The phase change would not be linear for the entire frequency band anyway. Symetrix makes very decent parametrics, with specific attention to phase behavior.
Daring, though to put an EQ in the system. Even the finest room treatment cannot always make the loudspeaker locations work well with the size and geometry of the smaller rooms...
Snarf
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If one hears bad music it is one's duty to drown it by one's conversation.
- Oscar Wilde