NHT Absolute Tower Loudspeaker Review

Looking at measurements alone, NHT engineers nailed the design of the $1100 per pair Absolute Tower loudspeaker.  This is among the best measuring loudspeakers I’ve come across in almost every measurement.  In the case of the NHT Absolute Tower, the measurements translate to a very good sounding speaker at a very reasonable price.  Interestingly, NHT chose the word “Absolute” when naming this speaker.  Absolute is defined as something that is not qualified or diminished in any way.  In the context of a reasonably priced small footprint tower crossed to a subwoofer in a typical living room, I would say the use of the word “Absolute” is justified. 

If you have been around audio for any time at all, there is a good chance that you are at least casually familiar with the NHT brand.  The company launched its first product in 1987 and has since built a strong reputation of offering high quality products at bargain prices.  NHT seems to prefer designing a really good loudspeaker every once in a while as opposed to pumping out speaker after speaker in an ever-changing market.  Staying relevant, this design has definitely adapted to the times with a very small footprint and cabinet for a 3-way tower loudspeaker.  Getting deep bass out of a small tower means the designer has to compromise something else such as efficiency and power handling.  NHT has designed a loudspeaker that trades deep bass for articulation, linear response and low distortion across the board.  The measurements are good because this speaker was designed to do everything that a subwoofer doesn’t do.

NHT Absolute Tower Speaker Video Review

NHT Absolute Tower Design Overview

NHT Absolute Tower Cabinet

As is the case with much of NHT’s lineup, the build quality is truly first rate.  The cabinet is made of MDF and has substantial bracing.  Due to the small enclosure size, bracing and thick MDF, the cabinet should not contribute much extraneous sound due to resonance.  This MDF is methodically finished with several layers of primer, paint and clear coat yielding a reasonably durable and beautiful piano black finish.

The top of the cabinet is slightly curved adding to the aesthetics.  The left and right sections of the baffle around the tweeter are substantially chamfered.  NHT claims this is done to randomize diffraction effects.  While this will divert reflected tweeter energy off-axis, it doesn’t look so random in the polar response as this energy is not destroyed and causes off-axis response anomalies discussed in the measurement section.

The speaker is a 3-way acoustic-suspension system with a separate internal enclosure volume for the woofers.  Separating the midrange from the woofers is essential as it prevents the woofer’s backwave from re-radiating through the midrange cone.  A separate enclosure also allows the designer to optimize the enclosure volume of the midrange.  Without this, I would suspect that the measurements would not have been nearly as good.

The cabinet base is solid and attaches with hearty machined Phillips head screws. Since the cabinets are relatively short at 37.9” and are not very top heavy, they feel relatively stable on carpet or hard surfaces.  They are not toddler proof, but should work well in the majority of homes.  The NHT Absolute Tower ships with floor spikes for carpet and cups to place the spikes in for hard floors.

NHT Absolute Tower Crossover

The loudspeaker crossover component count and quality is on par with what is found in this price classification.  There is a mixture of iron core and air core inductors.  The majority of the capacitors are electrolytic but there is a single polypropylene capacitor likely placed in series with the tweeter.  The component count is relatively low because the crossover is listed as 3rd order low pass and 2nd order high pass.  A shallow slope 2nd order crossover at 2.2kHz to a 1” aluminum dome tweeter is not something that typically works well unless the volume is kept low or the tweeter is beefy and fluid-cooled.

 

Absolute Tower Crossover

A 2nd order crossover reduces phase error, but as all things in engineering, there are tradeoffs.  Specifically, a 2nd order crossover has a shallower roll-off of low frequencies for a tweeter than higher order crossovers.  This means that a 2nd order crossover at the same crossover frequency as a higher order crossover will subject a tweeter to more output at frequencies below the crossover frequency.  If the crossover point is too low then this can significantly reduce power handling and increase distortion.  Every inductor and resistor in the crossover adds 90 degrees of delay to the signal heading for the speaker.  This means that for a signal going through two crossover components, the signal is 180 degrees out of phase compared to the original signal.  If the sound from two drivers radiates from the same plane and one goes through two crossover components and the other is directly connected then one driver will go in and the other will go out when the signal starts.  This will of course cause cancellations.  Luckily with a simple second order crossover, the driver polarity can be reversed and the phase response is corrected.  In the case of a crossover between a midrange and a tweeter, the acoustic center of the driver is not in the same range because the midrange radiates from the center of the cone which is typically an inch or more deeper than the acoustic center of the tweeter.  In an effort to create a linear phase speaker, the designer can either physically align the acoustic center of the drivers or use a ladder delay network to align the phase difference electrically.

