(Topic ID: 57737)

How to add a cheap sub, under $40 that sounds awesome to your WPC game


By markmon

6 years ago



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  • Latest reply 68 days ago by hawknole
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    WPC-95 Audio Filter Schematic.png

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    #1 6 years ago

    I've had a lot of separate discussions on this topic, so I figured I'd just take the time to post it all in one place. In short, this will be a guide that will allow you to build and add a cheap sub to your WPC game. This is for pre DCS games. DCS and WPC95 games would be a different (easier) guide. This is also solely for B/W pre DCS games. These are unique in that they have a single amplifier. Personally, I have found this to result in a better sound than flipper fidelity or pinball pro provides for about half the cost.

    Ok, it's a bit complex. But here goes.

    Williams wiring and speaker theory
    Pre DCS WPC games use a single amplifier. This is a 4 ohm capable amp. However, Williams obviously had no talent or brains when it came to audio engineering or even the slightest clue when it came to wiring. In order to get 3 speakers working well and keep the impedance into acceptable ranges, you have to wire some of the speakers in series, and others in parallel. If your impedance drops too low, you blow up your amplifier. If your impedance is too high, your amp loses its ability to power the speakers. Therefore, in an optimal setting, we want to run the speakers at exactly 4 ohms.

    Williams provides 3 speakers: 2 backbox are 4 ohm. 1 cabinet which is either 4 ohm or 8 ohm. They then wired it in series / parallel as follows: amp + goes to cabinet -. Cabinet - goes to left (5.25") +. left 5.25" - goes to amp -. Then they jumpered the left speaker + and - to the right speaker. Unfortunately, this results in very little bass and overall bad sound.

    Our solution
    Ideally, what we need to do is add a decent but cheap 8" subwoofer to the cabinet. It'll need to be 8 ohms. Then we will cross it over so it only produces the bass tones. We will allow the backbox speakers to work as the midrange and tweeter sounds. These are 4 ohm speakers, so if we wire these in series, they will also be 8 ohms. Then we will wire the 8 ohm load of backbox and 8 ohm load of the subwoofer to a single 4 ohm load resulting in some decent bass and balanced sound.

    Here is what we need:
    1) 8mh (or so) inductor, $14: http://www.parts-express.com/pe/showdetl.cfm?partnumber=266-576
    2) Cheap but very efficient 8" sub $21.50: amazon.com link »
    3) Some speaker wire. You can probably rip out and use the wire already in the machine.

    Now, the inductor is easy to wire. Attach one end of the inductor to the + on the subwoofer. It doesn't matter which end. Pretend the other end of the inductor is the + of the subwoofer and use it to attach the speaker wire. I usually just tie strap the inductor to the speaker, but you can attach it to the cabinet or wheverever so it doesnt rattle around.

    Now for the system wiring you need to do this:
    1) Amp + run to inductor lead.
    2) Amp + run also to backbox left speaker +
    3) Amp - run to subwoofer -.
    4) Amp - run also to backbox right speaker -.
    5) Run one wire from backbox left - to backbox right +

    You are done. You should find you have some decent bass sound as well as plenty of volume.

    To attach the 8" to the cabinet, just get a hammer and use the back end to pry out the 6" speaker that came with the game as well as the wood spacer that the speaker is attached to. Then use some #6 or #8 3/4" screws and screw the speaker to the bottom of the cabinet centered over the hole.

    This wiring will work to upgrade any of the WPC pre-DCS games such as addams, TZ, getaway, dr who, Fish Tales, creature, dracula, Black Rose, White Water, etc.

    Optionally, an l-pad could be wired in line on the backbox to allow further volume adjustments and bass balance. This adds some complexity to the wiring and in my opinion, isn't needed. http://www.parts-express.com/pe/showdetl.cfm?partnumber=260-248

    DCS games (includes wpc95):
    For those that may ask, there is a simpler solution for DCS and WPC 95 games. Simply swap the cabinet speaker with an efficient 4ohm sub. You don't even need a crossover because the cabinet speaker is already electronically crossed over at 300hz. There are two amps in the DCS games. This allows you to only worry about the subwoofer swap without backbox impedance and rewiring. If the cabinet speaker you choose is efficient enough, you can be done. But if not, you can add the L-Pad above or maybe just add a 20 ohm resistor (http://www.parts-express.com/pe/showdetl.cfm?partnumber=017-20) to lower the backbox volume.

