# Using a relay for retro clicky sound - how do I make it louder?

I'm building a battery operated retro device that I want to sound really clicky and old fashioned. I want to include the noisiest relay (sound noise not electric noise) possible in my project. Can anyone help me identify what characteristics are correlated with more noise? Actuation time? Release time? Weight? Amperage rating? or alterternatively recommend a relatively small relay that is known to be especially noisy? These relays are not intended for switching any loads. The usual google searches for relay and decibels or noise doesn't come up with anything useful.

I have considered using a turn signal but those devices are quite large.

• Have you considered a tiny MCU strapped to a speaker? You can make any sound you like with it. – Ignacio Vazquez-Abrams Oct 8 '16 at 17:38
• @IgnacioVazquez-Abrams: Yes, any sound digitized and reproduced that you want. If the OP is looking for a retro sound perhaps he enjoys the analog aspect of it. For example the timber/tone will always be slightly different in a real relay and will vary depending on humidity/temperature/lifetime/etc. – jbord39 Oct 8 '16 at 17:48
• Really a µC to fake a click? Man! A single, short impluse (from discrete electronic parts) into a speaker might do the trick very well. – try-catch-finally Oct 8 '16 at 18:19
• Maybe a thin bit of wood glued to the body of the relay would act as a soundboard. IME, you would want a relay with a transparent plastic cover. I can't get my old BBC Micro out to see if there is a part number on the cassette motor relay. – Andrew Morton Oct 8 '16 at 18:55
• Just use a micro solenoid. They are all naturally "clicky" and you can enhance the sound by using them to move strikers against a suitable acoustic body. – Brock Adams Oct 8 '16 at 21:40

Try using an inexpensive power relay such as the T90 series, and attach it to a resonator board which will act like the cone of a speaker. They draw about 1W each.

Since you're after an aesthetic effect you'll have to fiddle with it, I think.

Now if you really want buzzy clanky sounds, you can consider an AC powered "definite purpose contactor" as used in HVAC equipment which will be very noisy and retro sounding. They are not even that consistent in their sound (because of the AC power), which I suspect is useful in your application because they don't sound like a fake synthetic sound. You'll need something like an SSR or a small relay to control the contactor. They're huge and don't mount on PCBs.

You can get a similar effect (at less sound level) by feeding the DC relays with some kind of randomized power (such as a ramped sine or triangle wave started with random phase) to make them pull in less consistently. Again, you'll probably have to fiddle with it. You can consider the relay as a special kind of speaker with a really weird response (once they pull in and the magnetic circuit is closed the current has to be backed off a lot for anything much to happen). You could use the contacts to feed back the armature state to a micro. Use something related to your mains frequency such as 120Hz or 50Hz to get authentic mmm..buzz-click sounds. Lots of fun possibilities.

• Great suggestion. Right now I have the relay tacked right to the side of the plexiglass case which seems to radiate sound quite well. I have not tried varing the waveform sent to it but that sounds like a great idea. – Jeremy Gilbert Oct 8 '16 at 19:24
• By the way, these relays have been cloned for many years by the Chinese (and others), and can be very cheap especially if you are not deterred by the absence of (genuine) UL/CSA etc. listing (not really a problem in this application). As you say, they are also haptic transducers. – Spehro Pefhany Oct 8 '16 at 19:38

You might want to consider an auto starter solenoid. That is something you could get as salvage. If you want a big sound from something very small, you will need to reproduce the sound.

• a mic with amplifier can make it even louder – Tony Stewart Sunnyskyguy EE75 Oct 8 '16 at 18:40
• I suspect that the battery the OP is using will not be very effective with one of those. – Andrew Morton Oct 8 '16 at 18:47
• @AndrewMorton Yes. Another reason to reproduce the sound electronicaly rather than using something "authentic". – Charles Cowie Oct 8 '16 at 19:05
• Any ideas how to reproduce a solid clicking sound without resorting to samples? It's a surprisingly complex sound. I've done some spectral analysis and its got a lot going on. – Jeremy Gilbert Oct 8 '16 at 19:26
• I assume there is a simple way to store and play sound clips like those you can find by searching "sound effects." I have no idea how you would program a waveform generator to produce the kind of sound that large relays make. – Charles Cowie Oct 8 '16 at 22:07

Consider using a "pinball knocker", essentially a solenoid that strikes the inside wall of a pinball cabinet (or a strike plate of its assembly) to make that rapid clacking/knocking sound an various points in the game.

Tuning the control of that solenoid and the object it is striking can get you anything from a rapid series of clacks to a single dull thud that you can feel.

