As we discussed earlier, the weakest parts of any audio chain are cables and transducers. While many will tell you there are subtle differences between cable materials and construction, they are anything but subtle. Basically, you want copper conductors of the largest gauge you can afford and will fit your connectors. You want a jacket that will take a little abuse and, of course, the most solid mechanical connections you can achieve. Without going on a long expedition, suffice to say that the slew rate of your power amp (how fast the amp returns to zero after a signal) goes to hell when it has to drive a long length of undersized cable to get to the big subwoofer at the other end and the speaker cone flops around like a dying fish. Since cables are so simple to optimize, and buying good quality microphones and electronics will guarantee a reliable output signal, all that remains is to optimize the speaker array. We will do the best with what we have to work with and I will assume that you're not working with touring quality enclosures or dedicated microprocessor controls.
MI speakers aren't flat. Period. Not JBLs, not Mackies, not any of them. The hottest selling processing device in the last few years has been the dbx DriverackPA. This is a digital signal processor dedicated to compensating for the deficiencies of MI loudspeaker enclosures. If you already have an active crossover setup that features delay functions, you can accomplish about the same thing with a digital narrow-band equalizer and access to a real-time analyzer. An analog 31 band EQ will come close but will not be as accurate as the digital one (by the way, if your speaker enclosures aren't on the list of 'pre-programs' in the dbx unit, you'll be doing the same thing anyhow).
Take each speaker enclosure outside, away from any physical barriers (like walls, dumpsters, telephone poles, etc.) and stick it as high in the air as you can. Set up the RTA and microphone (again, avoiding any interfering objects, including the ground) and pump pink noise through an amp and out of the speaker. Adjust the DSP or EQ to be as flat as possible and then do it three or four more times with the microphone in different positions. Here's where the analog device falls WAY behind. If you're using an analog EQ, superglue the sliders in position and write the name of the speaker enclosure in huge letters on the top of the equalizer with a Sharpie. I now pronounce speaker and equalizer married forever. If you have a digital device, save the settings and, if you have a PC output jack, back it up. Pairing enclosures and processors this way is MUCH less expensive than buying touring quality speakers and will make a bar buster band sound GREAT!
In all my years in this business, it still amazes me that nine out of ten bad sounding shows are due to poor speaker placement. I have heard so-called professionals state that the appearance of their speakers is more important to them than their sound! Most musicians, store clerks, and self-proclaimed 'soundmen' have little or no idea how to properly position speaker enclosures in a given room. There is NO electronic means of compensating for bad speaker placement. Equalization can compensate for VERY minor problems, once speakers are correctly placed. While I highly recommend the the Yamaha Sound Reinforcement Handbook and the JBL Professional Sound System Design Manual (which can be downloaded FREE from jblpro.com), the best information I've seen on speaker placement is the PA Bible from Electrovoice (also a free download). It's beyond the scope of this post to elaborate on placement and besides, EV does a great job!
One personal word about speakers on a budget. Peavey. Early in their history, Peavey was known for producing very powerful amplifiers. They had a very difficult time finding loudspeakers that could handle the output of their cutting edge amps and earned an undeserved reputation of using 'cheap speakers'. They began manufacturing their own loudspeakers because they wanted better quality and were tired of their loading dock being piled with blown speakers. As far as I know, they are the only manufacturer that is willing to spend the few dollars extra to make their speakers field repairable (their speakers have 'bolt-on baskets' that circumvent the down time and inconvenience of having a blown speaker re-coned). They were one of the first MI suppliers to sell digital processors for their speaker enclosures and, in my humble opinion, provide the most reliable 'bang for the buck' in the MI world.
I chose to address speakers early on because this is an area where there is the most wrong information freely offered and it's easy to blow your budget in the wrong places. My feeling is that buying the best speakers you can afford and learning how to get good sound out of them is the most vital determinant of how good your system will sound. Next time, we'll talk about amps and limiters, then I'll separate the men from the boys and start explaining gain structure; the most essential concept in sound reinforcement.
Tuesday, August 12, 2008
Tuesday, July 29, 2008
Sound is vibration. What we perceive as music is a complex group of vibrations, transmitted through various media. These media can be air, water, wood, concrete, turnips, or underpants. Each medium transmits sound in a different way and at a different speed. That's why your ears can distinguish between a sound in the room you're standing in as opposed to a sound emanating from another location. The wall between us and the source of sound transmits the vibrations differently than air.
