[Guest Post from Matthew Mcglynn] I often get asked to recommend kick-drum microphones, and in the process of helping drummers and engineers decide what might work for them, I’ve realized that it is useful to classify the available microphones by type.
[Note from Chris: While some types of microphones may be better for recording studio's, this article shows you what's available on the market for live and studio work]
- Tailored Dynamics – dynamic mics pre-EQ’d with aggressively scooped mids. The most popular and best-known bassdrum mics belong to this category.
- Speaker Transducers – a small group of purpose-built dynamic bass instrument mics created from speaker or headphone drivers. These mics generally excel at pickup of low frequency information.
- Dual-element Mics – Specialized kick mics with two transducers, each optimized for a different sound.
- Broadcast Dynamics – High-end dynamic mics with essentially flat EQ profiles, these mics are recommended equally for kick drums and broadcast use.
- Boundary Mics – Also known as PZMs (for Pressure Zone Microphones), boundary mics offer wide polar coverage and clean pickup of transients.
- Large-diaphragm Condensers (LDC’s) – Your best vocal condenser probably sounds great on bass drums, too.
Needless to say, most any mic could be used on the kick drum, including counterintuitive choices like ribbons. The point of this article is not to suggest that the following are the only reasonable choices, but rather to classify the types of microphones most commonly used for this application.
Note that placement tends to differ across categories of microphones. For example, dynamics are usually placed inside the drum, anywhere from just inside the resonant head to an inch off the batter head. PZMs can lay inside the drum, or on the floor in front of it. Speaker driver mics tend to be placed outside the drum, against the resonant head. LDCs usually stand in front of the drum, as far as six feet away.
Why are there so many types of bass drum microphones?
I suspect it is because the bass drum is difficult to record well. Modern engineers typically want two sounds from one instrument — the round, resonant, low-frequency, sustained tone of the drum (usually 70-100Hz), and the sharp attack of the beater on the drum head (usually 2-4kHz). Reproducing both sounds well arguably requires using two different types of microphones, in two different places.
For example, the best place to hear the attack of the beater is inside the drum, close to the batter head. Mics placed here tend to be fairly well isolated from the sound of other drums, as well as pedal and throne noises. Yet this is a high-SPL environment, where many condenser microphones would overload. Dynamic mics are better suited for this task.
But audience members never sit inside the bass drum. Whatever that mic hears is not what bass drums sound like to most listeners.
A mic placed outside the kick drum will hear a much more natural sound. As with any non-close-miked application, condenser mics will typically deliver superior results, due to their higher sensitivity. Yet in this position, the mic will also hear the snare, toms, and cymbals clearly, as well as every other instrument in the room. Further, the attack of the drum is not as present in this position, which for some music styles is a dealbreaker.
The idea that neither single mic adequately captures both sounds leads many engineers to use two or more microphones on the kick drum. This, in turn, has led the manufacturers to develop specialized microphones. We’ve seen two main developments here — two classes of microphones designed specifically to address the challenges outlined above. Read on for an in-depth discussion of all six types of kick mics, including the problem-solvers I call Dual-element microphones and Tailored Dynamics.
Six Kinds of Bass Drum Microphones
One solution to the challenge of accentuating both the high-frequency click and low-frequency boooom of the bass drum is the class of dynamic mics with built-in “scooped mids” EQ curves. These mics were engineered to simultaneously enhance the attack sound as well as the resonant low-frequency tone of the drum.
But all tailored dynamics are not created equal. Each has its own EQ frequencies, which may or may not be approprite for the drum in question. Further, the amount of HF and LF boost varies significantly across this category of mics.
|Microphone||LF Peak Frequency||LF Boost||HF Peak Frequency||HF Boost|
|AKG D112||100 Hz||4 dB||3000 Hz||5 dB|
|Audix D6||60 Hz||10 dB||5500 Hz||15 dB|
|beyerdynamic Opus 99||110 Hz||4 dB||2500, 5000 Hz||12 dB|
|Blue Kickball||70 Hz||4 dB||4000 Hz||12 dB|
|ElectroVoice N/D868||55 Hz||8 dB||4800 Hz||8 dB|
|Heil Sound PR-48||70 Hz||12 dB||4000 Hz||10 dB|
|MXL A55 Kicker||90 Hz||6 dB||2500, 4500, 7000 Hz||8 dB|
|Shure Beta 52A||50 Hz||5 dB||4000 Hz||17 dB|
A drum’s natural resonant frequency depends primarily on the species, thickness, and construction of the shell. For example, birch tends to produce higher frequencies than do maple and mahogany. Thicker shells tend to produce higher frequencies than thinner.
