Auditioning the BiAmp Hummingbird

The BiAmp kit is a compact amplifier module specially developed for ease of biamping. I’ve been listening to this amplifier driving the Hummingbird for a few weeks already and I am more than pleased with her performance. It’s about time I take some measurements to verify the excellent sound quality.

Fig 1 – Dayton DSA135 Low Pass | Dayton ND25FW High Pass

Fig 1 shows the individual plots of the woofer and the tweeter derived from the BiAmp built-in crossover. The BiAmp chip amps are connected directly to the woofer and tweeter. No passive components are involved.

As can be seen in this measurement, the woofer and tweeter are crossing at about 2kHz. The Dayton DSA135 (Blue plot) is rolling-off at about 12dB/oct whereas for the Dayton ND25FW (Red plot), it’s at 18dB. They closely resemble the electrical crossover that’s in the BiAmp module.

Fig 2 – Summation of DSA135 with ND25FW

The woofer and the tweeter sum well (Black plot in Fig 2). This is with the tweeter wired in-phase. No cancellations are observed on either side of the crossover passband.

Fig 3 – Null Response

The violet plot in Fig 3 is with the tweeter wired in reversed phase. This resulted in a fairly deep notch at 1.8kHz. For all intents and purposes, this is time-aligned. Best of all, it’s done without any electronic delays. It is only by chance that the Dayton ND25FW horn brought the acoustic centers of the two drivers close enough for this to happen. 

Fig 4 – BiAmp Hummingbird Frequency Response

The Frequency Response of the Hummingbird driven by the BiAmp module is shown in Fig 4. Disregard the ugly notch at 150Hz. It’s caused by a floor bounce when the Hummingbird is placed 3ft above the ground.

What is important to note is the level of the bass. Small woofers like this 5-1/2″ Dayton DSA135 are notorious for their lack of bass. However, that is not the case with the Hummingbird. The bass is at the same level as the midrange (1kHz). This is measured in 4pi. When placed against a wall or nearer to a floor, we can expect the bass to be louder.

Moving up to the midrange, there is a 5dB rise at 2kHz that comes from the summation of the woofer and tweeter. This actually adds some presence to the midrange which I favor.

The treble is essentially flat up to 8kHz. Beyond that, there’s a 5dB drop but it still extends to 15kHz after which the tweeter dies off.

Fig 5 – ToneBurst Energy Storage

The BiAmp Hummingbird exhibits very little excess energy in the Toneburst measurement (Fig 5). Hints of excess energy is recorded from 2kHz ~ 5kHz but they are beyond our hearing.  

Fig 6 – BiAmp Hummingbird Wavelet

The Wavelet in Fig 6 is a 2 dimensional representation of the Toneburst in Fig 5. We can see the excess energy from 2kHz ~ 5kHz is largely dissipated by 3msec. Lasting for such a short time, it will not “smear” the upper midrange and treble.

Sound of the BiAmp Hummingbird

As I mentioned in the beginning of this post, I am pleasantly surprised by the performance of the Hummingbird powered by the BiAmp module. Frankly, the performance is beyond my expectations. The tonal balance is perfect for most people.

The bass is audible without being over-powering. The treble is not so loud that whenever the tweeter comes on, it’s shouting for attention. Most important of all, the midrange comes out clear.

In fact, a response of this nature is similar to the Harman Curve. Here is what a Harman Kardon Onyx Studio 6 frequency response looks like.

Fig 7 – Harman Kardon Onyx Studio 6 Frequency Response

And below is the frequency response of their high end JBL Synthesis. I believe electronic EQ was applied for this response. Point to note is the downward slope starting from 500Hz to 20kHz. Taking 80dB as the base line, 10kHz is 5dB down whereas 40Hz is 5dB higher. 

The Harman Curve is obviously not a flat response. The experts at Harman conducted extensive studies and concluded that the human ear favors a response of this nature

It’s just a coincidence that the BiAmp Hummingbird exhibits a similar response. I usually target a flat response in designing speakers because I want the music to be reproduced accurately when used in a recording studio. However, flat response speakers are not very pleasant musically. For general use, a response similar to the Harman Curve is more enjoyable.

The BiAmp module is not meant to be played at disco levels. There is a limit as to how loud the TDA2030A and the TDA2050 can go without causing the amplifiers to clip. Use the BiAmp well within her limits and you’ll enjoy your music.

For myself, the BiAmp Hummingbird is perfect for background music while I’m working on my pc. A simple solution to active biamping.

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