    If you choose to add the resistor, you would desolder the two wires that go to the 5.25" left speaker on the backbox. One goes to the amp, one goes to the right speaker. Separate the wires. Solder the resistor to the + lug of the 5.25" speaker. Solder the wire that goes to the + of the right speaker also to the + lug of the 5.25" speaker. Solder the wire that came from the amp to the other end of the resistor. That's it.

    Finally, for DCS games you'll want to choose a decent and efficient sub. The wh88 will work pretty well as it is extremely efficient. However, it's 8 ohm so it takes some power from the amp away in impedance. I recommend using one of these MCM 10" speakers: http://www.mcmelectronics.com/product/55-3211. They are 95db efficient so you may not need any resistors if you use this. You will lose some volume form the small 6" cutout on your cabinet but it's fine. If you choose this option, your entire cost for the DCS addon is around $15 shipped.

    #2 6 years ago

    Thank you for the write up! Am I reading right that you would not upgrade the back box speakers?

    #3 6 years ago
    Quoted from Capper96:

    Thank you for the write up! Am I reading right that you would not upgrade the back box speakers?

    Sure you can. But this was focused on the sub. For backbox, a 5.25" coax and 3.5" coax does the trick. A pair of each does two machines. With 4 ohm speakers, you want to wire them in series to keep the impedance in line.

    #4 6 years ago
    Quoted from Capper96:

    Thank you for the write up! Am I reading right that you would not upgrade the back box speakers?

    I can tell you that when it comes to bang for the buck, the difference in backbox speakers is very minimal if you also do the l-pad that Mark mentions. I decided a while ago to upgrade my Viper Night Drivin's sound, and once I got the sub done never bothered with the cabinet speakers because it made the whole thing sound five million times better.

    #5 6 years ago

    Great article. Thanks markmon for taking the time to share your expertise.

    #6 6 years ago

    Does this work on system11 games? In your opinion is it even worth upgrading?

    #7 6 years ago

    It's basically the same process for any game, it just depends on the game that you're doing. Mousin' Around is an OUTSTANDING game to upgrade, as I assume Space Station would be (hmmm... I should try that one!) but others don't have the low range that makes it as worth it in my opinion.

    #8 6 years ago

    ok ordering two sets, creech and TZ are getting subs in the trunk!

    1 month later
    #9 6 years ago

    Okay reporting back, I wired per Markmon instructions and replaced the cabinet speaker with the pyramid and man does this make a world of difference. Thank you again for the instructions.

    TZ shakes whenever you hit the rocket shot, and the left ramp car on creech just rumbles its great

    #10 6 years ago

    I bought my sub for 10 bucks at a garage sale and added it to my F-14.

    If you add a sub with a high level input (speaker level, instead of line) you don't need an additional crossover or impedance matching device.

    1 month later
    #11 5 years ago

    Installed the exact components listed by Markmon in the original post in my TAF. I had to turn up the volume a bit to get the bass to be where I wanted it, and it made the backbox speakers to loud. Ordered and installed the l-pad listed, and it's perfect.

    Thanks to OP for the write up. I can't wait to do this to the rest of my WPC games.

    #12 5 years ago

    Awesome stuff Markmon, thanks for the write-up!

    Bumped.

    #13 5 years ago

    Great thread - I'm about to do the same - subwoofer-only replacement.

    There is a lot of good info on upgrading your sound here: http://www.dziedzic.us/wpc_speaker_replacement.html and here: http://www.flippers.be/pinball_sound_upgrade.html

    The last link is interesting because it shows a more elegant way to control the cabinet/back box mix than an L-pad: a small potentiometer across R17. This is a great solution because it's potentially no soldering (I'll probably still solder mine), and the power amp no longer has to produce additional power (which can increase distortion and will very slightly increase your machine's power consumption), only to lose it in the L-pad. This fix reduces the volume going to the power amp, so it doesn't have to work as hard as it would with an L-pad. It's a pretty minor thing - if you are already using an L-pad I wouldn't worry about changing it.

    I looked at the schematics and saw that the R17 hack will work fine. However it will slightly change the frequency response of the last stage (U1C). U1C + R17 + R11 + C7 form an inverting low pass filter. From DC to about 15kHz, the gain is -1. Above 15kHz, the gain starts rolling off to ensure the signal doesn't have any artifacts from the digital-to-analog conversion done to generate the signal (read more here http://en.wikipedia.org/wiki/Reconstruction_filter). If you decrease R17, that reconstruction filter won't work as well. The WPC-95 R17 link says that a value of 9k across the existing 22k R17 seems to work well. That means the effective resistance of R17 = 1/(1/22k + 1/9k) = 6.6k. So if you do that, the new corner for the low pass filter will be 53kHz (from 15kHz). You probably won't hear a difference, but it's possible high-frequency noise from that signal could cause audible distortion.

