Amplification continuation thread, sort of


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Apr 11, 2008
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Kapolei, Hawaii
Since I have some time, I thought I'd start something that is not the begin all end all of topic knowledge, not intended to replace Budhuu's sticky by any means, but possibly add to it, with a focus on Public Address (PA) systems.

First things first, not unlike electronics on your instrument, you get what you pay for in PA systems. For this thread, we won't go into higher end digital boards which are super cool or Bose Sticks, both of which are super expensive, and if you have those, then this thread will be meaningless anyway. Basics. . .

Amplifier Power, otherwise known as "amp"

Mixing Board Control center

Cab Cabinet, sometimes referred to as a speaker, or combo amp of sorts

Combo amp Powered speaker usually designed for a particular type of instrument - electric guitar, Bass, Acoustic, keyboards, etc. This is usually what the threads in Uke Talk refers to as "amp"

Powered mixer Or powered head - mixing board with an amplifier onboard, usually has relatively minimal controls

Speaker Where the sound comes out of, passive

Powered Speaker Where the sound comes out of, active, meaning, there's an amp on board

Tops See Speaker, or Powered Speaker

Subwoofer Or sub - if you're playing acoustically and have a good full range speaker, you normally won't need this. If you mic a drum set, look into this.

Mains Speakers that face the audience; known as FOH (front of house)

Monitors Specifically designed speakers that face back to the performer

Placement Where your equipment goes, especially important for microphones, speakers, monitors, etc.

Speaker Cable Cable designed specifically for speakers, with at least two wires

Instrument Cable Cable designed specifically for instruments, with a single hot wire surrounded by a ground shield (or sheilds)

Balanced Cable Usually seen as XLR mic cables, also used to connect Direct Injection (DI) boxes to the mixer. Also used for Tip/ring/Sleeve (TRS) connections like AUX out from the Mixer; has at least two wires and an outer shield.

XLR 3 pin connector, standard is Pin 2 hot.

Dynamic mic What you'll use for live sound vocals

Condenser mic What you won't use for live sound vocals

Cardioid, Super-cardioid, Hyper-cardioid mic Polar pattern of the mic, relates to how much signal the mic picks up directly in front, sides or behind the mic

Frequency range usually seen as 20hz to 20khz (20,000hz) Lower frequency is the bass range, down to about 40hz. 100hz is a common "crossover" frequency where subs produce frequencies below 100hz, and tops produce frequencies above 100hz (if using a two-ways system); important to know when adjusting eq frequencies.

By the way, this needs to be said again - you get what you pay for.
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Lets break this down. If I don't go into to much detail, its because it TOO EASY to research on the internet, however, many fallacies abound, so I'll certainly take a stab at what I've learned through my experience (though not extensive) and research, so use what you can, and throw out what is garbage. If you find any statements to be incorrect, by all means, correct me

You make your own decision on whether to go with a Powered Mixer and Speakers, or Mixing Board/Amp/Speakers, or Mixing Board/Powered Speakers. Also decide what signal processors you'll insert between the board and the amp. Personally, once I learned to use a 31 channel eq, I realized why they have such a thing.

Powered Mixers
The powered mixers I've used are pretty much plug and play.
Note: Ohm load - pay attention to what the ohm load on your speakers are (probably 8ohm), and what your powered mixer can handle (probably 4ohm). If your powered mixer or amp can handle a 4 ohm load per channel, then you can hook up no more than two (2) 8ohm speakers to each channel.

Those with equalizers onboard (usually 7 or 9 channel) are famously set with a smiley face (see Fletcher-Munson curve for why). We'll get into eq more, later.

There are also effects on a lot of boards, learn how to use them, and not overuse them.

Main/Monitor mix - oftentimes, you can run a main mix off one channel, and a monitor mix off the other channel if you "split the amp". Its not really splitting an amp per se (or it may be, I'm not sure), but its basically sending two different signals to each channel - find the switch or button that takes care of this.

Powered boards are a good way to start, and a good place for some people to stay, especially if they don't take the time to learn about Pro Audio sound, which is different from Home or Auto sound, which is basically recorded music.

By the way, now is a good time to mention: Red is bad. For the rest of this thread, red is clipping, and is bad. You may disagree, and that's okay.

Mixing Boards
Mixing boards should have more controls over powered mixers - learn what they're for and how to use them. Learn to set your channel gain (and you'll know why when you plug in the sound guys says to play like you play, and sing like you sing, and there's nothing coming out of the mains), and what the high pass filter button is for right next to it.

