HSU VTF-15H Listening Impressions

I was really surprised to get as much output from the Hsu as I did. While it could definitely play loud enough to satisfy my need for high SPL's in even my very large laboratory, it did not posses the high damping at the lowest frequencies I prefer.  I have become used to hearing from more expensive and heavier subs made for high outputs typically used in the professional industry. (Yes, I am spoiled rotten). These subs often have overdamped responses at low volumes to compensate for the considerable heating effects from hours of constant use by the typical DJ trying to blow his audience away.  I was not expecting too much from the BASH amplifier, but despite that, I found it performed well, and more importantly I found Hsu's approach to his system design with limited power preferable to a “GO DOWN TO 20 Hz at all costs” approach, and to hell with the sensitivity.  The VTF-15H was clearly a well compromised effort based on maximum performance for the dollar.  While the output was sufficient, I would not describe the bass as tight or well controlled. (With a different tuning option, i.e., use of the supplied foam plugs, that opinion might well change). Frankly it had the sound of a speaker, that was compromised in terms of not having enough motor force (BL) (read magnet, metal and voice coil) to adequately damp the cone motions without a hint of ringing.  Bear in mind also, that this effect increases beyond the steady state measurement whenever the system is driven to or near its output limits.  I would like to have had a bigger motor on the woofer for greater control than what I had.  This correlates well in my mind with the CLIO curve which shows the slightly rising low end with both ports open.  When I rotated the control down to the 0.3 position (lowest Q and highest damping), I frankly noticed no improvement in the sound.  It might well be both audible and measurable, but I didn't hear it using music as a source.

Application

Because of the relatively small amount of amplifier output, I believe it would be best applied with music or home theater, limited, as it was during the test to having both ports open.  Performance down to 20 Hz, even for a large system, is going to require a bit more horsepower than this amp is capable of.  It is of little use to have a speaker which goes down to 20 Hz, and then find at maximum amplification, the SPL produced makes just enough 20 Hz to break the barrier of audibility.  What of dynamic range at 20 Hz?  How do we pick it out from the inevitable harmonics that are going to accompany it in music?  In the “professional” end of the market, it is not at all uncommon to see bands and PA's using big 18” speakers which get cut off at 50 or even 60 Hz, for the simple reason, they simply want the most loudness physically possible.  In music (as opposed to Home Theater sound, specifically movie soundtracks) with few exceptions, most “bass” is between 50 and 100 Hz.  This combination of driver size, (15”), amplifier power (350 “continuous” watts) and box size seems to want to naturally roll-off slightly below 30 Hz, and none of the music I played seemed thin or wanting bass because of it.  This box (in my opinion) is best for music, and while it will work for home theater, if you absolutely have to get that 20 Hz tone in your living room, be prepared to spend more $$ and get a system with a bigger amplifier, or do as Dr Hsu recommends and place the box in the room corner if at all possible.  Perhaps HSU will consider offering a hot rod version of this product (bigger amp, bigger driver motor) at a slight cost adder to those bass heads really wanting uncompromised true 20Hz extension. 

Dr. Poh Hsu and his company have written an excellent manual for how to position a subwoofer in a room, and in it makes a suggestion which makes a great deal of sense for a single sub system, and is applicable to ALL subwoofers made for home use.  PUT IT RIGHT NEXT TO YOUR LISTENING CHAIR.  This approach should minimize the room, maximize the direct to the reflected sound, and since the bottom end of the sub usually has the greatest group delay (time shift as delay) putting a single sub next to the listener makes a great deal of sense as an approach for maximum output where a corner is not available. 

If you want to check out the online user manual, it is available here:    http://www.hsuresearch.com/products/VTF-15HSubmanual.pdf

In addition to the full blown user manual, Hsu Research offers a very smartly written quick start guide, so that anyone in a big hurry to start using his new sub is not going to have to read hundreds of pages of manual just to figure out what each control does.  That guide can be found at the same link (above) as the manual, and is located in the box titled "Brochure" along with the full manual.

Overall Product Impression

Visual

The Hsu sub as submitted had a smooth black finish, neither attracting attention nor warranting special notice.  There were no issues to be seen with the cabinet finish, and I found the dual V shaped ports at the bottom of the cabinet both sound from an engineering standpoint, as well as visually appealing.  If you have the room for it, there is not too much chance it is going to clash with any of your furniture or draw much attention to itself.   What I liked most was that it's styling of the ports and grilles was both unique and attractive.  During his visit to my laboratory, I was informed by Dr Hsu, that the "Rosewood" would be available at a $999 price point.  For some reason, the $999 model is called "Rosenut" on the website. (It looks like Rosewood!)  Likely for the same reason that Champagne is called sparkling wine when the grapes are grown in California instead of the Champagne region of France, but I should leave that explanation to Dr. Hsu. 

Points in Favor of the Hsu VTF-15H Subwoofer

Strong engineering, excellent integration of the sub with the power amp and cabinet, and a surprising amount of output from the system given the relatively low output capacity of the amplifier used.  We have to remember under IDEAL conditions the fact that a 1db increase after 250 watts is 70 watts, after 320 watts Is 80 watts, after 400 watts is 100 watts, and as we try to put more and more wattage through the VC, the heating of the copper causes the speaker to grow less and less efficient.  While high power is necessary and desirable for short bursts (especially for subwoofers) in the long term it is simply heating up the voice coil and lessening the lifetime of your product.  Considering the relatively low cost of the product, one could opt for purchasing two VTF-15H's if more output is desired.  We are champions of multiple subwoofers for better and smoother bass distribution across the entire listening area.  Just make sure your spouse can handle two of these behemoths sitting in your living room.

Criticism of the Hsu VTF-15H Subwoofer

As I mentioned before, the bass did not have the tightness and control of the more expensive, higher powered and lower tuned models tested.  The conclusion I kept coming to was for the higher tuning, the system would have benefited from use of a lower Qts (read bigger magnet or higher BL).  I did not find the “q” control knob on this amp to be particularly useful, or at least offer me enough in the way of response modification over its range of motion that it justified its existence.  For SURE, I would have preferred to have a wider range of control over the included crossover so I could have run the sub up to a higher crossover frequency.  If the Clio curves showed anything, it is that this sub is very well suited to be used with smaller satellites at a higher than normal crossover frequency.  Again, that would work better with more power, but at this price point, I am nitpicking.