Javaman:
Have not built passive radiators. Essentially they are "vent substitutes". They should sound similar to vents.
Any difference with "drone cones"and vented systems is possibly due to the fact that the drone cone itself has a resonance, and this resonance detracts, not adds to the bass output of the speaker, forcing it to roll off at a greater slope. Looking at some charts, it seems that the slope of the effect of the passive radiator tuning starts about an octave and a half below the tuning frequency of the system, or Fb. So if your drone cone resonance, (as opposed to your enclosure resonance, or Fb), is 2 octaves below Fb, there probably should be no effect worth worrying about.
The Peerless drone cones are tuned to 6 Hz, I believe, and adding mass to them should tune them even lower. After, all, adding mass to a normal loudspeaker cone lowers it's resonance frequency, so this should be the same. This might be why Peerless tirelessly promotes these drone cones to go with their XLS systems.
I should add that Pioneer makes a drone cone that is very inexpensive. It is just Styrofoam with a foam surround attached to the frame. Theoretically, this should be all you need in a passive radiator, but web sites have stated that drone cones with a spider are superior. Why, I don't know. Maybe it has something to do with the weight-drone cones can get fairly heavy if you use more than one and you want to tune low.
Normally a 10 inch speaker is fine with a 3 inch vent, but the Dayton and Peerless XLS are not ordinary 10 inch speakers. If you want to go to a 4 inch diameter vent, it will be about 32 inches to tune at 2 cu ft box to 22 Hz or a 1.4 cu ft box to 25 Hz. Both vents take up less than a quarter of a cubic foot . You might wish to negotiate your size limits up slightly to accommodate.
Madisound sells 3 inch ports, flared at both ends, which should bring the vent volume down to less than 10% of box volume, yielding a negligible increase in Fb. A flared pipe is equivalent to a larger pipe, unflared. Apparently, from what I can see, the flared ports are designed to fit over a straight piece of PVC pipe.
If you use a 4", at 30+ inches, you will most likely want to use an elbow, easily obtained from building supply stores. If you use the flared 3" pipe, it will be shorter.
If I were building it, I would go with the Dayton Titanic 10 inch Mark II in a 2 cubic foot box. If it is already established that you can go to 2 cubic feet for a 12 inch, it seems to me that you ought to be able to go that high for a 10 inch.
For a long time, a .25 inch throw, either way was considered a very long throw woofer. With more than .5 inch excursion, the Dayton or Peerless really is equivalent to an old 15 inch, only with cubic foot requirements equivalent to a regular 10 inch. If these speakers can do that, the least you can do is give them a LITTLE extra room, LOL.
I am obviously not in a position to know your space requirements. But going down to the low twenties in a 2 cubic foot box is quite an accomplishment, in my opinion.
Let me know how this turns out.
There is another possiblity. The Blueprint 1001. The webpage is down, but you can Email for specs. As I recall, it had specs similar to the Dayton, but it cost only 79 bucks. At least that was the old price. The Email address is:
www.blueprintdrivers@hotmail.com. Blueprint invites inquiries.
Hope to hear from you soon.