For reference, quoting Irisbo from diyaudio:
Hello Lars Sorry to bother you again with this but have you been able to complete the 8 ohms version of the PTT8. I would need the TS parameters to check that it will fit in my project. Thanks in advance Jean-Claude
www.diyaudio.com
"frame-motor resonance: this is a generic thing for all electrodynamic drivers. there is a heavy motor hanging in the frame which is bolted to a box. The frame acts as a (very stiff) spring and the motor is a mass thus forming a mass spring oscillator. All the Newton forces of the driver goes through this mass-spring system.
This makes it very critical how the frame is fixed to the box since the high forces can cause rattling (ie high distortion).
It would be a lot better to mount the driver by its motor which is the source of the Newton forces but this is not standard. The best would be to bolt the motor onto a heavy solid chunk of metal serving as inertial reference to absorb the Newton forces.
Anyway, this is as mentioned a generic problem for all drivers but with the X stroke PTT drivers we have high Mms and a very strong motor in order to get low F3 in a compact box and this means the driver produces more Newtons force for the same SPL compared to a lower Mms driver.
This makes the mounting method more critical including how much torque and what materialsused etc.
When measuring on the driver laying on its magnet the problem is gone since the Newton forces terminate into the 'ground'and the frame is untermintaed so we do not have the mass-spring oscillator."
So are you saying that it doesn't matter, or that Alan provides poor customer service?
Alan's quoted elsewhere earlier in this thread stating that he considers the mitigation methods proprietary, that he doesn't want to disclose the methods, and asks if the bolts were tightened as he says that will impact distortion.