So I'm doing a project involving classifying electrophones according to MIMO's Hornbostel-Sachs system (see here) and I'm looking at musical floppy disk drives specifically (see here).

The drives make sounds mecahnically by electrically pulsing the motor at any number of positions to generate different frequencies (and different notes). For this reason, I've narrowed down my classification choice so far to "52. Electromechanical instruments and devices" which MIMO says are:

"Configurations of (electrically excited) silent, mechanical moving parts with encoded patterns, and electronic circuitry. The movement enables the encoded patterns to be transduced into an analogue fluctuation of an electric current"

Which makes sense to me.

They subdivide this into "Tone wheel instruments", "Photoelectric electromechanical instruments", "Record/playback devices", "Electromechanical samplers", and "Electromechnical sound processing devices". Having read through all of these and their examples, I feel like musical floppy drives are closest to tone wheel instruments such as the Telharmonium, but I am definitely not an expert on the subject.

Hopefully this is the right place to ask this, but is there a better classification in the Hornbostel-Sachs system? Or is this classification correct?

Thanks so much!

  • 5
    Not sure of this info so I won't post an answer, but from my understanding a tonewheel induces a current electromagnetically (Wikipedia compares the tonewheel operation it to the vibrations of guitar strings over electric guitar pickups). AFAIK the disk drive creates a series of noises mechanically and the sound comes directly from the moving parts rather than being represented in an analog current and amplified with a loudspeaker. Apr 17, 2018 at 14:19
  • @DarrenRinger The part of your comment about disk drives is absolutely correct. (I know nothing about tonewheels, so I've no opinion on the first half of your comment.) Apr 17, 2018 at 17:02

3 Answers 3


They are not. Tonewheel instruments have metal disks in them that are cut in a pattern and then a pickup (a coil of wire around a magnet) that is near each wheel. When the wheel spins, the pickup has a periodic current induced in it by the pattern cut in the wheel. The electric current induced in the pickup is normally muted but is unmuted when the appropriate keyboard key is pressed, and then all of the outputs from all of the pickups are mixed together and amplified.

The most famous tonewheel instrument is the Hammond B3 electric organ.

Musical floppy drives make mechanical noises in a way that can be pulsed. By pulsing the floppy drive at different rates, different frequencies of mechanical noise can be created. I don't think a floppy drive fits in any of the categories you listed. I might call it a "modulated friction" device or something like that.

If you want a more mundane example of something similar to a floppy drive, a squeaky door hinge is a good analogy. The faster you swing the door, the higher the pitch of the squeak. If you can swing the door at exactly the right speeds, back and forth, you could play a tune by making it squeak on pitch. The squeak is created by friction in the hinge. If you set up an electric motor to swing the door at set speeds and programmed a song into the motor's control circuit, you would have an electromechanical instrument that works similarly to the floppy drive.

  • 3
    IIRC at least some floppy systems change rotation speed depending on where the head is accessing, so tones might come both from head movement and the drive motor itself. Apr 17, 2018 at 14:36
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    @user3684314 Yes. According to Wikipedia, there is a category for electrophones for electrically actuated acoustic instruments, category 5.1, which IMHO applies to floppy drives. The specific acoustic category I would put floppy drives in is 1.3, Friction Idiophones, and I believe 1.3.2, Friction Plaques is probably the closest category. And further breakdown I would go to, Sets of Friction Plaques. So it's a complicated instrument. Apr 17, 2018 at 14:52
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    @user3684314 Ben Miller's categorization makes sense also. I think the problem is that the categorization system has become a bit dated and needs some work to take into account all modern instruments. The electrophones category is sorely lacking even if it is meant to indicate instruments with purely electrical sources, since a ROMpler is very different from a Theremin, and IMHO they should have separate subcategories. Apr 17, 2018 at 15:10
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    @ToddWilcox thank you so much (and Ben Miller as well!). I think I'll ultimately go with electro-acoustic idiophones based on your recommendation (I know it's a little lacking, but for my purposes it's more than enough). Thanks again! Apr 17, 2018 at 15:22
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    There was a youtube video of an organ that used stepper motors from floppy drives in a fashion similar to a Hammond organ, and I would regard that as being a tone wheel instrument, but most music projects using floppy drives use them to convert electrical signals into sound, while tone wheels convert motion into electrical waves.
    – supercat
    Apr 17, 2018 at 16:58

I’m going to say that the best fit for this would be 515: Transducers.

