: The P/R consists of a dampened hub (about a 1.25" by .250" steel disc resides inside this hub). The secondary cone of the p/r(the one you can't see from the outside) is only there to provide some additional mechanical control, as the primary cone (the one you can see) is acoustically mated (frequencies from the driver are allowed to contact the primary cone directly through holes on the basket between the two cones). This suggests the p/r produces not only the lower frequency of the enclosure but the bulk of all information. Removal of this p/r will not provide satisfactory results of any kind.

: THRAPPP!! The "thrapp" is caused by two events. First, "Thrapp I": the basket of the p/r is plastic, so it deflects along the sides and allows air to escape along its perimeter which actually produces a hi-fi "fart".

: Second, the plastic center hub with such speed and excursion, it flutters much like a helicopter's wings. This produces "Thrapp" II. Flat plastic was NOT the way to go here, Philips! Flat is bad!

: Attempts to reduce flutters and farts:

: 1) Port box: Nope, porting only gives the driver more freedom to move, adding more stress to the p/r so I'm chasing my tail.

: 2) Increase mechanical or acoustical damping of p/r: Various methods were applied to try and increase both the mass of the p/r and some mechanical methods were used also. Unfortunately, as we increase the acoustical mass, although the frequency drops, so does responsiveness and transients, another tail chase. Mechanical damping results are nearly identical.

: 3) Remove primary cone of p/r and bond acoustical foam to basket and secondary cone and bond basket to enclosure with silicone and additional screws, seal porting: This proved the best of the three results. The excursion of the cone was more controlled, the center hub and foam still permitted some transients and low frequency was still apparent. However, speed and the shape of the hub at greater volumes still produced the flutter.

: 4) Remove p/r: Dismal, most of the low frequency info is removed. The lighter and smaller driver cannot produce this stuff. Second, now the driver's cone is completely out of control beyond the limits of the voice coils. Ooooh, "THRAPP" III!

: 5) Throw sub enclosure across workbench: This made no change what-so-ever; a very sturdy enclosure and driver. Wouldn't you know it! Now, if it could only work.

: Ok, by now my sub is looking like the first atomic bomb at Los Alamos.

: Some have suggested replacing the p/r with another similar driver. One could fit another 5.25 driver with a shaved trim ring, it *will* fit and seal. However, I doubt this is the answer due to factors too involved even for this lengthy post.

: I am open to fielding ideas from anyone interested and can be reached by e-mail for that purpose. What was discovered by other companies and individuals is that bigger is better. The new HK woofer at an outrageous price demonstrates this.

: Could Philips have executed thier design better? Yes, the basket of the p/r could be steel or aluminum instead of plastic and the hub of the p/r convex instead of flat, and doped (again, way too complex for here). I hope this info helps in some way.