How does a bipole kill baffle step?

[jimmyjazz]

I've seen some references to the idea that a bipole driver configuration can eliminate baffle step effects. I'm not seeing it.

Any driver putting out long-wavelength frequencies (compared to box dimensions) is going to radiate into 4*pi steradians. Put two drivers on the front of a box, and both are going to "creep" around in the lower frequencies and drive the whole hemisphere. Put one on the front and one on the back, and both are going to do the same thing.

Am I misunderstanding the argument or is it not grounded in reality? At the end of the day, it shouldn't matter where you place a driver if the wavelengths it is sourcing are large compared to the box (baffle) dimensions.

[scottjoplin]

The creepage doesn't so much kill it as scare it away

[norman bates]

with a big enough baffle, maybe.

Or a ringing qts (like 1.2 - 2), maybe.

I had a 24" deep open baffle, dip near 280hz, peak near 140hz then seemingly nothing below.

I can dig up graphs that melonhead did (before he was banned) on measurements of a 2' deep open baffle.

[scottjoplin]

I think there is a misunderstanding? He said bipole, not dipole.

[ILikeFoodz]

I think the reason for this idea would be that if you have 2 identical mounted on identical baffles 180 degrees opposed, then above the baffle step frequency, you would just be hearing the driver pointing at you at its full sonic output and nothing from the one pointing away, and below the baffle step frequency you would hear half the sonic output of the driver pointing at you while half "creeped" around the back and would remain unheard, and you would hear half the output of the driver facing away from you, the half that "creeped" around the back relative its front.

[norman bates]

lol, yup, I was completely off base.

[jimmyjazz]

Originally Posted by ILikeFoodz

I think the reason for this idea would be that if you have 2 identical mounted on identical baffles 180 degrees opposed, then above the baffle step frequency, you would just be hearing the driver pointing at you at its full sonic output and nothing from the one pointing away, and below the baffle step frequency you would hear half the sonic output of the driver pointing at you while half "creeped" around the back and would remain unheard, and you would hear half the output of the driver facing away from you, the half that "creeped" around the back relative its front.

Correct, my assumption is that (below the baffle step frequency) we would hear the "front" half of the front-firing driver and also the "back" half of the rear-firing driver. Both radiate into the full room, thereby knocking each driver's contribution down by 50% in terms of local acoustic power density. I just don't see how this is an improvement.

[GM]

Originally Posted by norman bates

I can dig up graphs that melonhead did (before he was banned) on measurements of a 2' deep open baffle.

Saw a lot of interesting/good info in a quick browse, a pity he was banned [why?]: melonhead at diyaudio site:www.diyaudio.com - Google Search

GM

[scottjoplin]

Originally Posted by jimmyjazz

Correct, my assumption is that (below the baffle step frequency) we would hear the "front" half of the front-firing driver and also the "back" half of the rear-firing driver. Both radiate into the full room, thereby knocking each driver's contribution down by 50% in terms of local acoustic power density. I just don't see how this is an improvement.

What creeps round the front from the back replaces what's creeped round the back from the front, why would the one knock the other down, unless you are thinking of the way a dipole works?

[ILikeFoodz]

Well, there would be destructive interference between the sounde emitted by the rear and that from the front at certain frequencies, the specifics of which depend on the depth of the speaker cabinet.