    So another (and in my opinion the best) way to change the mix between the cabinet and the back box would be to remove one leg of R23 and insert a 200k or 250k potentiometer in series with R23 (between the free leg of R23 and the PCB hole where that leg of R23 used to go. This will attenuate the signal without changing the characteristics of the reconstruction filter.

    Again, any of the the different methods of changing the mix (L-pad, R17, or R23 mods) will probably sound identical in the real world, but the R23 mod is the best in theoretical terms, so if you're making a mod that's the one I'd recommend.

    I've attached a schematic of the WPC-95 audio filter stage (with corrections - the schematic had the + and - of the opamps backwards). I'll add pictures to this thread when I make my mod...

    WPC-95 Audio Filter Schematic.png

    #14 5 years ago

    I also just realized that you could adjust the balance without soldering by tacking on a pot across R22 instead of R17. Instead of reducing the gain of the backbox channel, you'd be increasing the gain of the cabinet channel. That's probably the cleanest way of all...

    #15 5 years ago

    I followed markmon's suggestions above with TZ and have outstanding results. To be fair though, some previous owner had a 4ohm woofer + capacitor + resistors wired up and it was just awful so I am not comparing against the original, whatever it was.

    Next up is finding an appropriate sub for my NF!

    #16 5 years ago
    Quoted from wayout440:

    I bought my sub for 10 bucks at a garage sale and added it to my F-14.
    If you add a sub with a high level input (speaker level, instead of line) you don't need an additional crossover or impedance matching device.

    How much of an improvement do you hear on the F-14? Are there enough low frequencies from this era machine to make it worth while?

    1 year later
    #17 4 years ago

    Posted to reference for speaker install. Thank you for the write-up!

    #18 4 years ago

    Cheap way to add a sub to a Williams game.. I can modify my headphone adapter with a audio out.
    $35 for the adapter wiring and free shipping then buy a powered sub

    image-668.jpgimage-907.jpg

    #19 4 years ago

    great thread

    #20 4 years ago

    In a different thread markmon recommended these for backbox replacement:
    http://www.parts-express.com/pyle-wave-plx52-5-1-4-coaxial-speaker-pair--267-776
    Followed his suggestions for a few Pre-DCS games and it sounds incredible.
    Added an L-Pad using the wiring diagram below:
    Pre-DCS-w-LPAD.jpg

    #21 4 years ago

    thanks for this thread. Really learned a lot.

    #22 4 years ago
    Quoted from lllvjr:

    Cheap way to add a sub to a Williams game.. I can modify my headphone adapter with a audio out.
    $35 for the adapter wiring and free shipping then buy a powered sub

    just WPC or sys11 too?
    -mof

    #23 4 years ago

    I bought the recommended MCM 10" speaker, http://www.mcmelectronics.com/product/55-3211.

    I don't really hear much difference on my TZ. I'm thinking it needs some type of crossover and additional amplification.

    I do like the speaker, but feel it needs something to make it shine in a TZ.

    #24 4 years ago
    Quoted from mof:

    just WPC or sys11 too?
    -mof

    Wpc 95
    Wpc Dcs
    Wpc dm
    I can do like above.... My stern Sam boards have them built in already

    3 weeks later
    #26 4 years ago

    Bought all the parts to do this, just need a jigsaw now so I can make the bigger holes that are needed.

    #27 4 years ago

    Huhwat? You don't need bigger holes

    #28 4 years ago
    Quoted from markmon:

    Huhwat? You don't need bigger holes

    For the subs, yeah I do. The old hole is too small, and the mounts are not big enough. I can post some pics tomorrow.

    #29 4 years ago

    nice if the hole IS the size for the woofer, but same time theres "do I want to cut into this cabinet?"
    sometimes MDF spacer rings are too large outside diameter, but a macrame hoop might be great?
    (can always make a custom narrow ring if needed too easy enough)
    for a pinball machine the 8" hole oughtta be allright for what a 10" woofer is going to put out, as long as theres 4-5mm clearance for the cone's surround, its gonna do what its gonna do and I get it. an 8 is about 50 sq in of cone, a 10 is about 75 so if its efficient means quite a lot more bass even barking through the same hole. it isnt like the amp section is going to get the 10 up to Xmax anyway, so I'd be really hesitant about cutting, unless maybe I were dropping in a booster amp and a 12 hehe..

    other options maybe, 2 adapter rings and mount from bottom-outside instead, oughtta give needed clearance for the magnet and cage, or build a shallow-ish ported cab to hang up and just use factory speaker leads? going that route you could tune the port down to 30-40hz might be cool. recently built a pair of cabs for 6.5" woofers with ports tuned just under 40hz, the bass off em is amazing!
    just sayin, if you're thinking cutting the cab, why not go better and further instead?

