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Discussion in 'Speakers' started by matt_kelty, May 28, 2003.
I am a complete newb.... What is dipole and what is bipole.
A dipole is a speaker which has matched drivers facing in opposite (really about 90 degrees) directions. So in a 2-way setup you will have two midrange/woofer drivers set opposite each other and two tweeters set opposite each other. None of the speakers should be directed to the prime listening area. In addition the speakers should be out of phase with one another (unlike all other drivers in your system, which should all be ‘in-phase’).
All of this is so that the sound is diffuse, or not easy to localize. The object is to recreate a theater environment, where the surround effects seem to come from everywhere.
In some cases we get speakers that are termed adaptive dipoles, which simply means that the tweeters are not in-phase, but the woofers are. This is to provide more mid-range and bass (due to the drivers being in-phase) while allowing for the diffuse effect, as the tweeters (with their easily localized high frequencies) are still out-of-phase.
Some persons write bipole when they really mean dipole.
Some other people make a distinction of changing a dipole to a bipole by rewiring the all drivers to be ‘in-phase’. So in this case a bipole physically looks like a dipole but provides somewhat more localization due to all drivers being ‘in-phase’. There are some other reasons to rewire the drivers to be in-phase, depending on the exact location of the speakers in the listening area.
In this context the term for speakers, whose drivers are intended to provide a localized sound (or point source) is monopole.
Hope that this helps and did not make things more confusing.
One other point, dipoles/bipoles work best when they are wall-mounted, placed about two feet above the audience ears.
Thanks for the knowledge.... I am learning and this site has helped greatly.
I disagree, somewhat.
Def Tech makes bipolar mains, which are *not* best placed wall-mounted, 2ft above your ears. In this case, and actually in most cases, bipolars are meant to be used exactly like monopoles (monopoles = "direct radiators"), except that the bipolar radiation pattern adds room coloration to the sound. (Essentially, imaging *might* suffer, but you get a bigger or "fatter" sound.)
One advantage of bipolar speakers, is that the typical placement recommendation for monopoles is at least 3 ft from any wall or boundary. With bipolars, placement closer to a wall doesn't degrade the sound quality as much as it would with a direct radiator. Another advantage with bipoles, is that typically, the sweet spot is larger than for direct radiators. You get better sound in larger area in your HT. (But remember, imaging usually isn't as good as for monopoles.)
That's why I personally consider bipoles (and Mirage Omnipolars) *potentially* the best of all worlds for HT. You get large amounts of direct sound, like for a direct radiator, which is critical for imaging, but you also get a large component of diffusenes, which is sometimes preferred for the surrounds and rears.
I still consider direct radiators the best way to go for 2 ch stereo listening, but for HT, bipoles and omnipolars give them a run for their money.
I personally don't advise the use of dipoles, because yeah, you do get more diffuseness, but the freq response of any dipolar speaker is terrible, specifically because they are designed to use off-axis sound to get to the listener. Rolls off the high freqs, which in addition causes imaging to suffer too. IMO, as soundtrack producers use more spatially relevant info in the surrounds and rears, dipoles take away from what is being intended.
Over the years, I have used monopoles and bipoles as the mains in my system, and dipoles, bipoles, and monopoles as the surrround (and rear) speakers.
But you have to decide for yourself and your room what might work best.
psst... just as you noted that bipoles don't have to be 2ft above ear levels to the side of the listener, but could be used as mains, so can dipolar speakers.
Perhaps it is just me, but I would only use dipoles or bipoles as surround speakers. Certainly I’d never use dipoles as the mains (where you need localization).
My reference to mounting them two feet above ear level, was under the assumption that the surround speakers would be used to recreate a theatre effect (note the placement of side speakers in most theaters).
Kevin is entirely correct when he states that soundtracks are tending to include more spatial information, reducing the advantages that dipoles have as surrounds.
My dipoles (only the tweeters are out of phase) (used as surrounds in a 5.1 system) don’t appear to roll-off at the higher frequencies (I used AVIA and a Radio Shack SPL meter when I set them up). I have been interested to see how the sound might change if I rewire them to be true bipoles. I may put this project a bit higher on my priority list.
I’ve never heard omnipoles, so I can’t comment as to their characteristics. The concept is intriguing, however.
As a side note, with the adaptation, I’ve read several instances of people setting up their systems with monopoles as the front three, dipoles on the side and monopoles again at the rear.
As an aside, some of the most musical speakers out there are dipoles.
martin logan, magnepan, innersound, sound labs come to mind.
Lets not forget that there are other speaker manufacturers that utilize Dipole technology and call it Direct Reflect technology.
Bose with their better sound through research.
Lets also not forget the newest type of wave radiation technology found in the Danish UFO speakers. And what about omnipolar speakers such as that of Mirage.
Even though i've heard some of the best dipoles setups out there, I'm still a huge fan of monopole loudspeakers.
I recently purchased a pair of Polk FXi30s. They come with a bipole/dipole switch on them which makes it very convenient to test out either mode(it would actually be *very* convenient if they put the switch on the front of the speaker instead of the back). I have a small room(10x12) and the speakers are mounted about 3' above the listening position, directly to the sides(about 5'). In my limited testing, using the Patriot Superbit DVD (uh, the Mel Gibson Patriot), I found the dipole setting to provide a greater sense of "in-the-movie" than the bipole setting. For example-- on the scene where Mel ambushes the Brits in the forrest with his sons there was an incredible sense of space and realism. Everything wasn't right in my ear. My small room might make this setting preferable. Having said that, the bipole switch definetly produced a cleaner, more articulate sound. The trade off being the speaker didn't quite as effectively disappear into the room. This was only one movie and one scene. I'm going to try out a few more comparisons when I get some time.
It is not correct to say that Bose uses either Bipole OR Dipole. direct-reflecting Bose speakers can still be called multipolar, but they use such a distorted version of bipole radiation that it can't even really be called bipole.
I never really inspected Bose floorstanding speakers but I guess you are right in that they use multipolar radiation in most of their speakers.
However, Given that a Bose driver is a part of a long "waveform" tube that opens up on the other side... Isn't this using a similar principle as a dipole?
An example of such Bose speaker is the acoustic wave music system or whatever it's called.
Perhaps "waveguide" is closer related to bass reflex technology. Either way, the sound eminates from the same driver in 2 locations.