[Brian Cheney]

To respond to "lowtech":

We have published curves on this very forum that show a dramatic drop in THD by means of proper tuning the PR with changes in its moving mass smaller than 1g. 

If this is not "conventional wisdom", then perhaps such fails to describe driver/system behavior adequately-- no surprise to many of us in the industry, or in the audio hobby.

[John Casler]

I am glad to here about the impedance measurement. I have played around with a lot of in room frequency response measurements and I couldn't see where the putty had much effect. But if as, Brian says, it can be used to get in the ballpark that would be great. I have two subs that have had the upgraded woofers and the passive radiators have been reconed so just getting in the ballpark would be a big help. I think I'll pick up a WT3

Tom

Hi Tom,

The mass loading of a Passive Radiator has 2 effects.

1) In the larger sense with greater mass adjustments it "tunes" the PR to respond at the correct sychronization with the active driver(s).  This will have an adjustive effect on frequency (although it is NOT a HUGE effect as it arrives from the factory already adjusted)

2) In the smaller adjustments the effect is in a reduction in the "distortion" of the interactive whole of the SUB drivers.  That is, where the two (or more) drivers interact with each other to produce a lower distortion acoustic response, as if they were one.

"In room" response via putty adjustments will be affected very little compared to the proper placement and "integration/blending" of the Sub(s) with the mains, in most cases.

Putty adjustments are not really like equalizations or other potential adjustments.  They will always be to coordinate the proper interaction of all the drivers to the signal and to fine tune the reduction of distortion to its lowest levels.

I might add, that B, generally pre-tunes all PRs that leave the factory. The only reason to perfrom your own experiments and adjustments is if you are a "tweaker" and recognize the enjoyment of simply "getting it closer" to the best it can be.

No one should take the tuning ability of the Passive Radiators to be a "given", and that it must be performed for the speakers to sound as good as other speakers.  Out of the box, they are already at least to that level.  The good news is that to those who care, they can take it to another level.

[Housteau]

The putty helps to match the bass to your choice of amplification also.  I believe that Brian may still ship speakers with passive crossovers a bit over damped, where you need to remove slight amounts of putty to tune them to your particular amps and room.  However, my guess is that since the active systems are shop tuned with the same amplifiers that the speakers ship with, this allows them to ship and arrive more accurately dialed in.

I remember asking Brian about my VLAs and he said they were shipped just they way he likes them to sound and behave, but to still experiment in my room.  I did end up removing very small amounts, but have since put it right back.

[Housteau]

I did end up removing very small amounts, but have since put it right back.

I just took it back off once again .  A friend and I both agreed with what we heard.

[Brian Cheney]

Fascinating, isn't it?

The putty adjustment compensates for source impedance of associated components, among other things, which the "coarse" tuning cannot address.  The adjustment mass is small and the adjustments even smaller.  There is no doubt, however, that the system would not be optimally tuned without the ability to change PR moving mass very slightly.