Sound Reinforcement (PA) - A Guide to Making Live Sound Work For You

Discussion in 'Bad Dog Cafe' started by simoncroft, Aug 2, 2019.

  1. simoncroft

    simoncroft Tele-Meister

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    As some of you may have looked at my Venue Acoustics thread and thought; "I wanted to know more about the actual gear, not just what the room is doing", this thread is all about live sound rigs – what used to be known as simply “the PA” when I started gigging back in the early 1970s.

    I’m also starting this in response to to the frustrations from a lot of players about their live sound. Some of this frustration comes from the complexities of the equipment itself, but often a major factor is a person referred to fondly as “the monkey behind the desk”, or worse. Hopefully, this thread will help whether you find yourself in a self-op situation, or negotiating with our simian friend in whose hands your fate rests.

    (Before anyone accuses me of being a complete hypocrite, I should admit I’ve been on both sides of this situation: as a live sound engineer for others and as a musician on stage saying: “Well I could turn down some more, but given I can’t hear a note I’m playing, I’m not sure how much further to go…” I’ve also been in the lucky position of being allowed to interview some truly great sound engineers, most of whom imparted their knowledge with considerable generosity. Let’s hope some of that wisdom has rubbed off.)

    This is a thread, not a seminar, so its shape and content is dictated by you, along with other forum members who chose to contribute. Although I’m working to a framework that progresses in a logical manner, I am happy to modify if you’d rather I get to a particular topic ‘sooner rather than later’.
     
  2. simoncroft

    simoncroft Tele-Meister

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    ******* A note on terminology *******

    I’ll refer to live sound rigs throughout as ‘Sound Reinforcement’. This is because such systems are commonly used to augment ‘backline’ instrument amplifiers, drum kits and acoustic instruments, as well as vocals. The systems we used to call PA (or Public Address) back in the day were used primarily for vocal amplification. These days, the term PA is mainly reserved for the speaker systems found in railway stations, airports and other public places.
     
  3. beyer160

    beyer160 Friend of Leo's

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    FYI- for those of us in the US, "PA" is accepted industry terminology for "Sound System" of any size, from pager speakers in the airport to stadium concert sound.
     
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  4. simoncroft

    simoncroft Tele-Meister

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    Thank you for the input. I'll be mindful of that, in order to avoid any confusion.
     
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  5. Ronkirn

    Ronkirn Doctor of Teleocity Vendor Member

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    patiently waiting with eager anticipation..

    r
     
  6. Mjark

    Mjark Doctor of Teleocity Silver Supporter

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    We're using the house PA tonight, one we had problems with last time. Trying to get all the monitors working. I think it was something really dumb, like the volume fader was way down or something. I hope it goes well tonight. It's not fun when you get stressed over stuff not working.
     
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  7. Chud

    Chud Poster Extraordinaire

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    Back when I used to be in the biz, I had a few tricks up my sleeve as the monkey behind the desk that always gave me a laugh. This one I only did with the particularly fussy members of a group, and only after we'd fully gotten a nice mix going. Once things were dialed in, the fussy guy (or girl) would ask for more of him or herself, more or less of this or that, the sound was too brown, too oblong, to creamy, etc...

    With my hands hidden from view, flat on the desk without touching anything, I'd look down and act like I was moving something for a second or two, then look back up and ask "how is that now?" Nine times out of ten I nailed it on the first try and the fussy one was fussy no more. :lol::lol:
     
  8. Mid Life Crisis

    Mid Life Crisis Friend of Leo's

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    Thanks for starting this thread. I'm sure it's going to be very useful and informative.

    Gotta say though, that I and everyone I know in bands would still say PA. Maybe it's different down on the South coast :D .
     
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  9. Ronkirn

    Ronkirn Doctor of Teleocity Vendor Member

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    Interesting parallel..

    when I was a Kid... My grandfather, an engineer, built and managed the HVAC (air conditioner) in the church we all attended.... often the women would adjust the thermostat.. and sigh saying how much better it felt... when in reality it would take considerable time for the temp to change in a building of that size... But GranDad got tired of it... so he relocated the real thermostat .. in a locked box.. and installed a "dummy" for the women to "adjust"... it kept them happy... thus ignorance was bliss..

    some guys have no idea what "bad sound" sounds like... all they know is turn it to 10... and rock...

    rk
     
  10. bftfender

    bftfender Friend of Leo's

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    My PA system of sound reinforcement..consists of (4x18) subs)-(8-15's). (4 15 )floor wedges (4 10) monitors to fill in the blanks on stage..set up the same pretty much all the time(outside & inside) It's adressing the public quite well & very consistent ...and...its well controlled on stage for all to hear properly cause that's what makes it sound good..set to kick & away we go...
     
