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The Sony MDR-NC500D headphones have somewhat weak audio performance. It doesn't fail spectacularly in any one area - all its test results are simply sub par. The headphones have good bass and an adequate mid-range response, but higher tones are underemphasized. There are small but consistent levels of distortion present at every frequency, but this shouldn't bother most users. The one area where the NC500D peaks above average is with isolation, but not by a large percentage. Really, the NC500D shouldn't upset the average user, but audiophiles should steer clear.
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About our testing:
Our testing rig consists of a Head and Torso Simulator (HATS) and an electro-acoustics analyzing program, SoundCheck (which was developed by our friends at Listen, Inc.). HATS wears the headphones and listens with its high-precision microphone ears. SoundCheck then collects data and uses science and mathematics to determine how good the headphones are. For more information on our tests, read this article.
Frequency Response (4.21) 
How the test works:
For this test, we play a frequency sweep through the headphones between 100 and 20,000 Hz, where each tone is being played back at a known decibel level. HATS listens to the playback, as filtered through the headphones, and SoundCheck uses the data to figure out how much emphasis the headphones are giving to each frequency. The left side of the graph represents the decibel level, and the bottom axis is the gamut of tested frequencies. If you'd like more info, click the orange icon above.
What we found:
The Sony MDR-NC500D's frequency response has some issues, but performs well enough overall. The bass receives a bit of a boost, but falls within our limits once they start. A set of mid-range tones receives a big boost, jutting outside our limits slightly. After this peak comes a jagged fall to the bottom limit. This means higher-pitched sounds might sound a bit softer than they should, but only by a very, very slight amount. Most won't notice.
When looking at a frequency response graph, you should always look out for sharp slopes, anything that darts upward or downward suddenly. This represents a sudden, quick change in decibel level without much change in frequency. For example, after the mid-range peak in the graph at right, the graph drops off fairly sharply, spikes up again, then falls again. The top of the second, smaller spike to the subsequent trough represents a 20-decibel drop. This is a noticeable difference; for reference, 65 decibels is like being in a moderately busy restaurant, and 80 decibels is like being in your kitchen when the garbage disposal is running. If you have an instrument that played in this range, the higher notes would be noticeably softer than the lower ones.
Again, the MDR-NC500Ds perform well overall, but the mid-range emphasis is a little erratic and the higher pitches sound slightly muffled.
How the Sony MDR-NC500D compares:
The average score for this section (as of this review) is 3.72, so comparatively the NC500Ds perform slightly better than average.
In terms of the comparison headphones below, it's trounced by two units: the SE-A1000 and the 6isolator. The SE-A1000s really don't add much of its own influence to the playback, producing a very smooth line that stays in the limits. The same goes for the 6isolator, only they have a slightly weaker bass response.
The HD 555s have the score closest to the NC500D's, which makes sense if you look at both. Both dip below the bottom limit toward the high end - meaning high-pitched sounds sound a bit muffled - but the HD 555s emphasize them less than the NC500Ds. The NC500Ds over-emphasizes a cluster of mid-range frequencies, but only slightly, whereas the HD 555s come close to underemphasizing them. The NC500Ds also beat the HD 555s in terms of bass response.
The two Bose headphones simply have problems with frequency response. Their emphasis becomes erratic in the mid-range frequencies, and just about everything but bass is under-emphasized. The NC500D performed far better than both.
Distortion (3.33)
How the test works:
Again, we play a frequency sweep through the headphones, this time from 100 Hz to 10 kHz. Since the frequency sweep is a known sound wave, we can measure the difference between it and what HATS ends up hearing. This difference is what's known as total harmonic distortion. Lower levels of distortion will only annoy an audiophile, but even a layperson's ear will find anything over 3 percent to be noticeable. In the graph, the left side represents the percentage of distortion, and the bottom of the graph represents the frequency spectrum we tested. If you'd like more info, click the orange "i" above.
What we found:
The Sony MDR-NC500D headphones feature a consistent amount of distortion, although at no point did that level ever get above 1 percent. Therefore, most people shouldn't notice any issues, but stringent audiophiles would find these levels to be less than ideal. There aren't any real spikes, although around 1 kHz the left channel shows slightly more distortion than the right.
Distortion like this, which is relatively minor but stretches across the whole spectrum, is only really noticeable if you compare it to the original. If you're a purist, these levels will be unacceptable, but for the average user, the Sony MDR-NC500Ds will be just fine.
How the Sony MDR-NC500D compares:
The Pioneer SE-A1000 and the 6isolator also feature continuous, low levels of distortion. Both of the Bose noise-cancelling headphones manage to show less overall distortion, although the QC2 has two small bumps. The Sennheiser HD 555 headphones have some issues with the low end, but are otherwise distortion-free.
