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Old 5th July 2007, 12:05 AM   #1
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Default Bipole, Dipole, and Chilliapedes

This board has been very useful, and I hope I don't annoy anyone by asking a question which is of no help whatsoever for anyone building speakers*.

I've gone quite potty with di and bi tonight.

Firstly, I notice some confusion on this board between bipole and dipole, which confused me a couple of months ago as a noob - please correct errors:

Bipole Indicates use of two drivers rather than one - such as in a WTW or WWT format.

Dipole Indicates use of one or more driver on a baffle, of which the rear is open to the room (neither boxed in nor ported).

I knew bi and di both mean two. If this is correct, can anyone explain how on earth this came about, or more specifically why the Greeks get credit for not putting their drivers in boxes, and the Romans get to name the use of two drivers?

I started confused:

Why is bipolar a form of depression, but dipole a speaker which fires in two directions?

Why are biannuals not diannuals (other than di being a bad 'sounding' prefix for a plant!) or a bisexual not a disexual (probaly because bi-directional is a familiar expression with a similar meaning, and again, di is certainly a bad 'sounding' prefix)

My "why's" went on, but like in this last example, it seemed to simply be that it 'sounded familiar/correct'.

Without worrying about an onset of OCD, I found
http://en.wikipedia.org/wiki/Numerical_prefix

If a millipede was Greek insteak of Roman, it would be a Chilliapede. Sort of. And A biopolar depressive would be dipolar.

So bi and di come from Latin and Greek respectively. This makes much more sense, with the exception of speakers: if bi and di mean the same thing, why is a bipole not a dipole and vice versa. Is there any logic as to which is which? I hope so, otherwise many a noob's confusion should probably be responded to with reasonable empathy


*Actually it might help some people work out what it is they're building :s
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Old 5th July 2007, 12:09 AM   #2
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Old 5th July 2007, 12:47 AM   #3
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Default pole dancing

Hi charliemouse,

I did a quick search to find a page which may help, but instead found (as you found) that there is a lot of confusion especially in relation to home theater surround speakers.

As it relates to speaker radiation, a bipole speaker could be a single speaker in an open baffle, the rear radiation is OUT OF PHASE with the front radiation which tends to produce a figure of 8 radiation pattern at bass frequencies.

A dipole speaker could be two speakers, in a box, one on the front and one on the back. Both speakers are IN PHASE which tends to produce omnipole or omnidirectional radiation at bass frequencies.

I believe if you add bipolar and omnidirectional radiation you will get a cardioid radiation pattern.
here is an interesting page
http://www.musicanddesign.com/u_frame.html

Regards Philip
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Old 5th July 2007, 03:18 AM   #4
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The confusion arises because both a Bipole & a Dipole radiate from both the front & the back of the "box".

In a dipole the rear radiation is out of phase with the front. This is most commonly seen in the form of an open baffle or planar speaker where 1 driver unit supplies both the front & rear radiation.

In a bipole the rear radiation is in phase with the front. This requires 2 drivers firing into a box.

dave
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Old 5th July 2007, 12:48 PM   #5
sreten is offline sreten  United Kingdom
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Hi, ]

Dipole comes from radio aerial theory, Bipolar from electrical theory.
I'd hazard a guess that Bipole is just an accepted marketing term.

/sreten.
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Old 5th July 2007, 06:39 PM   #6
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Quote:
Originally posted by planet10
The confusion arises because both a Bipole & a Dipole radiate from both the front & the back of the "box".

In a dipole the rear radiation is out of phase with the front. This is most commonly seen in the form of an open baffle or planar speaker where 1 driver unit supplies both the front & rear radiation.

In a bipole the rear radiation is in phase with the front. This requires 2 drivers firing into a box.

dave
I'm still not 100% sure why the specific prefix was chosen for each, but this is a much clearer description than the one I started with (for a start yours appears to be correct ) Thanks. Hopefully that will help a few others too!

Quote:
Originally posted by sreten
Hi, ]

Dipole comes from radio aerial theory, Bipolar from electrical theory.
I'd hazard a guess that Bipole is just an accepted marketing term.

/sreten.

Absolutely! Almost in stereo, i received the same response: I posted a similar rant on facebook, and a friend who did his PhD attaching aerials to seals was very excited at having the chance to explain it all to one of his friends Unsurprisingly another friend suggested I really shouldn't be allowed to be left alone with a computer anymore.

Quote:
Originally posted by footstony

here is an interesting page
http://www.musicanddesign.com/u_frame.html
[/B]
Philip, you're an absolute nuisance (joking ) You do realise that I can't ignore being sent things like that, and will now have to add another hour onto the day later tonight when I get home and intrigue gets the better of me again.
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