The following is another example of an EBS system. The driver is a KEF B200H with the following T/S parameters:
Fs = 29 Hz
In this example, the driver is used in an isobaric configuration, so the effective Vas is halved in value, i.e. 43.5 litres (1.54 cu.ft.)
The following are two possible ported alignments for this driver. The first alignment is a maximally-flat alignment. The second alignment is an EBS alignment using a box that's more than twice the size and a lower tuning frequency. From the graph below, you will notice that the EBS alignment produces more output below 50 Hz (and significantly more below 30 Hz), but about 3dB of midband efficiency is lost at 50 Hz. The creator of this particular design used a LP filter at 55 Hz, so the design is operates only in the "shelf" area of its response, making its effective -3dB point at approzimately 30 Hz.
Alignment: Maximally Flat
My thanks to Aaron Bohnen 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.