I'm working on a ported enclosure for my RS225. UniBox suggests a 25cm x 3" port for a 50L with an Fb of 29.5hz. I've used ThomasW's port measuring procedure shown below. Odd results (for me anyway), so I tried a few variations on port lengths out of curiousity. Here's what was measured:
Hz-----25cm-----10cm---4cm(box wall only)
50-----1.5-----1.5-----1.5
45-----1.5-----1.0-----1.4
40-----1.2-----0.7-----1.5
35-----0.7-----0.7-----1.6
30-----0.5-----0.7-----1.7
25-----0.4 ----0.7-----1.6
20-----0.3-----0.6-----1.3
15-----0.2-----0.3-----0.6
10-----0.0-----0.0-----0.0
Where is the rise? Any thoughts would be greatly appreciated.
-Frank
Hz-----25cm-----10cm---4cm(box wall only)
50-----1.5-----1.5-----1.5
45-----1.5-----1.0-----1.4
40-----1.2-----0.7-----1.5
35-----0.7-----0.7-----1.6
30-----0.5-----0.7-----1.7
25-----0.4 ----0.7-----1.6
20-----0.3-----0.6-----1.3
15-----0.2-----0.3-----0.6
10-----0.0-----0.0-----0.0
Where is the rise? Any thoughts would be greatly appreciated.
-Frank
To test the tuning frequency of a ported sub:
Wire the resistor in series with the (+) lead going from the amp to the (+) woofer input terminal. Wire the (-) lead normally from the amp to the (-) speaker terminal.
At low volume send 50Hz sine wave into the speaker.
Set the DMM to "AC" and measure the voltage across the +/- terminals of the woofer.
Set the output from the amp so the multi-meter reads between 1&2 volts.
Now lower the frequency in steps 5Hz at a time. Each time write down the voltage reading from the meter.
As you go down in frequency there will be a point where the voltage bottoms, then starts back up again with the next lower frequency. The lowest meter reading is the port tuning frequency.
For example:
50Hz-1.2V
45Hz 1.3V
40HZ 1.2V
35Hz-1.1V
30Hz-1.0V
25Hz-.75V
20Hz-.5V
15Hz-.75V
10Hz-1.1V
In this example the port tuning is 20Hz. That's where the meter reading shows the lowest voltage.
Wire the resistor in series with the (+) lead going from the amp to the (+) woofer input terminal. Wire the (-) lead normally from the amp to the (-) speaker terminal.
At low volume send 50Hz sine wave into the speaker.
Set the DMM to "AC" and measure the voltage across the +/- terminals of the woofer.
Set the output from the amp so the multi-meter reads between 1&2 volts.
Now lower the frequency in steps 5Hz at a time. Each time write down the voltage reading from the meter.
As you go down in frequency there will be a point where the voltage bottoms, then starts back up again with the next lower frequency. The lowest meter reading is the port tuning frequency.
For example:
50Hz-1.2V
45Hz 1.3V
40HZ 1.2V
35Hz-1.1V
30Hz-1.0V
25Hz-.75V
20Hz-.5V
15Hz-.75V
10Hz-1.1V
In this example the port tuning is 20Hz. That's where the meter reading shows the lowest voltage.
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