How Much Power Do Vandersteen 5a's Really Need?

A mere 100 Watts on a 5A is a waste of a good speaker. 

Fair to say I'm a bit baffled by the widely divergent opinions on the amount of power necessary. 

I do have a question that has me completely confused, though. It was explained to me, by the current owner, that you connect your preamp via interconnect cable, directly to the external crossovers/high pass filters, which then connect directly to your amplifier.

While a very unusual connection scheme, I can understand how that works. What I cannot come up with any answer for, nor can any of the three audiophile friends I posed it to, is, how do the internal amplifiers that drive the low end get a signal if the entire signal from the preamp is going into the external crossovers/high pass filters? We're lost in that regard. 

From vandersteen:  "This top of the line High Pass Filter is specifically designed to be inline in front of your amp to roll of frequencies below 100 Hz. which are passed to the Model 7 series speakers and reconstructed in the amplifier powering the bass driver."

So the bass amplifier knows the filter steepness of the HP filter and corrects for it.  Because the filter is a gentle rolloff (I think they use a simple first order curve), you're still getting signal below 20hz and it's just amplified right back up by the bass section's amp.

mostly because the OP has really yet to define in db how loud ? 

and Oz “ my brand “ of speaker include horns, stats, planer, cones in boxes...and Vandersteens.... I think I am at 9 pair,  The horns are at my Flyrod builders workshop....

I think IF horns were the only answer, everyone would own them...

To the OP, 5a owners are giving you real world inputs that vary because they listen at different levels in different rooms. Hook yours up and form your won judgement, just don’t clip your amps. 

The Vandersteen powered bass is very unique. the first order hi-pass filter is inserted inline before your power amp. This does three important things: preserves phase, any other filter does not. It also GREATly reduces load on the amplifier as it does not need to reproduce full amplitude low bass....ever ! this load reduction sweetens the midrange and highs because the amp is not working as hard. The sub amp built into the 5a is optimized to drive just one speaker on the planet - the unique aluminum honeycomb push pull sub driver in the 5a and the 7. Power factor and feed forward corrected. and because you are using a high level speaker connection to both sub and speaker, the transfer funtion of your CJ amp imprints on both - seamless. yes the sub amp restores the bass signal to flat. ......

Jim