Open baffle MTM questions

[kaameelis]

I had one more OB related question.
Simulation of U-frame OB shows that on first dipole peak U-frame radiation is nearly omnidirectional.
Is it really in this way or it is AKABAK simulation artifact?

 

[Juhazi]

Are there two woofers?

Perhaps the box is making that, but typically first dipole axial minima has poor directivity. U and H frame can't be simmed with the Edge...

 

[kaameelis]

There is only one woofer. Depth of U-frame is 300 mm.
Simulation was fully made on Akabak 3, additionally is added + 6dB per octave rise on lower than 100 Hz frequencies.
On Edge simulation I see that also frequencies lower than first dipole peak had poor directivity. On Akabak simulation directivity below first dipole peak is OK.

For comparison H-frame had excellent directivity. On image is 300+300 mm H-frame, on axis response is equalized .

 

[Juhazi]

I'm ready to believe AKABAK! I've never intuitively liked the idea of undamped U-frame.

But still there could be something wrong in parameters. Can you start a new sim with slightly different dimensions?

 

[kaameelis]

I had double-triple time checked all parameters, they seem for me correct, or at least they are same for U-frame and H-frame simulations. If U-frame had omni radiation because it is undamped, then H-frame must have also omni radiation frequencies, as it is also undamped on simulation?
What dimensions you mean, depth?

 

[Juhazi]

Actually, I'd like to see AKABAK sim of a dipole in wide baffle, then in 3 steps when the baffle plate transforms to make first a shallow and then deeper U. Just keep distance from driver's midpoint to edge/above the bend constant. Then we shoud be able to see gradual change in dispersion!

Damping in the U tube is supposed to make the response cardioid, but it can't be calculated I suppose. Kimmosto and Kreskowsky have been there, done that
DIY-dipole-1
Cardioid bass

 

[kaameelis]

Damping in the U tube is supposed to make the response cardioid, but it can't be calculated I suppose. Kimmosto and Kreskowsky have been there, done that
DIY-dipole-1

Two last images on this page shows same result as simulation, undamped U-frame is nearly omnidirectional at first dipole peak.

 

[Dan998]

Your speakers look great.

Hi,


Yes, I have built the flowers, or petal baffles. The intention was not to have a true dipole, as this clearly is not possible with an 8-inch fullrange driver, but to provide an optimal loading for the drivers with a baffle as large as possible (following Rudolf´s suggestions of not having more than 2.5 times pathlength vs. cone diameter) while avoiding any negative baffle effects. Choice of mounting and baffle material of course plays it´s role as well, but the main intention was to provide a clear, diffraction-free "flowing" shape from the central part of the driver to the rolled-off "edges" of the baffles, without any discontinouities especially between cone and baffle.


The flowers have been very time and money cosuming to build, and I have never done it a second time. A good compromise is a trapezoidal baffle with very small wings, which doesn´t perform like the flowers, but is a lot easier to build.


All the best


Mattes