Quote Originally Posted by bowtie427ss View Post
the zobel in the 30904 was designed for the 411 woofer in a sealed alignment. IMO, to assume it is in any way appropriate for a 416 in a vented alignment is an exercise in pure wankery(assuming you're reading Zilch posts).

The other half of the 30904 in addition to all the wonderful things you have read that it will do, will also alter the impedance load the crossover sees from the driver changing it's knee point, and likely other subtle characteristics.

My advice would be "slow down grasshopper! one change at a time, listen, evaluate, proceed"

Just my .02 of course, i'm not a big fan of the vacuum tube either so, you may want to take into account that i don't know "jack".
+1, saved me some typing............ I knew 'jack' once upon a time and still don't prefer tubes except in certain apps and even then not enough to return to that particular aggravation. There is a certain 'synergy' with compression horns and 'full-range' drivers though, so bi-amping is the best of both 'worlds' IME.

Anyway, for any basic point source+horn system, CD horn EQ [LCR network] to level match [tonally balance] the horn to the woofer is required, which in turn unfortunately shelves down the HF, which wasn't a problem when these systems were conceived since there were no recordings with any to speak of and the amp's high output impedance had a built in 'smiley face' EQ to boost the low/high ends, then later they just added bass, treble controls via variable damping [DF] to 'boost' it further.

Most of us nowadays don't have the proper tube electronics to do it up right, complete with the 'flabby'/loose bass as the trade-off, but we can easily do similar by adjusting the horn/woofer's tonal balance with the horn's attenuator and once this is dialed in we can 'lift up' the HF to blend in by adding a by-pass cap around it, i.e. essentially do what the M19's fancy XO allows.

IIRC 0.1-1 uF was the most used range way back when, but let your ears rule since we as a species have incredibly poor HF hearing once we get a little age on us and room acoustics, signal chains varies greatly. Zobels are only really needed for when there's a high output impedance source or have a complex passive XO and even then only if you're wanting a very flat frequency response like is required in a studio monitor type app.

Note women and especially children are [much] more sensitive to upper mids/HF, so they're the ones I used to find the best trade-off woofer/horn balance and cap value. Of course if it's a 'man cave' app.........

GM