Hsu VTF-2 Powered Subwoofer.

Manufacturer: Hsu Research, 14946 Shoemaker Avenue, Unit L, Santa Fe Springs, CA 90670; 800/ 554-0150

Price: $500

Source: Manufacturer loan

The last Hsu subwoofer I reviewed (in Issue 67, January/February, 1998), was the TN1220HO. It was and still is a tall, cylindrical-shaped, one-foot-in-diameter, "tower" unit that is wrapped with a black-colored knit fabric. The TN1220HO has a very robustly built, 12-inch woofer driver mounted in the top, facing upward (filling the top completely, actually), and makes use of a huge tubular port that exits from the bottom. To keep the port from being blocked, the enclosure is held off from the floor by three small, pointed legs. I currently use the system as the center-channel subwoofer in my main system. The TN1220 is a killer of a subwoofer that will subjectively match most of the very best superduper subs on the market. It is unpowered and its outboard amplifier/crossover, a 250-watt job at the time I reviewed the unit, can be located in a standard equipment cabinet. (Also now available is a 500-watt amp that can drive two of the systems in parallel.) That kind of ability allowed me to use standard speaker wires for the run to the sub, rather than the long shielded cables that I have to use with my Velodyne F1800RII (which I also reviewed in Issue 67).

Hookup flexibility notwithstanding, the TN might be a bit of a problem to locate in some rooms, both because of its size (it may be skinny, but it is also more than four feet tall), and because of the way it looks. It resembles a black water heater, which is not something a lot of spouses care to have sitting in the corner. In addition, the TN is probably a sonic-overkill item for some people. It can go deeper (to below 20 Hz, easily) than most music and virtually all home theater requires, and it can also play louder at the lowest frequencies than any sane person with a room smaller than 3000 cubic feet would ever need.

Consequently, for those with less aggressive tastes and with somewhat lighter-weight budgets, we have Hsu's VTF-2 subwoofer, reviewed here, which is not only smaller and cheaper than the TN1220, but is also more conventional in operation and appearance. The VTF-2 I have on hand to review is an updated version of the earlier model that appeared over a year ago. (Tom Nousaine reviewed a sample of the premier model in the May, 2000 issue of Sound & Vision.) Like the earlier version, it is a box-shaped unit that is 18.5 inches deep (not counting the heat sinks, which stick out another inch-and-a-half on the back), 16 inches wide, and 16 inches high (counting the contributions from the four feet that hold it off the floor). The finish is an unusual pebble-grain black coating that has a much denser texture than usual. This subwoofer definitely looks different from the pack, in spite of its rather conventional size and shape.

Like the earlier VTF-2, but unlike the TN1220, the VTF-2 has a built-in amp. As with the earlier version, that device is still rated at 150 watts (with a soft-clipping feature to minimize harmonic artifacts during high-output use), and it employs a low-pass filter that can be varied from 30 Hz to 90 Hz. The filter has a 24-dB-per-octave slope, and it can be bypassed (allowing the VTF-2 to easily dovetail with an outboard processor's subwoofer output) with the flick of a switch on the back of the cabinet.

The newer version of the sub includes upgrades that involve the low-pass adjustment range and the low-pass roll-off slope. The earlier version had a range of 60-125 Hz, with a 12-dB slope, and the filter also could not be bypassed for use with an outboard processor's subwoofer feed. In addition, the newer VTF-2 weighs in at a solid 47.5 pounds, which is seven pounds more than the earlier model. Most of the weight increase involves a heavier amplifier heat sink and more robust transformer, to better handle high sustained-power requirements. The driver also got a tad heavier.

I will discuss the tuning and adjustment advantages of these upgrades up ahead, but it should be noted that VTF-2 users who have the earlier version and are satisfied with what it can do need not fret about the abilities of those older units. While the changes do result in marginally improved performance, particularly at high output levels, most users would not be able to readily hear any difference. In addition, the crossover mods are basically embellishments to what was an already good design and not monumental in scope, although under some conditions (see below) they might come in handy.

The VTF-2 enclosure has two large-diameter ports, with one on each side, allowing for what Hsu calls a "variable tuning frequency." The sub comes from the factory with a dense, but easy to remove foam plug inserted into one of them. Which port it is inserted into does not matter, although Hsu says that if the unit is close to a side wall it is best to have the plug on that side. With the on-board, extension-mode (tuning) switch on the back panel set to 25 Hz and the port plug installed, the unit is rated to deliver strong, flat response down to 25 Hz.

