Whatever happened to the 15%?
Just to confuse the issue ...
The most difficulty shows up when the voice coil and gap are exactly equal. Simple xmax is zero, but the speaker still works and even makes a little bass. I think the older D130 and 130A (great-grandfather of the 2220) were built this way.
In this case, there was once a claim that that the gap fringing allowed on average an extra xmax of 15% of the gap length. It was extended to say xmax = VC length - 0.85*gap length, at least for overhung coils. IIRC, this came from a JBL paper in the JAES.
Re: Whatever happened to the 15%?
Hi Paul
Good point! Let's find that paper. :)
From an old post -
The 2121 has a voice coil winding depth of 0.280"
The 2122 has a voice coil winding depth of 0.180"
The 2123 has a voice coil winding depth of 0.420"
All three have a 0.280" top plate.
All three currently have a moving mass of roughly 26 grams.
The published xmax on these drivers:
.060"
.120"
.100"