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Multi-Way Conventional loudspeakers with crossovers

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Old 17th July 2019, 09:50 PM   #821
iMat is offline iMat  Croatia
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Hi jzagaja,
if you have inputs with same sensitivity you do not need calibration when measuring normal loudspeaker impedance. You will get error < 1%.
But, if you have different sensitivity or measure larger impedance you need calibration.
Do not be afraid of calibration, it gives us low measurement error.
Ivo
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Old 18th July 2019, 07:33 AM   #822
mbrennwa is offline mbrennwa  Switzerland
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Quote:
Originally Posted by jzagaja View Post
Works very well. Ref resistor 47R, 38R value in Limp to get proper reading. Is calibration necessary?
A pretty Manger MSW driver you have there! Make sure to remove it from the box to get proper impedance measurements. The driver needs to be suspended in free air to get the impedance curve right.
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Old 11th August 2019, 10:45 AM   #823
HighTower is offline HighTower  Netherlands
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I'm sorry if this is a double post but I was unable to find the answer, despite many attempts. A reference to a manual or post where this is covered would be appreciated.

I've been working with Arta a few months now while building our test setup and slowly things are falling into place. There is just on thing that I can't get my head around: measuring actual SPL.

What I've done so far:

Setup Audio Device (RME Babyface Pro using ASIO Drivers)
Sound Card Calibration
For the Microphone sensitivity I used the manufacturers specs for now. We are using (amongst others) MK 221 and MK 301 by Microtech Gefell so I am assuming that their spec is at least within a few dB accurate.
"Use microphone on" is checked and set to 5mv/Pa for the MK301, 50 mv/Pa for the MK221.
Hardware is set to semi-dual channel with right output looped back to right input.

We use Impulse response with sweeped measurement, center peak of impulse response, -12 dB (which in our setup corresponds to 2,00V rms or 1 Watt @ 4 ohm).

In the frequency response graph, Sound Pressure Units are set to db re 20 uPa/V.

Besides the measured SPL that is off by ~5 - 10 dB, ARTA seems to compensate for increased levels. This means that if I repeat the measurements on -12db, -9dB, -6dB etc. the resulting SPL graph keeps showing the same level rather than shifting 3 dB between measurements. So before I focus on getting the microphone sensitivity right I need to know what ARTA is doing:

How is ARTA calculating the SPL value and why the don't the levels increase between measurements performed on different levels.

It seems now that the only two options we have for SPL reference is 20uPa/V or 20 uPa/2,83V? And I'd say that the "V" part is dependant on the Measurement Level, so it would be better if we could reference to the actual output level? Please forgive my ignorance if I'm way off here, I'm not exactly an acoustics engineer (but I'm learning ).
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Old 11th August 2019, 09:37 PM   #824
iMat is offline iMat  Croatia
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Default Level mode and ratio mode

Hi,
You should be aware of two modes of measurements: level mode and ratio mode.

We usually measure input excitation ( u1) and output response (u2) of some system.

In ARTA, as in other Fourier analysers, we have two mode of response presentation:
1) Level mode shows u2 (in dBV or dB re 20uPa) (in spectrum analysis and octave band analysis)
2) Transfer function (or ratio) mode shows u2/u1 (dB V/V or dB re 20uPa /V) (in Imp and Fr modes).

(In Steps you can choose which mode to use in Measurement setup).

Normaly , the Level mode results depend on excitation (u1) while the transfer function mode gives result independent of input excitation level.
Transfer function always express results as if 1V of excitation is used (or you can choose 2.83V as reference).

Best,
Ivo
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Old 13th August 2019, 02:14 PM   #825
Datsun is offline Datsun  Russian Federation
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Hi, Ivo! How to take into account the internal distortion of the sound card when measuring an amplifier with distortions below the distortion of the sound card?
1. The "distortion" of the amplifier.
2. Sound card distortion, loopback mode.
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