IMPEDANCE IN HEADPHONES - WHAT YOU NEED TO KNOW PT - II

Previously (in part 1), i had explained about the significance of impedance in headphones and it's effect on loudness and quality of the sound delivered, in this part, we'll be going a bit deeper into the following -

1. What is impedance matching ?

2. Significance of impedance matching

3. Sensitivity 

4. When you require an amp

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1. Impedance Matching

It is a process that helps in extracting the best audio quality from a headphone. Each headphone comes with a particular impedance that is used to match with the impedance of the source that you're connecting to.

There exists a rule called "the rule of eighths" which states that the output (source) impedance should be less than 1/8th of the headphone impedance. For example, if someone purchases a headphone with 250 ohms, then the source impedance should be less than 31 ohms. Though decent results can be achieved with slightly greater source impedance, it should be kept in mind that there will be some deviation in the frequency range.

The headphone on the top is the Sennheiser HD 650 which comes with an impedance of 300 ohms and the one below is the Steinberg UR22 MK II which has a phone output impedance of 40 ohms.

So in this case, when we apply the 1/8th rule, the phone output impedance should ideally be 37.5 ohms (300/8=37.5) but as stated earlier you can still get away with a little mismatch with only a slight deviation in the frequency range.

2. Significance of Impedance Matching

For general use/casual listening, an impedance mismatch doesn't really matter much because the differences aren't really noticeable but when it comes to studio application/critical listening, it is very important that there is proper impedance matching else there will be some sort of frequency deviation (i.e. coloration) which will mislead the listener during a mix session etc.

In some cases there will be distortion, especially in the high frequencies and sometimes when you connect a high impedance headphone into a mobile phone or PC, there will be insufficient output volume which can be sorted out by using a suitable amp.

3. Sensitivity

In a nutshell, sensitivity refers to how loud the headphone can get. it also tells us how efficiently the electrical signal gets converted from the source device to an acoustical signal. More the sensitivity, more the loudness and vice versa. Similarly, more sensitivity requires less power while less sensitivity requires more power to obtain substantial loudness.

It should be kept in mind that a headphone with high sensitivity can also produce distortion at very high volume and may even damage the driver. It is advised to stick to a sensitivity rating of 100 dB which is a safe zone in terms of loudness (90dB is on the lower end while 110 dB is on the higher end).

4. When you require an amp

As discussed in part 1, there are 2 types of impedance - high and low. A headphone with an impedance rating of 100 ohms or more requires an amp to achieve substantial loudness. On the other hand, headphones with less than 50 ohms don't require any amplification as they are loud enough by nature.

The Beyerdynamic DT 770 PRO (80 ohms) being connected to the Fiio E11 headphone amp. 80 ohms lies in the grey area which means amplification is not really necessary at all times.

But buying an amp blindly will lead to more complications, so before one can invest in an amp, a ton of research should be done so that it actually compliments the headphone that is going to be plugged into. Factors such as impedance matching, rated sensitivity etc should be kept in mind while investing in an amp.

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Hope you all got an idea of what impedance matching and sensitivity is and the roles that they play in delivering proper sound quality - atleast to some extent. Had to do a ton of digging so that i could put it in the simplest way possible. If you've any queries/feedback do drop them in the comments below, will surely check them out. I will also be coming up with a headphone buying guide that'll help you decide what you want and what you don't want when it comes to headphones. So stay tuned!!



Check out the links below if you want to dive deep into the technical stuff -
1. NwAvGuy
2. Headphones impedance demystified

CABLES - BALANCED & UNBALANCED

From the home theater setup to the recording studios, we've all come across different kinds of cable being put into use, each having a purpose of it's own. In this blog, we're going discuss about the following stuff that one needs to be aware of before setting up their stuff -

1. What are Balanced & Unbalanced cables

2. Difference in terms of their output.

3.  Purpose & usage

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 1.1 Balanced Cable

A balanced cable is the one that has 2 conductors and a ground - total of 3 pins (thus, 3 wires). The 2 conductors carry audio signals which are identical to each other but 180° out of phase which helps in canceling the noise at the receiving end (more on this in section 2). The ground wire acts as a shield against the radio frequency interference that is caused during the transmission.

