NHT C3 Review (3-way speaker)

[Rottmannash]

It's crazy how much the distortion jumps up at the higher output measurement.

The sensitivity is low, and the impedance phase angles get pretty high (down to almost -50 degrees and up to almost +60 degrees).

Put all that together and these aren't speakers that are made to play super loud.

"impedance phase angles"...another thing to Google.

 

[Rottmannash]

These are screen grabs from the photos of the C3 on Amazon. I see at least one dimple in almost the same spot on the midrange driver in both angles.


View attachment 112090View attachment 112091

Is someone accidentally touching them when installing them? Are drivers manually placed in the enclosure and screwed in by humans or is a robot doing this type of work now?

 

[sejarzo]

Is someone accidentally touching them when installing them? Are drivers manually placed in the enclosure and screwed in by humans or is a robot doing this type of work now?

I thought the same thing, but I would think that any automated assembly would be in the production of the driver itself rather than the final speaker.

 

[amirm]

You all made me curios so I unpacked the second sample it looks perfect.

 

[dfuller]

You all made me curios so I unpacked the second sample it looks perfect.

Does it sound any different from the first, if you've given it a listen?

 

[amirm]

No, I literally just took it out of the box.

 

[MZKM]

"impedance phase angles"...another thing to Google.

Phase interacts with impedance. At 0°, the amp sees the raw impedance, at 45° it has to dissipate like 2x the heat (for Class-AB at least).

When Amir or anyone measures an amp, phase is 0° (unless I’m misunderstanding). Meaning, even if you have a full suite of measurements of your amp and your speaker, you really don’t fully know how they will interact.

However, this increase in heat dissipation is similar to the amp seeing a lower impedance (of 0°). This has allowed for a calculation to be made to generate the Equivalent Peak Dissipation Resistance (EPDR). I actually made a thread about this and Jack Oclee-Brown of KEF chimed in with the calculation. Erin (@hardisj) will be calculating it for his speaker reviews going forward. I also generated one for the Infinity R253 Amir measured, he doesn’t normally provide this data in his files though as it is a pretty large file (and I’m not gonna digitize every impedance/phase graph).

Here is Erin’s graph for the KEF R3:

 

[AnalogSteph]

"impedance phase angles"...another thing to Google.

Impedance is actually complex-valued, with both a magnitude and phase, or alternatively, a real and imaginary part depending on how you want to describe the vector.

This is much the same story as being billed for real vs. reactive or apparent power. The real part is what actually dissipates the power, but if the phase angle is large (read: the imaginary part is), considerable currents may be flowing out of phase that are stressing components.

 

[Rottmannash]

Impedance is actually complex-valued, with both a magnitude and phase, or alternatively, a real and imaginary part depending on how you want to describe the vector.

This is much the same story as being billed for real vs. reactive or apparent power. The real part is what actually dissipates the power, but if the phase angle is large (read: the imaginary part is), considerable currents may be flowing out of phase that are stressing components.

Impedance is actually complex-valued, with both a magnitude and phase, or alternatively, a real and imaginary part depending on how you want to describe the vector.

This is much the same story as being billed for real vs. reactive or apparent power. The real part is what actually dissipates the power, but if the phase angle is large (read: the imaginary part is), considerable currents may be flowing out of phase that are stressing components.

I have so much to learn. Is there a resource online where I can learn more about this? Thanks for the explanation.

 

[txbdan]

MIT Open Courseware. Become a EE for free. :-D
https://ocw.mit.edu/courses/electrical-engineering-and-computer-science/

 

[Rottmannash]

MIT Open Courseware. Become a EE for free. :-D
https://ocw.mit.edu/courses/electrical-engineering-and-computer-science/

 

[MrPeabody]

Even though the woofer is 6.5" according to the specifications, the actual diameter of the cone (plus 1/3 of the surround both sides) is right about 5". So this isn't a large woofer by any means, begging the question of how much advantage there is of a three-way design with a woofer this small. It avoids the need for a waveguide, to achieve good directivity match with the woofer, but I'm not entirely convinced that the directivity mismatch is a significant concern when the woofer is this small. And given the decision for it to be a 3-way speaker, is this 2" dome the ideal choice? Even using the 5" true diameter of the woofer, the ideal size for the midrange would still be 3". The dome profile for the midrange doesn't share the full advantage of the dome midrange for the tweeter. A cone with a true 3" diameter would have presented fewer tradeoffs. It would have allowed the crossover point to be lower, around 500 Hz maybe, and this in turn would have permitted using a woofer the same size but designed for deeper bass, with a lower Fs and greater excursion. Personally I am drawn to the sealed enclosure approach, however even allowing that the advantages of the sealed enclosure are real, they are slight advantages, and not significant enough to compensate for the poor choices for woofer and midrange. It is an interesting speaker, but at the discounted price of $1000/pair, I don't think I'd have much difficulty finding something else that I'd like better for less money. If there were a three-way speaker that cost about this much and that uses a sealed enclosure but with a slightly bigger woofer capable of deeper bass and a slightly larger midrange, I would look at it differently and would possibly be a buyer.

