Dynamic Microphone

Microphones / Miking

Published October 2023

Intended for both speech and music, Audix’s latest microphone demands to be seen as well as heard!

The rise of the ‘content creator’ has opened up a new market for quality microphones. Models such as the Shure SM7B and Electro‑Voice RE20, which once sold mainly into broadcast and studio environments, are now ubiquitous in podcasting, streaming and online video. And whereas the chunky form factor of these mics might previously have limited their use in on‑screen roles, it’s a selling point in Internet media. Expensive and highly visible mics have become status symbols, and in turn, manufacturers are making them even more visible.

That’s certainly the case with Audix and the PDX720 Signature Edition. It doesn’t bear the signature of anyone in particular, and there are currently no other versions, so the Signature Edition tag seems designed to introduce an air of exclusivity. So, too, does the mic’s distinctive appearance. With its asymmetric black body and shiny gold‑coloured grilles, the PDX720 is a pretty eye‑catching affair. Something about the styling also makes it look even larger than it actually is: my initial reaction was “Blimey, this is huge!”, though in fact it’s very similar in size to the SM7B.

Big Sig

Thanks to its size, its chunky metal shell and its integral standmount, the PDX720 is a hefty beast, weighing in at nearly 870g. Even if the standmount was removable, this is not a mic you’d want to use handheld! The standmount is functionally similar to the SM7B’s integrated yoke, except that it has a single pivot point located inside the microphone rather than one on either side. It allows the mic to be rotated through slightly more than 90 degrees along its front‑back axis, and provides enough friction to hold it in place without the need to tighten any thumbwheels.

As on the SM7B, the XLR output connector is integrated into the standmount. This is one aspect of the design that I wasn’t crazy about. Because the mount extends an inch or so beyond the socket, it gets in the way when you try to grip the connector on an attached cable, and Audix have used a high‑end Switchcraft XLR, which was a very tight fit with all the cables I tried.

The design influence of the SM7B is also apparent in the provision of two switches, located on the butt of the microphone. A key concern with this sort of feature on vocal mics is ensuring that switches can’t be moved by accident. Shure achieve this by using recessed slide switches that need a pointed tool to adjust, but Audix have taken a different approach. The switches themselves are simple toggles, but they’re hidden behind a removable end cap, which attaches magnetically. This is quite an elegant solution and certainly hinders unwanted changes, but it means there’s no way to tell at a glance whether the switches are engaged.

The base of the PDX720 houses the mic’s high‑pass filter and presence boost switches.

The functions of the switches are also comparable to those on the SM7B, albeit that there are more choices here. One engages a high‑pass filter turning over at either 120Hz or 155Hz, while the other introduces either a 1.5 or a 3 dB presence lift in the upper midrange. The published frequency response diagrams suggest that this is more or less a shelving boost from about 2kHz upwards.

It’s perhaps misleading to describe this as a boost, in fact, since the PDX720 is a passive moving‑coil dynamic mic just like the SM7B, with no active circuitry. It nevertheless produces a warmish output, with a specified sensitivity of 1.9mV/Pa. On paper, that should make it about 5dB hotter than the SM7B on the same source; in my tests, the difference was actually a little greater than this, and should mean there’s no need for a Cloudlifter or similar device with most mic preamps.

Audix describe the PDX720 as a hypercardioid mic, but the polar pattern plot on the spec sheet actually looks more like you’d expect to see from a subcardioid. I asked Audix about this, and they told me that although the capsule they use is hypercardioid, they make various modifications to it to adapt it for its intended close‑up use, and these relax the directionality somewhat. They also point out that their pattern graph has a 30dB scale rather than the 20dB used by some other manufacturers, which can make the same measurements look very different.

Although the capsule is a hypercardioid model, Audix’s implementation of it has made it less directional, which makes the PDX720 less sensitive to changes of mic position.

Smooth Operator

Although the point of these capsule adjustments is partly to reduce plosives and proximity effect, Audix definitely don’t intend the PDX720 as ‘merely’ a podcast or speech mic. They see it as a premium general‑purpose dynamic model that is equally at home in music recording — just as the SM7B and RE20 are. With that in mind, one thing that’s striking about the published frequency plot is the low‑end response. With the filters switched out, the graph is flat or even slightly above flat, all the way down to 20Hz (albeit at a measurement distance of 12 inches rather than the more standard 1 metre). Its performance at the other end of the spectrum is also very respectable, though its high‑end extension doesn’t rival capacitor mics in the way that the RE20 and the Sennheiser MD441 do. It’s broadly flat to about 8kHz, before a gentle roll‑off begins, with usable signal still present at 15kHz or so.

In the course of this review, I recorded all my test sources with both the PDX720 and an SM7B, although the size of both mics means that it’s not always easy to do A/B comparisons in similar positions on the same take. It was a good illustration of why published frequency response charts shouldn’t be taken as gospel. On paper, the response of the two mics with all the filters switched out should be very similar, with the PDX offering slightly greater low‑end extension and the SM7 a bit more in the 10kHz region. In practice, there was a clear difference between the two, especially on vocals, with the SM7B making everything sound quite a bit more present in the upper midrange. Experimenting with the PDX720’s switches actually suggested that the full +3dB presence boost came closest to matching the sound of the SM7B in its flat mode.

On vocals, it delivers a balanced sound that’s articulate and clear, yet comfortable to listen to for long periods, and never sibilant or harsh.

Not every moving‑coil dynamic merits the adjective ‘smooth’, but the PDX720 certainly does. On vocals, it delivers a balanced sound that’s articulate and clear, yet comfortable to listen to for long periods, and never sibilant or harsh. It doesn’t impose its own character, and the high‑pass filter settings are well chosen to correct for the proximity effect at typical distances in use. Used right up close, for example. I found the 155Hz setting compensated nicely for the additional bass boost, whereas if I went more than about six inches from the mic, I didn’t need the filter. Resistance to popping seemed pretty good, even without the filter engaged, and you can move off‑axis with relatively little change in tonality or sensitivity: it certainly doesn’t have the ‘beaminess’ you’d expect from a true hypercardioid.

Considered as a general‑purpose studio mic, the PDX720’s potential applications are a little limited by its size and weight, though no more so than the SM7B or RE20. I much preferred it to the SM7 as a kick drum mic: its low‑end response delivered more weight, and its smoother midrange made the overall sound less hard and boxy. It also put up an excellent performance on guitar amps, trading some of the SM7’s rock & roll thrill factor for a slightly more ‘hi‑fi’ yet very solid tone. And of course if you want to bring back some of that upper‑midrange excitement, the tone switch is only a thumb movement away.

The PDX720 Signature Edition is not a cheap microphone. You could get two SM7Bs or Beyer M88s for the same price, and it’s also more expensive than the RE20, competing head on with the Neumann BCM104, Sennheiser MD441 and Electro‑Voice RE27N/D at the top of the dynamic mic tree. From a functional point of view, it also faces off against rivals like the excellent Earthworks Ethos. Personally, I found its slightly bling-y styling less attractive than that of the Ethos, and it doesn’t have the utilitarian, engineering‑led charm of the SM7B and RE20. But that’s very much a matter of personal taste, and I’m sure there are many who will feel differently.

What’s important is how it sounds, and if it’s Audix’s aim to create a no‑expense‑spared dynamic mic that can hold its own against those rivals in almost any application, I’d say they’ve hit the nail on the head.