Impedance measurement / Not coming out right

[gljiva]

Hi to all,

I hope someone had same issues with measuring impedance and it may be an easy fix.
I have constantly different Fs measurement comparing with the speaker driver spec.

Things done so far:

1. used 2 dif laptops
2. used 2 dif desktops
3. used few dif speaker drivers
4. used 2 diff sound cards: behringer and focusrite
5. calibrated with 100ohm and 1kohm resistor
6. tested under linux/ubuntu,

and results, strange enough were always same.

Please find attached files during one session of testing DA tcp 115/8.
Driver Fs by the spec is 59,2 Hz, by measuring I get 77 Hz.

Best regards,

gljiva

 

[dcibel]

Looks fine. You're only highlighting the reason for measuring drivers at all. Throw away the datasheet, your driver is not the golden sample used for the document.

Furthermore, focus needs to be widened beyond a single parameter. If the purpose of TSP is to design the cabinet, then complete the full TSP process, simulate the driver in a cabinet, and compare that to the result of the datasheet if you want. That result should answer the question of whether or not you care about the difference in parameters.

Other thing to note is that TSP is very finicky, and susceptible to be influenced by many factors. Test voltage level, driver break-in, even ambient temperature in the room will affect the result among other things. There is no true standard for test conditions, and manufacturers often don't provide that level of detail, so best results will be obtained with confidence in your own measurement, simulation, followed by real world validation. FWIW TSP is defined as "at rest" parameters, so true TSP is obtained with a low voltage, 100-200mV, however some manufacturers will provide data at higher level like 1V and with a well broken in driver since it provides a lower Fs, which seems to be the first parameter anyone looks at.

 

[gljiva]

Hi dcibel,

Many thanks for your replay.
Yea, I understand what you are saying. I went to much in to a details and I expected to be 100% spot on. Hmm...

Will see what I can do with what I get.

And yes, it is to design the cabinet.

Thanks and regards,