TSP PROBLEM - Qes

[DR ANALOGUE]

Hello,

I measured the TSPs of my SCAN SPEAK 15W/8530K00 and the results are quite different compared with those from SCAN SPEAK.
The difference of 30% in Qes worries me. It brings the Qts close to 0.4 which would cause an alignment other than QB3.
The driver has a huge magnet. Could it be that this influences the measurement of Qes. Or have I done another mistake??
The measurement was done with extra-mass and low voltage.

SCAN SPEAK MEASURED
Re [Ohm] 5,8 5,8
Le [mH] 0,35 0,27
fs [Hz] 30 32,8
Qms 4,9 5,32
Qes 0,29 0,4
Qts 0,27 0,38
Vas [liter] 28 22
Mms [g] 13 13,22
B*I 7 Tm 6,4 Tm
SPL [dB] 85,5 84,7

Do have any ideas about the problem?


Kind Regards
Michael

[e-side]

It's possible that your measured results are different from manufacturer's data (Sometimes this is because loudspeakers with 'attractive' parameters (low Qes, Qts etc.) sell better).

It's hard to say if you made a mistake. You'll probably have to check your measurement method.

I would use my own measurement results...

[GM]

Greets!

Don't know how you measured/calc'd these, but when I punch in the other numbers I get Qes = 0.2901 for SS and 0.3858 for yours.

Punching the numbers into a BL calculator using SS's 95 cm Sd, I get 7.0063 N/A BL, 13.02 g Mms for SS and 6.5539 N/A BL, 13.864 g mms for yours using the calc'd 0.3858 Qes and BL drops to 6.4365 N/A with your 0.4 Qes (same high Mms of course), so there's some inconsistancies that need resolving.

Back to square one, I'm afraid, and since Vas is the one most folks get wrong using the added mass method, do it again with the sealed cab method, which is what manufacturers used/recommended back when I was actively building and please update us with your findings.

GM

[DR ANALOGUE]

Hello again,

Having read your recommandation and additionally the book of J. D'Appolito I decided to do two test series with different voltages, with "added mass" method and closed cabinet method.

I use the German software Hobbybox which seem to work in the same way as CLIO. According to reports, the differences in results are minor between Hobbybox and CLIO.

3 measurements (1/2/3) were done with approximately 100mV, as Thiele Small is a "small voltage" concept. However, I do not believe in this very high Q-factors.

fs=38,88/38,75/38,84Hz
Qes=0,49/0,49/0,48
Qms=7,51/7,45/7,30
Qts=0,46/0,46/0,45
Le=0,26/0,27/0,28mH(1000Hz)

added mass of 7,5/15,7gr:
Mms=12,81/12,93gr
Cms=1,25/1,25mm/N
Vas=16,7/16,6Litre
BL=6,2/6,2Tm

closed cabinet of 6,26Litre:
Mms=9,13gr
Cms=1,84mm/N
Vas=24,5Litre
BL=5,2Tm


As CLIO works with approximately 1,1Volts I did another series of measurements with around 1,3 Volts

fs=32,84/32,97/32,95Hz
Qes=0,43/0,41/0,42
Qms=5,51/5,30/5,35
Qts=0,40/0,38/0,39
Le=0,26/0,26/0,26mH(1000Hz)

added mass of 7,5/15,7gr:
Mms=13,08/12,61
Cms=1,72/1,77mm/N
Vas=22,9/23,6Litre
BL=6,1/6,2Tm

closed cabinet of 6,26Litre:
Mms=9,60gr
Cms=2,43mm/N
Vas=32,3Litre
BL=5,3Tm

Unfortunately the result for Vas is not reliable at all. My closed cabinet method deliveres Vas plus 40-50% compared to the added mass method. And the added mass method seems to be reliable as I get the same result with different masses. And it also leads to correct Mms, which is not the case with the closed cab method.
I did also a test series with different volumes (18/11/9 Litres) resulting in interdependent Vas (45/38/33 Lites). This was done in an experimental way, maybe with some inaccuracies, but the trend is obvious and leaves only open questions to me. ?????
I understood that the fc should be at least 50% higher that the fs, which was the case for all measurements. ???????

Big uncertainty for me......... ??????

I do hope that there are some experts here who can fill my gap in TSP-knowledge.

Best wishes
Michael


manufacture TSPs:
fs=30Hz
Qes=0,29
Qms=4,9
Qts=0,27
Le=0,35
Mms=13
Vas=28Litre
BL=7Tm
sd=95cm^2 (I calculated 96,8cm^2)

[e-side]

Strange.... I did have some problems with my measurements a while ago too. My first measurement was done at 0,99 V @ 100 Hz, with the following results:

Fs = 33 Hz
Qms = 4,65
Qes = 0,67
Qts = 0,58

Then I changed the voltage level to 0,75 V @ 200 Hz. The results were very different from the first measurement:

Fs = 30 Hz
Qms = 2,9
Qes = 0,42
Qts = 0,37

As you can see, Thiele and Small Parameters change with voltage level. Therefore, you should try a different measurement method, one with constant voltage. Search for 'Impedometer' or take a look at this article. With this procedure it's also possible to measure Vas by using a closed box. You should get reliable results this way.