Plugging rear ports of "bookshelf" speakers?

@immatthewj 

If the speakers came with plugs (e.g. many KEF models) they are designed to be plugged so that the sound will be more balanced when you place them closer to the wall.  The KEF LS50 for example has three modes- open port, half plugged and fully plugged.  The manual specifies the best position from the wall for each mode.  More plugged = closer to wall.  

However many ported speakers are not designed to have them plugged.  Woofer suspensions are such that they can be designed for stiffness / wide open port, hybrid stiffness where they can be both ported and plugged, or very loose suspensions that require them to be sealed.  

First step is to consult your manual to see how close they recommend placing them.  You can always experiment by plugging the ports.  I tried it once with speakers not designed to be plugged and it ruined the whole sound and distorted the midrange.  

Recently bought a pair of Ascend Sierra 1 bookshelves and then bought their brand port plugs, one set open and one closed.  Need to play around with them to find the best sound....they are quite small speakers but so far are pretty impressive....driven by NAD C 375BEE.....

The New EPOS Loudspeaker model ES-7N which was released in May 2024, has the feature of a switch on the back of each speaker to allow for near-wall  or free-space placement. The EPOS Loudspeaker line-up were designed by Karl-Heinz Fink, the owner of EPOS Loudpseakers and Fink Team - currently two EPOS models available with a third model to be shipping in September 2024. The ES-7N, the smallest model in the EPOS brand, can be purchased with much less concern over speaker location. EPOS is a very well thought-out speaker brand.

The reason for plugging port is the port can muddy the bass. A bass note is first sent out the front of the speaker then a delayed signal is sent out the rear port, hits the wall and arriving slightly later to the listener. The port is also 'tuned' to add a bloat sound at a certain frequency. Much like blowing air into a wine bottle and can be tuned higher or lower depending on volume or length. A cheap way to produce bass.

It's important to understand that if you seal the rear port completely (plugged) the excursion of the driver will be negatively affected. THIS IS NOT GOOD! This imparts a restriction on the driver and reduces the overall output of the speaker including the upper bass region. Even foam plugs or socks stuffed in the port will reduce excursion. 

An old method that lets the speaker breathe is placing a bundle of straws in the port. It disrupts the tuning of the port so the cheap sounding 'one note bloat' is eliminated yet still allows for full excursion.

If you then properly integrate a subwoofer the low bass should be greatly improved. 

@avanti1960 +10

Mike