Subwoofers - Grille off or on?

I'm with Johnk on this one. The rational part of my brain thinks the wavelengths of a subwoofer's output would be much longer than the point at which diffraction effects would be audible. However, sub grills can darn sure rattle. I'd get a test tone cd like the ones Rives or Stereophile sells and check to make sure no grill buzzes need attention. I've had to use dabs of Blutack to damp the odd buzz in a sub grill.

Grille cloth behaves differently at each frequency. In the bass, a great deal of air is literally always 'stuck' to a woofer's cone- the larger the woofer, the deeper/thicker that layer.

Therefore, any cloth will act as a drag on that moving mass. This means it inhibits dynamic response (not so much steady-state) with a time lag, as it follows the cone's motion imprecisely.

Cloth also keeps more air molecules trapped next to the cone, and next to itself. This again changes the moving mass (and also varying with the SPL), and therefore changes the cabinet's bass tuning (again, varying with the SPL).

We find it easy to hear cloth soften the attack of a kick-drum and reduce the percussiveness of a string bass. It is best described as hearing a 'mumble' or a 'stumble' in the 50-70Hz range.

However, in that frequency range, most subwoofers have tremendous amounts of time-delay/phase shift built-in, which swamps our ability to hear such a difference.

While we find that the cloth/no cloth difference in the bass is not bothersome to most anyone, we do remove them when evaluating gear and cables, as we can hear them conceal some differences.

Best regards,
Roy Johnson
Designer
Green Mountain Audio

website

We find it easy to hear cloth soften the attack of a kick-drum and reduce the percussiveness of a string bass. It is best described as hearing a 'mumble' or a 'stumble' in the 50-70Hz range.

Huh? The "attack" on a kick drum is around 5 KHz. Most sound engineers can confirm this for you. How this can affect a subwoofer would be a mystery unless it were run full range like a bass guitar amp/speaker.

The main issue (apart from some very slight attenuation in higher frequencies) with grills is the way the baffle is designed. Some baffles have very sharp corners and the grill acts to help reduce the severity of this baffle step and edge diffraction.

I would add that the baffle step is usually somewhere around 400 to 800 Hz and edge diffraction is something that affects imaging mostly in the midrange and treble. Neither of these frequencies are terribly important for a high quality subwoofer that should not output high amounts of harmonic distortion.