In the case of the Absolute Tower, the crossover between the midrange and tweeter is 2nd order electrically, but close to 4th order acoustically.  The difference is due to the fact that NHT specifically engineered the drivers to reduce output below the crossover frequency for the tweeter and above the crossover frequency for the midrange.  The woofer to midrange crossover is 3rd order electrically but also close to 4th order acoustically.  The 4th order acoustic crossover allows the NHT absolute towers to play at high power and still maintain relatively low distortion.

NHT Absolute Tower Speaker Drivers

This three way acoustic-suspension design uses two 5.25” woofers in a separate air volume, a 5.25” midrange and a 1” fluid-cooled aluminum dome tweeter.  All drivers are magnetically shielded with good-sized motors, materials and workmanship.  Since CRT TV’s and VHS tapes are not popular anymore, I’m not sure if the shielding provides much of a real world benefit.

The tweeter uses a neodymium magnet and appears to be well made as evidenced by the measurements.  Most metal dome tweeters have resonances in the 1-2kHz range and then again at higher frequencies.  The measurements for this tweeter do not reveal any resonance issues within the operating range up to 20kHz!

The woofers and midrange are all 5.25” drivers with matching polypropylene cones and full magnetic shielding for the rare application requiring magnetic shielding.  The motor structure looks pretty beefy and the spider and frame are also high quality.  Using two 5.25” woofers in a pretty small sealed enclosure does not provide a great deal of low frequency extension.  The response of the woofers is tuned pretty flat and rolls off at 12dB per octave.  This speaker can be used with a subwoofer with a 12dB per octave low pass at 80Hz without a high-pass filter on the loudspeakers.  For the two channel snobs, this means that the speaker will integrate with a subwoofer without any sound degrading high pass filter.

Absolute Tower Woofer

NHT Absolute Tower Set Up & Sound Quality Tests

The cardboard box surrounding the NHT Absolute Towers makes you think a much larger loudspeaker is coming out.  The speakers are very adequately protected with several thick foam ribs and a foam base and top.  The base of the loudspeaker comes in a separate box and is attached with four Phillips head screws.  The pair of Absolute Towers arrived in perfect condition.

In recent months, I have moved to a new home with a very different living room than what I’m used to.  Since my reference open-baffle loudspeakers take quite a bit of breathing room, they do not work in the new living space.  I’ve since designed a pair of large bookshelf speakers to overcome the placement issues.  There is a terrible null in this room at 80Hz, which I typically use RTA to analyze, and equalization to mask.  Given this, I only use this room for home theater testing.  The system in this room consists of an Oppo BDP-105 connected directly to an ATI 1505 amplifier.  The subwoofer out from the Oppo BDP-105 is connected to a miniDSP for bass management before routing to a HSU 12” subwoofer.The loudspeakers are approximately 8 feet forming an equilateral triangle with the listening position.

For two channel listening, I use a 12’x14’ office with a large area rug over hard floors.  In this configuration, I use Audirvana running on a MacBook connected to a high quality DIY Buffalo III SE digital to analog converter (DAC) via USB.  The DAC is based on the same converter chip used in the BDP-105 but has an excellent linear power supply and a different current-voltage stage yielding a slightly warmer bottom end.  The USB input interfaces with Audrivana and allows high resolution DSD playback.  I typically sit 6 feet from each speaker in an equilateral triangle.  

Sound Quality Tests

These listening tests were conducted in the mentioned listening environments without any form of room correction or high-pass filter for music. 

Café Cubana – Siboney

I had to go back to this recording because it is first recording I’d ever heard that made me realize the merits of audiophile systems compared to the unbalanced systems I had grown up with.  Instead of pumped highs and bloomy low frequencies, audiophile systems handled the midrange in a way that was simply more lifelike.  This combined with discovery of stereo imaging elicited a new passion that still burns strong.  While this recording is not the pinnacle of recording quality, it does present a very life like piano, bass and set of congas that just do not sound real without a good midrange presentation. 

