You've probably seen a microphone pop filter before in either videos, pictures, or in person. It's that thing in between the vocalist and the microphone.
What is a microphone pop filter, and when should you use one? A microphone pop filter is a device used to protect mic capsules from plosive energy. A pop filter helps to eliminate the popping sound associated with gusts of air from the human voice and other sources. Pop filters work by dissipating transient sound energy between a sound source and mic capsule.
Microphone pop filters are a crucial piece of any studio gear list. Let's discuss pop filters in more detail here, including how and when to use them.
To learn about my recommended microphone pop filters, check out my article Best Microphone Pop Filters.
What Is A Microphone Pop Filter And When Should You Use One?
As discussed in the first section, a microphone pop filter is a device that helps to eliminate plosive sounds from entering a microphone capsule. Pop filters are also referred to as pop shields or pop screens.
Before discussing the physical characteristics of a microphone pop filter, let's define the plosives they protect microphones against.
What Are Plosives?
When talking about microphone plosives, the conversation is always about human speech. That's because plosives are part of human speech.
Plosive sounds are made by fully blocking the flow of air as it leaves the mouth, followed by the blast of air produced along with the sound as the blocked air is released.
In English, there are 6 plosive sounds. From strongest to weakest, they are:
The amount of plosivity seems to depend on whereabouts the air is blocked as we make these plosive sounds.
- “P” and “B” plosives have an air blockage at the closed lips.
- “T” and “D” plosives have an air blockage with the tongue behind the teeth.
- “K” and “G” plosives have an air blockage at the palate.
Note that different languages have different plosive sounds and that we're only discussing English here.
The candlelight experiment is a classic test to try when learning about plosives. Light a candle, place it near your mouth and begin talking. You'll notice the hard transients of plosive sounds cause the flame to flicker or even go out. However, if you were to hold a vowel sound (like “ahh” or “ouu,” for example), the flame would stay relatively steady.
Just like the flame from a candle, microphone diaphragms are sensitive to plosive sounds. The blasts of air from plosives can wreak havoc on a microphone diaphragm.
Plosives And Microphone Diaphragms
A plosive hitting the diaphragm causes a massive pressure difference between the front and back of the diaphragm as the blast of air passes by.
In directional microphones, the blast of air basically creates high pressure on the front of the diaphragm while causing strong suction on the backside. It takes the diaphragm a long time (relative to the frequency of sound pressure vibrations) to regain its equilibrium after a plosive hit. All this causes a large asymmetrical peak/clip in the microphone signal.
These large asymmetrical peaks and microphone clips are considered a “microphone plosive.”
Note that omnidirectional microphones are very resistant to plosives. Omnidirectional microphones have the front side of their diaphragms open to external sound pressure, but the back side of the diaphragms closed in a tiny pocket of constant pressure. So although it's possible to overload an omni mic with a plosive sound, chances are the diaphragm will handle it well and bounce back quickly!
Microphone plosives often sound like a “thud” or “pop” in the lower frequencies and have the potential to overload the mic capsule and the mic preamplifier.
The effect plosives have on a microphone diaphragm is highly dependant on the distance between the mouth and microphone capsule/diaphragm.
For more information on microphone diaphragms and capsules, check out my articles What Is A Microphone Diaphragm? and What Is A Microphone Capsule? (Plus Top 3 Most Popular Capsules), respectively.
Think of having a conversation with someone versus having someone speak an inch from your ear. The plosive sounds are fine when at a distance but may even hurt at a very close distance to your ear. This is because the blasts of air are very directional at their source but dissipate quickly as they travel through the air.
I've mentioned the asymmetrical plosive peaks are often in the lower frequencies. I've also mentioned that plosives will have more of an effect on the microphone as the sound source gets closer to the mic capsule. This has to do with the proximity effect, which states that the closer a sound source is to a directional microphone, the more bass response that microphone will exhibit.
Let's Recap Our Definition Of Plosives:
- Plosives are the blasts of air that come from our mouths during the sounds P, B, T, D, K, and G (in English).
- Microphone plosives are the asymmetrical peaks and clips in a microphone signal associated with vocal plosives.
It goes without saying that if we’re getting plosives in the microphone signal, we’re not capturing the audio we want. A pop filter is a great protective device against the issue of plosive sounds.
To learn more about microphone plosives, check out my article Top 10 Tips For Eliminating Microphone Pops And Plosives.
How Are Pop Filters Built And How Do They Protect Microphone Capsules?
The effective part of a pop filter is most often disc-shaped and is made from acoustically semi-transparent material. This is often woven nylon stretched over a circular frame or a thin perforated metallic circle. This material basically allows sound waves through (and around) but dissipates the blasts of air caused by plosives.
So pop filters protect microphones from plosives by dissipating blasts of air into harmless turbulences. As a plosive from a vocalist's mouth hits the pop filter, the sound waves effectively pass through, but the gust of air gets scattered.
Conscious positioning of the pop filter is critical. Immediately after the pop filter, the air turbulences are still powerful enough to be dangerous for a microphone diaphragm. We must give them space to fully dissipate so that they do not “pop” the microphone capsule!
Another purpose of the microphone pop filter is to shield the microphone from saliva (and, unfortunately, sometimes food). This less discussed attribute has the potential to increase the longevity of your microphones. Pop filters are much easier to clean or replace than microphones. This benefit should not be understated!
Let's discuss the 3 general build types for pop filters:
Standalone Microphone Pop Filters
A pop filter is often comprised simply of the actual filter, a bendable arm, and a clip/clamp that attaches it to a mic stand. An example of this build is the popular Aokeo Dual-Mesh Pop Filter.
