HSU Research Subwoofers Review[Specs and Review]

 HSU Research Subwoofer VTF-2 MK5 Review

                                   "PROS AND CONS"


◉ Very good sound quality

◉ Feature rich for the price

◉ High dynamic range for the price

◉ Solid extension down to 18 Hz

◉ Not tremendously heavy or bulky


◉ More internal cabinet bracing would be nice


HSU Research  Subwoofer stf-2

VTF-2 mk5 Introduction:

It’s not easy being a middle childVTF2 facing left.jpg. The older sibling gets all the glory, and the younger sibling gets all the affection, but the middle child has to struggle just to get noticed. The same can be true of product lines from almost any manufacturer.

The entry-level product is the most accessible since it is the most affordable, the top-of-the-line product provokes the most excitement since it is usually the most powerful and/or most feature-packed, but the middle product often just elicits a shrug.

Hsu has recently updated the middle child of their VTF subwoofers, the VTF-2, to its fifth iteration, the mk5. In this review, we will determine whether the VTF-2 mk5 is a standout child or simply a middle rung in the ladder of Hsu’s VTF subwoofers.

The VTF-2 has been a part of Hsu Research’s VTF subwoofer line for 17 years and has developed considerably in that time through a number of iterations.

The ‘VTF’ stands for ‘Variable Tuning Frequency’ and is Hsu’s line of ported subwoofers that use multiple ports that adjust the tuning point to the user’s preference. The first VTF-2 used a down-firing 10” driver and a 150-watt regular Class AB amplifier in a 2.9 cubic foot cabinet. Through every version, it has steadily grown and improved, and the newest VTF-2 sports a front-firing 12” driver, a 350 watt BASH amplifier, and 3.9 cubic foot enclosure.

Happily, one aspect about the VTF-2 which has not substantially increased over the years is the price: the original sold for $499 whereas the mk5 sells for $539, and this is likely due to a combination of Hsu Research’s maturation as a manufacturer and also the lowering of cost of technology manufacturing in that time.

HSU Research  Subwoofer vtf 15h mk-1

Unpacking and Set Up:

The VTF-2 mk5 arrives in a large but not unmanageable box emblazoned with the Hsu logo. Like all Hsu subwoofers that are shipped in the continental USA, there is a demo CD in the packing envelope featuring a handful of orchestral tracks and a variety of test tones.

 The box is sealed with both heavy-duty staples and packing tape, and opening it reveals a thick foam top piece that looks very adequate for the task of protecting the subwoofer during rugged shipping. The VTF-2 is sandwiched by these large foam pieces, and a plastic bag covers the subwoofer to protect it from moisture. 

Altogether the packing is very practical and effective, and it would take particularly brutal shipment to damage this subwoofer.

The owner’s guide, which is also available on the company website product page, is appropriately accessible for novice subwoofer owners and contains good advice for fine-tuning and placement even for more experienced subwoofer owners. It’s more than a perfunctory guide and is a worthwhile read for new owners. 


At 20.5” high and 22” deep, the VTF-2 mk5 is probably not many people’s idea of a small subwoofer. That is not to say it is gigantic but perhaps on the large side. It has a rugged vinyl black finish that is not quite as fine as the satin black on Hsu’s higher end subwoofers, but it does present a clean appearance and would not be as easily scratched.

The VTF-2 mk5 will not dazzle anyone with beauty, but, with its rounded edges, it has a clean simplicity that would be innocuous in a room’s corner. It is a perfect height and shape to serve as an end table for those who want some near-field punch and can accommodate that kind of placement. With grille on, it is simple and smooth black box, but with grille off, a gleaming cone and two sleek ports exudes a readiness to rock. I prefer the VTF-2 mk5 with the grille off!

Design Overview:

It is difficult to pin down the foremost feature of the VTF-2 mk5 since it is an evenly balanced design. To begin discussion of its design, we will start with the feature that most distinguishes it from many competing subs, namely the dual-port variable tuning.

Hsu’s variable tuning subwoofers have been around for years now, and for those not acquainted with the idea, here’s a brief explanation. The function of ports on speakers and subwoofers is to produce sound more efficiently in low frequencies than the drivers are able to.

They do this by using the backward motion of the woofer into the cabinet to resonate the air mass within the port. The port’s length and width affect the frequencies at which the port generates sound; the longer a port is with respect to its width, the deeper frequencies it will produce. However, the wider a port is, the more output it will generate at its resonant frequency.