Unlike the powered boards, the monitor controls will probably be for the sound engineer, and not the performer's monitors. This will come in the form of auxiliary channels, the more channels, the more auxiliary mixes you can do.

Goal for your channel sliders (and main) is unity, to allow use of the available power, provide headroom, and avoid clipping. If you clip, get an amp/speaker setup that can go where you want it to.

Pick your poison on whether you choose to go from the board through an amp and speakers, or directly to powered speakers. As with powered mixers, pay attention to the ohm load of your amp. QSC GX series have good power for cost, but cannot go down to 2ohm load, which, most people don't do. Crown's XLS Drivecore Series is super light, as are some others. Decide what class of amp you want, old iron, newer D, etc. Newer amps have built in crossovers, so you can run subs and tops off of each channel, and put the tops on sticks you subscribe to that type of setup. We'll go over placement later.

Note: Here is a good time to state you cannot damage speakers by underpowering them, running them to distortion. The distorted sound was developed (I think) by running amps to their limit, causing distortion. As long as the distortion is not over the power limit of the speaker, you may be fine. Can you blow speakers by overpowering them? Umm, yes.

I'd worry less about overpowering powered speakers, the amps are built in. However, if you blow the amp, essentially, you've blown the speaker and you have to replace it. Again, pick your poison.
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There a well established myth that the larger speakers will go lower, and louder. There are also many anti-myths that debunk this. Search for yourself. Personally, I got rid of my JBL 15's for another set with 12" drivers. I now go just as low, louder, cleaner, with far less power because of efficiency of design. Yes, they cost more.

Personally, one of the key things to look for is speaker design. Externally, they may look the same, internally there is design going on, especially on subs. On the lower end, cheap speakers sound, well, cheap. Higher end speakers sound, well, like they're supposed to.

I've learned its not good to mix speakers, and more is not always better. Line Arrays are cool (more is better here) and I've seen JBL's Line Arrays on sticks. If you're at that level, you're probably laughing right now, and that's okay.

Once I got monitors, I learned why speakers turned on the side is not the best. Yes, many speakers are angled to use as monitors, and that's just what ends up happening, they're merely used as monitors. Think about it, speakers are designed for horizontal dispersion, so when you turn them on the side, you now have a very narrow vertical dispersion.

Want feedback? Easy, put a mic in front of a speaker. You should not feedback in the mains if placement is good. Monitor feedback, that's another thing. Learn to use an equalizer.

By the way, now is a good time to mention equalizers in pro audio. These are used to adjust the system to the room, and to notch out feedback in the monitors.
Channels equalizers are used to shape the signal coming through. Notch is usually more effective than boost. I've seen the bass knob on the channels famously boosted, resulting in a muddy sound. Why? The frequency of the signal is usually not that low, so you're boosting a false signal. IE: `Ukulele player wants the instrument to sound more "full" because its sounds too twangy, so boosts the bass on the channel. Result? Muddy sound. Why? The instrument was twangy to begin with, just now its louder.
Of course, there are other variables: system is crap, settings are crap, battery is dying, etc.

Its difficult to understand the spoken voice with effects. I like using a footswitch to turn it on and off.
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Placement part 2
I mentioned subs on sticks, so for those that run subs, look up placement and cancellation, particularly "power alley".
Basically, subs should be together and not spread apart, some small and very large venue's being the exception. Why do you see them split with tops on sticks? Its what looks normal, but doesn't mean it right. I don't run subs, but there's enough science out there, along with the experts that will show you the right way, rather than the way we've all seen.

Edit August 2013: I now have a sub, and love it for larger venues. I learned from a well known female vocalist (here) that when they run the sub, even though its just her, a male vocalist on guitar, and sometimes keys, the sound is fuller. I've heard elsewhere that its due to harmonics. Okay, whatever. Works for me, the amps cruise along without sweating when the frequencies are split.
Also, got me a dbx Driverack PA+. Still learning how to use it fully, but love the Feedback destroyer and programs saves. Also need it for my crossover when I run subs. Heck I even high pass my monitors now, just in case.

Since we're talking about "normal", if you want to see why speakers setup side by side (even though they were designed like that) is not the best, look up "comb filtering". Along those lines, research why Line Arrays, where the speakers are vertically aligned, work.

I'm going to take a break now, but there may be more coming. I hope what's been written is good enough for a baseline to get started, or a baseline to start conversation and/or research to say if I'm helping anyone, or hurting.

