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Warbler-TA The Warbler-TA is an upgrade to the earlier Warbler. In this version, my aim is to improve on the frequency response and to simplify the crossover. The Warbler crossover was just too elaborate for a budget speaker.
I started with a clean slate. The plot in Fig 1 is the RAW response of the 830656 with the microphone at 36 inches on tweeter axis. No smoothing is applied. Box is a bass reflex with internal volume of 13 liters. Baffle width is 8-1/2″.
The Blue plot in Fig 2 is the 830656 with a 2nd order Low Pass Filter in place. Since I’m trying to keep things simple, I did not install any other networks. So basically, the Blue plot is with 1 inductor and 1 capacitor.
Fig 3 shows the 830656 and the BC25SC08-04 crossing at 3kHz. This time round, I decided to use a 3rd order network for the tweeter instead of a 2nd order that is in the Warbler. There are only 2 capacitors and 1 inductor for the High Pass filter. Apart from that, a few resistors to pad down the tweeter.
As I had hoped, the crossover passband (Fig 4) shows the two drivers are summing well. No cancellations are observed on either side of 3kHz.
This is what I was aiming for. The frequency response in Fig 5 is much better than the Warbler and I managed to achieve this with the barest amount of components in the crossover.
The Violet plot in Fig 6 is the null response. It centers at about 3.2kHz, exactly where the two drivers are crossing. I did not have to use a delay network or a step for this. The time alignment is inherent in the Warbler-TA.
The Step response (Fig 7) of the Warbler-TA shows a smoother decay in the woofer when compared to the Warbler.
I just can’t help being amused by this budget speaker. The waterfall (Fig 8) shows a very clean response.
The light blue slices in Fig 9 shows the Toneburst plot confirms the Waterfall. The stored energy is lower than most.
The Warbler-TA is completely clean above 2kHz (Fig 10). Below that, there are a few excess energy but nothing to be alarmed about. The green spots are -50dB below the fundamental. More than that, they are fully dissipated by 5 msec.
The Warbler-TA is quite an easy load for power amplifiers. The Re is at 6.4Ω, so a Nominal Impedance of 8Ω is normally specified. However in the treble region, it dips down to 3Ω at 20kHz. This behavior is normal for 4Ω tweeters like the BC25SC08-04. It didn’t cause any distress to my amplifier but it’s something to take note of, particularly for chip amp users like the LM3886. If it is designed for 8Ω, it will surely trigger the protection circuitry. The Warbler-TA bass reflex tuning is exactly at 50Hz. No anomalies are observed in the impedance sweep. The electrical phase is almost linear from 200Hz upwards. SummaryThe Warbler-TA more than met my expectations. The response is flatter than the Warbler and it’s time aligned. The crossover has less components, resulting in a lower cost for the project. It is not often I have the pleasure to work with such friendly drivers. Everything just fell into place naturally. As far as the sound quality is concerned, I can find no fault with the Warbler-TA. It is a very pleasant speaker to listen to. The tonal balance is just about right. It doesn’t suffer from the small woofer syndrome of too much mids and highs. Surprisingly, there’s actually some punch in the upper bass from the 830656. This is one under-rated woofer. The Warbler-TA is a wonderful project for beginners or builders on a budget. It doesn’t cost much but sounds excellent. No harshness in voices and the treble. Unless otherwise stated, all measurements were made with the mic at 36 ins, tweeter axis. Impulse Window=5ms. No smoothing applied. |
November 14, 2020HIFI DRIVERS, Projects
Fig 1 – Peerless 830656 • Mic at 36 inches • Tweeter axis • No smoothing • 500Hz below in Nearfield
Fig 2 – Blue plot=Peerless 830656 with Low Pass
Fig 3 – Peerless 830656 with BC25SC08-04
Fig 4 – Crossover Passband
Fig 6 – Null response
Fig 7 – Warbler-TA Step Response
Fig 8 – Warbler-TA Waterfall
Fig 9 – Warbler-TA Toneburst Energy Storage
Fig 10 – Warbler-TA Spectrogram
Fig 11 – Warbler-TA Impedance