Do-It-Yourself Guide
to Pinball Speakers!

Speaker Selection Guide

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Last modified date: July 26, 2003.
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Speaker selection guide -- not everything is 100% true! (Disclaimer)

This part of the DIY guide is a bit different. This is the purely educational part of the guide, so no tools are necessary other than that lump of clay that keeps dust from accumulating between your ears. So grab some coffee, sit on the toilet (if necessary), and hang on!

Not everything in this document is going to be absolutely true. It is sometimes more illuminating to explain a concept to someone in a not-always-true way (so that they get a good working knowledge of the subject at hand) rather than an accurate and precise one.

There are a myriad of things that are involved in speaker selection that are beyond the scope of this document. I'm not interested in writing the ultimate speaker selection bible. I simply don't have the time to write it, and you don't have the time to read it! But I am interested in giving people enough information so that they can make reasonably informed choices about what they buy.

So again, not everything in this document is 100% true!

Think of this document as a collection of rules of thumb. This document will get you pointed in the right direction and headed down the right road, but it's not going to get you to your final destination. Don't take anything written here as pure Gospel and don't (whatever you do) don't take anything in this document to the extreme; that's not the intent with which I'm writing this! (Most likely, you'd wind up with worse sound if you did!)

Now that we have that sorted...

An apology...

While proofreading this document, I noticed that the document has an extreme slant towards Williams [/Bally] games, in particular System 11 and WPC games.

I apologize for this slant, but eighty to eighty-five percent of the machines that I own or have access to are from one or both of these two game periods. They say that when you're writing, you have to write what you know. Well, I know System 11 and WPC sound!

So if you own a Gottlieb, Data East, Capcom, Zaccaria, or Game Plan pinball machine, please bear with. It's not that I'm trying to slight other manufacturers, it's simply that I know the most about the Williams games.

Many (most?) things will still apply to your games, too!

What is a speaker?

Seems like a simple enough question, doesn't it? I know, I know, the hands of all the educated ones out there just shot up, started waving around, and involuntarily their mouths started saying, "Oo! Oo! Pick me! Pick me! Pick ME!"

OK, fine.... You, GoosePimp! What is a speaker?

"It's a noisemaker!"

Wrong! Good speakers are not noisemakers. The speakers that you find on a laptop computer, those are noisemakers. But the speakers that you want to use on your pinball machine have almost nothing in common with those.

Simply put, a speaker is an air pump. A speaker's main purpose in life is to move air, lots of air, back and forth quickly. The distinction is important because many of the things that you would do intuitively for an air pump are indeed good things to do for a speaker.

For example, when using an air pump, one wants to secure the pump in some fashion so that it doesn't bounce around, mash your toe, etc. Same thing goes for a good speaker; in order for it to produce a good sound, you need to securely fasten it to something. In the same vein, in order for an electric air pump to work well, you have to give it a good source of power. The same thing goes for speakers; if you want them to produce good sound, you have to give them good power, too. There are other similarities, but I'll stop here for now.

What are the parts of a speaker?

Here is a quick rundown of the parts of a speaker. (You need to know this so when a manufacturer says, "Kevlar reinforced pulp cone with inverted structural dome", you'll know what they're taking about!)

The basket (a.k.a. frame)

Starting at the outside, one first comes in contact with the basket, also sometimes called the frame of the woofer. This must be strong and stiff, for this is what holds the entire speaker together! Think of it like the foundation of a house; you don't want it to move or flex, and stronger is better.

The surround

The surround is an important piece of the speaker. The job of the surround is to hold the cone in place when the speaker isn't in use, while also preventing the speaker from ejecting the cone while it is in use. The other job of the surround is to return the cone to center if the signal to the speaker is removed.

You're going to find a lot of emphasis on the surround material, and some of it is warranted. Here's the quick and dirty on surround materials:

The cone

The cone is the part of the speaker that actually pushes all the air around. This is where manufacturers usually put their biggest gimmicks (mirrored finishes, strange humps, etc).

