Bipole,dipole, we all scream for two drivers

john dozier · 18th April 2011, 11:20 PM

There is apparently some confusion over these terms. If I place drivers on opposite sides of enclosure and wire them out of phase, what do I have. Simple minds want to know. Is it a good idea and does it have any advantages over standard both drivers in phase. Thanks

wakibaki · 18th April 2011, 11:30 PM

Where's the ice cream?

w

Richard Ellis · 18th April 2011, 11:38 PM

If you were to take two drivers wired out of phase on opposing sides of an enclosure you would get what is called an acoustic short circuit. There is another term that eludes me...You will get bass cancelation, as one driver moves forward creating a positive pressure wave, at the same time there will be negative wave at the rear......the net effect.......one driver will suck the life out of bass frequencies, nulling the output. The particular frequency will vary according to a host of variables, one being the distance one driver to the other.
Placing two drivers face to face on a single faceplate with one wired out of phase is the Isobaric Push-Pull. A pocket of air resides between the two drivers, the net effect is an improvement in non-linearities, and an enclosure that can be one-half size.

__________________________________________________ _______Rick........

john dozier · 18th April 2011, 11:53 PM

I ate the ice cream while thinking about this conumdrum. It seems to me that the driver moving back would re-inforce the driver moving out. Am I getting dottery in my old age? In phase the drivers would compress the air in the box, and moving out of phase there would be no compression. Would someone chime in who knows what is going on here and if my reasoning is correct or faulty. Regards

Richard Ellis · 19th April 2011, 12:08 AM

If the two drivers are in phase moving together there is still the "Air-Spring" as in a sealed system.....the air inside serving to damp out the resonant frequencies as per the "Air Suspension" type...designing the system....with all the math implied.
Out of phase a driver will see no Air-Spring and will likely move the cone farther than it should (without the damping) damaging it & sounding just plain bad.

__________________________________________________ _____Rick........

18Hurts · 19th April 2011, 01:05 AM

If you wired two drivers out of phase and mounted one on the front and other on the back--I figure it would act like a single driver on an open baffle. Would it sound better or worse than a dipole open baffle? They are coupled together in push-pull but...

planet10 · 19th April 2011, 04:08 AM

Consider the acoustic phase of the driver. If they are the same, you have a bipole. If they aren't you have a dipole.

As described by the OP, if both drivers are face out (magnets nside the box), a bipole, if one driver is face-in, a bipole.

dave

TerryO · 19th April 2011, 04:25 AM

I'll take a stab at this...why not?
If the drivers are wired out of phase and closely coupled, you'll probably get a bit less distortion. If they're on opposite sides of an enclosure they operate in a dipole fashion and there will be a null at an angle of around 90 degrees to the cabinet. OTOH, If they were wired in-phase and mounted on opposite sides, you'd have a Bi-pole and the enclosure would need twice the volume of what a single driver would need. BTW, in a di-pole configuration I believe the enclose would only need the displacement needed for a single driver, plus whatever the volume that is actually displaced by the second driver.

I'm probably wrong, but that's my take.

Best Regards,
TerryO

18Hurts · 19th April 2011, 04:39 AM

So if you put a woofer on the front, a woofer in the back out of phase it would require the space of one woofer. The remaining two sides can be used for passive radiators to make a .... mess?

TerryO · 19th April 2011, 05:11 AM

Quote:

Originally Posted by 18Hurts

So if you put a woofer on the front, a woofer in the back out of phase it would require the space of one woofer. The remaining two sides can be used for passive radiators to make a .... mess?

If the two driver are moving the same volume of air in a push-pull configuration, I'm not sure that a Passive radiator would work at all. But, just the same, every time I start to feel that I've got a handle on all this stuff, someone comes along.....