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  11. beagle

    beagle Friend of Leo's

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    Simon, the monkey behind the desk is waving at you. Oh wait, it's just Thrup'ny... carry on. :)
     
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  12. simoncroft

    simoncroft Tele-Meister

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    Thank you for your posts, I'll post some responses shortly. :)

    System overview 1 – the evolution of speakers and crossovers


    Because modern Sound Reinforcement systems are sophisticated – often using DSP (Digital Signal Processing) accessed via multi-function buttons and screens – it can be difficult to grasp what’s happening ‘under the hood’ if you don’t already know the basics.

    A better place to start to understand Sound Reinforcement is to turn the clock back to the mid 1960s, when systems were not much more complicated than guitar amps. (That’s not so surprising; they were often made by companies that mainly produced guitar amps.)

    Once we have the most basic system under our belts, we can accelerate the time line, to see how each limitation was met with new solutions. At first these were analog, with many of the later digital developments designed to mimic these devices in new systems that were cheaper, more compact and faster to use. But let’s not get ahead of ourselves.

    The first live sound systems I used with bands looked something like Diagram A. Although it was very simple, it was good enough for vocal amplification in small venues.

    Believe it or not, this was the sort of system The Beatles used to play Shea Stadium in 1965. Obviously, no-one could actually hear them, which is the main reason they retreated to the recording studio and never toured again.

    Being valve-based in the first instance and developed by companies more used to working with electric guitars, the mixer/amps in these basic systems had high impedance inputs on unbalanced jacks. We’ll go into the significance of balanced lines later on. For now it’s enough to note that unbalanced mics are not much less prone to interference than a 55 Strat.

    Screen Shot 2019-08-03 at 00.23.49.png
     
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  13. PastorJay

    PastorJay Tele-Afflicted

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    Following. Love what you're doing on the other thread. I had questions about how that affected PA systems (I think you call them Sound Reinforcement.).

    :)
     
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  14. simoncroft

    simoncroft Tele-Meister

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    Just like guitar amps of the day, the archetypal mixer/amp had passive tone controls, meaning they could cut a certain amount of treble, middle or bass but not boost it. Many had no reverb or delay, or even the connectors necessary to introduce external effects into the mix as a whole.

    But pop music was mutating into rock music by the 60s progressed, and as bands got louder, they wanted to put drum kits and instruments through the Sound Reinforcement system. This exposed the biggest limitation of the early systems. It wasn’t the mixer/amp, but the speakers.

    (This wasn’t the end of the old-style PA, but as technology moved on in the 70s and 80s, these systems were increasingly aimed at functions bands.)

    For vocal amplification, many manufacturers were using two column speaker cabinets, each loaded with four 12in speakers. Although there was not much in the way of high frequency extension, the results were quite acceptable to audiences who went home to phonograms with lift up lids and amplifiers often connected to not much more than a small elliptical speaker.

    Attempting to put a highly percussive source like a kick drum through the same system would be crazy! The massive transient peak signal caused by a beater hitting a drum head would probably drive the speakers to their end stops and the cone excursion required to reproduce the low frequencies would turn any vocals going through the system into a nasty, unintelligible mess.

    Trying to put an entire kit through the system would likely destroy the speakers in minutes if the system were turned up to anything like a usable volume.

    What was needed was a speaker system more like the ones used in movie theaters. Here, the frequency range of the program was split into typically two bands, with the low frequencies handled by 15in speakers mounted on a large wooden horn acting as an acoustic amplifier and the high frequencies handled by a compression driver mounted on a metal horn. Here are some classic designs from Ampex. http://www.itishifi.com/2012/05/early-ampex-corporation-theater-sound.html
     
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  15. simoncroft

    simoncroft Tele-Meister

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    Unfortunately for the rock ‘n’ roll business, the motion picture industry also used something called the Academy Curve, which was a controlled loss of high frequencies designed to mask the fact the old optical soundtrack that ran alongside the pictures on celluloid was noisier than a scratchy 78 record. In order to realize Sound Reinforcement that could act like a gigantic HiFi, rock ‘n’ roll rigs would typically need to split the frequency spectrum into three or more bands.

    Diagram B is a typical frequency plot that shows the bandwidth of the program divided into three ranges, which would be fed to low, mid and high frequency speakers. The device that makes this division possible is a ‘crossover’.


    Screen Shot 2019-08-03 at 00.36.24.png
     
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  16. beyer160

    beyer160 Friend of Leo's

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    There have been two major innovations in PA systems that allow us to deal more effectively with venue acoustics- the first was the evolution of the line array, which had its very beginnings in the Grateful Dead's Wall Of Sound. The idea is to break your system into individually aimed and controlled enclosures so you can control dispersion instead of just piling up a bunch of bins and chucking sound at the audience. They look like this:

    image-placeholder-title.jpg

    Now that's all well and good, but you need a way to figure out how to control them. That's where DSP comes in-

    Screen Shot 2019-08-02 at 7.44.39 PM.png
    Before I even arrive at a venue, I can program my system with the dimensions of the space and tell it where to put sound, and where NOT to put sound (like if there's a hard reflective wall at the back of the room). I tell it where the PA hangs are, and it tells me how to angle (or "splay") the boxes. The level of control you have over the coverage of a system like this is mindblowing compared to where we were 20 years ago.

