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

NHT 02-ARC Outdoor Speaker Measurements and Analysis

By

The measurements were conducted in conformance with Audioholics Loudspeaker Measurements Standard

spl_out.png 

NHT 02-ARC On-Axis Frequency Response

The on-axis frequency response was conducted with the measurement microphone at 1 meter from the speaker baffle between the woofer and tweeter with a 2.83V excitation signal. Audioholics measures sensitivity as the average sound pressure level (SPL) from 300 to 3kHz.  The Audioholics rated sensitivity for the NHT 02-ARC outdoor loudspeaker is an average 85.4dB.  The speaker approaches the manufacturer rated 88dB sensitivity at around 100 Hz and above 8kHz.  The overall frequency response of the loudspeaker is +/- 2.5 dB from 70Hz to approximately 15kHz.  Directly on-axis, the tweeter has a steep rising response above 15kHz. The rising response above 15kHz on-axis yields a flatter off-axis response, which may be a benefit for an outdoor loudspeaker.  The qualitative effect of a rising tweeter response above 15kHz depends on the hearing range of the listener.  Bass response in the sealed cabinet falls off very linearly at 12dB/octave below 80Hz allowing for simple integration with a subwoofer.

listening_window_out.png  

NHT 02-ARC Listening Window

The listening window response is the average of 5 measurements ranging from 30 degrees left to 30 degrees right plus measurements 15 degrees above the speaker and 15 degrees below the speaker.  When the loudspeaker has symmetry about the vertical axis, the right and left are equal and the total number of measurements is reduced to five. 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 seven positions and provides an idea of how the speaker performs throughout a listening area.  The listening window response for the NHT 02-ARC is excellent.  Notably, at 15 degrees off-axis the loudspeaker frequency response is very flat.

Polar_Response.jpg  

NHT 02-ARC Polar Response with Grill

The polar response graph shows how a loudspeaker performs at various seating positions in a room.  The polar response graph above was generated by measuring a loudspeaker at 7.5-degree intervals around a circle half way between the woofer and tweeter height at a distance of 1 meter.  The NHT 02-ARC has uniform polar response with slight aberrations in the upper treble range.  The grille of the loudspeaker has a squared off plastic edge that extends from the speaker baffle approximately ½”.  An additional polar response measurement was conducted without the grille yielding the response shown below.

Polar_Response_No_Grill.jpg  

NHT 02-ARC Polar Response Without Grille

Clearly, the loudspeaker grille has a substantial effect on the off-axis upper treble frequency response.  The performance of this loudspeaker is quantitatively superior with the grille removed.

impedance_out.png 

NHT 02-ARC Impedance

The impedance of the NHT 02-ARC loudspeaker dips far below the IEC 6.4 ohm minimum for a manufacturer rated 8-ohm speaker.  So much so that I checked all of the settings and connections several times to make sure the measurements were accurate.  When all else failed, I measured a speaker with known impedance to validate the test rig.  From 500Hz up, this speaker could be considered an 8-ohm speaker.  For frequencies below 500Hz, this speaker is clearly a 4-ohm speaker.  It is highly advisable to drive this loudspeaker with an amplifier that is 4-ohm stable.  If these were my speakers, I would get a label maker out and cover the 8-Ohm label with a 4-Ohm label. 

Distortion.bmp 

NHT 02-ARC Harmonic Distortion

The harmonic distortion graph was generated using a 90dB stepped sinusoid sweep measured at 2 meters.  This is the last test we perform on a loudspeaker since it really tortures loudspeakers.  This test was run full range putting the sealed 6.5” polypropylene woofer through the ringer.  Considering the size of this loudspeaker, the distortion remains very low averaging well below 1% for the 2nd and 3rd order harmonics above 60 Hz.  The offensive higher order harmonics are very well behaved. There is nothing to complain about here.  This is superlative performance and no doubt a major contributor to the speaker’s taut, controlled sound.

CSD.jpg  

NHT 02-ARC Cumulative Spectral Decay

Cumulative spectral decay (CSD) is derived from the impulse response measurement taken with a 90dB excitation signal at 1 meter.  The cumulative spectral decay shows how sound at various frequencies dies out as a function of time.  It is important to note that the leftmost ridge is not valid and is a product of the measurement technique.  The CSD for the NHT 02-ARC does not show any offensive artifacts except the ridge that reappears at 1500Hz at around 2ms.  One explanation, albeit not conclusive, is that the speaker is stand mounted.  Resonance and reflections from anything close to the speaker will affect the measurement and there isn’t much any manufacturer can do to fix this issue.  Since this is greater than 20dB below the reference level, it is nothing to worry about. 

Group Delay.bmp 

NHT 02-ARC 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 effect 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 NHT 02-ARC group delay values are below 1ms at 300Hz.

 

 

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

Recent Forum Posts:

hk2000 posts on February 25, 2014 10:25
gene, post: 1019285
Good question Jotham. A 2-way speaker like the 02-ARC performs better when mounted vertically. Horizontal mounting will result in a less even response due to lobing. You can surely mount them like this if you have no other choices but they are designed to be mounted vertically for best performance.

I Never new that. Thanks. Can you explain what lobing is, or point to a link that explains it, thanks. Does this also apply to surround speakers?
Also, a follow up question to Jotham's: Will it matter if they are mounted upside down with the woofer on top, if not, I think NHT should make the mounting bracket longer on one side? That would enable one to mount them low pointing up or high pointing down (Most likely). If the tweeter has to be on top, then obviously that makes them less than ideal for outdoor installation, after all this is for casual listening, No?
gene posts on February 24, 2014 17:54
jotham, post: 1019213
Thank you for the review! After we build our new deck, I'm looking forward to installing 4 new outdoor speakers so this review was very timely.

I do have a question about the mounting that was demonstrated. Wouldn't it make more sense to install them on their side, perhaps with tweeters on the outside? This would give greater adjustability for the sweet spot. I assume there was some acoustical reason it was installed upright but given the particular context, I can't figure it out.

thanks,

Jotham

Good question Jotham. A 2-way speaker like the 02-ARC performs better when mounted vertically. Horizontal mounting will result in a less even response due to lobing. You can surely mount them like this if you have no other choices but they are designed to be mounted vertically for best performance.
jotham posts on February 24, 2014 13:55
Thank you for the review! After we build our new deck, I'm looking forward to installing 4 new outdoor speakers so this review was very timely.

I do have a question about the mounting that was demonstrated. Wouldn't it make more sense to install them on their side, perhaps with tweeters on the outside? This would give greater adjustability for the sweet spot. I assume there was some acoustical reason it was installed upright but given the particular context, I can't figure it out.

thanks,

Jotham
Post Reply