Placing multiple ports in a speaker or subwoofer will act like one port that has the width of all the ports combined. In systems such as Hsu’s VTF subwoofers, the user can exchange output headroom at higher frequencies for lower frequency output by plugging one of its ports, thereby increasing the length of the ports with respect to their collective width. This enables the subwoofer to play deeper frequencies far more effectively but at the cost of output potential at some frequencies above that point. 

                                  HSU Research  Subwoofer amplifier

The VTF-2 mk5’s variable tuning system allows the user to have either bass extension down to 18 Hz or more output at 25 Hz and above. The exact amount of trade-off of deep bass extension vs. efficiency at higher bass frequencies can be seen in our measurements and analysis page.

The user can also seal both ports, which substantially reduces deep bass output. This can be handy in small rooms that can boost deep bass to excessive levels. Simply plugging or unplugging a port is not all there is to the VTF system.

A control switch on the amplifier plate changes the frequency of a low frequency filter since the driver needs to be protected below the tuning frequency of any ported system. Below the port tuning frequency, there is not enough resistance from internal air pressure on the back of the woofer to stop the driver from flying too freely and easily bottoming out which can potentially damage it.

When both ports are open, the filter switch labeled ‘operating mode’ should always be set to ‘EQ 2’, but any other combination of operating mode settings and port closures will be safe configurations to use

HSU Research  Subwoofer Review

For the VTF-2 mk5, Hsu has upgraded the BASH amplifier to a 350-watt unit, up from the 250-watt amp of the mk4. The BASH (Bridged Amplifier Switching Hybrid) amplifier technology combines the sound quality of AB amplifier topologies with the high efficiency of Class D amplifiers.

Among the features of the VTF-2’s amplifier, a Q control is used to manipulate the slope of the low-end rolloff. Speaker-level inputs allow the subwoofer to be used with systems that do not have an LFE output or a line-level output.

An adjustable low-pass filter ranging from 90 Hz to 30 Hz gives users control over the subwoofer’s bandwidth for setups that lack bass management. A voltage input switch makes the subwoofer useable in countries with different electrical standards.

The cabinet is constructed from ¾” thick MDF all around except for the front baffle, which is a bit thicker. There is a piece of bracing midway in the cabinet that supports the ports. The feet are firm rubber rings that may help damp any mechanical vibrations from the enclosure to the floor.

The grille guides use metal prongs instead of cheap plastic tabs, so the grille should not break easily. The cabinet is generously lined with polyfill that helps damp enclosure resonance. Two 3” flared ports protrude far back into the cabinet.

Overall, the enclosure is a simple and sturdy design. More bracing might be welcome, but the thick paneling should compensate for that to an extent. I never felt any sidewall vibration or detected panel resonance in my time with the VTF-2 mk5.

One note about the port and included port plugs is it can be a nuisance to remove the plugs if they are pushed in too far; make sure there is an edge of the port plug available from which to grab them to pull them out. They do not have to be shoved in very far to create an air-tight seal.

HSU VTF-2 mk5 Driver:

Examining the driver, the first thing that jumps out about it is the beefy magnet in the motor; a stack of two ¾” iron pieces with a 6.25” diameter which form the bulk of the 16 lbs. weight of the driver. The basket is made from stamped steel of a decent thickness with a rib on the spokes for additional rigidity. A butyl foam surround holds a treated paper cone that meets a nomex spider at what appears to be a 2” diameter former.

A bumped-out back plate has a pole vent for thermal management. The VTF-2 mk5 driver uses shorting rings to reduce flux modulation. Altogether, this driver looks to wisely allocate the bulk of the cost to the motor.


◉ 12” driver, ported enclosure

◉ 350w continuous amplifier

◉ 30 Hz- 90 Hz crossover frequency range, by-passable

◉ 24dB/octave crossover slope

◉ 0°/180° phase switch

◉ L/R Unbalanced inputs

◉ L/R Speaker-level inputs

◉ 0.7-0.3 Q control

◉ 430-watt power outlet requirement

◉ 62 lbs.

◉ Enclosure Dimensions: 20.5”H x 15”W x 22”D

◉ Dimensions w/ feet, grille, amp: 21.5”H x 15”W x 24”D

◉ 7 years woofer warranty/ 2 years amplifier warranty

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