D'Amore engine'ring SMD IM-SG, Owner'S Manual

Page: 19 / 48

19
The Significance of f
S
- Continued
Tweeter - Most tweeters have a measureable f
S
frequency.
There are some types of tweeters, (ribbons for instance)
that have an almost flat impedance across its operating
range. For this type of tweeter, follow manufacturer's
recommendations for crossover frequency.
For all moving
coil type tweeters, we can measure the f
S
just like a
subwoofer or midbass driver; you just have to look for it
more carefully. Typically, the impedance peak is not as
high as a subwoofer or midbass driver. Figure 2 shows
the impedance curve of a common 1.0 inch tweeter.
Figure 2 shows the impedance peak to occur at 1.59 kHz.
This is the f
S
for this tweeter. This information is useful for
determining a safe crossover frequency for this tweeter.
We suggest setting the high pass filter on tweeters 1
octave to 2 octaves higher than the driver's f
S
for best
power handling. Use 1 octave higher if using a
24dB/Octave crossover and 2 octaves higher if using a
12dB/Octave crossover.
This is not law by any means,
just a suggestion and good place to start.
24dB/octave Example: For 1 octave higher, take the
measured f
S
and multiply by 2. So for measured f
S
of 1.59
kHz, crossover should be set at 1.59 kHz X 2 = 3.18 kHz.
12dB/octave Example: For 2 octaves higher take the
measured f
S
and multiply by 4. So for measured f
S
of 1.59
kHz, crossover should be set at 1.59 kHz X 4 = 6.36 kHz.