[quote=GM;1830870][QUOTE]
In the times the 820 was designed for, full-range reproduction ('HIFI') was ~50-11 kHz with acceptable being only ~75-7 kHz and when driven with a period correct high output impedance it was nominally flat in-room to a half octave above/below this, so a stellar performer for its time.
I love the 820 it is one of the coolest looking speakers Altec ever made IMO with the little 808 multicell.

Today, with our ~16-20 kHz BW available on some music CDs we would need a ~11.3-28.28 kHz ~flat BW which no consumer system can come close to AFAIK, so by today's SOTA requirements it's woefully inadequate without a sub and super tweeter, but if all you do is spin vinyl and/or old tapes and/or mass market CDs, then you'll be hard pressed to want/need more BW.
That's essentially what I use most of the time I have a lot of vinyl.I bought a lot of the Mobile Fidelity Sound Lab Master Recordings.With a nice cartridge on my turntable they sound fantastic,nothing sounds better than those analog recordings.The gold CD's come in second IMO.So if we can get the LF cabinet to sing down to 30 Hz and the super tweeters that go to 23 kHz I think they would sound quite nice.


Cool, back in the days when squared off trees were used for floor, ceiling joists in all but the cheapest construction and if you live above the Mason-Dixon Line it's further ~'bulletproofed' for snow/ice.
Exactly ! The sill plates that go all the way around the top of the foundation are 6" x 8" with mortise and tenon joints that look like squared off trees.You don't see work like that anymore it is a lost art for all intensive purposes.

OK, that ear height is typical here in the USA, so it's your call as to which layout to use, though being use to the M19's so-so driver spacing WRT its XO point/slope that I wanted to improve on, you may find your preferred over/under layout as sounding very similar if a 500 Hz XO is used. Go with a higher XO point though and you'll need to roll off the lower woofer for best performance overall.
This is were I need your recommendation, what design should we use to get to 30 Hz while keeping it small enough to still be manageable ??

Added: Also which design would allow for more adjustment in case I need to do some tweaking.