SB17NRX2C35-8 not reliable specs!

diypass

Member
2012-04-01 9:35 am
hi guys,
some time ago i've bought a pair of SB17NRX2C-35-8.
now i started measuring the impedance in free air, but realy strange thing happened.
this is the official specs:
Screenshot-Official — imgbb.com

and this mine measured:
Screenshot-Measured — imgbb.com

please note the very different FS and Ohm, why this big difference ?
the woofer has not break-in is almost new, could this be the cause of the problem?
 
Try it and see?

Sometimes you will also see that the measured specs are quite different, but the system tolerance is very good and so you end up with roughly the same cabinet recommendations anyway (so that e.g. deviations in Fs, Vas and QMs more or less cancel each other out).
 

pkitt

Member
2009-02-24 12:32 am
As long as the ratios of Fs/Qts and the products of Vas x Fs2 are fairly close, the drivers will work pretty much the same in the same enclosure. For instance, if your measurements show both Fs and Qts to be ~20% higher than the published values, and at the same time your measured Vas was ~40% lower than the published value, you'd be pretty much good to go. Still all of us would like to see published specs that truly represent those of the drivers we buy.
Paul
 

diypass

Member
2012-04-01 9:35 am
at least 5 -10 minutes at Xmax or slightly over (observe Xlim), Fs/free air, before deciding published Fs is unrealistic. You can run it at xmax in a box but free air quarantees you wont use more power than necessary for the job or burn it up.

tried two hours, but very little change in impedance graph...what do you suggest ?
to continue the breakin or is not usefull ?
 
...but also when the driver is fresh out the box, or after break.in ?

After about 80-100 hours of break in using low frequency sine (5Hz-Fs of driver) with pauses in between. Initially I set volume to low, so the driver moves 2mm at most and in a day or so increase power but still keep excursion below its xmax. Usually flexes out a unit much faster but I leave them for some 3-4 days.
 
so i must continue the breakin ?

however you sad that schould be enough 5-10 min at xmax. why now you write 80-100 hours ?

I said below xmax - another forum member advised on using xmax. My opinion is to start in a gentle way and then increase the cone displacement. But its just because I think its better this way, and this doesn`t mean it is :))
 
Let the driver cool before measuring.
your nominal impedance looks about 2 ohms higher (~ 9ohms) than the manufacturers (~ 7 ohms). This could also result in artificially amplifying the resonance peak in s/w calculations. Are you using a calibration / series resistor? check value
I am unsure whether manufacturer measurement is on IEC baffle or free air. use same conditions
measure driver vertically - without back reflections (clamp magnet). laying a driver down on a board will not yield the same result