Review of AfterShokz Sportz M2 bone conducting headphones with mic

Introduction

At £69.99, the AfterShokz Sportz M2 headphones are in a price range occupied by relatively top-end earbuds and headphones targeted at the mobile market or moderately priced headphones aimed at the audiophile on a budget. In my view, the Sportz M2 cannot compete in terms of sound quality with others in this price range, so where's the value? The answer lies in what else you can do while you are listening to audio content using these headphones.

The cheekbone's connected to the earbone...

If you have ever had your ears tested by an audiologist, not only will you have been asked to listen to tones played through conventional headphones, you will probably also have had to listen to tones played through a strange contraption which sits on your face but which does not cover your ears. This is because it is known that sound can be perceived through vibrations in the cheekbones as well as through the external ear and ear canal. This phenomenon is called bone conduction and AfterShokz, like some other companies, make headphones which exploit this phenomenon so that you don't have to wear the headphones on or in your ears – you place the special speakers on the sides of your cheekbones.

Normal headphones and earbuds are usually designed in a way to ensure that you get the most from whatever audio content you are listening to while reducing or eliminating unwanted ambient noise. Since bone conduction headphones do not cover the ears, their whole purpose is to enable you to hear ambient sounds while you are using the headphones. AfterShokz have targeted those who like to listen to music or speech while jogging, exercising or otherwise moving about. They have also realised that visually impaired people might also be a special market for them since listening to ambient sounds is absolutely necessary while navigating outside. With the proliferation of GPS apps for blind people, bone conduction headphones seem ideal since one can listen to directions from a GPS system while still hearing 100% of ambient noise.

The Sportz M2 version of the AfterShokz line also has a microphone so they are ideal for hands free use of a phone as well.

What you get

The Sportz M2 come in a sturdy zip case which, unless you are a window cleaner, will not fit easily in your jacket pocket. Opening the case reveals the headphones with its tethered cable on one side behind an elasticated central band while there is a pouch on the other inner half of the case containing the USB cable for charging the battery and an adapter cable for non-3.5mm headphone sockets.

The rather flimsy headphone cable is connected to the headband on the left side and it drops down behind your left ear when you are wearing them. About 42cm along the cable, there is the battery and control pack which, in addition to the micro USB port, has a power on/off switch, along with play/mute button and volume buttons. There is then a generous amount of cable terminating in the usual 3.5mm jack.

Wearability and use

Without prior guidance, the first attempt at putting on these headphones may be accompanied by much fumbling and puzzled frowning. The key is to remember that the cable is attached to the headband near the left speaker. This understood, you discover that the two round speakers sit on your cheekbones close to the joint with your jaw, a little in front of your ears. From one speaker, the headband goes up and over the ear and down to your neck and back up again to the other ear. This rules out lying down or reclining with your head resting against something but this is quite the opposite of what AfterShokz have in mind since their phones are targeted for use when engaged in moving about. The headband is hard plastic but it is flexible and the resulting tension when worn should be sufficient to ensure that they do not slip off while jumping about or headbanging.

Different people have different preferences about wearing the conventional types of headphones: some hate earbuds which fit inside the ears while others can't stand wearing bulkier headphones with a headband across the top of the head. The AfterShokz feel quite different in that one is not normally used to a constant pressure at the edge of the cheekbones and some might find this weird or uncomfortable. Personally, I find that they are more noticeable than my earbuds but far more comfortable than my large studio headphones.

While the construction of the speakers and headband is robust, the same cannot be said of the cable. For headphones in their price range, the cable itself is very thin. This need not represent a problem in itself but it suggests that the connections to the headband, to both ends of the battery pack and to the jack plug have to be soldered with even greater care. The robustness of the cable and the connections is particularly relevant for headphones which are targeted at people who will be engaged in sports or other physical activities where the risk of tugging the cable will be greater than where the user is relatively sedentary.

