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?
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?
Break in the driver first or your measurements are useless.
All low frequency drivers and some high frequency drivers change dramatically after breakin. Your Fs will come down.
All low frequency drivers and some high frequency drivers change dramatically after breakin. Your Fs will come down.
ok, i'm agree with you, but i think the distance from the official data sheet is too much to be covered by break in.
don't you ?
don't you ?
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).
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).
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
Paul
ok, but please see the impedance graph for the box i've realized after simulating.
yyyyyyyyyyyyyyyyy — imgbb.com
about my point of view the second peack is realy too much.
right ?
yyyyyyyyyyyyyyyyy — imgbb.com
about my point of view the second peack is realy too much.
right ?
What I'm seeing is a vented box applied to the driver. The original spec is about 60 ohms at resonance, and yours is about half that- in a box! The tuning of the port will bring the peak down in magnitude, and shift it higher in frequency.
Later,
Wolf
Later,
Wolf
Try providing more serious data on measurement conditions and measurement gear if anyone is to analyze this in a professional manner.
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.
Provide more details on how you measured them and what is the setup you used. I have measured quite a lot of SB drivers and they`re spot on with the published data.
i use clio form audiomatica, tested and calibrated
you find that sb are on spot with published, but also when the driver is fresh out the box, or after break.in ?
you find that sb are on spot with published, but also when the driver is fresh out the box, or after break.in ?
No fair plugging the pole vent while testing either.. The datasheet on madisound says the T/S data is for a broken in driver.
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tried two hours, but very little change in impedance graph...what do you suggest ?
to continue the breakin or is not usefull ?
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 ?
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
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