Most of the gimmicks are pure bunk. But there are a few things that do make a difference:

So what should you choose? If money is no object, a Kevlar weave wins hands down. But back in the real world, I usually will wind up going with the best compromise (to me!), polypropylene cones. They're not as quick as paper cones, but they will take a lot of abuse and keep on going.

Before we leave the cone topic, here are a few common terms manufacturers throw around, and what they really mean:

The dust cap

The dust cap is in the center of the woofer. Its purpose is to prevent dust and other debris from getting in and mucking around where it shouldn't belong. This is usually where a manufacturer puts its fancy logo. Don't listen to any claims made about the dust cap. Inverted, regular, titanium, it makes no difference in the way the speaker sounds. (They're named dust caps for a reason, folks!!)

The magnet

The magnet is one of those structures that nobody thinks about until they get a speaker with a bad magnet. Put simply, any reputable manufacturer is going to put an appropriately sized magnet on their speaker. And truthfully, unless you're pushing lots of wattage (over 150 watts) through a speaker, having a larger magnet isn't going to make any difference. So until you've graduated to installing megawatt amplifiers, don't sweat the magnet details too much.

But don't skimp on the homework, either! Most manufacturers will be more than happy to let you know how large their magnets are, usually measured in ounces or grams. When looking to purchase speakers, get the magnet weight from a few different manufacturers, average it, and use that as a baseline. Don't worry if you're even as much as 20% under sized; if you're not pushing a lot of power it will simply not matter. But if you run across an awesomely cheap speaker that has 80% less magnet than the baseline, there's something definitely wrong with that speaker! Don't buy it!!

Don't bother getting a speaker that is magnetically shielded. There's no benefit to using one in a pinball machine, and they're more expensive. (Besides, the coils in the game are going to produce much stronger temporary magnetic fields!)

Check the mounting dimensions and impedance

Checking the mounting dimensions is very important because most of the places where you'd want to put a speaker in a pinball machine aren't very roomy. The last thing that you want to do is get a speaker home and then find that it doesn't fit!!

With that in mind, most System 11 games with dual speakers on the panel are set up with t-nuts already in place for a standard 6.5" speaker on the left side*. That makes the project 50% less difficult, since you will only have to cut out a speaker hole for one side. WPC DMD games, on the other hand, are set up to take a 5.25" speaker on the left side. (The DMD is slightly wider than the old 16 segment alphanumeric displays.)

* This is not true for original system 11 games such as High Speed and Pinbot. Those have a single oddball panel speaker, something like a 3x7 or a 4x8. It is possible to find speakers in these sizes. For these games, however, I would not make any plans to modify the speaker panel itself. (i.e. I would only replace the Craptastic speaker with the same size one.) It's difficult to modify the speaker panel due to the felt that Williams glued to the front of the speaker panel. Impossible, no, but more involved.

In addition to the speaker size, you also need to consider the mounting height when choosing a speaker. The mounting height is the amount of a speaker that sticks in front of the basket if you mount the speaker from behind. (This is NOT the same as the mounting depth!!) You don't have to worry about this if you're choosing a woofer/subwoofer, since they all have a mounting height of zero. But if you're choosing a panel speaker, pay attention! Williams made their panels out of 3/8ths inch thick wood. That means that the mounting height (or sometimes referred to as the tweeter height) can NOT be larger than this.

Unfortunately, many speaker manufacturers have stopped supplying the mounting height as a standard dimension. So you may have to wing it. But! There's a trick you may be able to use to get speakers that wouldn't normally fit to fit!

Many speaker manufacturers these days are putting these ridiculous (and sometimes massive!) tweeter "protectors" on their speakers. While they do protect a tweeter against an accidental bump, I really think they put them on because otherwise they wouldn't have any place they could put their fancy logo. You can (almost always) completely remove these tweeter protectors without any penalty. The speaker is going to have a metal grill over it anyway; why would we need another protector?

