My favourite audio geeks, I hope you are staying safe up to now and still exploring the magical world of sound engineering! Today, I will be sharing with you the last article in these long series, Microphone Characteristics!
We are going to sum up everything in the following article, but for today we will be focusing on Microphone Types.
As you might have realised, we have been mentioning some terms in the previous articles. Dynamic, Condenser, Large or Small Diaphram, Ribbon. All these are microphone types. And we are going to explore then all today and in addition a few more. One would expect this article should come first in the line, but trust me. It could have made things confusing. While now everything will come together! Let’s start!
Dynamic and Condenser Microphones
The separation between Dynamic and Condenser microphones is the biggest and most common one you are going to find out there. You can even say they are “Master” categories where everything else falls under them.
Let’s start with the Dynamic Microphones. Dynamic microphones use a moving-coil design to convert the Sound Pressure Level to Voltage and therefore an audio signal that can travel through the cable. For this to happen, the diaphragm of a Dynamic microphone is movable and a conductive coil is attached on it. That coil has been permanently magnetised by a process called induced magnetism. This, naturally, creates electromagnetic induction between the diaphragm and the coil. When the diaphragm moves (due to the SPL it is receiving) it oscillates within the induced magnetic field. Then, the coil picks up this oscillation as voltage which in turn, sends to the microphone’s output.
Key characteristics of Dynamic Microphones:
- They are passive (no power needed to operate)
- They use electromagnetic induction
- Small or Large Diaphragm
- They are quite resistant and they can tolerate hits
- They are used mostly in live environments
Moving on, we are going to talk about Condenser Microphones (not many other choices at the moment!). Condenser microphones are separated into another sub-category. Small and Large Diaphram Condenser Microphones
Both, Small and Large, Diaphram Condenser Microphones benefit from the principles of the electrostatic phenomena so they can convert the received SPL to Voltage. Instead of using a coil, within the condenser capsule, there are 2 parallel plates that hold a permanent and fixed electrostatic charge. The backplate is a stationary element of the microphone. But the front plate is the diaphragm and is able to move from its standard position depending on the SPL it is handling at the moment. When that happens, between the two, that fixed electrostatic charge changes values. During that process, the ratio of the charge between the plates changes and the microphone will produce an output voltage that is inverted proportionally to that value change.
Key characteristics of Small and Large Diaphragm Condenser Microphones:
- They are active (power needed to operate)
- They use the principles of electrostatic phenomena
- They use a backplate instead of a coil
- 0.5 inch (12.7 mm) or smaller diameter usually (Small Diaphragm only)
- 1 inch (25.4 mm) or larger diameter usually (Large Diaphragm only)
- They are much less tolerant and resistant to hits
- They are used mostly in studio and controlled environments
And now, is the part where you ask me:
“So, is the diameter the only real difference between Small and Large Condenser microphones?”
Of course, the answer could not be different than:
“Technically, yes but behaviourally, no!”
So let’s dive in quickly on how the diaphragm diameter can play a huge role in the behaviour and output of a condenser microphone.
The first major difference comes to their positioning because of the location of their capsule on their body. Large diaphragm condensers are usually big heavy microphones and their capsule, is typically on their upper body, pointing sideways. Small diaphragm condensers, as a rule of thumb, are quite tiny, like a pencil (so you might hear people calling them “Pencil Microphones” and their capsule is at the top facing upwards and therefore you need to point their top to the sound source instead of their side.
The next major difference is that Large Diaphragm Condenser microphones can capture more acoustic energy and that translates to a higher voltage output. Meaning that their Self Noise is considerably less than Small Diaphragm Condenser microphones and they provide a much better Signal to Noise Ratio.
Now, focusing on the Small Diaphragm Condenser microphones, there are a few interesting details about their benefits. Firstly and most importantly, they follow their Polar Pattern more accurately than a Large Diaphragm Condenser microphones. See, if you head back to the Frequency Response article, and head over to the cardioid Polar Pattern you will see that the pattern behaves differently on different frequencies. This aspect makes the Large Diaphragm Condensers more suitable for vocals and more “rich” recordings as they are a bit more tolerant in distance changing between the sound source and the microphone, i.e. see Proximity Effect. On the other hand, having a spot one accurate Polar Pattern on a Small Diaphragm Condenser microphone gives you that neutral pristine clarity and natural sound when you want to capture an instrument performance, and that is why you will see loads or piano and guitar recordings using them a lot. They can be good recording bass instruments too, however, it is usually prefered to use Large Diaphragm Condensers on these applications because of their colouring behaviour, due to the Polar Pattern reasons we just discussed.
Furthermore, Small Diaphragm Condenser Microphones are better in capturing transient sounds. This has to do a lot with their diaphragm size as the smaller it is, the less energy requires for moving. This allows them to capture much more detail in the recordings than a Large Diaphragm Condenser.
A disadvantage you might find on Small Diaphragm Condenser microphones is that, in general, they do not have the option to switch the Polar Pattern to something different. There are a few exceptions out there, that offer switchable polar patterns but they are a handful. Most Small Diaphragm Condenser microphones come with replaceable capsules that carry a different Polar Pattern, which means that there is a process involved in doing that instead of just flipping a switch.
Ribbon Microphones
And here we are! Got to the Ribbon microphones and guess what! They do split into two categories as well! Passive and Active Ribbon Microphones. Let’s find out how they work!
