Magpie-MDT (SB17NRX2C35-4 with Morel MDT29)

Magpie-MDT
18L Bass Reflex Bookshelf

This is an upgrade to the Magpie-DX. The woofer remains the same SB17NRX2C35-4. What I changed is the tweeter. The Magpie now sports a Morel MDT29. This tweeter is in the same price bracket as the SB17NRX, therefore a better match.

Fig 1 – Blue plot=SB17NRX2C35-4 with Low Pass network

The Black plot in Fig 1 is the RAW response of the SB17NRX in a 18 liters bass reflex. Baffle width is 9-1/2″. The Blue plot is with a new low pass network.

Fig 2 – Red plot=Morel MDT29 with High Pass network (Surface mounted)

The Red plot in Fig 2 is the Morel MDT29 with her high pass network. This is with the tweeter surface mounted. I found that flush mounting the MDT29 leads to an uneven response. 

Fig 3 – Black plot=Magpie-MDT Passband

The Black plot in Fig 3 shows the summation of the two drivers. The crossover passband shows no cancellations. This is a positive sign.

Fig 4 – Magpie-MDT Frequency Response

The frequency response of the Magpie-MDT is in Fig 4. The midrange is at the same level as the bass. I can expect some strong bass with a response like this.

Fig 5 – Magpie-MDT Null

Fig 5 is the null when I switched the tweeter wires around. The tip is about 1.7kHz which is where the two drivers are crossing in Fig 2.

Fig 6 – Step Response

The step response (Fig 6) of this Magpie-MDT looks different from that of the sealed box DX version. There are a few breaks in the attack whereas the sealed box was one continuous transient.

Fig 7 – Waterfall

Fig 8 – Toneburst Energy Storage

Fig 9 – Spectrogram

The Waterfall (Fig 7) and Toneburst (Fig 8) did not record anything out of the ordinary. The Spectrogram (Fig 9) shows a light streak at 1kHz. The energy is disspated by 7 msec. There’s a delayed hot spot at 2kHz which also dissipated by 7 msec. During playback, I did not detect any smearing from them.

Fig 10- Excess Group Delay

Fig 10 shows a 2.53 msec Excess Group Delay in the Magpie-MDT. This is pretty good for a bass reflex. 

Bass Reflex Alignment

Fig 11 – SB17NRX box modelling

Fig 11 is the box modeling of the SB17NRX in a ported box. I deliberately tuned the box to 39Hz for better transients. For an even tighter bass, simply seal the port. This will convert it to a sealed box design.  

Sound of Magpie-MDT

The Magpie-MDT shares the same strength as the previous Magpie-DX and that is their outstanding midrange. The clarity is still there even with a new crossover.

As for the treble, the Magpie-MDT is sweeter. That’s quite expected because the Morel MDT29 is almost 3 times the cost of the Peerless DX25TG59-04.

The Magpie-MDT bass sounds fine. Bass is full, fairly tight and extends down to 50Hz. Strangely, the bass is much better than the ported version of the Magpie-DX.

If you’re looking for a pair of speakers for relaxation, the Magpie-MDT is a good choice.

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.