What might a good to great 20uF film/foil capacitor for a woofer.

Tough question, have not tried it but my guess is why don’t you check Jantzen Standard Z cap, Clarity Cap ESA, Audyn cap Plus. Maybe more than enough for bass region but can handle extreme pulse, are low loss, and not so expensive for the required value.

Only the Jantzen comes in 400v, the other two in 630v but their values are in 22mf or 18 mf not 20mf.

You can check Humble Homemade HFi and HFi Collective for more info.

I'd go with the VH Audio ODAM, while I've yet to try it, many respected reviewers have and love it. Others I'd suggest are going to be much more costly, large and may not even come in that large value.

Forgot to mention, recently moved to Jantzen litz wax and solid core inductors, huge improvement over stock Khorn inductors!

for caps you might try Clarity CSA 

for inductors you could try Solen , 1% tolerance 

Do not, do NOT change DCR on coils willy-nilly.  Lower is not better.

As for bypass caps, Axon is fine in the large values.  Be careful replacing old electrolytes though, especially here.  Match or compensate for any significant differences in ESR.  Again, and most importantly here, lower ESR is bad.

I am starting to use Jantzen Audio’s Litz Wire Wax coils, crossovers are 95% done, I just have to decide on the bass cap. I was looking at Jentzan’s Supremum Z 20uF but they’re expensive $$$ for a pair of them compared to the Erse 400v and other caps I have considered. I don’t want to pay for a boutique priced cap when I am looking only to improve the bass and waste money (losing/wasting) the med and top end frequencies? I have used Axon in a couple tube amps with great results but should i consider them for a bass woofer? I will look into the VH Audio ODAM, never heard about them before. I was looking at Clarity caps when I ordered the Jantzen Litz Wire Wax coils. I should have grabbed a pair to try out because I already paid for shipping. It wouldn’t have added any to the shipping cost being they don’t weigh too much. I appreciate all the info/ideas.

I’ve also been using some remarkable 1939 NOS unused before Western Electric No. 10 Tinsel wire/cable switching out all the (1976) Cornwall’s driver wiring shortly after installing and listening to the upgraded B-2 crossovers. That made a remarkable improvement in sound quality. Also, I'm now using 1930-40 Western Electric cloth over silk over enamel 18 ga. solid copper wiring for the crossover wiring as well. Very nice sounding wire.

Hello,Sir

We are ERSE factory and we have stock of Erse 20uf 400v Cap.

Any requirements pls let me know.

Kind regards,

Wendy

@archiecb 

     Not certain which inductors you still need, but: I have a pair of these, somewhere around here: 

https://www.mundorf.com/audio/en/shop//MCoil+CFC14+AirCore/?card=5656

       If you're still in your x-over's design stage: I wouldn't think a <10% uptick, from what you desire/used prior, too hard to work around.

from my experience, bang for the buck, I would go for Clarity CSA.  If those are too high,  I personally would stick with Solen PPE.  I've listened to a bunch of budget friendly caps, they are more neutral than most and don't do any nasties that others do in lower treble region.