Hsu Research CCB-8 Bookshelf Speaker Review
- Design: two-way, coaxial ported bookshelf speaker
- High Frequency Driver: 1" aluminum dome tweeter
- Low Frequency Driver: 8” polypropylene cone woofer
- Frequency Range: 50Hz – 20kHz +/- 2 dB at 15 degrees off axis
- Sensitivity: 94dB (2.83V @ 1 Meter in half-space)
- Impedance: 8 ohms
- Crossover Frequency: 1,500 Hz
- Recommended Power: 10-400 Watts
- Cabinet: MDF
- Available Finishes: standard satin black and real wood Rosenut veneer
- Dimensions: 10.5" W x 15" H x 12.5" D
- Weight: 22 lbs.
- Outstanding imaging abilities
- Above average dynamic range
- Center speaker without usual compromises
- Rich, full soundstage
- Sounds the same at any distance
- Somewhat odd appearance
- Optimal setup requires relatively specific and unintuitive positioning
HSU CCB-8 Introduction
The Hsu Research CCB-8 is not your typical bookshelf speaker, and it only takes one glance at it to make that determination. Those folks who are not acquainted with the diversity of driver layouts (you know, ‘normal’ people, as opposed to us speaker nerds) might be wondering where the tweeter is on the CCB-8, since only the woofer is visible on the exterior. The CCB-8 uses a coaxial driver layout, meaning that the tweeter is centered in the middle of the woofer itself. This design decision carries with it a host of advantages that we will discuss when we get to the design overview section. When I asked the CCB-8’s designer, Dr. Poh Ser Hsu, what prompted the design and production of the CCB-8, he told me that me had always been impressed by the holographic imaging of point-source design such as coaxial speakers. He also said he wanted to address the problem of lobing that occurs with horizontally-oriented drivers that is very common on center channel speakers, and that a coaxial design is a perfect way to solve that issue. So now that we have a set of CCB-8s in house, this brings us to the question: how well do they achieve the objectives Dr. Hsu set out to accomplish?
Unpacking and Appearance
The CCB-8’s come packed in a heavy-duty cardboard box and sandwiched between two thick foam pieces. They are wrapped in a plastic bag on the outside and a cotton bag on the inside, to protect them from both moisture and scuffs and scratches. The owner’s guide is fairly standard, but it does include some good advice about placement. Due to the unique design of those speaker, some attention should be given to placement and positioning section of the manual, since their advised positioning differs somewhat from traditional bookshelf speakers.
The appearance of the CCB-8 speakers is a bit unusual from ordinary bookshelf speakers. A yellow cone with a black dustcap set against a fine satin-black cabinet begs a visual comparison with some kind of mechanical eye. The black metal grille does temper that likeness a bit by dimming the yellow. The grille is attached magnetically, so no grille guides clutter the front baffle. The CCB-8 is on the large side of bookshelf speakers, with a 15” height, a 10.5” width, and a 12” depth. Anyone intending to use these with bookshelf speaker mounts will need a heavy-duty mount, not just for their size but also their 22 lbs. weight. The satin-black finish is sleek, and, with the addition of the rounded edges, do lend the CCB-8s a sense of style beyond mere utilitarian. However, this speaker, without its grille, is not a conservatively styled speaker. It has personality, and it will clash in a home with traditional decor. That can be alleviated somewhat with the optional rosenut finish which does take the edge off the yellow cone and makes the CCB-8 look more refined. The bottom line is that it is a speaker with a peculiar style that is bound to turn some people off. Personally, I like it, however I like it when speakers have character. I prefer it when speakers look like speakers and do not pretend to be an innocuous piece of furniture.
Clearly, the chief distinction of the CCB-8 is the use of the coaxial driver. As mentioned before, the coaxial driver arrangement places the tweeter in the center of the woofer. In the CCB-8’s case, the tweeter is sunk back behind the motor of the 8” woofer. The tweeter is a 1” aluminum dome that uses the pole piece and polypropylene cone of the woofer as a waveguide. This design is seen mostly in live sound applications and professional, high-powered sound installations but is seldom used in home audio, although notable exceptions are the higher-end speakers from Tannoy. Since the tweeter is embedded deep behind the woofer, the ‘horn’ of the pole piece and woofer should contract the dispersion of the tweeter for a tightly-controlled spread of sound; this is called a constant directivity dispersion pattern.
