It's been 6 years since I have been back. Life got in the way. But this is a thread that I will start to walk through the redesigning of Loudspeakers in that are used in pinball machines. I have 90's version of machines. I will leave out the designs that have external speakers since that is already well covered elsewhere on the internet.

My information will come from Goldeneye, WCS (Bally) and Indiana Jones (Williams) machines.

As a reference I have been doing loudspeaker design since 1973 and do this as a side business for custom work for business and home applications.

First I will start to post testing of said above machines.

Impedance curve for the backbox of IJ.

Indiana_Jones_backbox_imp (resized).JPG

Here are Indiana Jones and WCS on same graph. Similar curves but resonance peak for IJ much higher.

Source material is also a concern. As I said first to step through and improve where is there first then deal with the source issue.

I saw on this board a few times about references to impedance as a single digit number on the back of the driver. Clearly over the frequency band it is not constant. Also my understanding is the power amplifiers on the machines are designed to run with a 4 ohm load.

Indiana_Jones_and_WCS.PDF

The redesign process that I will do is :

Characterize the current system both electrically and acoustically.

First is to examine the backbox and down firing speakers both impedance and also an pink noise rta spl measurement at the distance where the user of the pinball will be standing.

Measure the lower box to determine volume and also how "leaky" it is with all the perforations in the playfield and all the leaking around the seams. This will affect mostly the efficiency of the system.

After that I will then start to model the environment with "LEAP" and look for a better drivers. to replace the current models.

Install new drivers with new crossover designed. Test the system and see if some "tweeks" are needed for phase response mostly.

Measurement at 48 inches which is the approximate distance player would be standing from backbox. This is for WCS game.

This was with white noise input and using RTA for the frequency spectra. Speaker was driven from an 50watt instrument amplifier, Amplitude was chosen to be 50 dB above background noise.

WCS_Backbox_SPL (resized).png

Smoothing was done with 1/24 octave setting. Not a very smooth curve but for speakers made in the early 1990's not all that unusual for lower end drivers.

Maybe someone has the frequency curve for the amplifier on the sound board. When I do the tests on the lower frequency driver we can meld the curves together to get a system view.

As an example of what I will be doing is to eventually get to a simulation of audio output from a pinball game based on the environment the player is experiencing.

Since an earlier poster stated they already have a solution I will briefly simulate with the data I have on this pinwoofer solution from an acoustic perspective.

The drivers used are a Goldwood GW-8024 (Based on data from a spec sheet on Parts Express website) for bass in cabinet and the Backbox speakers are Pyle PL53BL. It should be noted that the Pyle typical for mobile application has very incomplete spec sheet since it provides not enough information as to on-axis and off-axis performance. An example I provided above about Impedance being a single number and sensitivity is a single number.

Only way to simulate the Pyle drivers is to get one and test it to find out what it really is.

I am going to provide the layout for the simulation and then the SPL output from the Goldwood driver at the players location.

Input power was 2 watts which a 2.83volt input form the amplifier. No electronic filtering is applied.

The 2 curves for spl is on-axis (red) which shows the diffraction effects of the cabinet. The blue curve is a power response which is the long-term(100ms) response which is more representative of constant output from the driver versus the transient response from on-axis provides.

On final note is the cost of both Drivers(Pyle sold as a pair) ; Goldwood is $25.96 , Pyle $18.98 prices from Parts Express

Goldwood_Pin_spl_sim.PDF

Simulation diagram (resized).jpg

New impedance curves. First graph is the backbox of Goldeneye. Since it is stereo tested both speakers independently.

Second Graph is the impedance of all three woofers in there respective cabinets.

Goldeneye Backbox imp (resized).JPG

Woofers_impedance (resized).JPG

Taking a closer look at Goldeneye speakers. The natural resonance of the backbox speakers are 727 Hz and the woofer is 100Hz.

From an efficiency you typically do not have much output from a driver below resonance. Thus the crossover point is this setup means that the woofer goes up to at least 800Hz. The bad of this is sound is pretty directional above 100Hz which means the audio will shift in listening in this range. Another bad is woofer of the size of 8 inch has breakup modes that causes non-linear response to occur. This is more of a mid-woofer since below 100 Hz is not really there in output. I will be doing SPL measurements next.

Goldeneye_impedance.JPG

WCS and Indiana Jones are mono. My understanding is though that they do a electronic crossover for the two different amplifiers which I confirmed off of the schematic. Again I will be doing SPL test in situ. Again though the woofer resonance is around 100hz which acoustically is more mid-bass region audio wise.

Indiana_Jones_impedance (resized).JPG

WCS_impedance (resized).JPG

Yes a custom design with all the details on how the engineering occurred. Best bang for buck. Outcome is to understand what the current system can do and what are the advantages on changing/adding parts. Big improvements can happen without a major investment.

Understanding the home environment where the games are being played. Like watching a movie audio is an important part of enjoying the experience of playing.

