The best rule of thumb I know of is the speakers and seating should both be at i/3 the room depth. If that is not possible 1/5, 1/3 works. The next would be 1/7
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In you 18x30 room I assume your speakers are on the short wall, thus you have a little under five feet to each side wall? If this is true the 1/3 dimension is 10. Meaning the best would be to start 10 to the speakers and 10 more to the chair. As you said, this is not practical. The next best is the speakers at 6 feet from the back wall to the tweeter face. This would still provide adequate soundstage depth. If this is not possible, the 1/7th dimension is 4.2 feet. If you need to go even closer keep trying the odd factor of dimension.
As per toe in, start straight out and test it. Keep toeing in until the center image becomes clear and defined. Small amounts from that point will allow you to tune it closer, making a solo vocalists mouth appear the correct size.
In you 18x30 room I assume your speakers are on the short wall, thus you have a little under five feet to each side wall? If this is true the 1/3 dimension is 10. Meaning the best would be to start 10 to the speakers and 10 more to the chair. As you said, this is not practical. The next best is the speakers at 6 feet from the back wall to the tweeter face. This would still provide adequate soundstage depth. If this is not possible, the 1/7th dimension is 4.2 feet. If you need to go even closer keep trying the odd factor of dimension.
As per toe in, start straight out and test it. Keep toeing in until the center image becomes clear and defined. Small amounts from that point will allow you to tune it closer, making a solo vocalists mouth appear the correct size.