Design

DESIGN BACKGROUND

When a new hi-fi speaker system is designed, a designer selects a set of speakers with certain performance characteristics and then designs an enclosure to support the speaker characteristics in the overall desired performance of the system.

In the case of a pinball machine, the enclosure volume and geometry are pre-determined and the speaker must be designed to match it.  This is a very complex task compounded by limited amplifier power to drive the speakers.

Three characteristics make the Pinballpro™ Sub-woofer system work better than any off-the-shelf hi-fi unit.

Speaker Design

    1.  The physical dynamics of the sub-woofer are matched to the air volume and geometry of the enclosure.
      Primary factors are:
      Cone shape, stiffness, weight, and surround resistance
      Voice coil diameter and power handling capability
      Magnetic field strength and steel concentrator
      Air gap and armature efficiency

      The multiplicity of factors make designing the base element an enormous task, but 30 years of design experience coupled with reverse engineering the characteristic tables with a computer, narrowed the formula down significantly.

    2. The next task was matching the available amplifier power and frequency distribution to the sub-woofer and back box speakers as a system. A power diversion concept was developed to focus more of the available energy to the sub-woofer and less to the back box speakers for a given volume level. The diversion process changes the power ratio to double the power applied to the sub-woofer.
    3. The last important part of the Pinball Pro™ system is the matching network tuned to the sub-woofer electrical characteristics to multiply the effect of bass reproduction. The network is close coupled to the voice coil with heavy gauge wire to form a resonant circuit. Even though lighter gauge wire brings the signal to the sub-woofer, the resonant system still functions properly. The inductance in each system is electrically tuned for peak performance. This is why the limited power of the pinball machine amplifier is used to it’s fullest in creating dynamic sound output.

Actual testing and charting over a 6 month period yielded the optimum solution for the Pinballpro™ Sub-woofer itself. Now over 3 years of fine-tuning has culminated in a fully optimized subwoofer and speaker system. The features above make the Pinball Pro™ sub-woofer system the best performer available. You cannot buy a set of components off the shelf that duplicate the performance of the Pinball Pro™ system.

 

Pinball Pro Lab

System Testing at Pinball Pro Laboratory

Here are some factors affecting selection of new speakers for the backboxes of pinball machines:

    1. Williams system 11 and WPC-89 games employ different configurations: 4 X 10 inch oval, 6 ½ inch round, and 5 ¼ inch round speaker and either a square plastic tweeter or round metal speaker (tweeter) mounted on the opposite side of the speaker panel. The result is most of the sound comes from the large speaker and less (and only the high frequencies) comes from the tweeter.  This configuration tends to give a little quasi-stereo effect even though these systems only have one amplifier (mono) that runs the backbox and the base cabinet speakers together. We also selected a coaxial tweeter to develop the high frequencies rather than relying on a plain or dual cone type.  The DACs in these games do not produce very high frequencies but the difference in a dual cone speaker versus a coaxial speaker is still noticeable.
    2. Williams WPC-95 games employ a 5 ¼ inch round speaker and a round metal speaker (tweeter) mounted on the opposite side of the box. The result is much the same as in the earlier games except the backbox speakers and base cabinet speaker are driven by different final amplifiers.  The system is still mono but the final amplifiers have been compensated to provide more bass to the base cabinet speaker and more mid and high frequencies to the backbox speakers. The backbox sound is still off center due to the characteristics of the cone speaker versus the tweeter.Our solution for replacement:  First and foremost is selection of quality speakers.  Our drivers have the largest magnets available in the industry and that translates into the highest efficiency. Speakers are current driven and that means a given amount of current passing through the voice coil in a given magnetic field produces a proportional deflection. More current or more magnetic field means louder sound and more bass response.  So bigger magnets mean more efficiency or louder sound for less current input. Second, to get better overall performance we developed a complimentary pair consisting of a 6 ½ inch or 5 ¼ inch round speaker that matches a 4 inch round speaker electrically. The 4 inch speaker is mounted on an adapter to fit the original tweeter location without requiring wood working skills to cut out the mounting plate. The result is all midrange frequencies like voice come out equally from each speaker and this centers the sound in the game. Music has the bass slightly accented on the left and the highest mid frequencies accented on the right to give a bit of stereo imaging rather than stark mono. This effect works to keep a little of the original feel of the game.  Expending the effort to make a 5 ¼ inch speaker fit where the tweeter was is a total waste of time but we will substitute one in place of the 4 inch and adapter if you insist.
    3. Data East/Stern games: The early Data East games employ three amplifiers and true stereo sound from the backbox.  The separation is minimal since it is about 18 inches but none the less it is stereo. Mid life Data East games became mono and some only have one backbox speaker with a block off plate for the missing one. Later Data East and Stern games are still mono but restored the second backbox speaker. Our kits are available in 5 configurations to fit each series with correct mounting hardware and wiring differences. The early games will bennefit the most from our speaker replacement basically because the original speakers are old and tired. The most recent Stern games have adequate speakers for the frequencies the DACs produce and do not warrant replacement in our opinion. We have diehard customers who insist, but we only recommend replacing the Data East speakers if warranted.

One last note: We recently developed and exceptionally nice 6 ½ inch replacement speaker (SP-6.5) for the base cabinet speaker in games the subwoofer approach is not desired. It features an extra heavy magnet for the highest efficiency available in this size speaker.

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