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This article may not be published in part or full without the express permission of AmpsLab.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

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