One of the advantages of coaxial designs is that the acoustic center of the woofer and tweeter remain the same irrespective of where you are in relation to the speaker – above, below, left, right, or center of the driver. That means once the drivers are time aligned on axis, they are time aligned at any off-axis angle. With a typical speaker where the tweeter is above the woofer, that is not true. When the speaker is time aligned on tweeter axis, standing above the speaker will place you closer to the tweeter, so the woofer and tweeter are no longer time aligned as the sound from the tweeter will arrive first. This affects the phase matching between the drivers and causes peaks and dips in the response. And, of course, the same is true if you are below the speaker, but in reverse; since you are closer to the woofer, the sound from the woofer will arrive first and is no longer time aligned.
Since there is very little distance between the woofer and tweeter in a coaxial driver, time-alignment is a problem that is easily solved, especially since the distance difference only occurs as a very small matter of depth, rather than a significant height or width difference as is the case with most speakers. This is one of the reasons they are called coaxial drivers, since the term ‘coaxial’ means ‘having a common axis.’ They are also sometimes called ‘coincidental’ driver, since their time alignment is so close (‘coincidental’ defined as ‘occurring at the same time’), and ‘concentric’ drivers (concentric: sharing the same center).
Most speakers are point-source designs, meaning that the sound is intended to act as if it is emitting from a single point. That point is called the ‘acoustic center’ and usually is at some imaginary point near the tweeter in normal multi-way speakers that have drivers spread out over the front baffle. There are tricks that speaker designers can use to align the drivers to conform their operation to that acoustic center, but many of these measures aren’t needed with coaxial drivers, since the acoustic center of the overall speaker is so close to the acoustic centers of the individual woofer and tweeter.
Given these advantages, one would expect coaxial speakers to be more prevalent, but, as with all design decisions regarding speakers, there are trade-offs. One drawback is the cost-complexity of manufacturing coaxial drivers. Indeed, Dr. Hsu tells me that the coaxial driver used in the CCB-8 costs six times as much as the tweeter and woofer used in Hsu’s HB-1 mk2 bookshelf speaker.
A part of the challenge of producing a coaxial driver is matching the directivity of the pole piece/cone horn for the tweeter to that of the woofer itself. In other words, the lower frequencies produced by the woofer itself has to ‘spray’ sound outward at the same angle as the higher frequencies being directed by the waveguide formed by the pole piece and cone of the woofer. Towards this end, Hsu Research contracted the legendary speaker scientist Don Keele, Jr. Among many of Keele’s achievements is being one of the developers of constant directivity horns in the mid 70’s, which provided a basis for many future horn designs. Hsu Research would have been hard-pressed to find a more qualified engineer for this task.
Looking under the hood of the CCB-8, we see a relatively elaborate crossover board for a two-way bookshelf speaker. Dacron or Polyfill line the interior panels. The cabinet panels are a beefy 1” thick MDF, but there is no cross-bracing to speak of. Perhaps Hsu thought that with such thick sidewalls, more internal bracing was not needed. The CCB-8 is vented and has two ports on the rear panel. Port plugs are provided, and these ports can be sealed to change the tuning point of the speaker if the user wishes. In our measurements and analysis section, we do show the effects on frequency response of sealing the ports. In the rear, we also see a terminal cup containing a pair of stout 5-way, gold-plated binding posts. There are no feet affixed to the CCB-8, since it is intended to be placed on any of its sides.
The woofer itself sports a cast aluminum basket and a good-sized magnet. The inverted surround is made from treated cloth, and the spider looks to have a healthy diameter for the size of the driver. The 2” diameter, edge-wound voice coil is large for a 8” midwoofer, but it needs to be since the throat of the horn for the tweeter may be too constricted otherwise. The tweeter itself has an aluminum heatsink mounted on the back. That, combined with the ferrofluid cooling, should do a lot to keep thermal compression at bay. These extra cooling measures might be required by the coaxial design, since the driver motors are so close to each other. The acoustic load of the horn allows for an unusually low crossover point of 1.5 kHz for an aluminum dome tweeter. The CCB-8 woofer and tweeter can be protected by the grille, which is a sturdy steel perforated metal screen. It really does protect the drivers from anything hitting them. As mentioned before, the grille attaches magnetically, but it does not come off easily.
It should be noted here that in theory the design of the CCB-8 should allow it to work nearly as well on its side as it does standing upright, since there should be no off-axis lobing patterns. In fact, the CCB-8 should have superior off-axis dispersion to traditional center speaker designs, which usually suffer from interference patterns where the horizontally aligned drivers cause cancellations in the frequency response. Audioholics has a host of articles discussing the trade-offs of traditional center-speaker designs such as: Vertical vs Horizontal Center Speaker Designs, Center Speaker Design Additional Considerations, and Vertical vs Horizontal Center Speaker Designs - An Alternate Perspective. Hsu Research sells the CCB-8 as a singly-packed center speaker as well as main speakers for these reasons.
