A few quick topics, based on emails I have received. Many thanks to you who make me feel so appreciated.
You don’t need to have the very best mics unless you are in the recording studio. There are many mics in the $50-75 range that are more than fine for playing live. The only real requirement is to make sure that they are “low impedance” and “cardiod” (meaning heart-shaped pattern), which means that they have lower noise, and they don’t pick up sounds from behind (so you don’t get as much feedback from the monitors). “High impedance” and “omni-directional” mics should be avoided, as should anything that is hardwired to a Â¼” jack. The 3-wire “XLR” jack is standard on any mic that isn’t a toy.
(Note: this is not about compressor effects for guitars)
The compressor is probably the most mis-understood and mis-used signal processor around. A compressor has two main purposes: first, to act as a limiter to protect the equipment (speakers) from being overloaded, and second, to reduce the dynamic range of the music so that the soft parts are not as soft and the loud parts are not as loud. The problem is that compressors tend to add noise and increase feedback. Don’t misunderstand, in the hands of an expert, a compressor can do wonderful things, and save a performance. But unless you really know how to use one, avoid it altogether.
The way most compressors work is that they reduce the signal as it gets louder, so if you play twice as loud, it comes out only 50% louder. The compressor leaves the quieter music alone. The amount of “compression” is usually adjustable, along with the response times. So if you have a song that has a 10-to-1 range of dynamics, the compressor might send it out to the PA with a 3-to-1 range. The good part is that the audience thinks they’re hearing 10:1, because the vocal strain and guitar distortions have increased, so the tones are reflective of louder music, even though it’s not as loud as you think.
My friend Peter is an up and coming “Billy Joel” piano man. He plays a wonderful Kurzweil electronic sampled keyboard, which has a wonderful grand piano voice. He plays coffee-houses with a new 200W PA. As with most musicians, by the third set, he’s gotten a bit louder than when he started the evening. When he plays ballads, the rich piano tones compliment his voice, and his adept playing is clear and refined. But when he starts banging out 8-note power-chords, jumping up and down behind the keyboard, his Kurzweil responds enthusiastically, and overloads the PA. This is much to everyone’s surprise, because it didn’t seem so loud a few minutes before. Here is a perfect case for a compressor. The keyboard is immune to feedback and is very quiet. The compressor will allow Peter to turn up enough to hear the delicate passages, but will keep the power parts from overloading the system. Again, the heavier tones created by the power chords will give the impression of loudness, even as the compressor keeps it under control.
The opposite is true of microphones. If you think a vocalist needs a compressor, teach him or her to do it Sinatra’s way; when you need to sing louder, pull the mic away from your face a bit. Watch a tape of any of the “Las Vegas” singers, male or female; they all do it, because it works. Using a compressor on vocals increases the possibility of feedback, because you can increase the volume (gain) for softer sounds. Also, the human voice is so full of dynamics that it is almost impossible to get the timing settings correct for all cases.
The last use for a compressor is to protect the equipment. Suppose you have a system that is usually run by different people (say, a house PA with different engineers, or a school auditorium set up). It can be a good investment to use a compressor in a “limiter” mode, which will but an absolute maximum on the power to the speakers, and thus prevent anyone from blowing them out. The system has to be big enough to do the intended job, so that the limiter doesn’t kick in under normal usage. In this arrangement, the compressor’s control may be very audible as it reduces the gain to protect the system.
In summary; a compressor can solve some very difficult problems, but consider it your last resort unless you really know how to use it.
Feedback Control Using an Equalizer
In an earlier column (The Mix Board), I suggested that the “breadloaf” EQ was best for live performances, where the highest and lowest frequencies were reduced, and the middle range were set at 0db, or “even”. However, you can use a graphic EQ to reduce a feedback issue that occurs at one specific frequency. This usually happens due to a set-up constraint based on a small stage.
If you think that this may happen, you can use your EQ to “ring-out” the system – that is to remove the “ringing”, which is the precursor to full acoustic feedback. Note, this is an annoying process and should never be done when paying customers are in the room.
With the stage and PA fully setup with the equalizers set to their nominal values, turn on all the microphones and turn the “front” PA up about halfway. Now turn up the monitor level until you begin to hear feedback. Quickly turn it down a little until the feedback stops. Next, starting with the monitor’s 1KHz EQ slider, move each slider up from the middle until you hear feedback start. Note which frequencies are the most sensitive (you move the slider up the least). Let’s say that the 2KHz and 4KHz bands started feeding back with only a 2dB boost, while all the others don’t start at less than 6dB. In this case, put all the EQ sliders back to their normal settings, and reduce the 2KHz and 4KHz sliders by about 4-6dB. If you have a 3.15KHz slider in between, reduce that one as well. You don’t want to have adjacent sliders at significantly different levels, as this causes odd phase distortions.
Now turn up the monitor level again and confirm that you can set it higher than before without feedback. You should be in good shape.
Two notes: First, your sound shouldn’t suffer too much because the house PA shouldn’t have to change, and the stage is unusually reflective at those frequencies anyway. Second, some set-ups have a really nasty resonance, and there is no reasonable fix. Try and figure out which mic is the most sensitive, and reposition it with respect to the monitors and the back walls.
As part of the disco age, and as a result of some technology “advances”, there is a style of speakers that has one large bass speaker and 2 or more tiny piezo-electric tweeters. This was great for disco because it allowed a lot of thump and sizzle with very little in the middle. I previously discussed the “smile” EQ as a popular setting because it allowed the music to be very loud, but you could still talk to your date (or the bartender). Piezos are also very power-efficient and usually rugged.
These speakers are not useful for full-range PA or monitor use. I strongly recommend that you disconnect the piezos and replace them with a more standard horn-driver. You may need a new cross-over network as well, but if the cabinets are well built, it may be more cost effective than replacing the entire speaker. Your local pro-sound store should be able to help you.
That’s all for now. Feel free to email me with your questions and comments. Thanks to the SeaSide Lady for her continued support.