The closest comparison I can think of is to a loudspeaker. You are sending an electrical signal to a device that converts it to mechanical motion and the sound comes from the resulting vibration.

It doesn’t seem to quite fit any of the other categories in the “5: Electrophones” section.

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    Agreed. The top-level category chosen in the question is wrong: "The movement enables the encoded patterns to be transduced into an analogue fluctuation of an electric current" (my emphasis) ... this is working in the opposite direction to what's needed here, generating electrical signals from mechanical motion, rather than using electrical signals to regulate a mechanical motion such that it produces the desired sound.
    – Jules
    Apr 17, 2018 at 17:37

Read the start of the "Electrophones" section.

Instruments that use materials generating acoustic sounds, mechanically-driven signal sources, electronically stored data or electronic circuitry to produce electrical signals that are passed to a loudspeaker to deliver sound.

A floppy drive does not "produce electrical signals that are passed to a loudspeaker". The noise from a floppy drive (or an electric drill, or any other piece of machinery) comes solely from the noise of the mechanical parts moving. The tone is produced in the same way as running a stick along a fence, as each tooth from each cog meshes with the next, with the timbre dictated by the structure and materials of the mechanism. Therefore by this definition it cannot be an electrophone.

What you actually have is an ideophone. Definition (section 1):-

The substance of the instrument itself, owing to its solidity and elasticity, vibrates and may radiate sound without requiring stretched membranes or strings.

Now to narrow it down. In all these cases, it's the meshing gears which cause the noise. So from that list, the best fit seems to be "112.24 Scraped wheels or cog rattles". Definition:-

A cog wheel, whose axle serves as the handle, and a tongue fixed in a frame which is free to turn on the handle; when whirled, the tongue strikes the teeth of the wheel one after another.

For meshing cog wheel, each cog wheel is effectively the "tongue" for the previous cog wheel, because that's what causes the noise. Note that it doesn't quite fit the definition, so the list should either be a little less prescriptive about the structure of that type, or it should have another type to fully cover noisy mechanisms.

And then of course it's actually 112.24-9 because it's mechanically driven.

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    Is it not "electrically actuated"? Mechanically driven to me seems like something powered by an engine or a water wheel (water powered organs have existed), etc. A floppy drive is electrically driven and electrically actuated (actuated meaning the thing that chooses which note is being played is electrical, rather than mechanical or human power). Apr 17, 2018 at 17:37
  • @ToddWilcox But if you could replace the electric motor with any other kind of motor and the resulting sound would be identical, then the electrical element is irrelevant. We don't need to reclassify church organs based on whether they have electric motors or small boys pumping the bellows, after all. :) All that matters is that there's some kind of mechanical drive to it, don't you think? Whether it's an electric motor, a compressed-air drive or a small steam engine in the next room, it's the mechanical action which matters.
    – Graham
    Apr 18, 2018 at 10:22
  • I think the classification system actually does take into account the different ways organs are powered and also actuated. Note that the actuation system and the power system are two different things. For a floppy drive, they are both electrical. Also, floppy drives are pulsed st audio rates, and I can’t think of a way to do that without using electronics. So unlike an organ, a floppy drive cannot make music without being electrically actuated. Apr 18, 2018 at 11:48
  • @ToddWilcox A stick running along a fence is pulsed at audio rates. :) My understanding is that this is more concerned with the electrical/electronic system providing some kind of control over the tone shaping, over and above simply making the thing move. Of course the drive rate sets the frequency, but I don't believe it does anything much with the tone. Just my opinion though. That's the problem with classification systems generally, of course - the pigeonholes often show the biases of the designers, and it isn't always obvious how to fit in things they didn't know about.
    – Graham
    Apr 18, 2018 at 11:56

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