When running DD-WRT firmware, slow speeds are seen or there is no connectivity?  Try to disable the Frame Burst rate in Wireless -> wl1-Advanced .  According to the definition, this can help with multiple devices.

CTS Protection Mode

The default value is Disabled. When set to Auto, a protection mechanism will ensure that your Wireless-B devices will connect to the Wireless-G router when many Wireless-G devices are present. However, performance of your Wireless-G devices may be decreased.

 

The default value is Disabled. Frame burst allows packet bursting which will increase overall network speed though this is only recommended for approx 1-3 wireless clients, Anymore clients and there can be a negative result and throughput will be affected.

 HS