The Finch-TA is a time-aligned speaker using a vintage Vifa PL18WO-09-08 with the Peerless BC25TG15-04 tweeter. The PL18 is one of my all time favorites. For those who are fortunate enough to have this driver, the Finch-TA is worthy of serious consideration.
Fig 1 – Vifa PL18WO-09-08 RAW Frequency Response • Baffle Width=8-3/4″
Fig 1 is the RAW frequency response of the PL18. She has a beautiful response, extending all the way to 5kHz. Best of all, her cone breakup is well controlled. No violent sharp spikes.
Fig 2 – Vifa PL18WO-09-08 with Peerless BC25TG15-04 (Flush Mounted)
The Blue plot is the PL18 with a low pass network. I did not have to compensate for baffle step as the bass is strong enough. The Red plot is the flush mounted BC25TG15 tweeter. The two drivers are crossing at 1.7kHz.
Fig 3 – Finch-TA Crossover Passband
The crossover passband is the Black plot in Fig 3. It shows good summation with no cancellations.
Fig 4 – Finch-TA Frequency Response
The final frequency response of the Finch-TA is in Fig 4. She is not as flat as the Lark-SM but that’s fine. She’s not a studio monitor. It’s musicality that I’m after.
Fig 5 – Finch-TA Null
The Violet plot in Fig 5 is what the Finch-TA is all about. The sharpness and the depth of the null indicates perfect time alignment. The center frequency is 1.7kHz, exactly where the PL18 and the BC25TG are crossing.
Fig 6 – Finch-TA Nearfield Frequency Response
The Blue plot in Fig 6 is the nearfield response spliced in at 500Hz. This is a good approximation of the Finch-TA response without room reflections. Note the huge notch at 150Hz is not in the nearfield plot. It’s caused by a floor bounce that my mic picked up.
Fig 7 – Finch-TA Port Output
To check on the back port output, I inserted the mic about 1/4″ into the mouth. The response (Fig 7) shows my port tuning is roughly 45Hz. It also recorded a pipe resonance at 900Hz. It is well below the port fundamental to cause any issues in the main response.
Fig 8 – Finch-TA Step Response
The Finch-TA Step response in Fig 8 is quite normal. There are two breaks at the bottom followed by a linear transient. The woofer hits 300 miscrosec by 90%, after which slowing down to hit the apex at 400 microsec.
Fig 9 – Finch-TA Waterfall
The Waterfall (Fig 9) plot recorded minimal artifacts in the treble. It is at 1kHz that has a long decay.
Fig 10 – Finch-TA Spectrogram
The Spectrogram (Fig 10) shows a streak at 1kHz. I did not detect any smearing during auditioning. As for the treble, it’s very clean.
Fig 11 – Finch-TA Box Modeling
Fig 11 is the bass reflex box tuning of the Finch-TA. The Fb is 46Hz, resulting in a flat tuning with a F3 of 47Hz. Of all the boxes I’ve tried, the bass sounds the best with this 15 liters box.
Fig 12 – Finch-TA Impedance
The Finch-TA is an easy load for power amplifiers. Most of the time, she stays above 6Ω, only dipping to 5Ω at 20khz. There’s almost not deviation in her electrical phase. In the bass, we can see the box tuning is at 45Hz.
Sound of Finch-TA
In terms of sound quality, the Finch-TA blows the Lark-SM away. The Vifa PL18 has a wonderful tone that’s missing in the SB Acoustics SB16PFC25-08. More than that, she’s lively and more dynamic. Her bass has “weight” and goes deeper. It is these differences that makes the Finch-TA such a joy to listen to.
As for the treble, some may question the wisdom of using a $15 budget tweeter with such a fine woofer like the PL18. Well, the short answer to that is she sounds great. As long as a driver gives me the sound I’m after, it doesn’t matter to me whether it’s cheap or expensive.
Since I’m on the topic of tweeters, I should add that I removed the ferrofluid in my Peerless BC25TG15-04. She sounds so much better. The sparkle in the treble came out and she sounds more open.
There is no danger in removing the ferrofluid. The only difference is in a lower power handling. For home use, the speaker is not played at concert levels. There’s really no necessity to use ferrofluid to increase power handling at the expense of sound quality.
Crossover is available on request. Free for DIY. Not for Commercial use.
March 10, 2021Projects