The rule-of thumb is 25 wireless clients per AP.
Now this rule-of-thumb can "stretch" or "shrink" depending on the type of traffic. If you're doing nothing but emails, web, FB then the number could potentially go up to 35 wireless clients to an AP. However, if you want to do HD video streaming then the number drops down to about 5 wireless clients to an AP.
Another factor which significantly affects the amount of wireless clients to an AP is the bandwidth of your LAN link (from the AP to the switch and from the switch to the WLC). Ideally you should have 1 Gbps. But if one of your link going to the WLC is 100 Mbps, then you're in a bind.
You need to be creative about where to install your APs. You may need to install your APs under the seat. But before you go about installing them, you'll need to do a comprehensive wireless site survey of this auditorium so you'll know exactly HOW MANY APs to install, where to install them and how to install them.
