ORION2 – Time and Phase Coherence

Orion2
Audax HM130C0 with Fountek CD3.5H

In the Orion, my aim was to achieve time and phase coherence. While I met my objective, I felt I wasn’t getting enough separation between the midrange and the treble. This is unavoidable as I had to use a first order network for the high and low pass.

The Orion2 seeks to address this issue. I will adopt a 2nd order network instead. In so doing, I may well compromise the time and phase coherency but it’s a sacrifice I’m prepared to accept.

ORION2 – 2nd Order Frequency Response

Fig 1 – Blue plot = Audax HM130C0. Red plot = Fountek CD3.5H. Nearfield below 500Hz.

The plot in Fig 1 shows the 2nd order high and low pass of the Orion2. Their roll-off is indeed steeper than the Orion, which uses a 1st order network.

Fig 2 – Orion2 Summed Response

Fig 2 shows the summed response of the Audax HM130C0 and the Fountek CD3.5H ribbon. In the summing region, no cancellations are observed, indicating optimum summing. 

Fig 3 – Orion2 Frequency Response. Nearfield below 500Hz.

For clarity, I removed the Audax and the Fountek plots, leaving only the summed response of the Orion2. This is a stunning plot. It is practically flat from 200Hz~20kHz.

Now that I got the frequency response sorted out, it’s time to check on the time coherence.

Fig 4 – Orion2 Step Response. (courtesy of REW)

Fig 4 is the Step Response of the Orion2. I couldn’t quite believe my eyes. I had to repeat the measurements a few times to convince myself. True enough, it is identical to the Orion. So, I am able to preserve the time coherency even with a 2nd order network. The next step is to investigate the phase coherency.

Fig 5 – Orion2 – Minimum Phase. (courtesy of REW)

Interestingly, the Orion2 is phase coherent as well. The minimum phase plot in Fig 5 shows 0 phase from 300Hz~10kHz.

Fig 6 – Orion2 Waterfall (courtesy of REW)

Fig 6 is a magnified view (1.2 ms time range) of the Orion2 waterfall plot. There’s virtually no artifacts above 4kHz, indicating an exceptionally clean tweeter.

Orion2 Toneburst Energy Storage

Fig 7 – Impulse Window =5 ms.

The Orion2 Toneburst Energy Storage plot of Fig 7 confirms the performance of the Fountek CD3.5H ribbon tweeter. Frequencies from 2.5kHz~20kHz contain no stored energy.

Orion2 Spectrogram

Fig 8 – Impulse Window =5 ms.

Fig 8 is the Spectrogram of the Orion2. The treble is exceptionally clean from 2.5kHz~20khz. This is in line with the Toneburst Energy Storage shown in Fig 7. 

Fig 9 – Orion2 Harmonic Distortion.

The Harmonic Distortion plot in Fig 9 shows the 2nd (Red) and 3rd (Violet) harmonics at -50dB below the fundamental. No anomalies are recorded particularly at the crossover frequency.

Fig 10 – Orion2 Impedance

Fig 10 is the Impedance plot of the Orion2. The lowest impedance is 4Ω from 10kHz~20kHz. The electrical phase is not stressful for power amplifiers. There’s a gentle dip of -50° at about 3kHz. Nothing to worry about.

The plot also reveals the bass reflex port tuning of the Orion2. It is recorded at 75Hz. This is the optimal tuning frequency of the Audax HM130C0.

the Orion2 in use

I’ve been running the Orion2 for a few days and it sounds exactly like any flat response speaker (Fig 3). While it is perfect as near field recording monitors, it doesn’t excite me when I’m listening to music. This is a common complaint with flat response speakers. I suppose one reason could be that our ears are anything but flat (see Fletcher–Munson curves).

Unable to stomach the dullness any longer, I eventually tweaked the crossover for my listening pleasure. It’s a light touch but it made a world of difference. The Orion2 now jumps to life. The vocals are much clearer. Even the treble sparkles. 

Fig 11 – Brown plot = Flat Response. Black plot = Adjusted for Music

The Black plot in Fig 11 is the Orion2 response tweaked for music. Tweaking is strictly by ear. Trying to voice a speaker with measurements is pretty useless at this stage of the development.

Having gotten the sound, I did another sweep and the plot shows a slight increase in the upper mids, about 1dB from 1.5kHz~3kHz.

Fig 12 – Orion2 Null Response

The Violet plot in Fig 12 is with the Fountek CD3.5H wired in absolute phase. A beautiful notch is seen, centering at 3kHz. This is a good indication of optimal summing between the Audax and the Fountek.

Fig 13 – Orion2 with Silver Flute W20RC38-08 Toucan Bandpass Subwoofer

To supplement the bass, I added the 8″ Silver Flute W20RC38-08 Toucan Bandpass Subwoofer (Fig 13). I crossed the subwoofer and the Orion2 with a 24dB/oct active crossover at 250Hz. So, the system is essentially bi-amped. One amplifier for the subwoofer, another for the Orion2. This is actually my preferred setup, active for the bass and passive for the mid/high. This method saves me on the crossover cost and allows for easy adjustment on the bass volume. 

For those that are contemplating building the Orion or the Orion2, I strongly suggest this version. 

Note: Unless otherwise stated, all measurements were made with the mic at 36 ins, tweeter axis. Impulse Window=5ms. No smoothing applied.