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Measuring driver parameters vs the data sheet values
Measuring driver parameters vs the data sheet values
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Old 11th February 2019, 11:35 PM   #41
ente is offline ente  Germany
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http://www.artalabs.hr/AppNotes/LIMP..._4_English.pdf
Technical Notes :: SB Acoustics

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Old 12th February 2019, 02:06 AM   #42
wintermute is offline wintermute  Australia
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Measuring driver parameters vs the data sheet values
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Originally Posted by ggidzinski View Post
I have just reviewed the TS measurement process in REW. Could you please outline the impedance measurement circuit that you use as there are a few different approaches (sound card only, separate amplifier, etc)?

Thanks,

George
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You need the impedance cable here Cables

Note that for REW and ARTA you ideally should use a 100 ohm resistor not 10 ohms as per the diagram.

Some soundcards struggle to drive a speaker directly. If that is the case then using an amplifier to drive the speaker may be needed, but make sure to keep the levels low. Use a 100Hz sine wave and an AC voltmeter to set your voltage to 1V or less. There is a risk that you can fry your soundcards input if you use and amp and don't have some sort of attenuation.

I myself use a Walin Jig II which I made. http://www.raymondaudio.nl/files/jig.pdf


Tony.
Note that I haven't measured any T/S params for a while (so I'm not sure if my focusrite 2i2 will drive a speaker direct). I was using my old Audigy II ZS (which had no problem at all driving a 4 ohm speaker directly) for doing the measurements.

I have also used my LM3886 AMP to drive the speakers, results were pretty much the same so I dispensed with the amp as it was more hassle to set up for testing. The Walin Jig has an attenuator and clipping zenners to protect the sound card from over-voltage, Claudio's simple cable does not.

Tony.
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Old 12th February 2019, 02:11 AM   #43
ggidzinski is offline ggidzinski  United States
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Thank you.
George
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Old 12th February 2019, 06:52 AM   #44
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This is just the beginning, just wait til you start doing impedance measurements of your loudspeaker boxes and the result is anything like your box simulations.
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Old 12th February 2019, 08:38 AM   #45
ggidzinski is offline ggidzinski  United States
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It is harder to get out of the starting blocks than I was expecting with all of the issues trying to get reliable measurements and trying to figure out how reliable the data sheets are. It’s funny because some people say to never design a box until you have the drivers in hand so that you can measure the actual units that you are going to use and some say that unless you have $5k to measure like a mnfg just design from the data sheet and tweak in the box.

Seemed clear cut as I was getting started, now not so much.

George
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Old 12th February 2019, 09:38 AM   #46
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Measuring driver parameters vs the data sheet values
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Originally Posted by celef View Post
This is just the beginning, just wait til you start doing impedance measurements of your loudspeaker boxes and the result is anything like your box simulations.
If the measurements are good then it should be pretty close.

Attached sim (blue) of 2 MW144's in a 10L sealed box, using T/S params measured and averaged from 4 drivers.

Black actual impedance measurement in the box which was actually two separate 5L volumes one for each driver.

Sure it's not a perfect match but it is certainly within the ball park.

I don't have a measurement of my 70L BR or tiny 4" BR cabinets to hand to do a comparison there. Likely they will show much bigger discrepencies, especially the 4" because I used a small slot port rather than a tube.

Tony.
Attached Images
File Type: png impedance_compare.PNG (46.6 KB, 72 views)
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Last edited by wintermute; 12th February 2019 at 09:40 AM. Reason: forgot the attachment.
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Old 12th February 2019, 09:54 AM   #47
Lojzek is offline Lojzek  Croatia
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Quote:
Originally Posted by ggidzinski View Post
...Also I can not read German. Do you have a link?

There is no link to freely download this data, only an option of purchasing the magazine issues 03/02 and 04/02 where it is explained under the section "Tricks of the pro's". This is a fairly simple procedure where you measure the voltage drops, one at the measurement resistor and the other at the DUT. Then you enter these two value in an equation (Ohms law) and get a magnitude value (Z).
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Old 12th February 2019, 10:20 AM   #48
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Measuring driver parameters vs the data sheet values
Rod Elliot has a method here Measuring Loudspeaker Driver Parameters
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Old 12th February 2019, 10:52 AM   #49
celef is offline celef
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Quote:
Originally Posted by wintermute View Post
If the measurements are good then it should be pretty close.

Attached sim (blue) of 2 MW144's in a 10L sealed box, using T/S params measured and averaged from 4 drivers.

Black actual impedance measurement in the box which was actually two separate 5L volumes one for each driver.

Sure it's not a perfect match but it is certainly within the ball park.

I don't have a measurement of my 70L BR or tiny 4" BR cabinets to hand to do a comparison there. Likely they will show much bigger discrepencies, especially the 4" because I used a small slot port rather than a tube.

Tony.
I am not so positive, what is this graph showing? have you simulated the box for best fit to the measured curve or is it prediction vs result?
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Old 12th February 2019, 11:11 AM   #50
wintermute is offline wintermute  Australia
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Measuring driver parameters vs the data sheet values
OK here is an M26WR-09-08 in 70L tuned to 32Hz Sim (using factory specs) and actual in box measurement. Note that I can't find the specs that I measured myself right now, which would have been what were used for the original box sim. I suspect that they are somewhere on my desktop which I don't have access to at the moment. Using those specs may be closer or further from the actual measured result.

This is simmed to match what was actually built. ie volume, port diameters and length put into the sim with factory T/S params.

edi: 2nd graph in speaker workshop to show phase as well.

Tony.
Attached Images
File Type: png M26WR0908_impedance_compare.png (37.8 KB, 62 views)
File Type: png m26wr09_08_phase.png (52.7 KB, 50 views)
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Last edited by wintermute; 12th February 2019 at 11:19 AM. Reason: add 2nd picture
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