21
Finding the f
C
of a Sealed Box Subwoofer
System
1. The f
C
is the driver's natural resonant frequency while in
the sealed enclosure. This will give you some idea of
the usable bandwidth of the speaker. Generally the
output of the sealed subwoofer system will start to
decrease as the frequency goes below f
C
.
2. To measure the f
C
, make sure the room or area around
the subwoofer is quiet and free from moving air.
3. Connect the test leads to the speaker system, if it has
multiple voice coils they all need to be connected. A
parallel connection will work fine.
Make sure there is
no amplifier connected or damage to the IM-SG
could occur!
4. Turn on the IM-SG by holding the
On
button for 1
second.
5. After the unit is operating, turn the frequency down as far
as it goes. Then slowly raise the frequency until the
peak in impedance is found. If you go too far and pass
the peak, just back down the frequency until the peak in
impedance is found. Figure 3 shows the f
C
of the same
15 inch woofer we tested in the
Finding the f
S
of a Raw
Speaker Driver
section, but now in a 2 cubic foot sealed
box. We measured the f
C
to be 40 Hz.
6. Record the Frequency where the Impedance reaches its
maximum value. This Frequency is the f
C
.
Summary of Contents for SMD IM-SG
Page 1: ...IM SG Impedance Meter Signal Generator Owner s Manual ...
Page 20: ...20 Figure 2 Impedance curve of a typical 4 ohm 1 tweeter Notice the fS at 1 59 kHz ...
Page 22: ...22 Figure 3 fC of a single 4 ohm 15 inch subwoofer in a 2 cubic feet sealed box ...
Page 44: ...44 Notes ...
Page 45: ...45 Notes ...