With the plug removed and the extension switch on the back panel set to 32 Hz, the unit is equally flat down to 32 Hz, but with a steeper rolloff below that frequency than what we have with the 25-Hz setting and plug installed. The advantage of using both ports and the 32-Hz switch setting is that above about 35 Hz the unit can play a bit louder than it can in the other mode, and with a bit less distortion. In the 25-Hz, single-port mode, it is able to go flatter, louder, and a bit cleaner below about 35 Hz.

As I see it, the 32-Hz mode might be the best option if the user were only going to use the sub for home theater or heavy-metal rock, or pop music with no particularly strong bass content below 35 Hz. With any kind of broad-bandwidth music (particularly pipe organ or seriously heavy classical stuff), the 25-Hz option would be preferable. To be truthful, I have found that a few sonic-blaster DVD movies do have significant low-bass content to below 30 Hz, which means that the 25-Hz option would be a good choice for them, too.

The downward-facing driver used in the VTF-2 is a 10-inch job that does not make use of the stacked magnet assembly found with the massive 12-incher that comes with the TN1220. However, it is a good unit (it has a polycotton spider that has a 10-fold fatigue-resistance factor, compared to standard cotton spiders), and it was specifically built to reach its maximum and clean excursion limit at the point where the on-board amp is just running out of steam. So, by making use of a careful balance between the amp, the enclosure, and the driver, it was possible to design a unit that could deliver exemplary performance, while keeping the cost low.

The on-board amplifier has a nondefeatable auto-on feature. There is a main-power switch, but when it is on the unit is signal-input sensitive and will only turn on if bass-carrying program material is being supplied. When that happens, the sub comes on and the auto feature will keep it turned on for roughly 30-minutes after a signal is removed.

I rather like this touch. On units that have typical 5-10 minute delayed turn offs in their auto/on modes, you could be listening to a symphony with very little bass during the middle sections and the sub would revert to the "standby" mode and then kick back on (probably with a very brief initial delay) during the finale. The Hsu's longer auto-on mode makes this kind of "on-to-standby/back-to-on" behavior unlikely. There is an LED in the rear of the cabinet that glows red when the unit is in the standby mode and switches to green when a signal is input to turn the unit on.

Connections include line-level and speaker-level inputs and outputs, but it should be remembered that both sets of outputs are full-bandwidth, because although the sub has low-pass filtering, it has no high-pass filtering like what he have with the crossover built into the TN1220 amplifier.

Now, normally I would say that this is not a good thing, because one of the advantages of using a powered subwoofer should be that the often quite small satellite speakers in a system are spared having to deal with the low-bass signals. By not including the high-pass section, the VTF-2 does not make use of this advantage, and so the small woofers on some satellites would be put at risk and would generate spurious distortion with high-output, low-frequency signals. The satellite amplifiers might also have to work unnecessarily hard.

However, we should remember that in this day and age most of those who use subwoofers hook them up to the sub-out jack of their processor, processor/amp, or surround-sound receiver. This is the fastest, easiest, and most efficient way to hook up a powered subwoofer, and it also saves having to run cable both to and from the unit. With the sub-out hookup, the processor or receiver does the low- and high-pass filtering work, and so the sub's crossover is not required at all. To allow this kind of hookup to be employed, the VTF-2 has the above-mentioned low-pass circuit bypass switch.

Now, the sub's low-pass filtering feature is not necessarily a wasted one under some operational conditions, and there is nothing stopping the user from engaging the VTF-2's low-pass section to fine-tune performance when the unit is hooked up to the subwoofer output of a processor or receiver. If that processor or receiver has a crossover point of, say, 80 Hz and the room tends to augment the bass between 80 and, say, 60 Hz, you could utilize the Hsu's variable low-pass adjustment to flatten out the bass over those frequencies, while still allowing for strong bass below 60 Hz. This is one of the advantages of the model upgrade I mentioned previously. You could not as effectively do that kind of response flattening with the older version's low-pass-range adjustment option and its 12 dB slope.

As with most other subwoofers, the VTF-2 comes with a 0/180 phase switch to optimize the crossover transition, no matter what kind of hookup option you choose. The line-level input impedance is 10k ohms and the speaker-level inputs are 1k ohms. There is a small, stylish logo on the front panel, just in case you forget what brand of subwoofer you own.

