It won't expand all frequencies. Each length will produce a peak at the frequency it's tuned for. So to start, your graph looks like a roller coaster. Then, TONS of phase cancellations from time delays...sound in air is roughly 1000 ft/sec so every foot is a millisecond delay or so.
Tuning is used to produce a peak where your woofer rolls off, or rather just below. The trade for the response is phase issues. relatively minor with one but multiplied by this design.
Back loading horns were abandoned mostly due to phase issues. They are still used as Pro woofs, but operated below the band produced from the front of the cone.






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