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Heil Sound PR40

Cardioid Dynamic Microphone
Published June 2009
By Paul White

Listening to the sound from this extraordinary dynamic mic, you might be forgiven for thinking it was a ribbon or a condenser.

Heil Sound PR40

There are days when the thought of one more 'me too' side‑address cardioid condenser vocal mic doesn't exactly thrill me, so I was pleased to discover that, despite its familiar appearance, the Heil Sound PR40 is not what it appears to be at first glance: although it looks like a large‑capsule condenser mic, behind that deceptive exterior lies an end‑address dynamic mic that's designed for use with voices, kick drums, bass instruments, guitar cabs and lots more.


Given its physical attributes and extended low‑end response, the PR40 will probably be compared with the Electrovoice RE20, although I also see performance parallels with the Sennheiser MD421. Either way, you know that if Bob Heil is involved in the design, you'll get something a bit out of the ordinary. Readers of our sister publication, Performing Musician, will know that Bob Heil is both a ham radio enthusiast and a live-sound guru with an impressive provenance, first coming to public notice in the early '70s when he set up the now‑legendary 'wall of sound' PA for the Grateful Dead. He's since been involved in the design of communications microphones, so he has a lot of expertise when it comes to designing mics with precise pattern‑control.

The PR40, which is assembled and tested at Heil Sound's facility in Illinois, USA, has a surprisingly wide frequency range for a dynamic microphone, covering 28Hz to 18kHz (‑3dB). It is designed to withstand very high SPLs, but at the same time it manages to sound more natural on voice and other instruments than most cardioid dynamic mics — many of which have a noticeably coloured sound, due to the complex porting needed to create the cardioid polar pattern. Although the frequency response is nominally flat between the upper and lower roll‑off points, there's the gentlest hint of a presence bump from 3‑5kHz. It only amounts to a couple of dB, but it gives a sense of air at the top end.

Bob Heil's approach to cardioid dynamic mics always seems to produce a tight polar pattern, with almost perfect rear‑rejection — a feat Bob attributes to "using the ideal combination of materials for the 1.125‑inch, low‑mass diaphragm and a special mixture of neodymium, iron and boron that gives the PR40 the strongest magnet structure available.” Aluminium is used for the voice coil and, as with the PR series hand‑held models, the large‑diameter dynamic capsule is mounted in a Sorbothane shock absorber to decouple it from the heavy steel body. An additional humbucking coil reduces the effect of interference from nearby electronic devices or transformers, and proximity bass‑boost has been minimised as far as is possible for a pressure gradient microphone.

The basket screen comprises two wire‑mesh screens of different diameters, augmented by what's described as an internal breath‑blast filter (I couldn't get into the microphone to see how this was arranged). It does, however, keep popping to a minimum when the mic is used for vocal work, and also helps avoid sibilance. A champagne‑coloured satin plating is used over the steel body, and the signal exits on the usual balanced XLR. A swivel stand‑adaptor is provided with the mic, which comes in a compact, foam‑lined aluminium case, with a paper banner around the mic reminding the user that, despite appearances, this is an end‑fire mic.

In Use

Bob Heil is particularly proud of this microphone's performance on kick drum, although it's also recommended as a broadcaster's voice mic. Given that most kick‑drum mics have a massaged frequency response, some heavy mid‑cut EQ may be necessary to achieve a contemporary kick sound, but there's no lack of low‑end extension, and you can get a great depth of sound. But this mic isn't only good for kick drum, by any means. I got some great djembe tones out of it, and on vocals it sounded impressively natural, but at the same time full and solid — which would be ideal for radio DJs, as well as for some types of studio vocal. However, you do need to be aware that the level changes hugely between what you get from singing right up against the grille and what you get when working three inches or more away, so it would be a good idea to use a pop shield, just to keep the singer back at a safe distance. The mic's susceptibility to popping is impressively low, given the extended bass response, but I'd still recommend using a low‑cut filter and pop shield for vocal work.

Because of its solid bass response, this mic works really well on bass guitar cabinets, and I loved it on electric guitar too, where the results were rather less 'honky' than I'm used to from dynamic models. It has an almost ribbon‑like smoothness on highs, but without any loss of transient detail or any dullness to the sound.

Another bonus is that, because the high end extends up to 18kHz, you can use the mic in many applications where a capacitor model would normally used — and if you have a clean, quiet preamp, it sounds fabulous on acoustic guitar, revealing plenty of detail and a dense mid‑range, but without the glassy grittiness that some budget capacitor mics seem to impart to the sound. In this respect, at least, its performance might best be compared with the Sennheiser MD441.

All Hail Heil?

The Heil Sound PR40 isn't a cheap mic, by any means, but then neither are the mics with which it compares. In fact, some of them cost quite a bit more. This has to rate as one of the best dynamic mics I've ever come across, both for tonality and versatility — and it's probably a good thing for the rest of the industry that Bob Heil hasn't yet turned his attention to condenser mics!  


The Electro-Voice RE20 overlaps in terms of applications and cosmetics, while both the Sennheiser MD421 and 441 models have the same 'desert island microphone' appeal, in that they can deal with almost anything you throw at them.

Published June 2009