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:
I was surprised by the quality binding posts at this price point:
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:
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:
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:
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:
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:
Distortion plot has a peak around 400 Hz:
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:
You can see why when we look at 10 degree sweeps vertically:
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:
Eye-candy Speaker Measurements
The contour graphs show what we already know:
I looked at the soundfield around 4 KHz and found the proof of our problem:
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.
------------
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/
With the grill removed, the T15 looks decent:
I was surprised by the quality binding posts at this price point:
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:
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:
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:
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:
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:
Distortion plot has a peak around 400 Hz:
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:
You can see why when we look at 10 degree sweeps vertically:
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:
Eye-candy Speaker Measurements
The contour graphs show what we already know:
I looked at the soundfield around 4 KHz and found the proof of our problem:
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.
------------
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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