Choosing Replacement Speakers
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Choosing Replacement Speakers

There are a LOT of different types of speakers to choose from; how can you possibly make the right decision? We can simplify the task by narrowing down the choices for back box speakers and cabinet speakers. Keep in mind that no single speaker can reproduce the entire audio frequency spectrum: different types of speakers perform better for certain frequency ranges.

Let's start by looking at some of the parameters that are important when choosing replacement speakers.

Important Speaker Parameters

There are several parameters you should keep in mind when choosing replacement speakers: impedance, power handling capability, and physical size. Rules of thumb:

bulletImpedance
Unless otherwise directed, choose a replacement speaker that has the same impedance as the original. With a few exceptions, all of the speakers used in Bally / Williams WPC-era games are 4 ohms impedance; the exceptions are the early games (Funhouse, Gilligan's Island, Harley Davidson, Party Zone, and The Machine: Bride of Pinbot) that used 8 ohm speakers.

Using a higher impedance speaker, such as one rated at 8 ohms, will not cause damage to the amplifier. It is not recommended to use speakers of less than 4 ohms impedance unless you know exactly what you're doing; this will overload the amplifier and may damage it over time, especially when run at high volume levels.

When we install replacement speakers in one of the early WPC games listed above we'll use 4 ohm speakers in the back box, wired in series to present an impedance of 8 ohms.

bulletPower Handling Capability
The amplifiers in the WPC-era sound systems are rated to produce no more than 25 watts continuous output power (also called RMS power). Choose a replacement speaker that is rated at least 25 watts RMS; paying extra for a speaker that is rated significantly more than 25 watts RMS while using the stock amplifier is a waste of money. Ignore the "peak" or "max" wattage rating; the RMS rating is the one that matters.

(See the note near the bottom of this page about myths regarding speaker wattage ratings.)

bulletPhysical Size (Diameter, Mounting Depth, Mounting Height)
The speaker diameter is a measurement of the outside diameter of the speaker frame (or equivalent diameter for non-circular frames), excluding any mounting lugs. The diameter is implied in the size; for example, a 6-1/2 inch speaker is 6-1/2 inches in diameter.

The speaker diameter is important if you don't want to re-configure the speaker mounting arrangements to accommodate a larger diameter speaker. The mounting hole size and mounting hardware locations for speakers of the same diameter class are more-or-less standardized; most speaker hardware mounting holes are also elongated so there's a bit of room for variation. The speaker specification sheet may or may not specify the mounting hardware spacing.

The speaker cutout diameter is a measurement of the mounting hole size that is required for the speaker surround and cone to clear the mounting plane.

The speaker mounting depth is a measurement of how far the rear-most part of the speaker projects from the front mounting plane.

Mounting depth is normally not an issue for the cabinet speaker. However, there are some games (such as Medieval Madness) that have limited clearance above the cabinet speaker when the playfield is in the operating position. It's an excellent idea to always check the vertical clearance immediately about the existing speaker with the playfield in place to be sure any replacement speaker isn't going to bump into an under-playfield assembly. Also check the vertical clearance when pulling the playfield out of the cabinet using the slide mechanisms.

Mounting depth is normally not an issue for the back box speakers: there's quite a bit of room behind the panel to accommodate fairly deep speakers, up to around 3 inches deep.

The speaker mounting height is a measurement of how far the front-most part of the speaker projects from the front mounting plane.

Mounting height may be an issue on some woofers. The surround on some woofers projects beyond the front mounting plane of the speaker; in this case the plastic speaker grille will interfere with movement of the surround and speaker cone. In these cases you'll need to use a spacer between the speaker and the speaker grille to provide clearance for the surround. You could simply remove the speaker grille, but that exposes the speaker to damage, and is not recommended.

Mounting height may be an issue on some coaxial speakers. The tweeter on most coaxial speakers projects beyond the front mounting plane of the speaker. If the tweeter projects further than the thickness of the mounting panel you'll need to use a spacer between the speaker and the panel so the tweeter doesn't hit the grille. On some speakers you can remove the plastic trim that covers the tweeter to reduce the front projection enough so the speaker will fit without a spacer; do so at your own risk, though!