A typical XLR cable

Examples of a balanced cable includes XLR, TRS etc. They can be quite long (as much as 25-30 meters) without much of any restriction since it is shielded properly.
 
1.2 Unbalanced Cable

An unbalanced is the one that has only 2 wires in it. One conductor and one ground wire, the conductor wire does the job of carrying the audio signal and the ground wire here does the job of shielding as well as carrying a bit of the audio signal (identical to that of the conductor). Thus, the shielding is naturally less effective than a balanced cable.

RCA cable that is used in most AV systems

Examples of  unbalanced cable includes RCA, TS etc. They cannot be longer than 4-5 meters as they tend to pickup a lot of noise along the way.

The TRS and TS cables are the ones that we often use a lot, they look pretty similar yet they are different with respect to their structure and output audio signal. The differences are as discussed below -

2. Difference between balanced and unbalanced cable outputs.

As you can see the one on top happens to be the TRS cable (Tip Ring Slip) while the one that's below is the TS cable (Tip & Sleeve).

The TRS cable has 2 conductors, one which carries a non inverted signal (Hot signal) & the other which carries an inverted signal (Cold signal). The signal that is being transmitted on both the conductors are identical to each other (including the noise) & at the receiving end, the inverted signal is reverted to the original polarity while the noise still remains inverted, which gets cancelled at the receiving end and finally, the original/input audio signal is obtained. 

On the other hand, the TS cable has only one conductor which carries the audio signal and due to this reason, the shielding is also poor which results in interference. Hence, at the receiving end you get a signal that is slightly distorted.

Now that we're done with discussing the differences, let's take a look at when and where they can be used -

3.1 The balanced cables are obviously better than unbalanced ones as they do a better job of removing the noise during the transmission of the audio from one point to another. Hence, it is preferred more than the later.

3.2 The unbalanced cables are preferred in an environment where the length of the cable required is short as longer distance will invite more noise/interference.

It should also be kept in mind that interchanging i.e using balanced cables instead of unbalanced cables (& vice versa) won't be of much use (in fact it may produce below par results). So one should always be aware of the type of connection that is available in the sending/receiving units and use the relevant type of cable connection.

Now that you're aware of balanced and unbalanced cables & it's usage, there's one more thing you should also know about, so hopefully you won't run into such issues while setting up your stuff.

BONUS SECTION!

Instrument cables and Microphone cables are some of the widely used things in a studio/live set up and more often than not, it is used in the wrong manner resulting in poor audio quality etc.

Let's talk about instrument cable first, they're designed to have high impedance and low power. It is usually used to carry a weak signal (for example, a guitar) to the amp. It is a co-axial cable consisting of a central conductor surrounded by a braided shield, this is because the weak signals can easily be distorted by outside RF/electromagnetic waves.

The speaker cable on the other hand is designed to have low impedance and high power. It is used to carry powerful signals from the amp to the speaker. It consists of 2 thick copper wires with no special shielding as it is far less affected by outside interference.

It is not advisable to use an instrument cable instead of a speaker cable because the thin wire in the instrument cable cannot handle the high power that comes out of an amp. It'll naturally generate a lot of heat and in some cases, might even damage the amp/speaker.

If you use a speaker cable in place of an instrument cable, the audio signal will be transmitted but with a lot of electromagnetic interference. Hence one should be aware of what to use and where it should be used.

I hope you found this post to be useful and practical. Do share it with people who might benefit from these tips and if you've enjoyed reading this or have any queries, then do drop them in the comments below, will definitely answer them asap!

Until next time.


References -
1. instrument cables arent the same as speaker cables
2. balanced vs. unabalanced cables