Problems With Mono Sound From Stereo Speakers 

This should be a TED talk.

This was the singular issue most successfully addressed by the Grateful Dead’s sound reinforcement many decades ago, when they built individual vertical arrays for each instrument in the band. I was fascinated by that at the time. It was a logistical nightmare to implement but a major sonic advancement.

I took the automatic transcription and edited it. Hope this is helpful: All right, my name is Dave Rat and today I'm going to talk about the same sound radiating from multiple sources - basically mixing in mono if we have a stereo sound system and we send the exact same signal to both sides. Or mixing in stereo or we send a different sound to each side. Over the years I've thought quite a bit about... sound reinforcement and the issues that we run into and various solutions - and one of the concepts that I've come up with is that nowhere in nature does the exact same sound radiate from multiple points in space. Whether it's a cow mooing or a waterfall or a woodpecker or any sound you could possibly run into in nature it occurs in a singular point in space or a range or an area and there is no identical mirror image of that occurring simultaneously somewhere else. Nowhere in nature does the exact same sound occur in multiple points in space. Yet with sound reinforcement we do it all the time. We take the exact same sound and we send a cloned mirror image perfect copy to another speaker nearby and another one and another one and when we do that we create all these... we create a series of issues. You get comb filtering you get time issues, interference from this identical source. If the sources are different we're not gonna have that problem. We don't have a problem with a cow mooing and a goat baying causing some phase interference that's audible that causes it to sound swishy. But if you take the exact same cow Moo and you run it to two different speakers then it'll cause a problem. So there's this these phase interference, this comb filtering issue is unique to electronic re-enforcement. It's not a natural event. Conversely that the opposite of that is that nowhere in nature do multiple unrelated sounds radiate from a single point in space. We don't have the sound of waves and trees rustling and a goat all coming out of a hole in a rock wall. It just doesn't happen that way. We have these sounds are coming from three-dimensional areas - closer, farther, up, down... and yet in live reinforcement or any kind of reinforcement home hi-fi - we do that all the time. We take a guitar, a bass, a kick, a vocal - put it all together and spit it out of a little round thing. Well, that's a completely unnatural event. Those two concepts I think are the basis for creating more audio realism and also for solving not only solving a lot of problems, but actually giving us a lot of solutions or assets. For example, having the same sound radiates from multiple speakers or a line array gives us the dispersion control and allows us to cover the audience. Having the exact same sound come out of two different sub-woofers that are spaced apart, slightly different times is what allows us to create a cardioid sub array. And also can create the cancellation. So we can use this to our advantage and it also can cause us issues. Being aware of it is the key. So when we're mixing shows we've got kicked drum run right down the middle, snare drum down the middle, bass down the middle, guitar down the middle, vocals down the middle and the stereo PA and we've taken all these instruments... we mix everything in mono you want everything to everyone to hear the exact same thing. Now we've got two speakers recreating nearly or exactly the same thing and we've created all these issues... these comb filtering, these phase and time issues. So I'm going to demonstrate some of that. And to do that I'm going to use pink noise source. So I've got two speakers here, little jam boxes wired up to my laptop there, with a mic right here and I'm gonna play pink noise. First thing I'm going to do - it's hard for me to mute it - so the first thing to do is I'm going to play mono pink noise and come out one of these two speakers and I'll move it around and you should be able to hear. Headphones probably will help with this, though it may work on some laptops or other speakers. So I'm gonna take a single pink noise source, move it around you can hear it move side to side. Then I'm going to go to peak noise run to both speakers. And I'm going to demonstrate, you should be able to hear the phase interference of the exact same sound - the comb filtering effect sort of a swish. I'm also going to do polarity reverse - pink noise polarity reverse into one speaker and not into the other. We should be able to demonstrate cancellation and then I'm going to do something that's really interesting... Start with.. [Demonstrates a single Pink Noise source to a single speaker] That little glitch is just the Pink Noise sample starting over again. Now here's two. Pink Noise coming out of both. [Demonstrates a single Pink Noise source to two speakers, audible interference] That's same Pink Noise out of both. [Demonstrates a single Pink Noise source to two speakers, one in reverse phase] Now what I'm going to do, is I'm going to put two different Pink Noise sources, a different Pink Noise generator going to each side. [Demonstrates a different Pink Noise source to two speakers] There's no interference! No longer do they... [Demonstrates a different Pink Noise source to two speakers, one in reverse phase] All right, so with single Pink Noise source by itself, mono source...no problem. Once you take the exact same signal and run it to both sides, then we started to give you interference between the two. When I polarity reversed the same signal going to both we were able to cancel it out and hear the significant issues with polarity. But when I went to two separate pink noise sources they no longer interfered, regardless of whether they're in or out of polarity. Even though each pink noise source sounded exactly the same. So we have two identical sounds, two different pink noise sources that sound identical to our ears. One set causes interference and the other does not. Now that's a really interesting concept. That means that theoretically if we were able to do that with instruments at a show...instead of running the exact same kick drum to both sides, if we were able to alter enough stuff about how we mic that kick drum, or how we reinforce that kick drum, we're gonna get different levels of interaction cancellation. If we take the internal kick mic and the second - we use two kick mics - and we put one to one side and one to the other but we EQ them same, we use two different types of mics, the sound would be slightly different on either side but the magnitude of the interference between both sides will be greatly reduced. That same thing can be applied to dual micing a guitar and other instruments. That's just one way we can use that concept. Another thing that's interesting with that is when measuring a sound system, using the same pink noise source... a single solitary Pink Noise source and running to multiple speakers is going to create a bunch of interference issues in your measurements. But if you use multiple pink noise sources and use it one pink noise for the left and other pink points for the right you no longer have interference between the left to right and you're actually able to measure the cover to the system without any comb filtering issues. Okay hope that's interesting and helpful and I will find you more soon.

