L to R: Ike Zimbel, Frank Lockwood — Toronto AES Section -- January 26, 2016
Frank Lockwood made the introductions and provided this background info:
Ike Zimbel, RF Technician and president of Zimbel Audio, is a 35-plus year veteran of the audio industry. He's worked extensively as a wireless microphone technician and coordinator, live sound engineer, recording studio technician, audio supervisor for TV broadcasts and has managed manufacturing and production companies. His company specializes in wireless frequency coordination and pro audio equipment repair and modifications.
Ike Zimbel "reprised" his Live Sound Expo presentations from the 137th (LA 2014) and 139th (NYC 2015) AES Live Sound Expos on wireless topics.
He emphasized he would not cover the coming "wireless spectrum apocalypse" noting that whatever spectrum we're left with, we'll need to know how to use it effectively and, more importantly, efficiently.
The meeting involved two parts.
Part One looked at "Practical Considerations" or "how to actually use the stuff". Mr. Zimbel talked about a variety of scenarios that one is likely to encounter in every-day use of wireless systems, highlighting both the issues that arise and a practical approach to resolve them or simply prevent them.
One of those issues is the production of additional frequencies known as intermodulation products of which he provided a practical demonstration. Wireless frequency coordination is a method used to calculate these additions so they can be avoided. Groups or Banks are a collection of pre-coordinated frequencies supplied by manufacturers that can be very effective when used with built in scanning features. Projecting a slide, Ike displayed a Group list showing duplicate frequencies and "close calls". Responding to a question Ike said avoiding this is not cut and dried, as it's determined by a number of issues. Groups work well as long as you stay in the group, and use one make and model of equipment and type of equipment.
Another way to avoid intermod distortion is to use a coordination program like Wireless Workbench 6; or hire a coordinator.
One other error to avoid is to put the transmitters too close. Other considerations involve keeping the receiving and transmitting antennas apart. In response to a question Ike prefers a safe distance of a minimum of 3 feet, 4 feet being preferred.
As well, placing receiving antennas behind transmitting antennas is good practice. Height is desirable also, to a point.
Other considerations involve using as little power as possible. RF is like digital: there's no benefit in going over 0 dBFS. More power creates more intermod distortion.
Before the break Ike shared some war stories under the theme "it's always a frequency problem until it isn't!" One such problem turned out to be the mic picking up the sound of about 100 cooling fans for their associated television lights.
Part Two looked at Coordination on the Road. He recalled his experiences of the recent Shania Twain tour which he just completed being five months on the road. Here, Ike was involved with getting over 50 channels of RF working in a total of 75 shows played out in 67 cities. It required a new frequency coordination for every city. The success in that area could be attested by the fact that there were no RF issues that were audible by the public.
Thru slides he went over equipment lists, displayed photos of antenna placement at concerts, and screenshots of software. On equipment he noted he really likes the Sennheiser A-5000 antenna, never a problem, expensive but really good. "They'll melt if they get too close to hot lights. Don't ask!"
He went over frequency coordination: a process that uses mathematical calculation to predict an interference free frequency for every required RF channel in advance.
His routine began before arriving at a venue: saving the current coordination as a new file; looking up local off-air TV stations in the database; and re-allocate frequencies as required. Once at the venue he would scan the RF environment with a spectrum analyzer. He'd then import the scan and note any variances from the database and adjust allocations as were necessary. This operation went so smoothly that once his work was done he could work on coordination for the next city during the show.
He compared the RF environments in different North American arenas, stating Anaheim California was the most challenging city to coordinate.
Overall, and with one exception for security reasons, there was never a frequency change needed during the show for necessity.
After a Q&A period, Ike gave a demo of the Intermodulation Analysis System software.
At the end of the meeting Ike was presented with a Toronto AES Certificate of Appreciation and official coffee mug.
