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NHT Pro M-00 Powered Monitor Review

PaulD

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I believe they're referring to baffle step, which will cause a bass bump in nearfield measurements if not corrected in software, though I assumed the Klippel corrected for this. The speakers may also very well just measure this way though - it's pretty common to see a bass bump right before the rolloff.
Doh! :facepalm:
(Of course...)
 

Biblob

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Thanks! Why don't you add the subwoofer to the measurements as well? It should be part of this system, doesn't it? :)
 
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amirm

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Thanks! Why don't you add the subwoofer to the measurements as well? It should be part of this system, doesn't it? :)
I will see if I can measure it by itself. I can't measure them together (not practical). There is a software option to stitch the two together but costs thousands of dollars so not going there. :)
 
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Folks do indeed love them so many thanks for including both :D



Edit: I do think these are easier to read now. However, I still have quite a bit of difficulty recognizing areas of cancellation, and at what specific angles they're happening. Obviously "bunched lines at a given frequency" is a sign of bad things, but for example, when there are asymmetries and loud-to-soft-to-loud transitions happening at certain angles, I honestly cannot figure that out at all from the SPL line graphs.

Maybe this is simply my lack of experience! But that's why I've been very vocal about preferring the contour plots.

The quality of data you can present using the Klippel is incredible, to say the least.
This is a review and detailed measurements of my NHT Pro M-00 powered studio monitor (speaker). I purchased it probably 15 years ago upon a hugely positive review from stereophile(?). It said some famous recording engineer used to mix a ton of popular albums. I bought the package with the S-00 subwoofer. Each speaker cost $249 and the sub was $500 for a total of $1,000.

Years later, NHT hit hard times and closed shop for a while. Then went online direct. I have not kept track of what they do now. These speakers are no longer available but as part of our effort to build up some "speaker measuring muscle," I thought it would make for a good second review. Be sure to read my first review of JBL 305P Mark ii to understand this data better.

The M-00 is a small but weighs like it is filled with rocks:


The case is made of some aluminum alloy which also acts as the heatsink for the internal amplifiers which are discrete, class AB. Here is the back side:


It has a very rough textured finish which can't be cleaned as you can see from all the scuff marks on mine.

There is nice connectivity in the form of both RCA and XLR/TRS inputs. There is also a switch for "near-field" vs "far-field." I tested it in the former mode because I have them on my desk and assumed that was the correct setting. It is supposed to lower the high frequencies some.

Speaker Spinorama Measurements
If you have read my previous review you know that the heart of our measurements are anechoic measurements of the speaker all around it. These measurements are grouped in different ways to give us insight into how the speaker can sound in our rooms:

View attachment 45647

Glancing at all four curves up above we instantly see a major issue with this speaker: a sudden rise in response or put inversely, a suck out in upper bass frequencies. We want our on-axis response in black to be as flat as possible. Here it shows that wide drop which audibly is bad because more musical notes fall in it and hence are lowered in amplitude.

There is also some peaking in high frequencies but if early reflections are allowed to get to you, they balance that out (since there is usually a drop off in high frequencies as you go off-axis from front of the speaker):
View attachment 45648

If on the other hand you think every studio needs to resemble an anechoic chamber with side walls fully absorptive, then the speaker may sound somewhat bright.

Guess what? We are done! We don't need 500 different graphs. The above tell the story and tell it well. But I know some of you want more data so let's provide a bit of that. As usual much more is available. For those of you who just want the top level message, I suggest jumping to listening tests.

Advanced Speaker Measurements
Folks like pretty and colorful graphs so here we are with contour plots in both horizontal and vertical axis:

View attachment 45649


View attachment 45650

The more uniformity and gradual change, the better in these graphs. Vertical axis performance tends to be worse in many speakers and such is the case here. So absorbing those if your room is not already too dead may be advised.

I took feedback to trim down these measurements some. Let me know if they are easier to read:
View attachment 45653

They tell us what the contour graphs do but without the fancy colors.

Informal Speaker Listening Tests
I setup the JBL 305P Mark ii as my left channel on my desk and the NHT Pro M-00 for the right. I matched the levels and then played one of the tracks I use for room optimization. The quality different was incredible. The 305P had a super balanced tone with lots of rich and warm detail in upper frequencies. The NTH M-00 in contrast sounded dead and bright.

Thinking I may be biased by my measurements I invited my wife to listen. As I was showing her the controls with her standing on my side she immediately pointed to the JBL 305P and said, "I like that one better!" Still, I forced her to sit down and do the test properly (in Adobe Audition by selecting one or the other channel to play the mono track). She again quickly concluded that the JBL 305 was much better.

Before leaving though, she said that if she was listening to guitar, she may like the NHT Pro better. She plays some guitar and brought it up to show me in person. Instantly I was reminded that neither speaker sounded as "real" has her guitar. :) That aside, she was tuning in to sharper tones in NHT thinking that it would allow her to distinguish the individual strings in an acoustic guitar better. I asked her if she just wanted to sit back and enjoy music, which one should would like and she said with confidence the JBL 305P Mark ii.