Shock-Mount/Pop Filter Combo
To learn more about microphone shock mounts, check out my articles What Is A Microphone Shock Mount And Why Is It Important? and Best Microphone Shock Mounts.
DIY Pop Filter
A common do-it-yourself pop filter entails bending a metal coat hanger into a circle shape and stretching a pair of pantyhose/leggings over the top. The coat hanger acts as the frame, while the pantyhose acts as a double layer of acoustically semi-transparent material. These household items work perfectly fine as an effective pop filter.
Pop Filter Materials
There are 2 common materials used in creating pop filters
Perforated Metal Alloy Pop Filters
Perforated metal alloys are often used in pop filters. This material is solid enough to hold its shape as a circular pop filter and doesn't need an outer frame. The holes in the perforated metal allow a large range of frequencies to pass through and dissipate plosive energies effectively.
These pop filters are similar to the metal grilles of many microphones. The reason, then, for using a metal alloy pop filter is that we can position it further away from the microphone capsule. The distance between the pop filter and mic diaphragm is critical in allowing the plosive energy to dissipate and not overload the capsule.
Manufacturers sometimes utilize multiple metal screens in their pop filters. These screens often have differing hole sizes for better results.
One such perforated metal alloy pop filter is the popular Stedman Corporation Proscreen XL:
Pros of Perforated Metal Alloy Pop Filters
- Bigger holes allow more high frequencies to pass through than typical woven nylon
- Easy to clean and dry
- Does not rip like woven nylon
- Generally smaller than their woven nylon counterparts
Cons of Perforated Metal Alloy Pop Filters
- Easily bent and hard to fix once bent
- Sometimes increases sibilance
- Sometimes induces phase issues
- A bit more expensive than woven nylon
Woven Nylon Pop Filters
Woven nylon pop filters are perhaps the most popular. Though nylon is the common material used in these fabric-style pop filters, other thin fabrics may also be used.
These industry-standard pop filters are made of woven nylon stretched over a circular frame (typically made of plastic or metal wire). These filters can be manufactured with one or more screens.
The thinly stretched nylon allows sound waves to pass through. The plosive energies, however, are impeded.
A great example of a woven nylon mesh pop filter is the Nady MPF-6:
Pros of Woven Nylon Pop Filters
- Clean passing of sound waves
- Easily replaceable or repairable with household items
Cons of Woven Nylon Pop Filters
- Easily ripped
- Slight attenuation of high-frequencies
- Harder to clean than perforated metal
Of course, it only takes a quick look at a message board to see how divided people are on the best material for a pop filter. Both nylon and metal pop filters work great if positioned correctly.
A Note On Acoustic Foam
Oftentimes acoustic foam windscreens are used as pop filters. These polyurethane acoustic foam screens typically slip directly onto a microphone. Because these foams do not create much distance between their surface and the microphone diaphragm, they aren't particularly effective at reducing plosives.
Acoustic foam windscreens are often excellent at reducing wind noise but not very good at reducing plosives. For that reason, they should be absolutely be utilized outdoors but not in the studio.
For more information on windscreens, check out my articles What Are Dead Cats And Why Are Outdoor Microphones Furry? and Best Microphone Windscreens.
How To Effectively Position A Pop Filter
When positioning a pop filter, I like to use the simple “one fist rule.” Position the pop filter one fist length away (thumb to pinky) from the microphone.
The pop filter should be placed in such a way that it eclipses the front of the microphone capsule from the performer's mouth. We want the pop filter to intercept all the plosives between our performer's mouth and the microphone diaphragm.
As for where the performers should position themselves, this varies from person to person and on the style of voice work. So long as the pop filter is positioned correctly between the performer's mouth and the microphone capsule, it should do its job.
When Should You Use A Pop Filter?
Well, if you haven't guessed by now, pop filters are typically used when recording vocals and speech. I suggest using a pop filter in front of any microphone (including the omnidirectional mics) when recording any type of voice, just to be safe.
My belief used to be “only use pop filters when necessary.” However, after fixing a few plosives in post-production from vocals I have recorded, I've started using them religiously! Anything to help at the back end. In my opinion, it's easier to boost a bit of the lost high-frequencies from a pop filter than it is to surgically fix each plosive or ask for another take from the performer.
Speaking of fixing noise issues in post-production, check out my article Top 7 Best Noise Reduction Plugins For Your DAW.
One could argue that kick drum microphones should require pop filters due to the large blasts of air projected from kick drums. I've personally never heard of anyone using a pop filter for this.
Some other engineers like to use pop filters when recording horns. Although the gusts of air created by horns are typically not as transient as vocal plosives, they still have the potential to cause issues at the microphone diaphragm.
The wind is another cause of gusts of air in microphones. However, a windscreen is the best bet in reducing wind noise. A windscreen covers the entire microphone grille/capsule, providing protection from wind noise.
Does wind cause plosives in microphones? Wind and plosives are both noises we do not want in microphones, but they are not the same. Wind noise happens as moving air hits a mic diaphragm or a surface near a mic. Plosives happen as a blast of air emerges from someone's mouth as they make “p,” “b,” “t,” “d,” “k,” or “g” sounds into a mic.
Are there techniques to reduce microphone plosives that do no include pop filters? Yes, there are techniques other than using pop filters to reduce microphone plosives. They are:
- Using an omnidirectional microphone
- Positioning the microphone off-axis from the performer
- Placing a pencil or pen up to the lips
- Distancing the performer from the microphone
- Using a high-pass filter
Choosing the right microphone(s) for your applications and budget can be a challenging task. For this reason, I've created My New Microphone's Comprehensive Microphone Buyer's Guide. Check it out for help in determining your next microphone purchase.