tuning reflex speakers to your room

[sreten]

In addtion to my penchant for overdamped alignments :

http://diyaudio.com/forums/showthrea...threadid=25762

Here's another of my pet theories.

work out your main rooms modes given f = 1/2 wavelenth at
room dimensions, velocity of sound =1120ft/s.

For a room 23ft x 15ft x 9ft gives 24Hz, 37Hz and 62Hz.

Tuning the port to these frequencies is not a good idea IMO.

The best frequencies are the frequencies musically centrally
between the mode frequencies, (multiply the two frequencies
and then square root), this gives : 30Hz and 48Hz.

Tunings near these frequencies will work well in the room,
the actual bass cuttoff off will be the next lower room mode.
(Especially true for overdamped bass alignments, see above)

The final option is to tune below the lowest room mode, dividing
by root2 (1.414), half an octave, for the above room this gives
17Hz, 1/3 octave gives 1.26 = 19Hz, 1/4 (1.19) gives 20Hz
One of these frequencies will be much better than 24Hz.

As another example say a room 20 x 14 x 8 (Ft)

Gives 28, 40 and 70 Hz to be avoided for port tuning.

Good frequencies are 33.5 and 53Hz.

Below 28Hz : 1/4 octave = 23.5Hz , 1/3 = 22Hz, 1/2 = 20Hz.

sreten.

[Mos Fetish]

This and the other post you made on overdamping have led me to ponder what design pronciples commercial manufacturers use. They are selling thousands of units of each model, every year, going into a variety of rooms and environments. They obviously have to play it safe. How would they go about doing that?

Mos

[sreten]

Overdamped alignments are common in good commercial speakers.

Some manasfacturers supply foam bungs for the ports
for troublesome rooms, not a paticularyly good solution.

Most mainstream stuff is now made for A/V, so design
below 80 is controled by setting the subwoofer, which
is relatively very flexible.

sreten.