Soliloquy-III (Tang Band W5-1685 with Peerless BC25SC08-04)


The Soliloquy-III is the first time I’m using a horn loaded tweeter, albeit a very small one, to match the Tang Band W5-1685. I hope that this Peerless BC25SC08-04 tweeter will integrate better than all the more expensive ones I used before. The Soliloquy-III is housed in a 13 liters bass reflex tuned to 50Hz. F3 is 43Hz. I should be getting some deep bass with this 5″ midwoofer. Baffle width is 8-1/2″.

Fig 1 – Tang Band W5-1685 • Mic at 36 inches • Tweeter axis • No smoothing • 500Hz below in Nearfield

Fig 1 is the RAW response of the W5-1685. This midwoofer has a beautiful flat response that extends all the way to 12kHz.

Fig 2 – Blue plot=Tand Band W5-1685 with Low Pass

The Blue plot in Fig 2 is the W5-1685 with a 2nd order Low Pass Filter in place. No other networks are needed. I didn’t even have to notch out the cone breakup at 8kHz. 

Fig 3 – Tang Band W5-1685 with BC25SC08-04

The Red plot in Fig 3 is the Peerless BC25SC08-04 tweeter with a 3rd order high pass filter. The two drivers are crossing at about 3kHz, which is my targeted frequency.

Fig 4 – Crossover Passband

Now this is what I call a proper crossover (Fig 4). The summation is spot on, exhibiting no cancellations in the passband (Black plot). I’ve been chasing this crossover for quite some time.

Fig 5 – Soliloquy-III Frequency Response

The Soliloquy-III final frequency response is in Fig 5. It is impressively flat throughout with slight emphasis at 8kHz. The Peerless tweeter extends to 15kHz, falling off sharply after that.

Fig 6 – Soliloquy-III Null response

The Null response is the Violet plot in Fig 6. It is not deep enough to be labeled time-aligned but it is perfectly acceptable. What is important is how it sounds like. There’s no point trying to time-align the drivers but ending up mangling the crossover.

Fig 7 – Soliloquy-III Step Response

The Soliloquy-III Step response (Fig 7) is quite smooth. The attack of the W5-1685 is fairly fast, exhibiting no breaks all the way to the apex. 

Fig 8 – Soliloquy-III Waterfall

The Waterfall plot (Fig 8) of the Soliloquy-III shows minimal artifacts in the treble.

Fig 9 – Soliloquy-III Toneburst Energy Storage

The light blue slices in Fig 9 shows some excess energy from 4kHz upwards. This corresponds to what was recorded in the waterfall plot.   

Fig 10 – Soliloquy-III Spectrogram

The Spectrogram (Fig 10) shows nothing that will effect the treble. It is completely clean from 2kHz to 20kHz. There are a few hot spots below 2kHz but they die out by 5 msec. With these measurements, I do not expect to hear any smearing in the upper midrange and the treble.

Fig 11 – Soliloquy-III Harmonic Distortion

The Soliloquy-III recorded one of the lowest distortions in all my speakers (Fig 11). The 2nd harmonic (Red plot) and 3rd (Violet plot) are -60dB below the fundamental. 

Fig 12 – Soliloquy-III Impedance

The Nominal Impedance of the Soliloquy-III is 4Ω. As is typical of 4Ω tweeters, the impedance dips at 5kHz, reaching 3Ω at 20kHz. It didn’t cause my amplifier to clip but chip amp users should ensure their amplifiers are designed to handle 4Ω. The electrical phase is quite well behaved, thus easing the demands on the amplifier. The bass reflex port tuning is exactly at 50Hz.


After numerous attempts, the Peerless BC25SC08-04 tweeter is the perfect match for the Tang Band W5-1685. The summation in the crossover is far better than in my previous projects where I used the Seas 27TBFC and the HiVi RT1C. The irony is that this Peerless tweeter cost a lot less.

The tonal balance of the Soliloquy-III has mass appeal. There is no hint of harshness in the treble. The vocals are not recessed nor over sibilant. And the bass, what can I say. This W5-1685 is a 5″ midwoofer yet the bass sounds like an 8″. 

Fig 13 – Soliloquy-III Room Response

To have a better idea of the bass, I included the room response below 500Hz (Black plot in Fig 13). Disregard the suck-out at 150Hz. That’s an anomaly caused by a floor bounce. Note the region from 100Hz to 60Hz. It is almost level with the midrange and treble. And this is without applying any BSC or electronic EQ to boost the bass. Because of this, the Soliloquy-III works best in Full Space (4 pi) and prefers a fairly large room. Otherwise, the bass will be over-powering.

Unless otherwise stated, all measurements were made with the mic at 36 ins, tweeter axis. Impulse Window=5ms. No smoothing applied.