 

[More Dynamics Please]

^ An interesting concept for a modestly priced 3-way sealed bookshelf speaker would be a hypothetical Infinity Reference 183. It would combine the existing 1" CMMD tweeter with waveguide and 4" CMMD flat piston midrange from the RC263 with one of Harman's existing 8" woofers. Crossover points would be in the ~300 and ~3,000 Hz range. It could be designed for maximum SPL like the RC263 to be -3dB at 80 Hz for a classic THX reference sealed satellite/sub crossover point or with extended bass and more limited SPL. Given the track record of other Infinity Reference models it would measure better than its price would suggest, especially during one of Harman's many Infinity speaker sales.

 

[Frank Dernie]

Even though the woofer is 6.5" according to the specifications

Certainly the "standard", such at it is, for driver diameter has been the chassis diameter not cone diameter for at least 50 years (here in the UK anyway). So, given the usual long travel surround, no driver's have cones anywhere near the nominal size.
I usually look at the actual piston area myself by measuring the actual cone.
One of the misconceptions caused here is that often several small drivers are claimed to be equivalent to a big one but often, comparing the actual cone areas, they are nowhere near equivalent particularly since the periphery of multiple units is also longer than the periphery of one big cone.
You can't fit a huge driver in a small box

 

[bennybbbx]

This is a review and detailed measurements of the NHT C3 3-way, sealed speaker. It was purchased new by a member and kindly drop shipped to me. It costs US $391 on Amazon for a single unit.

I must say, I was impressed by the fit and finish of the C3:

View attachment 111852

The enclosure is sold and dense with a beautiful piano black finish.

I love that the back panel has threaded screw holes to mount the speaker to the wall/ceiling for surround/Atmos applications:

View attachment 111853

Speaker is manufactured in China.

Measurements that you are about to see were performed using the Klippel Near-field Scanner (NFS). This is a robotic measurement system that analyzes the speaker all around and is able (using advanced mathematics and dual scan) to subtract room reflections (so where I measure it doesn't matter). It also measures the speaker at close distance ("near-field") which sharply reduces the impact of room noise. Both of these factors enable testing in ordinary rooms yet results that can be more accurate than an anechoic chamber. In a nutshell, the measurements show the actual sound coming out of the speaker independent of the room.

I performed over 1000 measurement which resulted in error rate of around 1%.

It is down to freezing outside so the best I could do was raise the temperature to 56 degrees. Speaker however was kept warm indoors prior to measurements.

Reference axis was that of the tweeter. Grills were not used.

Measurements are compliant with latest speaker research into what can predict the speaker preference and is standardized in CEA/CTA-2034 ANSI specifications. Likewise listening tests are performed per research that shows mono listening is much more revealing of differences between speakers than stereo or multichannel.

NHT C3 Measurements
Acoustic measurements can be grouped in a way that can be perceptually analyzed to determine how good a speaker is and how it can be used in a room. This so called spinorama shows us just about everything we need to know about the speaker with respect to tonality and some flaws:

View attachment 111854

EDIT: looks like the mid-range is damaged in this unit. It has a dimple on the bottom of it. This could explain the mid-frequency dip. Unfortunately I only have one unit to test so can't verify.

On-axis response is kind of wavy. This was unexpected as measurements performed elsewhere are much flatter. My in-room measurements showed the same so I don't think it is an issue with NFS measurements. Likely a design change was made to tilt up the highs more to keep up with the competition in the showroom. We can see the uneven response in individual driver response:

View attachment 111855

Seems like one could push up the tweeter level a bit or else, bring the tweeter down. The tweeter by itself has uneven response.

As noted in the first graph directivity is good so for good or bad, early window reflections follow on-axis irregularities:
View attachment 111856

Predicted in-room response shows very little tilt so speaker is going to sound bright:

View attachment 111857

As I noted, directivity is good due to use of mid-range driver:

View attachment 111858
View attachment 111859

If you are going to use this up high for surround applications, be sure to tilt it down some:

View attachment 111860

Distortion was two completely different stories depending on level:
View attachment 111861

At 86 dB, this is professional monitor level of distortion, not a budget passive speaker! Push it though and things get bad especially with that tweeter. I have not seen one fall apart this badly. Fortunately that is where we have elevated response so we would want to EQ that down anyway and that should help keep that distortion in check.

