31
Finding the characteristics of a 4th order
Bandpass Box (single reflex)
1. With the IM-SG, it is possible to find the port tuning
frequency and the approximate bandwidth of a single
reflex bandpass subwoofer system.
2. To measure the impedance characteristics of the
subwoofer system, 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 a
first
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. Let us call this frequency
peak
f
L
. See figure 6
6. Continue increasing the frequency slowly until a
second
peak in the impedance is found. Let us call
this frequency peak
f
H
. Single reflex bandpass
enclosures have two impedance peaks, see Figure x.
7. Now slowly decrease the frequency, you are looking
for the
minimum
impedance that is between
f
L
and
f
H
.
8. The frequency at which this minimum impedance
occurs between
f
L
and
f
H
is called
f
B
. This is the
tuning frequency of the ported chamber.
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 ...
