You have probably noticed that some mics will need more gain from a preamp than others to get to the same signal level. Therefore, some mics are more sensitive than others. But, what is microphone sensitivity? Let’s find out…
- Let’s Look At What Microphone Sensitivity Isn’t
- The Sensitivity Rating
- A Transducer
- High Or Low – Part 1
- What Is Microphone sensitivity?
- How Does It Work?
- Microphone Input
- Microphone Output
- Does it Matter?
- High or Low – Part 2
- Sensitivity in Active Against Passive Microphones
- Sensitivity In The Microphone is Not Adjustable
- The Multi-Pattern mic
- Misunderstanding and Misuse of the Word Sensitivity
- What Determines the Sensitivity of a Microphone?
- Dynamic, Moving Coil Microphones
- Dynamic, Ribbon Microphone
- Condenser Microphones
- At This Point
- What Is Microphone Sensitivity – What To Use and Where
- But… Generally Speaking
- Looking for more high-quality microphone options?
- What Is Microphone Sensitivity – Making the right choice
Let’s Look At What Microphone Sensitivity Isn’t
The first thing to clear up is that the sensitivity of a microphone is not adjustable. When you change the volume of the mic, you are not making changes to its sensitivity. Increase the volume, and the volume will, of course, go up, but the sensitivity of the mic stays exactly the same.
It will output a defined amount of signal when there is a certain Sound Pressure level.
The Sensitivity Rating
This is determined by the strength of the audio signal or, in other words, the output voltage in relation to the SPL.
The sensitivity of a mic is measured by how well it works as a transducer. And if you’re not sure what a transducer is, let’s explain that a little more…
All microphones can be described as a transducer. The job of the transducer is to take acoustic energy and convert that into electrical energy. In other words, taking sound and converting it into an electrical signal. That is what microphones do.
We can measure the sensitivity of a mic by how well it achieves this. The type of transducer can be defined by how it works. There are two main types, Dynamic and Condenser. More on those a bit later.
High Or Low – Part 1
Choosing a mic with a high or low sensitivity might seem like a simple decision. But it will depend on the situation it is going to be used in. And there is a lot to consider before making that decision.
This article is about microphone sensitivity. And therefore how it has an effect on what we are using it for and what to consider when choosing a microphone.
What Is Microphone sensitivity?
Having looked at what it isn’t, let’s consider what it is. You can describe it as a certain input giving you an amount of output. The input means the sound pressure level that is operative at the diaphragm of the mic.
It is measured using a standard input signal as a reference. This is a kHz sine wave at an SPL of 94dB, or to use another term 1 Pascal or Pa.
How Does It Work?
As I have already said, all microphones can be considered as transducers. They convert energy from one form to another. With a microphone, that is converting mechanical energy into electrical energy.
The Input and Output of the microphone have different forms of energy. Without getting too deep into Pascal or Newtonian physics, here is a very brief description.
The Input to the mic is the level of sound pressure that is received at the diaphragm. It is measured in dB SPL or Pa. The dB SPL is the decibels of sound referenced with the human hearing threshold. That is 0dB SPL.
This is the voltage delivered across the output connection. This is measured in mV or dBV.
The sensitivity of analog and digital microphones are measured differently. Analog is measured using mV/Pa units. Digital mics are measured by assessing the output generated at a 94 dB SPL input. The calculations to identify both are different.
Does it Matter?
We are looking at calculations and descriptions that mean nothing to many people. So does it really matter?
It certainly does to audio engineers. And it also matters to you if you are using a microphone. It is important to understand microphone sensitivity and use it accordingly. It is a benefit to know how much of our signal we can expect to receive from our mic. You may ask why.
High or Low – Part 2
If you are trying to record an instrument with a loud sound source, it will be different from recording an instrument with a quieter sound. As an example, if you are trying to record a kick drum, the sudden powerful sound source will generate a high SPL.
