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:
And interesting cover an an inside out horn of some type adorns the rear port:
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:
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:
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:
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:
The horizontal beamwidth shows the directivity error we talked about:
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:
And vertical:
Speaker Distortion Measurements
Comparing 86 and 96 dB SPL in room we get:
It is common for bass distortion to heavily increase with level but those spikes between 500 and 1 kHz are excessive:
Looking at driver components near-field we get:
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:
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.
-----------
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/
If I did not tell you the price, you would think the S15 retails for $1000 given its very nice and "high-end" looks:
And interesting cover an an inside out horn of some type adorns the rear port:
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:
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:
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:
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:
The horizontal beamwidth shows the directivity error we talked about:
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:
And vertical:
Speaker Distortion Measurements
Comparing 86 and 96 dB SPL in room we get:
It is common for bass distortion to heavily increase with level but those spikes between 500 and 1 kHz are excessive:
Looking at driver components near-field we get:
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:
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.
-----------
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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