At the beginning it is capturing what the system is doing and then evaluate on next steps.

I know that mostly new back box drivers have centered on 5 1/4 inch sized co-axial drivers. I took measurements of my machines of the grill size hole.

Goldeneye about 3 5/8 inches in diameter which is roughly 92mm
Indiana Jones about 4 1/2 inches in diameter which is roughly 114mm
World Cup Soccer about 3 3/4 inches in diameter which is roughly 95 mm

The diaphragm of the speaker cone should not really be larger than the grill hole to not interfere with the upper midrange frequencies. The dispersion pattern of a driver especially in off-axis is correlated to diaphragm size and frequency.

A car 5 1/4 speaker has a working diaphragm size 113 mm. This would be okay for IJ but two large for the other games.

The desire for larger speakers is bass response is better. However based on my impedance measurements the need below 100 Hz might not be needed.

If someone knows what the frequency response from the games amplifiers that would be useful. If no one has that data I will measure it during game play and will look at the schematics to see what the filters they put in the inpuy to the output amplifiers.

Slight delay because of holiday.

Next up this week will be test spl of Goldeneye system using pink noise and instrument microphone.

Going to be installing replacement backbox speakers with Dayton Audio CX120-8 4" Coaxial Driver with 3/4" Silk tweeter. This is a tweeter driver mounted co-linear in driver. Frequency response is on paper proper sensitivity to match current driver mounted.

Focus of woofer(not sub-woofer) selection will be aimed looking a pro-drivers because they have higher sensitivity, this is accomplished through a lighter cone mass and larger motor. This also drives up the Vas however considering how large the lower box not a problem with pinball machines that are solid state. Looking in the 40-50 Hz natural resonance (Fs) though I do not have data as to the frequency response needed for a game.

I am having discussions with Misco company about considering a low frequency driver as a straight replacement for the OEM in the lower cabinet. Both 8 and 6 1/2 inch sizes. More of a vintage suspension system that would improve efficiency but with modern materials and magnetic motor.

This would need the large space thus not designed around mobile application which drivers are designed with a very small space.

In speaker parameters (Vas) will be a critical value for good performance in pinball machines. An example of a design like this is JBL Pro 2235H, though a 15 inch driver the lightweight cone (mms) and large magnetic motor gives a great lowend performance down into the 30-40 Hz range.

Really sorry I got delayed. Cancer kind of slows you down.

Back and kicking in to redesign and starting with my IJ game first.

Included a schematic for the speakers. Also included the impedance I am concern of the range 250-600 Hz with it dipping below 4 ohms.

Is the power amplifer Williams okay or do I need to pad this up?

impedance dual dayton audio cx120-8.pdf

schematic dual dayton audio cx120-8.pdf

Below is the CNC pdf I created in Vcarve pro for the back panel of IJ. Yes it has the extra Jackpot cutouts,

Backbox cnc IJ.pdf

Crossover for backbox goldeneye stereo version. Using Dayton audio cx120-8 drivers.

Goldeneye crossover.pdf

The 2 ohm resistor on the tweeters for both crossovers is level reduction of the unit which on-axis is a little "hot".
When I get them installed I will test them to see what the level should be.

Also double checked the power amplifier chip and the impedance dips to 3.5 ohm should not be an issue. output level for 1 watt on the simulation seems pretty solid. See image which is each drivers woofer and tweeter and combine output 1 watt at 1 meter.

IJ and WCS backbox SPL.pdf

Link to the mechanical changes to be done DIY for Williams games is

http://www.dziedzic.us/wpc_speaker_replacement.html

As I get into the Goldeneye for Sega seems a more straight forward part replacement.

I am making my own replacement panels for the speakers using 12mm baltic birch plywood which is pricey right now.

Initial costs for IJ game.

costs.pdf

Back side of IJ panel ready to paint.

back panel back (resized).jpg

IJ Front CNC panel

back panel front (resized).jpg

Finalized the designed and installed the changes.

Since the 6 1/2 inch woofer from Dayton Audio was of lower sensitivity I need to change the output going to the backbox speakers. I also turned up the volume from 15 to 23 get the same output.

I used an Lpad to find the right values for the crossover.

IJ and WCS Impedance (resized).JPG

IJ and WCS SPL (resized).JPG

IJ and WCS Schematic (resized).JPG

Here are picts first is the backbox without grill.

IJ Naked Backbox (resized).jpg

Now the connection to the soundboard.
I upgraded to 18Ga wire for both the feed to the crossover and the cabinet woofer.

Lowering the signal loss on such small wiring.

WCS Soundboard Connect (resized).jpg

Now for crossover pictures. also I used a terminal strip between the soundboard and the crossover if I wanted to remove anything easily.

Crossover (resized).jpg

WCS Junction2 (resized).jpg

What the back of the panel looks like loaded with speakers.

WCS Backbox inside (resized).jpg

Finally the WCS look with the grills that I customize with a template I created.

WCS Backbox complete (resized).jpg