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NHT C3 Review (3-way speaker)

Fafnar

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Been looking forward to this one, thanks for taking the time to do it Amir. Also it saved me from having to send mine in, so thank you to whomever sent it!

I feel like I definitely hear the benefits of the sealed design in the bass as you pointed out, but is there any benefit to this unit being a 3 way, or is it more of a selling point and could be achieved with just two drivers?
I have them as well, and didn't want to give them up to get them measured so thanks again to the person who did send it in.

I read the sealed design eliminates issues with placement around walls/corners since there is no port. That's the main reason I use them - they are truly bookshelf speakers in my case.
 

Robbo99999

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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.

------------
As always, questions, comments, recommendations, etc. are welcome.

Appreciate any donations using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/
Kinda surprised you gave it such a good rating given that it's a 6.5" woofer with very little bass, along with a quite a funky frequency response. When you say "the benefits of a sealed enclosure was there with its ability to play sub-bass without getting distorted", I'm quite surprised by that because sub-bass is below 60Hz and judging from the spinorama with the bass starting to roll off quite steeply at 90Hz I'm surprised there'd be any sub-bass to be heard at all? I would think this speaker would need to have a Low Shelf Bass boost via EQ of at least 5dB to even start noticing the sub-bass, but then you'd be pushing the speaker towards it's 94dB measured level which would put it into unhappy distortion territory? Given that this is a 6.5" woofer it should be able to play lower, and I don't think it really deserves it's awarded status.

EDIT: even on their spec page for the speaker they list the Frequency Response as 55Hz-20kHz, so that's not really covering the sub-bass below 60Hz
https://www.nhthifi.com/products/16546-c-3-bookshelf-loudspeaker#specs
 
Last edited:

pierre

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Score 4.36 with EQ 6.25

Here is an automated compute EQ, you can take as many filters you want in order. The first 4 to 6 are the most effective.

Code:
EQ for NHT C3 computed from ASR data
Preference Score 4.4 with EQ 6.2
Generated from http://github.com/pierreaubert/spinorama/generate_peqs.py v0.5
Dated: 2021-02-11-08:23:21

Preamp: -2.1 dB

Filter  1: ON PK Fc  1014 Hz Gain +1.96 dB Q 2.56
Filter  2: ON PK Fc 13194 Hz Gain -3.17 dB Q 0.39
Filter  3: ON PK Fc  2737 Hz Gain +1.85 dB Q 12.00
Filter  4: ON PK Fc   453 Hz Gain -1.44 dB Q 3.26
Filter  5: ON PK Fc   547 Hz Gain -0.64 dB Q 12.00
Filter  6: ON PK Fc   745 Hz Gain +1.17 dB Q 5.33
Filter  7: ON PK Fc   942 Hz Gain -0.54 dB Q 12.00
Filter  8: ON PK Fc  1552 Hz Gain +1.22 dB Q 12.00
Filter  9: ON PK Fc  1133 Hz Gain +0.53 dB Q 12.00
Filter 10: ON PK Fc  2086 Hz Gain -0.68 dB Q 12.00
Filter 11: ON PK Fc  1337 Hz Gain -0.66 dB Q 12.00
Filter 12: ON PK Fc  2275 Hz Gain +0.82 dB Q 12.00
Filter 13: ON PK Fc  2481 Hz Gain -0.62 dB Q 12.00
Filter 14: ON PK Fc  1897 Hz Gain +0.68 dB Q 12.00
Filter 15: ON PK Fc  1737 Hz Gain -0.61 dB Q 12.00
Filter 16: ON PK Fc  3704 Hz Gain -0.84 dB Q 12.00
Filter 17: ON PK Fc  3231 Hz Gain +0.57 dB Q 12.00
Filter 18: ON PK Fc  2102 Hz Gain -0.38 dB Q 12.00
Filter 19: ON PK Fc  9816 Hz Gain +0.52 dB Q 5.09
Filter 20: ON PK Fc   370 Hz Gain -0.49 dB Q 12.00

Here is the filter (graphically) and its impact on the LW:
filter.jpg


Here is the spinorama (and friends) without EQ and with EQ.
2cols.jpg



and with EQ:
2cols_eq.jpg
 

lurkera

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Apologies, my technical knowledge is low. Would it be useful to check distortion measurements after it's been eq'ed? And also show the highest SPL where there is no significant distortion at that eq setting? My thought process is that it would be interesting to compare speakers after they have been eq'ed, possibly have an eq low price speaker champ.
 

abdo123

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Score 4.36 with EQ 6.25

Here is an automated compute EQ, you can take as many filters you want in order. The first 4 to 6 are the most effective.

