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Should We Run Our PA System In Mono Or Stereo?

6:00 am Live Sound

We’ve all gotten used to hearing recorded music in stereo by now. Only real old-timers (like me) can remember when all records were mono and a “hi-fi” system only needed one speaker. Stereo arrived in the mid-60s, and following a brief period when each record was available in separate mono and stereo versions, often with very different mixes (see Pepper, Sgt.), we finally reached the point where all records, all cassettes, all CDs are now in stereo.

Lots of bands that play live have PA systems with two main speakers. Since home stereo systems also have two speakers on the left and right, the question arises, should we create a stereo mix of the PA signals to play through the “stereo” PA speakers? My answer is basically no, but before I go into why, let’s quickly review exactly what stereo is in the first place. (Audio engineers can skip the next section.)

Stereo 101

Before there was stereo (short for “stereophonic”) there was mono (short for “monophonic” or “monaural”). In a mono music system, there is one audio signal containing all of the instruments and vocals. If you play the mono signal through a single speaker, you hear everything.

In a stereo music system, there are two audio signals, designated left and right. The left and right signals together contain all of the instruments and vocals, but the two signals are different from each other in a special way that creates the familiar left-to-right stereo “spread” in front of the listener (or inside her head if she’s using earphones!).

Instruments that are panned all the way left or right appear in only one of the two signals and thus are heard full volume from that speaker and not at all from the other one. Instruments that appear at an equal level in both the left and right signals will seem to be centered, coming from a “phantom” source midway between the speakers.

Please note that if you send a mono signal to two speakers at once, it is still mono, not stereo. Stereo means “two signals,” not “two speakers.”

So, Mono Or Stereo PA?

Once again: since our band uses a stereo mixer with L-R pan controls, and we have two main speakers to the left and right of the stage, should we create a stereo mix of the PA signals to send through the speakers? Well, except for one special case, I would suggest sticking with mono. Set all the pan controls all the way to the left or right and use only that output for the mains. But why? Well, here are some of the problems with using stereo:

1. Many (or most) audience members will hear an unbalanced mix.

With a stereo mix, some instruments and vocals will come mostly from the left speaker while others are mostly from the right speaker. (Otherwise it wouldn’t be a stereo mix!) People sitting quite close to the left speaker will hear the “left” signals quite loudly and the “right” signals much less or not at all, with the reverse being the case for the poor sods right in front of the right speaker. Only the part of the audience in the “sweet spot” (centered, partway back) will hear the intended stereo mix.

2. The sound man is probably not in the “sweet spot” himself.

At typical gigs, the sound man is off to the side or right up by the band, making it impossible to create a stereo mix that sounds right in the centered “sweet spot.” Sure, he can use earphones to monitor, but then he’s not hearing the contribution of the onstage amps, plus that makes it hard to judge overall room volume. Also, the audience is not using earphones!

I guess you could go nuts and set up a stereo mic at a centered monitoring point in the audience and listen to that in earphones, but I would question whether it is worth the effort (see Problem 4).

3. An additional amplification channel is required.

Most power amplifiers that get paired with stereo mixers in live settings have two separate sections, which are generally used for the main speakers and the onstage monitor speakers. (See my article A Basic Live Sound Setup Diagram for typical connection info.) For a stereo mix, you will need to use one side for the left speaker and one for the right speaker (remember, the signals are different). This means you will need to buy an additional power amplifier for the monitors. Naturally, the additional equipment and wiring will increase your transport and setup time.

4. It’s just not worth it.

If you do go with stereo, you’re going to have to keep everything panned fairly close to the center to avoid Problems 1 and 2. So it’s going to be almost mono anyway. Plus, the way band sound richochets around inside a typical club or venue, do you think anyone will even notice your subtle stereo mix? Not bloody likely. It’s hard enough to produce and maintain a decent mono mix. Why complicate your life?