As you might expect, the speakers which sit on your cheekbones vibrate in a special way so as to make proper bone conduction possible. We are talking serious vibration here, quite different from the standard electro-acoustic transducers used in conventional headphones. For example, if you have the solid circular type of in-ear phones, you will get practically no bone conduction going at all if you place them on your cheekbones. The side effect of employing bone conduction is that you feel the vibrations as well as hearing the audio although this only really becomes noticeable at higher volumes.

How they sound

Is it really possible to reproduce high fidelity audio through the cheekbones as opposed to in the conventional way? The answer is both yes and no. For a start, not all of the audio you hear from the Sportz M2 is perceived just through the cheekbones. It seems that higher frequencies do not pass as easily through the bones as do the lower frequencies and you can test this yourself by placing your fingers firmly in your ears while listening to music with these headphones. You still hear most of the sound at about the same volume but the high frequencies are lost, resulting in a noticeably muffled sound. So, in order to work properly, it seems that there is no such thing as 100% bone conduction – the high frequencies are picked up by the ears in the normal way as ambient sound emanating from the speakers.

Does this mean that audio leakage is greater than with conventional headphones and earbuds? Definitely! Don't use these headphones if you plan on listening to confidential material at moderate to high volume in earshot of others. Although perfect for listening to notes and documents at meetings while keeping abreast of what is being said in the room, you will have to adjust your listening level so that others either cannot hear or are not too distracted.

It is probably not possible to measure objectively the audio performance of these headphones. With conventional designs, you can place special calibration mics on the speakers and measure general volume, frequency response and distortion but objectivity goes out the window when you take into account that different users will experience different results depending on the anatomy of their skulls and how well their particular bones conduct audio to the inner ear receptors. Also, if you have no brain, you can expect excessive reverberation.

Volume

Not all headphones and earbuds carry the audio at the same volume. Much depends on the impedance of the headphones, so some can be louder than others. Add to that the fact that the Sportz M2 are active headphones, meaning that you hear nothing unless they are switched on. Turning the headphones' own volume level to maximum showed that they are considerably quieter than the earphones which come supplied with my Samsung Galaxy S3. When listening to some internet radio stations that are streamed at relatively low volumes, turning up the volume on my S3 to compensate triggers a deafening announcement from Talkback that listening at high volumes can damage your hearing. The output of the Sportz M2 is low enough to result in your having to turn up the volume on your device by quite some way, resulting in faster battery drain on your device.

Frequency response

That is the tone to the non-audiophiles out there. As discussed above, the higher frequencies which make the sound brighter are generally perceived mainly through the external ear and although this might seem inefficient, the end result for me anyway is that the higher frequencies are perceived very well indeed with scintillating cymbals and crisp vocals. Bass is not so evident so if you are looking for the kind of subwoofing bass which would normally make your teeth shake, you will not get that experience from these headphones. However, depending on exactly where you place the speakers on your cheekbones, the bass perception is acceptable if a little weak.

Stereo imaging

Now I come to the point which has caused me some grief since I purchased these headphones back in December 2012. For many people, it is enough that they can (a) hear the sound at all, (b) hear the treble reasonably well or (c) hear enough bass. If you are anything of an audiophile, you will also want the stereo imaging to be reproduced accurately. This means that mono signals should appear focused in the centre of the stereo image and that music should be spread across the stereo spectrum as intended with central sounds such as lead vocals, bass and snare drums etc. appearing in the middle. Not so with the Sportz M2 I purchased. I believe the problem is all about incorrect phase.

I immediately noticed that the stereo imaging was very poor indeed and that what I was listening to bore all the hallmarks of headphones with incorrect phase resulting from improper wiring. Those of you who have ever connected a set of loudspeakers using the typical double-wire arrangement for each speaker will know that if you plug the two wires into one speaker in a way which does not match how you connect them to the other, you end up by putting the speakers out of phase with each other. This results in a stereo image which is skewed, with central sounds appearing either left or right or seeming to spread across the whole stereo spectrum. This is exactly how the Sportz SM2 sound to me – and to some others.

