Polk S30 Center Speaker Review

[richard12511]

For sub users, where bass performance is mostly not needed, do you think it would help to plug the port? Did you try listening with the port plugged.

Regardless, thanks for the great review. This looks like a great performer, at least in the vertical orientation) Unfortunately, I think most end users will likely use it horizontally. Actually, it may improve dialog clarity a bit for one person right in the middle, but side sit listeners will be not so happy.

 

[beaRA]

@amirm thanks for taking the time to review my speaker! Results are predictable for the most part, but a bit more positive than expected. General neutrality matches my subjective experience and the narrow dispersion is unavoidable with this driver configuration (although not the worst MTM we've seen). With how much Polk touts their "Power Port", it's odd to see so many of their speakers with a strong port resonance. Glad they finally got it worked out for the Reserve series. Did you find the port resonance distracting in your listening test? I occasionally found myself annoyed by some male voices, but I don't know if the 940Hz resonance could be the culprit.

 

[amirm]

Did you find the port resonance distracting in your listening test?

It is impossible to know the effect of such artifacts with normal listening. This is why I made an EQ for it and turned it on and off. As I noted the review, it seemed to make a distinct improvement in clarity especially in vocals.

 

[richard12511]

Surprisingly decent measurements for a low budget implementation of the per se flawed MTM configuration, a pair could be even used as a standing pseudo D'Appolito stereo setup giving added max SPL thanks to the 2nd midwoofer which can be seen also at the distorion plots:

By the way, wouldn't the red approximately -40 dB = 1% base line be better shifted on the right plot 10 dB higher?

I think he uses the same 50dB line for all speakers, though I could be wrong.

 

[amirm]

I think he uses the same 50dB line for all speakers, though I could be wrong.

I do. It is an ad-hoc threshold.

 

[beaRA]

Axes flipped:
View attachment 139133

​

Listening window much more similar to on-axis.

Is it possible to calculate the preference score for this orientation?

 

[beaRA]

It is impossible to know the effect of such artifacts with normal listening. This is why I made an EQ for it and turned it on and off. As I noted the review, it seemed to make a distinct improvement in clarity especially in vocals.

Good to know you thought it improved vocals. This center has been replaced in my main system, but I may hook it up again to see if I can discern the improvement with the port resonance knocked down.

 

[MZKM]

Is it possible to calculate the preference score for this orientation?

It’s very similar.

Now, would be interesting to see if this is 100% identical to measuring it that way (differences in diffraction maybe).

 

[YSC]

View attachment 139098

Do you want to have the blue response on the left or right? Left is using it as shipped in horizontal configuration. This is why you normally want a 3-way center speaker that would have a single mid-range producing this part of the spectrum, than dual woofers.

Hum~~ question for this one, I think placing it horizontally as in the picture at the start would be actually better?

the use case of a center speaker I can imagine is in a 3.1/6/1 surround setup, where the center speaker will be put under a TV, be it at a low bench or floor, at such, the LP is likely to be 30 degrees off center vertically than horizontally as I doubt you will sit very near to the TV and at sideway of it for comfortable viewing. and if you are sitting so sideway in a surround system the whole system sound balance will be heavily interfered by comb filtering and all sort of reflection anyway no?

 

[Kachda]

So this centerspeaker is recommending in its vertical orientation ?

 

[PraetoriansLoveMoney]

Thanks as always for the review Amir!

A few weeks ago my neighbor and I were playing around and we took two Elac Debut C6's and used them vertically as mains, we were both surprised that the sound seemed better than two Debut B6's in their normal configuration. Of course we were sitting dead center with the C6's toed in - with a sub in a 2.1 setup - and we started to wonder if you could use a pair of center channel speakers vertically. I did some research and found the Mid Tweeter Mid has been labeled a bad design for multiple reasons that people who are smarter than I have discovered so I left it there.

After reading this review and seeing the recommendation I have to wonder why speaker mfg.'s aren't building center channels that can be used vertically in pairs. I know HSU has a coaxial that can be used in either configuration but no one else does. I know they probably don't want to cannibalize their traditional models, but if two centers can sound better than two mains, why not explore that? I'm just thinking out loud so if there is a valid reason, please let me know so I can learn.

Additionally, when the center drops to 3.4 ohms of resistance how does that affect an AVR or Integrated Amp that has a factory rating of 6 ohms as being the lowest certified rating. Would prolonged exposure to repeated dips to such a low resistance damage anything or can most equipment handle this dip in resistance with no long-term ills? After reading various opinions on this matter I need some clarification because there is a lot of conflicting information out there on the web.

Thanks in advance for any information anyone can share. Also let me know if these questions have already been answered here and I will search for the information instead of asking someone to repeat information.