I wish I could have learned from you 30 years ago Dave. Brilliant video, thank you. You're able to demonstrate so clearly what other people talk about but cannot show.

This explains why A/B systems are so appreciated in reinforcement in Broadway Reinforcement.

I think you just summarized the entire history of sound reproduction science in 10 minutes. We are blessed 🙌

Reminds me of when I studied PsychoAcoustics, the brain distinguishes seperate sounds when their time difference is over 45 or 50 milliseconds. That is the conceptual difference where "reverb" becomes "delay" or "echo" for our mind's perception... great stuff, Dave, hi from Caracas !

Mind blown. That literally just changed everything for me. Thanks Dave

I told some audiophile buddies that my stereo sounded quite a bit better when I was running mismatched tweeters and they laughed at the possibility. I knew what I heard. Can't wait to show them this. My only question is why did RU-vid take so long to show ME this?

When so many out there are trying to make the concept of sound reinforcement as difficult to understand as possible, it's so refreshing to find someone who can explain so many aspects of it so well. Thank you very much Dave.

The first time you used Pink noise on both speakers it brought to mind the end of The Subhumans album The Day the Country Died. Cool vid Dave, Cheers.

been wacthing your stuff for years Thank you !!!! for all you do for Sound

Wow! Amazing Dave. it really does work. you just re-oriented my mindset on sound reinforcement. thanks Dave. looking forward to many more

Love your insights Dave. Always on a level any aspiring or experienced audio operator would benefit from. Keep em coming.

Great demo! Love the idea of using multiple pink noise sources when running measurements.

Last weekend I was at a small church to help them with their PA system. After watching this video, I did an experiment. I ran the pastor's voice through the headset mic on the left side, and the pulpit mic on the right side. The improvement in quality and gain before feedback was astonishing! I walked from side to side and I could hear very little difference between the two mics. Before seeing this video, I would have though such an experiment would be completely insane! Now I'm curious how a recording would sound. My guess is that in a more controlled environment such as headphones or a decently absorptive room, that the different mics would be noticeable and distracting. But live, it was amazing.

wow! such a great demo! completely blew my mind when the two separate pink noise sources were introduced!

Really appreciate your sharing your thoughts and experience on here Dave. Fantastic advice reduced to it's core elements, presented with no BS.Thank you!

Dave, your videos are incredibly helpful, even for someone who has been doing live sound for 20+ years. I always learn something new from you. Well done.

Thank you Dave for once again being so generous with your expertise and time. This tutorial was incredibly beneficial.

Seriously the freaking best. I always walk away from your vids with new interest and insight

Genius at work. That nature example is mind blowing. You're a huge inspiration to anyone in audio Dave. Thanks so much!

I've been intrigued ever since you came to my school and gave us a seminar a couple years ago. I believe you did the same demo but I think I understand it a lot more than I did now that I'm working with live sound every day. Please do more videos Dave!!

Excellent demonstration. I wish we had more thinkers like you!

I've thought about how phase relations probably matter a lot in sound as our ears are so sensitive to it, mainly while thinking about why digital pipe organs dont sound as good as actual pipe organs; but this applies the same principle to the most basic stereo setup. Really very insightful and supremely helpful. Thanks a lot!

