is that they are less visually obtrusive, they may be available in several colors, to enable audio engineers to select the color that will blend best with the surface they will be placed on or mounted on, in order to further reduce the mic's visual obtrusiveness. Some boundary mics come with a paint mask to facilitate the custom painting of the housing. Custom painting can be used to provide an exact color match with a wall, in cases where the building architects wish there to be minimal visual impact (e.g. a historical church or a Classical music stage). The housing also varies according to the intended usage. A model intended to be placed on a tabletop does not have to be that heavy-duty, as it is in a place where it is relatively safe from impacts. On the other hand, a boundary mic intended for use on a music theater stage is much more likely to face impacts (e.g. being stepped on), so it needs a robust, thick steel casing. Another variation on housing is the size. When concealing the mic is important, such as with film production, a smaller housing may be desirable. Sanken's CUB-01 boundary microphone has a 32 mm diameter and 12 mm height, which makes it easier to hide in TV and film field shooting and easier to reposition or temporarily mount in locations (e.g. taping it onto the inside ceiling of a car). Boundary mics may have XLR or 1/4" TRS jacks. Some use mini-XLR or 1/8" TRS jacks. Some boundary mics have a "bass roll-off" switch, to reduce boominess in the low frequency range, such as in cases where the mic will be used to pick up speech. The Crown PZM-30D has a switchable filter that allows you to switch between a flat response or a “brighter” sound. Gold Line's CBM1 boundary microphone and Crown's "Sound Grabber II" have an internal battery to power the condenser. Schoeps' BLM 3 boundary microphone is unusual in that it has a "pressure transducer" capsule that provides a hemispherical pickup pattern. AKG's PZM11 is a weather-resistant boundary microphone. It can be installed outdoors in places such as fast-food restaurant drive-through lanes, toll road booths, and security intercoms. It has a plastic membrane that keeps rainwater away from the capsule. Directional boundary microphone A directional boundary microphone is a boundary microphone with a directional polar pattern such as cardioid