Another advantage of the coaxial design is that since the sound of the tweeter and woofer come integrated ‘right out of the gate,’ so to speak, they should be able to be used as near-field speakers, if one so desired. Most other speakers need some distance before the sound of their individual drivers ‘coalesce’, or properly sum in phase, so you can’t simply use any bookshelf speaker for near-field listening, at least if you don’t want to hear the drivers fighting around the crossover frequency. Due to their near-field phase coherence, a design like the CCB-8s can be used as desktop speaker, if one had desktop space for such large bookshelf speakers. However, as with all speakers used on a desktop, the user should try to elevate the speakers as far off the desktop itself as possible while keeping the tweeter at ear level. Desktop reflections, or any nearby surfaces can cause unpleasant spikes in mid bass and upper bass frequencies. If the user can not prop a desktop speaker up off the desktop surface with something like a desktop speaker stand then they should be ready to measure the frequency response and equalize down any severe reflection peaks.
One peculiar feature of the CCB-8 is the recommendation by Hsu to toe the speakers in front of the listener where the listener ends up 15 degrees off the direct axis. In fact, the CCB-8 is engineered from the ground up to be listened to off axis around a 15-degree angle. The reason for this is because Hsu is leveraging a phenomena known as ‘time-intensity trading’ to create a strong stereo image across a wider listening area, so that listeners do not have to sit in a single position to experience good imaging. Time-intensity trading is, in very simple terms, when our perception of hearing can be fooled into thinking something sounds closer to us than it actually is, because it is louder.
The two primary ways that we determine the location of a sound is the differences in the time arrival of the sound between both our ears and differences in amplitude of sound (that we perceive as loudness) between our ears. If we hear something sooner in one ear than the other, the origin of the sound will be perceived to be in the direction of the ear which first sensed the sound. If we hear something louder in one ear than the other, the origin of the sound will be perceived to be somewhere in the direction of the ear that sensed the sound to be the loudest. That, of course, is a very simple explanation of these seemingly common-sense aspects of our hearing, which are called Interaural Time Difference (ITD) and Interaural Intensity Difference (IID), respectively.
In normal stereo speaker systems, the closer you are to one speaker, the more the stereo image shifts in its direction, so the imaging will very often be heavily weighted toward the speaker that you are closest to, and this is due to ITD and IID. It is because of this that the listening position of a stereo system is always right between the speakers, usually forming an equilateral triangle with the speakers themselves, and with the speakers toed-in to face the listener directly. But what if you could alter that effect by compensating the time arrival difference between right and left ears with the amplitude difference between right and left ears? This is the logic of the 15-degree inner toe-in of the CCB-8s. If you are sitting off center in a system that is built for such an arrangement, the speaker facing you will be louder, but that isn’t the speaker that is closest to you and so will have a later time arrival. By balancing time arrival with loudness, we can preserve a sharp stereo image, even when we are sitting off the “sweet spot.’ The is the effect achieved with time-intensity trading, and it is something that a constant directivity design like the CCB-8 should excel at; in fact, a wide-dispersion speaker would not work well for this kind of setup. For a more comprehensive guide on time-intensity trading in speaker placement, read Bill Waslo’s article: Setup of Controlled-Directivity Waveguide Speakers.
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Pogre, post: 1202989, member: 79914
“Verisimilitude”?! It's not often I learn a new word.
By coincidence, I learned that word in the Audio magazine review of the Duntech Sovereign speaker, written by Bert Whyte.
By the way, here are some mounts which are basically the same as the AM40 Pinpoints but a bit cheaper, and also have slots for a strap in case you want a tighter hold but without drilling into the speaker. You might as well use those if you go with the KEFs.
I'm currently auditioning a pair of the new KEF Q150s in my living room, and think they sound great, but dialogue is a little lacking. I'm not sure if the slightly older R100s would be a step up or not. That said, I also am not using a center channel at the moment, so I'm sure getting a 3rd Q150 for a dedicated center, or even going to the Q350 to use as a center would definitely alleviate that issue, as minor as it is (dialogue isn't bad eve in 2.1, it's just that my giant Klipsch RC-7 in my prior 3.1 setup was about as clear as it gets).