Associated Equipment:
Digital Front End
Hsu Research HO 1220 Subwoofer

The Race for Bass

Dan Dzuban

14 April 2003


HO 1220 Subwoofer
Frequency Response +/-1 dB 20 Hz up, to -6dB at crossover (Linkwitz-Riley alignment) using Hsu Research crossover or amp
Power Handling: 250 W RMS 18 Hz up
Nominal Impedance: 4 ohms
Sensitivity: 93 dB @ 1m, 2.83V RMS in the mid to upper bass in half space
Finish: Seamless black knit cloth
Size: 12 inches in diameter, 51 inches high (with spikes)
Shipping Weight: 36 lbs
Feet Black-anodized aluminum spiked feet (three)
Passive design--requires an external amp
Warranty: 5 years warranty against manufacturing defects
Price: $499

250 Watt Amp
Crossover type: line level 24dB/octave Linkwitz-Riley, low pass
Crossover Frequency: 30 - 90 Hz, continuously variable. Can be bypassed
Input Impedance: 10 k ohms
Inputs Speaker and line level: Gold plated RCA jacks and gold plated 5 way binding posts
Outputs Speaker level: (6 dB/Octave high pass, approx 90 Hz for 8 ohm speakers)
Controls: Level control, low pass frequency control, phase inversion switch, EQ switch (TN1220HO/1225HO), and crossover in/out switch
Shipping Weight: 20 lbs
Size: 11" (width) × 11"(height) × 5.5" (depth)
Power Requirements: 120 VAC, 400W
Warranty: 1 year for electronics (2 year electronics warranty when ordered factory direct)
Price: $400

Package price for HO 1220 with 250 watt amp: $849

Hsu Research, Inc.
3160 E. La Palma Ave, Unit D
Anaheim, CA 92806
Telephone: 1-800-554-0150

Working Within the Law of Unintended Consequences

One of the effects of the home theater revolution in hifi (no pun intended) is the proliferation of subwoofers. If your main speakers need a little bass augmentation, it seems that in 2003, there are more choices than ever for subwoofers. Superficially it seems like a good thing to have so many brands and models to choose from. The catch is, "me-too-ism" is running rampant. Other than the Bob Carver/Sunfire-influenced mini cube sized subwoofer, there really seems to be little to distinguish one from another. And even Carver's mini design has been copied so much that every brand seems to have its own token 10" × 10" × 10" box sub. The other catch is that most subs seem to fall into the measures-great-but-sounds-terrible trap. The sub bass for an adequate home theater does not require much musical pitch definition or finesse. It only requires the ability to generate a rumble, and perhaps if you are lucky maybe even some sort of startling rumble. Hell, most of the rumbling doesn't even qualify as true sub bass. The bottom line is that it is still difficult as ever to find a subwoofer that satisfies your cinema sweet tooth while giving you the musical nutrition you need. There certainly are subwoofers that can do this, but like much else in life, you have got to pay to play.

After putting up with my rambling about rumbling, you can understand why I am impressed with what Dr. Poh Ser Hsu has accomplished at Hsu Research. I am always impressed by a clearly effective solution to a problem. But I am particularly impressed when an audiophile-type problem is solved by a mass-fi priced product. Dr. Hsu has garnered a reputation for building subwoofers that have some of the deepest bass output on the market-but at reasonable prices. Specifically, Dr. Hsu has created a subwoofer that certainly does not fit the usual mold, and perhaps can literally be termed "outside of the box". Hsu's solution is the HO 1220 (and its slightly smaller and less expensive sibling the HO 1225).

Freudian Issues

The 1220 is a slender 12" diameter by 50 or so inch tall cylinder covered in a black fabric wrap. It has a 12" paper-coned woofer mounted in its top end, and a port venting from its bottom. As advertised, its 12" footprint really doesn't take up much real estate, and a pair of them actually hid behind my Quads quite well. However, the catch with the columnar design and top-mounted woofer, is that it is very top-heavy. This has me a bit concerned now that I have a mobile one-year-old daughter. (Dr. Hsu says the '1220s are actually just as effective laying down on their side, and 2 of them can be even more effective if they are placed on their side, woofer to woofer, with one woofer wired out of phase). It was also a bit disconcerting to find that the outboard amplifiers are in "raw" form; i.e., they are amps that are typically mounted on the side of a powered sub, albeit with a plastic housing covering the actual circuitry. I was a bit uncomfortable with them exposed in their nakedness, sitting there on my living room floor. This was a bit too hobbyist for me, and didn't seem right for a commercial product. But then again, I don't think there was anything unsafe about them, so maybe it was just a case of some Freudian obsessive-compulsiveness of mine that their nakedness should be hidden. Either way, if I owned them, the first thing I would do would be to build a black MDF box to mount each of them in.

Other than the top-heaviness and amp nakedness issues, there was really nothing else to complain about with these subs, because they performed as advertised; they gave me extremely deep bass and gobs of it. It is easy to get lulled into thinking that the usual 35-40 Hz home theater schlock-boxes give you sub bass because so many of them peter out at 35-40 Hz regardless of specs. But when you hear a sub with legitimate sub-20 Hz bass, you won't forget it. Caveat being that in many respects, you actually don't hear it. With a crossover low-passed at 40 Hz, there often isn't much below that frequency to hear. And below 20 Hz, you can't hear it anyway. But you sure can feel it. You get an air shuddering effect that truly heightens the sense of realism in a movie. As such, the '1220s were a great addition to my Quads for movies. Although the Quads are supposedly rated down to 30 Hz, the '1220s made it perfectly clear that there was a lot of low level information that was not otherwise ever being close to being reproduced. And the bass was reproduced tightly, without being boomy. However, at such low frequencies you have to begin worrying about the interaction of your listening room. Specifically, everything from the walls, to furniture, to almost every tchotcke in my listening room began to vibrate and rattle. This actually made me wonder if a little less bass below 20 Hz might be a good thing, but that may not be an issue in other listening rooms.