Here are some pictures that illustrate the various physical dimensions of a speaker:

Other Speaker Characteristics

There are some speaker characteristics that aren't as critical as the above parameters, but you should still keep these characteristics in mind when selecting replacement speakers:

bulletCone Material
Speaker cones were originally made from paper; over the years manufacturers have introduced other materials such as polypropylene, Mylar, aluminum, Kevlar, carbon fiber, and other exotics. The ideal material would be very stiff so it doesn't deform when moved, but still be light enough to respond quickly to changes in the electrical signal. In reality paper isn't that bad of a material; polypropylene is a good choice for a step up, and is the material I'd recommend. Going with Kevlar or carbon fiber is overkill for a pinball machine sound system.

bulletSurround Material
The "surround" is the material that attaches the speaker cone to the frame (or "basket"). The ideal material would be very strong and very flexible. Low-end speakers will often use cloth or rolled paper as the surround material; this is OK for an el-cheapo speaker, but other materials are more flexible and allow better sound reproduction. The better surround material choices are foam (good) or rubber / butyl rubber (best).

bulletMagnet Weight
If you have a choice between two speakers of similar ratings and construction, in general the speaker with the heavier magnet will be more efficient, and thus produce higher sound levels. Don't get hung up on weight, though, as most manufacturers of mid-priced speakers will use an appropriately sized magnet.

bulletShielding
Some speakers are shielded so the magnetic field produced by the speaker magnet does not interfere with nearby electronic equipment; this is particularly important for speakers next to cathode ray tubes (CRTs) used as television displays. Shielding is not necessary for speakers used in pinball machines; there are already a LOT of solenoid coils in a modern pinball machine that produce their own magnetic fields. There is no harm in using a shielded speaker in a pinball machine; at worst you'll be paying for unnecessary shielding.

Note: The suggestions for specific speaker models in the sections that follow are based on my personal experience. Sound quality is a highly subjective thing: a speaker that sounds great to one person will be considered junk by another. The absolute best way to choose a speaker is to listen to it in person. Bring a CD with a favorite song to a local dealer and audition different brands; set the equalization of the amplifier flat so you're comparing speakers equally. That said, I don't think you'll be disappointed with the suggested models; they're a big step up from the existing speakers in your game.

Note: Speaker manufacturers seem to change models on a yearly basis, so some of the models I list below may no longer be available.  If you notice this, please let me know and I'll make the appropriate changes.

Let's look at the back box and cabinet speakers separately.

Back Box Speakers

Overview

Williams used two different types of speakers in the back box: a midrange on the left side and a tweeter on the right side. In most games the left side speaker is a 5-1/4 inch midrange, and the right side speaker is a 3 inch tweeter. Some of the early WPC games with the Bally-style back box (Gilligan's Island, Harley Davidson, and Party Zone) used a 6 inch midrange on the left side and a 4 inch piezo tweeter on the right side. The early WPC games with an alphanumeric display (Funhouse and The Machine: Bride of Pinbot) also used a 6 inch midrange on the left side and a 4 inch piezo tweeter on the right side.

This particular arrangement provides a fairly wide frequency response range, but it also causes a directional effect to the sound: mid frequencies appear to originate on the left side, and high frequencies appear to originate on the right side. While some may call this a "stereo effect", it really has nothing to do with stereophonic sound. The selection of speakers used was driven solely by economic concerns: wide-range speakers on each side would have been more expensive than the separate midrange and tweeter. Why bother spending too much money on sound reproduction when that will likely be masked out by other sounds in a noisy arcade?

Replacement Speaker Sizing

If you want balanced sound that appears to come from straight ahead it is necessary to use identical speakers on the left and right sides of the back box.

For games with a metal speaker panel you're in luck: both openings are already sized to accommodate identical speakers (after you remove the adapter plates installed on the panel). For games with a wooden or plastic display panel this means you'll have to either modify the right side of the display panel to accommodate a larger speaker, or fabricate some sort of adapter plate.

Modifying the display panel isn't difficult for games that have a wooden display panel; you need to enlarge the existing right side speaker cutout in the panel and drill four new mounting holes for the screws that mount the speaker to the panel. The hardest part will be accurately cutting a new circular cutout for the right side speaker.

