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Parts Express DIY C-Note Speaker Review

amirm

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#1
This is a review and detailed measurements of the Parts Express C-Note DIY Kit. It was kindly purchased, put together and shipped to me by member @Winkleswizard. A pair of these with everything you need including the cabinet "flat pack" costs just US $100. And that includes free shipping if you are in US. So quite a bargain if it performs well.

Being unfinshed MDF, there is not much to look at as far as asthetics:
Parts Express C-Note MT Bookshelf Speaker DIY Kit Review.jpg


But there are some technical points to note. First is the inclusion of a waveguide around the tweeter to bring the "directivity" (spread of the sound wave) closer to that of the woofer at crossover point (woofer gets directional there). The tweeter is also moved closer to woofer to reduce the center to center distance as to improve vertical directivity. The waveguide is NOT notched however. The woofer simply overlaps it.

The MDF cabinet felt quite stout to me both in feel and in use. There is certainly more to it than what you get in budget speakers.

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 anechoic chamber. In a nutshell, the measurements show the actual sound coming out of the speaker independent of the room.

All measurements are referenced to the tweeter axis with frequency resolution of 2.7 Hz.

Due to reduced bass response (I think), the accuracy of projected frequency response degraded a lot below 70 Hz. It was an unusual development which I think was caused both by the speaker output and longer distance I used to measure it. So don't be concerned about that portion of the graph not being as clean as it normally is.

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:

Parts Express C-Note MT Bookshelf Speaker DIY Kit CEA-2034 Spinorama Audio Measurements.png


My first reaction to the graph was "this is not good." But there are really two things that visually look bad as noted on the measurement. The bass level is generally lower and there is peaking around 700 Hz. Sensitivity is on the low side as well depending on where you draw the line (i.e. what frequency range you average).

Those issues aside, for a budget speaker the response seems reasonably flat in the critical area. Directivity is reasonable as well around crossover point.

Sum of important "early" reflections shows rather smooth response, sans the aforementioned 700 Hz resonance:

Parts Express C-Note MT Bookshelf Speaker DIY Kit CEA-2034 Spinorama Early Reflections Audio M...png


Predicted response in a simulated "average" listening room reflects what we have already learned:

Parts Express C-Note MT Bookshelf Speaker DIY Kit CEA-2034 Spinorama Predicted In-Room Respons...png


Impedance is rather high for a bookshelf speaker which is easier on the amplifier:

Parts Express C-Note MT Bookshelf Speaker DIY Kit Impedance.png


Most of the time we see impedance dips below 4 ohm.

I didn't note it on the graph but there is a "kink" in the phase and amplitude response around problematic 700 Hz. This does not show up as harmonic distortion though:

Parts Express C-Note MT Bookshelf Speaker DIY Kit Distortion Mesaurements.png


Instead we see the rising distortion at crossover point which could either be the woofer going too high, or tweeter going too low.

Here is the in-room response (of the lab) and absolute level of distortion, this time averaged to 1/20 Hz to make it easier to read:

Parts Express C-Note MT Bookshelf Speaker DIY Kit In-room Frequency Response and Distortion Me...png


You can see the same shelving of the bass response, 700 Hz boost, etc. Worst case response above 1 kHz is 40 dB below listening level.

Horizontal directivity shows that you don't want to toe in/out the speaker too much:

Parts Express C-Note MT Bookshelf Speaker DIY Kit Horizontal Directivity Frequency Response Me...png


Parts Express C-Note MT Bookshelf Speaker DIY Kit Vertical Directivity Frequency Response Meas...png


Waterfall display shows the pesky resonance at 700 Hz:

Parts Express C-Note MT Bookshelf Speaker DIY Kit CSD Waterfall measurements.png


Speaker Listening Test
I was set to not like this speaker, biased by what I saw in the spinorama and that turned out to be the case with the first female vocal track I played. The sound was a bit dull and tonally wrong for a female voice. Before going further, I thought I dial in a parametric filter around 700 Hz and see if it improves things:

Parts Express C-Note MT Bookshelf Speaker DIY Kit Parametric EQ Settings.png


That it did! Detailed improved as did tonality. I ran through a bunch of my reference tracks that sound good on my system (Revel Salon 2 speakers) and almost all translated well to this little speaker! The sound was quite enjoyable and not too bright. Interestingly, there was good bass there. Even better was the fact that this speaker could play loud, really loud. I am talking filling a very large open space with just one speaker playing and no sign of bottoming out!

I think there is something clever going on with bass here. But having it be at lower level it doesn't push the woofer hard. Indeed I could barely see it moving unlike some other speakers I have tested where the woofer cone seems to want to jettison out. Perhaps room enforcement is helping. It is certainly a deviation from "ideal measurement" that seems to work.

I should note that I was not entirely happy with the sound of female vocals at the end but with playing more with EQ you could get there possibly.

Regardless, I sat there and listened to track after track and did not want to stop. Whoever says you need two speakers to enjoy music is clearly wrong. With the right speaker response, a single one can sound really good.

Conclusions
The Parts Express DIY C-Note kit doesn't have an ideal response but seemingly what it has is very good. It can play loud in a pleasant manner with good detail and solid bass. I have tested other budge speakers but they don't play this loud and this well.

If can handle a bit of gluing and finishing, you can have a very good sounding budget speaker here.

I am going to put the C-Note on my recommended list of budget speakers.

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

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amirm

amirm

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Thread Starter #2
Here is a nice video on how to put them together:


Clever use of polyurethane "gorilla" glue to hold down the crossover. I would hate to take it apart if needed though. And this glue stains your hands so be sure to wear gloves.
 

MZKM

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#6
The issues ~800Hz do not show in the woofer driver's measurements.

The FR measurement <600Hz also don't closely match the one PartsExpress gives, and the FR+distortion measurement that this user got does match. I wonder if there is some error in the building of this model.
 
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amirm

amirm

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Thread Starter #9
The FR measurement also don't closely match the one PartsExpress gives, and the FR+distortion measurement that this user got does match
His graph has a 100 dB scale which hides some variations. And room modes are too prevalent there to trust his measurements.
 

MZKM

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#11
His graph has a 100 dB scale which hides some variations. And room modes are too prevalent there to trust his measurements.
Even if disregarding that, the FR measurement from PartsExpress has 200Hz being louder than most of the treble. Now, we don't know how they measured it, so that could be why. As for unit-to-unit variance I do not know, but Dayton doesn't show that ~700Hz resonance:
Screen Shot 2020-04-18 at 7.26.55 PM.png
 
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amirm

amirm

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Thread Starter #12
Even if disregarding that, the FR measurement from PartsExpress has 200Hz being louder than most of the treble.
They do show some wigglyness in 700 Hz region:

1587252659968.png


That aside, the very smooth response prior to that says this is a two-piece measurement which typically exaggerates low frequencies due to near field measurement.
 

617

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#15
Christ Amir, I could design such a great speaker if I had that measurement system. If there was a way to export the data into a form I can use i.cpild redesign the crossover very easily.
 

dwkdnvr

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#17
Any chance that the 700Hz problem is a port resonance? Throwing together a quick model for the DSA135, withthe 1.5" port used in the kit I can get a port resonance in that region if I tune a bit low. Pretty nasty port resonance, though.
 

Francis Vaughan

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#18
Given the success of some simple equalising one suspects that the score formula could usefully include yet another output. Score with equalisation. Not a trivial thing to compute, but in the modern world, one where just about every AVR has the ability to provide equalisation, not unreasonable. This would emphasise the balance across the polar response and de-emphasise flatness of response. But smoothness would still need to be included where it is not reasonable to tweak out irregularities. Something to ponder.

It does suggest that there is something of a sea change in the requirements of modern speaker design. It is becoming more important to get directivity under control than pure on-axis frequency response. Which is an inversion of previous practice. So long, of course, that you are not selling to the golden eared purist. It is certainly one reason why integrated powered/active speakers have a significant set of advantages in cost/performance.
 

dwkdnvr

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#19
Christ Amir, I could design such a great speaker if I had that measurement system. If there was a way to export the data into a form I can use i.cpild redesign the crossover very easily.
As you can imagine, there is a fair bit of discussion on this kit in the DIY community. I believe that the consensus was that the xover wasn't bad, and the only mod that got any traction was a .22uf cap across L2 to tame the woofer break-up a bit. That's up around 8k though - not related to whatever is going on at 700Hz.
 

JohnBooty

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#20
I've been enjoying mine for a couple of years now on my desktop. Great all around. Very similar to the JBL 3-series, though without the godlike constant directivity. Great bass down to ~40hz in a typical desktop setup where you have a wall behind them.
How many hours to build?
Anywhere from... let's say 3 to 10 hours? Depends on if you're familiar with basic soldering, and how fancy you go with the finish.

There are some drying steps involved so it wouldn't be 3-10 consecutive hours :)

At the most basic level, you could sand the MDF and spray paint it. Or throw some chalk paint on there and then give it a wax seal rub. Or at the high end you could go for true furniture quality veneer finish, or get crazy with automotive paints and 1200grit sandpaper.

The assembly video Amir linked to above should give you a good idea what you're in for. On the product page, PartsExpress also gives you a PDF manual that lists additional supplies (wood glue, etc) that you'll need.
 
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