I first tried out the VTF-2 in my main system, in place of my Velodyne F1800RII. In some respects, this room is maybe a bit too large for a small-box subwoofer with a 10-inch driver, but as it turned out the Hsu had no problems with my 3400 cubic foot area at all, as long as I did not require super-deep bass that approached lease-breaking levels. As with the F1800, the hookup involved the sub-out connection of my Yamaha DSP-A1 processor/amp, and so the crossover point was 90 Hz, with a 24 dB low-pass slope and a 12 dB high-pass slope. I initially set the Hsu low-pass filter to the bypass position. I left the port plug in place and used the 25-Hz setting of the contour switch. After initial balancing by means of some test signals and my AudioControl RTA, I sat back and listened to several recordings that would show off the subwoofer.

The first item was Music For the Organ, a selection of works by Franck (Gothic 49125). This music on this disc, played on the Visser-Rowland tracker organ and the University of Texas at Austin, does not exhibit super-deep, super loud pedal notes, and so the Hsu had no problem at all with delivering sound as forthright and clean as what I could get out of my F1800RII. I think that it could do equally well with 95% of the music available today, including most other organ recordings.

The next item was a recording that Hsu supplied with the subwoofer, a perk that all Hsu customers receive. I previously reviewed this release, which involved organist Virgil Fox playing selections from Bach, Franck, Dupre, and a few others (Laserlight 15-313), at the same time I reviewed the TN1220 subwoofer, and I was impressed with how well the VTF-2 could handle the material. (I was also again impressed with the recording itself, originally made in 1977 by Bert Whyte, even though the recorded acoustics were a tad on the dry side.) The very deepest pedals were not quite as authoritatively handled as what I found when I listened with the TN1220, but for the most part the VTF-2 did fine job.

Another disc that I had on hand also involved Fox, but this time it was a contemporary release, Virgil Fox Memorial Concert, that was made during a live, series of performances in his honor (Gothic 49122). Eight different organists pulled out the stops playing a variety of works by Bach, Jongen, and others on the organ at Riverside Church in New York City. This two-disc set also has some very deep pedal notes and again the VTF-2 showed its stuff by doing a fine job. It was not quite a match for my bigger Velodyne or the TN1220, but it was difficult at all times to pinpoint any lack of output below 25 Hz.

My next try involved my old standby: Mendelssohn Organ Works (Argo 414 420), which has a few selections that contain sustained and loud pedal notes to below 20 Hz. In this case, there were clear differences between what the TN1220 could do and what the VTF-2 could deliver, but those differences were fleeting and only showed up on the very lowest pedal tones. With the bulk of the recording, the small sub held its own against the bigger Hsu unit, as well as against the big Velodyne.

With this bit of initial subjective experimenting out of the way, I got busy with my AudioControl SA-3051 RTA and did some response measurements. Because it is often tricky to do near-field measurements of reflex-type systems, I did in-room measurements of the VTF-2 in combination with my IC-20 "satellites," and compared the results to what I also measured with the TN1220 and F1800RII.

I discovered that when using the Yamaha crossover the unit was powerful and strong down to about 31.5 Hz, with a rolloff below that frequency that amounted to -3 dB at 25 Hz, compared to the TN1220 and F1800, which are both flat to well below that frequency. If I pulled the plug from the port and used the 32-Hz setting of the contour switch, the response was close to unchanged above 31.5 Hz, but was a full 8 dB lower at 25 Hz.

I reset things for the lower cutoff frequency and after doing some additional experimenting I discovered that if I engaged the sub's low-pass filter circuit and set it to about 50 Hz, I could then readjust the unit's amplifier volume level somewhat and extend the low bass even lower. This is because boosting the output level at that crossover setting would allow the amp to compensate for the slight rolloff below 31.5 Hz by essentially boosting only the very low frequencies. When I did this, the response was flat to 25 Hz, and the sub not only measured almost identical to the TN1220 and F18100RII, but also sounded essentially the same at reasonably listening levels - even with program sources, such as Bass Mekanik Quad Maximus (Pandisc 8848), that went quite low. Indeed, I re-listened to some of the material I previously mentioned, and this time the differences between the VTF-2 and the bigger subs were borderline inconsequential.

However, I should note that the solid performance between 25 and 31.5 Hz was possible only if I kept the smaller Hsu sub's output levels within reasonable bounds. There is no way the VTF-2 would be able to match those big jobs down really low at very high outputs. I will note that during extended listening at levels that simulated live-performance impact quite nicely, the sub amp's heat sinks got only moderately warm.