Best Regards,
TerryO

18th April 2011, 11:20 PM	#1
john dozier diyAudio Member Join Date: Dec 2010 Location: columbia sc	Bipole,dipole, we all scream for two drivers There is apparently some confusion over these terms. If I place drivers on opposite sides of enclosure and wire them out of phase, what do I have. Simple minds want to know. Is it a good idea and does it have any advantages over standard both drivers in phase. Thanks

19th April 2011, 04:08 AM	#7
planet10 frugal-phile(tm) diyAudio Moderator Join Date: Oct 2001 Location: Victoria, BC, NA, Sol III Blog Entries: 4	Consider the acoustic phase of the driver. If they are the same, you have a bipole. If they aren't you have a dipole. As described by the OP, if both drivers are face out (magnets nside the box), a bipole, if one driver is face-in, a bipole. dave __________________ community sites t-linespeakers.org, frugal-horn.com ........ commercial site planet10-HiFi p10-hifi forum here at diyA

19th April 2011, 04:25 AM	#8
TerryO diyAudio Member Join Date: Nov 2002 Location: Seattle,Wash.	I'll take a stab at this...why not? If the drivers are wired out of phase and closely coupled, you'll probably get a bit less distortion. If they're on opposite sides of an enclosure they operate in a dipole fashion and there will be a null at an angle of around 90 degrees to the cabinet. OTOH, If they were wired in-phase and mounted on opposite sides, you'd have a Bi-pole and the enclosure would need twice the volume of what a single driver would need. BTW, in a di-pole configuration I believe the enclose would only need the displacement needed for a single driver, plus whatever the volume that is actually displaced by the second driver. I'm probably wrong, but that's my take. Best Regards, TerryO __________________ "If you have to ask why, then you're probably on the right track." quote from Terry Olson's DIYaudio Forum application

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18th April 2011, 11:30 PM	#2
wakibaki Banned Join Date: Jan 2008 Blog Entries: 2	Where's the ice cream? w

18th April 2011, 11:38 PM	#3
Richard Ellis diyAudio Member Join Date: Sep 2006 Location: Mar del Plata, a BIG seasonal getaway city, can see the Ocean from our residence.	If you were to take two drivers wired out of phase on opposing sides of an enclosure you would get what is called an acoustic short circuit. There is another term that eludes me...You will get bass cancelation, as one driver moves forward creating a positive pressure wave, at the same time there will be negative wave at the rear......the net effect.......one driver will suck the life out of bass frequencies, nulling the output. The particular frequency will vary according to a host of variables, one being the distance one driver to the other. Placing two drivers face to face on a single faceplate with one wired out of phase is the Isobaric Push-Pull. A pocket of air resides between the two drivers, the net effect is an improvement in non-linearities, and an enclosure that can be one-half size. __________________________________________________ _______Rick........

18th April 2011, 11:53 PM	#4
john dozier diyAudio Member Join Date: Dec 2010 Location: columbia sc	I ate the ice cream while thinking about this conumdrum. It seems to me that the driver moving back would re-inforce the driver moving out. Am I getting dottery in my old age? In phase the drivers would compress the air in the box, and moving out of phase there would be no compression. Would someone chime in who knows what is going on here and if my reasoning is correct or faulty. Regards

19th April 2011, 12:08 AM	#5
Richard Ellis diyAudio Member Join Date: Sep 2006 Location: Mar del Plata, a BIG seasonal getaway city, can see the Ocean from our residence.	If the two drivers are in phase moving together there is still the "Air-Spring" as in a sealed system.....the air inside serving to damp out the resonant frequencies as per the "Air Suspension" type...designing the system....with all the math implied. Out of phase a driver will see no Air-Spring and will likely move the cone farther than it should (without the damping) damaging it & sounding just plain bad. __________________________________________________ _____Rick........

19th April 2011, 01:05 AM	#6
18Hurts diyAudio Member Join Date: Nov 2010	If you wired two drivers out of phase and mounted one on the front and other on the back--I figure it would act like a single driver on an open baffle. Would it sound better or worse than a dipole open baffle? They are coupled together in push-pull but...

19th April 2011, 04:39 AM	#9
18Hurts diyAudio Member Join Date: Nov 2010	So if you put a woofer on the front, a woofer in the back out of phase it would require the space of one woofer. The remaining two sides can be used for passive radiators to make a .... mess?

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