The perfect sound source would be an infinitely small point in space capable of projecting unlimited quantities of sound equally in all directions. It would also be capable of producing vibrations accurately from less than 20 'wiggles per second' to more than 20,000.
A common misconception is that sound moves air. Subwoofer enthusiasts will tell you that really big speakers make the best subs because they 'move more air'. That's a yes and a definite no. They move air more. What's the diff? Ah, therein lies rub, my aurally curious compadre!
If big, powerful sound systems moved large quantities of air, the audience would be literally blown out of the venue. Here's how it REALLY works. Drop a stone in a pond and observe the beautifully symmetrical ripples expanding from the point of impact. That's how it actually works. The source of the sound creates alternate compression and rarefaction of the adjacent air molecules, which like the proverbial row of dominoes, move more adjacent molecules. Now imagine dropping a hundred stones in a real pond that already has some ripples in it, and try to identify whether the ripples are symmetrical and accurately formed. And you thought the sound man's job was easy!
In the real world, we have to accept a LOT of tradeoffs to reproduce sound accurately. Which tradeoffs? That depends. I'm going to spit out some very subjective and crude terms here, for the sake of sanity. There is an environment I call 'hi-fi' that is typified by a small room with very few inhabitants listening to recorded music that has been VERY heavily processed so your home stereo can process it without puking. Before the mid-40s, recorded music was played on mechanical devices with no electronic intervention. Yes, Virginia, the movie industry already had sound systems, as did the theaters that played their output and they had 'PA systems' at the county fair. Ma and Pa listened to monaural (one channel, no stereo) records on a Victrola and when they went to a concert or dance, the band was acoustic (no amplifiers), except for the very largest venues where they might have a single microphone and loudspeaker. During World War II, our grandfathers got a big bonus. Between freezing and starving and getting shot at, the benevolent movie industry provided them with regular entertainment featuring current celebrities. In order to make this a less expensive and logistically horrifying task, the USO started using sound systems to make the shows audible to huge crowds of GIs and also to compensate for having a smaller orchestra. Great strides were being made by guys like Les Paul and later Leo Fender in promoting the use of electronic devices in the recording and performance arenas. When the GIs got home, those Victrolas didn't sound that good, especially playing the new 'big bands' and the 'hi-fi' industry was born. The advent of wide screens in the movie houses created a problem for the sound techs because, when an actor walked from one end of the screen to the other, the sound stayed in the same apparent location and detracted from the realism of the movie. Soon, theater owners (at that time, usually the studios themselves) began installing multi-channel sound systems and utilizing multi-track recording techniques so they could 'place' sounds appropriately to the images. The audience didn't even know they were getting shafted. Why? Because one out of ten got to hear the whole movie! The rest heard either one channel of the stereo program or both channels at slightly different times. For stereo imaging to work, you have to be sitting in the 'sweet spot' midway between the sound sources. As home hi-fi sets began to become available in stereo, many consumers raved about how much 'better' it sounded. Long story short, stereo is great for living rooms with a single listener in the sweet spot and hi-fi equipment sounds pretty good in small rooms with soft surfaces. In large, hard rooms, they sound like crap.
The other end of the sound system spectrum is what I call the 'touring' environment. This is where the big boys live. The tradeoffs here are less overall and the focus is on pattern control. Huge amounts of money are being spent to focus high quality, high volume sound on the audience while keeping the neighbors happy and the sound off the stage area, where it could create serious acoustic feedback or timing problems for the performers. Sound must be distributed over long distances in an even, controllable pattern.