    If you have a bad acoustical space though, even though the cool toys will help a LOT, they're just band-aids on the problem. The best tool to fix poorly designed acoustical spaces is this-

    Wrecking-ball-sports-data.jpg
     
  17. simoncroft

    simoncroft Tele-Meister

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    I really sympathize. The European jam sessions organized on Strat-Talk nearly always involve a rig none of us have seen until we get in the room. I've had to bail, due to on-going tinnitus issues, but I used to find out what the desk was ahead of time, download the User Manual and make sure I knew what all the ins and outs were, as well as the main functions.

    The problem is, as soon as you get in the room, you often discover the system isn't wired quite the way you'd expect! Trying to trouble-shoot someone else's rig at short notice is indeed 'stressful'. And if anything is going to be lacking, it's often the stage monitors, which can make it really hard to know how it's sounding out front.

    Oh yes! I can remember a few recording sessions where someone who isn't the engineer adjusted a control (usually without asking if that's OK) and made things 'better'. This works even if the EQ, aux sent etc, on that channel isn't in the signal chain.

    Same psychology! In the UK, back in the 1970/80s, we had this really bad heating system based on 'storage radiators'. The deal was, they used cheap off-peak electricity during the night to heat up these big concrete heat-sinks that would then put out heat all the following day. The big problem was you had to second-guess how much heat you wanted the next day, meaning the thermostat dial gave you tomorrow's heat setting, not today's.

    No matter how many times I explained this to my girlfriend at the time, she would turn up the dial because she was feeling cold at the time! This made her feel better, but turned the house into an oven the next day, if I didn't spot what she had done.

    Over here in Europe, we talk about band 'PA' too. I say it myself sometimes, so let's treat the two terms as meaning the same thing for the purpose of this thread. I hope you find this thread useful, but please call out if there are things you want to know that are not being covered, or is not clear.

    That's a pretty decent rig you have there. Am I right in thinking it's a mobile system for your band? Please feel welcome to post about anything you think is useful on this thread, including any area you feel I could have explained better. Or, start a Conversation with me, and I'll happily send you the text I'm intending to put on-line.

    Haha! Is Thrup'ny Bit active on this thread? I don't see a tag for him.

     
    Last edited: Aug 2, 2019
  18. simoncroft

    simoncroft Tele-Meister

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    You've gone straight for straight for the show closer and the encore there fella! Massive kudos to you. I take it you are a concert touring engineer with a serious track record.

    I would really value your input on this thread, but I want to start with the most basic concepts first. Line arrays are not only difficult to explain, they are very easy to get wrong if you don't understand exactly what you're doing on the day. Likewise DSP is quite a mind-bender before we've got to "what's a cardioid mic?" and "why do I need to stick the mid/highs on poles?"

    Would you like me to send you the text for this thread as a Conversation? If you have the time, we could incorporate your ideas before posting them. I'm hoping to keep this accessible to forum members at all levels, but your input would be great.

    As for the wrecking ball: the engineer in me says 'yes' but the businessman in me says we've just lost $150m on a small tour of the Southern States. :D
     
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  19. 3-Chord-Genius

    3-Chord-Genius Poster Extraordinaire

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    I heard that some HVAC companies are requested to install dummy thermostats in offices. People complain that it's too hot or too cold, but if they think they are in control of the temperature, they stop complaining.

    EDIT: I now see that somebody above mentioned this very same thing also.
     
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  20. bftfender

    bftfender Friend of Leo's

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    We usually hold 2-4 band shows. I found out long time ago. Like to practice & play live ..same everything. Usually hard rock..Guitar 1 side-Bass other. I have all my amps settings to be used at level of a kick drum set up & its great level for studio anyways. Once balanced...we fill holes with monitors nice..sides as needed & def the singer catered to in the middle monitor wise. Then we push it forward in front of us with subs & 15's. As a band..we have no set up other than hooking our stuff up..nobody walking over mid set & turning knobs to throw the soundboard all off.All super low goes to those subs ..really clears up the mix. 1 band off..next on...simple mic the amp..set level & off we go again...No more di bands on our shows..we prefer to mic the amp...no one sets their pods global vol right & no way fixing their sound all night.. ! Old school all the way..been doing it this way since day one...never had 1 sound issue.l...sound check..we out all wireless until it is super balanced..it will rock properly.
     
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