SMR logoHsu Research Sub-woofer Review

Do you want thunderous rumbles from a sub-woofer which isn't the size of a house and doesn't cost the same amount of money?  Moreover, is it possible to manufacture such a thing?  John R. Potis Jr., discovers the wonderful world of Hsu Research - and their ability to fulfil both criteria.

Many thanks go to Dr. Poh Ser Hsu for his help and for providing the review sample.

HSU Research TN1225HO Sub-woofer Specifications

Sub-woofer design: Ported Bass Reflex
Dimensions: 12¼ inch diameter by 32inches tall
Weight: 25lbs.
Frequency response +/-2dB: 25 100Hz
Efficiency: 92dB
Impedance: 4 Ohms
Price: $350

Sub-woofer Amp

Dimensions: 10" h x 8" w x 6½" deep (including heat sinks)
Power Rating: 150 watts
Price: $275-($225 with sub)

(All specifications as per manufacturer)

The HSU Research TN1225HO Sub-woofer


Initial Impressions

HSU Research TN1225HO     My first observation as I lifted the HSU Research TN1225HO from its box was with regard to how delightfully light it was.  I own speaker stands that tilt the scales more.  Given the amount of schlepping equipment up and down the stairs I do, it was not an unwelcome one!  While at twenty five pounds it definitely belongs in the feather-weight class, let me warn you now, lest you fail to take it seriously, it packs the wallop of a heavy weight.

     The second thing I noticed was the bare bones essentials of its design.  Getting to the heart of the matter, the HSU will not win any awards for aesthetics.  Its a 12 inch driver capping one end of a large tube without even the amenity of a grill.  At the other end of the tube is the end cap with a single set of knurled 5-way bindings posts, a large tuned port right in the center and three screw-in aluminum legs.  Covering the tube is a black knit sock.   Next unpacked was the 150 watt amp that came in a separate box.  I recognized it (it doesnt take a rocket scientist!) as the typical type of amp module one sees built into the rear of a typical powered sub-woofer.  As the HSU is round, it cant accommodate the amp, so Dr. Poh Ser Hsu did the logical thing and placed the amp in separate enclosure.  This box is a granite finished housing with four rubber feet on the bottom and the HSU gold colored plaque on the rear (or is it the front?).

Nothing but the essentials

     If you think I was rather blasé about the cosmetics so far, I can understand why you may think that, but you are mistaken.   On one hand, I wasnt looking at the hardwood opulence one finds on more expensive products, but on the other, I was looking at a very inexpensive sub-woofer.  The mere fact that HSU Research sub-woofers have built an enviable reputation for putting out sub-woofers that can really "put out" kept me from looking down my nose at it.  I was actually impressed at the ingenuity that went into this piece and its utter simplicity.  All bells and whistles were spared in order to bring to market a truly budget priced sub-woofer that doesnt have to apologize to anyone for its performance.  And believe me, it holds its own with any but the biggest boys on the block!

     The HSU TN1225HO has a 12 inch driver (the first 12 in the model number is my assumption) with a bass extension of 25Hz (the second number).  Ill guess that the HO stands for "High Output" (that guess was easy, Ive heard this thing!).   The sub-woofer, which is sold sans amp for $350, has an efficiency rating of 92db.   The enclosure seems to be an industrial sized cellulose tube, akin to that used by building contractors for pouring concrete beds used for the anchoring of pillars and poles.  HSU says that the tube is even made from recycles materials.   As the speaker enclosure is tubular, it has the distinction of being inherently structurally strong.  As the enclosure is round, it has the benefit of no flexing of the side-walls due to the fact that its tubular design means that any point on the side walls is already as expanded from the center of the enclosure as it can be.   The lack of corners and parallel surfaces also minimizes internal standing waves.   One gets all the performance of conventional enclosures without the need for heavy internal bracing, without the added cost of wood finishing and with the incidental savings in the shipping charges of the lighter unit.  Are you starting to be as impressed as I was?

