The following design method for bass reflex enclosures is reproduced from the April 1960 issue of the famous "Audio" Magazine.

The design parameters used in this method are based upon empirical data derived from real-life experiments using real enclosures and real loudspeakers.

The graph reproduced here is supported by a full explanatory article that provides the methodology used and results obtained.

Regrettably, I do not have the full article so can only reproduce what is available to me.

Notice: © Copyright and intellectual property in these design methodologies remains with their original author and publisher

Note: For those preferring a more scientific method utilising comprehensive parameters, the Eminence USA Enclosure Designer Software is recommended. For details see http://www.eminence.com/support/designing-enclosures/


Determine the resonant frequency of the loudspeaker

To do this refer to the manufacturer's specifications or use an audio oscillator

IMPORTANT: The enclosure vent must be designed to match the actual loudspeaker resonance - not the cabinet. Using a longer tunnel than needed to match actual loudspeaker resonance reduces bass response (SPL) at frequencies lower than the loudspeaker resonance. Some tolerance is permissible so extreme accuracy is not required.

STEP 2: Determine Enclosure Volume

Determine the size of the enclosure to be constructed

This is expressed in cubic inches, because in this nomagraph the volume of the enclosure is expressed in cubic inches

Note: One cubic metre equals 61,047 cubic inches

In this nomagraph the volume of the loudspeaker is not included in the enclosure volume, so must be subtracted from the gross volume

The enclosure volume is calculated by multiplying the height times the width times the depth


Note: One inch equals 25.4 mm or 2.54 cm

STEP 3: Determine Port Aspect Ratio

Select the preferred Port Aspect Ratio

This is the ratio of port width to port height - eg an 8" wide x 2" high port would have an aspect ratio of 4

As will be seen from the graph, a square shaped port (Aspect Ratio of 1) offers the lowest port area and tunnel length


STEP 4: Calculate the required parameters from the graph.

4.1    Select the Resonant Frequency of the loudspeaker at the bottom right hand axis of the graph

4.2    Draw a vertical line straight up from the selected frequency until it intersects the Enclosure Volume axis

4.3    Project a horizontal line to the left until it intersects with the Aspect Ratio axis

4.4    Project a vertical line up until it intersects with the Port Area axis

4.5    Project a horizontal line to the left until it intersects with the Duct (Tunnel) Length axis

STEP 5: Determine final dimensions for the Bass Reflex Enclosure

Experiment with different values of Enclosure Volume, Port Area, Aspect Ratio and Duct Length until the design is optimised for your purpose.

For further information Contact:

Dennis Grimwood

Email:      contact

Location: Perth, Western Australia, AUSTRALIA

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This page last amended 22 May 2013

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