“My Xeport 5010-8 continues to impress me. I’m starting to hear grain in the midrange now. Also, there’s even more space than before, providing an “out of the head” type of headstage. The positioning of instruments reminds me of my VSonic GR06+Atrio X combo. The treble is not edgy, but has minimal sparkle and good extension (depending on your source). Also, there’s the front and back positioning of the 5010-8 and yes, that’s how I knew it was 3D, because it goes left, right, front, back and sometimes diagonally. Yeah, I wonder why Xeport would sell this great IEM for a low price? Hmmmmm……”

– www.head-fi.org

Xeport designs and produces the earphones with different considerations in mind. Each design is uniquely done to satisfy differences of people’s listening preferences.

7010 provides most evenly distributed spectrum so that the earphones are good for most types of music. With this type of earphones, you listen to the original recordings when the music was made. You need to reply on EQs on your playing device in case you prefer different timbre.

5010 was designed with emphasized low frequencies for people who demand more bass. Many audiophiles consider themselves Bass Head and demand stronger beats. 5010 is perfect for people who have such preference. At mean time, with the three sets of tuning buttons coming with the whole package, you actually could adjust the low frequency response to satisfy your listening preferences for various types of music.

3010 on other hand has slightly emphasized high frequencies to give more details and clarity. It is more suitable for classical music, new age music and the most pop music.

3. The size matters

As we discussed in the last post, the speaker cone size is limited by the sound frequencies that the speaker is trying to produce. Once the sound frequency is high enough, even the speaker cone could be made perfectly rigid; the sound output would start to decrease due to the interaction from the different areas of the speaker cone. In real life, no one could make a speaker cone completely rigid since all materials have their own mechanical properties. When the frequency increases, the speaker cone itself would start to get into various modes. In other words, at high frequencies, the speaker cone would no long be a uniformed diaphragm like a piston and start to deform. Once in this situation, certain part of the diaphragm would push the air forward while some other areas would pull the air in. This effect would reduce the sound output and made the frequency response very bumpy.

Beside the effect above, another concern of generating sound at high frequency with a large speaker is that the high frequency sound would be modulated by the lower frequency sound due to the Doppler Effect. Most people have some experience of how Doppler Effect sounds like. When a train passing by while whistling, one would hear higher pitch sound when the train is coming towards him and lower pitch when the train is going away. If the speaker generates two frequencies, the pitch of the high frequency sound would be modulated up and down since the same speaker cone is moving back and forth like a train. The higher the frequency, the more modulation there would be.

Based on the effects above, it is desirable to limit the sound frequency range according to the size of the speaker cone and those are other reasons for having different size speakers in home speaker system.

2. The size matters

I am sure you have noticed that there are always multiple speakers on most of the high-end home stereo systems. Normally a good speaker system would have a woofer, a mid-range speaker and a tweeter. Very often you would need a sub-woofer for even lower sound. So why do we need to have multiple speakers instead of just one, a very good one? It all has to do with law of physics. The amount of sound radiation from a loudspeaker is a function of the diameter (area) of the speaker cone as well as the acceleration of the cone.

For the acceleration part, we mentioned in Part 1 that once a speaker operates above its resonant frequency, the weight (mass) of the cone becomes the dominant force a speaker has to against. According to Newton’s law, F = ma indicating that a constant force crossing various frequencies would give a constant acceleration which in turn would generate a constant sound output. This is why speakers are designed to have a resonant frequency at the low side of its spectrum to ensure the flat frequency response above that frequency.

