diy instruments apprehension engine part 1

DIY Instruments: The Apprehension Engine Part 1: Introduction

Embracing the do-it-yourself spirit, this is the first post in a series about DIY instruments. And we’re kicking things off with a really interesting, film composer-specific instrument dubbed “The Apprehension Engine.” It combines many unique elements to produce bone-chilling sounds that are perfect for a horror movie. Let’s look at what it does and how it works. Then in future posts, we’ll look at how we can replicate its elements to create unique sounds for our own horror movie scores.

(note: As an Amazon Associate I earn from qualifying purchases.)

What is the Apprehension Engine?

Simply put, the Apprehension Engine is a musical instrument purpose built to create sounds for horror films. Commissioned by film composer Mark Korven and built by guitar maker Tony Duggan-Smith, it features many unusual parts that combine to create eerie sounds. It rose to fame in the past year with an NPR story about it, and a short doc video by Great Big Story getting more than five million views.

That video is probably the best introduction to what the machine does. Check it out below:

How Does It Work?

At its heart, the Apprehension Engine is a series of simple noisemakers built around a resonating chamber, wired with pickups and microphones. Plugged into an amplifier (or straight into an audio interface), these sounds can be heard and recorded. As evidenced in the videos, there are a couple key components:


There are a series of metal rulers bolted to the resonating chamber. The different lengths create different tones, and they can be plucked or bowed. They’re just rulers!


Two tuned strings that are played by a rotating, hand-cranked wheel. An old-fashioned method of producing unnaturally long, sustained notes. In this case, disquieting harmonies are possible rather than the traditional octave or fifth intervals.

Electric Guitar Strings with E-Bow

An E-Bow uses electromagnetic fields to produce sound

Sitting next to the hurdy-gurdy are several more strings, this time from an electric guitar, that are played with an e-bow. The e-bow is an interesting device. It’s basically an electromagnet that makes metallic strings resonate. By moving it around the strings, or moving closer/farther away, you can get different overtones. This is turned into a current by a guitar pickup, then sent out to an amplifier.

Spring Reverb

Probably taken from an electric guitar amplifier, a spring reverb device is a series of springs suspended over a metal plate. When the springs vibrate, a small current is produced and sent out to an amplifier – like a microphone. They can be plucked, hit, or played with the e-bow.

Spiral Springs

These appear to be thin, coiled torsion springs as seen in the trunks of some cars – basically long strips of metal bent into a spiral. Again, they are plucked or bowed to produce a sound, which is captured by a microphone.

Weighted Pendulums

Thin weights at the end of long, flexible, metal sticks. They tap against the wood of the resonator as they rhythmically bounce up and down. This causes a sound akin to a tapping finger, except with inhuman precision.

Magnetic Fragments

There is a small hollow wooden chamber at the top of the Apprehension Engine, where it appears there are just several pieces of metal (probably iron) sitting inside. These metal fragments jump up and strike the wood as a strong magnet is passed over the lid of the box. The movement here is more random without being recognizably organic, therefore becoming even more unsettling.

How to Make Your Own

Mark Korven is selling copies of his instrument on his website, and we aren’t going to attempt to reproduce his design. But, if you don’t have the $10,000 base price to order one of the limited edition instruments yourself, you can still learn from the basic ideas to craft your own DIY Instrument.

In the next post we’ll look at exactly how to implement some of these ideas to create our own uniquely terrifying horror movie instrument!

Film Composer Mark Korven

Mark Korven has had a long career in film composing, starting with 1987’s I’ve Heard the Mermaids Singing. Some of his more notable projects are composing for the first revival of The Twilight Zone in the late eighties, and the 90’s cult horror film The Cube. More recently, he scored The Witch in 2015, which is a period horror film. That film, in particular, is interesting for its music because it uses no electronic instruments whatsoever (in keeping with its period aesthetic). He told NPR:

“The Witch was a very unusual score in that Robert Eggers, the director, he didn’t want anything that was electronic at all. He didn’t want even reverb. He wanted it to be very flat, very dry, very real. So that was an unusual score but it did inspire this machine.”

(for more on working with directors, check out this post)

If you haven’t seen that film, definitely check it out. It’s very atmospheric and creepy. Bonus points if you can watch it with the lights off!

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