Don't believe me? Look at how far the tweeter protruded on my example speaker before (and after) I removed the tweeter protector.

Click here or here!

Last but not least, when choosing speakers one also needs to check the mounting depth. This is the opposite measurement from the mounting height; it's the amount of the speaker that is going to extend from the back after you mount it. If choosing panel speakers, most Williams games can handle pretty much anything up to 2.25 inches, sometimes more. If choosing a cabinet speaker, the acceptable mounting depth varies greatly depending on the game. You will need to measure from the cabinet bottom to the lowest hanging object from the playfield, then subtract an inch.

A good rule of thumb is that many WPC & Sytem 11 games can handle a cabinet speaker with a mounting depth of seven inches or so. Some games (like STTNG) can handle a mounting depth of close to nine inches! Some other games (CFTBL) have components that stick down _so_ low or have other gook (like the hologram projector) that take up space in the bottom of the cabinet that replacing the speaker at all is a dicey proposition at best.

Because I can't figure out where else to put this, make sure the impedance of the speakers you choose is at least four ohms. Speakers with larger impedance (8 ohms) will not hurt anything, but speakers with too little impedance (two ohms or less) will cause too much current to flow through the amplifier. This will quite likely cause the amplifier to go into clipping or overheat or both, which are bad thing.

Match the panel speakers

For best sound, you should always match the panel speakers. This is a major point that people often overlook, and where I disagree with some of the "kit" speaker providers.

The simple fact is that all of Williams' games (and many other manufacturers!) were designed with monophonic sound. That means (more or less... remember, not 100% true!) that the game was designed to have the sound coming from straight ahead of the player.

The only way to achieve that effect with more than one speaker is to put two of the same model speaker equidistant from the player. If you use one speaker on the left side and a different speaker on the right side you'll get sound, but it will not sound right. The reason is because two different speakers are going to (by definition!) have two difference response characteristics, which means that the sound waves being emitted from both of them are going to (as a result) be somewhat different. This difference is what can easily "muddy up" the sound, so that voices aren't as clear as they should be, high frequencies are off, etc.etc.etc.

Now if you're one of those folks that bought one of those kit speaker projects, don't go off in a huff or get all defensive saying, "My speakers sound just fine!" or "Korn hates my rig!". It's not that at all. You can get decent sound out of mismatched speakers on the panel. What I'm talking about is the difference between doing it, and doing it the right way. It's somewhat similar to the difference between re-balling a game with stock balls, and re-balling a game with balls that you've polished in a tumbler for a few hours. Either will work and be fine, but if you've ever seen/heard it done the correct way, any other way will always be sub-par.

Don't buy "dual cone" panel speakers

This one is short and sweet. Don't buy dual cone speakers! What is a dual cone speaker, you ask? Put simply, it's a single speaker with two cones glued together, run by the same magnet! The idea is that the larger cone would do the lower frequencies, and the smaller cone will do the higher frequencies. It doesn't work; all frequencies wind up sounding like garbage out of this baby. Check out the picture below so you know what a dual cone speaker looks like.

Unfortunately for the buyer, there is another class of speaker that looks fairly similar to a "dual cone" speaker that is actually what is preferred for a panel speaker. That kind of speaker is called a coaxial speaker, or sometimes called a biaxial or triaxial speaker. This kind of speaker has separate elements for the low notes and the high notes, and they don't affect each other.

Check out the picture below. I was trying to show that I could move the woofer without moving the tweeter on a coaxial speaker. (Ignore the left to right movement of the tweeter; that was simply my inability to hold the whole speaker absolutely still while pushing down on part of it!)

My brain is about ready to explode! Can you summarize?

OK, here is the quick and dirty version up to this point:

Now really, was that so bad?

I'm ready! How do I buy something?

