Nov 1, 2002 12:00 PM
Temps as Trendsetters
I enjoyed “Line Out: Just a Dip in the Stream” in the August 2002 issue, and I wanted to inform you of a trend that we are seeing. For the most part, our business has been providing freelance audiovisual technicians to rental and staging firms throughout the country. But recently, we have seen an uptick in our installation division. Permanent-installation companies have a need for professional freelancers. I think that many of them are hesitant to hire permanent techs at this point, yet they still have projects that need to be done. Therefore, they are turning to temps to fill the void. If they like them, they hire them after working with them on a few jobs. I am not too sure how long this will last, but it is helping us broaden our business.
vice president of sales
You may be right, but another reason for this, I think, is that there is a great shortage of installation professionals in our segment. The average age of contractors keeps rising, partially because of the computer and related industries and telecoms. It doesn't surprise me that the gap in workers is being filled by organizations such as yours.
— Nat Hecht
Need Help with Grounding
- Is it true that in the October 2000 column “Clean Signals: Which End Should I Ground?” the author is saying that, as an example, if connecting a tuner or a preamplifier to a receiver or an amplifier, it is better to ground the 3-conductor cable at the tuner and not at the receiver?
- But if these two items have no common ground, should I ground that 3-conductor cable at both ends?
- With a low-impedance microphone, are you saying to ground the cable at the microphone and leave it not grounded at the amplifier?
- If my previous question's answer is yes, then what about a potential voltage shock hazard when touching the metal microphone and something else that may be grounded?
- The entire column is about balanced, line-level interconnections. The consumer electronics you mention (tuners, preamplifiers, and receivers) rarely have balanced connections. Consumer audio, or RCA, connections are unbalanced regardless of how many shields or conductors are used in the construction of their cables. In unbalanced interconnections, the shield is a required part of the signal circuit — disconnecting one end or the other is not a viable option. With balanced interconnections, the shield itself is an option — the signal circuit does not involve the shield at all. Open telephone lines strung on wooden poles are prime examples of completely unshielded balanced audio circuits. That being said, if your consumer equipment has balanced interconnections, the advantages described in the column will accrue from grounding the shield at the tuner only.
- Yes. When otherwise ungrounded equipment is involved, the shield then becomes the only path for small power-line leakage currents to flow. If these tiny currents have no path, common-mode voltages can become quite large, creating rejection problems for the equipment's balanced input or output circuits.
- Microphones are special cases of truly floating or ungrounded signal sources. In those cases, cable shields must be grounded at the receiving inputs.
- Microphone housings are connected by the cable shield to the amplifying equipment. The safety regulations that apply to this equipment make it and the microphone safe. These regulations require proper safety grounding for equipment having a three-prong plug or the use of agency-approved equipment having a two-prong plug.
— Bill Whitlock
I tore up the September 2002 issue of S&VC. Literally, I ripped out “Management Perspectives: Dear Customer: You're Fired,” the tutorial on reflections, the tutorial on digital signal processing, the article on gain structure, and the article about the cruise-ship installation. I have a client I'm trying to educate on the systems integration market, and S&VC is, as usual, the benchmark for teaching people everything from the basics to the advanced concepts.
High Country MarCom
I am a reader of S&VC for nearly 20 years. The balance your magazine strikes between audio and video, technical and anecdotal information, and sound business advice has always been refreshing for me. The effort put into the magazine by all involved is readily apparent in its content, and I thank all for making me a more competent and better-informed professional in the industry over the many years.
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