Starting with the Passive Ribbon microphones, these are essentially dynamic microphones but there are some differences when it comes to their way of capturing the sound. Their diaphragm (which looks like a Ribbon – hence the name) is the conductor itself, and therefore, there is no need for a coil; The induced magnetism is still a thing with Passive Ribbon microphones but this time, it’s the diaphragm itself interacting with the magnetic field and produce the voltage output of the microphone.
These ribbon diaphragms are made typically by aluminium. That renders the microphone very fragile and needs to be handled very cautiously. It’s not a type of microphones you want to be dropped or get hit by something, and that’s a direct comparison to Dynamic Microphones that are the exact opposite!
Also, Passive Ribbon microphones, have very low Sensitivity values. Even lower than Dynamic microphones.
However, Passive Ribbon microphones, have a much more natural sound when capturing sound sources, but you need to take note that there is a natural top end roll off. The reason for that is that due to the aluminium constructed diaphragm, high frequencies have difficulty in moving it (as they lack the energy the lower frequencies have).
Another interesting fact about Ribbon microphones is that due to their design, they are Bidirectional by definition. There are ways for Ribbon microphones to adapt other Polar Patterns too, but it is not that common.
Key characteristics of Passive Ribbon Microphones:
- They are passive (no power needed to operate)
- They use electromagnetic induction
- Small or Large Diaphragm
- They are very fragile and they cannot tolerate hits or drops
- They are used mostly in studio environments
- They are Bidirectional by default
Active Ribbon microphones are not that much of a different story. Essentially they are different from the Passive Ribbon microphones because they have an amplifier fitted internally which allows them to output higher voltage. However, for these microphones to operate, you need to feed them with power. But let me tell you a quick story now about that!
Active Ribbon microphones did not always exist. There is a “myth” that is going around that if you feed a Passive Ribbon microphone with power (even Phantom Power) it will tear the diaphragm apart and fry the microphone. This “myth” is true to an extent but not in its entirety.
There are some vintage microphones with their output transformer being centre-taped to the earth connection. If you fed a microphone like that with power, it would flow via the transformer which was not designed to handle power and you would now have a fried microphone. Fortunately, you will not find many of them around nowadays.
The next episode on “How to fry your Ribbon Mic” covers the case of short circuiting. Passive Ribbon microphones, mainly do not have their output transformer centre-taped to the earth connection. And that is good news, but there is danger still. Let’s assume you have a Passive Ribbon microphone on the other end and, mistakenly, feed it with Phantom Power. Chances are the microphone will survive under normal circumstances as their output transformer is designed to block any incoming power travelling through the cable.
You can have a cables knowledge refreshed by checking out the Audio Cables: The Basics article in regards to Microphone/XLR cables.
In the odd situation where your cable is faulty, this scenario changes dramatically. If the XLR conductors short circuit themselves and the signal ones get grounded, a short power surge will flow through the transformer even if it wasn’t supposed to, resulting in the transformer reversing its function and sending that surge to the ribbon diaphragm and tearing it apart.
This is a very odd scenario and requires a really not well maintained cable to cause this damage. Even if you hotplug a ribbon microphone with Phantom Power on, you should be alright, as XLR plugs are designed so that Pin 1 makes contact first, and this way, grounding the connection before Pins 2 & 3 make contact. However, this failsafe does not stand for TRS patch bay connections. So, if you are running Phantom Power via a patch bay, through a TRS connection, and you plug in or out the TRS jack, you are probably going to fry the microphone. Due to the design of the TRS plugs, the process of plugging/unplugging them involves short circuiting of the conductors, and if Phantom Power is present, a short power surge will make its way to the microphone and fry it, if it cannot tolerate it.
So these are some obvious reasons why that “myth” exists. And they are the same when comes down as to why there is a misconception out there about Ribbon Microphones not needing power to operate. For Passive Ribbon Microphones, it’s true, but since the Active Ribbon Microphones made it recently into the industry, this “myth” is becoming more unpopular gradually. Active Ribbon microphones will conveniently provide a higher output, and even some of them, are Active versions of Passive Ribbon microphones.
Pressure Zone/Boundary Microphones
A special mention to the Pressure Zone/Boundary Microphones here.
Just to clarify, although the PZM and Boundary terms have been associated with the microphone type, in reality, they actually relate to the Polar Pattern these microphones use.
These microphones, as you can notice on the image to the right, have a hemispherical polar pattern. This is achieved with the microphone having a flat surface exactly at the back of the capsule, this way removing any unwanted reflections and phase cancellation that might occur. Known uses for PZM/Boundary microphones are within a kick drum or as room mics!
Note that this Polar Pattern cannot be achieved with any other microphone. Essentially, Omnidirectional or Cardioid polar patterns are used within these microphones but due to the design of their chassis having a flat surface right behind the capsule, forces the pattern to behave as a hemispherical one.
Finally, to close this short mention to PZM/Boundary microphones, it’s worth mentioning that they are condenser microphones.
Microphone Characteristics: Wrapped
This article sums up everything within this serious! Microphones are a massive subject in sound engineering and producing and we just scratched the surface here. But you now have more than enough assets to work on and begin your journey!
I will post another article later on so I can sum everything up for you with links and short descriptions so you can guide yourself through the series with ease!
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