Games with a plastic display panel have separate (removable) plastic mounting plates for each speaker. In an ideal world you could simply replace the plastic mounting plate for the smaller right speaker with one designed for the left speaker; unfortunately, that part is not available. You might be able to buy a plastic display panel from a parted-out game, and use the left side plate from that panel, but you'll have a hard time finding a plastic display panel. Perhaps one of the companies that specialize in plastic reproduction parts might produce this plate some day in the future.

There are two options to consider if you can't locate an original style plastic mounting plate for the right side speaker: fabricating an adapter plate from MDF board and using a smaller 3-1/2 inch speaker, or fabricating a new mounting plate from MDF board (replacing the original right side one) and using a 5-1/4 inch speaker.

The adapter plate for the 3-1/2 inch speaker is somewhat simpler to fabricate than the replacement mounting plate for the 5-1/4 inch speaker. However, a 3-1/2 inch speaker is not an ideal solution; the sound produced by this arrangement may be somewhat off-center, since the different sized speakers will have different efficiencies. If you pick speakers that have similar efficiency ratings the difference may not be that noticeable. Try to find speakers that differ in their SPL (Sound Pressure Level) rating by no more than 1 dB (decibel). I am presently testing this method on my Scared Stiff and will post the results.

*EDITORIAL NOTE: Post the results*

The new mounting plate is the most complicated fabrication job outlined in this guide, and may be more suited to those with intermediate woodworking skills. If you're careful and take time when laying out the measurements, fabricating a new mounting plate may be worth considering. This will allow you to use identical speakers on the left and right side of the display panel.

Types of Speakers to Consider

Since our goal is to improve the sound reproduction of the game, we want to pick replacement speakers that can reproduce the widest range of sound frequencies. A great choice is to use a special variety of speaker that combines two different types of speakers - a midrange and a tweeter - into a single physical package; this hybrid is called a coaxial speaker.

A coaxial speaker consists of a midrange speaker with a smaller tweeter mounted in a nested fashion on the central axis of the speaker:

A coaxial speaker is sometimes called a 2-way speaker, referring to the two different speakers sharing a common mounting arrangement.

A good coaxial speaker can reproduce a very wide range of frequencies, and is ideal for our needs. Don't confuse a dual-cone speaker with a coaxial speaker. A dual-cone speaker is a cheap alternative that simply glues a smaller cone to the center of the main speaker cone, in theory allowing the speaker to better reproduce high frequencies. It works - sort of - but isn't ideal, so stick with coaxial speakers.

Coaxial speakers are very popular with the car audio crowd. You can buy a decent pair of coaxial speakers for less than $50 (see suggestions below); if you pay significantly more than that you're wasting money. If you don't mind buying last year's model you can often get some great deals on eBay, but watch the shipping charges: some sellers really jack up the shipping charges to make a profit on the sale. Check your local stores, too; Best Buy, Circuit City, and auto parts stores often have good sales on current-model car audio speakers.

The tweeters of some coaxial speakers are mounted on a swivel so the tweeter can be aimed for better high-frequency sound dispersion. A swivel tweeter isn't necessary for this application, but feel free to use a speaker with one; it won't cause any problems. Just be sure to aim the tweeter straight ahead before you install the speaker!

Something you should keep in mind is the color of the speaker cone: many car audio speakers have blue, red, or silver mirrored cones that can be seen through the perforated metal speaker grilles on the front of the display panel. In some cases where the display panel has a screened plastic cover this actually looks pretty neat. For example, here's a blue mirrored speaker installed on a Twilight Zone:

If the tweeter cover has some sort of design (like above) be sure to align the covers of the tweeters on the left and right speakers before installing them. You'll be able to see the outlines of the cover behind the speaker grille when the speaker is installed, and it's very irritating to go back and remove the speakers after installation when you realize the tweeter covers don't line up!

For games with a plastic display panel or metal speaker panel you may want to stick with a plain black cone that will be less obvious than a brightly colored or mirrored cone.

What to Buy

Back box speakers should be 4 ohm impedance and be rated to handle at least 25 watts RMS power. It's actually somewhat difficult to find speakers of this size that aren't rated at least 25 watts, particularly if you choose speakers intended for car audio applications. Polypropylene is a good speaker cone material, and foam or rubber are good speaker surround materials.

