TSP: REW asks for added mass while using closed box method - Home Theater Forum and Systems - HomeTheaterShack.com

 
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post #1 of 4 Old 09-14-14, 09:47 AM Thread Starter
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TSP: REW asks for added mass while using closed box method

Hello everyone,

First I would like to say thanks to the author of REW. Life has become a lot easier for DIY enthusiasts compared to a decade ago, when I started building loudspeakers and such great tools were not readily available.

I have measured the impedance of some 6.5" and 15" drivers from 0Hz - 20kHz, both in free air and using the closed box method, as explained in the Online Help. Measurement results are smooth, consistent, and match previous manual measurements obtained using a voltage divider. However, when I try to compute the TSP for my Zeuz and Audax drivers (attached), REW shows the following error:

"Invalid added mass figure
Secondary measurement appears to be made with added mass (fs is lower than free air) but the added mass value entered is zero, please enter the added mass figure"

This is clearly false, as the closed box fb's are significantly higher than the free air fs's, as can be seen from the attached mdat files. Also tried a different frequency domain (10Hz - 4kHz) but the error remains.

What is going on here?
I am using REW V5.01 Beta 22 Build 3423 on Windows 7 (32bit).

Additional info:
Audax: DC Re = 10.0 Ohms, sealed box volume = 5.895L, Sd=128.7 cm^2
Zeuz: DC Re = 6.3 Ohms, sealed box volume = 61L, Sd=814 cm^2

Best,
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post #2 of 4 Old 09-14-14, 12:28 PM
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Re: TSP: REW asks for added mass while using closed box method

It was a bug introduced when the model was last modified, I have fixed it for the next beta release (due in about 2 weeks). In the meantime here are the results for those measurements, let me know if these look reasonable:

TSP: REW asks for added mass while using closed box method-ts.jpg

TSP: REW asks for added mass while using closed box method-ts2.jpg
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post #3 of 4 Old 09-15-14, 05:14 AM Thread Starter
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Re: TSP: REW asks for added mass while using closed box method

Dear John,

Quote:
JohnM wrote: View Post
It was a bug introduced when the model was last modified, I have fixed it for the next beta release (due in about 2 weeks). In the meantime here are the results for those measurements, let me know if these look reasonable
Yes, these results are reasonable and closely match my previous voltage divider results!

Perhaps somewhat off-topic, but how much do voice coil DC resistance and Sd errors affect the final results? My DMM tends to show DC resistance slightly higher than the maximum value accepted by REW, which is what I use for input. Repeating calculations for different Re values appeared to have no effect on the Qt parameters.
The online help mentions this issue but unfortunately I do not have a reliable DC source (a 9V battery with 1k series resistor yields even higher values in my case...)

Thank you, and I'm looking forward to the next beta!
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post #4 of 4 Old 09-15-14, 03:32 PM
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Re: TSP: REW asks for added mass while using closed box method

DC R doesn't make much difference as long as it is not too high, REW's model estimation adapts an additional dR value to get the best fit.

Cms and eta both depend on the square of the area.
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