Mind blown as usual, thanks Dave!

Dave Rat is my best resource for actually learning something when I watch his videos. Thanks DAVE

You are a genius! Couldn't possibly think of a better way to explain it. Thanks for sharing your knowledge!

Fascinating! Thanks for conducting this physical experiment. Well done :-)

One of the best videos I ever seen .Thanks Dave ! Real Passion !

Wow! Just...wow! This is profound mind-blowing stuff! It makes total sense, but to actually HEAR it!!!

Crazy stuff. It’s insane how we’ve been taught to shoot for consistency sending the same source the same signal to everywhere. Awesome demo. Will be trying this on my next show no doubt.

Dave thanks for always putting up great content. You're a great teacher. I enjoy every vid!

hands down some of the best information ive gotten

So good. So glad that after 30 years of being a live sound guy, I still keep learning new concepts to apply. Anything I know, both what to do and often what not to do, I have learned from others. I've figured much out on my own as well. Dave Rat, thank you and bless you for sharing your insights with others, and in such a humble manner. Truly a great blessing to us all.

Thanks Dave. This was truly a Zen moment.

Excellent video Dave. I have been saying this for years but this was a great way to demonstrate. We play small venue gigs and have recently taken our subs to one side to reduce cancellation and boosting in the lows. Sounds much clearer all around the venue now. What we need is a see through single source line array to run down the middle (ha ha) !! Cheers.

this video blows my mind!! thank you Dave!!

Dave you are the best, ive learned so much from you and this vid is a total banger. Thank you!!

Now I get why you hard pan your kick Left and Right. Brilliant stuff, thank you so much for sharing this info!

That's one hell of a good point! I've kind of known that before, but your explanation is highly insightful! That's definitely going to influence my work.

Great great video. Thank you Dave, i really dig your demonstrations

Dave, you just blew my mind. I have been toying with the idea of creating a system where i can send each source to its unique speaker. However, it would make the system hard to scale for additional instruments/sources. You just gave me an alternate solution with the multiple inputs from the same source.

Between Dave Rat and Big Mick, we are seriously blessed. Thanks Dave.

Thanks Dave, it's mindblowing ! It will change the way i mix !

Super interesting topic that I'd never considered in that way. It also suggests sound design ideas.

Extremely well explained. It seems so simple. Many thanks!

Dave, as always... GREAT stuff. Thank you :)

Why does this video not have more views!?!?! Very good watch, sir. 👍

Wow Dave! this is friggin awesome. I would have maybe guessed 80% of this. the two source pink noise is the most interesting. cool ideas with using two different mics on one kick or multiple pink noise sources for RTA tuning. wow. this is great. thanks!

That was totally cool! I understand the concept of cancellation and reinforcement using two sources of the same sound. I didn't know it would affect pink noise - although now it makes perfect sense. Your idea of sending slightly different versions of the same source (e.g. kick) to left and right to minimize the cancellation issues has got me thinking... Thank you!

That was an interesting demo -- one that I will keep in mind. I'll give further thought to what I can do to my mono mix. Thanks!

Another excellent video, Dave. Thanks!

Fantastic demonstration. Just fantastic...

One of the finest audio engineers I was very fortunate to have learned from told me that having slight differences in voice coil alignment is far worse than having a major difference. Not unlike when you have a three part harmony slightly off vs totally off. The dissonance is more noticeable when the harmony slightly off vs. totally off.

AAHHH brings back memories of Syn Aud Con from 30 years ago....My brain hurts..but my ears ike it..Thanks for simplified the "basics"...wish they'd teach this stuff as relevant in all those fancy music tech schools...

Great video Dave. I actually saw this video back in 2016 but thought i would come back and tap the like button. Whenever possible I have tried to run drums stereo and separated rhythm and lead guitars but since watching your video I have strived to give all instruments slightly different identities or placement in the left and right speakers. I felt this had greatly improved my mixing skills and my approach to the sound over all. Thank you sir. Of course this approach doesn't always work given the music genre, the room size and speaker placement limitations.

Learned more in this video than years of fighting with it onstage. Thanks, Dave!

Hi, Dave! I'm from Brazil and I want to thank you for all the knowledge you are sharing with us! I used to be a monitor engineer and studio assistant before pandemics and now I wonder to run some FOH as it is possible here. So, I'm learning a lot with your channel "classes". Thank you, Man!!!