• That's not a comment. That's a solid answer. – Passerby Oct 12 '16 at 15:38
• On the flip side (pun totally intended), pinball knocker sound files would make for a great source for a digital solution. – Passerby Oct 12 '16 at 15:43
• From the picture, "Don't hold it down, it may get hot and explode." Isn't that what a BRB is intended to do? – Andrew Morton Oct 14 '16 at 21:31

It will probably be smaller, cheaper, and easier to implement to mimic the sound of a relay than to use a genuine relay. Relay actions only take a few 100 ms at most, even for really big klunky ones.

Even the sound simply recorded and played back thru a small PC mount speaker wouldn't take much memory. Let's be pessimistic and say you need 12 bit samples at 20 kHz sample rate (most likely 8 bit samples at 10 kHz is sufficient). That comes out to 30 kBytes/s, or 3 kBytes for 100 ms duration. You probably have a spare 3 kB of program memory in your microcontroller already. Even if not, upgrading to the next larger micro is going to be a lot cheaper, take less space, and require less power, than adding a relay.

• But, it will not be nearly as genuine if the goal is to create a retro sound. It will also sound the exact same every time. As opposed to real relay which will change timber and tone as humidity and lifetime alter it. – jbord39 Oct 8 '16 at 17:46
• @jbor: There is no reason it should sound any different from the real thing. Most users aren't going to notice the sound of a relay changing with age, but you can add randomness to the playback too. Playing the stored sound in 80 to 120 ms instead of the nominal 100 ms is probably good enough. – Olin Lathrop Oct 8 '16 at 17:49
• Sure, and most people can't really tell the difference between a tube amplifier and a transistor amplifier. Or $25 bottle and$500 bottle of wine. But, there is still a difference, and if the OP is specifically looking for a retro sound, perhaps he likes the analog aspect of it? – jbord39 Oct 8 '16 at 17:56
• @Jbord: You are making up specs. The OP didn't say anything about whether the $25 or$500 bottle of wine is good enough. This is a suggestion and meets his specs. Even so, a speaker playing the right sound and the genuine article inside a box probably can't be distinguished in a double blind test. After all, there is no such thing as a standard relay sound. There range of authentic relay sounds is quite large. – Olin Lathrop Oct 8 '16 at 22:10
• Sometimes people give answers to the question asked. Sometimes people give answers to the problem faced. This the latter. You have to appreciate both, and both are allowed. – Passerby Oct 12 '16 at 15:37

A lot of relays may advertise how quiet they are. So you can check the datasheets for louder relays, or those that do not specifically advertise so. As an example see this datasheet: random relay datasheet

You can see that there are a few models

• Low Noise Models: G5RL-1A(-E)-LN
• High-Inrush Models: G5RL-1(A)-E-HR, G5RL-1A-E-TV8
• etc

Avoid the low noise models, obviously.

As a rule of thumb I would say that the higher current the relay can handle, the louder the click of the relay.

Also, you could hit the relay a bit harder when activating it: drive it with a higher input slope (stronger/faster driver).

• You should consider doing it with a microcontroller and a small speaker. That would cost less, be smaller, and take less power. It can also be made louder than a real relay while keeping the sound the same, which is one of the problems the OP alluded to in the question title. – Olin Lathrop Oct 10 '16 at 19:51

Solenoids usually produce a loud click so use internally a solenoid that activates when any of the relays activate. The solenoid doesn't have to do anything useful of course.

clunky solenoids with a battery just slightly above the Vmin for the coil will be the slowest chatter clunk, and then the max rated voltage for the coil will have the loudest but solid clunk.

for small relays here's 4.5V one that can be mounted glued to a panel to amplify the sound,that will,operate from a LiPo cell down to 3.1V

http://www.digikey.com/product-detail/en/panasonic-electric-works/APF3034H/255-4085-5-ND/2202482

If using a 9V battery then use matching coil voltage give or take 50%

To make it buzz and stick and buzz when you hit it if it sticks... Use the above and wire the coil in series with 3.7V Lipo battery and NC ( ormally closed ) contacts and then it will buzz and vibrate albeit with some electrical noise... (don't touch contacts). As battery wears out in 10 hours. it will,buzz slower and slower until it sticks , you shake it and it buzzes some more. until battery is drained.

But for sound bytes... just put the mic in contact with the relay and record it. or record an A/C solenoid

At least as important as picking the right relay is the mechanical design of the part the relay is attached to.

In order to emitt sound efficiently you need acoustical impedance matching so the tiny (but strong) mechanical osciallation of the relays moves as much air as possible.

This can be accomplishged, e.g. by placing the relays onto a large board that is free to oscillate or the chassis of the device.

We regulary use an inexpensive 200mW relay to obtain the authentic click sound. In a plausible but futile experiment, we tried to shortly overpower the relay, connecting 5V coil to 24V supply. Unfortunately, the sound level was not noticeably increased. However, different relays behave very differently, so the choice of a right type is a key decision.