JBL P941 woofer enclosure volume

[goto2003]

Hi, I am a beginer in speaker diy commnity and would like to have help from you fellow diyers.

I got a pair of 9" woofers of JBL P941 in-wall speakers and want to mate them with seas H1304 and H1499 for a speaker project. It seems the type of speaker with this 9" woofer should be a closed-box type given the fact P941 is an in-wall type of speaker that is cloest to closed-box. But what's the optimal volume for them? Below is the spec. of JBL P941.
General
Recommended Power 15W – 200W
Nominal Impedance 8 Ohms
Sensitivity (2.83V @ 1m) 89dB
Frequency Response (-6db) 32Hz – 20kHz
Crossover Frequencies 300Hz, 2kHz; 24dB/Octave
High-Frequency Transducer 1" Pure-titanium dome
Midrange Transducer 3-1/2"
Low-Frequency Transducer 9" OCC (Organic Ceramic Composite)
Baffle Cast aluminum
Port None
Network SSP™ (Straight-Line Signal Path™)
Grille Material and Finish Gray cloth with metal wire frame
Terminals 5-Way, gold-plated binding posts
Dimensions (H x W x D) 20-5/8" x 13-9/16" x 3-1/2" (515mm x 345mm x 89mm)
Cutout Dimensions (H x W) 19-1/8" x 12-1/2" (486mm x 318mm)
Weight 15 lb/7kg