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NHT Pro M-00 Powered Monitor Review

Francis Vaughan

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#41
Those psychedelic, LSD inspired, infra-red heat map style representations are bad enough, what have you got in mind?
Minimally choosing better colours. :) Psuedo 3d shaded greycale maybe. But there is a lot that can be done with the huge amount of data the Klippel system must generate. A tool like Bokeh brings an entirely new aspect to the game - you can make 3D dynamically interactive data presentations that are rendered in your browser.

I suspect that as more speakers are tested we will start to actually be able to do more than just test and rate them. There will be new insights generated. Getting into the data is a huge part of doing this. The site's name is Audio Science Review. Time for some of that science.
 

Krunok

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#42
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.


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.
Exactly - for that reason I'm wondering if this is some kind of a mistake in a setup.
 

Krunok

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#43
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.
Do you really think that woofer cone cavity and/or cone edge can cause such dip at 4kHz? If that would be the case wouldn't that happen with all similar designs?

Anyway, my question was not about the cause of the 4kHz dip but about the fact that Early reflection DI doesn't seem to be calculated as Listening window - Early reflections.
 

JIW

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#44
Exactly - for that reason I'm wondering if this is some kind of a mistake in a setup.
I have found some more data (from Harman, no less) from a Klippel measurement system that shows the same for Revel Performa F228Be. Look eg. at 1.5 kHz. Source.


This suggests that the Klippel software calculates the early reflections DI wrongly as early reflections less sound power rather than listening window less early reflections.
 

Krunok

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#45
I have found some more data (from Harman, no less) from a Klippel measurement system that shows the same for Revel Performa F228Be. Look eg. at 1.5 kHz. Source.


This suggests that the Klippel software calculates the early reflections DI wrongly as early reflections less sound power rather than listening window less early reflections.
Yep, that was my original point. This is how it is supposed to be calculated, hence the similar shape of both curves.

DI.png
 

JIW

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#46
Yep, that was my original point. This is how it is supposed to be calculated, hence the similar shape of both curves.

View attachment 45684
No, those data share the same defect. Compare to the other measurements at about 230 Hz as I mentioned in my previous post.

For a proper calculation, here is Harman's own measurement for the LSR305. Compare again at about 160 Hz. It is similar to @amirm's measurements at 230 Hz. Source.


Further, here is Harman's own measurement for the Revel Performa F208. Look eg. between 1-5 kHz. Source.
 

Krunok

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#47
No, those data share the same defect. Compare to the other measurements at about 230 Hz as I mentioned in my previous post.

For a proper calculation, here is Harman's own measurement for the LSR305. Compare again at about 160 Hz. It is similar to @amirm's measurements at 230 Hz. Source.


Further, here is Harman's own measurement for the Revel Performa F208. Look eg. between 1-5 kHz. Source.
I was referring to the text, not the curves. :)

Yes, the same defect is present in 305 Mkii measurement as well. It really looks like Klippel is doing it wrong. ;)

JBL 305p MKii.png
 

Shadrach

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#48
Thanks for the review amirm.
I found this review easier to make sense of. I've been doing a bit of reading which helps a bit.
 
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#49
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.
Sorry, I wasn't very attentive earlier.
Had a better look and the dip seems to be caused by edge diffraction.
Also misunderstood what you wrote. The dip isn't present in early reflections indeed. It is present in the sound power directivity index. And it isn't present in early reflections directivity index (the blue dotted line in the bottom). I'm not sure what the early reflections directivity index is exactly representing but it's safe to say it isn't the sound power directivity index - (minus) early reflections. I'm guessing it represents the directivity index of the sound in a room. The grey dotted line is the directivity index offset which I have no idea what it's supposed to mean.
 

Krunok

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#51
Most important part of the review- the wife could tell the difference immediately. Why have you not utilized her in your DAC reviews? :D
In a properly conducted "wife test" wife should be able to tell the difference from the kitchen, not from LP. But this is certainly a good start! :D
 
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restorer-john

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#53
I can't believe the dearth of technical details companies like Yamaha in the 70s and 80s provided in their sales information. It must have been such a terrible time for audiophiles... ;)

NS-25T. (an inexpensive two way speaker in the range)
scan423.jpg


I honestly don't know how they could have possibly made considered choices, do you?
 
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sergeauckland

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#54
I can't believe the dearth of technical details companies like Yamaha in the 70s and 80s provided in their sales information. It must have been such a terrible time for audiophiles... ;)

NS-25T. (an inexpensive two way speaker in the range)


I honestly don't know how they could have possibly made considered choices, do you?

It was a time when buyers were either knowledgeable or were impressed by detailed specifications even if they didn't fully understand them. Then the rot set in with 'subjective' reviewers like Paul Messenger who persuaded people that specifications didn't matter, and what mattered was how the product made you feel. Did your feet tap to the music?

Magazines encouraged that as subjective scribblers came cheaper than having to pay proper engineering rates for a technical review.

