Hi Joe,
Well quite simply changing the mass (adding or subtracting putty) on your Passive Radiator allows you to tailor the response of your woofer system to the electrical impules of your amps output.
All amps have varying ability to send current to your woofers voice coil. Generally those with larger current capabilities and higher Dampening ratios can move the woofers more effectively.
Lesser powered amps and those with lower dampening ability cannot. If you run tube equipment, you will probably have to remove substantial putty.
If you run 600+wpc with 500+ dampening then you may need to remove none or even add.
As Brian says the symtoms of too much putty (mass) and too little (are) the same. The sound becomes muffled and boomy, or wooly.
When the mass is right, you have a dryer, tighter and deeper bass, with pretty good definition.
Since the signal from the amp is going to be the same every time you play a certain cut at a designated power setting, the only alternative to getting the bass reasonably accurate is to make that mass adjustment.
It is not all that hard and many times it has to be made by what you hear and not what you measure.
If you remove too much putty, then the signal from the amp will "overdrive" the system and it will not sound right. Usually muffled and boomy, not sharp and defined.
If you under drive the woofers they will sound the same way since they will respond too slowly because they are too heavy.
So the idea is to find the amount of putty that gives you the cleanest, most detailed bass.
And a couple hints in doing this. Use the listening volume you would normally listen at for making adjustments. This will yield the best overall result.
And if you change the amp or location of the woofer, you may have to re-adjust the putty so save all putty removed in a small plastic bag.
And newer suspensions being stiffer may require you remove a bit more putty to then add a bit back 6 months or a year later.
The method is usually to first lsten to the bass with some deep bass passages. Remember what the bass sounds like now. Then reach under and take off a bit of putty about the size of a pea. Now listen again.
Listen carefully. Look for attack, leading edge, boominess, droneing, all the qualities bass can have.
If it sounds right, remove a "fingernail" full more. Listen again.
Repeat this process until you hear the quality deteriorate to a wooly, loose sound. At the first notice of that, add back the last "fingernail" and listen again. You may have to add back two fingernails but that should be just about the right amount.
Some of the best music to use is Jazz String bass cuts, since they have good attack and definition when well adjusted.
So to recap:
Too much putty = slower woofer and muffled sound
Too little putty = over driven woofer and boomy sound
Just right putty = tight, deep, defined, bass.
Hope that helps and Brian can correct me if I stepped on (or in)something
