There are two problems with irregular rooms: 1) Depending on the shape of the room, it may be difficult to properly place speakers. 2) This makes predicting low frequency modes much more difficult to deal with.  As you might understand, the ability to solve either of these problems depends on the shape of the room.  In the case of low frequency modes, we try to predict where these modal resonances cancel bass and avoid placing seats there.  If you don’t have the ability to predict such things, the best solution is to use an audio generator playing a sine wave to find the lowest mode frequencies by changing frequency until the tone becomes very loud.  You then can find the cancellation points and avoid them when placing seats.  This process is taught in the THX-HAA Advanced class and is much easier if you also have a high resolution RTA to use.