How to Adjust Bass Damping on Floor-Standing VMPS Speakers

The most important adjustment to your speakers is the bass damping, which permits altering the tonal balance and clarity of the system for maximum accuracy or to compensate for room problems or differences in damping factors of various pieces of equipment such as tube amplifiers.

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, so that in almost all cases, you will tune the speakers by removing mass from the PR, which 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.

First: Set the speaker level controls. Make the adjustment with a screwdriver, not your fingers. Get used to the feel of moving the control the smallest possible increment, moving the wiper one potentiometer turn at a time. You can barely see this increment, but you can feel it. Second: Place the speakers as close as a few inches from the back wall up to the middle of the room. Third: Toe the speakers in so that they crossfire a foot or two in front of your listening position. Midrange and tweeter arrays should face the center of the room. You are now ready to make the damping adjustment. Warning: Do not elevate the speakers or put spikes under them.

Play the system with wide-range music material you are familiar with (orchestra with voice and good bass is suitable). Locate the adjustment mass in the center of the PR of one speaker and remove a fingernail’s full, no more. It is important to make small adjustments since it is easy to go right by the correct setting. Listen again for clearer sound with fuller, more extended bass. If the sound is clear or less boomy, without sacrificing bass extension, you have made an improvement, and you can repeat the process at the other speaker. Now repeat the above, one speaker at a time, and one fingernail’s full of putty at a time between listening. If at any time during your adjustments the sound becomes fuzzy, less focused or dry, replace putty that you have removed (the last removed amount). Typically, you will end up removing an amount the size of a green pea. Do the mass adjustment until there is no further improvement. Caution: too much putty or too little putty on the PR sounds similar. All you can tell is that the sound is not optimally clear, tight, and extended. Go slowly and take your time.

Now, adjust the level controls one at time, making the smallest possible change on each control, one speaker at a time. Go slowly and take time to familiarize yourself with the sound of the adjustments you have made, with various recordings of different music.

Sometimes just a small reduction in midrange or tweeter level (smallest possible increment) will produce increased definition, in tandem with the damping adjustment. Go slowly: the combination of level control settings and PR moving mass that is optimum for your room, speaker placement, and associated equipment will take about an hour to discover, using five to six different music selections. Go slowly.

The bass damping adjustment affects the entire frequency range. Correspondingly, adjustments to level controls and bass damping interact. A fuzzy mid range may be cause by the incorrect bass damping. On the other hand, incorrect setting of the treble control will soften or diminish apparent bass level and tightness. Take the time to get to know the adjustments and their effects and you will get good sound from your VMPS speakers. Neglecting these adjustments may result in poor performance.