<font color='#000000'>Check to see your speakers' lowest frequency limit, usually 40hz to 50Hz stated at the back of the cabinet as frequency range. This is just an indication. Speaker placement will have a bearing on whether you will hear them or not in your listening couch. Now that's room frequency respsonse - room plus speaker accoustics conniving to what eventually will end up in your ears.
Personally, I just do a lot of listening to check how well the integration is between the sub and speakers. I start out setting the speakers to large; and putting crossover frequency, at the receiver end as well as the sub, to coincide with the speakers lowest frequency range limit, usually at 50Hz. Then I tinker the controls going up or down as it suits my listening on various CD titles. I have no fast rules on this, though I usually end up with the crossover frequency on the sub about a few Hz lower than what my main speakers can generate. That usually takes care of any frequency overlaps where both subs and speakers end up generating. Those cutover filters are never precise, at least not in mid-priced gears. I also use a CD with test tones ("My Disc" test CD from Sheffield labs). And that is why I prefer floorstanders over bookshelfs, the integrattion between speaker and sub seems to be more accomodating.
Setting the speakers to SMALL is generally reserved to speakers that are challenged generating the LF down to 60Hz -50Hz flat. In a way, that also relieves the receiver amps from amplifying LF which tend to drive the power amps to extract from current, thus heating the amp more. Those LF can better be amplified by the powerd sub which is dedicated to the purpose. However, in my experience, seamless integration seems more problematic, as the sub can have a peaking characteristic in the 80Hz-120Hz (boomy) that would otherwise be flatter in a floorstander. This is usually the crossover points when setting the receiver to SMALL. Perhaps using more expensive subs will do a better integration. Just my 2 cents.</font>
