It takes more than a couple of watts to flush out the potential within these speakers. A strong high quality P-P design such as the TORIIMK2 is the perfect complement for driving these speakers. It takes an amplification factor of this magnitude for which to bring the full potential of the bottom end to life with a presence of unparalleled quality.

The small S.E.T. amps will not supply enough sustained usable energy to  drive these speakers within these lower limits with the kind of finesse and aggressive stance that higher amplification factors will provide. The S.E.T. Amps will produce the bass notes clearly, but with very limited involvement for which makes it very difficult for the listener to become engaged.

It absolutely takes an adequate amount of power to produce the true level of response from these speakers in the lower registers. These speakers love clean power, responding quite favorably to a healthy dose of it. Otherwise, these speakers will appear to be bass shy which is far from the truth.


There is a transition at around 1/4 to 1/3 of the TORIIMK2 power curve that dials in the ideal condition for which the magic of the speakers is revealed. Below this point, the low-end just does not show it’s true splendor in form. Once the ideal power curve is matched, the physical presence becomes quite intriguing to say the least! It only gets better with additional clean power. Once you have heard these speakers powered by this amp in a room with ideal acoustical factors, you will be stunned by what really lies within the potential of these speakers.

By the time that you utilize half to three-quarter of the TORIIMK2’s power, you will be fooled into thinking that there are much more powerful amplifiers in use along with supplemental subwoofer augmentation to produce such incredible low-end response.

The bottom end  response is similar to that of the WO32 (audiophile version), but  with much cleaner transients  producing detail that would be very difficult for an external subwoofer to reproduce on this level.

Outside of the WO32 with clean amplification factors (yes I have built one with a great deal of  listening experience), it would take something along the lines of Steve’s Imperial  Sub cabinets to produce the QUALITY of  bass which is presented by  my modified HDT versions. Quality is the key factor here! Not merely SPL alone, but the correct blend of attributes which constitute accuracy and articulation with absolute presence and physical connection.

I will state that low frequency detail articulation is a major strongpoint of this design as done the way  shown here. I am so satisfied with the degree of clarity and the intensity of the punch felt from the lower notes, that I strongly recommend keeping this specification exactly as shown.

I do however like your modification with the adjustable tensioning rods as done with the plates on the MKII version. Other than that, I would not change anything else that I did.

The only way for you to know the difference within these modifications is by direct comparison. If you change anything on these speakers other than what I did, the speakers will not be within the same  sound characteristics.

You may obtain just as good of results and possibly even better results with alternative measures. I can only suggest that you duplicate the build exactly as I had done if you want to be sure of  hearing the performance that I get out of mine. It would really be interesting to have a side by side comparison between my modified version and that of what you come up with.


I have a couple  sets of high-end T-Line speaker designs which produce incredible depth and definition throughout the lower registers, these of  which I feel are some of the cleanest sounding designs ever experienced.  The depth of detail, the speed of  transient response, and the resulting pace and rhythm produced from these modified HDT’s as shown , easily sets a new standard which clearly surpasses the leading T-line designs.

It really comes down to total and absolute satisfaction for which you can finally listen with complete confidence in these designs and know without reservation that there is not one single fault to be formulated from their presentation. The seamless transition and purity of the musical form is just so natural and unrestrained throughout the full spectrum, that you are quickly reminded just how bad other speaker designs can be, and usually are by comparison.

When you hear something this good, it heightens your awareness to the flaws and shortcomings of inferior speaker designs which may have seemed very good prior to this enlightenment. They have definitely raised my standard by a very large degree.

All that I can surmise from this concept is that in general overview, I seem to be showing some very rare performance potential that many others are reporting as non-existent or lackluster at best.

When I  examined the speaker arrangement, acoustic conditions, and general equipment used with many of those speaker evaluations, it became very clear as to why the majority of these negative conditions prevailed.

Unfortunately, it seems to be easier for the typical person to point blame upon the speaker rather than the actual problem which renders the speakers performance substandard in their specific application. I really find it to be laughable when  critical factors such as these are neglected from an individual who insists that something is bad  with a speaker or component in general, when  the true cause is clearly revealed elsewhere (usually in set-up/acoustical factors),  but somehow evades  sensibility from that individual.


Arguing with someone in this state of mind is like trying to teach  Quantum-Physics to a  monkey after years of prolonged  exposure to mind altering chemicals. The difference has to be experienced  by them before the light comes on with any substantial reinforcement as to it‘s credibility.