Code:
EQ for NHT C3 computed from ASR data
Preference Score 4.4 with EQ 6.2
Generated from http://github.com/pierreaubert/spinorama/generate_peqs.py v0.5
Dated: 2021-02-11-08:23:21

Preamp: -2.1 dB

Filter  1: ON PK Fc  1014 Hz Gain +1.96 dB Q 2.56
Filter  2: ON PK Fc 13194 Hz Gain -3.17 dB Q 0.39
Filter  3: ON PK Fc  2737 Hz Gain +1.85 dB Q 12.00
Filter  4: ON PK Fc   453 Hz Gain -1.44 dB Q 3.26
Filter  5: ON PK Fc   547 Hz Gain -0.64 dB Q 12.00
Filter  6: ON PK Fc   745 Hz Gain +1.17 dB Q 5.33
Filter  7: ON PK Fc   942 Hz Gain -0.54 dB Q 12.00
Filter  8: ON PK Fc  1552 Hz Gain +1.22 dB Q 12.00
Filter  9: ON PK Fc  1133 Hz Gain +0.53 dB Q 12.00
Filter 10: ON PK Fc  2086 Hz Gain -0.68 dB Q 12.00
Filter 11: ON PK Fc  1337 Hz Gain -0.66 dB Q 12.00
Filter 12: ON PK Fc  2275 Hz Gain +0.82 dB Q 12.00
Filter 13: ON PK Fc  2481 Hz Gain -0.62 dB Q 12.00
Filter 14: ON PK Fc  1897 Hz Gain +0.68 dB Q 12.00
Filter 15: ON PK Fc  1737 Hz Gain -0.61 dB Q 12.00
Filter 16: ON PK Fc  3704 Hz Gain -0.84 dB Q 12.00
Filter 17: ON PK Fc  3231 Hz Gain +0.57 dB Q 12.00
Filter 18: ON PK Fc  2102 Hz Gain -0.38 dB Q 12.00
Filter 19: ON PK Fc  9816 Hz Gain +0.52 dB Q 5.09
Filter 20: ON PK Fc   370 Hz Gain -0.49 dB Q 12.00

Here is the filter (graphically) and its impact on the LW:
View attachment 111890

Here is the spinorama (and friends) without EQ and with EQ.
View attachment 111885


and with EQ:
View attachment 111886

Why would you generate EQ for a defective unit?
 

Frank Dernie

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Whilst the tweeter distortion is very high it really only takes off around 6.5 to 7 kHz, meaning its first component (2nd harmonic) will be at 13 to14 kHz wher our ears are beginning to lose sensitivity according to equal loudness curves (100% in the case of some older listeners!) so, apart from it being a technical shortcoming does anybody think it would be audible?
Compared to distortion from 200 to 750 Hz where the music levels are high and the harmonics in the ear's sensitive range surely not a big problem?
 

YSC

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Kinda surprised you gave it such a good rating given that it's a 6.5" woofer with very little bass, along with a quite a funky frequency response. When you say "the benefits of a sealed enclosure was there with its ability to play sub-bass without getting distorted", I'm quite surprised by that because sub-bass is below 60Hz and judging from the spinorama with the bass starting to roll off quite steeply at 90Hz I'm surprised there'd be any sub-bass to be heard at all? I would think this speaker would need to have a Low Shelf Bass boost via EQ of at least 5dB to even start noticing the sub-bass, but then you'd be pushing the speaker towards it's 94dB measured level which would put it into unhappy distortion territory? Given that this is a 6.5" woofer it should be able to play lower, and I don't think it really deserves it's awarded status.

