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.
February 13, 2021Projects