Here is where the fun part is! You need a piece of music that you're ultimately familiar with. A recording that you've heard fifty million times. A recording that you know every note of, every little nuance of the singer's voice, every slightly missed beat and every last bass note.

The demo music that retail stores provide is intended to sell speakers. It is NOT going to tell you which speaker is better!

The problem with buying speakers is that even if two speakers measure similarly (i.e. have the same frequency response), the sound produced by them can be radically different. Frequency response measures sound quantity, not sound quality. While there are some measures (total harmonic distortion) that will tell you if a speaker is doing something massively wrong, they really do not tell you the overall quality of the reproduction. But don't fret; every human has two sound quality measuring devices, the ears! So grab a box of Q-tips and (literally!) clean out your ears.

Grab your music from above and head on out to a retail store (Best Booty, Circuit Crappy, etc.). While you're there, put the piece of music that you love so much on infinite repeat, and don't let the sales monkeys play with the controls. Keep the volume at a constant level, and switch between perspective speakers. What you don't want is the speaker that goes boom or the tweeter that sizzles. That's fine for listening to rap at 130 dB, but we're listening to music from a pinball machine. What you want is the speaker that makes your music sound the most natural. Close your eyes when you're listening to the different speakers; the one that comes closest to fooling you into believing that the performer is in front of you is the speaker that you want. And that's never the boomy hissy speaker!

One last thing before we're done with this section. Don't go overboard and buy the most expensive set of speakers in the place! Never forget that these speakers are going into a pinball machine, a loud and noisy machine with a not-so-great signal to begin with. In other words, a pair of $250 Alpine speakers is dramatic overkill. The truth of the matter is that any speaker that you're going to find at retail (with the exception of a dual cone speaker, of course!) is going to be so far and away better than the stock speakers that you're almost guaranteed success!

"Wait a minute. All those fancy graphs they give for speakers are useless!??"

Oh, you want to go there. You're a "by the numbers" kind of guy. Well, we can go there.

No Virginia, the frequency response graphs that the manufacturer give aren't useless. But they're not as useful as some (and some manufacturers!) would lead you to believe. The golden rule is how does the speaker sound? If the speaker sounds just fine, then don't worry about the numbers and the charts and all that gobbledygook.

But if you're an engineering type like myself and want to know what the charts mean, then strap in! Let's start with a response graph for a subwoofer from a particular manufacturer of speakers...

Ideally, this graph would be ruler flat! But as you can see, this graph is anything but flat, and this is an expensive very high quality speaker! The point here is that even though something on paper might look bad, it still might sound pretty darn good.

In order to read that graph, you have to remember that a graph like this tells you nothing in regards to the quality of the sound. All this graph tells you is how much sound you're going to get at any particular frequency from this speaker.

Back to the point, the low frequencies (bass, kick drum, tympani, and explosions) are on the left, and the high frequencies (this particular graph ends right around male human voices) are on the right. Human hearing starts at 20 Hz, which I marked on the graph with the big red arrow. So anything to the left (lower) than the big red arrow doesn't matter.

So what's the upshot? Well, without comparing it to another graph for another speaker, the first graph doesn't mean much. So let's go find another graph from another quality manufacturer and compare the two:

So what is the difference when we compare the two? Where human hearing starts, the first speaker is almost five decibels higher. (Every difference of three decibels equates to a doubling of acoustical power.) In addition, the first speaker's "hump" is centered around 70 Hz, while the second peaks more around 100 Hz. The upshot is that the first speaker will appear to play lower and louder than the second.

So should you run out and buy speaker number one straight away? Absolutely not! Again, these graphs tell you nothing about the quality of the sound. The first speaker could sound like a guy banging a garbage can. So don't buy a speaker based solely on its graph. But you can use the graph to compile a "short list" of speakers you want to audition.

Always trust your ears. If it sounds good, to heck with what the graphs say!

Now get out there and buy some speakers!

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