[moij]

We all know that U-frame OB needs damping as shown for example at: http://www.musicanddesign.com/NaO-II-U-frame.html
My question is: can Karlson slot ( http://home.planet.nl/%7Eulfman/theory.htm ) be used for damping U-frame?
Or it is bad idea as usually U-frame length is less than width or damping did not work for other reasons?

[sfdoddsy]

You could probably (although it would take some serious experimentation) design one to effect the exact frequency of the dipole peak, but would it still be an open baffle?

To me the defining advantage of OB speakers is often overlooked because it seems so obvious. I don't think it is SL's dipole radiation, or John K's hybrid cardiod, or Gradient's sideways CD, or Magggie's line source dipole etc etc that produces the magic.

It is the simple lack of boxes.

And adding a resonating box to cure a resonance seems like it would be a step back.

[panomaniac]

+1

[moij]

This is good point but --- for passive use simple OB had -6dB/octave bass under dipole peak and U-baffle can little be for help to play lower frequencies in reasonable baffle size.
I find good thread related to this at Part Express forum: http://techtalk.parts-express.com/showthread.php?t=215276

[el`Ol]

I built U-Frames with a tube in it

The rear response looks like the one at the NaO website

but with the volume of the peaks far lower than shown, so they are not visible in the front response.

The measurements were made in the center of a room with the microphone quite close to the speaker, uncalibrated.

[moij]

What was the distance of mic to speaker on front and on rear measurements?
I had little bit similar, two peaks on rear measurement, but I not get from what is lower peak (about 130 Hz) as I had much smaller U-frame and peak must be at about 260 Hz (calculated from 1/4 wave length)

[el`Ol]

Distance must have been an arm-length or so. MJK once told me in a mail that a tube open on both ends is a half-wave resonator, no quarter-wave resonator.

[moij]

Are you sure about 1/2 wave, it means things are worse, peak must be at 520 Hz but is at ~130. U-frame length is 30 cm, speaker cone with magnet is inside U-frame.

Measured rear response at/on u-frame opening in center, with HolmImpulse.

[el`Ol]

In my example U-frame height 90 cm (open at both ends) half wave would refer to the lower peak and U-frame width 55 cm full wave (closed at both ends) would refer to the upper peak.
I don't know whether that with the full wave for resonators closed at both ends is true, but it would explain my data.

[moij]

I had closed U-frame, box 30x49x49 cm, it mean "nearly" tube with length of 30 cm and cross-section area 49x49 cm.
On measurement image speaker has passive 2.-order LP filter at about 270 Hz.