[musiclear]

I'm looking at the possibility of using mass loading the cone of a woofer to lower the FS a bit. 

I would like to reduce delay and tune a little lower. 

[JLM]

VMPS used to use a bit of putty to tweak their woofers.  It was done by ear.  Sorry but don't recall the purpose of the tweak.

Where did you get this idea?  Even if it's possible, changing F3 from 28 to 22 Hz is a 1/3rd of an octave (seems like a big change).  If it is possible, why don't more people do it?  Doesn't quite make sense to me.  Have you tried posting this question in the Lab Circle?

[musiclear]

Hey... sorry to have missed you reply.  I've heard of a couple ways to lower FS.  To increase mass which really lowers efficiency and takes a lot of the benefit out of it, and raising  CMS by reducing the compliance of the suspension which seems to work pretty well in theory. 

My purpose is to lower fs and lower tuning frequency which increased efficiency down low.  Some modeling I did suggests that in an application I am looking at, lowering the fs of my driver from 25hz to 20hz and tuning appropriately, I would gain about 3db at 24hz which is equivalent to doubling the power needed to produce that frequency.  It seems like a pretty good trade off.  Reduce the total power the driver can take by reaching xmax with less power, but producing more of the frequency I want with less power.

[Duke]

My purpose is to lower fs and lower tuning frequency which increased efficiency down low.  Some modeling I did suggests that in an application I am looking at, lowering the fs of my driver from 25hz to 20hz and tuning appropriately, I would gain about 3db at 24hz which is equivalent to doubling the power needed to produce that frequency.  It seems like a pretty good trade off.  Reduce the total power the driver can take by reaching xmax with less power, but producing more of the frequency I want with less power.

Adding mass to the cone to lower Fs from 25 Hz to 20 Hz has a negligible (less than 1 dB) effect on efficiency south of 30 Hz, but it does significantly decrease the efficiency higher up, which can make it look like an increase in efficiency if you're comparing the -3 dB points.  But from ballpark 30 hz on up, the higher Fs version will have higher efficiency.

Also, the suspension system (spider & surround) might not keep the voice coil centered in the gap over the years with the added mass, so you'd probably want to rotate the speaker 180 degrees every year or so.