So I have an AC/DC Premium and it has this huge 12" woofer in it. I agree that stock, it sounds better than other Sterns in the past have stock. But with a 12" woofer, I would expect the bass in this thing to blow away my Ironman, Tron, 24, or any other Stern with an 8" Pro sub. It doesn't. I had to solve that. The result was a more powerful bass than provided by even a $100 external powered sub - and for cheaper. Read on.
Details and theory
If you don't care about any of this, just skip down to "the solution". I'll try to keep this brief.
The Stern SAM systems are driven by two 18w 4 ohm amps. One is used for the backbox hooked up with the red wires, the other is used for the cabinet sub, hooked up with yellow wires. The cabinet sub is running full range. The speakers used in the back cabinet are cheap 4" speakers. These are run in series.
The problem in AC/DC is three fold: 1) There is no crossover on the sub so it doubles up on what is already handled by the backbox. 2) There is no volume control on the sub so you cannot get more bass. 3) This is the big one: The 2030 amp on SAM boards is no where near enough power to drive this 12" speaker. To make matters worse, Stern used an 8 ohm speaker which further lowers the amp's capabilities of driving the sub.
To test the amp theory in #3 above, I pulled out the 12" sub and installed a decent 8" sub I had laying around. I stuck a 100hz crossover on it, and wow, the bass coming from this was way greater than the bass coming from the 12". Why? Because the 18 watt amp is enough to drive this cheap 8" sub but when it comes to a 12", it is not. To make matters worse, Stern used an 8 ohm 12" sub. This reduces the amp's power to it probably closer to 12 watts. You can tell the speaker is under driven as the speaker hardly moves.
I have a polk audio 10" powered external sub laying around. For a while, I had just hooked this up. The bass coming from this was quite good. The 12" provided some decent mids. But I didnt like having the external speaker. It makes moving the pin a hassle. It has to be internal.
So I had this cheap powered amplifier laying around. I decided to try this out. It provides 100 watts. But most importantly, it has a built in crossover and a volume knob. I put the 12" sub in again and this time hooked up the amplifier. And wow, the 12" just came alive. The bass coming from this 12" absolutely blew away the external powered sub. Not only that, but when you're playing the game you can feel the cabinet shaking in your hands as well as massive streams of air shooting up through the glass onto your hands. The external sub does not allow this.
One reason why an internal sub is a good move is because you can get much lower bass due to the baffle. See, subs are designed to be used in an enclosure. The enclosure provides some air resistance so that when the speaker moves, the resistance of air pushes the speaker back out. The cone, therefore, does not move as much as it would without that air resistance. The size of the box helps tune the resonation frequency of the sound. The bigger the box, the more the speaker moves but the deeper the resonation frequency. The cheap FF and PPro subs are rated around 45 hz. But you actually get a bit lower bass out of these due to the fact that they're not installed in an enclosure, but a baffle. The speaker cabinet is the huge pinball cabinet. The air resistance is lower, but the speaker moves a lot more due to this providing lower bass. The downside is you cannot get near the volume you'd get if the speaker was in an enclosure. But this is OK because the cheap pinball 2030 amps only provide 18 watts. You cant get much volume anyway. Because of this, the pro subs work absolutely wonderful in a pinball box. You get deep bass that those cheap 8" would generally not produce, and the pinball volume cant really go that high anyway. (Off topic, but my home theater subs use this theory. I have a massive raised seat platform for a speaker box. Running 4 specially made 12" infinite baffle subs - the infinite baffle allows the speakers to hit 10hz flat!). The 12" Stern sub running in the baffle produced phenomenally low bass. It way out performs the cheaper external subs.
Get a cheap sub amp such as one of these:
$60 - http://www.parts-express.com/pe/showdetl.cfm?Partnumber=300-784
I used one of these, but it's probably over kill. I used this because I happened to have it just laying around:
$90 - http://www.parts-express.com/pe/showdetl.cfm?Partnumber=300-802
1) Plug the power cable into your service port. The amp turns off when there's no audio signal to it, so this works fine. Stick the amp in the back part of the cabinet. It can just set there. If you want you can velcro or tie strap it down, but it's not needed unless you're going to put your pin on its back.
2) Remove the yellow and white speaker wires from the 12" positive and put it on "High input" or "from amp" red on left speaker input on the amp.
3) Remove the yellow and black speaker wires from the 12" negative terminal and put it on "high input" or "from amp" black on left speaker input on the amp.
4) Wire the red wire from the amp to the + terminal on the 12" speaker (where the yellow white was)
5) Wire the black wire from the amp to the - terminal on the 12" speaker (where the yellow black was).
6) Test and adjust. The amp has a knob for gain. This is the sub volume. Adjust it to where you want it. There is a freq knob. This is your crossover. I put mine somewhere near 100hz. You want to cut all the ugly higher vibration sounds out of the sub and have it only producing bass. That's what this knob will do for you.
7) Your 12" speaker is now going to move so much that it will pound on the metal grate that stern provided. You have two options: 1) Remove that metal plate or 2) Space the speaker up slightly. This is easy. I got a cardboard box. The one that the amp came in works. Cut it up and fold the cardboard into small squares 4 layers thick (just cut like 1" wide x 4 inch long strip and fold it 4 times into a square). Loosen the 8 5/16th nuts that hold the speaker down just enough to be able to shove in the cardboard, and insert these cardboard spacers around the edge of the speaker between the nuts. Insert 4-8 of these cardboard spacers. Try to keep them around the edge as you don't want the speaker cone to pound these instead. Then tighten the speaker nuts down. Dont crank them. Just make sure that the bolts are tight enough so that the speaker doesn't move.
8. Last, the speaker will be so aggressive that your glass is going to massively rattle on bass notes such as pop bumpers. Remove your glass and line the edges with electric tape. This will tighten the glass preventing it from rattling.
When I'm playing my AC/DC with the vol up, the 12" is moving so much that I feel streams of air shooting up through the lockdown bar onto my hands when the bass hits. It's absolutely awesome!
Optional (under $20): Now for the highs - AC/DC is music based. Unlike most other pins, it requires decent treble to replicate cymbals. Therefore, replace the backbox speakers to get some decent highs. You need a coax speaker. Anything on this page will do. Pick something around $18 if you want to go cheap. I actually used these clarions for about $28. They're great speakers for the price: amazon.com link »
If you replace these, remove the little blue cap on the right speaker from the circuit. It's not needed and only serves to remove some of the mids. It was needed on sterns' speakers that had no real tweeters. But on coax, you don't want it. Just desolder it, unscrew it, and throw it away. Connect the wire that connected to this directly to your speaker.
$100 external powered sub - The external sub is blown away by this 12" internal sub with a $60 amp. The amp is cheaper, just as easy to install as the external sub. And, everything is internal in the machine.
Stock: there's no comparison between this set up and the stock set up. You'll be blown away.
Pinball Pro or FF kit: They haven't come out with anything yet, but I can't see how it would be better.