Originally Posted by jevansoh
This is the perfect example to prove that reducing "EARLY" reflections and increasing your ISD Gap will increase liveliness and spaciousness, not decrease it.
to clarify: in such a 2ch response, the ISD-gap dictates the perceived size of the acoustical space. eg, the distance (time) of the first significant reflection with respect to the direct signal. in small rooms, the ISD is naturally shorter than in larger rooms, as the speed of sound is a constant within that medium. attenuating the natural first-order reflections artificially increases the perceived size of the acoustical space without modifying the actual boundaries - as you are artificially delaying in time when the first indirect energy impedes the listening position. attenuating these high-gain signals within the haas interval also increases accuracy of localization, imaging, and intelligibility with respect to the direct signal. attenuating the high-gain first-order reflections also removes (minimizes) the 3d spatial polar lobing which results in the comb-filter interference pattern manifested within the 2d frequency plot. "comb-filtering" is not all inconsequential and "1/4 inch wide" ... the polar lobes and nulls can be many feet wide!.
the gain of the first significant reflection will dictate the liveliness. if you are reintroducing energy to the listening position (terminating the effectively anechoic ISD gap), the gain of this termination (sharply delineating the ISD) will dictate the liveliness of the space. a higher gain (with respect to the direct signal) of this first significant energy will be perceived as more lively than that of an indirect signal lower in gain.
the characteristics of the later-arriving sound-field dictate spaciousness. the energy is allowed to become more "well-mixed" in large rooms than small (where the energy is quite sparse/specular) - and this is why diffusers (reflection phase gratings of QRD or PRD variety) are used to artificially mix (spatially and temporally disperse) the energy as would naturally happen in larger, more "spacious" rooms. the diffusion breaks up the high-gain sparse
reflection into MANY reflections scattered across the given hemisphere that are also delayed in time which thus induce MANY polar lobes which result in comb-filtering that is DENSER and MORE CLOSELY SPACED together in the 2d frequency response (eg, minimizing the "sparse" comb-filtering gaps).
in this particular 2ch response, accuracy (with respect to the direct signal) is maintained while still providing a sense of the room via the energy management and subsequent reintroduction of indirect energy to the listening position WITHOUT being destructive (in time and frequency domains). the ISD-gap dictates the perceived size of the acoustical space, the high-gain termination dictates liveliness (while removing the directional cues of the later arriving energy a la haas trigger), and the laterally arriving
, exponentially decaying dense diffused soundfield provides the sense of envelopment and spaciousness (a la Dr. Manfred Schroeder's EU concert hall research).