Now let’s talk about the Size. When the frequency of a sound is very low, the wavelength is very long. You can use Frequency x Wavelength = 344 (the speed of sound) to determine the wavelength of a sound. For 20 Hz, the sound wavelength is roughly 17 meter. With that long wavelength, any speakers we have at home is considered as very small (relatively speaking) so that the sound pressure cross the speaker cone is uniformed. When the sound frequency increases, the wavelength gets shorter and shorter. When the wavelength gets close to the size of a speaker, we start to have problems. What happened is the sound generated at one side of the speaker would start to against and eventually cancel the sound generated from other side due to the short wavelength. In theory, when the speaker diameter is near to ¼ of the wavelength, the speaker output would start to decrease at a rate of 6dB/Octave. The frequency at this time is called Cutoff Frequency of a speaker. For a 12” woofer, the Cutoff Frequency is roughly 280 Hz. This is why we need multiple speakers in a good stereo system and each speaker only covers its own range of frequencies. The higher frequency, the smaller speaker has to be.

Beside the cutoff frequency that would limit the size of the speaker, there are two other factors, i.e. Doppler Effect and cone rigidness which are also having impacts when come to the size of a speaker. I will provide more details in my next post. Stay tuned.

Imagine a spring hinged door that could swing back and forth, when you push the door slightly and let it go, the door would bounce back and forth at a certain rate, and eventually settle down to its steady position. Now if you swing the door back and forth even slower, you would only feel the resistance generated by the spring of the hinge, the harder the spring there is, the more difficult to move the door. Now if you slightly increase your rate of swing the door and eventually you would find a situation where the door would start swing back and forth violently with even a small force been applied. The door is now in a resonant state. Now if you try to swing the door back and forth even faster, then the weight of the door would eventually become the dominant force you have to against, the heavier the door it is, the harder to swing the door. Once again, if you push the door back and forth even faster, let’s say 20 times every second, then that door would become a speaker generating sound due to its interaction with the air. Of course, I am sure that no one could move a door that fast.

The reason I am using the door as the analogy of a speaker is because that a speaker has a very similar mechanical structure as a spring hinged door I described above. A speaker has a resonant frequency at low side of its spectrum. Any frequency that is lower than the resonant frequency would have difficulties to radiate sound and in theory, it would go down 12dB/Octave as the frequency decreases. When the frequency goes higher than its resonant frequency, the sound output would become flat cross the frequencies until reaching its cutoff frequency. I would describe more of this effect in the next article.

One of the most difficult parts of making a good speaker is to find a speaker cone that has very light weight to be pushed back and forth rather easily while the speaker cone has to be very rigid. If you could find such material that is better than the ones used in today’s speakers, please let me know and we could make a business out of it.

6. Distortion

Normally earphones manufactures do not specify distortion value since most of the earphones have negligible distortion due to the low output power. You may have experience of what distortion sounds like when you listen to music through a mobile phone loudspeaker since at that time, you are forcing a small speaker to deliver a much larger output sound in order to hear the music from a far distance.

The distortion is caused by non-linear properties of an audio transducer which generates harmonics that is not in the original recording. When a transducer is linear, it means that the output of the device is proportion to the input of the device. For example, if the relationship between the output and the input of a device is 1 to 2, then ideally, when the input level is 1 volt, the output should be 2 volt. When the input is doubled or halfed, the output should follow the 1 to 2 relationship strictly. Under this condition, there should be no distortion at the output. However, when the signal gets larger, very often, the output could no longer follow that 1 to 2 ratio and become 1 to 1.9 or even less. By then the output is no longer exact the same as input so that distortion would occur.

Once a distortion occurs, there would be harmonics of the original signal generated. For example, when a 1kHz tone is applied to an earphone, the harmonics would be 2kHz, 3kHz and so on. The ratio between the total energy of all those harmonics and the energy of the original signal defines how much distortion there is in terms of dB or percent. Most earphones has less than 1% (-20dB) of distortion.

Again, distortion figure for an earphone is normally a less important spec while some poorly made earphones still could have poor distortion performance. One way to tell if a distortion is a problem for your earphones is to listen to the music at different levels to see if the overall sound quality changes.

One more thing, for most of audio transducers, especially for loudspeakers, the distortion normally happens at lower frequencies since the excursion of the speaker cones is much larger at low frequencies.