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Polk Audio Signature S15 Speaker Review

amirm

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This is a review and detailed measurements of the Polk Audio Signature S15 bookshelf speaker. It was kindly sent to me by a member for the review and costs US $229 per pair.

If I did not tell you the price, you would think the S15 retails for $1000 given its very nice and "high-end" looks:

Polk Audio Signature S15 Bookshelf Speaker Review.jpg


And interesting cover an an inside out horn of some type adorns the rear port:

Polk Audio Signature S15 Bookshelf Speaker Back Panel Binding Posts Review.jpg


There is a genius at work getting a budget speaker to look this interesting and differentiated from a massive crowd of 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 an anechoic chamber. In a nutshell, the measurements show the actual sound coming out of the speaker independent of the room.

I used over 800 measurement point which was enough to compute the sound field of the speaker within 1% to 2% error.

Temperature was 81 degrees. Measurement location is at sea level so you compute the pressure.

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.

Spinorama Audio 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 Audio Signature S15 Bookshelf Speaker Measurements.png


We would like on-axis response (in black) to be flat and smooth which it is not here. We have peaking especially around 1 kHz and rising level in treble. There is also directivity error meaning the woofer beam gets narrow before handing off sound duty to tweeter which has a wide beam at the same position (hence the dip in solid red line at the bottom). This causes off-axis response to vary form on-axis making the speaker more room dependent.

Early reflections -- if one excludes the directivity error -- is not bad:

Polk Audio Signature S15 Bookshelf Speaker Spinorama Early Reflections Frequency Response  Mea...png


For a lot of speakers of this type it is best to have absorption on the floor (thick carpet) and high ceiling -- both of which I have in my room. That helps reduce that directivity error.

Combining everything we get this predicted response in our simulated room:

Polk Audio Signature S15 Bookshelf Speaker Spinorama Predicted In-Room Frequency Response  Mea...png


How to draw that line is tricky but assuming you go with what I have done, speaker will likely be bright and have too much energy in lower midrange/upper bass (I use the terms interchangeably).

Impedance is a low 3.7 ohm so be prepared to have good amplification that can tolerate such:
Polk Audio Signature S15 Bookshelf Speaker Impedance and Phase Measurements.png



The horizontal beamwidth shows the directivity error we talked about:

Polk Audio Signature S15 Bookshelf Speaker Beamwidth Measurements.png


The tweeter starts to "beam" (its response narrows) as frequencies get high. So definitely not a textbook response we like to see (which would be horizontal red line).

Same in 3-D heatmap:

Polk Audio Signature S15 Bookshelf Speaker Horizontal Directivity Measurements.png


And vertical:

Polk Audio Signature S15 Bookshelf Speaker Vertical Directivity Measurements.png


Speaker Distortion Measurements
Comparing 86 and 96 dB SPL in room we get:

Polk Audio Signature S15 Bookshelf Speaker relative distortion Measurements.png


It is common for bass distortion to heavily increase with level but those spikes between 500 and 1 kHz are excessive:

Polk Audio Signature S15 Bookshelf Speaker distortion Measurements.png


Looking at driver components near-field we get:

Polk Audio Signature S15 Bookshelf Speaker Woofer Tweeter Port Frequency Response Measurements.png


Seems like the disturbances in on-axis response are due to resonances from the port.

There is some attempt to roll off the highs above 12 kHz or so. This means if they wanted, they could have brought the level down earlier so likely they want the accentuated highs (to sell better in a showroom).

I am leaving out the CSD/waterfall plot.

Speaker Listening Tests
I listened to S15 without looking at the measurements. Immediate impression was accentuated upper bass which showed up in tubby electronic drums in the first track I played (I call anything in hundreds of hertz "upper bass"). In addition, there was brightness especially in female vocals. This was with the speaker directed at my ears. Having it toe out more helped a bit but not enough to get rid of brightness.

I tried some EQ by trying to fill in the holes and that naturally did not work due to the problem being directivity error. So I decided to pull the extra energy down instead:

Polk Audio Signature S15 Bookshelf Speaker Equalization.png


This worked well although the shelving filter is a poor choice here (you want a gradual rolling off filter which Roon does not have). Once there, there was still a hint of brightness in female vocals which I did not like but otherwise, good improvement.

