Please help me to understand the transfer function of a bi-pole. (not dipole)

[brianpowers27]

Please help me to understand the transfer function of a bi-pole.

In the past I have used the baffle simulator in Jeff B's Response Modeler 2.1 to visualize the transfer function of a dipole based on the the total path length (x dimension) from driver to driver.

I imagine that the characteristic of a bi pole is the perfect inversion of the transfer function above.

Is this a good assumption?

[augerpro]

Bipole is more or less two in phase monopole sources separated by some distance.

[brianpowers27]

Bipole is more or less two in phase monopole sources separated by some distance.

Agreed. But there must still be phase interaction between the front and rear drivers, at the frequencies where they are omnidirectional.

[augerpro]

It's sort of the inverse of the dipole. At lower frequncies the outputs become more and more in phase and additive. At some point the separation distance will be significant compared to the frequency and it will comb filter like dipole would. The pattern would probably be similar too, just a mirror image of the dipole pattern all other things being the same. I would imagine instead of a big dipole peak, you would have a deep bipole null, which separates the increasingly additive low frequencies from the comb filtering high frequencies. Anyway that would be my "off the top of my head" answer as I haven't really looked at bipoles much, but I have looked at dipoles and they should be inverses of each other more or less.

[brianpowers27]

That seems to be in accordance with what I had in my head. I am wondering how much gain I will see from the combined bipole sources below the bipole frequency....

Instead of seeing nulls on the sides one would likely see 3db peaks... That could be somewhat destructive to the overall presentation if used in a sense where the woofers are oriented front/back.

If I were to rotate 90 degrees this would be negated but it would likely reshape the fr. Right now I am having a hard time envisioning how this would look.

[augerpro]

Under the bipole null you could get closer and closer to a true omni, or pulsing sphere sort of radiation. To me the draw of a bipole is if you want very wide dispersion, with a soundfield that has similar response at very wide angles. Of course as teh frequency gets higher you run into the same problems of comb filtering as dipole. But for wide dispersion surrounds I think bipole could be a very good solution. Maybe even for mains if you really worked the concept well enough.

[Dennis H]

The thing that saves bipoles from comb filtering is the sound starts beaming, depending on baffle width and driver diameter. One cool side effect of that is no BSC is required.

[brianpowers27]

The thing that saves bipoles from comb filtering is the sound starts beaming, depending on baffle width and driver diameter. One cool side effect of that is no BSC is required.

I may do this with 2 rs225 woofers in a three way configuration.