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Multi-Way Conventional loudspeakers with crossovers

Measuring speaker stuff starting with Thiele-Small parameters
Measuring speaker stuff starting with Thiele-Small parameters
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Old 9th January 2019, 11:41 AM   #11
Lojzek is online now Lojzek  Croatia
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Audiomatica Clio 4.51 standard small signal TSP evaluation has got 1Vrms of output voltage in a measurement setup that includes driver only in the circuit, the so called internal mode of measurement, and the output impedance of clio card is 100R.


You can make trial measurements with lesser voltages and investigate if there are significant differences. I get consistent results by having 15R of a resistor in the circuit and a driver, powered by a headphone out of a laptop sound chip at Vout=0.5V rms. In that case, the output impedance of a sound chip is 68R.
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Old 9th January 2019, 05:52 PM   #12
DualTriode is offline DualTriode  United States
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Hello JohnPM and Lojzek,

There is a range; 0.1 - 1.0 volts.

I will start low and work my way up.

The AP hardware has a test amplifier with a fixed gain of 20 and has the recommendation for small signal of not exceeding 1 volt output. Kind of interesting that the instructions are so fuzzy on the topic.

Thanks DT
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Old 9th January 2019, 06:43 PM   #13
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Quote:
Originally Posted by DualTriode View Post
I am thinking of using the added weight method as opposed to the known volume box to do the measurements.
FWIW the pioneers determined that the net box volume [Vb] raise Fs by > 1.56x, so lowering it > 1.56x is theoretically the most accurate, which from dim memory is ~1.5x Mms, so can get pretty heavy for [sub] woofers.

GM
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Old 10th January 2019, 02:59 AM   #14
Jack Hidley is offline Jack Hidley  United States
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Measuring speaker stuff starting with Thiele-Small parameters
Never attach a magnet or any ferrous material to the cone. If you do this near the dust cap, so it doesn't excite any rocking modes, it is going to affect the magnetic forces in the gap. If you do it near the surround, there will be rocking modes and it will change the parameters.

If you use a 50/50 mix of blue tack and standard hardware store blue stick for hanging things on the walls, the mixture will not be sticky enough to damage any cones.

If you want the most accurate results for the perturbation derived parameters, add the known weight to the cone and take a nearfield frequency response before and after. In the passband, subtract one response measurement from the other. Given the known added mass, this makes it very easy to determine the drivers moving mass perfectly. You then use this to calculate everything else.

To determine an optimum drive level, take multiple impedance curves starting at the lowest level and increasing to the maximum level. Look at the frequency of Fs. The best accuracy will happen when you use the drive level where the Fs measurement is the lowest.
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Old 10th January 2019, 03:24 AM   #15
Dave R is offline Dave R  United States
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Another useful fact is that a US nickel is 5 grams.

I like the non-residue blue tack, and I have a mass scale to accurately measure within 0.1 gram. Harbor freight had an inexpensive mass scale on sale recently (around $10). Don't know how accurate it is, but you could check against a quantity of nickels or AA batteries, etc.
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Old 11th January 2019, 07:07 AM   #16
DualTriode is offline DualTriode  United States
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Hello,

An old friend told me about the Zen of Motorcycle Maintenance; the motorcycle needs to know that you are not afraid to break it, only then will the motorcycle cooperate.

I am afraid of breaking my APx 1701 transducer interface adaptor.

This afternoon I spent an hour with customer service in Beaverton. I am all set now for monitoring voltage and current across the sense resistor and monitoring voltage across the driver under test.

All I need now is to put together a XLR test lead to connect the analyzer to the DUT.

Thanks DT
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Old 11th January 2019, 07:36 AM   #17
Lojzek is online now Lojzek  Croatia
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There is specs for APx1701 that say maximum of 10Vpk for balanced and 5 Vpk unbalanced. Before you connect wires to AP's input, you can check the voltage that is supposed to enter the AP with a multimeter first.
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Old 11th January 2019, 08:51 PM   #18
DualTriode is offline DualTriode  United States
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Quote:
Originally Posted by Lojzek View Post
There is specs for APx1701 that say maximum of 10Vpk for balanced and 5 Vpk unbalanced. Before you connect wires to AP's input, you can check the voltage that is supposed to enter the AP with a multimeter first.
Thank you, sounds like a job for mister Fluke.

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Old 11th January 2019, 09:06 PM   #19
Jack Hidley is offline Jack Hidley  United States
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Measuring speaker stuff starting with Thiele-Small parameters
If you are going to measure low impedances with the AP, you should just build a current source. It is extremely accurate, the wiring is super simple and there is no chance of damaging the input circuitry.
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Old 11th January 2019, 10:51 PM   #20
DualTriode is offline DualTriode  United States
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Originally Posted by Jack Hidley View Post
If you are going to measure low impedances with the AP, you should just build a current source. It is extremely accurate, the wiring is super simple and there is no chance of damaging the input circuitry.
Jack,

The amplifiers in the apx1701 are pretty much a voltage source. The specified output impedance is 0.13R including the 0.1R sense resistor.

Please tell me more about what you are thinking about with a current source and low impedance measurement!

I am cautious about the voltage; one day a long ago I stuck a probe into a tube circuit and shorted B+ volts into my the SYS2522. Duke fixed it for me.

Thank You DT
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