 

[ThatM1key]

Sale on the white only. https://www.polkaudio.com/en-us/product/center-channel-speakers/signature-s30

For the RTI/RTI A guys, this is still on-sale (Cherry only). Bigger woofers than the S30 but the S30 goes lower in bass. https://www.polkaudio.com/en-us/product/center-channel-speakers/csia6-cherry or https://www.crutchfield.com/S-kTmLtyBgTv0/p_107CSIA6C/Polk-Audio-CSi-A6-Cherry.html (Extra $10 off if you choose slower shipping on CrutchField).

 

[amirm]

So this centerspeaker is recommending in its vertical orientation ?

Nothing wrong with using it that way if you have the space. I did that with my first home theater. Projection screen was high enough that I had three MTMs vertically oriented. Mind you, you could use it in horizontal configuration just don't sit too far from the center or mid-frequencies suffer.

 

[Maiky76]

This is a review and detailed measurements of the Polk S30 center speaker. It is on kind loan from a member and costs US $229 from Amazon including Prime shipping.

Polk has really nailed the luxury look of the S series despite the budget pricing:

View attachment 139087

It actually looks better in person than the picture above. Even the back looks interesting:

View attachment 139088

This is an "MTM" design which stands for Mid-woofer, Tweeter and Mid-woofer. As you will see later, this presents some interesting radiation pattern which you want to know about in center speakers. This review is also more detailed for that reason and another to come.

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 2%. Temperature was 78 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 without the grill.

Polk S30 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:

View attachment 139089

Ignoring that bump for a second, the on axis response looks pretty good! Indeed I could see that even in the in-room measurements I make for distortion. Very nice to see attention being paid to this important aspect of speaker design. Back to the bump around 940 Hz, a near field measurement by the port shows the exact reason:

View attachment 139090

If that peak was a few hundred hertz lower, the woofer output would drawn it out but it is where crossover is acting on the woofer making the resonance be louder than its output. We will analyze this many ways through the rest of the measurements starting with our early window reflections:

View attachment 139091

Let's highlight the rear reflections (sound coming from behind the speaker hitting the wall):
View attachment 139092

So we have further proof that this is coming out the port. This is good news in a way that it will not be as strong hitting you and you can try to absorb it (but there is a better tool -- see listening section of the review).

Predicted in-room response shows that, some dipping due to directivity error and brightness:
View attachment 139093

We will qualify this through listening tests later.

As further evidence of the resonance coming out the rear, we can look at a "balloon" visualization of sound field of the speaker as we look at the side of it with tweeter pointing to the right:

View attachment 139094

The redder the color, the stronger the signal. We see the woofer on the right pumping out signal but so is the port in the back on the left. Ideally that would be in green to blue color.

As I mentioned in the intro, MTM configuration causes a problem in that the two drivers start to cancel each other out as the sound wave length approaches the distance between the two drivers and how far you are angled to left or right of the speaker. We clearly see this in the horizontal beam width narrowing:

View attachment 139095

This is a problem for a center speaker because you want to have broad coverage of seating area. With just 40 degrees to play with, you better sit pretty far to get decent width with good frequency response.

Note how the rear port resonance shows up here just the same because it spits out sound to the rear so widens the coverage there.

Horizontal directivity shows the same problem again:

View attachment 139096

But notice how much better vertical coverage is:

View attachment 139097

Alas, we don't need vertical coverage. We need horizontal. As noted, if you can do it, you should use it vertically. We can see the effect of that on frequency response at 30 degrees:

View attachment 139098

Do you want to have the blue response on the left or right? Left is using it as shipped in horizontal configuration. This is why you normally want a 3-way center speaker that would have a single mid-range producing this part of the spectrum, than dual woofers.

Dual woofers do have a benefit though in more power handling. We see that in very low distortion of the S30:

View attachment 139099

View attachment 139100

Film sound mixers usually put even effects in the center channel to "anchor" them to the screen so that channel works very hard. As such you need good power handling and low distortion which the S30 delivers.

Our impedance graph shows our port resonance and others:

View attachment 139101

It also says the "8 ohm" spec from the company is fantasy. In reality, it dips below 4 ohm. Fortunately efficiency is good so you shouldn't have a lot of problem driving it with mass market AVRs.

I usually don't post CSD/Waterfall graphs for passive speakers but to nail the coffin on resonances , here it is:

View attachment 139102

See how we can nail the story of a speaker from multiple angles and arrive at high accuracy conclusions?

Polk S30 Listening Tests and Equalization
I placed the S30 in my usual listening location in far field. I didn't need to play more than a clip or two to realize that on-axis, this is a very good sounding speaker. The nearly flat on-axis response is a great filter that separates good speakers from poor. Wanting to hear the effect of that resonance, I dialed in an EQ at its frequency:

View attachment 139103

The effect was subtle and most resulted in better clarity but was low enough that could be an error. Still, I tried it a few times blind and preferred removal of it. The overall tonality a bit bright on some tracks so I put in a quick shelving filter. As usual, you should use EQ to implement a sloping down target response for your system and adjust this to taste.