The third 'rough division' is what's known as the MI environment. This term was coined by equipment manufacturers to describe systems normally sold in Musical Instrument stores. While many of the tradeoffs with MI gear is similar to touring gear there a couple of major differences. Most obvious is the difference in average venue size associated with this market and thus the smaller and less specialized speaker systems and their associated amplifiers, although there has been a recent upsurge in loudspeaker management systems (digital processing of the signal to closely tailor it to the specific speaker array) in the MI arena. Also a major consideration is that most 'working bands' must transport their gear in consumer vehicles, as opposed to tractor trailer rigs. Equipment is optimized a great deal more than touring gear for both size and budget considerations. People will tell you about how much better this electronic device is than that one. Electronics are a VERY LEVEL playing field. The overall quality and specs of most electronics in a sound system are virtually identical. Pay more attention to the features you need and avoid the obviously crap quality stuff. You may notice .001% THD in your living room but in a live show with building mechanicals and crowd noise approaching 50-60dB, .01% is going to sound awful close. The weak links in the chain are transducers and cables. There's a lot of hype about cables and most of it is just plain not true. There is more variation with cables than with electronics but if you stick with the name brands, you'll do just as well as the esoteric ones and spend a lot less money. Use the right cables for the right job and get rid of each and every 1/4 inch phone plug (TS, TRS plugs) you possibly can. Likewise banana plugs and jacks. If all your speakers have only 'Speakon' (NL4) jacks, idiots cannot patch them with guitar cords. A cable designed to handle a 100 millivolt signal is simply NOT going to deal with a 1000 watt amp output well at all. Make sure all your cable ends are soldered on, as well as mechanically sound without the solder (can you say 'strain relief'?). Make sure every cable that isn't plugged into a guitar or bass is a balanced, XLR type. Coil every cable gently and store them as if you spent 40% of your total system investment on them (oh yeah, you DID!).
OK, transducers are the last thing this time. This means microphones and speakers. Dust off your old physics book and you'll remember that an electrical current in a conductor induces a magnetic field. Interestingly enough, a magnet moved in a coil of wire produces electrical current. In other words, an electrical signal can be 'transduced' to a magnetic signal and vice versa. Why do were care? Well. Poindexter, the induction of an electrical current by a magnet moving inside a coil of wire could, if the magnet were mechanically attached to a flat surface to sense acoustic vibration, create what we call a dynamic microphone (you can do this with two charged plates as well but you'd need a battery to charge them up). The charged plate one is called a condenser or electret microphone and the two comprise the vast majority of input transducers used in recording and sound reinforcement. If you take a pretty big electrical signal, say big enough to energize a couple of pounds of electromagnet enough to move a 3 or 4 inch diameter coil a few millimeters either way, you have what we call a loudspeaker. Both microphones and loudspeakers do the same thing the same way just in opposite directions. Like the electronic stuff, they are sold by showing you a bunch of numbers hammered out by the guys in the lab coats but I want you to notice something. The number they sell the electronics with is called THD. That stands for Total Harmonic Distortion. It represents the simplest way to express how accurate the output of the device matches the input. Identical is good; different is called distortion and is definitely bad. There are other kinds of distortion but this one is the big kahuna. Now look at the fancy microphone and loudspeaker numbers. Where's the distortion figures? You'll never see them. Mechanical transducers can't come anywhere near the accuracy of electronic gear. I must say that, in over 40 years in the business, I have never seen any mike come close to a Shure SM58. Overall the best vocal mike ever made, used by thousands of sound companies and bar bands, the SM58 is the predominant player and used throughout the MI and touring world. It's a mechanical transducer and subject to the innacuracies of the beast and probably wont be the one you'll use in the studio but on the road it cant be beat. So, if Ernie Lipshitz down at the Elks on Friday and Mick Jagger use SM58s, I guess we're not gonna solve the microphone end of the weak link issue. That leaves speakers. A cone loudspeaker produces about 3-5% of the electrical signal presented to it as sound output. Any guesses where the rest of that energy goes? So much for the 'power handling' number they love to throw at you. 'Peak power handling' refers to the power at which a speaker melts into slag in a few microseconds. The loudspeaker industry is renowned for having the most vague standards imaginable. In fact, some manufacturers downplay the 'power handling' issue and stress things like 'efficiency' you know, that how many decibels at 1 watt at one meter thing. So, if you're going to play a 1kHz tone at one watt for an audience 3.3 feet in front of your enclosure, this isolated value may be of some use. Fact is, speaker manufacturers consider hundreds of factors in designing each loudspeaker, each of which affects different characteristics of the speaker. This is not even considering the enclosure the speaker is mounted in, which accounts for as much if not more than the speaker alone. Suffice to say that any link in an electromechanical chain that wastes 95-97% of its input as undesirable and destructive output is, by definition, a weak link. Next time, we'll talk about improving your odds in this area.
