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Polk T15 Bookshelf Speaker Review

amirm

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This is a review and detailed measurements of the Polk T15 "Home Theater and Music Bookshelf Speaker." I purchased it last month. The T15 is supposed to cost US $115 but I think I only paid US $70 for my pair.

With the grill removed, the T15 looks decent:

Polk T15 Bookshelf Budget Speakers Audio review.jpg

I was surprised by the quality binding posts at this price point:

Polk T15 Bookshelf Budget Speakers back panel connector Audio review.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. 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 reference to tweeter axis with the grill removed.

Over 1000 points around the speaker were measured (from 20 to 20 kHz) which resulted in well under 1% error in identification of the sound field in all but the 4 to 6 kHz where the error is about 2% Final database of measurements and data is 1.0 Gigabytes in size.

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:

Polk T15 Bookshelf Budget Speakers CEA-2034 Spinorama Audio Measurements.png


Yup. Not pretty. Horrific drop in upper mids/lower treble region of 3 to 6 kHz. This is likely due to tweeter and woofer getting out of phase and causing cancellation on-axis. We also have peaks here and there.

Zooming into directivity plot shows that on and off-axis response vary a ton:
Polk T15 Bookshelf Budget Speakers CEA-2034 Spinorama Directivity Audio Measurements.png


So how and where you listen to these speakers matters a lot with respect to the sound you get.

Computer prediction of response you get in the room is troubling of course:

Polk T15 Bookshelf Budget Speakers CEA-2034 Spinorama Predicted In-room Response Audio Measure...png


No matter which way you look at the performance of T15 speaker, it is going to be colored, modifying the intent of the content producer (who likely has a much more flat response speaker than these).

Basic Speaker Measurements
Impedance range is stated as 6 to 8 ohms which doesn't match reality:
Polk T15 Bookshelf Budget Speakers Phase and Impedance Audio Measurements.png


In low frequencies where we need power due to high spectrum of music and effects, impedance is pretty close to 4 ohm.

We also have a number of kinks in the response which typically indicates resonances. Maybe you can see them in this waterfall graph:

Polk T15 Bookshelf Budget Speakers CSD Audio Measurements.png


Distortion plot has a peak around 400 Hz:

Polk T15 Bookshelf Budget Speakers Distortion Audio Measurements.png


When I was listening to the sweeps during the measurement, I would hear a ghost of the same sweep at a higher pitch and a bit delayed.

Advanced Speaker Measurements

Floor reflections are usually not good but in this case, the off-axis is better than on-axis so they help fill that hole some:

Polk T15 Bookshelf Budget Speakers CEA-2034 Spinorama early window Audio Measurements.png


You can see why when we look at 10 degree sweeps vertically:

Polk T15 Bookshelf Budget Speakers CEA-2034 Spinorama Full Vertical Directivity Audio Measurem...png


Usually the on-axis curve in red is the top one but it is not here. The top and hence one with least droop is + and - 20 degrees or so. Best not to listen to this speaker straight on. Place it lower or higher than your ear level.

There is not much help for horizontal issues:
Polk T15 Bookshelf Budget Speakers CEA-2034 Spinorama Full Horizontal Directivity Audio Measur...png


Polk T15 Bookshelf Budget Speakers CEA-2034 Spinorama Horizontal Directivity Audio Measurements.png


Polk T15 Bookshelf Budget Speakers CEA-2034 Spinorama Vertical Directivity Audio Measurements.png


Eye-candy Speaker Measurements
The contour graphs show what we already know:
Polk T15 Bookshelf Budget Speakers Horizontal Contour Audio Measurements.png


Polk T15 Bookshelf Budget Speakers Vertical Contour Audio Measurements.png


I looked at the soundfield around 4 KHz and found the proof of our problem:


Polk T15 Bookshelf Budget Speakers Crossover region Audio Measurements.png


We see the radiation from tweeter and woofer cancelling out in the middle. Go higher and lower and you are better.

Speaker Listening Tests
I set the T15 up in my near-field setup on my desk to the left. Levels were matched against the Pioneer SP-BS22-LR on the right of my monitor. Matching levels was a bit challenging as it was content specific due to high frequency response variation of T15. But I tried and got it close.

I expected the T15 to sound horrid but that was not the case! Likely due to bounce from my desk, I was not hearing the ditch in the response in full glory. The pioneer was much better because it had first and foremost more bass and hence warmer sound. Secondary, I could hear instruments recessing behind in the T15. But overall, it just didn't sound that horrible. Power capability seemed to actually be a bit better than the Pioneer.

So yeh, a bit of quandary.

Conclusions
The Polk Audio T15 hits an incredibly low price point while producing something that doesn't look like trash. Measured performance does show trash and good bit of it. Normally this would be enough to get it a headless panther but post listening tests, I thought that would be too much damning so gave it one notch above.