For games with a metal speaker panel purchase a pair of 6-1/2 inch coaxial speakers. No modifications to the speaker panel are required, other than removing the original adapters mounted to the rear of the panel. 6-1/2 inch coaxial speakers are often quite a bit more expensive than the 5-1/4 inch variety. You could choose to use 5-1/4 inch speakers and fabricate a simple adapter plate to mount the 5-1/4 inch speakers to the panel.

For games with a wooden display panel with a dot matrix display purchase a pair of 5-1/4 inch coaxial speakers; we'll modify the right speaker mounting arrangement on the display panel to accommodate the larger speaker. Games with an alphanumeric display (Funhouse and The Machine: Bride of Pinbot) will need 6-1/2 inch coaxial speakers.

For games with a plastic display panel your choices are a little more complicated. If you can find the 5-1/4 inch mounting plate from a parted-out game you can go with a pair of 5-1/4 inch coaxial speakers. An alternative for games with a plastic display panel is to use a 5-1/4 coaxial speaker on the left side and a 3-1/2 inch coaxial speaker on the right side; that option will require an adapter plate for the right side speaker, as the original speaker is actually a 3 inch unit. Another option involves fabricating a replacement mounting plate from MDF board and using 5-1/4 inch coaxial speakers on each side.

Suggested Models

Jensen JX254 (~$25), Jensen XS542 (~$30), and MA Audio Y3050K (~$35 at Parts Express) are good 5-1/4 inch coaxial speakers.

Blaupunkt PCX652 (~$50), Jensen JS65 (~$40), and Jensen XS652 (~$50) are good 6-1/2 inch coaxial speakers.

The 5-1/4 inch MA Audio speaker is a particularly good choice for games with wooden or plastic display panels because it has minimal front projection of the tweeter, and won't require a spacer between the speaker and the display panel. The other 5-1/4 inch speakers require a spacer as the tweeter projects too far from the mounting plane of the speaker.

If you want to use two different sized replacement coaxial speakers for games with a plastic display panel, I'd suggest using an MA Audio Y3050K (5-1/4 inch) for the left speaker and an MA Audio Y2035K (3-1/2 inch) for the right speaker; both models are available from Parts Express. You'll have to buy one set of each size as these speakers are only sold in pairs. (The guideline prices listed above are for a pair of speakers.)

Cabinet Speaker

Overview

Williams used a 6 inch cabinet speaker rated at 25 watts; it could probably be classified as a "wide range" speaker, but in reality the bass and treble response are pretty poor. We'll replace this speaker with a woofer that will provide improved bass response; the back box speakers will provide plenty of midrange and high frequency sound to complement the woofer.

Replacement Speaker Sizing

The mounting hardware for the existing 6 inch cabinet speaker lines up nicely with the mounting holes on a more conventionally sized 6-1/2 inch speaker. However, on some woofers the surround may be slightly larger in diameter than the hole in the existing cabinet speaker mounting block (5-5/8 inch), or the surround may project beyond the mounting plane of the speaker. In either of these cases the surround and speaker cone will not be able to move freely due to interference with the mounting block or speaker grille, so you'll need to use a spacer between the speaker and the speaker grille to provide clearance for the surround.

You can also choose to go with a larger woofer than the original cabinet speaker to really showcase the bass effects. A larger speaker can move a greater volume of air than a smaller one, and will typically have a better low-frequency response. For example, a good 6-1/2 inch woofer might respond to frequencies as low as 45 - 50 Hz; a similar quality 8 inch woofer might be able to respond to frequencies of 35 Hz or lower.

Unfortunately, the physical layout of some games precludes the use of a larger woofer: Creature from the Black Lagoon is the best example. The cabinet speaker on Creature is mounted next to the left cabinet wall to provide room for the hologram projection lamp's beam to shine on the rocking mirror assembly; a larger speaker would interfere with the lamp beam. If you have a Creature you're limited to replacing the existing cabinet speaker with a 6-1/2 inch woofer. Check the game-specific information section for a list of other games that present similar issues.