Chances are that this individual will never resolve the actual problem, but  instead choose to find some other addition in order to pacify the existing degree of  unfavorable factors within the listening environment, since they obviously do not truly understand the underlying condition of the problem within itself. This occurs quite often as I’ve seen many examples to suggest this with what I’ve observed in the past.

Putting a band-aid over a cancerous growth will not stop the spread of the deadly cell mutation.

I have a good bit of experience with the NFX models using the very same drivers that are in the modified HDT models.

Considering that all influenced factors between these model evaluations have been regulated within identical parameters, I can fairly surmise a reasonably correct  affirmation of their differences.

For myself to grade the merits of a speaker design, the speaker needs to be considered from all aspects which constitute the desirable traits associated with musical transformation inherent of naturalistic form.

The speaker must  present a completely coherent and natural degree of  embodiment which flows seamlessly across the entire spectrum without a hint of departure. I expect to hear sound with realistic dimensional cues as I would in real time within my natural environment.

In order for this level of coherency to unravel  within these perceived coordinates, it is only fair to insure that the rooms acoustical value is of prime setting. No speaker in the world is going to reveal it’s true worth if not presented  in an ideal environment for which it becomes possible to disclose that worth to the maximum degree.

I have found  generally as the rule,  a design based upon a single full-range driver placed within a well designed T-line  structure or that of a folded horn  technique with the proper degree of coupling, free from any form of crossover network, is the basis for ideal and optimal results.

I am so sure of this, that this is the only direction for which I will focus my future design concepts.

The magic lies within the cabinet design itself for which the driver simply becomes the focal point for that magic to work it‘s wonder. The surrounding room elements are responsible for the complete transformation in which the speaker  is portrayed within those elements. To have the ultimate sounding speaker is an impossibility without the reinforced structure for which to present  the very basis for ultimate sound reproduction.

I evaluated the NFX designs within two different  acoustical situations with rooms of different sizes. What I concluded  for which I had anticipated, was that these provide much better results within a larger room for which plenty of space is allowed around and between the speakers. When this is done along with adequate acoustical control measures, the  NFX  concept becomes one of the most openly sounding, transparently coherent speakers that one could experience above 50 Hz.

It is my experience that the set of HDT’s that I built are even better, with a more articulated in- depth presentation of the midrange.

From 50 Hz on up, the NFX speakers generally comply with my expectations to where they are quite respectable in the manner for which they interact  with the surrounding elements. Dimensional placement with widespread spatial properties is the strongpoint for which these designs excel in form.

A positive trait of equal magnitude must be attributed to the coherency factor for which the mid range and higher frequency qualities are of  exceptional clarity when the DFR-8 driver is employed within this design. This is another example of a single full range driver concept, free from any crossover network introduced within it’s path. The main factors  which influence this speakers sound quality outside of the driver itself, is contributed almost exclusively by the surrounding elements and the speaker structure itself.

Matt,

Thanks. I too wish I had pursued this design concept many years ago. If I had known then what I know now (hindsight is truly 20/20), things would have been much different in pursuit of my design goals. I actually started the HDT project over three years ago with the intention of building the MK2’s. I became sidetracked with much more important issues which put this project away for some time. The funny thing is that I’ve had all the parts necessary to build two complete sets of HDT’s for quite some time. When Bob Z. moved away from Phoenix back to the east coast, he basically donated enough spare  pre-cut parts from MDF to assemble the set shown here. I took a lot of stuff off his hands to help him make his transition, with these parts being an added bonus. Bob also set me up with the passives which I am grateful for. I already had the drivers which were installed in the NFX designs. Finally, not like I needed to have another set of speakers taking up space, curiosity got the best of me for which I pulled the parts out of storage and the rest is history.

Turned out to be the best speakers which ever graced my audio system! These were the speakers which held the key to providing me with what I desired in a speaker’s presentation all along.

Imagine having the answer to your needs in front of you all this time, and never letting it reveal itself. This is what happens when things are allowed to be put off.

I find it interesting that Steve’s original speaker design has proven to be the ultimate single driver ‘stand-alone’ concept for which still stands  as the elite design that others strive to  match. Perhaps the only contender to  exceed it’s potential (let alone even matching) being that of the Imperials when overall performance parameters are considered in the complete scheme of  musical presentation.

When one balances the weight and size factors which separate these two radically different designs, both of which provide reference quality sound character to the ultimate degree, the modified HDT would still be at the top of the list when the elements of weight, size, cost, and efficiency are brought into play where ‘performance-to-size’ ratio‘s are the determining factors by scale.