You can simulate this effect yourself if you have the hard type of in-ear phones. What you do is to start off by listening to a mono signal with both phones located as normal and then take one slightly out of your ear and turn it just over 90 degrees so that it points to the ceiling, making sure that it is still held close enough to your ear so that you can hear its output. You will notice that the mono signal, which was formerly focused centrally, will now be smeared all over the stereo spectrum.

A couple of weeks after purchasing my headphones through Amazon.co.uk, I reported this to AfterShokz.com using their online contact form (there is no obvious email address for customer support). They never replied. What I was wondering was whether the very nature of bone conduction causes the perception of this out-of-phase phenomenon or whether the headphones had just been improperly wired. It then occurred to me that I could put the headphone speakers directly over my ears in the normal way (turning down the volume of course) but this did not get rid of the stereo problem at all. The logical conclusion was that the headphones were out-of-phase.

Eventually, I met Rodney Annet, the MD of AfterShokz UK at an exhibition some months later and he immediately took up the problem and offered a replacement pair which is what I now have. They sound identical to the first pair I bought. Rod reported that tests carried out on the phones I returned to AfterShokz could not replicate the problem I was describing.

I am not sure what tests AfterShokz have been conducting but other users of AfterShokz headphones, as well as others who have tried my headphones, have all reported to me exactly the same stereo problem.

Thankfully, since I acquired my pair for the purpose of listening to GPS announcements when I am out and about, I am not really bothered about the stereo issue but it would be nice if the stereo were accurately reproduced. In fact, there is at least one app I use where stereo positioning is critical: the vOICe for Android. The vOICe uses your phone's camera (or camera glasses if they are connected to a netbook) to take snapshot images which are then analyzed and reproduced as sound in short bursts. Using the full stereo spectrum, the blips of sound you hear should tell you where objects are located from left to right as you look at them. However, the Sportz M2 with this stereo problem will do a poor job of indicating objects located centrally in the image since the phasing issue will cause them to be almost randomly panned.

I may be entirely wrong in attributing the perceived stereo issue to phasing, however, in about 35 years of experience in recording and audio engineering, it sounds like a phasing issue to me.

The microphone

Why tell you about it when you can hear it for yourself. This recording was made using the mic on the Sportz M2 plugged directly into my iPod Touch and recording a voice note. The recording is raw and has not been normalised or processed in any way. For a headset mic, I think the results are excellent.

Buttons

There are separate buttons for increasing and decreasing volume located on the side of the battery unit, along with the power switch and covered charger port. The single play/mute button is situated on the front side of the battery unit and, in addition to playing or muting audio, it also serves as a means of answering phone calls.

The battery

The micro USB charger port is covered by a flexible cover which remains tethered to the battery unit when you peel it back. Again, the impression is that this cover could be easily pulled off and it may not be so easy to put it back again. AfterShokz say that with three hours' battery charge, you should get up to twelve hours of playing time at low volume.

I have a relatively inexpensive bluetooth earpiece which has a built-in voice which announces battery status when you turn the unit on. This is something which I would like to see in the AfterShokz models since for those who cannot see, there is no other way of detecting battery status.

Conclusion

AfterShokz themselves, as well as other reviewers, are at pains to point out that these bone conduction headphones are not aimed at those looking for high quality sound reproduction. The whole point of bone conduction is that whatever you are listening to will get mixed in with ambient noises which, in some respects, will be what you are concentrating on as the music or other audio from your headphones remains in the background. Inevitably, the audio quality of these headphones will very much depend on the anatomy of the user but I still think that the jury is out on the question as to whether the stereo imaging problem is caused by a phase issue.

I got my AfterShokz Sportz M2 for GPS navigation outside and book reading/radio listening indoors when engaged in other tasks, listening out for the doorbell or even while wearing earbuds connected to another device. The Sportz M2 phones are brilliant for those purposes and they are also ideal as a high quality hands-free headset for your phone or other portable device. The AfterShokz range has also been extended with the introduction of a bluetooth version for those who really don't like cables.

You will probably not want to purchase the Sportz M2 as your only headphones but they are thoroughly recommended for the uses described above.

Paul Warner

27 May 2013