problem with thiel-small calcs

[Jay Doorly]

First thank you John Mulcahy for giving away this fantastic software: Professional grade software and direct access to the author- what a treat!

Having completed my first round of testing SPL and Impedance with REW on my newly built speakers, i ran into a problem doing the Thiel-Small calculations: i enter 3.18 ohms for voice coil DC resistance (which i had measured with my digital meter) and get an error when i press "Calculate" saying:

"The blocked impedance deltaR value is high, this is probably due to the DC resistance value being too low, try running the calculation again with the a DC resistance value of around 4 ohm, the deltaR value will be automatically adjusted to obtain the correct Re figuer."

Then when i change the DC resistance to 4 and press "Calculate" i get another error message saying-

"The DC resistance value is greater than the minimum resistance, please enter a DC resistance less than 3.1 ohm."

I then enter 3.0 and the vicious cycle repeats...

So two questions:
1) How do i get past these errors?
2) How questionable are theThiel-Small results if i ignore these errors?

The mdat is attached. i'm using version 5.18. The first two SPL tests are my Dayton Audio B652 speakers (right [closer to corner] then left). They are 28" apart (on each side of my 20" monitor) They are on my desk which is in a corner of an 9 x 11.5 x 13.3 foot room. The third SPL is the speaker i just built on left. The woofer under test is a Silver Flute W14RS25-04 5-1/2" wool cone crossed at 2000hz. i'm an currently experimenting with bass traps between the right speaker and the corner.

The two impedance plots are my new speaker in free air (baffle attached) and with 4 nickels tapped to the cone. i used a 100 ohm .1% metal film resister (that measures 100.35 ohms on my meter) and the left and right channels of my integrated pc sound chip. I'm using a car receiver/cd and amp on my desk with networked speakers.

So crappy placement but that's why i'm trying to analyse/fix it with REW!

 

[John Mulcahy]

Your soundcard cal file contains a room measurement, not a soundcard loopback measurement, so best remove that from your measurements and from the soundcard preferences. It isn't critical so OK to work without it until you can get a fresh, good loopback measurement.

For the drive unit measurement try adding much less mass, a single nickel, for example, and make the measurement between 15 Hz and 20 kHz to avoid the response deviations at the frequency extremes. There is a problem with the curve fit for the added mass measurement for some reason, that might be due to the large added mass.

 

[Jay Doorly]

John, just wanted to confirm your suggestions worked perfectly (of course!) and to say thanks again.

 

[guiga5]

Hello!

I'm having similar issues here, but I made John suggestions and the problem is still there.

Someone have any other idea?

 

[John Mulcahy]

Your phase is shifted 180 degrees, typically caused by having the input channel selections the wrong way around (input channel set to left when it should be right or vice-versa). REW would usually show a warning about that.

 

[guiga5]

Dear John, thank you for the Help! I´ve made the changes and now I have the following measurements. I think I still have a problem, because the Q parameters are not good. Whats your opinion?

 

[John Mulcahy]

The mass you are adding is very large, should be close to or a bit less than Mms.

 

[guiga5]

Hello John,

I've changed the to 23,9g and 4,4g, but the results still the same... This loudspeaker its no new, and have already been refurbished... The original parameters to this one were bellow (model 25W87):

 

[John Mulcahy]

If you post the mdat file I can check that the model fit looks sensible, but the results look pretty consistent. You appear to be using an old REW version though, you should use the current build - a bug affecting Qms and Rms was fixed in 5.20.1.