how did i miss this before:
HiFi Speaker Design © mhSoft <%=year(now())%>
@Jeep - does that calculator give you the same / similar results to your design?
EDIT: GAH, spoke too soon, its just the BBC quantized version :(
EDIT2: hmm... a very simple diffusor could be made with the BBC "formula" using 5cm square wood in 5,10,15,20cm lengths, it would be effective from 860 to 3440hz... tempting!
Paul