GUITAR AMPS PAGE
SECTION
10: REFLEX LOUDSPEAKER ENCLOSURE DESIGN
The
following design method for 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 available.
For technical parameters see https://eminence.com/pages/support__understanding-loudspeaker-data
STEP 1:
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
IMPORTANT - ALL MEASUREMENTS ARE INTERNAL
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 – e.g. 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
Reflex Enclosure
Experiment with different values of Enclosure
Volume, Port Area, Aspect Ratio and Duct Length until the design is optimised
for your purpose.
To fine tune a port simply progressively
cover it by sliding over a piece of plywood or particle board until optimum
performance is achieved.
Start with the port fully covered then watch
the cone movement as the port is progressively uncovered/opened.
Cone movement is an indicator of adequate
back pressure. Inadequate back pressure will reduce power handling capacity and
affect response.
If a signal generator/audio oscillator is
available then use that for precise settings.
STEP
6: CHANGING SPEAKER DRIVER UNIT.
If the Speaker/Driver unit is changed then
the port must be re-tuned to match the replacement speaker characteristics.
Email: contact
Location: Perth, Western Australia, AUSTRALIA
This page last amended 13 July 2023
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