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Aaron, I came across this and thanks for taking the time to write this. Lots of questions about electronics these days
Aaron, I came across this and thanks for taking the time to write this. Lots of questions about electronics these days

Thanks. I haven't been around for a while and I've some catching up to do. BUT, I do have more info to share (to the 200 some odd views :) )

More on running subs:
Lets start with my update above - if you have the opportunity to try subs, you should, especially if they're setup and run correctly. Not going into the why - you can research that yourself. So what do we need to know about running subs?

Once again, they're out there (mine is in my dbx Driverack PA+), read up, use 'em.

Basically, you'll see a hearable frequency range of 20hz to 20khz. Personally, my age limits me to about 16khz on the top end. As I understand, dubstep goes downs below 40hz. Low E on a bass guitar is around 41hz. Many tops are crossed over at about 100hz, depending on the top, and the sub.

High Pass/Low Pass/Slope
A high pass filter allows musical content above the frequency of the high pass filter to pass through. A low pass filter allows musical content below the filter frequency to pass through. Slope is the angle at which the filters are applied. I'll try to explain - a 100hz low pass filter on the subs is not a "hard" 100 hz, but rather a sloping one. You can adjust the aggressiveness of that slope, with different types of slopes (BW, LR, etc). The softer the slope, the more "bleed" you'll have into other frequencies. You may or may not want this. Not going into detail here, but something to definitely get familiar with.

Passive speakers with amps - lets stick with that for now. If you have powered speakers and subs, you probably have an internal crossover; not going into that here.
One of the biggest advantages I realized in running a sub is that all of the frequencies below 100hz (where I set the low pass for the sub) is handled by the sub, allowing the tops to take everything from 100hz (where I set the high pass for the tops) and up. This affords the separate amps great efficiency, and the full range tops (that I use) just cruise along, and the amps stay cool. Most bass heavy content requires more subs than tops. In my acoustic setting, I've run one sub with two tops, and currently don't see a need for more subs. Note: the lower the frequency, the more power it takes to generate musical content. I've been using volts as a measure of amp output, but most amp and speaker manufacturers go by watts. Just read up the manufacturer, and learn about efficiencies. I've come to very efficient tops speakers, and when I run them next to more "popular" tops, my amp is at 1/2 the attenuation.

Where to use crossover filters
This is for you to figure out with your system. But, here's an example: I know my musical content won't reach below 40hz (my sub is not "capable" of that anyway), and I know my tops, while good to 40hz, really start going after 100hz. SO, I put a 40hz high pass AND 100hz low pass on the sub, and I'll put a 100hz high pass on the tops. The dbx Driverack PA+, and how I have it setup, doesn't have a low pass for the tops (in a top & sub configuration). This keeps all musical content between 40hz and 100hz in the subs, and everything above 100hz in the tops.

Note: supposedly, bass content below 100hz is omnidirectional, which means you can't hear a point source where its coming from (does not apply to power alleys, sort of), so cluster your subs.
Note 2: Because my monitors are not designed to run bass content, and there's often feedback at high frequencies, I'll put a highpass of about 100-120hz and a low pass of 10khz on the monitors. This narrows the passband, protecting the monitors from low frequency content as well as high frequency contents, which has a tendency to feedback. None of the vocalists sing over 10khz anyway.

dbx Driverack PA+
Okay, I mentioned this a few times. I happened to get one, and while I'm still learning how to use it more effectively, this is a fun toy. Probably not needed with a digital board, which I don't have. Suffice to say, its taken the place of my 31-band eq (even though it only has 28), but also has a crossover and feedback suppressor. I've baselined the auto-eq and saved 3 different profiles each with full range tops, and with tops and subs. There is a learning curve, but for 1 rack space, it effectively (for me) takes the place of a few items I probably wouldn't buy.
My amps have internal crossovers, so if I didn't have the DRPA, I'd probably spring for a dbx AFS (automatic feedback suppressor), which has 24 filters instead of the DRPA's 12. This would require 3 rack spaces for my eq and AFS. I'm trying to go smaller.
Yes, I did have the Berry DEQ2496. If you think the learning curve on the dbx is steep, the Berry more so. At least dbx has a forum, which helps. If you get a DRPA, go there and read read read.

As with the original post, any misleading or incorrect info that I've shared, please correct me. Except, don't correct what my experiences were - that, even I cannot change.
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