Therefore, you will be better using a low-sensitivity microphone. The same would apply if you were micing up a guitar at volume or a bass guitar. They are likely to create huge peaks of sound, a high SPL.
Some microphones are specially designed to record sound pressure levels that are high. The diaphragm of a mic is made from a thin layer of material that can be vulnerable.
Push too much sound pressure at it, and it will be damaged. Not a situation you want. So on that basis, audio engineers will know this and will prefer low-sensitivity microphones when they are recording a loud sound source.
And there is always a but. Low sensitivity mics are great for sounds with high volume, but what about quieter sounds? A Low sensitivity mic may not offer the level of output you need.
Applying a lot of preamp gain to a mic with low sensitivity is not a good idea. It will increase the level of ambient sound in the recording and could also introduce preamp noise. It will also increase the signal-to-noise ratio and, therefore, will reduce the quality of the audio signal.
But you might need to record quieter, nuanced, more subtle instruments. Or maybe sounds that are in the distance. In that case, you are probably better off with a High sensitivity mic. They are designed for softer instruments that do not generate too much SPL.
The acceptable Sound Pressure Level is designed to be much lower in a high-sensitive mic. They, therefore, do not work well with ‘hot’ sound sources, such as the kick drum I just covered.
Sensitivity in Active Against Passive Microphones
Speaking generally, an active mic will be more sensitive than a passive mic. This isn’t to do with the diaphragm design. This greater sensitivity is because of the internal components that amplify the sound before the output of the microphone.
Sensitivity In The Microphone is Not Adjustable
As already mentioned, you cannot alter the mic’s sensitivity. Increasing the volume is not adjusting the sensitivity. The sensitivity remains constant, putting out a given signal when it is subjected to a certain sound pressure level.
So on that basis, anything we do to the mic cannot alter that or change the sensitivity, is that right?. Well, no, that is not exactly true.
The Multi-Pattern mic
The interesting thing here is that there are mics that feature up to four different polar patterns. As you switch between these polar patterns, some of the specifications of the collection of the sound will change. And that can include sensitivity.
Varying the Polar Pattern can therefore have a minor effect upon the sensitivity of the mic.
Misunderstanding and Misuse of the Word Sensitivity
Sometimes the word is used as a synonym for reactive or fragile. But in the world of the microphone, they mean different things.
If a diaphragm is fragile, that has nothing to do with sensitivity, as we are discussing it here. The conversion of sound into current has nothing to do with the amount of impact the diaphragm can take before being damaged.
As an example, we all know that the diaphragm of a ribbon microphone can be very fragile. So does that mean it is also sensitive? Not necessarily. The least sensitive mic is a passive dynamic ribbon when compared to dynamic, condenser, and active ribbon mics.
How the diaphragm reacts will play an important part in converting energy into a signal. But this role is more to do with signal quality, meaning transient response or frequency response. The Diaphragm reactivity is not a vital part of the sensitivity of the microphone. It refers more to the quality.
For example, using the Ribbon mic again, they are often more reactive than a condenser or moving-coil mic. But a ribbon mic will usually have the lowest sensitivity measurement.
What Determines the Sensitivity of a Microphone?
I have already mentioned that how effective the microphone is as a transducer will determine its sensitivity. But within that action of conversion, there are three separate actions that have an effect.
- The reaction of the diaphragm to the different sound pressure levels.
- The efficiency of the transducer type.
- Audio signal amplification within the mic.
There are two types of transducers we are most familiar with. These are the Condenser and the Moving-Coil Dynamic. But we can create a third if we include a moving-coil dynamic ribbon mic. Let’s take a brief look at all three variants.
Dynamic, Moving Coil Microphones
These mics operate by using electromagnetism. They have a coil of wire made of copper that is fixed to a moving diaphragm. The diaphragm itself is in a magnetic field. The wire moves through the magnetic field and, by doing so, produces an audio signal or AC voltage.
However, many engineers think that this is not efficient. The combination of the diaphragm and the wire makes it heavy and not as reactive. The voltage that is produced is very small, and sometimes a passive device is required to increase output.