Needless to say, at 94 dBSPL it exceeds our threshold:
View attachment 111862

Impedance is typical of these speakers, down to 4 ohm or so:

View attachment 111863

I forgot to mention earlier that sensitivity is rather low, dropping to 82 to 83 dB in mid-range area. Company advertises 87 dB which would only be true of the peaking tweeter.

NHT C3 Listening Tests and Equalization
The high frequency peaking was not obnoxious but clearly overdone (as appealing as that could be for a few seconds). So had to EQ that anyway and while there, might as well tweak the rest:

View attachment 111864

Filling that little but wide dip in upper bass was important in providing balance relative to highs (which I did not fully cure on purpose). I then filled in the 1 to 4 kHz region and job was done. Once there, the benefits of a sealed enclosure was there with its ability to play sub-bass without getting distorted. Alas, without the boosted upper bass that we get from ported speakers, the bass was a bit light but I was fine with that.

Dynamics was very good and speaker could handle a lot of power. And a lot of power is what I had to feed it so don't get a 50 watt amp. You need more than that.

Conclusions
It is a shame we didn't measure the C3 as well as others had. That would have made it a lot closer to ideal. As is, without EQ it is bright and hence "detailed." To my ears, that gets old fast so EQ is mandatory in my book. And so is filling in the other two dips. Speaker takes EQ well since we are not trying to push it where distortion is highest.

Overall, I was happy with the NHT C3 and would recommend it with EQ. No without.

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Is it possible to show a CSD waterfall which is normalized to 1khz 0 db for this test and maybe all other tests ?. very intresring to see how fast this speaker with a seperate midrange is. When it is normalize at 1 khz then it is possible to compare the speed of speaker good at 1 khz. because fast mid range is usefull for this reason. in this video i have do a test, please like if you hear this and dislike if you hear this not. so can see how many can hear this and how many not in compare

https://www.sciencedirect.com/topics/medicine-and-dentistry/binaural-hearing

Binaural hearing

uses two main acoustic cues: interaural time difference (ITD) and interaural level difference (ILD) (Doerbecker and Ernst, 1996; Francart et al., 2011):
•
ITD is the delay between both ears. It is efficient for low frequencies (below 850 Hz). It is due to the envelope of the signal reaching the two ears. It can be reminded that a sound coming from the side at 90° has an ITD of 0.6 ms. When the source is situated in the front (azimuth 0°), the so-called front target, the ITD is 0 ms.
•
ILD is related to the intensity reaching the two ears. The signal is more or less attenuated by the head shadow. This effect is mostly perceptible with high frequencies (above 3 kHz). ILD is 0 for the front target.

a period time of 1 ms is 1 khz frequency. humans are able in tests to detect 10-20 microseconds can read here. thats less than 1/ 44.1 khz sample
here is delay time table. for example ~0.08 ms is 10 degreee
https://www.sfu.ca/sonic-studio-webdav/handbook/Binaural_Hearing.html

 

[Frank Dernie]

thats less than 1/ 44.1 khz sample
here is delay

what has that got to do with it?

 

[pma]

what has that got to do with it?

Nothing. Even @j_j tried to explain to him, with no effect.

 

[Frank Dernie]

Nothing. Even @j_j tried to explain to him, with no effect.

OK I missed that.

 

[bennybbbx]

what has that got to do with it?

the reason wy it is usefull to have in all speaker tests a CSD waterfall. for example this test have a CSD. https://www.audiosciencereview.com/...rk-rokit-5-gen-4-review-studio-monitor.20711/ many other have this not. If its not possible to normalize to 1khz then such cumulative spectral decay as in the krk 5 test is usefull too when all speakers have this. because of the ITD human hearing it is usefull when mid range speaker have short rise and fall delays even if they need only output frequency upto 3 khz.

 

[Frank Dernie]

the reason wy it is usefull to have in all speaker tests a CSD waterfall. for example this test have a CSD. https://www.audiosciencereview.com/...rk-rokit-5-gen-4-review-studio-monitor.20711/ many other have this not. If its not possible to normalize to 1khz then such cumulative spectral decay as in the krk 5 test is usefull too when all speakers have this. because of the ITD human hearing it is usefull when mid range speaker have short rise and fall delays even if they need only output frequency upto 3 khz.

Yes but what has the sampling rate of CD to do with that?