Mesured Qts difference

REALFLEO · 11th December 2006, 12:59 PM

Hi,

I mesured Thiele/Small params with voltage divider technique and I experienced some differences. Fs are close to Vifa's specs but not Qts.

Vifa
Fs:39Hz
Qts:0.35

Mesured
Fs:39.5Hz and 40.5Hz
Qts:0.40 and 0.44

What should I do, use an average of mesured Qts, average of all Qts(including Vifa's Qts) ? I guess I'm building 2 cabinet of the same size ?

Thanks,

REALFLEO

richie00boy · 11th December 2006, 01:23 PM

I would use average of what you have measured, ignoring Vifa specs. As that's what you will be actually working with.

infinia · 11th December 2006, 02:24 PM

Hi
Now you must measure Vas.
Fs is right on.
Q is higher by some margin, run test again with smaller Rtest and current. <0R5 ohm

As you prob aready know the drivers should be "broken in" before results can be trusted.

REALFLEO · 11th December 2006, 03:26 PM

I didn't use too much current. All mesures were between 0.2-0.3V and I used a 1000 Ohms resistance.

I don't understand why you asked me to use a smaller resistance, I tought it was the point of the potential divider technique to use a "infinite" resistance ?

Thanks,

REALFLEO

REALFLEO · 11th December 2006, 03:31 PM

About Vas, I wanted to use Vifa's one because I read that a 25% error in Vas produce a small difference in QB3 vented alignment.

and yeah I broke in my drivers.

Thanks,

REALFLEO

infinia · 11th December 2006, 03:46 PM

Hi
I wanted you to use a completly different setup closer to the final application. If the results are the same, thereby verifing your initial test. You need a PA, sig gen, and a precision current measurement you will use I instead of V.
So I take it you don't want to measure Vas then. Often Vas varies with the Q for each driver resulting in a similar alignment for a constant box size.

REALFLEO · 11th December 2006, 04:51 PM

It's not that I don't want to mesure Vas, but I won't do it for nothing ...

I understand your point of counter verifying it with current. I'll do it to be sure.

Thank,

REALFLEO

REALFLEO · 11th December 2006, 04:52 PM

sorry

what do you think about this technique:

http://sound.westhost.com/tsp.htm

infinia · 11th December 2006, 05:10 PM

Regarding the link above.
Yes that is a good reference, he uses 10 ohms to measure the current. Might be more accurate for most AC meters. Use as much precision as you can before you do the math ..i.e. 1% resistor and 2% VAC.

Svante · 11th December 2006, 08:31 PM

Could you provide us with details on how you measured Qts?

11th December 2006, 12:59 PM	#1
REALFLEO diyAudio Member Join Date: Nov 2006	Mesured Qts difference Hi, I mesured Thiele/Small params with voltage divider technique and I experienced some differences. Fs are close to Vifa's specs but not Qts. Vifa Fs:39Hz Qts:0.35 Mesured Fs:39.5Hz and 40.5Hz Qts:0.40 and 0.44 What should I do, use an average of mesured Qts, average of all Qts(including Vifa's Qts) ? I guess I'm building 2 cabinet of the same size ? Thanks, REALFLEO

11th December 2006, 01:23 PM	#2
richie00boy Did it Himself diyAudio Member Join Date: Nov 2003 Location: Gloucestershire, England, UK	I would use average of what you have measured, ignoring Vifa specs. As that's what you will be actually working with. __________________ www.readresearch.co.uk my website for UK diy audio people - designs, PCBs, kits and more

11th December 2006, 02:24 PM	#3
infinia diyAudio Member Join Date: May 2005 Location: Californication	Hi Now you must measure Vas. Fs is right on. Q is higher by some margin, run test again with smaller Rtest and current. <0R5 ohm As you prob aready know the drivers should be "broken in" before results can be trusted. __________________ like four million tons of hydrogen exploding on the sun like the whisper of the termites building castles in the dust

11th December 2006, 03:46 PM	#6
infinia diyAudio Member Join Date: May 2005 Location: Californication	Hi I wanted you to use a completly different setup closer to the final application. If the results are the same, thereby verifing your initial test. You need a PA, sig gen, and a precision current measurement you will use I instead of V. So I take it you don't want to measure Vas then. Often Vas varies with the Q for each driver resulting in a similar alignment for a constant box size. __________________ like four million tons of hydrogen exploding on the sun like the whisper of the termites building castles in the dust

11th December 2006, 05:10 PM	#9
infinia diyAudio Member Join Date: May 2005 Location: Californication	Regarding the link above. Yes that is a good reference, he uses 10 ohms to measure the current. Might be more accurate for most AC meters. Use as much precision as you can before you do the math ..i.e. 1% resistor and 2% VAC. __________________ like four million tons of hydrogen exploding on the sun like the whisper of the termites building castles in the dust


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11th December 2006, 03:26 PM	#4
REALFLEO diyAudio Member Join Date: Nov 2006	I didn't use too much current. All mesures were between 0.2-0.3V and I used a 1000 Ohms resistance. I don't understand why you asked me to use a smaller resistance, I tought it was the point of the potential divider technique to use a "infinite" resistance ? Thanks, REALFLEO

11th December 2006, 03:31 PM	#5
REALFLEO diyAudio Member Join Date: Nov 2006	About Vas, I wanted to use Vifa's one because I read that a 25% error in Vas produce a small difference in QB3 vented alignment. and yeah I broke in my drivers. Thanks, REALFLEO

11th December 2006, 04:51 PM	#7
REALFLEO diyAudio Member Join Date: Nov 2006	It's not that I don't want to mesure Vas, but I won't do it for nothing ... I understand your point of counter verifying it with current. I'll do it to be sure. Thank, REALFLEO

11th December 2006, 04:52 PM	#8
REALFLEO diyAudio Member Join Date: Nov 2006	sorry what do you think about this technique: http://sound.westhost.com/tsp.htm

11th December 2006, 08:31 PM	#10
Svante diyAudio Member Join Date: Feb 2004 Location: Stockholm	Could you provide us with details on how you measured Qts? __________________ Simulate loudspeakers: Basta! Simulate the baffle step: The Edge

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