“Let our rigorous testing and reviews be your guidelines to A/V equipment – not marketing slogans”
Facebook Youtube Twitter instagram pinterest

NHT Absolute Tower Measurements and Analysis

By

The measurements were conducted in conformance with Audioholics Loudspeaker Measurements Standard

NHT Absolute Tower On-Axis Frequency Response

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

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

NHT Absolute Tower Polar Response

NHT Absolute Tower ChamferRemember 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

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

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

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

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.

 

Confused about what AV Gear to buy or how to set it up? Join our Exclusive Audioholics E-Book Membership Program!

Recent Forum Posts:

Steve81 posts on August 13, 2014 12:40
konajoe, post: 1045846
But, in this particular case, the author went out of his way to report that this speaker was different in this respect.

Hi Joe,

The issue in question isn't uncommon:
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.

This is a simple matter of a directivity mismatch, which is to say a 1“ tweeter will have a very wide dispersion pattern at the bottom of its passband (i.e. where the wavelengths are large with respect to driver diameter), while a 5.25” midrange driver's dispersion will be narrowing at the top of its passband (i.e. where the wavelengths are getting smaller with respect to driver diameter).

There are a couple common ways around this:

1. As seen in NHT's Classic 4 tower and Classic 3 bookshelf, you can use a smaller midrange driver; in the case of the NHTs, they use a 2" dome midrange down to 800Hz, which ensures a wide dispersion pattern throughout the midrange.

2. Use a waveguide or horn to constrain the tweeter's dispersion, which you can see on a lot of Harman speakers (JBL, Infinity, Revel), KEF, etc.

XTZ also looks to have an interesting solution with their Cinema series, i.e. use an array of tightly spaced tweeters down to a lower XO point of 1.2kHz, with only one of them handling the band above 3kHz.
alphaiii posts on August 13, 2014 12:19
I think the reviewer is making the point that, because of the chamfered baffle, some excess off-axis energy in the 3-5kHz range is projected into the room… In a reflective room, this excess may be perceived as brightness, or unforgiving mid-treble. As the reviewer mentions, some placement adjustments can help counter that.

I found the Absolute Towers to sound bit forward in my room, and liked the Classic Three better (which did not sound forward in my room)… but I can't say it was because of that 3-5kHz region…
AcuDefTechGuy posts on August 13, 2014 12:07
konajoe, post: 1045846
But, in this particular case, the author went out of his way to report that this speaker was different in this respect. He doesn't say “unforgiving in reflective rooms” about all speakers. He goes out of his way to explain, in depth, why this would be so. I'm not sure he would go out of his way to note this as a ‘con’ if it were true for all speakers.

As a total newb, I hate to appear that I am disagreeing with knowledgeable folks who have been very helpful.

My younger brother still has the NHT SuperZero bookshelf speakers + SW2P sub I gave him. The NHT system now resides in his large family room. This room is reflective as hell - I mean you can hear the echo when you clap your hands.

Amazingly, the NHT still manages to sound good.

I think the take-home message here is that in general, great speakers tend to sound good in most rooms. They sound best in the better rooms, but they still sound pretty good in lesser rooms. These NHT speakers are just one such example.
zieglj01 posts on August 13, 2014 11:36
konajoe, post: 1045846
But, in this particular case, the author went out of his way to report that this speaker was different in this respect. He doesn't say “unforgiving in reflective rooms” about all speakers. He goes out of his way to explain, in depth, why this would be so. I'm not sure he would go out of his way to note this as a ‘con’ if it were true for all speakers.

As a total newb, I hate to appear that I am disagreeing with knowledgeable folks who have been very helpful.

NHT does not make sharp/edgy and aggressive speakers - their speakers do measure nice.

I have owned about 85 sets of speakers, including some NHT ones - and the room/rooms, are important.
None of these speakers would sound good with hard and reflective surfaces all around. Now it is really cool,
what reducing reflections can do - with something like carpet/rugs, curtains, some soft furniture - and with
some pictures and/or other type things on walls that do help. Do not need to get real fancy - however, it is
cool and nice, to even tame the first reflections.

Your option choice and call - do what you wish - may (hope) you enjoy the adventure.
konajoe posts on August 13, 2014 06:34
But, in this particular case, the author went out of his way to report that this speaker was different in this respect. He doesn't say “unforgiving in reflective rooms” about all speakers. He goes out of his way to explain, in depth, why this would be so. I'm not sure he would go out of his way to note this as a ‘con’ if it were true for all speakers.

As a total newb, I hate to appear that I am disagreeing with knowledgeable folks who have been very helpful.
Post Reply