The Sparrow-SB19 is a compact 8 liters bass reflex based on the SB13PFC25-04, a 5″ woofer by SB Acoustics. The PFC woofers sports a plastic frame to reduce cost. This may give the impression that the performance is not as good as the cast frame ones. I do not see any indications of this in their spec sheet. Only after testing the woofer out can I deliver a judgement.
Fig 1 – SB13PFC25-04 RAW Frequency Response • Baffle Width=8-3/4″
Fig 1 is the RAW response of the SB13PFC in a 8 liters bass reflex with a baffle width of 8-3/4″. I avoided a narrower width as I didn’t want the baffle step to be that severe. As it turned out, I didn’t need to install a compensation network to tame the baffle step. When I bought this SB13PFC in 2017, I couldn’t wrap my head around the early roll-off. Instead of extending flat to 4kHz, she started to roll-off at 1.5kHz. This meant I will have to cross a tweeter about 1.8kHz. I struggled with that because most hifi tweeters have difficulty crossing that low. I tried horns with compression drivers but the cost does not equate with a budget woofer like the SB13PFC.
Fig 2 – SB13PFC25-04 with Low Pass network
Now that I’ve found a way to cross tweeters below 2kHz, it’s time to examine the SB13PFC again. I will take advantage of the roll-off and cross at about 1.8kHz. The Blue plot in Fig 2 is with a low pass network. I didn’t use a notch filter because the cone breakup peak is already -20dB less. That’s one of the benefits of crossing low.
Fig 3 – SB13PFC25-04 with SB19ST-C000-4 (Flush Mounted)
The Red plot in Fig 3 is the SB19ST tweeter with a high pass network. I adjusted the crossover for 1.8kHz. She looks fairly flat except for a light dip at 5.5kHz. That’s caused by diffraction at the edge of the front baffle. Chamfering the edges should mitigate the dip. Remember to flush mount the SB19. Very important.
Fig 4 – Sparrow-SB19 Passband
The Sparrow-SB19 crossover is in Fig 4. The two drivers are crossing properly. Summation looks good. No cancellations are recorded in the passband. I am relieved to see the woofer’s cone breakup is not causing any cancellations in the tweeter otherwise I’ll need to use a notch filter.
Fig 5 – Sparrow-SB19 Frequency Response
Fig 5 is a beautiful response of the Sparrow-SB19. She is not ruler flat but that’s not really necessary. Her response from 500Hz upwards doesn’t deviate by more than +/-1dB. That’s very impressive.
Fig 6 – Sparrow-SB19 Null
To check on the alignment of the drivers, I flipped the tweeter wires around. It resulted in a null (Violet plot in Fig 6), centering at 1.9kHz. The depth of the null is -25dB down, indicating the woofer and the tweeter are very close in alignment.
Fig 7 – Sparrow-SB19 Nearfield
The nearfield response (Blue plot) of the Sparrow-SB19 is in Fig 7. This is an approximation of the response below 500Hz without any room reflections. Notice the ugly suck-out at 150Hz is no longer there. That was caused by a floor bounce my mic picked up.
Fig 8 – Sparrow-SB19 Port
The Brown plot in Fig 8 is the response of the port. Measurement is made with the mic inserted about 1/4″ into the mouth. It shows the box is tuned to about 70Hz. The pipe resonance is at 1.5kHz. There’s no indication it’s affecting the response of the Sparrow-SB19.
Fig 9 – Sparrow-SB19 Step Response
The Sparrow-SB19 step response is in Fig 9. The sharp tip at the bottom indicates the two drivers are very close in alignment. The transient of the woofer is smooth and fast as one would expect from a 5″ woofer. She hits 100% at 250 microsec.
Fig 10 – Sparrow-SB19 Waterfall
The Waterfall in Fig 10 shows a bunch of frequencies from 5kHz~7kHz. They are from the cone breakup of the woofer. Apart from that, the treble looks clean.
Fig 11 – Sparrow-SB19 Toneburst Energy Storage
The Toneburst plot in Fig 11 shows unwanted excess energy at 5kHz~7kHz. They are the same ones in the Waterfall, except that now, the display is reference in cycles. It’s interesting that there’s virtually no excess energy at 1kHz.
Fig 12 – Sparrow-SB19 Spectrogram
Strangely, the Spectrogram (Fig 12), displayed some excess energy at 1kHz. I did not detect any smearing during auditioning, so nothing to be concerned about.
Fig 13 – Sparrow-SB19 Excess Group Delay
The Sparrow-SB19 Excess Group Delay (Fig 13) is -1.37 msec at 58Hz. This is not too bad for a bass reflex.
Fig 14 – Sparrow-SB19 Box Modeling
The bass reflex alignment of the Sparrow-SB19 is in Fig 14. Tuning is with a 1.5″ PVC pipe cut to a length of 3″. The -3dB (F3) is 65Hz.
Fig 15 – Sparrow-SB19 Impedance
The Sparrow-SB19 nominal impedance is 4Ω. She does dip to 3Ω at 7kHz but should not present any difficulties with amplifiers designed for 4Ω. The saddle on the left shows the bass reflex tuning at 65Hz.
The Sparrow-SB19 may be too taxing for chip amps. I have not tried her out with my LM3886 and TDA7293 so I don’t really know whether their over-current protection circuitry will be triggered when the impedance hits 3Ω. It’s a shame because the Sparrow-SB19 sensitivity is quite high, about 89dB (2.83V/1m).
Fig 16 – Sparrow-SB19 Harmonic Distortion
It is strange that the SB13PFC25-04 is dominated by 3rd order harmonics (Violet plot) from 500Hz to 3kHz (Fig 16). During playback, the odd order harmonics did not irritate me so I wouldn’t worry too much.
Sound of Sparrow-SB19
I am surprised at the performance of the Sparrow-SB19. Considering the plastic frame PFC series is SB Acoustics entry level woofers, this particular SB13PFC25-4 actually surpasses the SB16PFC. She even blew away the cast frame SB17NRX that I used in the Magpie-XT. Crazy.
Believe it or not, I managed to make this Sparrow-SB19 punch. No kidding. Just listen to Hotel California (Eagles-Hell Freezes Over). There’s even detail in the bass notes.
For harmony, I played It’s So Hard to Say Goodbye to Yesterday by Boyz II Men. The vocals are clearly focused. Equally important is the excellent separation between the bass and the midrange.
If you are looking for excellent sound in a small package, the Sparrow-SB19 is the one. The crossover component count is high but it’s well worth the cost. And before I forget, the Sparrow-SB19 can easily be converted into a 5 liters sealed box. She can then be used as satellites + subwoofers or as the mid-high combi in a 3-way.
Crossover is available on request. Free for DIY. Not for Commercial use.
March 20, 2021Projects