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Old 23rd February 2012, 10:23 PM   #1
ilardi is offline ilardi  United States
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Default Measuring Ported Speakers

When I measure the near field response of a ported speaker, I follow the directions in D'Appolito's book and separately measure the response at the speaker and the port (adjusting for size) and add the responses together. According to Keele, this is only accurate up to about 1.6 Fb due to contamination of the port measurement with radiation from the diaphragm.

I have only used this method when the port and the speaker are on opposite sides of the box and it seems to work well (meaning it matched predicted response closely). So does this same 1.6 Fb limitation occur when the port and speaker are located on opposite sides of the box? If the port and speaker are on the same side could the measurement contamination be minimized using some sort of baffle –or will that alter the measurement from the measured diaphragm or port? What do others do improve the accuracy of measuring ported speakers?

Thanks.

Terry
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Old 24th February 2012, 06:04 AM   #2
mdocod is offline mdocod  United States
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Hi Terry,

I could be wrong, however, I believe that the size of the baffle required to fully and effectively isolate the driver from the port would have to be prohibitively large and rigid as a standalone device. The way to achieve something "close enough IMO," would be to use an existing wall between rooms, or something to that effect. A test "window" built between 2 rooms that the speaker could be placed into (with a custom baffle board "insert" to match the box size) might just do the trick.

Regards,
Eric
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Old 24th February 2012, 06:06 PM   #3
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What do others do improve the accuracy of measuring ported speakers?
Measure outside in half space at a distance from 1 to 10 meters depending on the size of the speaker.
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Old 24th February 2012, 10:16 PM   #4
ilardi is offline ilardi  United States
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weltersys:

Do I need to either bury the speaker or raise it on a stand well above ground level in order to do this accurately?

Does anyone have experience with ground plane measurements?

Terry
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Old 25th February 2012, 01:26 AM   #5
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weltersys:

Do I need to either bury the speaker or raise it on a stand well above ground level in order to do this accurately?

Does anyone have experience with ground plane measurements?

Terry
I have done extensive testing of low frequency speakers with ground plane measurements.
Low frequency measurements are accurate when the speaker and microphone are both on the ground. The response of a speaker does change with proximity to boundaries, but a half space measurement is fairly representative of most use regarding low frequencies.

Raising the speaker and microphone high above the ground (a wavelength or more at the lowest frequency of interest) gives a full space reading, appropriate for the high frequency range.
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Old 25th February 2012, 02:17 AM   #6
a.wayne is offline a.wayne  United States
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Measure outside in half space at a distance from 1 to 10 meters depending on the size of the speaker.
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Originally Posted by weltersys View Post
I have done extensive testing of low frequency speakers with ground plane measurements.
Low frequency measurements are accurate when the speaker and microphone are both on the ground. The response of a speaker does change with proximity to boundaries, but a half space measurement is fairly representative of most use regarding low frequencies.

Raising the speaker and microphone high above the ground (a wavelength or more at the lowest frequency of interest) gives a full space reading, appropriate for the high frequency range.

+10

Still don't understand why more people here don't drag their speakers outside for more accurate ground plane measurements .....
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Old 25th February 2012, 06:46 PM   #7
ilardi is offline ilardi  United States
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+10

Still don't understand why more people here don't drag their speakers outside for more accurate ground plane measurements .....
Well for one-I do most of my speaker work fairly late at night and I don't really want to work in a cold, dark yard and more importantly my neighbors probably don't want to listen to me do it.

Also, it is kind of inconvenient. I don't really want to lug out the speaker, the mike, the amplifier, the laptop, etc. every time I want to test out a change in my design.

But, could I do these measurements in my garage? I have about 20 by 20 (feet) of empty floor space-would that work?

Terry
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Old 25th February 2012, 06:50 PM   #8
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+10

Still don't understand why more people here don't drag their speakers outside for more accurate ground plane measurements .....
'Cos my front room is bigger than my garden?
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Old 25th February 2012, 06:55 PM   #9
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But, could I do these measurements in my garage? I have about 20 by 20 (feet) of empty floor space-would that work?

Terry
The garage will be the same as measurements in your house, other than the room modes will be different.

The reason for outdoor measurement is simply to measure the speaker, rather than the speaker and room.

No need to lug out the speaker, the mike, the amplifier, the laptop, etc. every time you make a change in your design, you may want to design with your particular room and listening and speaker location in mind.
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Old 25th February 2012, 07:03 PM   #10
ilardi is offline ilardi  United States
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The garage will be the same as measurements in your house, other than the room modes will be different.

The reason for outdoor measurement is simply to measure the speaker, rather than the speaker and room.
The reason I mention the garage is because I have more 'free' space there than any other place in the house. I can at least keep the mike 10 feet from walls or other objects. I can't manage that much anywhere else in my basement and testing in the living areas of my home is a non starter (for me).

Terry
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