With that being said, by proportional measures, I would be hard pressed to believe that any speaker with the volume displacement of the HDT structure could even come close to the complete  presentation which these so effortlessly convey with  absolute authority. That presentation hinges upon a seamless, and utterly transparent  focus which spans ideally from 20 Hz to 20 kHz in a stand-alone configuration with an ideally flat frequency  correlation across the entire spectrum.

It would be very difficult for any speaker to surpass what this model does in this regard, let alone the aspects of  efficiency, speed, definition, timbre, and the overall culmination for which  three dimensional presence prevails in such a dominating manner.

The Imperials will of course dominate by shear size in a larger room which would warrant such a design to couple with the surrounding elements more effectively. In a typical room of moderate proportions however, the Imperials would be too large and counter productive just as the HDT’s would not be able to provide the same level of influence in a large space to compete with the  much larger Imperials for which they are a better match to scale.

It is on my list of future things to build for which a set of Imperials (or at least the sub-only versions) will be added  to my  dedicated custom audio room. There needs to be more updated information on the forum board concerning appropriate driver matching for these cabinets before I make the commitment to pursue that build.

At this time, that would be the only build which fosters any real excitement within me for which I feel would go beyond the HDT experience. There are many folded horn concepts which capture my attention with great potential by design, although I am not convinced that any of them can outperform or even come within range of  the rated performance standard for which the current modified DFR-8 HDT holds with such  firm  integrity. I will of course push the limits of any design with a fair objective toward testing parameters. In the end, accuracy will be displayed through the test results as well as controlled listening evaluations to confirm the conclusion.

Resonance is the key to success with which you must fine tune to extract the optimal tonal balance. If the structure is rendered too dead with an excess of solid mass, the outcome will be perceived as so. You may have to try different techniques before you zone in on that special integration of material which meets the ultimate objective. It is a given that a solid MDF structure will have far different tonal qualities than that  constructed from plywood. The structural integrity will be far greater with Russian grade Baltic Birch composite(13 thin layers) than that of  inferior 5-ply material in common plywood. The resulting sound would reflect this to a large degree. Stiffness, density, and mass play the major elements for proper cabinet design.

Plywood will produce a livelier sound than that of MDF. Whether or not this is to your advantage hinges upon the technique which it is employed within the construction phase. This can make all the difference as to how the midrange qualities are perceived as the tonal balance will be directly influenced by the composition. If you were to build the same speaker design with the only variance being that one is MDF versus the other made from Baltic Birch, it is assured that these two speakers will sound nothing alike. It may take a combination of MDF in key areas of isolation in conjunction with layered wood composite in other areas to find the appropriate balance.

I have read reports of these comparisons where the builder proved the MDF to be sonically inert by comparison, while the Birch plywood provided just the right degree of tonal balance throughout the musical spectrum. I tend to believe that the much superior Baltic Birch would have a sonic advantage over the MDF in most cases. Baltic Birch will always be a better choice over standard plywood or particle board due to it’s multi-layer composition providing increased structural density. The only way to confirm this theory is by actual performance testing under strict guidelines. In the end, your ears will disclose the absolute truth. I would place my money on the composite material constructed with the highest degree of  isolation and density.

It is known that high grade Sitka Spruce provides some of the most  ideal material for musical instruments  due to it’s superior sound qualities. This material is hard to acquire and very expensive. Finely crafted musical instruments utilizing this material for the body will undoubtedly sound very special with a price tag reflecting it’s degree of quality.

Could you imagine the construction of your speaker cabinets with an outer composite wall made from Baltic Birch with the inner surface constructed from the Sitka Spruce? I would imagine that this would have a very unique tonal quality to it that would be near to ideal. Still live enough to produce good harmonics while providing enough mass to keep things under control with the proper degree of tuning.

If Sitka Spruce is favored  for  use in quality musical instruments for it’s tonal balance, then it stands to reason what it could do for the sound of speaker cabinets. I for one would like to try this as I am sure that there is something to it’s credibility. It would be very costly to take this approach but the end result could be vastly superior.

I do know that the last thing that one wants is to render the cabinet so dead that it becomes completely inert. Too much mass can have a negative effect, while insufficient mass will be just as detrimental. You have to find the right balance between the two for which to find the right sound quality. Trial and error usually comes into play for which to determine this. This is one of the major aspects which separates exotic high-end speakers from the ordinary for which these are clearly superior by a vast degree.