Research shows that quality of bass is worth almost 30% in overall preference for a speaker. Best not get that wrong as is the case with the NHT. Fortunately there is a matching sub for it that helps mitigate some of this.

Conclusions
Like a mechanic that listens to an engine and can quickly determine what may be the issue, I hope you are starting to get a feel for the power of these measurements. Even though the measurements are from "anechoic" origin (computed in this case), they are still powerful predictors of listener preference. You better not violate the edict of flat on-axis and smooth early reflection directivity easily.

Knowing what I know know, I would not remotely use the NHT M-00 relative to JBL 305P Mark ii. The difference in overall fidelity and pleasantness is immense. So don't go looking for used NHT M-00. I would have given it a cut-off-head panther award but I want us to get more experience with other speakers to know whether it ranks at the bottom or not.

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

I feel so poor I had to winterize our RV (camper) myself instead of having someone else crawl under the darn thing. I hope you feel sorry enough for me to donate generously using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/
The color polar plots are impossible for the color blind to read. Please keep the 2D B&W SPL Horizontal and Vertical.

I am disappointed you removed the curves for each early reflection. These give details that cannot be seen in the composite early reflection curve. These have never been published before. For those of us who have studied the CEA-2034 results for years these added curves provide fascinating details on the composition of the total early reflection curve.

As a minima the I would ask you to keep the total vertical and horizontal reflection curves which can be very different yet average to a similar looking total early reflection curve.

If you test a speaker with the drivers not placed in vertical alignment you will need the SPL Horizontal at + and – angles since they will no longer be symmetric.

It would be useful if you could present the SPL Vertical as 2 graphs. One for positive angles and one for negative angles. This gives more insight on crossover performance. Angles larger than +/- 20 degrees are not typically presented in SPL Vertical plots.

These SPL Vertical curves are more typically present with 5 degree increments. The difference listener position (sitting or standing) changes in 5 degree increments especially when the height of the listener is considered.
 

Blumlein 88

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As Amir noted in this review. You don't need all that many graphs to separate the wheat from the chaff. This one chart will do that once you know what the various lines are showing you and how they fit together. You'll want an in room response too.
1578902534571.png

1578902623673.png



Since Amir asked, I prefer this type of graph over the colored polar plots.
1578902833375.png


I agree with Authur Edwards about liking the curves showing each early reflection separately. Perhaps you can include these extras as an attachment to the posted measurement review. You get to keep just the essential stuff shown so it isn't so cluttered, and those wanting to delve deeper can get the extra info from the attached file(s).
 
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JustIntonation

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Just a bit curious what you refer to as the "bass" frequencies.
I personally say 20-200Hz is bass, 200-2000Hz is mids, 2000Hz - 20kHz is treble. So instead of a bass suckout between 200Hz-900Hz I'd say that is lower mids?
Btw, Wikipedia defines bass as 16Hz-256Hz. (and treble as 2048 - 16384Hz)
 

Krunok

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First let me say these speakers measurements are extremely interesting and usefull, thank you for that!

I have question here: how comes that Early reflections DI doesn't show dip at 4kHz? As value of Listening window at 4kHz is app 73dB and value of Early reflections is app 72dB I would expect Early reflections DI to drop to a value of 1 at 4kHz, but it is not so. How comes?

Btw, as bass suck out from 200 to 900Hz exists in all 3 (4) curves would you say it can be corrected via EQ? Following that logic dip at 4kHz seems more problematic..


NHT M-00 Powered Studio Monitor Speaker CEA-2034 Spinorama.png
 

daftcombo

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Thanks Amir for the great review once again!
 

JustIntonation

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First let me say these speakers measurements are extremely interesting and usefull, thank you for that!

I have question here: how comes that Early reflections DI doesn't show dip at 4kHz? As value of Listening window at 4kHz is app 73dB and value of Early reflections is app 72dB I would expect Early reflections DI to drop to a value of 1 at 4kHz, but it is not so. How comes?


View attachment 45674
It's because the crossover (at that freq) is not in phase on axis (part cause of the dip), the tweeter doesn't beam at that freq and (less) because of edge diffraction effects which change under angle. So the response is different under different angles particularly at that (crossover) freq.
 

Francis Vaughan

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Data presentation is hard. You can make a career out of it all by itself.

Personally I find the coloured polar plots easy to read, and hate jumbled overlapping graphs where you simply cannot untangle what is going on. That said, the polar plots look a lot as if they were generated with about three lines of Python using matplotlib. Creating more useful/readable data plots with modern tools could be looked into. One assumes that there is raw data to be had. Perhaps making some of it available could encourage some of us to have a play with more interesting representations.
 
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Krunok

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It's because the crossover (at that freq) is not in phase on axis (part cause of the dip), the tweeter doesn't beam at that freq and (less) because of edge diffraction effects which change under angle. So the response is different under different angles particularly at that (crossover) freq.

It is hard to speculate about reason for 4kHz dip in Listening window response without even knowing where XO is, but my question was why Early reflection DI doesn't show that same dip as Sound power DI does?
 
