JBL C55 speaker modification question

[Jimbo]

JBL high efficiency speakers, (2) 130B woofers, (1) 275 compression driver and (1) 075 Tweeter per side. JBL C55 rear horn loaded enclosure.
Problem: Need more low bass extension.
Would a rear loaded horn or a bass reflex enclosure work better for a home music system? The C55 enclosure has approx. 22 to 23 cubic feet internal volume. If I convert the C55 to a bass reflex system, would the enclosure be too big or is bigger better? The flex port would have to be approx. 210 to 220 square inches according to JBL specs. The enclosure could be partitioned off to have a smaller woofer chamber. I would mount the woofers and put the reflex port in the lower section of the enclosure where the horn mouth is now. The horn mouth opening is 27" x 32". By covering the horn mouth with different size openings I was able to increase low bass extension but greatly reducing upper bass, especially at 125htz (over -10db.). The smaller the opening the bigger the change. For example, I tried 3", 5", 7", 9" and 12" x 32" openings. I wonder with the woofers and port on the bottom of the enclosure if that would change. I am open for suggestions and any ideas you might have to improve my speakers.
Thanks Jimbo

[Fangio]

Are they original C55's?

If yes, well what I see is a vintage JBL cabinet, even with wonderful veneer for home use apparently, and definitely speakers you don't find often in this condition. If they were mine I would probably not get to the idea to alter them. Only conservation and maintenance were in order IMO, given their rarity.

If you need more lowend extension consider building sub(s) to go with them, and skip the idea of modding. Just my 2 cent.

[speakerdave]

I'm with Fangio on this. Even if they are not factory speakers they are very nice specimens and should be preserved (your choice, of course; they are yours, after all).

Besides it would actually be much easier to start from scratch.

You would also need to use different woofers, and that entails a change to the midrange crossover, unless you are crossing over to that potato masher too low now.

To get near the same dynamic capacity (you will not have the same efficiency) you will want a pair of foam edged fifteens (2234's would be a good choice) and a 10" midrange to lead up to the potato masher at about 1200 Hz.

Can of worms, heh?

David