After finagling with the Absolute Towers I found toeing them in slightly so I was sitting directly on-axis provided the best sound and imaging to my ears.  The speakers sound very good overall and have a great tonal balance leaning slightly toward the bright side.  In fairness, the Absolute Towers were designed for use with a subwoofer and I do not have one set up in the office.  This speaker sounded very fast and very clean at any volume I dare listen to it.  The stereo imaging was present but is not the speaker’s strongest suit.  What did strike me is the clarity in the upper bass.  The speaker is designed for a flat response summed with a subwoofer at 80Hz instead of trying to fake the bass response as many other small towers do.  Craving some integration with a subwoofer, I moved these to the living room setup. In the living room, the seamless integration with the subwoofer was easy.  I set the subwoofer to an 80Hz crossover point, level matched using a calibrated RTA and was on my way in just a few minutes.  The clean and fast bass response of these speakers was excellent.  I found that in this acoustic environment, the imaging was not as good but their excellent frequency response made for a very enjoyable listening experience.

Lindsey Stirling – Crystallize

I’m not a huge fan of electronic music but this track really has a good mix of low, middle and upper bass that isn’t found in many recordings.  Lindsey Stirling is an excellent American violinist that mixes her performances with electronica.  In the living room with the subwoofer in place, this recording comes alive with smooth bass transitioning perfectly from subwoofer to the Absolute Towers.  The stereo panning of the violin oscillates gently from the center creating an ethereal smearing of the violin that you chase around the acoustic scene as you listen.  Several synthesizer pads play in the background that have a sense of non-locality.  This song is fun to listen to on the Absolute Towers.

Lindsey Stirling - Lindsey Stirling

Tuck & Patti – Time After Time

This recording has that analog tube recording feeling:  It’s just a warm sounding recording with tons of dynamic range and imaging in spades.  The Absolute Towers did not disappoint on this song either.  Everything sounded lush and the Absolute Towers were able to handle the dynamics of this song at very loud volumes without any evidence of strain.  There was a slight sibilance in the treble region but this is likely due to room acoustics.

Tuck and Patti - Tears of Joy

Hi-Res DSD: Keith Greeninger & Dayan Kai – Looking For A Home

The merits of high-resolution recordings have been questionable to my engineering brain.  In school, I was taught that there is a reason CD’s were cut at 16 bit and 44.1kHz and the reasoning is very convincing.  Audiophiles, prepare to scoff. I haven’t heard a discernable difference beyond my own doubt when downsampling high-resolution music so long as the sample rate was an integer multiple of the original (For Example 96kHz to 48kHz). However, this recording is way different.  There is just something about this recording that I haven’t heard in any other music.  I tried converting the DSD track to a lossless AAC track using Korg Audiogate but the sound quality was noticeably worse.  I do not know if the algorithm Korg uses causes aliasing issues, but I do know it was not the same.  I tried the same thing with 2L albums with similar results.  Is DSD that much better?  I’m not really sure but there is a level of realism to DSD that I cannot explain.

With that out of the way, this track with the Absolute Towers back in the office is out of this world.  The realism of the duet and guitars through the Absolute Towers and a high quality DSD capable DAC is an experience to say the least.  Imaging was good and it just feels live and intimate and evokes the feeling music should. 

NHT Absolute Tower Measurements and Analysis

The measurements were conducted in conformance with Audioholics Loudspeaker Measurements Standard

NHT Absolute Tower On-Axis Frequency Response

The on-axis frequency response of the NHT Absolute Tower was conducted with the measurement microphone at 2 meters with a 2.83V excitation signal. The results are scaled to 1 meter mathematically. The manufacturer rates this loudspeaker’s sensitivity as 86dB at 1 meter with a 2.83V input. Audioholics measures sensitivity as the average sound pressure level (SPL) from 300 to 3kHz. The Audioholics rated sensitivity for the Absolute Tower is reasonably close at 84.9dB. With respect to frequency response, the slight dip from 500Hz to 3kHz along with the rising response from 3kHz to 20kHz yields a slightly bright presentation. Note that this speaker has a very flat response but +/- 2dB over many octaves causes a certain perception of tonal balance. The steep rising response above 16kHz is at the edge of my hearing so I did not notice anything offensive. If you desire flat frequency response, this loudspeaker system is flatter than most studio monitors I have measured.

 

NHT Absolute Tower Listening Window

The listening window response for the NHT Absolute Tower is conducted with a 2.83V input signal at 2 meters from 7 locations. The measurement provides a picture of how the loudspeaker performs from seating locations that are not directly on axis with the speaker. The top curve is the average of the other positions and provides an average of how the speaker performs throughout the listening area. Subjectively, the off-axis response within the listening window is extremely uniform with no roll-off of high frequencies at angles up to 30 degrees. This means that the direct sound from the speaker will sound very similar for most of the listening area.

