Let's talk about wireless mics.
While the first big splash was really made by DJI and then Røde we're seeing these types of two transmitter of one receiver 2.4 GHz systems being developed by anyone and everyone from Smallrig and Neewer, to Hollyland and Comica, and many brands you may never heard of. But everyone is making them because the demand is there for more and more content.
I'm a fan of these mics. They're remarkable pieces of kit and give a good improvement over camera or phone audio and are significantly easier to use than holding a wired headset up in front of you for those devices which still have input jacks.
However, they do come with a few issues, which we'll discuss here.
1. Size
For some reason, all these microphones have been designed with a very large boxy shape while this may have initially been just to incorporate all the necessary electronics, by and large these have been designed as statement pieces with a brand name right on the front. They're bulky, and generally cumbersome.
As a result, you'll see a lot of content creators holding these mics in their hands or clipping them awkwardly to the collars of their clothing or sticking them on the back of rulers even business cards. This works, and creates a particular DIY style, but not one that looks generally comfortable, and can make the mics prone to handling noise.
It's not impossible to do and a little bit of work with clever clothing placement and some tape can yield very very good results but overall it puts a large weight where they wouldn't naturally be one on a costume.
2. Frequency
These microphones are commonly referred to as 2.4 GHz systems. The reason for this is they operate in this specific frequency band, which is the same band used by most modern electronics. Anything from Wi-Fi to cellular communications runs on either 2.4 or 5 GHz.
This is a spectrum used for consumer digital communications and while it is crowded by so many modern devices because all these devices are transmitting their signal digitally, and are individually paired interference is uncommon unless one is in a very crowded environment, such as a production set, stadium or large expo with a lot of wireless communication channels.
In these difficult environments these microphones can often suffer from interference, and you have to rely on the onboard recording -- if it is there -- to ensure that you've got your audio files at the end of the day. It's in these situations that we often switch over to UHF systems, which depending on the frequencies they use can avoid interference from other surfaces, but also penetrate buildings more easily or make use of reflections.
The downside here is that, across the world, radio frequencies are a licensed. 2.4 and 5 GHz is universally free-for-all but that's what makes it unreliable. UHF on the other hand is licensed in order to control levels of interference and ensure that people can use frequencies without being disrupted. Frequencies are licensed per day and the availability and costs vary per country.
3. Placement
As said above, these mics can be difficult to place because they're bulky. However they need to be placed in an optimal position and that is as close to the talent as possible, while still avoiding breath sounds in the forms hisses, rumbles, and plosives.
To this end, often the best place to put them is in the center of the chest. This gives a good decent chest resonance and can be pointed up towards the mouth and if you're a close-up won't be seen on camera. However, the way you fix it is important and dependent on the costume that is being worn. If someone is wearing eg. a loose jumper or a thin shirt, any movement can mean this flops around and that will be heard.
So a good solution can be to place them nearby by hiding them in a plant or on a desk, but one needs to be considerate of ambient sounds like typing or scratching, and talent moving their heads -- think Lina Lamont in Singing in the Rain.
The easiest way to solve this is to use the lavalier microphones (lavs) that these are often accompanied with. Lavs are generally small omnidirectional, condenser microphones. This is the type of microphone that is in the device itself, but can also be at the end of a cable that is (sometimes) supplied. The benefits of a cabled lav is that it is very lightweight and so it can be secured to clothing or to skin with specialist tapes. Because they are lighter they are less likely to cause noise by being moved around however, they do come with a cable and noise will come through the cable and so how the cable is placed around the body of your talent is very important and this often necessitates catching the cable to the talent in the way that they can still move comfortably or making it part of the costume.
Hiding these microphones leads to another problem in that if the element is obscured in any way, this is going to affect the quality of sound, so this means a placing microphone in a wig or on the skin or a jacket can create a muffled sound if not done carefully.
4. Wired lavs
Not all microphones are created equal, and depending on the manufacturer the lavs supplied with these devices can be of varying quality. While the wired lav certainly makes life easier for the points I've mentioned above, one manufacturer may supply a very high-quality microphone while another manufacturer may supply a low quality one and in audio test you can sometimes hear the difference between the onboard microphone and the wired microphone. This creates a dilemma in which you have to make a choice between ease of use or quality of sound. Sometimes the difference can be notable, but sometimes it can be particularly noticeable and where you are doing an audio first solution, such as an audio podcast or voiceover narration you will want to prioritize audio quality.
This also means that you may need to consider higher quality lavs as part of your budget, and good ones are more expensive than most 2.4ghz wireless systems.
5. Directionality
When we speak of directionality in microphones were referring to the pick up pattern: omni-directional, cardoid, super cardoid, hyper cardoid, figure-of-eight, or semi spherical in the case of boundary microphones. Lavalier microphones are almost universally omni-directional. This has several advantages one being that the microphone can be placed in the vicinity of the talent, and still pick them up, simply using the proximity to hear them over the ambient noise. Two is that they do not experience what is known as the proximity effect meaning their bass response is consistent no matter the distance to the sound source.
These are great benefits, but of course have their cons. Picking up sound from all sides means that you are more likely to pick up the sound of footsteps, clothing rustle and other voices in the vicinity. The proximity effect as well is something which is quite desired in Voiceover, and also in singing and standup where distance from the mic creates a very rich tone which can be used artistically.
So as these microphones become more ubiquitous because of these issues, they still don't replace handheld dynamic microphones, large diagram condensers, or boomed shotgun microphones. Generally, when doing a production, the sound of the boom microphone is always preferred over the lass with the lavs being used often as a backup, or where it is very difficult to get the boom close enough. Similarly in Voiceover or audiobook narration, a quiet environment, and a large diaphragm condenser with a cardoid pattern is preferred to give that buttery voiceover sound. The same as true in music production where different microphones will be more useful for different instruments and directionality is required in separating parts such as you would in an orchestra or band.
At the end of the day, there is no one solution for any any project and I've certainly found ways to make these microphones work in all the different scenarios. I've mentioned here but it's important to be aware of these factors so that they don't create surprises in your project.