What this means is that even one of these specialized, pre-EQ’d microphones might be unsuitable for some kick drums. If the drum’s resonant frequency is 50Hz, the AKG D112 might sound thin — you’d get much more low end from the Beta 52. Conversely, a small jazz bass drum might not be well served by a Beta 52, N/D868, or Audix D6 — whereas the MXL A55 or D112 might shine.
Just for fun I measured the two kick drums I have handy. This illustrates the point that one hard-wired EQ curve doesn’t fit every drum:
|16×22” Tama Granstar II, 9mm birch||40 Hz|
|18×20” Tama Starclassic Maple, 7mm maple||70 Hz|
High-quality dynamic microphones are naturally able to withstand high SPLs, and generally sound good on any loud or close-miked source. I most often see these placed very near the resonant head, unless the drum is ported, in which case the mic is placed through the hole into the drum.
The Electro-Voice RE20 — aka PL-20 — is probably the best-known example of this class. This microphone is known for its excellent Cardioid pattern control and 15dB worth of rejection for off-axis sounds.
The Sennheiser Electronics Corporation MD 421 is another common choice. Current production units have a high-frequency presence peak not found on the RE20; this would tend to bring out the attack of the drum.
The low-frequency response of most LDCs extends to 30Hz or below, making these mics very suitable for kick drum. Usually they are placed at least one foot, if not 4–6 feet away from the resonant head.
Because this placement enables the mic to hear the rest of the drum kit, the guitar amp, and the rattling light fixture too, many engineers will build a tunnel or “doghouse” in front of the drum, to create some isolation for the microphone.
I don’t know of any LDCs built specifically for kick drum, but I’d recommend trying whatever LDCs you already have. The limiting factor in most cases is the mic’s max SPL rating; a sensitive mic without adequate padding can easily overload. Check your mics’ sensitivity and SPL ratings in the mic database.
The Neumann U47 fet is possibly the most famous LDC cited for kick-drum usage. Because these don’t turn up on eBay too frequently, you might instead seek out David Bock’s homage to the Fet 47, the Soundelux ifet7, or the Wunder Audio CM7Fet, or the Lawson L47Fet.
The Audio-Technica AT4047/SV often turns up in lists of recommended kick-drum mics, both for its 47Fet heritage and its rising low-frequency response.
Boundary mics, and their close cousins PZMs, contain a small condenser capsule next to a reflective metal plate. The capsule is usually a miniature omnidirectional electret; the resulting polar pattern is called “half spherical.” The mic operates on the principle that sound reflected from a surface is in phase with its direct signal, within a few millimeters of the surface (aka boundary). Therefore, the direct and reflected signals reinforce one another, giving a 6dB boost as compared to the level of non-directional or ambient sounds.
I’ve never understood the appeal of boundary mics for bass drums. Physics require that for best low-frequency response, the boundary’s longest dimension must be equal to the wavelength of the frequency to be recorded. For an 80Hz tone, that’s 14.125 feet. I’ve never seen a bass drum that long.
[Update — I've studied PZM math somewhat more closely since initially posting this article.
- A 4'x4' boundary loses 6dB of signal between 47Hz and 178Hz.
- An 8'x8' boundary loses 6dB between 23Hz and 94Hz.
- Mounting the PZM near a 90° junction (in a room corner) doubles or triples the depth of the shelf. Near a tricorner, you'll lose 18dB of LF response.
- If the PZM is mounted very close to the sound source — closer than the shortest dimension of the boundary panel — the LF shelf disappears.