 

NHT Absolute Tower Polar Response

Remember that chamfering around the tweeter we discussed earlier? Its effects are clearly visible in the polar response graph. Specifically between 3kHz and 5kHz we see an odd flanging of the polar response. This effect is due to the angled baffle surrounding the tweeter. Above 5kHz, the tweeter output bounces off of the flat section of the baffle and the polar response narrows. Between the crossover point of 2.2kHz and 5kHz, the tweeter is transitioning across the angled chamfer, increasing the output off-axis. This seems like a good thing because the response is close to linear when sitting up to 30 degrees off axis. However, this has consequences in rooms without acoustic treatments. There is now extra acoustic energy in a limited band being launched into a room at higher angles than other bands. Human perception of sound includes reflections and direct sound. Therefore, the typical quasi-anechoic frequency response does not tell the entire story of how a loudspeaker will sound in a room. While I was able to get the Absolute Tower to sound very good in my listening environment, it did take some coercion and adjustment. Please consider your room before purchasing this speaker, this would not be my go-to speaker if my room was all hard surfaces without any treatment.

Loudspeaker imaging is something that is hard to quantify. However, there is a strong link between a loudspeaker’s polar response and imaging. This is because the human brain determines location based on two cues. Specifically, the brain can determine the location of the source of a sound by the difference in loudness between the ears or by the difference in signal arrival time. Room reflections cause delayed signals to reach the listener distorting the acoustic image. The NHT Absolute Towers created a respectable acoustic image, but it was not with the pinpoint accuracy found in some more expensive speakers. I believe it is due to the polar response due to the chamfered baffle. While this improves off-axis measurements within the typical listening area, it has tradeoffs in stereo imaging.

 

NHT Absolute Tower Impedance

The impedance of the NHT Absolute Tower is listed as 8-ohm average with a 4-ohm minimum. The minimum measured impedance was 4.2-ohms which places it below the 4.8-ohm minimum rating for a 6-ohm speaker. Therefore, Audioholics conservatively recommends that a 4-ohm stable amplifier to drive the Absolute Towers.

 

NHT Absolute Tower Harmonic Distortion

The harmonic distortion graph was generated using a 90dB stepped sinusoid sweep measured at 2 meters. The distortion measurements are very low across the operating range. Crossed over to a subwoofer, it is possible to create a low distortion system at a very reasonable cost.

 

NHT Absolute Tower Cumulative Spectral Decay

The cumulative spectral decay measurement provides a picture of how quickly a loudspeaker stops playing after the signal stops. The NHT Absolute Tower has an extremely clean cumulative spectral decay meaning there are no offensive cabinet or system resonance issues. The left most edge that looks bad is simply a limitation of the measurement technique and should be ignored. I was unable to see any resonance in this metal dome tweeter.

 

NHT Absolute Tower Group Delay

The group delay graph shows the rate of change of the slope of a loudspeaker’s phase. As a rule of thumb, values below 1.6ms in the mid to high frequencies will likely not affect perception of sound quality. Increasing group delay in the low frequencies is not as objectionable as it is in the mid to high frequency ranges. The group delay stays below 2.5ms for the woofers and decreases significantly for midrange and tweeter frequencies.

NHT Absolute Tower Conclusion

NHT Absolute Tower Pair

The NHT Absolute Tower is really a well engineered speaker system at a reasonable price. Audiophile sound, superb measurements and awesome finish and build make this a high value speaker at $1100 per pair. A subwoofer is required but easy to mate. The polar response can cause a little extra energy in the 3-5kHz region if the room is full of hard surfaces but otherwise the on and off-axis response are very flat throughout its intended design range. This is truly a great speaker with legendary NHT performance. This speaker has a small footprint and will work equally well for 2.1 channel listening or home theater. Highly recommended!

NHT Absolute Tower Speaker Video Review

The Score Card

The scoring below is based on each piece of equipment doing the duty it is designed for. The numbers are weighed heavily with respect to the individual cost of each unit, thus giving a rating roughly equal to:

Performance × Price Factor/Value = Rating

Audioholics.com note: The ratings indicated below are based on subjective listening and objective testing of the product in question. The rating scale is based on performance/value ratio. If you notice better performing products in future reviews that have lower numbers in certain areas, be aware that the value factor is most likely the culprit. Other Audioholics reviewers may rate products solely based on performance, and each reviewer has his/her own system for ratings.

Audioholics Rating Scale

• — Excellent
• — Very Good
• — Good
• — Fair
• — Poor

Metric	Rating
Build Quality
Appearance
Treble Extension
Treble Smoothness
Midrange Accuracy
Bass Extension
Bass Accuracy
Imaging
Soundstage
Dynamic Range
Fit and Finish
Performance
Value