The following is an example of an EBS system. The driver is a Scan-Speak 25W/8565-01 with the following T/S parameters:
Fs = 19.0 Hz
The following are two possible ported alignments for this driver. The first alignment is a standard B4 alignment, using tables from the Loudspeaker Design Cookbook, by Vance Dickason. The second alignment is an EBS alignment from LEAP, a loudspeaker design page. You will notice that the EBS alignment requires a larger box, but the cutoff frequency is lower (some mid-band efficiency is sacrificed).
My thanks to Douglas M. Stabler of the BASS and DIY Loudspeakers Mailing List for providing me with this particular example of an EBS system. The graph was generated using my PORTED.XLS design spreasheet.