Dorset Sound & Communications

Sound system design for the 21st Century

SoundTips
Wireless Microphones

It is becoming rare to find the church sound system that does not have some form of wireless microphone. Twenty years ago a good basic wireless microphone systems cost fifteen hundred to two thousand dollars. Today better systems can be acquired in the four to seven hundred dollar range.

There are a couple of things to keep in mind when adding a wireless microphone to your sound system that will greatly improve reliability. When the microphone transmitter is shut off, the receiver is just looking for something outside on its frequency. In the Washington DC and other congested metropolitan areas worldwide it will usually find something. It is important to buy your system in the right frequency range and have the receiver correctly adjusted to reject as much outside interference as possible. The receiver must be located correctly with respect to radio frequency hearing assistance transmitters and digital signal processing equipment that may cause interference. 

There are other complications if you are  a wireless microphone user.  Below is a Facebook note I wrote that explains some of it. Check to see if any of your existing wireless microphones are in the 700MHz band. If you buy a wireless mic system today, you should be okay regarding frequency. What we don't know is if the FCC will outlaw 700MHz wireless mics or finally require each of us to obtain licenses and what our rights will be in relation to coming 'white spaces' devices.

I have spoken to a number of you about the turmoil the last two years caused by the Federal Communications Commission Digital TV mandate. Briefly, in June the FCC presided over the end of analog TV transmission in the US and conversion of all over the air TV broadcast to digital. During the several year transition period, stations "doubled up" with both their old analog signals and new digital signals on adjacent channels. You should know that your wireless microphones transmit in the TV bands, residing in the open channels. Doubling up reduced the space for wireless mics. In June analog transmitters were turned off, instantly opening up space. Knowing that there would be all this open "free" bandwidth, the FCC decided to make some money and proceeded to reallocate the upper UHF channels for public safety communications and commercial applications. The frequencies between 698MHz and 800MHz, also called the 700MHz band, were placed off limits to all new wireless microphones. About eighteen months ago all wireless manufacturers stopped selling 700MHz band systems. Much of that 700MHz bandwidth has been sold to large national communications providers such as AT&T and Verizon netting the government billions of dollars. Most manufacturers, audio professional groups and a number of theater, broadcast and religious organizations petitioned the FCC to allow us to continue operation in protected parts of the 700MHz band to no avail. The interpretation is that all unlicensed 700MHz systems are prohibited. Technically, unlicensed wireless microphones (virtually all) have been illegal the last 40 years. The FCC just chose not to pursue enforcement and a whole segment of the industry has been allowed to be established. As of January 15, 2010 the FCC finally handed down the law that all unlicensed 700 MHz band wireless microphones must cease operation by June 12, 2010. If Verizon or ATT decide to start new service in your area before then, they may demand you quit the air. Some manufacturers are offering rebates to turn in and convert to new, legal systems (though still technically illegal). For clients with multiple systems, replacements could still cost thousands of dollars.

See the Sennheiser website, http://www.sennheiserusa.com/RFServices, for more information. Audio Technica (Audio-Technica.com) and Shure (Shure.com) also have information on their websites.

With their most recent ruling The FCC introduced a further monkeywrench, licensing and Part 15 unlicensed operation. The vexing issue is one of protecting all the rest of my clients many wireless microphones and replacing the few 700MHz systems. The FCC wants more immediate bandwidth for wireless internet. They are allowing broadcasters to resell any excess already licensed. That will further constrict legal frequencies. The FCC and wireless communications operators are anxious to reap profits from new “white space” 4G personal data devices. It will mean hundreds of thousands to millions of new users. These are proposed to work in the recently abandoned analog TV channel spectrum - right on top of present wireless microphones. They are supposed to detect and avoid interference. Public tests have not yet worked with wireless mics. The FCC is currently debating whether to allow licensed protection to wireless microphone users, and who will be considered licensable. It has been proposed to classify churches and non-professional theater and non-professional broadcast users non-critical, un-licensable and unprotected from interference. They will be considered Part15 users. Unlicensed, legal, however the lowest priority. You cannot interfere with licensed services, they can interfere with you, you have no recourse. Licensing millions of semi-professional users will eat up bandwidth that they want to auction for another winfall. My bet is that money will win out.