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JustIntonation

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I hope in the future we can see calibrated distortion measurements as well. Including IMD measurements. And are detailed waterfall plots a possibility with your measurement system to identify cabinet resonances etc?
In addition, a description of the audibility of ports / passive membranes / transmission line etc and measurements of port noise / resonances / changing response at different SPL would be good as these are important regarding soundquality too.
 

JustIntonation

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That would be my guess as well, but my question was why Early reflection DI doesn't show that same dip as Sound power DI does?
This is the question I answered.
At certain different verticle angles the drivers will be more in phase at that freq and add up better, also the tweeter start beaming a bit above that freq and the mid beams below that freq so at off-axis the freq that has the dip doesn't drop in volume while it does above and below that freq, and edge diffraction can be part of the cause of that dip which will be different at other angles. So all in all this causes that freq to not dip any further at the particular weighted average taken for the first reflections response (while other frequencies above and below it do drop).
 

Krunok

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This is the question I answered.
At certain different verticle angles the drivers will be more in phase at that freq and add up better, also the tweeter start beaming a bit above that freq and the mid beams below that freq so at off-axis the freq that has the dip doesn't drop in volume while it does above and below that freq, and edge diffraction can be part of the cause of that dip which will be different at other angles. So all in all this causes that freq to not dip any further at the particular weighted average taken for the first reflections response (while other frequencies above and below it do drop).

No, you didn't. You were speculating about reasons for dip in Listening window but the problem I see is that dip exists in Sound power DI but not in Eary refelecitons DI.

As I explained in my question, as Early reflection DI is calculated as Listening window - Early Reflecions, looking at those 2 curves at 4kHz it value should be app 1 instead of app 3.5. As dip is present only in Listening window but not in Early reflections and in Sound power the same dip should exists in Early reflections DI as it exists in Sound power DI.
 

Krunok

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This is the question I answered.
At certain different verticle angles the drivers will be more in phase at that freq and add up better, also the tweeter start beaming a bit above that freq and the mid beams below that freq so at off-axis the freq that has the dip doesn't drop in volume while it does above and below that freq, and edge diffraction can be part of the cause of that dip which will be different at other angles. So all in all this causes that freq to not dip any further at the particular weighted average taken for the first reflections response (while other frequencies above and below it do drop).


Btw, that dip certainly isn't caused by phase mismatch of the drivers. This speaker has fourth order (24dB/octave) XO at 2200Hz. At 4kHz output of the woofer is attenuated app 20dB so it has no impact on FR.
 

Francis Vaughan

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If you look at the vertical plot the suck out clearly is dependant on angle, but it is messy. 4kHz is about 7cm, which suggests to me that the effect is due to a resonant interaction with the woofer cone cavity and/or cone edge.
 

JIW

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No, you didn't. You were speculating about reasons for dip in Listening window but the problem I see is that dip exists in Sound power DI but not in Eary refelecitons DI.

As I explained in my question, as Early reflection DI is calculated as Listening window - Early Reflecions, looking at those 2 curves at 4kHz it value should be app 1 instead of app 3.5. As dip is present only in Listening window but not in Early reflections and in Sound power the same dip should exists in Early reflections DI as it exists in Sound power DI.

The plotted data for the early reflections DI look quite a bit like the difference between early reflections and sound power.

Incidentally, this also seems to be the case for the measurements of the 305P. Compare e.g. at ~230 Hz right after the point where the listening window, early reflections and sound power coincide. While the early reflections and sound power both fall below the listening window as frequency increases, for a short interval, they are still almost coincident while both are about 0.5 dB below the listening window. Curiously, the early reflections DI remains close to 0 while the sound power DI already has increased to about 0.5 dB.
index.php


Similarly, this seems to also be the case with the Control 1 Pro. Compare e.g. 8.5 kHz. It's similar to your observation about the NHT measurements at 4 kHz.
index.php
 

restorer-john

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Personally I find the coloured polar plots easy to read

Coloured? I'm old school, give me black and white polar plots. ;)

Perhaps making some of it available could encourage some of us to have a play with more interesting representations.

Those psychedelic, LSD inspired, infra-red heat map style representations are bad enough, what have you got in mind?
 

Wombat

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Coloured? I'm old school, give me black and white polar plots. ;)



Those psychedelic, LSD inspired, infra-red heat map style representations are bad enough, what have you got in mind?


Yes, KISS for the majority of members.

Amir, you have to realise that the average member has no way of understanding what those AP and Klippel plots mean. Maybe possibly in the earlier days, but certainly not now.
 

daftcombo

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It's because the crossover (at that freq) is not in phase on axis (part cause of the dip), the tweeter doesn't beam at that freq and (less) because of edge diffraction effects which change under angle. So the response is different under different angles particularly at that (crossover) freq.
Your explanation may be right, but it doesn't corroborate what Amir wrote in the JBL 305p mkII review:
The more useful of the two in my opinion is the dashed blue with is the early reflection index. It is the difference between listening window and early reflection graphs.
 
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