[Frank Stearns]

(Scott Dorsey) writes:

In article ,
Les Cargill wrote:

Suppose you are designing a ported speaker enclosure. Suppose this
design wants two 2 inch ports @ 0.80 inches.

Suppose also you are using 3/4" plywood.

Must the port extend 0.80 into the internal volume of the speaker box
or would the slightly less than .75 inches of the box material suffice?

.75 is well within the margin of error anyway. You're going to have to
do some cut-and-try work outdoors with a measurement system and see.
You may even find the thickness of the box material adds too much delay.

The plumbing section of your local home center can be your friend, particularly the
bins of 2"-3" Schedule 40 ABS drain pipe and parts. Pick whichever; then plug that
value into the port field of your speaker box calculation software. (Inside
diameter)

Get a sleeve coupling or two. Use a chop saw to slice through the middle so that you
cut right through the internal stop ridge. Now you have ring(s) that can be
glued into a rough hole in your baffle.

Next, chop up some of the pipe that will fit the sleeves you made. Cut lengths at
what the software indicated, as well as incrementally longer and shorter. Buff off
the really sharp edges. (I use na 1/8" rounding bit in a laminate finishing router
and spun it around the inside and outside of the pipe ends.)

Insert the "ideal" port length. What's handy here is that it slides right in. Take a
measurement. Is it "perfect"? You're done. But you might try some different length
sleeves; see how the different port lengths affect the system.

In this way, you can completely dial in the ideal port length to compensate
for any errors in box volume calculation as well as variances in the drivers.

With that sleeve-and-pipe approach to port tuning it's fairly easy.

Frank
Mobile Audio



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