Hsu Sub-woofer AmplifierUnfortunately&

     I was a little less impressed with the amp that sold for the extremely low price of $275 ($225 if purchased with the woofer).  My biggest gripe is with the fact that this amp is a large-ish box that wont fit between my non-adjustable shelves.  At 10" high, its a little awkward.  I suppose it could be placed on its side, which would make it a touch under 8 ½" tall, but you still have to allow for the speaker cable which will, in this case, attach at the top of the amp.  This may not be altogether an unreasonable dimension, but its still too tall for my racks.  It could be placed over by the speakers/sub though - more on this in a moment.  Hmmm, I guess you could even place it on its face, which would allow it to fit between shelves with a 6½" spacing.  OK, I guess its not too bad, although my rack still wont accommodate that on any but the top shelf.

     My other caveat with the system is my last.  System connections are rather sparse.  There is a single RCA input, which is excellent and all you need if you are using the TN1225HO for the LFE output on a Dolby Digital" surround processor.  But if you are using it for two-channel music, things are a little more difficult.  It is not overwhelming, just a little awkward.  There is an XLR input on the rear.  What you do, (and its really not difficult - if I can do it, anybody can) is connect an XLR plug to a pair of speaker cables and then the other end of the speaker cable to your speaker outputs.  As there isnt much current flow through the wire, economical zip cord or the like is all you need.  You solder one channels "positive" wire to pin "one", the other channels "positive" to pin "two" and you sum the two ground wires and solder them to pin "three".  JUST MAKE SURE YOU ARE USING A COMMON GROUND AMP, which most happen to be!  As I hinted before, the amp can be located in a remote location in this manor.  As you are making your own interconnect, you can make it any length you desire, and it doesnt cost very much at all.  Or, if you dont feel comfortable with a soldering iron, HSU Research will be glad to make one of these up for you.  Connection between the amp and sub is via a single length of speaker wire of your choosing.  Both the amp and the sub-woofer are fitted with a nice pair of knurled gold plated binding posts.  You can use pins, bare wire, bananas or spade lugs.

     Unfortunately, for those who are looking to high pass their speakers (filter out the bass), this system does not include high pass filters.

Hsu Sub-woofer AmplifierOK, now the good news!

     First, once tucked away into a corner of the room, I think its a great looking sub.  With a diameter of only 12¼", it can even be placed on its side and tucked behind the sofa!

     Second, if the lack of a grill bothers you, in the 1225s documentation, you will find a Radio Shack part number for an appropriate grill and you can go pick one up for cheap!

     Third, the amp, as unconventional is it may seem, works splendidly.  It ran only moderately warm during use and exhibited no idiosyncrasies what-so-ever.  Shortcomings regarding connections not withstanding, the amp does have a full compliment of controls-volume, adjustable low pass and a continuously adjustable phase adjustment.  This degree of adjustment and a 150 watt mono amp for $225 (when bought with the sub) just has to be looked at as an absolute steal.  Oh, and as for the fact that it may be hard to sit on a shelf?   It has a current sensing circuit which senses when a signal is present and it turns itself on and off which means that you can tuck it somewhere out of the way, if you like.

     And last, but not least, this is an excellent sounding sub.  Notice I didnt say excellent sounding "budget sub".  The fact is that it came embarrassingly close to the output of my 15inch 400 watt servo controlled Velodyne ULD 15.  It didnt quite make it, but it came subjectively close.  Not bad performance for a system costing $575 when you consider the thrice priced Velodyne.


