Why Do Pinball Machines Pop?


Why Do Pinball Machines Pop?

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Owning a pinball machine is one of life’s greatest joys. We’re talking endless amounts of uninterrupted playtime and that extra ‘cool’ factor when you have company over. One thing your guests may not be prepared for, however, is the insanely loud ‘pop’ sound that can sometimes occur in a pinball machine. As everyone wonders if the machine is broken, you calmly state that the machine pops all the time. But maybe even you can’t explain why. Yet.

So why do pinball machines ‘pop’? The popping sound that occurs in the pinball machine is coming from a mechanism in the game called a knocker. The knocker makes a loud sound to announce you’ve won a free game. While there is much speculation as to why the manufacturers designed games to have that pop, the most popular working theory is that it was meant to announce to an entire arcade that you achieved something, so as to pull focus to the individual and gameplay at hand.

The popping of the pinball machine certainly splits a room. Some people love the sound, feeling a sense of nostalgia and pride in what the slamming of the knocker represents. Others find the sound not only annoying but also ear splittingly loud. In this article, we will get down to the bottom of why it occurs and how you can disable this feature if it’s perhaps not your (or your partner or roommate’s) thing.

If you want to see some current pinball machines or other retro arcade machines just click here.

What is the Knocker Feature in a Pinball Machine?

Sometimes when you just finished a game, and you are about to see if your score matches the number needed for a free game – POP! Out of nowhere – as though a golf ball has shot into the backside of your pinball cabinet. That earth-shattering thwack is indeed indicating “Congrats! You just won a free game!” It also occurs when your bonus on the last ball allowed you to score a replay. This is commonly referred to as the ‘credit knocker,’ or as the ‘replay knocker.’

The knocker is attached to the side of the cabinet or the backbox. It is essentially a solenoid with a doorbell plunger in it, so that when it fires, it literally ‘knocks’ the side of the cabinet. A solenoid (in this instance, we’re referring to a solenoid chime) is a coil of enameled wire that is wound around a rod-shaped piece of metal, often made from solid iron, steel or powdered iron.

They act as miniature receiving antennas. The inside of the metal rod (or its core) is made of magnetic lines of flux. Thus, when a current runs through the coil, the magnetic field pulls the core upward with a tremendous amount of force. The inertia of this carries the core above the center of the coil, where it can then strike against an opposing piece of metal or object to create noise.

Solenoids are what doorbell chimes are made of. In the case of a pinball machine, the solenoid knocker slams itself against the cabinet instead of a beautiful sounding chime (normally like that of a Xylophone.)

How do you Disable the ‘Replay’ Knocker Noise in your Pinball Machine?

Some love the pop of the knocker, as though it is the sound of victory incarnate! Others find it scares the living daylights out of them. Of course, if you have a decent knocker in your pinball machine, it should technically be loud enough to scare the life out of you, since it is meant to alert an entire arcade building of your resounding success.

However, if your spouse, for example, is downstairs cooking and finds herself accidentally flinging salad around the kitchen out of a primal fear reaction to your ‘toy’ upstairs, you may be asked to disable the knocker (or you may come to this conclusion yourself upon seeing your wife’s angry face.) Either way. It is helpful to know how to disable this mechanism in the event you’d like to, ya know, save your marriage (or whatever your very valid reason is for removing this from your machine.)

Disabling an Electronic Knocker

Some people have reported the Stern knocker inside their electronic pinball machine to be worse and more frightening than the old school mechanical knocker. Some report it sounds like someone plugging a guitar into an amp cranked up to 100. However, no matter what, a digital Stern knocker is never going to be as loud as an old school mechanical one.

In newer models of pinball machines, the knocker element is likely to be electronic, and controlled from within the menu. When you go into the menu of your pinball machine, there should be a folder called “adjustments.” Click on this menu, then click on “standard adjustments.” From here, scroll over to the adjustment that reads “knocker volume.” You can change it to low, medium, high, or off.

If that still sounds confusing to you, you can watch the video below to teach you how to eliminate the ‘squelching’ sound of your electronic stern knocker. 

Disabling a Mechanical Knocker

Turning off the mechanical credit knocker in an older, classic pinball machine is obviously a little more complicated. Unlike the Stern knocker that is now entirely digital and can be switched off with the press of a button, a mechanical solenoid has to be manually disabled by physically going inside and altering the machine.

Some users of classic machines have reported placing a cloth in where the knocker slams into the cabinet to help pad some of the noise, so that knocker is at least less jarring. Others have suggested going in and cutting the wire to the knocker so no pulses can be sent through the solenoid in the first place. However, you should take extreme care and caution if you attempt to cut any electrical wires inside your pinball machine. You must first ensure it is the correct wire. Then, upon cutting it, you must attach electrical tape to the ends of the wires so that you don’t start an electrical fire by loose wires touching. However, if you ever decide to enable the knocker, this is much more difficult  to do when you’ve cut wires.

Another excellent option, of course, is to contact a pinball machine repairman and have someone professionally disable the knocker. Of course, this costs money, so if you are able to find an alternative route to this, all the better.

To better understand the transition from old school mechanical pinball machines to the modern pinball machine, Mark Gibson has a traveling exhibition called Fun With Pinball, which explains the science behind all the pinball components (flappers, bumpers, and yes, solenoids!)

The Key Take Away?

A credit or replay knocker is a pretty neat feature inside a pinball machine (especially the classic mechanical ones with all the analog bells and whistles.) The more modern, electronic knockers (which are just a loud mp3 track that sounds upon notice of a free game) are less intense, but clearly keeping the knocker feature was important for pinball manufacturers and players.

The thwack of the knocker sound is rather nostalgic. However, not everyone appreciates its rather abrupt and shocking pop – thus, at least now you have the tools necessary to disable the knocker in your pinball machine should you find it annoying or unnecessary.

Perhaps most importantly, you now know the banging sound in your pinball machines is caused by knockers. Now head to your nearest pinball machine and get to playing. Hopefully, you won’t have to use up too many quarters before you get that knocker.

Matt Robbs

There is nothing quite so enjoyable as bringing back memories from your childhood. We used to spend hours playing pinball in my friends basement and that really got me involved in everything retro!

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