The perfect sound source would be an infinitely small point in space capable of projecting unlimited quantities of sound equally in all directions. It would also be capable of producing vibrations accurately from less than 20 'wiggles per second' to more than 20,000.
A common misconception is that sound moves air. Subwoofer enthusiasts will tell you that really big speakers make the best subs because they 'move more air'. That's a yes and a definite no. They move air more. What's the diff? Ah, therein lies rub, my aurally curious compadre!
If big, powerful sound systems moved large quantities of air, the audience would be literally blown out of the venue. Here's how it REALLY works. Drop a stone in a pond and observe the beautifully symmetrical ripples expanding from the point of impact. That's how it actually works. The source of the sound creates alternate compression and rarefaction of the adjacent air molecules, which like the proverbial row of dominoes, move more adjacent molecules. Now imagine dropping a hundred stones in a real pond that already has some ripples in it, and try to identify whether the ripples are symmetrical and accurately formed. And you thought the sound man's job was easy!
In the real world, we have to accept a LOT of tradeoffs to reproduce sound accurately. Which tradeoffs? That depends. I'm going to spit out some very subjective and crude terms here, for the sake of sanity. There is an environment I call 'hi-fi' that is typified by a small room with very few inhabitants listening to recorded music that has been VERY heavily processed so your home stereo can process it without puking. Before the mid-40s, recorded music was played on mechanical devices with no electronic intervention. Yes, Virginia, the movie industry already had sound systems, as did the theaters that played their output and they had 'PA systems' at the county fair. Ma and Pa listened to monaural (one channel, no stereo) records on a Victrola and when they went to a concert or dance, the band was acoustic (no amplifiers), except for the very largest venues where they might have a single microphone and loudspeaker. During World War II, our grandfathers got a big bonus. Between freezing and starving and getting shot at, the benevolent movie industry provided them with regular entertainment featuring current celebrities. In order to make this a less expensive and logistically horrifying task, the USO started using sound systems to make the shows audible to huge crowds of GIs and also to compensate for having a smaller orchestra. Great strides were being made by guys like Les Paul and later Leo Fender in promoting the use of electronic devices in the recording and performance arenas. When the GIs got home, those Victrolas didn't sound that good, especially playing the new 'big bands' and the 'hi-fi' industry was born. The advent of wide screens in the movie houses created a problem for the sound techs because, when an actor walked from one end of the screen to the other, the sound stayed in the same apparent location and detracted from the realism of the movie. Soon, theater owners (at that time, usually the studios themselves) began installing multi-channel sound systems and utilizing multi-track recording techniques so they could 'place' sounds appropriately to the images. The audience didn't even know they were getting shafted. Why? Because one out of ten got to hear the whole movie! The rest heard either one channel of the stereo program or both channels at slightly different times. For stereo imaging to work, you have to be sitting in the 'sweet spot' midway between the sound sources. As home hi-fi sets began to become available in stereo, many consumers raved about how much 'better' it sounded. Long story short, stereo is great for living rooms with a single listener in the sweet spot and hi-fi equipment sounds pretty good in small rooms with soft surfaces. In large, hard rooms, they sound like crap.
The other end of the sound system spectrum is what I call the 'touring' environment. This is where the big boys live. The tradeoffs here are less overall and the focus is on pattern control. Huge amounts of money are being spent to focus high quality, high volume sound on the audience while keeping the neighbors happy and the sound off the stage area, where it could create serious acoustic feedback or timing problems for the performers. Sound must be distributed over long distances in an even, controllable pattern.