If you do choose to use a larger woofer for the cabinet speaker you should seriously consider enlarging the existing cutout in the cabinet bottom to accommodate the new speaker. The required cutout is usually around 7-1/8 inches in diameter, but check the speaker specification sheet for an exact dimension. The existing cutout is about 5-5/8 inches in diameter; if you don't enlarge the cutout that will restrict the airflow of the new speaker by some thirty percent. This is one reason why I don't like using larger speakers with an adapter plate: the adapter restricts the airflow.

Perhaps more importantly, an adapter plate raises the new speaker at least 3/4 inch higher above the cabinet bottom panel, which increases the chances the speaker magnet will bump into an under-playfield assembly of some type. This can present a problem on some games such as Medieval Madness; check the game-specific information section for details on games with known cabinet speaker clearance issues.

For my restorations I fabricate a new mounting block for the larger speaker and enlarge the cabinet cutout; this results in a more "factory" appearance than an adapter block. You can also mount the new speaker directly to the cabinet bottom. If you go this route you can use #8-32 T-nuts on the bottom side of the cabinet and #8-32 round head machine screws of the appropriate length to mount the speaker to the cabinet. This doesn't look quite as original as a separate mounting block, but does work pretty well.

Here's a picture of an 8-inch woofer in place on its new mounting block in a Twilight Zone I recently restored:

You don't even need to hook that puppy up to imagine the rumble it's going to produce!

NOTE: Most woofers weigh quite a lot compared to the original cabinet speaker, which means the original mounting block - held in place by a few brads and glue - may break loose when you move the game. If you decide to use an adapter plate with a larger speaker be sure to add a few screws to the existing mounting block to secure it firmly to the cabinet. You might even want to use T-nuts on the bottom side of the cabinet and flat head machine screws through the existing mounting block for extra security.

The car audio market is a good source for replacement woofers: you can also purchase decent units from audio electronic suppliers such as Parts Express or Audio Outfitters. Shop around and you can get a good woofer for under $50 (see suggestions below). As with the back box speakers, look for a rubber surround and a stiff cone material, although it's hard to find woofers with anything other than a paper cone at this price point.

What to Buy

Regardless of which size woofer you choose, you want to go with one that has the best low-end response.  Look for a low frequency response of at least 35 Hz; a smaller number is better here.

Purchase a woofer rated to handle at least 25 watts RMS. The required impedance will differ depending on the sound system used in the game. Here are the rules:

bulletAny DCS game - select a 4 ohm woofer
bulletPre-DCS game - select an 8 ohm woofer

If you're having a hard time finding a 4 ohm woofer for a DCS game you can safely use an 8 ohm woofer instead. Note that the volume level of the woofer will be reduced somewhat in this case.

You may find some woofers classified as "DVC" or "dual voice coil"; these speakers have two individual magnet coils mounted to the speaker cone. A DVC woofer is great for car audio applications because it allows you to connect two different channels of an amplifier (left & right) to a single woofer. A DVC woofer normally has a pair of 4 ohm voice coils; you can connect the two voice coils in series to result in an 8 ohm speaker.

Suggested 6-1/2 inch models

4 ohm: Dayton DC160S-4 (~$20 at Parts Express); Rockford-Fosgate RFP3406, RFP4406

8 ohm: Dayton DC160-8 (~$18 at Parts Express); Peerless 833599 ($40 at Parts Express); Rockford-Fosgate RFP3806, RFP4806

Suggested 8 inch models

4 ohm: Dayton Quatro (~$50 at Parts Express); Rockford-Fosgate RFP3408, RFP4408

8 ohm: Pioneer B20GR30-51F (~$35 at Parts Express); Peerless 850136 CSX (~$50 at Parts Express); AudioBahn AW831, Rockford-Fosgate RFP3808, RFP4808

Myths About Speaker Power Ratings

You may be concerned that if you install a speaker rated at 200 watts it will cause the amplifier on the sound board to self-destruct. That's a common misunderstanding: the speaker power rating has absolutely no effect on the amplifier, since the speaker doesn't actually "draw" power from the amplifier. The speaker power rating is simply an indication of how much power the speaker can dissipate before damage to the speaker occurs.

NEXT: crossovers and level controls

HOME: WPC speaker replacement

Copyright 2005 by Joseph A. Dziedzic. All rights reserved.