Falcon
Peerless
830869 | RS52AN | XT25SC90
3-Way Bass Reflex
by
Michael Chua
This design is free for DIY. Not for Commercial
Use.
This article may not be published in part or full without
the express permission of AmpsLab.
|
|
|
Dayton RS52AN
The Falcon is based on a rather unique midrange driver by
Dayton, the RS52AN-8. Unlike typical cone midrange drivers,
the RS52 has a 2" Aluminum Dome diaphragm. Fig 1 shows
the undamped Resonance Frequency to be at 350Hz. |
Fig
1 - Impedance Sweep of Dayton RS52AN-8
RS52AN Frequency Response
The Black trace in Fig 2 is the Raw response of the RS52.
What is most noticeable is the sharp peak at about 12.5kHz.
This is caused by the breakup of the aluminum diaphragm.
Designing a network for the RS52 is going to be a bit of
a challenge. Apart from the sharp impedance peak at resonance
and the diaphragm breakup peak, the bandwidth is rather
limited. I'll be lucky to get 750Hz-3.5kHz. This falls short
of my preferred minimum bandwidth of 3 octaves.
After
some adjustment, the Blue trace is the final response
of the RS52. Basically, it's a 2nd order Bandpass with
a LCR to EQ the Impedance at Resonance.
|
Fig
2 - Frequency Response of RS52AN-8
(mic 1 meter RS52AN Axis | 5ms Impulse Window | 1/12 oct smoothing)
RS52AN Distortion
Fig 3 are the Distortion plots of the RS52 with the Bandpass
Network installed. A LCR was installed to EQ the Impedance
at resonance. Despite the reasonably low cost, the RS52
records impressively low harmonics from 2nd - 5th. Any harshness
or brittleness in the mids is therefore not attributed to
the RS52 but on failure to integrate it properly in a 3-way
design. |
Fig
3 - Distortion of RS52AN with BandPass + LCR
(mic 20 ins On Axis with RS52 | 5ms Impulse Window | 1/12 oct
smoothing)
Falcon
Frequency Response
Now that the RS52AN is sorted out, the Vifa XT25SC90 and
the Peerless can be blended in. Having worked on the SC90
tweeter before, I'm confident it'll be straightforward when
crossed at 4kHz.
Fig
5 is the Frequency Response of the Falcon. Due to room
limitations, measurements below 500Hz should be disregarded.
The
eventual network has the RS52 crossing at 900Hz to the
830869 and 4kHz to the SC90. To keep it simple, all the
filters are 2nd order. By doing so, inverting the phase
of the RS52 correctly sums the RS52 with 8" midwoofer.
At the other end, the summation to the SC90 is correct
too. The resulting response is shown in the Black trace
which is reliefed for clarity.
|
Fig
5 - Falcon Frequency Response
(mic 1 meter RS52AN Axis | 5ms Impulse Window | 1/12 oct smoothing)
Falcon
Distortion
The Falcon's Distortion Plot (Fig 6) is one of the best
I've ever seen. From 200Hz right up to 10kHz, distortion
is exceptionally low. Equally low is the distortion in the
bass. This is a clear indication that the 830869 is a well
designed driver. |
Fig 6 - Falcon Distortion
(mic 20 ins On Axis with RS52AN | 5ms Impulse Window | 1/12 oct
smoothing)
Falcon
Dispersion
The Horizontal Polar response (Fig 7) of the Falcon is outstanding.
From 1Khz to 20kHz, all three drivers combine well for an
even dispersion up to +/- 30° off-axis. |
Fig
7 - Falcon Horizontal Polar Response
Falcon
Impedance & Phase
Fig 8 is the Impedance and Phase plots of the Falcon.
Generally, it's a friendly load for power amplifiers.
The dip in the Phase Angle at 3.5Khz to -24° corresponds
to 6 ohms. In the bass region, the Phase extreme of -60°
is at impedance above 25 ohms. Modern day power amplifiers
will be able to cope well with the Falcon.
|
Fig
8 - Falcon Impedance & Phase Response
Falcon
Crossover Network
Fig
9 shows the complete network of the Falcon. With an 8"
Peerless, the Falcon can be used without subwoofers (omit
the 160uF capacitor).
To preserve the sonic integrity of the Falcon, I prefer
to run them fully passive. The way I integrate my Active
Subs with the Falcon is to run the Subs at 24dB/oct at
about 90Hz with an electronic crossover. The Active Highpass
is not used for the Falcon. A 160uF capacitor is used
as a 1st order filter instead. This way, the Falcon is
not comtaminated by the electronics of the active crossover.
If you opt to use this method, a quality capacitor is
essential for the 160uF.
|
Fig 9 - Falcon Crossover Network
the
sound of Falcon
|
The highlight of the Falcon is the baffleless Midrange and
Tweeter. In one stroke, this completely eliminated any issues
with Baffle Diffraction.
It
is in the auditioning of the Falcon that the baffleness
RS52 and SC90 became really apparent. Though the vocals
and treble were exceptionally "clean" and "transparent",
what was eerie about the Falcon was like they don't exist.
They simply vanished, leaving just music.
I should mention that the Falcon's mids and highs are not
"Open Baffle".
They
are the ultimate - Baffleless.
Oct
6, 2013
|
|
|
|
|
|
