jamma cabinet speaker impedance?

[krick]

I've got a question regarding the proper impedance for the speaker(s) in a Jamma cabinet.

Most older games had only one speaker.
Many new cabinets have two speakers.

Assume I had an old (mono sound) machine where the cabinet had one 8 ohm speaker.  I think it's safe to assume that the board in it was designed to drive a single 8 ohm speaker.

Now if I was to move the board to a new cabinet with two 8 ohm speakers, I have 3 speaker hookup options...

1) connect only one speaker (8 ohms)

2) connect both speakers in series (equal to 16 ohms)

3) connect both speakers in parallel (equal to 4 ohms)


What is the correct thing to do?

Can I damage anything (like the board's amplifier?) by hooking it up the wrong way?

Am I correct in assuming old cabs had 8 ohm speakers?

Am I correct in assuming that new cabs have two 8 ohm speakers?

...
Krick

[Dave_K.]

You can damage the sound amp if you do anything but hook it up to a single 8ohm speaker.  I don't see the difference since its mono anyway  .  Only other option is to see if there is an aux out on your board (some have it hidden like on NBA Jam)...you could then optionally send that to a stereo driving 2 8ohm speakers.

[krick]

When I got my cab, there were two 8 ohm speakers wired in parallel connected to the standard JAMMA pins (L & 10).  I'm in the process of MAME-ing my cabinet and I want to try to leave the wiring as close to original as possible in the event that the cabinet is ever used for real JAMMA boards again.

I think that two speakers were used in this cab so that it could be used with games that have real stereo sound rather than the default mono. (capcom games, MK series, etc...)

Also, it's a little odd to hear sound coming out of just the speaker on one side, even if it is mono.

[Redseven80]

I wondered this myself I have a old twin speaker jamma cab that is running old mono pcb's is there a way I can safely split the sound in to two speakers if so what would there Independence be?

[krick]

Having an impedance too low (not enough load) can damage the amplifier.

Higher impedance will not damage amplifier but will result in reduced volume output.

speakers wired in series = sum of speaker impedances

If your cabinet has 2 x 4ohm speakers, the resulting load when wired in series is 8ohms.

If your cabinet has 2 x 8ohm speakers, the resulting load when wired in series is 16ohms.

So to connect your two speakers to a mono board without damaging anything,
make sure you wire them in series as in the diagram below.

I would run all 4 wires down to the area where your board is mounted in the cabinet and terminate it with a 4 pin connector.

[Ken Layton]

Having an impedance too low will damage your amplifier because the lower the impedance the more current will be drawn through it. Generally wiring in parallel reduces impedance. Two 8 ohm speakers in parallel is 4 ohms. If you had two 4 ohm speakers in parallel you'd have 2 ohms (effectively a dead short) and you'd have a cooked amplifier.

[whammoed]

If you have two 8 ohm speakers and you want to hook it up to a mono source meant for 8 ohm why not just wire in parallel and add an 8 ohm resistor to each speaker?

[Redseven80]

So If I were to use 2 4ohm speakers (2 way) rated at 140w each in series, what would the result of this be? good sound with 100% no amplifier damage? Thanks for your help.

[Ken Layton]

Two 4 ohm speakers wired in series would be 8 ohms. Your amplifier will be very happy with that and you'll have good sound.

[quadmasta]

Sensitivity will be a huge issue.  Get the most sensitive 4 ohm speakers you can find so they'll make the best use of the power.

[Redseven80]

Alrighty, you know your stuff Ken, cheers!

[Witchboard]

So if the equation of speakers wired in series is the sum of speaker impedance, what's the equation of speakers wired in parallel?  Sum of impedance divided by number of speakers?  Just an example, 3 speakers, two 4 ohm and an 8 ohm speaker.  What's the impedance if all 3 are wired in parallel?

[whammoed]

Remember that "Rt" means Total resistance of the circuit.
R1, R2, etc. are Resistor one, Resistor two, etc.
 
1    1    1    1 
-- = -- + -- + -- 
Rt   R1   R2   R3

answer is 1.6

 

[krick]

So if the equation of speakers wired in series is the sum of speaker impedance, what's the equation of speakers wired in parallel?

[krick]

For anyone trying to go the other way, i.e. putting stereo output through a mono speaker, this page has pretty good instructions on how to do that correctly...

http://www.pobtastic.co.uk/guide/stereomono.htm

[Witchboard]

Thanks guys.