Performing with accompaniment tracks
The following technique will work with choruses (25 to 50) as well as 10 to 20 voice "holiday" and other “singout” ensembles. “Logitech” makes a portable (rechargable battery) “Wireless Boombox” (approx. $130 - Amazon.com) which plays music from an ipad or iphone. Use one “Wireless Boombox” unit for small 10 to 15 voice ensembles... and two (2) “Wireless Boombox” units (spread apart) for larger ensembles. If you need to use more than one “Wireless Boombox” unit, you can’t use the wireless feature (connection) from your ipad or iphone. You’ll need to use a “Y” patchcord (http://www.cnaweb.com/6-3-5mm-y-patch-cord.aspx) ($1.25) plus two 3.5mm 6 foot stereo “male to male” extender patchcords (http://www.cablestogo.com/product_list.asp?cat_id=2002) ($ 5 ea.) from your iphone or ipad to each “Wireless Boombox” unit. Download the accompaniment track to your iphone, ipad, press play, and you’re good to go!
First of all, there should be no risers in these singing situations. If you’re using one speaker unit, position it just behind the back row, center of the ensemble. If you’re using two speaker units, position the speaker units BEHIND the chorus or small ensemble with the speakers spread apart about 7 to 15 feet (depending upon the size of the ensemble). Put the speakers on the floor (or better on a chair or stool, if available). Have one of the ladies be the "sound lady" in the back row (center), turning it on and off, change the tracks (if you have more than just one accompaniment track). She should still be able to sing without a problem, once the accompaniment track begins and adequate volume level has been established. If you're moving around in a shopping mall situation, have various ladies take turns carrying the speaker unit(s). They are extremely light-weight. Make sure the 6 hour, rechargable batteries on the speakers have been fully charged prior to the singout!
Practice with this set-up several times to get the "sound lady" (and all singers) comfortable with everything involved.... and mostly with a track volume level that allows all chorus members to hear the track JUST ENOUGH to tune and sync with it. Mark, or note the volume level on the iphone/pad that seems to be about right. Then use it as a basic reference starting point. Every place you move to will have different acoustic characteristics (and audience noise... talking, etc.), so the track volume level may need to change. The ladies, especially towards the back of the chorus must realize they will NOT hear their voices as much as they're used to hearing as they sing along with an accompaniment track!
Don't worry about the audience hearing the track. It will be slightly muffled set up behind the chorus, but the chorus will definitely be featured above the sound of the accompaniment track,... and the audience should hear just enough of the track for it to add positively to the over-all performance.
(updated for current technology 2012)