The following warning has been mandated by the FCC for all wireless microphone products using the frequency bands in question:
CONSUMER ALERT
Most users do not need a license to operate this wireless microphone system. Nevertheless, operating this microphone system without a license is subject to certain restrictions: the system may not cause harmful interference; it must operate at a low power level (not in excess of 50 milliwatts); and it has no protection from interference received from any other device. Purchasers should also be aware that the FCC is currently evaluating use of wireless microphone systems, and these rules are subject to change. For more information, call the FCC at 1-888-CALL-FCC (TTY: 1-888-TELL-FCC) or visit the FCC’s wireless microphone website at www.fcc.gov/cgb/wirelessmicrophones.

None of this is new. It is as it has always been. Only now, with the pending introduction of hundreds of thousands of  licensed white space devices, we are hundreds of times more likely to run into interference and have no recourse.

I have been looking for options to get us out of the 500-700 MHz band. There are few so far:

1. Sabine has traditionally styled wireless microphone systems in the 900MHz band. They are in a similar price range to products from Sennheiser, AudioTechnica, MiPro and Shure. So far as I know they are the only American manufacturer in that range. They tried the 2.4GHz range, but are abandoning it due to other interference from cell phones and WiFi devices. This illustrates the problem we are up against. 4 clip-on mics, $2559

2. Audio Technica SpectraPulse are advanced wireless conference microphones that operate digitally. SpectraPulse operates at much higher 6.3GHz encrypted frequencies. They are currently limited to a desk stand mic and a flat table mic. The range is only 75 feet. The system accommodates 14 mics. They are expensive. 4 mics, $12,000.

3. RevoLabs is another digital conference system that operates in the 1.9 Ghz range. It is still has some oddities. They have a table top mic transmitter, a pocket-clip transmitter that houses it’s own mic, and has a jack for an optional lapel or earset mic, and a wireless adapter transmitter that plugs onto any handheld microphone. They have single, dual and multiple microphone receiver systems. A system can accommodate up to 32 microphones by combining receivers. 4 transmitters, $5128

4. Listen Technologies has introduced an infrared light wireless microphone system incorporated into their ListenPoint system. This bypasses the whole radio interference issue. Sounds like a great idea, but is not really a stand alone product. ListenPoint is oriented to small rooms. The all in one candy-bar shaped transmitter with integrated mic must be clipped outside of clothing and can be used handheld or with an earpiece or clip-on mic attached. It’s a little awkward, but I may start specifying it for lecture and classrooms. 4 mics with the integrated PA electronics package, $2558.

5. Buy the usual 500-698MHz systems and hope for the best. If you only need one wireless mic I recommend buying something like the inexpensive Audio Technica 700 series or 2000 Series. They only tune 8 and 10 channels respectively. $250-$365. I want to limit your exposure should the FCC turn against us. Those clients desiring more have one system will have to spring for more expensive AT 3000 Series, Sennheiser EW100G3 or Sabine 915MHz systems in the $500-$660 per system range. They can tune from 200 to 1200 channels depending on manufacturer and cost. The extra flexibility is necessary to coordinate multiple mics and to try to tune around future interference. Audio Technica, Sennheiser and a couple of others have 700 MHz rebate programs extended until June. Call me and we can work out what is applicable and advantageous.

I expect that once the FCC makes up it’s mind we will see traditional wireless mic system manufacturers introduce innovations to cope.

Continued...

The cheap garage band wireless systems often forego effective receiver filtering and signal companding that give the best sound. They cannot be rack mounted and the antennas are permanently attached to the chassis. Plastic cases do not shield the electronics from interference. The system you select will have a number of microphone options that will be dictated by your intended use. The belt pack and microphone of a clip-on system should have a connector allowing you to swap microphones in an emergency and simplifying repair (you should have a spare microphone). An miniature earset mic can be substituted.

Receiver antennas need to be correctly sited for the best signal coverage. Except for non-critical sound systems, you should only consider diversity type wireless microphone systems. These systems have two antennas and completely eliminate signal dropouts. The antennas should be removeable so they can be remote sited when the receiver is mounted in your steel equipment rack or to place then in better position. Multiple systems should have their antennas combined through an antenna distributor which will often incorporate power supply distribution.

Most modern wireless systems will work about eight  hours on two AA batteries. Alkaline batteries are specified by all manufacturers --not carbon/zinc, or "heavy duty" batteries. See the Sound Tip on batteries for further information. Give DS&C a call for help specifying and installing your church wireless microphone system and the training to use it effectively. We can also set up preventive measures and scheduled maintenance visits for the rest of your sound systems. Don't be caught unprepared. Enjoy effortless sound. Do it now!

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