Bose QuietComfort 2 Headphones Review - Performance

The dotted lines indicate the limits we look for; if anything was to veer too widely above or below these limits, that would indicate the headphones are either overly emphasizing or supressing those frequencies, which would make the music sound unnatural. The Bose QuietComfort 2 headphones had some problems here; although the frequency response is reasonably smooth and within our limits for much of the curve, it got somewhat erratic at the higher end, with several large peaks and troughs. This could be a problem for the audio quality; it means two nearby frequencies would be reproduced at different levels, which could add an unnatural quality to the sound. The amount of these differences is significant on the QuietComfort 2 headphones, which leads to their disappointing score.

Another possibility here is that the active noise cancelling feature of the QuietComfort 2 headphones is interfering with the frequency response; if you look at the isolation section below, you can see some of the peaks and troughs are at the top end of the range this feature seems to work on, so it may be having an effect here. However, as the headphones don't work unless this feature is enabled, we were unable to test this.

On the upside, the QuietComfort 2 headphones have good low frequency response, meaning bass notes should be clear and deep. Most of the curve in the mid range frequencies is smooth as well.

Distortion (6.98)
Distortion is a problem; if the sound gets clipped or otherwise distorted, you don't get the same sound the producers of the sound intended. The QuietComfort 2 headphones didn't show a huge amount of distortion, but there is some evidence of minor distortion there. In the below graph, the green line represents the left ear cup, and the red line is the right.

Our system examines the distortion headphones introduce by playing back a series of very tightly controlled sounds at the typical listening level of around 78 dBSPL and examining the results for any differences from the original waveform. The graph below shows what's called the Total Harmonic Distortion (THD), which is the amount of distortion (as a percentage) of the basic frequency, as well as the higher frequency harmonics that provide the tone and texture of a sound; ideally, all of these should be reproduced accurately. The graph starts with low, bassy frequencies at the left and goes up to high frequencies at the right. Again, the green line is the left channel and the red line is the right.

The QuietComfort 2 has generally low distortion, but we did notice a few peaks in the graph, which indicate distortion at particular frequencies, especially at around 2kHz in the left channel. There is also some distortion in the low frequencies, but again this could be caused by the noise canceling feature being active all the time.

Tracking (5.65)
Headphones have one channel for each ear, so it is important that the two sides produce the same sound. That's what we look at in this test; how well balanced the two sides of the headphones are. The QuietComfort 2s has some minor issues here; the balance of sound shifts to a slight degree from side to side.

Our test system produces the graph below, which shows the tracking across the frequency range of 80 to 10kHz. If the line is at 0 percent, that indicates the sound at that frequency is identical in both channels. If it goes above that line, the left channel is stronger, and if it goes below, the right channel is putting out more. The QuietComfort 2s don't have a specific bias to one channel; the tracking goes from right to left and back again as the frequencies vary. This variance is a bit more than we like to see; it reaches a maximum of just more than 5 percent, which is very significant (we don't use the tracking data above 7kHz in our scoring, as it isn't always accurate).
 

Maximum Usable Volume(9.61)
The distortion test we do above is run at a pretty high listening level of 90 dBSPL, but some people like it loud, so we also test how high we can crank up the volume. We test this by how high we can take the volume until the distortion in the sound reaches 3 percent, where it becomes audible and annoying.

The QC2s managed to reach an ear-splitting118 dBSPL before our testing system called a halt to the test; that's loud enough that even the most avid loud music fans can enjoy distortion-free tunes (unless you like metal or punk, where it's kind of mandatory). You should remember that, although our testing system has replaceable ears, you don't. If you crank the volume up that high, you're likely to permanently damage them.

Isolation (6.17)
Isolation is one of the big selling points of the QuietComfort 2 headphones; Bose claims its active noise cancelling circuitry identifies and cancels noise, and our tests show that these headphones did a very good job of this.

The graph below shows the frequency range of 100-10,000Hz, with the line indicating how much sound is blocked at that frequency; higher is better. The green line is for with the headphones in place, but with the sound cancelling turned off. The blue line represents performance with noise cancelling enabled. In both cases, the higher the line, the more noise the headphones block.

As you can see, the active noise cancelling (the blue line) does a much more effective job, especially at lower frequencies. With these low frequency noises (such as you would get inside an airplane in flight), the headphones with noise cancelling turned off don't block anything; low frequency rumbles go straight through them.  But with the noise cancelling turned on, a significant amount of these noises are blocked; over the entire frequency range, they block an average of about 18.5 dB of noise. It is also interesting to note that enabling the noise cancelling circuitry seems to make the noise blocking slightly worse in the mid range (where the blue line goes below the green one at around 1Khz); this seems to be at the edge of the frequency range that the active noise cancelling circuitry tries to block, so it may end up actually amplifying the noise slightly.

However, it is worth comparing the effectiveness of these against another type of headphones; the in-ear ear canal ones, such as the Etymotic ER6i and Shure SE210. Both of these blocked more noise than the QuietComfort 2 headphones, because they effectively act as earplugs, blocking the ear canal with an average reduction of about 30dB. They do a more effective job overall than both the QuietComfort 2 and their siblings, the QuietComfort 3, but many people don't like putting things in their ears. For these people, the QuietConfort 2 headphones do an effective job blocking out unwanted sounds.

Leakage (3.69)
Although the QuietComfort 2 headphones do a reasonable job blocking sound from reaching your ears, they let quite a lot escape to annoy your friends and neighbors; with the headphones set at a high 90 dBSPL level, the sound could easily be heard several feet away. This is because the over-ear design doesn't form a perfect seal; there are some gaps that allow the sound to escape, no matter how carefully the headphones are placed.