    #30 4 years ago

    little app called "box-notes" is saying 7" thick, 16" wide, 28" long (from 3/4 stuff)..
    with a port 50mm diameter and 130mm long, should tune it to 35hz. its a freebie app, you can find to DL and use to input any cab dimensions, port length and diameter, 1 or 2 ports, and choose 8-12" woofers for decent ballpark estimates of what a cab is going to do for ya.

    with the dimensions I'd just popped in, I'd mount so the port is 5-6" from the wall behind the machine (obvious its where I'd place the port), the woofer's center 10" back from front edge and 1/2" off center, comes up looking decent on the app's lower graph for avoiding overlapping resonant freq's.
    dimensions were a quick guess what'd easily hide hung up underneath, cut from 1/2 sheet (4'x4').

    #31 4 years ago

    'adding a cheap sub' is misleading. Since *sub*woofer' typically refers to a separately powered unit.

    You are just upgrading the woofer and adding a crossover if needed.
    Same amp. Expectations should be tempered as to results.

    IMO much better to put that money towards an external powered sub. Even the cheapie 50w polk is going to give much better results.

    #32 4 years ago
    Quoted from Evan55:

    'adding a cheap sub' is misleading. Since *sub*woofer' typically refers to a separately powered unit.

    It's actually not misleading at all. What you're describing is adding a "powered sub" which is not what this post is about. A subwoofer does not mean external and separate amp powered. It means a dedicated speaker for sub bass frequencies. Adding a bigger speaker and crossover accomplishes this just fine. Many people, like me, have absolutely no interest in having a separate external sub attached to the machine.

    Quoted from dsuperbee:

    For the subs, yeah I do. The old hole is too small, and the mounts are not big enough. I can post some pics tomorrow.

    Well no, you don't. Did you even read the first post of the thread or just come in here and start typing? You can easily mount a 10" over a 6.5" cutout and benefit from the bass with the low power these onboard amps put out.

    #33 4 years ago
    Quoted from markmon:

    It's actually not misleading at all. What you're describing is adding a "powered sub" which is not what this post is about. A subwoofer does not mean external and separate amp powered. It means a dedicated speaker for sub bass frequencies. Adding a bigger speaker and crossover accomplishes this just fine. Many people, like me, have absolutely no interest in having a separate external sub attached to the machine.

    Well no, you don't. Did you even read the first post of the thread or just come in here and start typing? You can easily mount a 10" over a 6.5" cutout and benefit from the bass with the low power these onboard amps put out.

    Yes I did read, thank you. MY particular situation requires some cutting. See at one point someone put in a rinky dink little speaker in the cab AND replaced the mounting board to fit the stupid speaker size. So yes, I have to cut, as well as replace the mounting screws.

    #34 4 years ago
    Quoted from dsuperbee:

    Yes I did read, thank you. MY particular situation requires some cutting. See at one point someone put in a rinky dink little speaker in the cab AND replaced the mounting board to fit the stupid speaker size. So yes, I have to cut, as well as replace the mounting screws.

    So what, they got some putty and filled in the hole? You dont need the mounting board or mounting screws (as the instructions state). You pull the stuff out and screw the speaker to the floor of the cabinet. I doubt the original hole in yours was magically shrunk.

    #35 4 years ago
    Quoted from markmon:

    So what, they got some putty and filled in the hole? You dont need the mounting board or mounting screws (as the instructions state). You pull the stuff out and screw the speaker to the floor of the cabinet. I doubt the original hole in yours was magically shrunk.

    Here is the new speaker mounted, and what was in the game when I bought it. For what it's worth whomever had the game last did go through the trouble of creating a new mounting plate for the small speaker they stuck in there. Made it a little easier to cut out a bigger hole, but I do suck with a jigsaw image.jpg

    #36 4 years ago

    Yea you didn't need any of that. The mounting plate pries out and you screw the speaker to the floor over whatever hole is there - which would have been the stock 6". Also what game is that? I think you'll need the inductor on it unless it's not wired in yet. All the games in your listed collection would require it.