Regarding serious output levels, I the next day I did some maximum-output measurements at 31.5 and 20 Hz. With the microphone placed at my regular listening position, about 17 feet from the subwoofer in the left-front corner of the room, the VTF-2 could hit 106 dB at 31.5 Hz and 90 Hz at 20 Hz. I could squeeze another 3 dB out of it by pushing things, but doing that resulted in some audible doubling. That is what I got with 25-Hz extension setting and the plug installed.

With the other option, I obtained 105 dB at 32 Hz and only 80 dB at 20 Hz. Obviously, these measurements were taken at frequencies below the point where the 32-Hz setting is able to offer higher maximum output. I did not bother to measure maximum outputs at higher bass frequencies, because in my opinion, the 25-Hz setting is so superior down really low that the 32-Hz option is a non starter. Serious music lovers simply would not have a need for the 32-Hz setting.

To supply some points of reference, the considerably bigger and more powerful TN1220 could hit 112 and 110 dB at 32 and 20 Hz, respectively, and a sub like the Velodyne FSR-12 (reviewed in issue 67), which is about the same size as the VTF-2, could hit 104 and 97 dB. Another Velodyne sub, the CT-120 (reviewed in issue 85), and which also about the same size as the small Hsu, could hit 100 and 90, and the considerably bigger Velodyne CT-150 (reviewed in issue 79) could hit 108 and 94.

All of these units cost more than the VTF-2, and yet none but Hsu's own TN1220 has significant maximum edge over the smaller Hsu system. In the case of the CT Velodyne models, the VTF-2 was in their league in terms of maximum-output ability, and it was also cleaner sounding than the CT-120 at high outputs, at least with those test tones. The Velodyne FSR-12 was a tad cleaner at 20 Hz than the VTF-2, and was able to play significantly louder at that frequency. It also measured flatter down there, but with a list price over 2.5 times as high I would expect it do deliver somewhat better performance at the extreme bottom.

I listened to a number of other good recordings on the VTF-2 in my main system, but it was not until I installed it in my smaller living-room system that it really showed its practical abilities. First off, when directly comparing the sub to the $600 Velodyne CT-120 (level matched and with quick switching), there was just no contest. (To be fair, the CT-120 has a typically discounted street price of about $500.) With music, the Hsu often exhibited a slightly better ultimate bottom end, and with test tones it just walked off and left the CT-120, both in terms of extension below 30 Hz and also in terms of the cleanness of the reproduction down that low. Those who listen mainly to jazz and pop would probably never be able to consistently spot differences between these subs, but with seriously deep pipe-organ music they would be able to in short order.

When I switched to the servo-controlled Velodyne FSR-12, the tables were turned at frequencies below 25 Hz, but from that point on up the Hsu could hold its own with the $1300 Velodyne, even though with test tones the FSR-12 was a tad cleaner. Musically, they were subjectively identical with anything but the very deepest organ-pedal notes.

The satellites in the living-room system are AR Phantom 8.3 models, and as I noted in their review (in issue 82), they have a bass peak centered at about 80 Hz, augmented at the primary listening position in the living room by a small standing-wave rise. This anomaly bugs me to a considerable degree.

The receiver in use in the living room at the time I was reviewing the VTF-2 was the Outlaw 1050 (reviewed in Issue 86). When I set its adjustable, sub-out crossover point to 100 Hz, the peak from the Phantoms was attenuated to a substantial degree. In order to not have the sub excite the standing-wave resonance, I engaged its low-pass filter and set it at about 60 Hz. The result was uniform overall response down to about 60 Hz, with a modest increase in output dialed in with the sub's level control down to about 25 Hz. We are talking about some really good sub/satellite performance, here.

Out in the living room, I had a chance to listen to the same material as I listened to in the big room and also listened to such bass-potent beauties as Alan Morrison playing the organ at St. Philips Cathedral in Atlanta (Gothic 49083) and Billy Cobham's Power Play (GRP 9536). Over the next few weeks I continued to audition the VTF-2 with a variety of other releases, including the James Taylor Live At the Beacon Theater DVD (done in Dolby Digital 5.1), and I can say right here and now that it is an unbelievably good buy for $500.

Unless you absolutely must have a sub that can deal with the likes of the low pedals on the Mendelssohn Organ Works recording noted previously, I can think of no reason to obtain any other sub for small-to-moderate size room use. However, you do need to remember that for the best results it needs to work with a processor or outboard crossover that includes high-pass filtering for the satellites.