Note that I find having too much energy around 1 kHz is better than not enough. It creates some extra "life" there as opposed to recessing the tones in that important region.

What was super impressive about this speaker is its bass response and ability to play loud. Despite using just one speaker, the S15 had no problem with my super low bass track. I could turn it up without the woofer bottoming out to exceedingly loud level! I don't think I have had a speaker this size at any price play bass so well!

Conclusions
I must confess I expected a mess when I went into this review given the aggressive retail focus Polk has. Perhaps it was based on that expectation that I did not find the measurements defects as bad as I would normally assume. Subjectively even without EQ, the very nice bass response creates a nice experience. The exaggerated highs did get to me so it is not a speaker I would buy. But I can see the appeal of it when combined with bass response.

Given the incredible looks and build quality, combined with speaker's amazing bass reproduction, I am going to marginally put the Polk Audio Signature S15 on my recommended list.

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

The panthers want to have a pool party before the summer ends. They have been shopping for all kinds of fancy bathing suites and pool toys. I keep telling them I don't have money for that stuff but they show me their teeth as to what they could do to me if I don't go along. So, for my safety, please donate what you can to buy what they need using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/
 

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ROOSKIE

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Not bad for what I imagine is the intended market.

I had the bigger version, the S20 around for a few weeks and listened quite a bit to it. It was very decent. Same as with this S15 the S20 could hit bass hard and play loudly with basically good balance. Just don't toe it in much if at all.

I took the S20 apart and it was well built for the class ($200-400). I paid $150 from Adorama on holiday special so it was very low cost at that time.
 

Blumlein 88

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Lol imagine if Stereophile awarded marginal recommendations.
Well they do have A thru D classifications of recommended gear.

Maybe Amir could further divide up his reviews by varying the level of pinkness in the panther. Hot pink for the best down to a very washed out barely pink for marginally okay gear.
 

gvl

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Would they be a good choice for desktop use/nearfield?

Port cover is likely to allow mounting directly to the wall, neat.
 

Francis Vaughan

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The port cover and mount hole seems to suggest a clear intent that this is for wall mounting. But no mechanism to correct for bass response when wall mounting makes this a bit difficult to judge. Given the constrained geometry inherent in mounting on a wall, the actual listening experience might be a trifle underwhelming. Still very hard to imagine passing up the JBL 305P mkII for anything else in its class.
 

Beave

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The port cover and mount hole seems to suggest a clear intent that this is for wall mounting...

Practically all of Polk's recent non-tower speakers have had similar port covers on the back, so it isn't indicative of them being designed for wall mounting.
 

restorer-john

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The port cover and mount hole seems to suggest a clear intent that this is for wall mounting. But no mechanism to correct for bass response when wall mounting makes this a bit difficult to judge.

Isn't it a moulded inverted diffuser over the port (behind the plate) with exit slots top, bottom and on each side?

Polk call it a "power port".

1597903366516.png


edit: it is.
 
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Francis Vaughan

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Practically all of Polk's recent non-tower speakers have had similar port covers on the back, so it isn't indicative of them being designed for wall mounting.
The hook hole OTOH looks pretty much like it is. My point is that they can't have it both ways. One feels pretty sure the motivation for the design of the back plate is partly to allow for effective wall mounting. A diffuser function is reasonable, and has a long history. Interesting to see it resurface.
 
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amirm

amirm

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?
When you Google ”Polk S15”, the first link is to the Amazon page (~$221 currently), it is also on Crutchfield.
Somehow I missed the Amazon one. I corrected the review.
 

uwotm8

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If I did not tell you the price, you would think the S15 retails for $1000
Excuse me, but it looks cheaper than a typical extremely cheap junk speaker. Dat shiny plastic face... Shiny plastic drivers... Ohh
Worse than JBL 3 series and a lot of micro-hi-fi system stock speakers, the impossible things done here:oops:
These "brutal" screws also, Polk please.
 

carlosmante

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daftcombo

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This worked well although the shelving filter is a poor choice here (you want a gradual rolling off filter which Roon does not have). Once there, there was still a hint of brightness in female vocals which I did not like but otherwise, good improvement.
Thanks Amir for the review!
Can't you use something like a Peak EQ, - 5 dB, Q=1, centered around 25 kHz, to create a slow roll-off filter in Roon?
 
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