Systems List › HSU Research › VTF-15H
HSU Research's largest most powerful subwoofer in the current lineup the VTF-15H utilizes a 15" driver in a large vented cabinet with an amplifier rated at 350 watts rms and 1400 watts peak. The vent system is a pair of triangular ports in the bottom corners of the cabinet. The VTF-15H is a large system as commercial units go, one of the largest that has been tested by Data-Bass and weighs in at near 100lbs. The amplifier features detachable power cord, RCA type input jacks, high level input jacks, and the controls for the typical phase, gain and low pass frequency. In addition there are controls for 120 or 240 volt operation, auto on/ off, EQ1/EQ2 and a variable "Q" control which varies the amount of damping from 0.3 to 0.7. The VTF-15H offers three modes of operation: 2 Ports open for highest output but the least amount of extension, 1 Port open for deeper extension but a little less overall output and sealed operation which offers the least amount of headroom but also removes the port contribution and its issues with resonance and ringing from the equation. In order to tailor the subwoofer performance for each of the 3 modes the EQ1/EQ2 toggle on the amplifier modifies the EQ and rumble filter setting to protect the driver. The sealed and single port modes can be used with either of the EQ settings safely but the system must be operated in the EQ2 setting when used with 2 ports open. A pair of supplied thick, triangular, gray foam wedges are used to block off or open the ports. The "Q" control has an effect on the amount of low end the VTF-15H has relative to the upper bass frequencies and can help tailor the system to suit the size of the room it is operating in. This adds up to a very flexible subwoofer system which presents the user with a lot of possibilities to tailer the performance to suit the room, application or individual tastes. The purchase price direct from HSU is $879 plus $143 freight shipping to the lower 48 for a grand total of $1022 shipped in the basic satin black finish. A more upscale rosenut veneer is available for a $120 up charge. The warranty terms are 2 years on the electronics and 7 years on everything else.
The VTF-15H is delivered by a freight company in a very large box. The factory packaging appears more than adequate to protect the subwoofer from damage especially considering the shipping method. As previously mentioned the VTF-15H is a big sub as commercial systems go. The finishing and construction quality is good but this is not a sub that is going to rate very well on the WAF scale even in the rosenut veneer as it is too big to hide especially when viewed from the side where it is roughly 26"x27". However this is the price that you have to pay if you want big bass for a reasonable amount of cash. The grille is a CNC cut MDF frame wrapped in black fabric that due to the triangular slot ports has an odd 5 sided shape. Removing the driver reveals that the enclosure is what appears to be 1" thick MDF construction for the most part. Internally the enclosure has a few small panel braces other than the ports themselves but no large cross panel braces. The interior is lined with thick foam material. The 15" driver itself is constructed on a stamped steel frame with a cork front gasket and uses a pressed paper cone with a large black inverted dust cap. The suspension system consists of a very large foam half roll surround and what appears to be a single 6" spider. The single voice coil appears to be 2.5" in diameter and the motor is a simple modestly sized unit that utilizes a single 6" diameter 1" thick magnet slug and a top plate of about 8mm thickness. The back plate is bumped out to clear excursion and has a small pole vent about a half inch in diameter. The motor seems to indicate that this is not what would be considered a high power driver with a lot of xmax but the bumped back plate and oversized surround along with the observed and measured performance indicate that it is a soft bottom motor limited design that likely has the coil leaving the gap entirely before mechanical bottoming can occur. It is not a particularly powerful or visually impressive driver and it is likely very inexpensive to manufacture but it appears to do the job at hand and keep costs down, which is what matters. The amplifier is an efficient Class D topology which had plenty of power on hand for the driver and at times it seemed a bit more than needed. It ran cool and didn't get much more than warm even during ground plane testing in 80deg weather with sine waves. One issue that was encountered was a very loud hum and electrical noise from the VTF-15H. This is ocassionally encountered with subs using unbalanced inputs and ungrounded powr cords, but usually it can be if not eliminated at least beaten down quite a bit. However the VTF-15H seems to have a very high input sensitivity compared to most other powered subs that have crossed the test bench because it was very noisy and loud and even with the gain lowered significantly was clearly audible. Typically the gain on the subwoofers will be run at maximum so as to insure that the maximum output from the subwoofer is recorded and that the input section of the amplifier is not overloaded before the amplifier can produce full power. In the case of the VTF-15H the hum and noise was so bad at maximum gain that eventually it was set at the center detent instead as none of the typical tricks seemed to get rid of it. Even at half gain there was still some residual hum which shows up in the low volume measurements and in the distortion and decay measurements, but this compromise was chosen in order to make sure that the sub could still produce it's maximum output without the input being overloaded.
Listening to the VTF-15H corner loaded in a medium size 3300 cubic foot cement slab room in all 3 modes of operation resulted in a slight preference for the 2 port mode over the 1 port mode. The 2 port mode has less extension but the highest amount of output overall. 1 port open was nearly as good. Sealed mode was the least favorite as it simply gave up too much headroom in the deep bass and allowed the driver to be overloaded at high volume more easily with big bass events in action movies. The VTF-15H offered good headroom in the ported modes with useful extension into the 15-20Hz range and sounded composed and linear with music. With movie playback at generous levels in a fairly large room it offered a good sense of power and depth but the driver will produce some obvious grumbles and overload noise if presented with too much deep bass level. This was also apparent during the outdoor measurements and is worst in the sealed operation mode where the driver could be made to produce obvious distress fairly early. The 2 port mode was most immune to being overloaded in the deep bass. It seems like the driver does not have enough clean excursion to support the displacements demanded of it below 20Hz and a tighter, earlier limiter clamp or a more aggressive high pass filter would probably prevent this a bit better. This is the only real performance gripe with the VTF-15H other than the crazy hot input gain, and perhaps the size aesthetics. There was a little bit of vent noise in 1 port mode with test signals outdoors but it would be harder to distinguish with typical content indoors. 2 ports open mode was more immune to vent noise due to the doubled port area.
The VTF-15H offers a lot of bang for the buck, HSU's customer service and generous amounts of output and dynamic reserve for $1000 with only a few real competitors in the $1000 and under class. If you need a lot of sub to cover a big room or you just like to listen loudly but the budget is limited the VTF-15H should be one of the top considerations in this price class.