Helmholtz synthesizer experiment

berkeman
Mentor
Hello all!

Inspired by the Helmholtz synthesizer, I am experimenting with electromagnetic excitation and tuning forks.

http://www.sites.hps.cam.ac.uk/whipple/explore/acoustics/hermanvonhelmholtz/helmholtzssynthesizer/

How can I determine the size and charge of an electromagnet in order to excite a tuning fork and produce sound?

Fun project!

Do you want the audio output from the tuning forks to be heard throughout your audience area, or will you be using microphones close-in to record the sounds? That will obviously affect the power you need to use to drive the tuning forks (and the size of the coils and tuning forks).

Assuming that you will use microphones to pick up the individual sounds from the different coil drivers and tuning forks, I would start with an initial estimate of 1 Watt per drive coil. That's not much power for a drive circuit, and would give you plenty of sound to pick up with a microphone.

dlgoff and Maria B
dlgoff
Gold Member
Fun project!
Yes it is. Back in the early 1960's at our little towns annual carnival, Bell Telephone Laboratories had a booth and I was given a Speech Synthesis kit. I still have the booklet. Here's some pictures from it:

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jim hardy, Asymptotic, berkeman and 1 other person
Fun project!

Do you want the audio output from the tuning forks to be heard throughout your audience area, or will you be using microphones close-in to record the sounds? That will obviously affect the power you need to use to drive the tuning forks (and the size of the coils and tuning forks).

Assuming that you will use microphones to pick up the individual sounds from the different coil drivers and tuning forks, I would start with an initial estimate of 1 Watt per drive coil. That's not much power for a drive circuit, and would give you plenty of sound to pick up with a microphone.

Yes it is coming up to be a really fun thing to do!! I am afraid we do not want to use amplification since it is an sound art piece, it would ruin the "experience." Do you believe using more than 1 Watt is possible?

How about the relation between the number of turns of the electromagnet and the tuning fork´s vibration? I assume there should be one, right?

Thank you so much!!!!!

Yes it is. Back in the early 1960's at our little towns annual carnival, Bell Telephone Laboratories had a booth and I was given a Speech Synthesis kit. I still have the booklet. Here's some pictures from it:
View attachment 226448
View attachment 226449
View attachment 226450

WOW dlgoff this is AMAZING!!! Thanks a lot! And what an important piece of history you have with you!! Sharing is caring, thank youuu

dlgoff
tech99
Gold Member
Maria. The electrically sustained tuning fork was a standard method of obtaining a stable low frequency from roughly 1918 until 1970. In the example you show, each fork is next to a Helmholtz Resonator, which is a vessel used as a resonator to increase the sound. Originally, the tuning fork had electrical contacts, so it worked like a buzzer, but later on it was used with the two electomagnets in conjunction with an amplifier. You are not going to do this without some analogue electronics experience.

Maria B and berkeman
Yes it is coming up to be a really fun thing to do!! I am afraid we do not want to use amplification since it is an sound art piece, it would ruin the "experience." Do you believe using more than 1 Watt is possible?

How about the relation between the number of turns of the electromagnet and the tuning fork´s vibration? I assume there should be one, right?

Thank you so much!!!!!

It does sound like fun. I'm not sure you will get too far with calculations on the number of turns for an electromagnet, I suspect there are far too many unknowns for that. I'd start with some experiments. I'm assuming you have the tuning forks? And that they are ferro-magnetic? I'd try taking the coils from some old speakers, and just trying it with an audio signal that matches the tuning fork frequency.

Let us know how it goes.

Maria B
tech99
Gold Member
As a guideline for the coils, try about 200 turns of 30 AWG/SWG enameled wire on steel bolts. Check that the tuning forks are magnetic. I suggest an amplifier giving a few watts. If no oscillation, reverse one pair of wires.

Maria B
tech99
Gold Member
As a guideline for the coils, try about 200 turns of 30 AWG/SWG enameled wire on steel bolts. Check that the tuning forks are magnetic. I suggest an amplifier giving a few watts. If no oscillation, reverse one pair of wires.
I also remembered that the magnets on which the coils are wound must be permanent ones. This creates a standing attraction which increases or reduces according to the applied sine wave. If the core is not magnetised, there are two pulls per cycle, so the amplifier is operating at twice frequency. It is the same principle as with the old style telephone earpiece. In practice, I think a button magnet could be stuck to each bolt.

Maria B
I also remembered that the magnets on which the coils are wound must be permanent ones. This creates a standing attraction which increases or reduces according to the applied sine wave. If the core is not magnetised, there are two pulls per cycle, so the amplifier is operating at twice frequency. It is the same principle as with the old style telephone earpiece. In practice, I think a button magnet could be stuck to each bolt.
A strong second harmonic might sound nice!

Maria B
tech99
Gold Member
A strong second harmonic might sound nice!
I agree that second harmonic can make sounds more pleasant, but unless the magnets are permanently magnetised it will not oscillate.This is because we require a magnet for the pick up device (generator effect). Also the Helmholtz Resonator is tuned to the fundamental of the tuning fork.

Maria B
It does sound like fun. I'm not sure you will get too far with calculations on the number of turns for an electromagnet, I suspect there are far too many unknowns for that. I'd start with some experiments. I'm assuming you have the tuning forks? And that they are ferro-magnetic? I'd try taking the coils from some old speakers, and just trying it with an audio signal that matches the tuning fork frequency.

Let us know how it goes.

Hi, and thank you for your reply! I do have the tuning forks, but no, they are not ferromagnetic. I was expecting to induce some charge to the coil by connecting it to a power source. Does this make any sense at all?

Maria. The electrically sustained tuning fork was a standard method of obtaining a stable low frequency from roughly 1918 until 1970. In the example you show, each fork is next to a Helmholtz Resonator, which is a vessel used as a resonator to increase the sound. Originally, the tuning fork had electrical contacts, so it worked like a buzzer, but later on it was used with the two electomagnets in conjunction with an amplifier. You are not going to do this without some analogue electronics experience.

Hi and thank you for your interest in my project! I am aware of all the facts you mentioned above, although I am not experienced in electronics, I have worked as audio engineer for more than 10 years. Electronics are not my strength, but I certainly know how to connect devices and power things up! I am grateful for all your comments and suggestions

I also remembered that the magnets on which the coils are wound must be permanent ones. This creates a standing attraction which increases or reduces according to the applied sine wave. If the core is not magnetised, there are two pulls per cycle, so the amplifier is operating at twice frequency. It is the same principle as with the old style telephone earpiece. In practice, I think a button magnet could be stuck to each bolt.

Great tips!! I came across a connection diagram for an old style telephone earpiece, now that you mention it. Will definitively look into that!! thanks!

tech99
Gold Member
If the forks are not ferromagnetic, maybe glue a little button magnet to each fork?

Tom.G
Add as little to the tuning fork as possible, a small thin piece of Iron for instance. By adding mass to a tuning fork you lower its frequency. You will have to retune by removing material from the same general area of the fork.
I was expecting to induce some charge to the coil by connecting it to a power source. Does this make any sense at all?
I don't think so, at least as stated. How about a few more details on what you have in mind and what you expect for results?

Baluncore