MOREL CAT 378 Soft Dome Horn Tweeter



The Morel CAT 378 is a 1-1/8″ Soft Dome, Horn loaded tweeter. This tweeter is noted for it’s flatness when crossed with a first order network. Fig 1 below is the frequency response of the CAT 378 published by Morel.

MOREL CAT 378 FRFig 1 – Morel CAT 378 Frequency Response

Morel CAT 378 in a 13 Liters Box (Baffle Width = 8.5″)

CAT 378 MORELFig 2 – Morel CAT 378 RAW Frequency Response. Mic on axis. No Smoothing applied.

This is one of those rare occasions where my measurement is similar to the manufacturer’s. The Black plot in Fig 2 is without any capacitor in the signal path. The Red plot is with a 5uF capacitor.

MOREL CAT 378 Cumulative Spectral Decay (CSD) – Baffle Width = 8.5″

Fig 3 – MOREL CAT 378 CSD. Window = 2ms ( 500Hz ), Time Range = 2ms, Rise Time = 0.5ms

Fig 3 is the Waterfall plot of the CAT 378. This measurement is done with a 5uF to protect the tweeter. To make it easier to see the artifacts, I shortened the Time Range to 2ms. So this is a very closed up view.

First impression is that the CAT 378 is not as clean as expected. There are some some artifacts, the largest one between 2kHz ~3kHz. Next is a narrow one at about 4.5kHz. Finally, two very narrow ones at 12kHz and 15kHz.

One should be careful with interpreting measurements. All the artifacts I mentioned earlier are not from the MOREL CAT 378. They are caused by Baffle Diffraction. Flush mounting the CAT 378 will eliminate those from 12kHz~15kHz. As for the ones between 2kHz~4kHz, they are from the edge of the baffle. Waterfall plot is by courtesy of REW.

MOREL CAT 378 Toneburst Energy Storage ( TES ) – (Baffle Width=8.5″)

Fig 4 – MOREL CAT 378 Toneburst Energy Storage. Impulse Window = 3.5ms. Mic on tweeter axis.

The sweep in Fig 4 is with a 5uF in series with the CAT 378. We can see there are some stored energy between 2kHz~3kHz and a lesser amount from 10kHz~20kHz. This confirms the CSD in Fig 3.

MOREL CAT 378 Spectrogram (Baffle Width = 8.5″)

morel CAR 378 SPECTROGRAMFig 5 – MOREL CAT 378 with 5uF capacitor in series. Impulse Window = 5ms

The Spectrogram in Fig 5 shows some smearing 2kHz~4kHz. Up in the treble, slight smearing from 10kHz onwards. This reaffirms the Waterfall (Fig 3) and the Toneburst (Fig 4).

MOREL CAT 378 Harmonic Distortion

MOREL CAT 378 HARMONIC DISTORTIONFig 6 – MOREL CAT 378 Harmonic Distortion

The plot in Fig 5 is with a 5uF capacitor in series with the CAT 378. 2nd (Red plot) and 3rd (Violet plot) Harmonics are generally at about -60dB below the fundamental. Considering that this is with only a 5uF capacitor in place, it’s quite encouraging. It’ll be interesting to design a minimalist 1st order speaker with this CAT 378.

MOREL CAT 378 Impedance

MOREL CAT 378 IMPEDANCE PLOTFig 7 – MOREL CAT 378 Impedance Sweep

The Impedance sweep in Fig 7 doesn’t show any anomalies. The CAT 378 Resonant Frequency is at 850Hz. Judging from the peak, it’s likely that I will need to use a conjugate network (LCR) for a 1st order filter.

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