Measurement setup /graph

Sanon · 25th July 2011, 04:48 AM

Hi,
Please have a look at the image below , I want to know where the test mic is placed from the driver (1m away). Is it location 'A' or 'B' open field (outdoor) test.

----------

Below is a driver specification (freq response) from a chinese company , on the LHS the dB scale is written as 0~ 25dB , is this reading at 1Wrms applied to speaker.I just want to know what type of graph / specification is this from more experienced members.

Thanks for your time.

Loren42 · 25th July 2011, 12:03 PM

I would choose B as the measuring position, 1 or even 2 meter away for the on-axis performance.

You can move the mic in arc (same distance from the end of the horn's center) at 7.5°*intervals if you want to get off axis response (horizontal and vertical).

The driver should be mounted in its intended baffle first.

The dB scale on the plot must be arbitrary or relative. Any driver that only produces 20 dB at 1 Watt probably has a rat stuffed in its throat.

Sanon · 26th July 2011, 05:54 AM

Quote:

Originally Posted by Loren42

I would choose B as the measuring position, 1 or even 2 meter away for the on-axis performance.

You can move the mic in arc (same distance from the end of the horn's center) at 7.5°*intervals if you want to get off axis response (horizontal and vertical).

The driver should be mounted in its intended baffle first.

The dB scale on the plot must be arbitrary or relative. Any driver that only produces 20 dB at 1 Watt probably has a rat stuffed in its throat.

Thanks for the reply , The reading at point B comes out to be exactly 6dB lower than that at point A . Is this ok to measure like this.

speaker dave · 26th July 2011, 10:58 AM

"Which is correct A or B" is an interesting question, as it is a bit arbitrary. I would tend to agree with B but there is a case for either. B is 6dB less because it is twice as far away as A. It would be more accurate to move farther, say 2 or 4 meters, and then correct for distance (add 6 or add 12 respectively). I believe measuring from the horn mouth is more conventional.

The graph is uncalibrated. The 0 to 25 scale is just the scale that came with the graph paper (looks like a copy of old B&K strip charts). They should have given a calibration reference such as: "0dB equals 90dB for 2.83 volts at 1 meter".

Regards,
David S.

25th July 2011, 04:48 AM	#1
Sanon diyAudio Member Join Date: Sep 2010	Measurement setup /graph Hi, Please have a look at the image below , I want to know where the test mic is placed from the driver (1m away). Is it location 'A' or 'B' open field (outdoor) test. ---------- Below is a driver specification (freq response) from a chinese company , on the LHS the dB scale is written as 0~ 25dB , is this reading at 1Wrms applied to speaker.I just want to know what type of graph / specification is this from more experienced members. Thanks for your time.

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25th July 2011, 12:03 PM	#2
Loren42 diyAudio Member Join Date: Sep 2008 Location: "Space Coast" Florida, USA	I would choose B as the measuring position, 1 or even 2 meter away for the on-axis performance. You can move the mic in arc (same distance from the end of the horn's center) at 7.5°*intervals if you want to get off axis response (horizontal and vertical). The driver should be mounted in its intended baffle first. The dB scale on the plot must be arbitrary or relative. Any driver that only produces 20 dB at 1 Watt probably has a rat stuffed in its throat.

26th July 2011, 10:58 AM	#4
speaker dave diyAudio Member Join Date: Nov 2009 Location: Toronto	"Which is correct A or B" is an interesting question, as it is a bit arbitrary. I would tend to agree with B but there is a case for either. B is 6dB less because it is twice as far away as A. It would be more accurate to move farther, say 2 or 4 meters, and then correct for distance (add 6 or add 12 respectively). I believe measuring from the horn mouth is more conventional. The graph is uncalibrated. The 0 to 25 scale is just the scale that came with the graph paper (looks like a copy of old B&K strip charts). They should have given a calibration reference such as: "0dB equals 90dB for 2.83 volts at 1 meter". Regards, David S.

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