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KEF Q350 Speaker Review

amirm

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#1
This is a review and detailed measurements of the KEF Q350 Bookshelf/stand-mount speaker. It was purchased new by a member and kindly drop shipped to me for testing. The Q350 costs US $700 on Amazon including prime shipping.

As with other KEF coaxial speakers, the look is unique and quite attractive:

KEF Q350 Bookshelf Speaker Review.jpg


Gone are the curves of the LS50 but replaced with a rectangular box with larger woofer which should spell better bass output.

There is a port in the back and a foam plug is provided with an insert to play with level of exhaust there:

KEF Q350 Bookshelf Speaker Back Panel Port Binding Posts Review.jpg


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.

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

KEF Q350 Bookshelf Speaker CEA-2034 Spinorama Frequency Response Measurements.png


Overall on-axis is reasonably flat which is what we like to see. Bass response is stepped though, being much higher above 100 Hz. There are two problematic resonances at 700 and 1.2 kHz as noted. Maybe we can see those in the waterfall plot:

KEF Q350 Bookshelf Speaker CSD waterfall Measurements.png


A kink in the impedance flat around 650 Hz confirms the issue there:

KEF Q350 Bookshelf Speaker Impedance and phase Measurements.png


On the good news front, directivity (now good on and off-axis response are) is quite good resulting in reflections that more or less mirror on-axis response:

KEF Q350 Bookshelf Speaker CEA-2034 Spinorama Early Reflections Frequency Response Measurements.png


Putting all of this together, this is our predicted response in a typical room:
KEF Q350 Bookshelf Speaker CEA-2034 Spinorama Predicted In-room Frequency Response Measurements.png


Directivity plots in both horizontal and vertical are rather pretty, courtesy of that coaxial driver:

KEF Q350 Bookshelf Speaker Horizontal Directivity Measurements.png



KEF Q350 Bookshelf Speaker Vertical Directivity Measurements.png


Notice however that horizontal directivity is narrow in the low to me frequencies.

Here is our distortion and in-room response with or without plug:

KEF Q350 Bookshelf Speaker Distortion THD 86 dB Measurements.png


I tried stuffing the plug half way and then all the way but it made next to no difference. The plug is pretty porous and I could tell it reducing the port action but definitely doesn't plug it fully.

Above was at 86 dB. Boosting to 96 dB creates tons more distortion:

KEF Q350 Bookshelf Speaker Distortion THD Percentage Measurements.png


Subjective Speaker Listening Tests
My first impression was "blah" with sound that was rudder muddy and coming from smack center of the speaker. I first turned off my room mode EQ to give some help to 100 Hz. That helped a bit but there were still problems.

Next I attacked the two resonances with two quick filters and results were positive:

KEF Q350 Bookshelf Speaker Correction Filters Roon.png


That upper bass slight tubbiness required more work than I was willing to put in it. And at any rate, would require in-situ (in-room) measurements to proper correct.

With the two quick filters in place, the sound became pleasant but I could not get past the point focus of it. The optical bias is strong here so may be in a blind test it won't stand out as much. But I think narrow directivity from 500 to 1000 Hz may be at fault here. For new readers, my testing is in mono (one speaker to the left).

Conclusions
There is clear engineering effort here to produce a speaker with good objective metrics. Alas, the upper bass boost may not work for everyone and lack of control of the two resonances has a high impact on clarity and detail. Directivity control due to coaxial driver seems to create a much more of a point source which many people think they like, but was not my cup of tea.

So, reasonably good objective measurements but doesn't do it for me. I can't recommend the KEF Q350 despite its positive attributes.

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

Going to run off to dig more ditches for tomato plants. I think I am up to 60 plants! I don't do anything half-way. :) When I come back with another back pain, I hope there is more money in my pocket form you all's donations : https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/
 

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q3cpma

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#2
> reasonably fat on-axis
Get ready to be stormed by fat activists. Looks like you duplicated the PIR graph.

Thanks again for the two THD curves, really gives a good idea. If only Klippel could be automated to do three or four, it'd be superb.
On the THD subject, even at 86 dB, this isn't as good as it could be. Maybe the model is gimped in favour of the more expensive range, as I can't imagine KEF not being able to solve these resonances.
 
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amirm

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Thread Starter #3
> reasonably fat on-axis
Get ready to be stormed by fat activists. Looks like you duplicated the PIR graph.
Fixed. :)
 
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amirm

amirm

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Thanks again for the two THD curves, really gives a good idea. If only Klippel could be automated to do three or four, it'd be superb.
I actually created an automation based on input voltage to the speaker (can't do SPL as that is manual). I have run it from 1 to 10 volts. I will create a separate thread for it later to see if someone can take all that data and create graphs for us.
 

q3cpma

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I actually created an automation based on input voltage to the speaker (can't do SPL as that is manual). I have run it from 1 to 10 volts. I will create a separate thread for it later to see if someone can take all that data and create graphs for us.
Now that's nice. Personally, I felt that an accurate THD:SPL graph was the missing link to properly show power handling.
 

GelbeMusik

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#13
… it seems that discrepancy between speaker's preference score and our host's listening impressions is growing.
There is a predicted in-room response from the spinorama. Doesn't it look quite different from what the measurement titled "distortion and in-room response with or without plug" shows? I've noticed the measuring distance, yes. The evaluating procedures within the spinorama might assume a special, specified room, a particular listening distance, some toe-in or not, and so forth. Only that the actual measurement @1m indicates the muffled sound as was subjectively found.
 

hardisj

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#16
Here is our distortion and in-room response with or without plug:



I tried stuffing the plug half way and then all the way but it made next to no difference. The plug is pretty porous and I could tell it reducing the port action but definitely doesn't plug it fully.

Question/Caution here:
Your graphic says "near-field". With the port being at the back a near-field measurement will likely not be able to sum with the woofer response at the typical near-field distance (distance << speaker size). For this kind of comparison you should be measuring the response in the farfield (or have the NFS measure and extrapolate).
 
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amirm

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Thread Starter #17

hardisj

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#18



Not a fan of this response. We've definitely seen better.

People lost their minds when the Buchardt S400 had a high-Q resonance at ~500hz and that had a Q of about 15. The first peak in the Kef Q350 is at about 700hz with the -3dB points at about 600 and 800hz. That's a Q of about 3.5. Ruh-roh. I expect no less than 15 pages of people arguing over what the culprit of this is. ;) :D

The steep drop in the low bass, even though it is probably an octave lower than where most would cross it over to a subwoofer may cause some trouble unless you have in phase matching the response in the 40-50hz region. Again, depending on where you cross your subwoofer.
 
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amirm

amirm

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Question/Caution here:
Your graphic says "near-field". With the port being at the back a near-field measurement will likely not be able to sum with the woofer response at the typical near-field distance (distance << speaker size). For this kind of comparison you should be measuring the response in the farfield (or have the NFS measure and extrapolate).
That is why I noted it on the graph. NFS could do it but I would not want to run it for another 2 hours just for this purpose. :) Stereophile has an approximation of it.
 

Thomas savage

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#20
Not American enough! :D It must only sound good to people who drive on the wrong side of the road, me thinks. :D:D
Maybe if KEF get bought out by Samsung you'll like it better.
 

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