Curtis, Schwarzenegger - 'True Lies'     The HSU Research TN1225HO came with a suggestion list of, let me say, "bass potent material".  On the suggested video list was "True Lies".  It directed me to the beginning of the third side.  When the movie cued up I found myself immersed in helicopter noise!   MAJOR HELICOPTER NOISE!!  Bass was loud, powerful and completely satisfying.   From there it was a short trip to exploding bombs and jet fighters and gunfire and&and& and I was having a ball!  Once the side was over, I did a little comparison with the Velodyne and a smaller, less expensive sub I had on hand.   DONT TRY THIS AT HOME!  As I didnt use earplugs, I was almost deaf by the afternoons end!  I could have gotten out the SPL meter, but as I had no way to account for distortion, I had to suffer (did I say suffer?) through the movie scenes with each sub-woofer.  I turned them up to just before the point where they were adding extraneous character to the sound.  In other words, where distortions caused the subs to take on a sound of their own, over and above the rumble.  At this point, I was actually judging SPLs by the pressure I was feeling in my ears.  Believe me, I dont recommend this technique, but I really wanted to get a feel for how loud this baby could get.  Believe too that I only did it for a short period of time and as far as I can tell, my ears have recovered!

     Well, the HSU clearly smoked its less expensive opposition.  It wasnt close.  It went deeper and much louder.  It was much closer to the Velodyne in terms of quality, output, power and authority.  It didnt quite shake the foundation like the Velodyne, which does go several Hz lower, but it sounded very impressive all the same - particularly in light of its flyweight price tag.  I kid you not, by the time I finished this, my ears were numb.  Numbness not withstanding, I had to go back and watch the movie from the beginning albeit at more subdued volume levels!

     On Jurassic Park, again the Velodyne outperformed the TN1225HO when it came to the deep, off in the distance rumble of the T-Rex.  It just didnt go quite deep enough to keep pace.  But as the foot stomps grew closer (and higher in frequency), the HSU grew louder and more intense.   Once the bass gets out of the truly infrasonic range, this thing is incredible and never suffered in comparison when used at down-to-earth (read normal) listening levels.

Attenborough, Dern, Neill - 'Jurassic Park'     Now, run of the mill soundtracks dont posses this kind of bass.  Most soundtracks dont have much bass below 30Hz or so, hence on most of the other movies I watched, the TN1225HO did all I could ask in my medium sized viewing room.  Dr Hsu makes a point of making clear that the reason the TN1225HO was tuned for a bottom of only 25Hz was so that he could optimize output above that point.  In other words, he could have tuned it lower, but in doing so would have compromised ultimate output in terms of dBs.  I have to agree that, for video, ultimate extension was a good trade off for ultimate output.   In any case, I never had to look back for the Velodyne.  Im sorry if I sound like a broken record, but this was in impressive achievement in light of the bargain basement price of the HSU.

Cue up the music!

     Yeah, I know that this is called SMR Home Theatre, but the fact is that man does not live on movies alone!  I dont anyway.  So I hoisted the whole system upstairs into my music room upstairs and put it in line with a pair of ACI Sapphire IIIs [reviewed here].  It was in this system that I found that the TN1225HO minds its manners on music too.  I found it to be a very ingratiating sub-woofer and I was able to achieve a very nice blend with the main speakers.  No need to go into the specific recordings I ran through the system, there have been far too many!  But suffice it to say that I was never disappointed by what I heard.  No, thats not fair to the TN1225HO, lets make that suffice it to say I was delighted by what I heard.


     The HSU Research TN1225HO subwoofer is a "filet mignon" performer at a "hamburger" price.  For the money, you get a ludicrous measure of bass and even more value.   If you want more than a taste of what the largest subwoofers can do but need to do it on a budget, you need not look further than the HSU. For even better performance you can step up to HSUs larger TN1220HO which has useable bass down to 16Hz and costs only $100 more!

     On the other hand, if you are watching your pennies, this is a superior piece of work and I cant imagine anyone being disappointed with the performance of the HSU Research TN1225HO.  It may feel like a featherweight, but after experiencing its punch, you will be TKOed- thoroughly knocked out!


Good luck and listening,

© 1998.


More information about Hsu Research sub-woofers can be found at the Official Hsu Research Web Site.

Text © John R. Potis Jr.; HTML © SMR Home Theatre and Images © SMR Home Theatre cannot be reproduced without permission. "Dolby Digital" is a trademark of Dolby Laboratories Licensing Corporation.

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Last updated 19 June, 1998

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