S.
 

anmpr1

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#55
NHT made a pretty big splash due to their 'measurement driven' designs. At least that was how it was reported. Main guy Ken Kantor had been an engineer at Acoustic Research (how many folks who later made their own branded speakers migrated from AR!). For the times NHT had mostly good reviews. I was living in Central Florida when NHT had been purchased by an outfit in the Lake Mary area (north of Orlando) called Recoton. They sold car audio accessories, Discwasher record things, and NHT speakers out of their warehouse. You could buy NHT for give-away prices back then. "Stack 'em High and Watch 'em Fly... Stack 'em Deep and Sell 'em Cheap" was sort of their unofficial motto.

I see they now sell factory direct. Not too expensive. Not too cheap. I have no idea about them today, but my guess is that they are decent value. I'm not sure why anyone would buy NHT over any other comparable brand. It's really hard to buy a horrible speaker anymore. Not like it was when I first became interested in the hobby.

PS: from their Web it looks like their new speakers are mostly lower sensitivity acoustic suspension designs. They recommend at least 100 watts per channel minimum for their speakers (into 4 ohms). So for home theater you're going to have to have a pretty beefy set up to get these to work for you. I don't see that as a selling point for the average cat looking to set up a moderately priced home system.
 
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Frank Dernie

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#56
Yes, keep it really simple, just like they did in the 70s... ;)

View attachment 45686
These were comfortably the best speakers I had heard when I first heard them. I saved up for the NS1000M and still have the ones I bought new. The Ebony ones were too expensive but I wish I had them instead.
 

napilopez

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#57
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.
Buchardt actually does this - which I appreciated, because it shows that the ceiling and horizontal reflections are very well controlled, but the floor reflection is the biggest culprit. But yes, it's very rare to see.

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?
While distortion would be fun, it would require a totally different setup and more effort. Considering distortion accounts for a very minimal amount of user preference in studies... there's the question of whether it's practical and worth the time. Not saying no, just something to consider. He'd need to invest in new hardware, I believe., for meaningful indoors distortion data.

Waterfall plots are pretty but not necessary to identify resonances as any resonance will show up as a bump that is consistent throughout the on and off axis plots. Waterfall plots can also misrepresent the importance of some time domain data.

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).

Your explanation may be right, but it doesn't corroborate what Amir wrote in the JBL 305p mkII review:
I thought about phase too, but that doesn't make sense. When I was trying to figure out how to make my own early reflections and sound power curve, I thought I would have to include phase data but according to CTA-2034-A:

"The following composite response curves[AKA the average curves] shall be calculated. In each instance a power average of the specified magnitude responses shall be calculated. " (Emphasis mine). I took this to mean the averages ignore phase data, though someone correct me if I'm wrong.

Also, indeed:

For the purposes of this standard the Sound Power Directivity Index is defined as the difference between the listening window curve and the sound power curve. An SPDI of 0 dB indicates omnidirectional radiation. The larger the SPDI, the more directional the loudspeaker is in the direction of the reference axis.

Early Reflections Directivity Index (ERDI) The Early Reflections Directivity Index is defined as the difference between the listening window curve and the early reflections curve.

All this information is present in the CTA-3024-A Document (formerly known as CEA-2034-A), which again, is a free download.
 

Krunok

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#58
I thought about phase too, but that doesn't make sense. When I was trying to figure out how to make my own early reflections and sound power curve, I thought I would have to include phase data but according to CTA-2034-A:

"The following composite response curves[AKA the average curves] shall be calculated. In each instance a power average of the specified magnitude responses shall be calculated. " (Emphasis mine). I took this to mean the averages ignore phase data, though someone correct me if I'm wrong.
If there would be dips caused by phase cancellation between drivers that would come to play only close to XO point, which is not the case with this speaker as XO is at 2.2kHz and dip is at 4kHz. Generally speaking, why bother with phase when it's effect would show in magnitude response around XO?
 
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617

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#59
If there would be dips caused by phase cancellation between drivers that would come to play only close to XO point, which is not the case with this speaker as XO is at 2.2kHz and dip is at 4kHz. Generally speaking, why bother with phase when it's effect would show in magnitude response around XO?
I think your intuition is correct, but in extreme cases a breakup from a woofer can be well past the crossover point and still high enough in amplitude to create a dip.
 
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#60
While distortion would be fun, it would require a totally different setup and more effort. Considering distortion accounts for a very minimal amount of user preference in studies... there's the question of whether it's practical and worth the time. Not saying no, just something to consider. He'd need to invest in new hardware, I believe., for meaningful indoors distortion data.

Waterfall plots are pretty but not necessary to identify resonances as any resonance will show up as a bump that is consistent throughout the on and off axis plots. Waterfall plots can also misrepresent the importance of some time domain data.
Distortion matters a great deal of course. It determines SPL capability, how loud you can play the speakers without the sound falling apart.
The JBL LSR3-5p mkII don't go very loud for instance before distortion becomes well audible, and don't go very loud beyond that point before they fall apart completely.
And IMD is a particularly audible form of distortion which does not always go hand in hand with harmonic distortion with different drivers like it mostly does with for instance DACs.

As for box resonances and some other issues and waterfall plots. A waterfall plot will allow you to identify non-minimal phase issues that you can't differentiate based on the frequency response as it has no time information. The audibility can be much larger for such issues and they can't be EQ-ed out unlike a minimal phase driver response issue.
 
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