Stimmen - 3, Durchschnittliche Bewertung: 4 ( )

Hersteller: Fender Dateigröße: 10.23 mb Dateiname: Unterrichtssprache:

Check the specifications for the equipment you are using. Grounding for Safety Outdoors The most common safety problems outdoors are improperly wired portable AC cables and wet ground or stages (and, of course, rain). Check your wiring carefully, the same as you would indoors. Consider canceling a performance if rain begins. If you must perform on wet ground or in the rain, the best way to avoid shock hazards to the performers is to use wireless microphones and wireless guitar transmitters. These same outdoor problems, of course, can develop indoors on a damp floor, so watch out! Grounding to Reduce External Noise Pickup One myth about grounding is that you must ground your equipment to avoid noise pickup. Anyone who owns a portable cassette machine knows that that simply isn’t true. The primary reason we ground our audio equipment is for safety. An important secondary reason is that, with AC powered equipment, under some conditions, proper grounding can help reduce external noise pickup. The third reason that we must pay attention to grounding is that, while proper grounding won’t always reduce external noise pickup, poor grounding can unquestionably increase external noise pickup! Poor grounding practice usually results in “ground loops" and avoiding these ground loops is the second most important part of proper grounding (the first most important part, of course, is maintaining the safety ground). A couple of examples will help explain what a ground loop is and how to avoid them. In Example 1, the loop is between two audio cables that connect a limiter to a 3000 Mixer. This is an example of an unavoidable ground loop. The best way to deal with this type of ground loop is to physically place the two audio cables as close together as possible (lace or tape them together if your setup will allow it). This reduces the area enclosed by the loop which will significantly reduce the pickup of external noise. This same situation could result if you were connecting the Left and Right Pre Amp Out jacks from your 3000 Mixer to the left and right inputs of an external power amplifier. Again, the best way to reduce the pickup of external noise from this unavoidable ground loop is to run the two cables very close to each other. In the second example, the ground loop occurs between a 3000 Mixer and an external monitor power amplifier. Even though there is only one audio cable connecting the two devices, a second ground connection, through the AC cables of the devices, makes the return connection and forms a ground Ground Loops Example 1: Unavoidable Ground Loop (keep cables close together). 3000 Mixer Limiter Example 2: Ground Loop Through AC Line. 3000 Mixer loop. The only way to break this ground loop is to lift the AC ground on the power amplifier with a two-wire to three-wire AC adapter (leaving the loose wire on the adapter unconnected). Because this practice is in conflict with the AC safety ground, here are two rules to minimize the safety conflict: 1) Don’t lift the safety ground on any piece of equipment unless it demonstrably reduces noise pickup. 2) Never defeat the AC safety ground on your 3000 Mixer by using a two-wire to three-wire AC adapter in this manner. The reason for this second rule is that your Mixer chassis is connected to the chassis of all your microphones and only by properly grounding the Mixer can you be assured of a safe ground on your microphones! Always maintain at least this one ground for safety! It’s worth noting that, by using balanced connections between two pieces of audio equipment, you can “lift” (disconnect) the shield at the “sending” end of the audio cable to interrupt the type of ground loop discussed in Example 2. Since, in a balanced line, the shield does not carry audio signal, you can disconnect the shield at one end without interrupting the audio signal (and without disrupting the effectiveness of the shield). Unfortunately, this is not a very practical solution to the problem in a portable audio system because it would require special cables which have the shield disconnected on one end. Using Proper Shielding to Reduce Noise Pickup Proper grounding helps prevent pickup of noise that is transmitted magnetically. Magnetically transmitted noise most often comes from motors or, more commonly in audio, from large AC power transformers (either building transformers or the power transformers in a power amplifier or other piece of audio equipment). Proper shielding, on the other hand, helps prevent pickup of noise that is transmitted capacitively. Capacitively transmitted noise may be in the form of radio waves from a radio station or CB radio or it may be in the form of "static" from certain types of motors or from lighting dimmers. (Noise from lighting dimmers may also come through the AC lines, as discussed below.) Fortunately, proper shielding is pretty easy. Just make sure that you are using high-quality shielded cables on all microphones and on all lin...

Herunterladen

Geben Sie zwei Ziffern: