• WANTED: Happy members who like to discuss audio and other topics related to our interest. Desire to learn and share knowledge of science required as is 20 years of participation in forums (not all true). Come here to have fun, be ready to be teased and not take online life too seriously. We now measure and review equipment for free! Click here for details.

Polk Monitor 40 Series II Review (Speaker)

amirm

Founder/Admin
Staff Member
CFO (Chief Fun Officer)
Joined
Feb 13, 2016
Messages
33,680
Likes
117,916
Location
Seattle Area
#1
This is a review and detailed measurements of the Polk Monitor 40 Series II bookshelf "MTM" speaker. It is on kind loan from a member and costs US $200 on Amazon for a pair including Prime shipping.

The Monitor 40 looks pretty decent for such a budget speaker:

Polk Monitor 40 Series II Review Bookshelf Speaker.jpg


After decades of surviving in brutal consumer market for speakers, Polk knows what it is doing here. And that involves super lightweight design and shoddy construction that allowed the front baffle completely separate itself from the enclosure in shipping!

Polk Monitor 40 Series II speaker teardown drivers.jpg


They have a rabbet all around which provides for large surface area for the glue and air tight construction. Why did they resort to these wedges that gave out due to weak fibers in the MDF? A couple of screws would have helped keep it there as well.

At least there is some foam inside:
Polk Monitor 40 Series II speaker teardown port.jpg


They put money toward bi-wiring terminals that no one uses but likely checks a box for marketing:

Polk Monitor 40 Series II Review Bookshelf back panel Speaker.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.

I performed over 1000 measurement which resulted in error rate of less than 1% or so.

Temperature was 68 degrees F.

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.

Reference axis was the tweeter center.

Polk Monitor 40 Series II 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:

Polk Monitor 40 Series II Frequency Response Measurements Bookshelf Speaker.png


Lots of issues here starting with tweeter frequency not being flat and elevated. The woofers are getting more directional before tweeter takes over and presents a wider dispersion. Near-field measurement shows the many flaws:

Polk Monitor 40 Series II near field Frequency Response Measurements Bookshelf Speaker.png


We clearly see the issues with the tweeter but also the port letting out a resonance right at the crossover. The woofers are allowed to play up to 5 kHz making me wonder if the filter for it has too little slope.

Early window response has no choice but to be messy:

Polk Monitor 40 Series II Early Window Frequency Response Measurements Bookshelf Speaker.png


Summing these produces an estimated response in your room that is likely to be quite bright:

Polk Monitor 40 Series II Predicted In-room Frequency Response Measurements Bookshelf Speaker.png


Bass response is low which helps keep distortion in check especially given the dual woofers:
Polk Monitor 40 Series II Distortion Percentage Measurements Bookshelf Speaker.png


Polk Monitor 40 Series II Distortion THD Measurements Bookshelf Speaker.png


Horizontal beam width is not pretty as we could already guess from the spin graph:

Polk Monitor 40 Series II horizontal beam width Measurements Bookshelf Speaker.png


Polk Monitor 40 Series II horizontal directivity width Measurements Bookshelf Speaker.png


I think this is the first MTM configuration speaker we have tested so its classic dispersion is nice to see:

Polk Monitor 40 Series II vertical directivity width Measurements Bookshelf Speaker.png


Edit: forgot the impedance and phase:
Polk Monitor 40 Series II Impedance and phase Measurements Bookshelf Speaker.png



Polk Monitor 40 Series II Listening Tests
Oh wow, this speaker is bright! High frequency notes literally jump out of the speaker and meet you half way! I must say, I can see the appeal of that in a showroom and with casual listeners. Bad choice to throw at me though as I am super sensitive to high frequency accentuation (spent so much time training to hear distortion in them). So I had to pull out the parametric EQ tool in Roon right away:

Polk Monitor 40 Series II speaker equalization eq.png


This is a quick and dirty correction to make the sound bearable. It was still bright but likely if you add a sub, it would balance it out.

