The Hsu Research CCB-8 bookshelf speakers were measured in free air at a height of approximately 9 feet and gated at 14 ms. At this window gate, some resolution is lost below 140 Hz, and accuracy is completely lost below 70 Hz and so that range should be ignored. The microphone was placed 1 meter away from the speaker at a height level with the tweeter. All measurements are unsmoothed.

Hsu Research CCB-8 bookshelf speaker response curves

The direct-axis frequency response curve for the CCB-8 is not perfect but it is not bad either. It should be kept in mind when viewing these curves that this speaker was not intended to be listened to on its direct axis, but around 15 degrees off axis. The 100 Hz bump is more of a measurement anomaly than the speaker’s actual low frequency performance. Up to 10 kHz, the response is respectable, if imperfect. It stays within a +/- 3 dB window, although we do see a slight bump and dip near the crossover frequency of 1,500 Hz. These narrow ripples and dips are imperfections, to be sure, but the overall response stays within a baseline amplitude, and, in terms of audibility and accuracy, this is much more preferable to wide bands of elevation or depression. Once we hit 10 kHz, the treble hits some spikiness on direct axis that rapidly falls down as we go off axis, although there is still some of it at 10 degrees off axis. If listened to on its direct axis, this is likely to make the CCB-8 a bright speaker, but we see in the directivity indexes and sound power that this elevated treble is very directional. One interesting feature that can be gleaned here is to see how the horn affects directivity above the crossover point, where the dispersion becomes much more restricted.

Hsu Research CCB-8 Bookshelf Speakers horizontal frequency response +/-90 degrees from axis: 3D view

Hsu Research CCB-8 Bookshelf Speakers horizontal frequency response +/-90 degrees from axis: 2D view

The above graphs depict the CCB-8’s axial response out to 90 degrees in 10-degree increments. As was alluded to by the directivity indexes, the CCB-8s rapidly narrows its dispersion pattern above the crossover point. The dispersion of treble frequencies is tightly contained. We also see the high-frequency response above 10 kHz has come down substantially at 20 degrees without heavily impacting the rest of the response. This speaker’s most neutral overall response looks to be between 15 degrees and 25 degrees, and it is at this angle that it is best listened too. While our measured response at 15 degrees is not bad, they do not match Hsu’s claims of +/-2dB from 50 Hz to 20 kHz. Those who suffer from high-frequency hearing loss (a huge chunk of the older adult male population) might benefit from listening to the CCB-8s on the direct axis, but most listeners would be more comfortable listening at the said 15-25 degree angle.

Hsu Research CCB-8 Bookshelf Speaker Polar Map

The above polar map of the horizontal dispersion of the Hsu CCB-8 speakers depict the same information as the two waterfall graphs above it, but tells the story in a different way that can offer further insight regarding its behavior. In this graph we get a better idea of the kind of controlled directivity that is occurring at high frequencies. Dispersion is kept nicely uniform above 5 kHz. Below 5 kHz there is some broadening to the mids, and that looks to be the horn’s way of controlling the tweeter’s output. The dispersion seen here overall is not as broad as other speakers I have measured, which is exactly what one would expect from a constant directivity design. As we saw with the waterfall graphs, the most linear axis looks to be around 15 to 25 degrees.

Hsu Research CCB-8 Bookshelf Speakers vertical frequency response +/-90 degrees from axis: 3D view

The above graph depicts the CCB-8’s frequency response behavior on the vertical axis. As one would predict by its design, there is not much difference in performance between the vertical and horizontal axis. Orientation does little to affect its performance, so it can be used on any of its sides without any serious acoustic penalty. This can be handy for those who want a powerful bookshelf speaker but have a height restriction of less than 11.” The absence of any lobing artifacts demonstrates why the CCB-8 makes for a good center channel speaker. On traditional center speakers, woofers are aligned on a horizontal plane, and this will cause cancellation artifacts off-axis, sometimes as close as 10 degrees off-axis. This can result in an erratic sound for those who have to sit off to the side of the direct axis of the center speaker. The Hsu CCB-8 has none of these drawbacks. One drawback that it does have is that, since the upper treble on the direct axis is elevated, users may want to aim the tweeter above or below the listening position by 15 to 25 degrees. In my own listening, I aimed the tweeter over my head when seated at the listening position for an approximate 15-degree angle.

Hsu Research CCB-8 Electrical Impedance and Phase

The impedance profile of the CCB-8 doesn’t exhibit anything problematic. We can see that the port tuning frequency is just above 60 Hz. That was performed with two ports open, and if we sealed a port, that saddle shape would move down in frequency. Hsu states the nominal impedance of the CCB-8 to be 6 ohms, and that looks to be correct. Our measured impedance minima shows 5 ohms, but Hsu states 4 ohms in their specifications. No reasonably engineered amplifier would have a problem with this load, and even budget AVR amps should be able to handle this without too much of a problem. The toughest part of this profile would be the 5-ohm dip just under 200 Hz, but the phase angle is not very steep here.

Hsu reports the CCB-8 sensitivity in half-space at 94 dB at 1 meter for 2.83v, and our measurement of 93.8 dB largely agrees with their specification. Of course, half-space sensitivity converted to full-space sensitivity means a drop of 6 dB, which puts the CCB-8 at 88 dB sensitive full-space by their own specifications. That is above average for a bookshelf speaker, but do not mistake its half-space spec to mean it is a high-powered speaker that can handle THX Reference levels in a large room. The half-space sensitivity specification is simply the result of the setting it was measured in. In a medium-sized room, the CCB-8s can get louder than most people would ever want, but those who like loud-listening in a large room are going to need some much larger speakers.

Hsu Research CCB-8 port sealing effects

We did groundplane measurements to gauge the effects of sealing the ports on the CCB-8. Sealing the ports will only affect the low frequencies, so we restrict our window to that region. Leaving both ports open gives a slight rise at 90 to 100 Hz of almost 2 dB. Sealing one port gives the CCB-8s the most neutral response and also a bit more low-frequency extension. Sealing both ports effectively rolls off the response at a gradual 12 dB/octave slope starting at 100 Hz. Those who like beefier bass would be advised to leave both ports open, and this configuration necessitates a subwoofer crossed over at 80 Hz. While the use of a subwoofer is recommended with the CCB-8s, if no sub is available, sealing one port would be the preferred mode of operation, since it provides the most deep bass at tangible levels between all modes. Those who want the flattest response should also run the CCB-8s with one port sealed.