Dumb question about xmax

Hi all,
I have some doubt about xmax, some companies declare a value with plus minus for example B&C 18tbx100 is +/- 9 mm, some companies an absolute value for example rcf l18p400 is 8 mm. So for the 18tbx1000 the total absolute value is 18mm? or for the RCF is +/- 8 mm?

They are both the same the RCF will also be +/- 8mm Note that they are both probably calculated with a fudge factor. Actual Xmax will be slightly lower.

Actual Xmax for overhung voice coils = (voice coil height - gap height)/2

Tony

rcf declares this formula (hvc-hg)/2+hg/4 but the "maximum excursion before damage peak to peak" is 50 mm. This is confusing me at all...

bitzo wrote: rcf declares this formula (hvc-hg)/2+hg/4 but the "maximum excursion before damage peak to peak" is 50 mm. This is confusing me at all...

The +hg/4 is the fudge factor. I am having a bit of an argument with a guy on SP about this very subject at the moment. As far as I am concerned this fudge factor was added as a marketing tool to enhance the specs. The fact that different manufacturers use a different fudge factor only adds to the confusion.

I have always ignored the Xdamage figure and assumed that all competent speaker manufacturers would ensure that Xdamage was sufficient to enable the driver to work to spec.

Tony

thanks Tony, very clear smiley20

Some manufacturers have now moved away from a calculated Xmax and prefer to measure it instead. One way of doing this is to determine the excursion when a set level of distortion is produced due to the driver moving into a non-linear region. Very similar to the way that amplifier power is specified at eg 1% THD. This is why B&C give two figures, Xmax and Xvar.

chaudio wrote: Some manufacturers have now moved away from a calculated Xmax and prefer to measure it instead. One way of doing this is to determine the excursion when a set level of distortion is produced due to the driver moving into a non-linear region. Very similar to the way that amplifier power is specified at eg 1% THD. This is why B&C give two figures, Xmax and Xvar.

I have no problems with this Xmax enhanced method of rating this parameter I just think that it needs to be constant. Probably best if it is stated as the distance that BL drops to a stated percentage i.e. 80%.
At the moment some companies quote actual Xmax and other enhance it by up to +Hg/3.

If I was in the business of building cabs for a living I would obviously not take the T/S parameters as read anyway and make sure that all the drivers that I used had been measured independently just to be safe.

Tony

Personally I'm not sure if 1mm difference in Xmax is really that important. I'm not in the habit of running drivers to their absolute limit, nor do I work with particularly sub-heavy music genres. Add to that the fact that simulations of excursion are a rough guide at best and unlikely to be representative of real-world usage.....

Totally agree Chris, Unless it is a small Xmax horn driver then the extra movement that the enhanced figures give hardly increases the Max. O/P at all.

I am way more interested in how they work within the limits.

Tony