The Lark-XT is the first time I’m mating the SB16PFC25-08 with the Peerless XT25TG30-04 ring radiator tweeter. It is a fairly compact bass reflex with a volume of only 13 liters. My aim is to achieve as flat a response as possible and with minimum parts in the crossover. I think it’s achievable with the XT25TG30 tweeter.
Fig 1 – Black plot=SB16PFC25-08 RAW Response
The Black plot in Fig 1 is the RAW response of the SB16PFC25-08. It has a beautiful flat response from 600Hz~3.5kHz. The problem with using it this way is the outcome will not have much bass. That’s fine if a subwoofer is used but that’s not my intention. I want the bass to be on par with the midrange.
The Blue plot is with a new low pass network. This network is basically a 2nd order electrical filter, meaning an inductor and a capacitor.
Fig 2 – Blue plot=SB16PFC25-08 Low Pass • Red plot=Peerless XT25TG30-04 High Pass
The Red plot in Fig 2 is the Peerless XT25TG30-04 tweeter. Again, the High Pass filter is an electrical 2nd order, a capacitor and an inductor.
Fig 3 – Black plot=Lark-XT Passband
The Black plot in Fig 3 is the passband of the crossover. The summation shows no cancellations in the passband.
Fig 4 – Lark-XT Frequency Response
Fig 4 is the final frequency response of the Lark-XT. I don’t think it can get flatter than this. The bass is at the same level as the mid and high. It is not emphasized or too soft.
Fig 5 – Lark-XT Null
Fig 5 is the null when I flipped the tweeter wires around. It’s not a deep notch but it does exhibit good symmetry. This is more than I expected considering that I am using as few crossover components as possible. If I want a deeper null, I can add a step to the woofer or tilt the front baffle. Something to keep in mid for a future project.
Fig 6 – Step Response
The Lark-XT Step response in Fig 6 is interesting. Right at the bottom, the tip is not sharp. That’s probably caused by the woofer and tweeter not being in perfect alignment. After the woofer takes off, the transient is not linear. It slows down slightly at the 50% mark, hitting the top at about 450 microsec. The tip is sharp, indicating no overhang. For a budget mid-woofer, this is quite impressive.
Fig 7 – Waterfall
Fig 8 – Toneburst Energy Storage
The Waterfall (Fig 7) and Toneburst (Fig 8) plots show minimal artifacts in the treble. However, there seems to have some light blue slices from 1kHz~2kHz. They last for up to 8 cycles.
Fig 9 – Spectrogram
The Spectrogram (Fig 9) provides a better picture of those excess energy at 1kHz~2kHz. The three yellow spots are the light blue slices when viewed in the time domain. They lose their energy by 6 msec, so I doubt they’ll cause smearing.
Sound of Lark-XT
For a 13 liter bass reflex, the Lark-XT is quite impressive. I’m surprised that she is actually quite musical. She doesn’t sound dull or lifeless like some flat response speakers.
To test the bass, I had on If You Leave Me Now (Peter Cetera). The bass came out loud and clear. It didn’t drown out the vocals. For dynamics, I played She Works Hard for the Money (Donna Summer). The bass is fairly tight and punchy. Nowhere did she sound shrill. For bass texture and clarity, I tested the Lark-XT out with Put Your Lights On (Santana). Not too bad, considering the low price of the SB16PFC. In all these, there’s no grating highs in the treble. The Peerless performs flawlessly. Not once did the tweeter try to outshine the vocals.
Of all the Larks before this, the Lark-XT is the one that I’m most proud of. She sounds great. The SB16PFC25-8 is only $28. So is the Peerless XT25TG30-04. Add in say $10 for the crossover and the total cost per speaker amounts to $66. That’s very reasonable for a speaker with this level of performance.
Crossover is available on request. Free for DIY. Not for Commercial use.
January 30, 2021Projects