clearance

We used to need speakers as large as file cabinets if we expected to hear any satisfying low frequencies. Today, you can get respectable “grunt” out of absurdly small cabinets. What changed? (a) lots of power, and (b) ported enclosures.

The power part is pretty easy to understand. More power = the speaker cone moves more air  = more happy… up to a point.

A small speaker cone can’t move enough air by itself to accurately deliver the lowest frequencies. Adding a bass port gives a second source of moving air, extending the range to a lower frequency than would be possible with no port. The bass port can be on the front or back of the cabinet.

OK… so what?

Speakers with rear-facing ports need to be some distance from the back wall to minimize cancellation of certain frequencies. (This is different from the bass boosting effect of having the speaker in a corner. We’ll save that discussion for another time.)

The sound coming from the rear port reflects off the back wall, then combines with the sound coming from the front of the cabinet. Depending on the distance from the back wall, some audible frequencies between about 40-400Hz will be out of phase by the time they reach the front. Greater distance equals lower frequency (sometimes up to 30″).

This cancellation can’t be fixed by equalization. A larger initial amplitude will produce an equally larger cancelling wave, for zero net improvement.

Rear-ported speakers were originally designed for use in a recording studio, where the mixing desk is usually several feet away from the wall. Some radio studios have a similar layout, and would be able to achieve the clearance needed.

However, for the studio that has no rear clearance, the best solution is to use speakers that have the bass port on the front of the cabinet. The primary sound and the port sound are always in phase… no problem. Now, you can push the speaker right up against the wall, if necessary.

Genelec, Tannoy, Mackie, M-Audio, Alesis, Dynaudio, JBL, and Yamaha are among those that favor rear ports. Adam, Behringer, Edirol, KRK, and Samson favor front ports.

Fortunately, BSW has a great selection of both types here.

One thought

  1. Why hasn’t anyone pursued “Transmission Line” speakers for a studio environment? I thought that method was superior to any type of port. Yeah it seems to be complex but we do have computers and robots today that can handle the complex stuff. Right?

    I presume that all of these speakers don’t have any port noise at the extreem low frequencies. What about round port vs. slotted port? Are the slotted ports superior to round ports?

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