Moral: if you're using a PZM, study the math first, and be prepared to do a lot of experimentation.]
So, you could put the mic on a board in front of the kick drum, but then it’s a room mic, and that HF boost is going to capture a lot of cymbal sound, especially considering that most boundary mics have a rising/bright HF response.
I have one boundary mic, a Crown PZM-30GP (aka PZM-30D). Its plate measures 5×6 inches. In the absence of a larger boundary surface, this mic effectively has a shelf filter of -6dB below 2200Hz, because the wavelength of a 2.2kHz tone is about 6 inches. Meaning, if I lay this mic inside the drum on a pad, I’m going to get a great big attack and probably not much else. [Update: subsequent study suggests that by placing the PZM within 5 inches of the batter head, the shelf might disappear.] My own tests bear this out — inside the drum, the PZM produces a nice beater impact, but no tone. On a long shelf board in front of the drum (or on the floor), the sound is much fuller. Listen for yourself; you’ll hear two hits from inside, two from outside, and a repeat:
(Note that the tighter “inside” samples will sound great over small speakers. Connect a subwoofer to your monitoring environment to hear the “outside” samples come to life.)
This is a general-purpose PZM, not necessarily intended for kick-drum use. But as the mic’s manual states (and the laws of fluid dynamics require), “Low-frequency response depends on size of surface.” This would be true for any boundary mic. Nonetheless, there are several on the market built specifically for kick drum:
The Sennheiser Electronics Corporation e 901 is unique among this group for having a somewhat tailored EQ curve built in to the mic, although the LF response depends on proximity (as well as boundary size).
The Shure Beta 91 is another popular choice.
OK, at this point everyone has heard of the idea of wiring a speaker driver to an XLR jack: instant “subkick.” The speaker cone becomes a very large diaphragm that is relatively insensitive to mid and high frequencies.
Be aware that these mics are rarely used alone, because they just won’t capture the impact of the drum. I most often see them paired with a second mic near the batter head.
The Yamaha Subkick is the most famous commercial implementation of this idea. The Subkick uses a 6.5” speaker mounted inside a wooden drum shell.
The Moon Mics DK20/DK27 uses an 8” driver. It ships complete with a Pearl drum stand and — usefully — a polarity switch.
Like the “Tailored Dynamics,” dual-element mics are another solution to the challenge of getting two different sounds from one instrument.
Many engineers will put two mics on the drum — a dynamic near the beater, and a condenser outside the drum. This approach presents two problems: one, these two mics are probably out of phase with one another; and two, the outside mic either records lots of unwanted sound, or requires the additional complexity of setting up an isolation tunnel.
Mic manufacturers have responded by combining the two transducers in a single housing. Each capsule has its own output, so these mics require two preamp channels. But their signals are guaranteed to be in phase, because the capsules are aligned. Further, because the condenser is inside the drum, it won’t pick up as much ambient sound.
Will it adequately capture the desired tone, though? I have not tried one of these mics, so I have no relevant experience. I’ll refer you to the reviews of the microphones below — these are two dual-element kick mics on the market today:
The Audio-Technica AE2500 was the first dual-element kick-drum mic. It has a premium price ($699 MSRP; see the mic profile for current street pricing), but its reviews are excellent.
A-T followed the AE2500 with the ATM250DE, using off-the-shelf parts rather than custom-designed components.
More kick mic possibilities
This article was not intended as a comprehensive guide to kick-drum microphone choices, but because we’re partway there already, I’ll mention a couple more that don’t fit neatly into the categories outlined above.
Ribbons are a natural for capturing transients, and their proximity effect can lead to a great low-end sound. The risk is that ribbon transducers are highly sensitive to air blasts. Put a ribbon mic in front of the port on a bass drum, and the element will split.
So, if you’re using a ribbon mic, keep it out of the air blast. Also, tilt it forward 45°.
This article has been re-printed (and shorted) from Matthew Mcglynn’s article on his site Recording Hacks. See the full article: Six Types of Kick Drum Microphones.
Question(s): What do you use? What tricks have you learned?
top image source = http://www.flickr.com/photos/wbrowar/3872389983/