Hi,
I've had the woofer tester for some time and have been using the added mass method for VAS etc measurment.
Until recently I thought this was working accurately, but now I am not so sure.
I have some 8" Dynaudio woofers out of a Volvo, the aftermarket equivalent driver would be the MW180 which looks to share the same cone/VC/former and softparts (I can't see Dyn retooling these parts for a Volvo driver)-MMS of the MW180 is 36.5g, my WT3 measurement comes back with 23.80g for one driver and 22.43g for the other-well off from what I was expecting.
So I thought to try using different weights, tried a few and the MMS changes with each different weight.
Am I doing something wrong or has anyone else noticed this?
I've had the woofer tester for some time and have been using the added mass method for VAS etc measurment.
Until recently I thought this was working accurately, but now I am not so sure.
I have some 8" Dynaudio woofers out of a Volvo, the aftermarket equivalent driver would be the MW180 which looks to share the same cone/VC/former and softparts (I can't see Dyn retooling these parts for a Volvo driver)-MMS of the MW180 is 36.5g, my WT3 measurement comes back with 23.80g for one driver and 22.43g for the other-well off from what I was expecting.
So I thought to try using different weights, tried a few and the MMS changes with each different weight.
Am I doing something wrong or has anyone else noticed this?
23.80 an 22.43 are very similar, some average +/- 5%. If your weight is elastically coupled to the voice coil, by say being a mass attached to the center of the middle dome of the cone. Then some flexing could partly uncouple the mass and thus changing the measurement fo MMS.
If you run the measurement five times with the same load, do you get spot on the same value?
If you run the measurement five times with the same load, do you get spot on the same value?
Try the Delta Compliance Method. Mount the driver to a Closed Box with a known volume. This will avoid the inaccuracies that you sometimes can encounter with Added Mass.
I bought a .1% 10 Ohm resistor to calibrate it with. It is just as accurate as my big bench DVM.
With T/S, within 20% you are fine. Don't sweat the details. OEM specs vary. How much glue was used varies. The slightest vibration of the mass in the mass displacement measurement, or the tiniest of air leaks in the sealed box measurement will cause much bigger issues.
With T/S, within 20% you are fine. Don't sweat the details. OEM specs vary. How much glue was used varies. The slightest vibration of the mass in the mass displacement measurement, or the tiniest of air leaks in the sealed box measurement will cause much bigger issues.
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