Tracking (6.25)
How the test works:
Like the previous tests, our tracking test involves playing a frequency sweep through the headphones. In this case, however, we at the decibel outputs of each ear cup. Ideally, both channels should have the same volume, but since they never do, we graph how the volume levels differ as they sweep back and forth from cup to cup. When the blue line rises above zero, the left channel is outputting more decibels; below the zero line and the right channel is louder. Like most of our tests, long, steep slopes are bad, because they represent a sudden, drastic change.
What we found:
The MDR-NC500Ds perform well on this test, for the most part, sticking to even emphasis for a good chunk of the graph. Toward the high end the graph starts looking a bit erratic, but we've seen worse. Really, there isn't much to say abou this one since it stays so relatively flat. This is not performance to worry about unless you're an audiophile.
How the Sony MDR-NC500D compares:
Just from looking at numbers, you can tell the NC500D is just over the hump of the bell curve. It's also somewhat easy to tell from just looking at the graphs: a flat horizontal line is ideal, a bunch of squiggles is bad. For a great example of close to perfect, check out the 6isolator's tracking graph. For an example of what's bad, check out either QuietComfort, which look like seismographs.
Maximum Usable Volume (7.67)
How the test works:
This test is actually a series of distortion tests. Our distortion test above plays back a frequency sweep at a set decibel level. On this test, we keep bumping the volume up until we reach 3 percent distortion. This level of distortion would be noticeable and annoying.
What we found:
The Sony MDR-NC500Ds are capable of outputting 110.22 decibels. We typically look for headphones to output 120 decibels, since some like their music loud (any more than that and you're going deaf). A maximum usable volume of 110 decibels is by no means horrible, however, as it's always safer to listen at lower levels. This should be loud enough for most, although those who really want to pop their ear drums or those who are hard of hearing might want a bit more.
Typically headphones score between 110 and 125 decibels. While the NC500Ds score toward the bottom of this range, the differences therein really aren't gigantic.
Isolation (5.19)
How the test works:
For this test, we throw the headphones on HATS, then bombard them with pink noise (it's like white noise only less random - every octave has equal energy). HATS listens, and sees what gets through. The MDR-NC500Ds actually have a few different noise cancellation settings, so we let it listen to the pink noise and use its AI to figure out what setting is the best. In the graph below, the blue line represents how many decibels of each frequency the headphones are able to block out with active cancelling and the green line represents how well the headphones block out noise by physically obstructing your ears.
What we found:
Active cancellation helps block out quite a good deal of bass, which otherwise would flow into your head unimpeded. That being said, the active cancellation actually slightly hinders the headphones' performance in terms of high-mid cancellation.
How the Sony MDR-NC500D compares:
For the majority of those reading this review, this section is the most important one. Exactly how well does the NC500D's noise cancellation do, compared to other competitors - or, for that matter, how well does active noise cancellation even work to begin with? If you find yourself asking that question, then we certainly have an exciting array of graphs for you. Again, the blue lines are active cancellation, green lines are passive. No blue line means no active cancellation.
First of all, good ol' earplugs seem to beat noise cancellation in terms of overall isolation, as evidenced by the 6isolators. If you're looking for some spot reduction on bass, however, then active cancellation is something to look into. In this regard, the MDR-NC500D headphones score between the QuietComfort 2 and 3. The QuietComfort 2s form a poor seal with the head (the padding is fuzzy and about as air-tight as a stuffed bear) so we weren't surprised to see the NC500D win that match-up. It's very similar to the QC3s in terms of forming a tight seal with your head (both headphones use similar material on their pads), but the QC3s block out a bit more bass.
While the NC500D and its noise cancellation aren't the worst out of the headphones we've reviewed, they aren't as good as the Bose QuietComfort 3 headphones, and both underperform versus a pair of in-ear headphones.
Leakage (4.46)
How the test works
To test leakage, we put the headphones on HATS and set up a microphone six inches away from HATS's ear. We then play pink noise through the headphones and see how much of it makes it to the microphone.
What we found:
The MDR-NC500D aren't the quietest headphones ever - on the contrary, they actually leak a bit more that you'd think, given their cancellation abilities. This being said, the NC500D has the second-highest score in this category for a non-in-ear headphone (the Sony MDR-DS6000 currently occupies first place). This achievement doesn't say all that much for the NC500D, but it also doesn't say much for non-in-ear headphones in general. If you like listening to your music really loud, someone sitting next to you will probably hear it. If you're in a library or quiet office, everyone will glower at you.
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