The third 'rough division' is what's known as the MI environment. This term was coined by equipment manufacturers to describe systems normally sold in Musical Instrument stores. While many of the tradeoffs with MI gear is similar to touring gear there a couple of major differences. Most obvious is the difference in average venue size associated with this market and thus the smaller and less specialized speaker systems and their associated amplifiers, although there has been a recent upsurge in loudspeaker management systems (digital processing of the signal to closely tailor it to the specific speaker array) in the MI arena. Also a major consideration is that most 'working bands' must transport their gear in consumer vehicles, as opposed to tractor trailer rigs. Equipment is optimized a great deal more than touring gear for both size and budget considerations. People will tell you about how much better this electronic device is than that one. Electronics are a VERY LEVEL playing field. The overall quality and specs of most electronics in a sound system are virtually identical. Pay more attention to the features you need and avoid the obviously crap quality stuff. You may notice .001% THD in your living room but in a live show with building mechanicals and crowd noise approaching 50-60dB, .01% is going to sound awful close. The weak links in the chain are transducers and cables. There's a lot of hype about cables and most of it is just plain not true. There is more variation with cables than with electronics but if you stick with the name brands, you'll do just as well as the esoteric ones and spend a lot less money. Use the right cables for the right job and get rid of each and every 1/4 inch phone plug (TS, TRS plugs) you possibly can. Likewise banana plugs and jacks. If all your speakers have only 'Speakon' (NL4) jacks, idiots cannot patch them with guitar cords. A cable designed to handle a 100 millivolt signal is simply NOT going to deal with a 1000 watt amp output well at all. Make sure all your cable ends are soldered on, as well as mechanically sound without the solder (can you say 'strain relief'?). Make sure every cable that isn't plugged into a guitar or bass is a balanced, XLR type. Coil every cable gently and store them as if you spent 40% of your total system investment on them (oh yeah, you DID!).
OK, transducers are the last thing this time. This means microphones and speakers. Dust off your old physics book and you'll remember that an electrical current in a conductor induces a magnetic field. Interestingly enough, a magnet moved in a coil of wire produces electrical current. In other words, an electrical signal can be 'transduced' to a magnetic signal and vice versa. Why do were care? Well. Poindexter, the induction of an electrical current by a magnet moving inside a coil of wire could, if the magnet were mechanically attached to a flat surface to sense acoustic vibration, create what we call a dynamic microphone (you can do this with two charged plates as well but you'd need a battery to charge them up). The charged plate one is called a condenser or electret microphone and the two comprise the vast majority of input transducers used in recording and sound reinforcement. If you take a pretty big electrical signal, say big enough to energize a couple of pounds of electromagnet enough to move a 3 or 4 inch diameter coil a few millimeters either way, you have what we call a loudspeaker. Both microphones and loudspeakers do the same thing the same way just in opposite directions. Like the electronic stuff, they are sold by showing you a bunch of numbers hammered out by the guys in the lab coats but I want you to notice something. The number they sell the electronics with is called THD. That stands for Total Harmonic Distortion. It represents the simplest way to express how accurate the output of the device matches the input. Identical is good; different is called distortion and is definitely bad. There are other kinds of distortion but this one is the big kahuna. Now look at the fancy microphone and loudspeaker numbers. Where's the distortion figures? You'll never see them. Mechanical transducers can't come anywhere near the accuracy of electronic gear. I must say that, in over 40 years in the business, I have never seen any mike come close to a Shure SM58. Overall the best vocal mike ever made, used by thousands of sound companies and bar bands, the SM58 is the predominant player and used throughout the MI and touring world. It's a mechanical transducer and subject to the innacuracies of the beast and probably wont be the one you'll use in the studio but on the road it cant be beat. So, if Ernie Lipshitz down at the Elks on Friday and Mick Jagger use SM58s, I guess we're not gonna solve the microphone end of the weak link issue. That leaves speakers. A cone loudspeaker produces about 3-5% of the electrical signal presented to it as sound output. Any guesses where the rest of that energy goes? So much for the 'power handling' number they love to throw at you. 'Peak power handling' refers to the power at which a speaker melts into slag in a few microseconds. The loudspeaker industry is renowned for having the most vague standards imaginable. In fact, some manufacturers downplay the 'power handling' issue and stress things like 'efficiency' you know, that how many decibels at 1 watt at one meter thing. So, if you're going to play a 1kHz tone at one watt for an audience 3.3 feet in front of your enclosure, this isolated value may be of some use. Fact is, speaker manufacturers consider hundreds of factors in designing each loudspeaker, each of which affects different characteristics of the speaker. This is not even considering the enclosure the speaker is mounted in, which accounts for as much if not more than the speaker alone. Suffice to say that any link in an electromechanical chain that wastes 95-97% of its input as undesirable and destructive output is, by definition, a weak link. Next time, we'll talk about improving your odds in this area.
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