So What About The Music?

Ok, so the '1220s could rumble with the best of 'em for movies, but what about music? They performed very well here also. Except that they performed very well on their own, independent of what was going on with the Quads. They certainly were everything I could ask for in terms of performance (within the realm of a sub $10,000 sub), but I never really felt that they were a good match for the Quads. So if the subs had any weakness, it may have been in integration with the electrostats. Now don't get me wrong, they did nothing overtly wrong, they just didn't get things as right as I would have liked. What I mean here is that ideally, I would like to be tricked into thinking that my Quads, by themselves, were somehow capable of going flat to 20 Hz. Instead, it seemed to me that I had an electrostat combined with a sub that was flat to 20 Hz. This is a subtle, but important, difference and should be noted. But it should also be put into perspective; there are not many subs on the face of the planet that can integrate well with the Quads, so this is less of a criticism of the '1220, and more of comment on the state of affairs for subwoofers generally. As such, you can take my comments in the negative and say that since the '1220s could just quite miss integrating perfectly with one of the toughest-to-integrate speakers on the planet, what could it do with the other thousands of speakers out there; especially at its price? Alas, I did not have any dynamic speakers to test the '1220s with, but I am confident there should be no practical integration issues on the vast majority of other speakers.

Are Two Heads Better Than One?

If you have been paying attention, you noticed that I had a stereo pair of '1220s and their respective amplifiers. It was a treat to hear that much bass, but in my room it was overkill. I have heard about the phenomena of "room lock" with dual subs, but in my medium-sized room, I really could not hear much of a difference; maybe a slight difference, but not material. On the contrary, I think dual subs tend to cause more room vibration. Maybe a larger room might benefit from two subs, and the relatively low price of the '1220 makes this an option for more listeners than usual, but I think that it is a testament to the performance of the '1220 that one sub did the job by itself. I did notice two other unexpected phenomena associated with 2 subs; placement of a sub behind each Quad served as a sort of room treatment that could change the soundstaging of the speakers depending on exactly where the sub was oriented behind the dipole Quads. Interesting. Furthermore, when I ran two subs, I'll be damned if playing with the subwoofer crossover phase adjustments couldn't increase or decrease the perceived bass of the Quads in that crossover region. For example, running the '1220s with a 50 Hz low pass out of phase with the main speakers seemed to reduce a slight bass hump I was otherwise hearing from the main speakers at around 60-70 Hz. It was slight, but I am reasonably sure of its existence.

As for specific musical examples, the most dramatic example of the '1220's performance was on Enya's "Longships" from Watermark [Reprise 9 26774-2]. I had heard about there being deep bass on this track and had listened to it many times, but through my supposedly 25 Hz-capable Paradigm PS1000 subwoofer, I had never before heard these powerful bass notes. The bass really began to kick in in the last minute or so of the song, which artistically made the song a totally different experience. And to stress once again, the bass itself coming from the sub was itself ideal; tight, deep, powerful, agile and reflective of changes in pitch. Keep in mind that the Paradigm sub is a $550 or so sub, and is itself a good bargain for its performance. But not only was it in a totally different league than the '1220s for a couple hundred dollars difference, but it could not integrate with the Quads (which is why I typically only have the sub hooked up to the subwoofer output of a home theater receiver for only home theater use).

There were other clear examples of what the '1220s could do, such as when playing some miscellaneous recordings of pipe organs; e.g., they made the air shake the same way a live pipe organ could (which the Quads alone certainly could not do). But what really made the '1220s worth it was their ability to not be heard, except in their absence. This subtle difference made the overall sonic portrayal more spacious and the presentation more powerful. In other words, for $800 and change, my system sounded much more life-like. It's rare to get that correspondingly large of an increase in realism-especially at that price.


Well, I never felt as though I quite got the '1220s completely integrated with my Quads. But that is not necessarily a knock on the '1220s. Indeed there are probably only a few subs that will seamlessly integrate with the Quads-and they probably cost multiples of a pair of '1220s-let alone a single '1220. But for the other 99.99% of speakers out there, a single '1220 is likely all the subwoofer ever needed. And for the even smaller population who have especially large rooms, dual 1220s are all that will ever be needed. In fact, some of the '1220's only competition at their pricepoint may in fact be Hsu's own new VTF-3 subwoofer. I have not heard it, but at roughly the same price, it has achieved some positive press. True, the VTF-3 is a conventional big box design, but then again it wouldn't have the top heaviness issues or the naked outboard amp that the 1220 has.

The bottom line is that $800 and change will get you a huge variety of mid-fi wannabe subs that just plain won't cut it in a system with high-end aspirations. But the Hsu Research HO 1220 is no ordinary sub: for a mid-fi price you can snag a high-end sub that has a 99% chance of being the finish line in your race for bass.






















































Hsu Research HO 1220 Subwoofer