We make our own bass drivers for decades and do not use anything short of best possible for the purpose. That means custom made Woven Carbon Fibre cones in various sizes, natural rubber surrounds, 300W voicecoils, 2.3kg magnets. Driving our woofers with 20Hz signal to loudness of 115 dB we can see (not just theorize) cone travels of at least plus/minus 15 mm. Also, we are unique in suspending the spider on bass drivers. Check the articles Cone Talk – Materials and Why suspend a spider? to learn more on bass drivers construction.
All drivers on all speakers except some options for our subwoofers have phase plugs instead of usual dustcaps. Appropriately designed phase plugs are superior to any kind of dustcap, inverted or not. The phase plugs are precisely the length and bluntness needed to move the woofer acoustic center forward to match the planar sections.
In place of noisy ports at large speakers there is a tunable passive radiator (PR). It is plenty fast for music and has the heft, extension and output levels for HT. Sealed designs either cut off an octave or two higher than the PR design, or are very inefficient. Not what you want.
A PR is basically a tunable vent and allows you to match system Q to the series R of your speaker wire and output impedance of your amp. A necessary feature for good bass. While we tune the PR at the factory for what sounds right on our gear, yours and your room are certainly different. Just follow the setup instructions.
So, all our drivers are custom and almost all are made in US, by VMPS or custom for VMPS. There is no clones of our speakers out there.
VMPS Bass system
The Passive Radiator (PR) located in the bottom of the cabinet already has a certain amount of mass attached to the center, by the factory. By adding or subtracting mass from the PR, it is possible to make system tonal balance warmer (higher Q) or tighter (lower Q). This is accomplished by changing an inert mass such as Mortite rope putty, the substance attached to the PR. You can buy additional putty at most hardware stores but your speaker is delivered over-damped (a bit too much putty), so that in almost all cases, you will tune the speakers by removing mass from the PR. Mass is accessible by inserting your hand into the slot formed by the base and the bottom of the cabinet. Removing a very small amount, no more than 1gram of putty, will be sufficient to make the adjustment.
Moving mass of PR is very low. Since a PR is driven equally over its entire surface by the active woofer’s backwave, the diaphragm will move pistonically even if it is not rigid. The PR cones are treated paper. Paper is fine as long as you don’t have to listen to their high frequency noise and distortion products. Facing the PR down and slot-loading it out the front filters such products out nicely.
We invented the slot-loaded PR and decided not to patent it, since we would spend our life in court defending against copies. We knew we were on the right track when we saw a Klipsch monitor at the AES in 1984 with a slot-loaded PR.
Shown above is a bottom side of the Larger subwoofer that forms a slot-loading with the floor, showing 38cm (15″) PR with added mass at the center of the PR