EDIT: even on their spec page for the speaker they list the Frequency Response as 55Hz-20kHz, so that's not really covering the sub-bass below 60Hz
https://www.nhthifi.com/products/16546-c-3-bookshelf-loudspeaker#specs
I think for sealed boxes you would get much less bass impact than same driver size ported speakers so it makes sense, for sub bass comment I have no clue also
 

MZKM

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Sensitivity: 83dB (spec: 87dB)
Note that the NRC measurement axis was between the midrange and tweeter, which could account for a *little* of the differences shown in the response in the midrange to lower treble.
I emailed Gordon (their head/only speaker designer I believe) mainly about NRC sensitivity difference and he had this to say:

We use the average anechoic SPL over a range (~500-2KHz) @ 1M, on-axis with 2.83 VRMS driving voltage.

We generally recommend the tweeter axis as the preferred listening position but it is not super critical.

I don’t think the different axis is the reason for the difference in sensitivity. More likely differences in measurement and equipment. Things like microphone calibration, ambient temperature, amplifier gain accuracy, measurement smoothing, microphone positioning, etc.

From my measurements @ 100Hz, 5.9 ohms @ -41 deg.

However, using 20kHz to determine microphone positioning accuracy, I am showing Amir being too much to the right by about 10° and being too high by above 5°.
___________________
I can't help but wonder if this is a unit-to-unit variation, possibly in crossover component tolerances,
Looking at the NRC impedance/phase plots:
impedance.png


electrical_phase.png


Looks pretty similar.

_________________

even on their spec page for the speaker they list the Frequency Response as 55Hz-20kHz,
I’m getting an LFX of 51Hz, so yeah.

Their website claims this though:
the C-3 has bass response down to 40Hz, making a subwoofer optional instead of a necessity when listening to music
 
Last edited:

Beave

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Yeah, the impedance plots definitely look similar, but not exactly the same (the peaks in Amir's measements of magnitude are a couple of Ohms lower than the peaks in the NRC plot). I have no idea what's normal unit-to-unit variation and what is due to different measurement techniques.
 

Beave

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I read somewhere on the internet that this speaker uses a version of this Seas tweeter, but I haven't seen any official confirmation of this:

Seas Prestige 27mm Aluminum Dome tweeter

I think this speaker uses the same woofer and midrange as the previous generation Classic Three, but with this new tweeter instead of the previous one's 22mm (3/4") dome.
 

celroid

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I dislike the look of the cut left and right side of the woofer. Where's the full circle? :(
 

Frank Dernie

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I think for sealed boxes you would get much less bass impact than same driver size ported speakers so it makes sense, for sub bass comment I have no clue also
Roll off is slower in closed boxes, so whilst the -3dB point is higher for a given box size the bass extends well in room because the wall and floor gain have "something to work with", ie some output to augment, whereas with a reflex the level below port tuning is so low it isn't augmented and around port tuning it can be excessive particularly if the room has a principle mode near that frequency.
A slow roll off in the bass, starting even at 100-200 Hz often gives good in room results and needs less/no room correction.
 

Frank Dernie

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I dislike the look of the cut left and right side of the woofer. Where's the full circle? :(
The full circle would have zero acoustic benefit and this allows a less obtrusive cabinet.
OTOH there are hundreds of speakers with round drivers, if that is important to you, so you could consider one of them instead?
 

celroid

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The full circle would have zero acoustic benefit and this allows a less obtrusive cabinet.
OTOH there are hundreds of speakers with round drivers, if that is important to you, so you could consider one of them instead?
Yes, I have the DBR-62 actually. I just read the review of this speaker and that bit was bugging me, it's just my comment on that. Nothing against those that actually like the looks
 

Frank Dernie

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Yes, I have the DBR-62 actually. I just read the review of this speaker and that bit was bugging me, it's just my comment on that. Nothing against those that actually like the looks
Its funny how we all differ. I have spent my life designing stuff with space and weight constraints and this looked pretty sensible to me.
I didn't consider it may look odd to anybody!
 
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