On Sun, 21 Dec 2003 19:52:13 -0000, "Wally"
wrote:

Just been here...

http://www.nch.com.au/tonegen/index.html

...and downloaded their tone generator prog to have a play. Turns out that
you can set up tones and save them as wave files, so I duly made a test tone
CD with the following frequencies played as 0dB sine waves lasting a few
seconds each...

100, 90, 80, 70, 60, 50, 40, 35, 30, 20, 20

I duly fired it onto the hifi and got the following impressions of volume
for each...

100 - 5
90 - 5+
80 - 5
70 - 4+
60 - 4
50 - 3+
40 - 2
35 - 1
30 - 1
25 - 2
20 - 1-

90Hz came across as a distinct peak amongst the upper frequencies which
otherwise seem to lose volume smoothly from 100 to 50Hz. There was a big
drop in volume going from 50 to 40Hz. 25Hz was a surprise peak at the lower
end - not mega loud, but clear and present compared to the other low tones,
which seemed to require listening for. 20Hz is there but barely audible.

The f0 of the driver is 25Hz, so perhaps that could explain the improved
volume at that frequency. They're old home-brew speakers using the KEF
Concerto drivers and baffle. They also use the Concerto reflex pipe, but
are built into larger cabinets. In other words, compared with the Concerto,
my reflex pipes are relatively small for the cabinet size. Could this be the
cause of the peak around 90Hz, and/or the dip below 50Hz?

Yes. Sounds like the cabinet is now tuned to 25 Hz, which is too low
for the B139 driver. Hence, the curve dips badly in the 30-35 Hz area,
where it needs the port to support the active driver, and picks up
again briefly at the lower 25 Hz resonsnce before collapsing.

--

Stewart Pinkerton | Music is Art - Audio is Engineering