I like to encourage you to save more money and buy the Pioneer if you can. Despite being much cheaper, I can't justify recommending the Polk T15 even though subjective performance was not horrible.

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

Don't make me tell you another bad joke to get you to donate money. Do it on your own by using : https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/
 

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Ron Texas

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Another great review. $115 speakers worth nothing. A dip in the 3 to 6 Khz range makes dialogue unintelligible, not to mention a severe coloration of music.
 

MZKM

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Usually the on-axis curve in red is the top one but it is not here. The top and hence one with least droop is + and - 20 degrees or so. Best not to listen to this speaker straight on. Place it lower or higher than your ear level.

Audioholics found that the tweeter height is not the reference angle:

image

image

image

image


Seeing as how these are marketed as surrounds, this makes plenty sense.

@amirm, did you compute the minimum far-field distance? And as asked by others, can this be a standard aspect to include?
And, I'm guessing it's too much to ask to re-measure but at -20V degrees being reference? Just changing the on-axis to the -20V bumped the preference score to a 1.4, over a full point boost.
 
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wwenze

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I guess this is why Klipsch is more expensive and sound better than them...
 

laudio

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Klipsch and Polk probably sell a ton of speakers at low end. I don't think it matters to them how flat the curve is. What matters is people who buy one then buy the other and say one sounds different (and better). Market differentiation.
 

Doodski

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Klipsch and Polk probably sell a ton of speakers at low end. I don't think it matters to them how flat the curve is. What matters is people who buy one then buy the other and say one sounds different (and better). Market differentiation.
I sold a boatload of speakers back in my retailing days and I've seen all sorts of sales people. The majority of people buy what they are told to buy and they think they got the best. Some sales people don't let the speakers sell on it's own merits.
 

laudio

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I sold a boatload of speakers back in my retailing days and I've seen all sorts of sales people. The majority of people buy what they are told to buy and they think they got the best. Some sales people don't let the speakers sell on it's own merits.

Same for internet sales with all the reviews. My point is even with those measurements amir didn't think it sounded horrible. Not sure measuring cheap speakers like this looking for the flat curve means much. They are built for a target market and the curve might be intentional.
 

Xulonn

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Seeing as how these are marketed as surrounds, this makes plenty sense.

And unlikely candidates for desktop or nearfield monitor use - unless you placed them upside down or tilted them back 45°. :rolleyes:

Since they are marketed as "bookshelf" and surround speakers, would it not be important to say "These speakers are designed to sit above ear level because the sound is directed downwards at 20°. They are not designed for nearfield monitoring or desktop use - see our model XYS series for desktop and monitor applications." The Amazon description - where they are currently selling for $99 with free shipping sez:
  • Get Superior Home Theater Experience With Immersive Surround Sound – Featuring (1) 0. 75″ Tweeter & (1) 5. 25″ Dynamic Balance Driver, These Speakers Are Designed to Produce a Natural, Well-Balanced Sound With Massive Bass Even at the Lowest Frequencies.
  • Use These Wall-Mountable Bookshelf Speakers As Front, Left-Right Setup, Surrounds or As Rear Speakers and Get Mesmerized by Detailed Audio With Crystal Clear Vocals, Enough to Fill Any Small to Medium Sized Room .
However, is it necessary to have such a deep response "trough" on axis to get good response at 20° down?
 

Xulonn

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Why this one didn't get headless panther?

Clearly explained by Amir at the end of his review - you apparently did not read through to the end. o_O
 
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MZKM

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And unlikely candidates for desktop or nearfield monitor use - unless you placed them upside down or tilted them back 45°. :rolleyes:

Since they are marketed as "bookshelf" and surround speakers, would it not be important to say "These speakers are designed to sit above ear level because the sound is directed downwards at 20°. They are not designed for nearfield monitoring or desktop use - see our model XYS series for desktop and monitor applications." The Amazon description - where they are currently selling for $99 with free shipping sez:
However, is it necessary to have such a deep response "trough" on axis to get good response at 20° down?
However, the manual makes no statement about vertical positioning, just general placement in the horizontal plane.

However, +20V is better than on-axis, so if you place these on a desk aimed at your chest, they will sound better than if you angled them up at your ears.
 

laudio

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You guys can analyze the measurements... They look pretty and cost $70. Some people don't like mids. I don't fault Polk for selling them
 

restorer-john

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However, the manual makes no statement about vertical positioning, just general placement in the horizontal plane.

They have a keyhole mount on the rear panel. That has but one purpose: to hang on the wall. They are another cheap rear surround speaker.
 

Cahudson42

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The T15 cries for independent DSP and AMPs for each driver. Our are members who are capable of that can do so, and then report?
 
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