Stereo-Mono Downmixing

[Trimoor]

I have a cab with only one speaker that I would like to MAME.
Whats the best way to downmix stereo to mono?

Do I just wire the two channels toghether?
Do I need a resistor? What value?

Thanks!

[pmc]

You might be able to wire both channels to the same speaker. I never tried that and I'm not sure what would happen.

Also, check your Windows "Sound and Multimedia" Control Panel. Mine has an option to set the output to mono. Then you can simply wire the speaker as either R or L and you'll get both channnels on that speaker.

Lastly, assuming your source is from an 1/8" audio jack, you  can pick up a "stereo to mono" jack adapter at Rat Shack or wherever. It'll just combine the L and R through both channels. Make sure you adapt the correct direction (stereo to mono versus mono to stereo) or you'll just get the left channel.

-p

[D_Zoot]

Yes, you can just wire both speaker channels together and it *will* work.  It's not "correct", but will function.  

Doing this, post amp, can cause odd amp loading, in addition, due to the cancellation effect of out of phase material, can yield some discrepencies in the output.

Doing this pre-amp can cause phase cancellation issues as well.  

But honestly, most people wouldn't be able to tell.

The best solution is to fabricate a summing amplifier, some electronics background would be needed, but it's not a complicated circuit.  Here's one example:
http://www.ecircuitcenter.com/Circuits/opsum/opsum.htm
You could purchase one, pre-made, but this may concept may be overkill for a game cab.  Here's an example:
http://www.extron.com/product/product.asp?id=asa101&subtype=127&view=desc


A summing amplifier would go between your sound card and whatever you were using for an amplifier. It mixes both channels together into one mono signal.


As an alternative, there may be a way to do it in software.  Check your sound card documentation, there may be a mono setting you can apply.

Also, note that a large number of MAME games, most of the classics, were mono anyway, so if you only hooked up one speaker you would be fine.


D

[krick]

This pages have info on how to electrically combine stereo into mono without damaging anything...

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

http://www.ionpool.net/arcade/gauntlet/jamma/sound.html

[D_Zoot]

This pages have info on how to electrically combine stereo into mono without damaging anything...

Trimoor,

Are you going to be using the cab for anything else besides MAME ??  Those two pages show circuits that help reduce the likelyhood of improper amp loading, but those circuits won't do anything to prevent phase cancellation.  With games, it won't matter much, but if you were to use the cab for jukebox functions, movies or anything like that, you'll still need to look at a method to sum the L and R channels.


D
   

[Trimoor]

Its a vertical monitor, so nothing but vertical mame games.
I already built a dedecated jukebox, so I don't need support for that.

I'll be using the monitor's built in mono amp to drive the speaker.

It's going to be running some form of DOS, so the windoze mixer is out of the question. (damn you micro$oft!!!)

I'll probably just use two 1K resistors.

Thanks all!

[neuromancer]

Are any vertical mame games stereo?

I know most of them are classic games, and for the classics, you can just wire them together, because they're all mono.

Bob