I ran in mono for years and now have the full system in stereo after reading one of your articles on this Dave. Can't find the article now but love this video. I did notice less interference for sure. Now I need to work on the double mic techniques. I sure hope Bob McCarthy sees this... He is not a Stereo guy for live sound.

Really useful visualisation, Dave! Thanks mate.

Dave, it seems this demonstration and topic has a lot of sound guys going back to the drawing board and rethinking the way they do things, excellent demonstration!!!

Dave, thanks for the thought provoking video! I will try to use separate pink noise sources the next time I room tune a system. It was so interesting to hear the differences. Thanks again for sharing the knowledge.

changed my whole world. I've been mixing for 40 years, I've been keeping my left right different in many ways, but dual sources of single instruments may change everything

Thanks for this valued lesson @Dave. I've been dealing with producing directional soundscapes, but always felt I was missing this sonic space issue. Now I can understand, that I have to let the user's ears and listening position do more of the dimensional processing. I'll be incorporating more Mono source positioning in my productions. 😎 💪

This absolutely just blew my goddamn mind. Bravo sir! Bravo!

Hey Dave I like all your videos you always have interesting insight. Specially this one

That was outstanding, thank you Dave!

Fantastic, easy to understand demonstration on sound re-enforcement. Hard to give it a description, just watch it and learn something. Valuable for musicians & engineers.

Very thoughtful Dave. This is just one of the reasons that I use stereo mics on just about every recording.

I just had my mind absolutely blown to smitherines, it's almost unbelievable how this works.

Very interesting. Thanks Dave!

wow! glad I watched. will have to give this a go with the LCR system we have at church.

Thank you Dave. I have been doing audio on and off for most of my life but on a very non-professional basis. I had never heard what comb filtering actually sounded like until now. I feel silly saying that - I know a decent amount about what I do and the musicians I work with trust me and enjoy working with me which has always been my goal. Anyhow thanks again for teaching things that most people would only learn on the job or in an apprentice role. All of your videos are informative - my only fear is that I will have too many ideas and changes at one time and I'll have to pace myself :)

This makes an interesting argument for mixing any PA in stereo. I have always run my system in Stereo although I don't always get to mix the Pam section but everybody I've talked to that has more experience? than me usually runs mono. They do the whole thing in mono whereas once my mix starts settling down and I have more than one instrument I like to start panting things a little. I'm mostly self-taught but I've always done this sort of without fully realizing it. Just found your channels a few weeks ago and threw some videos in the my watch later list. I think I might have seen one of those with the windows behind you way back before without realizing it, either way I was subscribed by the first video I watched this year.

Just watched this again and it clicked! What you said at the end about using twondifferent pick noise sources when pink noise tuning a stereo PA system. Would theoretically fix the comb filtering issues across the listening area when tuning. Genius! Going to the garage to test that out right now!

Just wow. Thank You. Learning so much from You.

Dave who put you up to this, was it John Meyer? -Love yA buddy. So good :-) you know, sound people are so rare. It is wonderful to hear your bemused observations. well done! well done!

Invaluable stuff! Thanks Dave! 🤘🏻

brilliant demonstration, well done! :-)

Thanks so much Dave. Such a great pearl of wisdom.

Thank you for this informative vid Dave!

Brilliance is an understatement!!

So interesting!!!! its make a lot of sense. Thanks Dave. Would love to see a video of monitor setup for minimum feedback.

Tremenda demostración práctica, gracias Dave!

What a great demonstartion!

that's genius! In fact for measuring a stereo setup with different pink noise sources. But i doubt, that slightly different mic phase do the same effect. None of the less, thanks!

Tnx for your videos! Well explained and very Interesting..

Amazing demonstration to get this concept down!

THANKS AGAIN DAVE!!!

While you were talking I began to think about how the Beatles panned things when they went stereo. All the drums on the left etc. I always found that type of thing more interesting to listen to, it creates a picture in your head about where things are located.

This here is the reason I will always love playing acoustic guitar. Although the six strings resonate into the one box, all the other little sounds across the guitar can’t be captured and replicated easily by a speaker. I’m studying EE and I hope to make it easier one day to get that natural sound Dave is talking about here. I think we will get close in my life time.

I love your videos Dave. thank you

Excellent demo!

This is amazing. Thank you for sharing

GREAT talk! Thank you for this

Thank you, Dave great work!

This is the most informative live audio related video I've seen on RU-vid

Thanx Dave.Great video. please do a video on how you would mix a band with this technique.

546 likes and no dislikes. Goes to show how great and informative this video really is. Thanks for the amazing video Dave!