set speakers large or small?

m/n sf128vx1o its about 12 years old,friend gave it to me.i called velodyne and they said to set the receiver at 80 and the sub crossover at 100.there is not a on/off direct switch on the sub

Reason for setting sub above xover point of recv'r/preamp is to make sure the range transfer for lack of better phrase is not missed. Example...if you set sub to 60 hz and recvr to 80hz....the info between the two settings would not get to sub therefore setting sub at or just above recvr/bass management setting will ensure there is no gap or more important too much overlap.

BReynolds is correct about the 100hz setting...you would be able to localize the sub with those higher freqs being sent to it. Sub should disappear in room so to speak. You should hear/feel it but not tell where it actually is. Do 80hz and listen to various material with large setting and small setting...you decide which is fuller and smoother.

ok if i set the sub at 80 what should i set my recv. at

Sounds below 80 Hz can be localized. The issue to address is not localization, but rather, a smooth, linear transition between mains and sub. It might be possible at 80 Hz, but highly doubt it could be done any lower with the Thiel 1.6. Velodyne's recommendation may be based on the fact that subs generally have a rising response in the mid-bass, by having a little 'gap' in the crossover it could help smooth out the hump, or the logic could be to help tame common room modes that often occur in the same frequency range. No matter how one looks at it, calibrating a sub is difficult. It requires time and patience.