The Model B is currently available with four viewing surfaces:
1. Matte White (Gain 1.0)
2. Video Spectra 1.5 (Gain 1.5)
3. Glass Beaded (Gain 2.5)
4. High power (Gain 2.8)
None of these are acoustically transparent. The acoustically transparent Da-Lite surface is called Audio Vision (Gain 1.0) and is perforated. It is not normally available on the Model B but it might be obtained on special order according to a rep I spoke with at a trade show recently. Normally the Audio Vision surface is only available stock with side tensioned Da-Lite models such as the Advantage, Cosmopolitan, Designer Da-Tab, Director, Dual-Masking, Executive, or Horizon Electrols, all roll-down, and the stationary (wall-mount) Imager Video Screen and Da-Snap models. Generally, I suspect the Audio Vision surface will not stay adequately flat if not side tensioned, although there may be some non-tensioned presentation (portable stand-mounted) models which you can special order with the Audio-Vision surface.
In order to be acoustically transparent at high frequencies, a screen must have both a sufficient density of perforations (actually, have small enough land areas between the perforations), and be quite thin, which is probably why they are normally available only tensioned, in order to keep them flat. Even with the dense perforations and thin materials, there is significant high frequency loss which is why an equalizer is required to restore flat response. There are also (sound)reflections between the back of the screen and loudspeaker, and between the back of the screen and any wall immediately behind the screen. These reflections cause significant response variations that cannot be practically removed by an equalizer, although treating the front of the loudspeaker baffle and/or wall can improve the overall smoothness of response. Nevertheless, most purists will want to have a perforated screen in order to provide the best directional realism for dialog.