If I recall, the backbox speakers are wired in parallel. So, two 4 ohm speakers in parallel would be TWO ohms. That's way too low of impedance for the amplifier circuitry.

I would be using 8 ohm backbox speakers. That's what the factory used.

You could overdrive the amp if you use 4ohm speakers and set it to 8ohm in settings, and go past half volume. I experienced sound cut outs when I did this.

I've found discrepancies between Spike1 and Spike2 hardware.

Spike1 boards use 4 ohm backbox speakers and 8 ohm cabinet speaker.

There is a thread discussion about speaker replacement in a JP, and the consensus is the current JP Pro/Prem machines use 4-inch 8ohm back box, while the JP-LE version uses 5-1/4 inch 4ohm speakers! So it appears the SPIKE2 hardware is INTENDED to support either 4 or 8 ohm speakers in the back-box, which is settable. What type of speakers did you settle on?

Does anyone know the sensitivity of factory stern speakers? Specifically this is a jp premium, so the newer ones. I'm trying to understand all of this speaker information and one thing I've picked up is you need an efficient speaker for pinball machines. If you don't have an efficient speaker and you only replace the cab speakers with inefficient speakers, the balance between cab and backbox will be messed up. The only way around that is to add resistors (or get new speakers), but I have no idea how many ohms of resistance I would need to add because I don't know the sensitivity of stern speakers. According to Amazon the speakers I bought have a sensitivity of 82 dB

Contact pinwoofer, amazing difference

I'm cheap, I know there are quality systems out there. Not interested though

Ok, u don't know what yr missing

i upgraded my games to the LE speakers in the back box, anyone have a recommended Spike 2 Sub replacement?

Easy. Don’t replace them with inefficient speakers. Haha. Sorry I have no idea what you mean here.

Also since these new games don’t need color dmd, put that money towards Pinwoofer. Haha. Better than any topper you’ll see as well. And way less expensive.

I'm not sure, but 82dB is ridiculously insensitive and you'd certainly need an external amp to drive them properly imo. I just purchased some new 5 1/4" coax speakers fo upgrade my Pro, and found some at 93dB. My guess is, much like cheaper car audio speakers, that the stock speakers are very efficient and most likely above 90dB to allow for the weak af in-built amplifier.

It's perhaps better to discuss speakers for pinball in your own words rather than trying to compare speaker specs, since most folks won't really care as much about rated efficiency or sensitivity. I would suggest that what they care about is :
1) Is the sound quality of the game good? Does the audio sound crisp as it should be, and can they feel the lows. Do voices sound natural? Are sound effects believeable?
2) Is the volume enough for the space you are playing the machine? In a small room, you typically need less volume, but in a larger room you could use more.

Best to describe what you are hearing (or not hearing) and then decide what to do and see what others are doing...

Hey dudes.

You can control the balance between the backbox and cabinet speakers with the balance menu setting. I believe all of the Spike-2 systems have this feature. Also, Spike-2 is Stereo (SAM is mono) which means you can run either 4 Ohm or 8 Ohm, cabinet or backbox speakers regardless of trim pack. I've seen some mention of guys running a dual voice-coil cabinet speaker using the stock amp (i.e. from the MPU board). This is a no-no if you run 4 Ohm voice coils in parallel because you'll be presenting the amplifier with a 2 Ohm load and this will likely cause heating and premature wear-out of the amplifier section of the MPU board (a.k.a. the de-rated clock radio amplifier).

Finally, totally agree - PinWoofer is the way to go!

I disagree. We need to discuss speakers that suit the pinball machine's amplifier. Everything else can come later (tonal preferences). I assure you if you offer your machine's amp an 82dB 4ohm speaker, you will hear next-no-nothing and your amplifier will most likely not last long. The cheap speakers most commonly used, are selected to suit a low-powered amplifier module on the audio board. So in order to improve the sound without additional amplification, you will need to meet or exceed the stock speaker sensitivity rating (rated in decibels at 1w at 1m). At a guess this would be between 88 and 91 from the factory. I would select 88db as an absolute minimum. This is the first spec you need to look at when selecting a speaker. Then if it's Spike 1 you most likely want an 8ohm driver (uncommon) or Spike 2 is fine with 8 or 4ohm drivers. Then and only then can you look to the other specs such as frequency response, your favourite colour etc etc.