like the way JM Lab Utopia series does it. the "speaker grilles" are actually solid wood "speaker protectors." They are to be put in place so that the maid can come through the room and clean things up without damaging the speakers. Of course, this would work well for women and children also. So, obviously, with these speakers you would remove the grilles for listening.

Thanks for the great thoght sharing. I do understand that sometimes I'd take them off but UNfortunately my kid taps the drivers only during listening. He doesn't care about the drivers or speakers any other time!

The Thiel CS1.5 grille is unique in that it actually has a sizeable rounded wood frame which gives the front of the speaker ALL of its anti-diffraction properties. In other words, without the grilles in place, the front of the speaker has no rounded corners at all. The Thiel CS2.3s are not like this and I'm sure that very few speaker grilles are designed this way. I never thought about it but the CS1.5 would be a good speaker to experiment with to see if the rounded shape actually makes an audible difference. I have my CS1.5s set up as my main speakers right now so I will try to do this experiment and post some results in the next day or two.