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OEM RM40 woofer siting is Megawoofer at bottom, midbass up top. Upon inverting them (MW to top, midbass to bottom) the sound quality improved. I did not perceive the minimized low-bass output Brian predicts. PR mass adjustments were minor (removed three-four thumbnail slivers). Besides minimizing two room modes below 100Hz there are reasons to believe it is an overall improvement.
The reason I tried it is my wife's ubiquitous complaint of an upward image shift when the music emphasized the mid-bass driver’s range. As frequency increases the output skews more & more toward the MB vs. the MW. Floor bounce path-lengths are shorter than those from the ceiling, & higher in frequency than the MB pass band. Plus floors usually are carpeted, further absorbing & minimizing bounce & consistent with the relocation. Before the mod, while listening to one channel, with my eyes closed, she alternately blocked & unblocked the upper 10s output with a pillow (close to but not touching the woofer). It sounded better blocked. Try it yourself. The assistant must stand off to the speaker’s side. Flesh is almost 100% absorptive & could alter the frequency response.
Instructions To Perform The Mod
Lay the cabinet on its back. Remove the sixteen screws fastening both woofers. (Notes: foam gasket tape was applied to the rear of the woofer basket for an airtight seal where it contacts the baffle. The screws were tightened, the tape compressed & air was expelled from the foam cells, resulting in a speaker-to-baffle suction. The suction exists till the screws are removed, time expires, air refills the foam cells, & the tape expands.)
Place four 1-1/2” wood blocks on the floor in a rectangular shape, spaced about 7” x 36”. Carefully lay the cabinet face down onto the blocks, arranging the blocks to flank the outermost mids. The blocks create a space into which the woofers will drop when gravity disgorges them from the baffle. If soft carpeting is not under the woofers, place something there to absorb the shock when they fall out. The heavier Megawoofer will probably break loose first.
After both woofers have broken loose, carefully rotate the cabinet onto one side (the woofers lay on the floor). Remove the wire quick-disconnects. Rotate the cabinet onto its rear.
Pieces of the gasket tape may need to be removed from the baffle for reuse (removal eased with judicious use of hair dryer on low setting). I have been able to reuse broken pieces to make a good seal. The 5/16th”-wide replacement tape may be hard to find. Send VMPS a SASE & a request for replacement tape if necessary. You may desire to have replacement tape on hand to avoid potential re-installation delays. One of my kit builder mods is to replace this gasket tape with clear silicone sealant, audibly improving transients via a more solid link between the woofer & the cabinet mass (the tape acts as a shock-absorber, blurring transients). The silicone is messy both in installing, & when/if servicing/removing drivers.
Install the double-magnet at the top, the single-magnet at the bottom. Place woofers face down on the midrange ribbons. One of the two sets of woofer terminals is preferred over the other. Imagine the terminals facing you & rotated to the 12 o’clock position. The N-S terminals are preferred, not E-W. Also, rotate both woofers so their terminals are closest to the tweeters (these two points will increase wire reach). If the quick-disconnect tension is too loose, use wire snips to compress both ends of the tunnels. If too tight, use a flat screwdriver to spread open the slot between the tunnels. Treat contacts with Caig Pro Gold, using a rag behind the woofer terminals to protect the cone. After installing the quick-disconnects, bend the speaker terminals away from the cones, preventing wire-to-cone contact.