    #37 4 years ago
    Quoted from markmon:

    Yea you didn't need any of that. The mounting plate pries out and you screw the speaker to the floor over whatever hole is there - which would have been the stock 6". Also what game is that? I think you'll need the inductor on it unless it's not wired in yet. All the games in your listed collection would require it.

    It's a dw. I want to keep it as stock looking as possible, so I wanted to keep the plate. I will be doing the same to my wh2o. Unfortunately the crazy wind has finally blown down one of my fences, so the speaker project is on hold until I can get the fence at least braced and then replaced.

    #38 4 years ago

    You can buy the sub and inductor on Amazon right now for $35.25 with free shipping. Just ordered mine for BSD. Great thread!

    1 week later
    #39 4 years ago

    After some searching I found a © 1992 NOS 8" speaker that I'm going to use in my JD? Pretty impressive SPL of 98db.
    image.jpgimage-773.jpgimage-217.jpg

    #40 4 years ago

    98db/w/m is really really good for an 8, that oughtta thump hard, nice score!

    #41 4 years ago
    Quoted from zizzlemeplease:

    98db/w/m is really really good for an 8, that oughtta thump hard, nice score!

    Spent a looooooong time surfing the web to find an 8" with sensitivity this high plus a low end frequency response too that wasn't super expensive. Now I've got to put it in and hear what it does.

    #42 4 years ago

    This thread is awesome, upgraded 8" pyramid cabinet sub on TAF sounds awesome.

    #43 4 years ago

    Yes, Seance sounds really good with a sub

    4 months later
    #44 4 years ago

    Just got a Whirlwind and was set to order this upgrade, but the inductors are out of stock. Thing is, Amazon is almost out of stock on the speakers... I can guess what will happen if I wait for the inductors to come back in :/ Is there another inductor that would work?

    Also, anyone have any insight on using this for a System 9? I've read that Space Shuttle benefits from a boost visa other means, but I like the elegance of this system. Thing is, that era machine only uses one oval speaker in the backbox, and I'm not sure how the onboard amp is spec'd... I can research this later, but figured I would ask if anyone already "knows" one way or another?

    #45 4 years ago

    Why not a separate powered subwoofer under the pin? I picked up a really nice Polk 10" sub for $40. Sounds fantastic on my ST Pro.

    #46 4 years ago

    Polk!!! the way to go!

    #47 4 years ago

    Very new....noob question.....Both my pins (T2/RK) look to have original subs in them...don't need it to "thump"...just don't want ripped ones......can I just pop old one out and new one in...or are there other things I must do.....(I read the OP...I don't want to "upgrade"...I just don't want ripped ones)......Thank you..................Joey

    #48 4 years ago

    OK, just for reference, after a bit of reading, if I understand correctly a quick & dirty rule of thumb would be a lower inductance (mh) value raises the crossover frequency; a higher value lowers the frequency. Which is what I suspected, but confirmation is always good.

    According to the chart I found here:

    http://www.apicsllc.com/apics/Misc/filter1.html

    For the 8ohm Pyramid woofer, a 8mh inductor value yields a 159Hz crossover. Going to 7mh yields 182Hz; going to 9mh yields 141Hz.

    My personal preference is not to drown out the backbox speakers as some have reported, so I went with the 7mh value to pass some of the higher frequencies, though overall it sounds like it should still be heavily low-end focused. Guess I'll find out soon enough...!

    #49 4 years ago
    Quoted from Breaking_Dad:

    can I just pop old one out and new one in...or are there other things I must do.....(I read the OP...I don't want to "upgrade"...I just don't want ripped ones)

    In general, changing nothing else, you want to match the size (cone diameter and/or mounting flange, for fit), and the impedance rating (in ohms). The impedance is important as that will match the rest of the circuitry - deviating too much can cause poor sound or even damage other components. Usually the impedance is marked on the speaker and easily identified. So just pick a speaker of the right size with a matching ohm value (usually either 8, 6, or 4 ohms), and that's that for a quick safe swap (make sure to keep the + and - terminals correct).

    Of course there "can" be other considerations: speakers are also spec'd by efficiency, freq response, power, etc... things get more complicated when you pursue the rabbit hole of "better sound" or even "best theoretically possible replacement"... but if you just want to fix a rattling rip, stick with size and impedance, any new decent speaker shouldn't be much worse than what was there originally.

    #50 4 years ago

    ^^^...Thank you....so in manual they call for 8 ohm 6".....what about watts....watts are not specified...can any damage be done by using the wrong watts..???....Thank you again..............Joey

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