Enlightenment – Scanspeak 15WU with Morel CAT378

ScanSpeak 15WU/4741T00

I would like to thank my buddy Mark Nash for sending his midwoofer for testing. The 15WU is the top of the line midwoofer by Scanspeak. It features an under-hung voice coil, a neodymium motor and a linear excursion of +/- 9mm. All very desirable. It’s only 5″ yet cost an astronomical $337 at Madisound.

As with all new drivers, I started by listening to the 15WU without any crossover or tweeter. This will give me an idea of the character of the driver. Even in this unadulterated raw state, it is obvious that this is no ordinary midwoofer. To preserve the sonic signature of this midwoofer, I decided on 1st order. Anything higher and I risk destroying the sound.

The only tweeter at my disposal that can match the 15WU is my Morel CAT378. This is one tweeter that’s capable of working comfortably with a 1st order filter. An added benefit is the acoustic center is nearer to that of the 15WU because of the horn. 

Fig 1 – SS 15WU Frequency Response. Below 500Hz in Nearfield.

The Black plot in Fig 1 is the RAW response of the 15WU in a 10 liters ported box with a baffle width of 8″. In it’s natural state, the response rises from 1kHz onwards, culminating with a peak at 5kHz. This peak is a bit worrisome. If not tamed, it will surely intrude into the treble.

The Blue plot is with my 1st order Low Pass network. I made quite a bit of adjustments to get the crossover looking like this. Now it’s ready for the CAT378. 

Fig 2 – SS 15WU LPF with CAT378 HPF

The Red plot in Fig 2 is my CAT378 with a 1st order High Pass network. The two drivers are crossing at my targeted crossover frequency of 2.5kHz. 

Fig 3 – Summed Response

The Black plot in Fig 3 is the summed response of the 15WU and the CAT378. Note that there are no cancellation in the passband. This indicates the drivers are crossing properly.

Fig 4 – Enlightenment Frequency Response

For clarity, I removed the individual drivers, leaving the summed response only (Fig 4 – Black plot). There’s a light depression from 3kHz~5kHz which is caused by the CAT378 . There’s nothing much I can do about it because it’s inherent in the CAT378. As long as I don’t hear it, it’s fine.

Fig 5 – RAW and Nearfield Overlay

The Black plot below 500Hz in Fig 5 is the response of the Enlightenment with room reflections. Disregard the notch at 150Hz. That’s caused by a floor bounce. What interests me is the bass. It is exactly at the same level as the midrange, meaning it’s not necessary to boost the bass with an EQ. 

Fig 6 – Step Response

The Step Response of the Enlightenment shows excellent transient in the 15WU (Fig 6). It is almost perfect till it reaches 50% where there’s a glitch. It slowed down slightly till at 70%, it faces a second glitch. By the time it reaches the apex, it is at 200 microsec. 

Fig 7 – Excess Phase

The Excess Phase of the Enlightenment is outstanding (Fig 7). There is only one glitch at 3.5kHz. This is because the two drivers are not fully time and phase coherent. If I tilt the front baffle or use a step for the 15WU, the glitch will disappear. 

Fig 8 – Waterfall

Fig 9 – Toneburst Energy Storage

The Waterfall (Fig 8) and Toneburst (Fig 9) plots show minimal artifacts in the treble. What is remarkable is the Toneburst shows no excess energy at 1kHz. 

Fig 10 – Spectrogram

The Spectrogram in Fig 10 shows an exceptionally clean response. There’s hardly any excess energy in the 15WU. 

Fig 11 – Impedance of Enlightenment

The Enlightenment is not a difficult load for power amplifiers. It touches 5Ω at 150Hz and that’s the lowest. At the port tuning of 50Hz, it’s almost 6Ω. Electrical phase doesn’t deviate much from 200Hz upwards.

What the Enlightenment likes is an amplifier with a beefy power supply. This baby is power hungry. Tube amps won’t do. It needs solid state of 200W RMS into 4Ω.

Auditioning the Enlightenment

When I first heard the 15WU in its RAW state, I couldn’t believe my ears. In all my years working with different drivers, I’ve never heard anything like the 15WU. The bass and the midrange is so well separated it’s like listening to two separate drivers. When used with a tweeter, it sounds like in a 3-way. But it’s not an ordinary 3-way.

The bass of the 15WU is exactly the kind of bass that I strive for. It reproduces all the nuances in the bass. The attack is instant. No bloom meaning the braking is excellent. Bass notes are full of texture. The only driver that has similar characteristics is my Peerless NE265W-04 but that is strictly made for bass.

In designing the Enlightenment, I focused on the best feature of the 15WU, the bass. It’s a crime not to. That doesn’t mean the midrange is lacking. Not at all. The 15WU is outstanding in the midrange too. But it is in the bass that it stands out against all others.

The Morel CAT378 simply completes what is already there. I would have liked to use a $300 tweeter but I don’t have pockets that deep. Furthermore, I don’t want the tweeter to outshine the 15WU.

Is the price of the 15WU justifiable? To me, it’s an emphatic yes. It’s worth every penny. You have to hear it to fully appreciate what a top quality driver sounds like. If the 15WU is a car, it would be in the Lamborghini class. It’s that good.

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