I mentioned a special case where stereo sound makes sense. This would be a concert type situation, perhaps in an auditorium, where the band and the speakers are way up front and the audience is confined to a fairly narrow area between the left and right speakers and somewhat back from them. In this one case, assuming the sound man is centered, you can present an impressive stereo PA mix to the audience, since most or all of them are in the “sweet spot.”

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9 Responses
  1. John Boyd :

    Date: May 1, 2009 @ 11:54 pm

    30 years of musical experience, both on-stage and in the studio, and until now I didn’t understand the virtues of going mono when performing live. Yes, of course! In small, club-like settings you set your levels and each of the two speaker towers expresses your vision of the show. Some audience members are on the right, some are on the left. They both get a balanced, equal experience.

    Thank you so very much!

  2. shipwrecktown :

    Date: May 21, 2009 @ 7:53 pm

    So I take it you mean- on a stereo mixer, don’t pan left or right, but set it down the middle. also if you have any suggestions on where to place a monitor relative to 2 vocal mics to avois feedback- please let me know.

  3. iah hassan :

    Date: August 22, 2009 @ 12:39 am

    good tip tq

  4. Cal :

    Date: September 5, 2009 @ 12:27 am

    Mono PA systems always sound like the music is inside your head. I vote for stereo - no, not to pan instruments toward the left or right (although perhaps just a little), but to use stereo effects that provide spaciousness to the mix. That gets rid of the monotonous din created by a boring, monotonous mix. Yes, it is tough to get the mix just right, but if you spend plenty of time on the sound check at each gig, the payoff is tremendous.

  5. Cal :

    Date: September 28, 2009 @ 11:35 pm

    Also, for shipwrecktown, your monitor should be on the floor pointing up toward your head. That way, the mic faces away from the monitor and you can hear the sound coming up from the monitor. If you have feedback, then you will need a graphic EQ to filter out the frequencies that feed back. Get a good 31 band EQ so that you can just notch out the offending frequencies without altering the overall sound too much. The best setup is to have an EQ for the monitor mix, and a separate EQ for the mains. If you are running in stereo, then you actually need at least 3 EQs at minimum.

  6. MARVDEEMAN :

    Date: April 18, 2011 @ 3:12 pm

    IF IM UNDERSTANDING THIS COR. ON A ”MONO” SET-UP I SHOULD PAN ALL THE WAY TO EITHER R OR L ? MY QUESTION IS, WHY SHOULD’NT IT BE IN THE CENTER ?? P.S. I’M AN AVID FAN, YOU’VE HELPED ME ALOT ON ALOT OF DIF. ISSUES. MUCH APPRECIATED, THANKS ! MARV

  7. MARVDEEMAN :

    Date: June 13, 2011 @ 12:40 pm

    I feel really stupid asking this, but im a drummer who just got put in charge of all the audio stuff !! I need to buy a new / used power amp and i see alot of CHEAP priced “DJ” amps out there. (here goes !) WHAT IS THE DIFERENCE BETWEEN A ‘DJ’ AMP AND THE OTHER TYPE ?? when a dj amp says 3000 watts does that mean at PEAK or sustained like the reg amps ?? or do i just have it ‘ALL’ wrong ? please, help. You have ‘ALWAYS’ come thru for me in the past. thank you so much, marvdeeman (or marvdeedumbA#%)

  8. John Bishop :

    Date: July 24, 2012 @ 3:59 pm

    Hi. Great article. Just one case to consider? Micing a Leslie speaker. The only way to hea a realistic les effect if you have to mic up is 2 mics opposite each other on the top rotor and the one on the right is panned fully right, one on the left is panned fully left. “Real Les” out of the pa. Of course, and audience member well off centre line will not hear full les effect but this is the best it can be? Same with bottom rotor but because Les effect is not so marked at lower frequencies, I’ve found one mic will do.

  9. Steve :

    Date: September 16, 2012 @ 12:46 am

    Just bought a 73 postal truck. Previously used as an ice cream truck. Installed a stereo system. Want to hook up the PA speaker that came with the truck to the stereo system. Attempted to hook it directly to the stereo but couldn’t get sound. Can this be done? Would appreciate your expertise.

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