Fig 1 – Black plot=SB17NRX2C35-4 RAW Response
The Magpie is the first time I’m working with the SB Acoustics SB17NRX2C35-4 woofer. I installed it in a 27 liter bass reflex and had a listen without any crossover. I liked what I heard. Good clean vocals and a tight bass. The treble, on the other hand, is atrocious. After I took a sweep of the RAW woofer (Fig 1), I can see why. It’s caused by a massive +12dB cone breakup peak.
Fig 2 – Blue plot=SB17NRX2C35-4 with Low Pass Filter (LPF)
The Blue plot in Fig 2 is the SB17NRX with a Low Pass network. I’ve not made any attempts to notch out the cone breakup. Should it be problematic later, I will have no choice but to install an EQ network.
Fig 3 – Blue plot=SB17NRX2C35-4 Low Pass • Red plot=Seas 27TBFC High Pass
The Red plot in Fig 3 is the Seas 27TBFC tweeter crossing to the SB17NRX at 1.8kHz. The cone breakup peak of the SB17NRX is about -10dB below that of the tweeter. This is cutting it a bit too thin but let’s see what happens.
Fig 4 – Black plot=Magpie Passband
The Black plot in Fig 4 is the summation of the crossover. No cancellations are recorded in the passband. However, where the cone breakup is, it caused a slight dip in the treble from 4.5kHz~6kHz. It’s very minor. I don’t think it’s worth the extra cost to notch it out.
Fig 5 – Magpie Frequency Response
Fig 5 is the final frequency response of the Magpie. We can see the bass region is higher than the midrange by +5dB. With a response like this, the Magpie won’t sound lean on the bass.
Fig 6 – Magpie Null
Fig 6 is a beautiful, deep null when I reversed the tweeter wires. The Magpie is Time-Aligned. Not that I set out to get this. Sometimes, things just fall into place naturally.
Fig 7 – Magpie Step Response
The SB17NRX transient is quite graceful. There are no breaks from take-off to the apex. At the 90% mark, she’s at 300 microsec. She then slows down, hitting the apex at 400 microsec. The tip is not chopped off or jagged like some other woofers.
Fig 8 – Magpie Waterfall
Fig 9 – Magpie Toneburst Energy Storage
The Toneburst plot (Fig 9) shows the Magpie has minimal energy storage. There are some light blue slices in the treble but they are quite benign. It is those at 1kHz that may cause smearing.
Fig 10 – SB17NRX2C35-4 RAW Toneburst Energy Storage
For comparison, Fig 10 is the Toneburst plot of the SB17NRX without any crossover. No tweeter is connected. What a frequency response measurement shows is only the grey slices. The +10dB cone breakup is clearly visible. What is doesn’t record is what happens thereafter. The light blue slices are the unwanted sound. Think of it as ringing. In Fig 9, we can see these offensive bunch of light blue slices are largely suppressed by the low pass network.
Fig 11 – Magpie Spectrogram
As expected, the Magpie doesn’t exhibit any smearing. There are some faint hot spots at about 2.2kHz but they vanished by 6 msec. As for the SB17NRX cone breakup, it’s not there.
Sound of Magpie
The Magpie sounds very different from the Grosbeak-TBFC. The Magpie is livelier. Sounds faster. I picked this up when I heard the SB17NRX without any crossover. Checking their Mms, the SB17NRX is 12.85g whereas the Peerless 835025 is heavier at 18.62g. But that doesn’t mean the Magpie wins hands down. No. The Grosbeak-TBFC bass has more impact. So, it all boils down to preference. If you like a stronger, punchier bass, go for the Grosbeak-TBFC. The Magpie’s bass is tighter and more controlled. Some listeners prefer this.
I am actually quite impressed by this SB17NRX. She is in the same class as the Peerless 835025 and the 830874. I have no problem using either one of them.
Crossover is available on request. Free for DIY. Not for Commercial use.
January 26, 2021Projects