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Old 24th July 2004, 05:39 AM   #1
JinMTVT is offline JinMTVT  Canada
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Default Bipolar speaker configuration ... need info! accoustical pros and cons ?

My understanding of loudspeaker is coming together slowly!
Thanks to all of you ..

Yet after a few hours of search, i never found the answer to a question in here or elsewhere.
what i found is the "marketing" reasons why they use this arrangement, but never found the accoustical reasons.

So i would like to know what exactly are the benefits of a bipolar
"push-push" arrangement of drivers in an enclosure.
I've been using Mirage speakers for a tad over 3 years now,
all 3 of em beeing bipolar "omnipolar" systems.

Else than having way to many relfections in a small room
I have not been able to point the other advantages.
So that is what i would like to learn tonight from you

all in all.. what are the pros and cons ( and the implications toward deisgning the systems ) of Bipolar arrangement of drivers.

Also would appreciate pointers on the design itself,
sub, mid and high freq if there is differences or problems associated with each Vs bipolar

Beeing here with you guys ,

compare for me Bipolar and Dipolar configuration in terms of
accoustical performance

Thanks again all for your time and efforts !!
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Old 24th July 2004, 06:34 AM   #2
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hi

amongst other benefits -push pull reduces distortion

acts as a better piston to push air

and increases power handling of the drivers

suranjan

transducer design engineer
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Old 24th July 2004, 06:44 AM   #3
navin is offline navin  India
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i think we are talking push push here though.

dave (planet 10)'s site has a horde of info on push push (esp TLs).

u do get reduced distortion. in some desings the rear woofer is used to compensate for BSC so this also improves sensitivity.

also for the bass you get twice the ammount of volume or air displaced and hence a bit more low bass SPL capability.
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Old 24th July 2004, 10:42 AM   #4
SY is offline SY  United States
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Depends on the design. Bipolar operation can give a polar pattern which is closer to omni, if that's what's desired. It can have a psychoacoustic effect that some will find pleasant due to increased reverberant energy and a degree of comb-filtering of in-room response. Woofers can be braced one against the other to reduce reaction forces. Using bipolar in selected ranges can do things like equalize reverberant energy (e.g., the rear tweeter in some Snell designs) or to compensate for baffle spreading loss.

Like everything else, it's a design choice with tradeoffs, not some sort of panacea.
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Old 24th July 2004, 02:35 PM   #5
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I think most will agree that dipolar midrange is not a good idea for main speakers. It is probably more suitable for surrounds. The reason is that you are at the mercy of the room. The room will most certainly colour the sound and add its own signature. As mentioned, some may actually like this effect, but it is less accurate.

Bipole vs Dipole. Dipole will have less bass due to cancellation. For midrange, you might consider dipole with two sets of drivers facing in opposite directions for a surround speaker. You might also try this with bipoles. You can switch quickly by chaning the wiring.

However, for main speakers it is better to look into open baffle if you want dipole. This has a very different interaction with the room. With bipolar you are at the mercy of the room due to the way the signature of the room is imparted to the sound. With dipoles, one of their main strengths is the way they reduce room interaction, although it's not quite as simple as that.
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Old 24th July 2004, 04:12 PM   #6
Variac is offline Variac  United States
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It seems like the bi-pole speaker would always compensate for baffle step. Dave thinks so I believe.... Although I haven't seen measurements to prove this.

To rephrase another coment: Dipole will have less bass than bipole IF it isn't in an adequately sized open baffle (or in a very wide box the same size as the required open baffle I guess?)
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Old 24th July 2004, 04:21 PM   #7
JinMTVT is offline JinMTVT  Canada
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By baffle step, what do you guys mean exactly?
i am not familiar with the term ... thanks
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Old 24th July 2004, 05:12 PM   #8
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Quote:
Originally posted by Variac
It seems like the bi-pole speaker would always compensate for baffle step. Dave thinks so I believe.... Although I haven't seen measurements to prove this.

To rephrase another coment: Dipole will have less bass than bipole IF it isn't in an adequately sized open baffle (or in a very wide box the same size as the required open baffle I guess?)
The idea that a bipole would automatically have BSC would be true if the absorption if its output resulted in -3db above the point at which 3db bafflestep occurs.

re: dipoles and bass it depends on what you are comparing to. Even with a baffle suitably large, the output will at best equal a sealed box, but this will be less than a vented box. This is what fequal indicates, the point at which output is equal to a sealed box monopole.

Quote:
Originally posted by JinMTVT
By baffle step, what do you guys mean exactly?
i am not familiar with the term ... thanks
The baffle gives boost to the output above a certain point. For a typical tall floorstander with a 8" wide baffle, output above ~500 Hz will be +3db ... this is a gradual not a abrupt "baffle step." This point can be determined by the formula:

f-3 = 115/ baffle width (metres)

thus you need a baffle of 1m to get this f-3 point to 115 Hz.

Mostly this is dealt with in the crossover, where the midrange and treble above this point is attenuated. However, an alternative way with say a tweeter and a midbass is to add an idential midbass but roll it off above a certain point, which yields +3 db to the bass and lower midrange. This is called a 2.5 way design.

Here is a good article to describe it more fully.
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Old 24th July 2004, 07:18 PM   #9
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Quote:
Originally posted by Variac
It seems like the bi-pole speaker would always compensate for baffle step. Dave thinks so I believe.... Although I haven't seen measurements to prove this.
Click the image to open in full size.

Quote:
Originally posted by JinMTVT
By baffle step, what do you guys mean exactly?
i am not familiar with the term ...
http://www.t-linespeakers.org/tech/b...intro-bds.html
http://www.t-linespeakers.org/tech/b...tep/index.html

dave
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Old 24th July 2004, 08:01 PM   #10
Variac is offline Variac  United States
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Well, I guess I've seen measurements now!!!
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