And if you try to boost the signal too much, you will get distortion and a reduction in frequency response.
Dynamic, Ribbon Microphone
The capsule of a Ribbon mic is made from very thin aluminum. This sits between two magnets. The sound pressure will move the ribbon across the magnetic field. This gives you the AC voltage or audio signal.
The ribbon can be very fragile. This is a physical failing. As we discussed, sensitivity and fragility are different things. Again with this system, the voltage that is created by the ribbon is very small.
There are two types of Ribbon mics, and they both have their own way of taking the voltage to a level that can be used.
- Passive Ribbon mics use built-in transformers to increase voltage.
- Active Ribbon mics use active electronics to achieve the same.
They operate on an electrostatic principle. There are two parallel plates that form a capacitor. One is stationary, and one is a moveable diaphragm. The plates have an external DC charge, or some have electret material that maintains a permanent voltage.
The gap between the plates will change in relation to the amount of sound pressure. Therefore the capacitance will change. This causes a variation in the output of AC voltage, the audio signal.
Output voltage, though, is still relatively low, and active electronics are used to boost the signal before output.
At This Point
It might be worth just mentioning that there are differences in the way that the sensitivity is measured. There is a European Sensitivity measurement and an American version.
Both systems are used, and observers all have their own favorite ways of measuring sensitivity. I only mention this, so you are aware. Because there is not enough space here to go into a detailed explanation of the differences and how the results are measured,
What Is Microphone Sensitivity – What To Use and Where
Realistically there are no set rules. No one description of functionality that fits all purposes and uses. In other words no set-in-stone rules for when to use a High or a Low sensitive mic.
There are variables in whichever way you approach the problem. One of which is the quality of the preamp the microphone is being plugged into. A lower sensitive mic will need more gain from the preamp, which can often add problems in terms of unwanted noise to your signal.
If you are going to use a low-sensitive mic for recording the quieter sound sources, the preamp will need to be very good.
But… Generally Speaking
Generalizing can always be a risky business. But for the purpose of this article, there do need to be some basic guidelines.
What Are Low Sensitive Mics Better For:
- The close micing of drum kits, especially the kick.
- If you mic up a guitar or bass amp.
- Recording horns.
- Some Vocals (depending on the natural volume and style of the singer).
- Any instrument or sound effect that produces a high SPL.
What Are High sensitive Mics Better For
- Recording natural sound, especially at a distance.
- Voice Overs
- Acoustic Guitar.
- Acoustic Piano (but that may depend on the aggressive playing nature of the piece).
- Stringed instruments, solo or group.
- Woodwind and gentle brass.
- Some softer Vocals.
So there we are. The basis of microphone sensitivity and why it is important. So, you should now know just about everything you need to know on the subject. If you are thinking of buying a new mic for a particular purpose, here are some examples of each of the three Microphones we looked at:
A Legendary Dynamic Mic, the Shure SM57, a quality Ribbon Microphone that is fantastic for vocals or a mono overhead, the AEA R84A Ribbon Microphone, and finally, probably the most renowned condenser mic you can buy, fantastic on vocals and just about everything else, the Neumann U 87.
Looking for more high-quality microphone options?
Then take a look at our in-depth reviews of the Best Dynamic Microphones, the Best Vocal Mics, the Best Condenser Microphones, the Best Interview Microphones, and the Best Wireless Microphones currently on the market.
Or how about the Best XLR Microphones, the Best Choir Microphones, the Best Shure Microphones, the Best XLR Microphones, and the Best Microphones for Recording Par Vocals you can buy in 2023.
You may also be interested in our reviews of the Best Microphone Preamps to make sure you have enough power for your mics.
What Is Microphone Sensitivity – Making the right choice
Choosing the correct mic with the right sensitivity is important, as you now appreciate. There are crossovers, of course, where a Low sensitive mic might handle a highly sensitive situation. But getting the sensitivity right will help you on your way to a great recording.