Kookaburra (Morel CAW634 with CAT378)

Kookaburra
18 Liters Bass Reflex

It took me a while to gather myself mentally while working on the Kookaburra. I’ve not designed speakers for 10 days so my hearing needs to be re-calibrated. To make matters worse, I’m am not motivated to work on this Morel CAW634 mainly because she measured out of spec. It’s like I was looking forward to grilling a mouth watering Angus ribeye steak only to find that I was sold on an ordinary ribeye instead. There goes my appetite. Anyway, since I already paid a king’s ransom for the CAW634, I might as well try to salvage something out of it.

Fig 1 – Morel CAW634 RAW Frequency Response • Baffle Width=9-1/2″

The response in Fig 1 is the Morel CAW634 in an 18 liters ported box with a baffle width of 9-1/2″. The woofer starts to roll off at about 1.2kHz. By 2kHz, she is already down by 5dB. That means I have to cross below 2kHz. 

Fig 2 – Morel CAW634 with Low Pass network

After a few attempts, I finally settled on the low pass network for the CAW634 (Fig 2). I brought the midrange down by about 2dB otherwise the Kookaburra will end up with mainly midrange and treble. That will make it very tiring to listen to. With this network, the peak at 4kHz is attentuated by -20dB. It should not present any issues once I integrate the tweeter in.

Fig 3 – Morel CAW634 with CAT378 (Surface Mounted)

The Red plot in Fig 3 is the Morel CAT378 tweeter. She is one of my favorite tweeters. I didn’t have to flush mount the tweeter because she doesn’t suffer from baffle diffraction. That’s the beauty of a good horn. You can flush mount the CAT378 if it makes you feel better.

Fig 4 – Kookaburra Passband

The Black plot in Fig 4 is the crossover passband. The two drivers are summing properly at 1.7kHz. I am encouraged to see the peak at 4kHz did not disturb the treble. That saved me a notch filter.

Fig 5 – Kookaburra Frequency Response

Fig 5 is the final response of the Kookaburra. There is a light depression at 2kHz. With a response like this, the presence in the vocals will be slightly less. This is ideal for listeners that find sibilance irritating.

Fig 6 – Kookaburra Null

The violet plot in Fig 6 is the null when I reversed the tweeter wiring. It is not as sharp as I would like but at least it’s there. The shape of the null indicates the woofer and the tweeter rolling off too early. For a deep null, I will probably need to lower the tweeter crossover to about 1.5kHz. However, I’m not prepared to invest more time on the CAW634. The Kookaburra sounded fine on playback even though the drivers are not perfectly aligned.

Fig 7 – Kookaburra Nearfield

The Blue plot in Fig 7 is a nearfield response of the CAW634. This was made with the microphone about 1/4″ away from the surface of the cone. Due to the close proximity, room reflections are not recorded. The ugly deep notch at 150Hz is not in the nearfield measurement, meaning that it’s not from the woofer but cause by a floor bounce.

Fig 8 – Kookaburra Port

Fig 8 is the nearfield response of the Kookaburra with the output of the port (Brown plot). The pipe resonance at 1kHz to 1.7kHz is quite harmless because they are buried about -20dB below the fundamental.

Fig 9 – Kookaburra Step Response

The step response (Fig 9) of the Kookaburra is mediocre. There is a break right after takeoff at the bottom. My guess is it’s caused by the two drivers not being perfectly aligned in the crossover. At the apex, there’s some hesitation just before hitting 100%. 

Fig 10 – Kookaburra Waterfall

The Waterfall plot in Fig 10 shows extended decays from 3kHz to 4kHz. They are actually not that serious. I’m more concerned with those at 1kHz.

Fig 11 – Kookaburra Toneburst Energy Storage

The Toneburst plot in Fig 11 shows excess energy from 3kHz to 4kHz. They are the same ones recorded in the waterfall.

Fig 12 – Kookaburra Spectrogram

The Spectrogram (Fig 12) shows a streak at 1kHz which is missing in the Toneburst plot. It dissipated by 7 msec. During playback, I did not detect any smearing.

Fig 13 – Kookaburra Box Modeling

Fig 13 is my box tuning for the Kookaburra. This is the best option for a Qts of 0.59. By the way, this is what a cheapo woofer tuning looks like. 

Fig 14 – Kookaburra tuning based on Morel specs

Using Morel’s CAW634 specs, the same tuning would look like in Fig 14. See how much higher the EBP is. The bass would be much tighter, faster and with definition.

Fig 15 – Kookaburra Impedance

The Kookaburra is an easy load for power amplifiers. The lowest impedance is about 5Ω at 125Hz. From then on, she varies from 6Ω to a high of 9Ω at 4kHz. There’s also very little variation in the electrical phase. 

The saddle on the left shows the Kookaburra tuned to about 40Hz. This is close to the box modeling of 44Hz.

Sound of Kookaburra

The Kookaburra would have sounded outstanding had the Qts been what is in their specs, that is 0.42. Unfortunately, that is not the case. The bass sounds like a woofer with a Qts of 0.59. It’s not fast nor tight. For a woofer that cost $154, that’s really pathetic.

Still, I managed to get a decent sound out of the CAW634. I have no issues with the midrange and the treble but the bass is nowhere close to the Seas U18RNX. And that woofer cost $110. If that isn’t bad enough, it can’t even compete with the Anarchy-704 which cost only $66. So unless one is an idiot or has too much money to waste, I would avoid this CAW634.

Crossover is available on request. Free for DIY. Not for Commercial use.
Unless otherwise stated, all measurements were made in Full Space (4 pi) with the mic at 36 ins, tweeter axis. Impulse Window=5ms. No smoothing applied.