I placed the speaker on its side and enjoyed its high dynamic range. It has nice tuning of bass frequencies in that it doesn't reproduce sub-bass that makes other speakers distort easily. This may be the reason the highs stand out a bit more than they would otherwise.

Conclusions
The Polk S30 presents a good design with two clear flaws, one architectural and the other, implementation. The former being the classic MTM horizontal cancellation and the latter, the resonance in the enclosure escaping from the port. You can deal with the MTM issue by using only for a sweet spot or placing it vertically. The port resonance can easily be fixed with EQ.

Overall, I enjoyed my time with this speaker. It is a lovely looking one despite its budget price. You could buy it and just use it as mains on its side.

I am going to put the Polk S30 Center on my recommendation list. If you use it vertically with a bit of EQ, I would upgrade that recommendation to a strong one.

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

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

Hi,

Here is my take on the EQ.

These EQ are anechoic EQ to get the speaker right before room integration. If you able to implement these EQs you must add EQ at LF for room integration, that usually not optional… see hints there: https://www.audiosciencereview.com/...helf-speaker-review.11144/page-26#post-800725

The raw data with corrected ER and PIR:

Score no EQ: 3.6
With Sub: 6.2

Spinorama with no EQ:

• large resonances
• Poor directivity in general

Directivity:
Better stay at tweeter height and azimuth.

EQ design:

I have generated One EQ. The APO config file is attached.

• The EQs are designed in the context of regular stereo use i.e. domestic environment.

Score EQ Score: 5.0
with sub: 7.4

Polk S30 APO EQ Score 96000Hz
July052021-121720

Preamp: -2.3 dB

Filter 1: ON HPQ Fc 45.40,    0.00,    1.25
Filter 2: ON PK Fc 106.00,    -2.92,    1.72
Filter 3: ON PK Fc 456.00,    -1.00,    2.72
Filter 4: ON PK Fc 603.66,    -1.43,    3.76
Filter 5: ON PK Fc 2656.42,    -2.00,    2.95
Filter 6: ON PK Fc 924.14,    -5.49,    6.39
Filter 7: ON PK Fc 1332.83,    2.00,    0.90
Filter 8: ON PK Fc 2722.07,    2.21,    1.34
Filter 9: ON PK Fc 4900.07,    -1.21,    2.34
Filter 10: ON PK Fc 7263.45,    -1.97,    0.45

Spinorama EQ Score

Zoom PIR-LW-ON

Regression - Tonal flat after EQ

Radar no EQ vs EQ score
Nice improvements but still sub par IMO.

The rest of the plots is attached.

 

[amirm]

Additionally, when the center drops to 3.4 ohms of resistance how does that affect an AVR or Integrated Amp that has a factory rating of 6 ohms as being the lowest certified rating. Would prolonged exposure to repeated dips to such a low resistance damage anything or can most equipment handle this dip in resistance with no long-term ills?

Chances of damage are exceedingly small. The amp has a protection circuit which should trigger should it get overloaded. Those 6 ohm ratings are for regulatory reasons. I test all AVRs at 4 ohm and they all do fine.

 

[amirm]

Hum~~ question for this one, I think placing it horizontally as in the picture at the start would be actually better?

the use case of a center speaker I can imagine is in a 3.1/6/1 surround setup, where the center speaker will be put under a TV, be it at a low bench or floor, at such, the LP is likely to be 30 degrees off center vertically than horizontally as I doubt you will sit very near to the TV and at sideway of it for comfortable viewing. and if you are sitting so sideway in a surround system the whole system sound balance will be heavily interfered by comb filtering and all sort of reflection anyway no?

Dialog is in the center channel so you want most clarify for that even if you sit far to the side. As to being too low, just tilt it up a bit. That is how I have my center speaker.

 

[thewas]

I think he uses the same 50dB line for all speakers, though I could be wrong.

Which doesn't make really sense though for different levels as it makes distortion at higher levels look worse than it is perceived, that's why for example a -40dB = 1% line is more often used.

 

[voodooless]

So this centerspeaker is recommending in its vertical orientation ?

What do you mean by “this centerspeaker”? It’s not just this center. Probably 80 to 90 % of centers available are MTM’s like this one. Very few of them employ a 2.5-way crossover that would mostly mitigate the problem. This travesty has been going on for decades and nobody seems to care..

 

[Robbo99999]

That is a nice looking speaker aesthetically, possibly the best looking one we've had on here.....I think it has some nuclear 1950's vibes combined with modern elements. Combined with generally measuring well and being quite low priced, with a few usage limitations re directivity it's a good package overall.

 

[xema]

So the mid frequency is from the port???