Power handling was excellent because there is essentially no sub-bass reproduction so my killer tracks of this kind did not do much to Monitor 40.

Conclusions
The Polk Monitor 40 Series II is a great example of what you have to do to bring the cost down to crazy low yet keep the showroom appeal high. is this the most broken thing Polk could design? No, that would require a lot of distortion as well which I did not find. Still, without equalization and lots of playing around with that I don't see this being a useful speaker to live with, monetary savings be damned. Eat less outdoors, save the money, and buy something better please!

I can not recommend the Polk Monitor 40 Series II.

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

Had a miserable day yesterday. Why is it that all plumbing work is hell? We spent a fortune to have a yard guy dig trenches in our orchard for sprinklers. We were not here to watch the guy and he used the thinnest PVC tubes he could to save money -- much like Polk above. Worse yet, didn't know much about plumbing and created many sources of water leaks. This is the second time I have had to dig a ditch 3 feet down in thick mud and clay. :( I could barely expose the failure point and have to dig more to make space to fix it. So more muddy miserable days are awaiting me until I get this thing fixed....

Appreciate any donations using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/
 

Attachments

Last edited:

richard12511

Major Contributor
Forum Donor
Joined
Jan 23, 2020
Messages
3,569
Likes
4,929
#4
Hmm, doesn't look terrible, but also definitely not good.
 

Tks

Major Contributor
Joined
Apr 1, 2019
Messages
2,688
Likes
4,202
#5
Disappointing that polk produces some decent speakers at the high end, and this poor one as well. They know what is right, and choose not to apply it here.
They do? By what metric?
 

dfuller

Major Contributor
Joined
Apr 26, 2020
Messages
1,125
Likes
1,366
#10
At some level, I can't expect much for $200/pr. At another, even going $100 more gets you something substantially better in the JBL A130.

Related - @amirm when you had it open you didn't happen to take a peek at the crossover did you? I bet a fair bit of this could be improved just by fixing the woofer filter and padding down the tweeter a bit (L-pad maybe?).
 

restorer-john

Major Contributor
Joined
Mar 1, 2018
Messages
7,093
Likes
18,040
Location
Gold Coast, Queensland, Australia
#11
Definitely one for gr reserch to sell tube connectors
And upgrade the crossover, wiring, both woofers and a new tweeter. Oh, and mod all the interior panels with damping material. ;)
 
OP
amirm

amirm

Founder/Admin
Staff Member
CFO (Chief Fun Officer)
Joined
Feb 13, 2016
Messages
33,680
Likes
117,916
Location
Seattle Area
Thread Starter #13
Related - @amirm when you had it open you didn't happen to take a peek at the crossover did you?
I didn't, sorry. :) Was in a hurry to repair it so I could measure it. Thought the one picture would show it but realized today it was covered by the padding.
 

dfuller

Major Contributor
Joined
Apr 26, 2020
Messages
1,125
Likes
1,366
#17
I didn't, sorry. :) Was in a hurry to repair it so I could measure it. Thought the one picture would show it but realized today it was covered by the padding.
Found a schematic on Parts Express. I think I understand why the tweeter is so hot... I think if you added another resistor with R1 and made an L-pad you could reduce the level without substantially changing the impedance. As for the woofers, that roll-off doesn't seem right to me for a 2nd order electrical filter.
1623459231312.png
 

bequietjk

Senior Member
Joined
Jan 4, 2019
Messages
339
Likes
371
#19
'Back in the day' when I used to work at Fry's in 2012 I never really liked to demo Polk speakers. They sounded decent in the store but for the most part imo could not compete with some of the other options like Infinity.

However, I LOVED the Polk MM series car audio speakers. They could take a beating and sounded real good during closing shifts :]
 

YSC

Major Contributor
Joined
Dec 31, 2019
Messages
1,252
Likes
849
#20
Nice looking but kind of poor performance … should sound kind of ok off axis which tend to roll off highs a bit with directivity though. I bet those who buy this is likely to not point the speakers towards their ears and listen off axis
 
Top Bottom