Thiele-Small Calculation Issue

[RexJohnston]

Hi,

First off, thanks for this software. Much appreciated.

I have an issue calculating the above characteristics. I'm using REW5.2 on a linux laptop, set up with a decent amplifier, 5Ohm sense resistor, ~1/100 padding on the card inputs.

First up, the free air measurement of a 10" woofer



Added mass measurement



The final error message, after clicking through the dialog box about reducing the resistor value (which always appears, no matter the input value).



Looks to me like it's not figuring out the Fs properly, but I'd love to be able to fix this.

TIA, Rex

 

[John Mulcahy]

Phase is about 180 degrees off at resonance, the input channels are probably the wrong way around. The screen shots show 5.19, should probably try the measurements in the latest V5.20 build (which would have shown a message about that phase disparity).

 

[RexJohnston]

Fantastic! Sorry about the incorrect version. I should have checked. All good now.

Cheers, Rex

 

[RobertoG]

Hi, I don't want to start new topic, so I would like to post here, because it refers also TS praram calculation. Would it be OK? Some values like Qms, Ots are far away from the spec. And I wondering what may be reason of that. I read instruction carefully and I hope that I did what I should (ohh, maybe speaker position was not as it was suggested because it was horizontaly assembled). Could you advice please, what I did incorrect? Thank you.

 

[John Mulcahy]

You can find good tips on measurement setup on the Speakerbench website. The 25.5 g mass is too high, best to use masses lower than the Mms of the driver. The 3.2 g mass is a little low, but the model fits are good so the results look valid. Vertical mounting may shift things a little. Make sure the voltage at the driver terminals is not too high, the sweep should not sound loud. It is not unusual to find results that differ from the data sheet, but those results are very different so it is a little difficult to explain.

 

[Bernard]

I tried the dual added mass method. Search in thread 52444.
It takes more time but it gives more accurate results.

In order of appearance:
1. put the speaker vertically *
2. stick 4 plots of 4 g each on the membrane near the dust cover, two by two opposite each other, to obtain a total mass equal to about 90% of the manufacturer's mms; in your case, 17.5 g.
3. perform the m1 measurement (total mass)
4. remove very, very carefully 2 opposite plots so as not to "stress" the speaker
5. perform the m2 measurement (mass reduced by half)
6. remove the two remaining pellets as gently as in step 4
7. perform measurement without plots for m0 measurement

The Speakerbench verdict must be Good or Excellent for the measure to be considered valid.
Patience is required.

* In my case, with REW and a horizontal loudspeaker I get a 117 litre Vas and with the vertical loudspeaker 144 litres; with other softwares the difference is the same.

 

[RobertoG]

OK, thank you for suggestion. I will try once again, in vertical position. However gluing sticky parts to paper membrane might be risky .

 

[Bernard]

Risk is minimal with a fresh and clean Blu-tack (free advertisement...) that you will buy especially for the operation. ;-)