I don't know what loudness you're looking for. Kef B200 are not efficient speakers. If the room is big, why are you trying to make the Kef box smaller?
The Creek is a good match for the B200 which has very low power handling compared to modern drivers. It would not be a good match for a modern speaker that plays tight deep in a smallish enclosures because it would have insufficient power. The laws of physics dictate that good bass in small enclosures requires large drivers and large amounts of power.
If you put the B200 in small enclosure there will be less bass extension plus there will be raised upper bass as explained by others earlier. For small speakers (i.e. computer monitors) the bump tends to disguise a bit the lack of actual bass and is often, probably usually, present. In comparison with a reasonable hifi speaker with 8" midwoofers though the lack of actual bass will be obvious.
Your speakers are currently in the optimum enclosure for reproducing bass in terms of bass extension and clean output. That's why the enclosure has a port and is the size it is. If you put the driver in a small sealed enclosure the response will be worse. If you equalise that response in the crossover or with an electronic equalizer the speaker will be less efficient and require more power to get the same output level. Unfortunately the 50 year old driver has low power handling and you amplifier has low power output. It isn't likely to be a good option but, as mentioned above, you can hear all this for yourself by simply blocking off the port and much of the internal volume of your current speaker.
50 year old standard range drivers that are (almost certainly) out of spec can be useful for experimenting with but not much else. Personally I still have 2 or 3 70s KEF drivers in a draw that I use now and again if I need a driver that I don't mind sacrificing when messing about with electronics. The rest went in a skip as not worth transporting when moving house a decade or two ago.
@Abolf , the closed cabinet of 55 l is small even for factory data (Qtc=0.9). No need to waste time with a smaller box. You will get a Qtc greater than 1, and then the series capacitor won't help much either.
As I said, you should first try to close the bass reflex opening, but it is persistently bypassed.
https://www.lautsprechershop.de/tools/zy1_main_en.htm
As I said, you should first try to close the bass reflex opening, but it is persistently bypassed.
https://www.lautsprechershop.de/tools/zy1_main_en.htm
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Small infinite baffle speakers can be specially designed with a bass roll off characteristic that permits mounting then close to a rear wall.
When placed close to the rear wall, the bass frequencies are boosted, thus compensating for the bass shyness.
Not everyone wants large speakers way out in the listening room, and to mount those close to the wall would produce too much bass reinforcement.
I am getting more and more convinced to just keep them as they are. Maybe I’ll give it another try in the future. At the moment I’m giving the B&O cx100 a fair chance. Maybe I “need” another amp… I am missing my old Cyrus One.
