dipole bass help

[amo]

Hi-

I have been looking into the dipole theory on SL's site, however, I can not find an answer to what seems to be a simple and fundemental question. When you place woofers in opposite directions, ie one magnet facing towards you and one away so that you cut down on even order harmonic distortion, then the two subs radiate 180 deg out of phase directly in front and behind the woofer. So how come these two woofers do not cancel each other out? Does this have to do with wavelenghths of lower frequencies? On the same note, how come mid-bass woofers are not placed this way? For example, if you look at the beethoven midbasses, they are facing the same way!

[Guss]

Inverted polarity???

[amo]

Originally posted by Guss
Inverted polarity???

I am pretty sure this is not the case, otherwise they would simply face the same way.

[catapult]

Reverse the wiring on one driver so both cones move toward the listener at the same time when the signal is applied. The two drivers are electrically out of phase but acoustically in phase.

Part of the even order distortion is due to mechanical differences between the cone moving forward and backward. Mounting and wiring them so one cone is moving toward the magnet while the other moves away from the magnet (but both are moving toward the listener) cancels that particular form of distortion.

[amo]

Originally posted by catapult
Reverse the wiring on one driver so both cones move toward the listener at the same time when the signal is applied. The two drivers are electrically out of phase but acoustically in phase.

By reversing the wiring on one of the drivers, both drivers become electrically in phase, not out. By having both cones move in the same direction, the entire reverse placement of one of the drivers is circumvented. In other words, instead of reversing one driver phisically and then reversing the wiring on that driver, why not just leave the river in place and leave the wiring as is. It will acomplish the same thing! There must be something else to it!

[catapult]

I can't explain it any more clearly than I did. Please reread. It's all there and there are no mistakes. Your "corrections" are incorrect.

[amo]

Originally posted by catapult
I can't explain it any more clearly than I did. Please reread. It's all there and there are no mistakes. Your "corrections" are incorrect.

Ok, I understand. Basically you are saying that in order to cut down on even order hormonic distortion, you need to get one cone moving toward the magnet and one away, but both in the same general direction. Thank you.

[catapult]

Hey amo,

My bad. I see you posted your reply before I finished editing my posting so what I wrote wasn't all that clear.

About why he doesn't do it with mids, it depends on the sound coming out of the front and back of the driver being about the same. It works at bass frequencies but, when you go higher, the basket and magnet make the frequency and polar response different on the back side of the driver. So at higher frequencies, you have to keep both cones facing forward -- lesser of two evils.

[Bose(o)]

It is simple actually, the waves do cancel, but only at certain frequencies and at certain areas. I know, for example, that my H-baffle woofer, will cancel at lower frequencies (150Hz. and below, perhaps lower) thus, producing the Dipolar effect. In this case a linear Dipole effect.

I believe that the Woofers are facing opposite direction and that they are wired appropriately (+ to + and - to -). Otherwise, what would the point of firing in opposing directions be? I also, like to consider the waves as propagating from the driver's cone thus, I can infer that the waves do not meet at an appropriate time in which cancellation from waves, directed from the front of the baffle, can occur. Meaning, that the amplitude, phase, and wavelength of the waves are not met. The requirements for cancellation which are of course: a (amplitude)=a, l(wavelength)=l and phase of b=- phase of c.

Another example: (I hope this one helps if not the latter)
picture a starting point. This is the baffle. Now draw a line of say, about 10 cm. This is the length of the room, and assume that for the time of the second wave to be propagated into the room that it is half this length. This means that by the time the first wave reflects off the wall, changing wave characteristics, that the second wave which has not been affected is at the half-way point. They meet, at 7.5cm. whilst not cancelling each other out. (At certain frequencies they may, but that's a diff. story that I don't have the answer too.)

Just my way of thinking of it...as catapult would say, mine is the acoustical aspect of phase.

[catapult]

I believe that the Woofers are facing opposite direction and that they are wired appropriately (+ to + and - to -). Otherwise, what would the point of firing in opposing directions be?

I'm not sure I followed what you are saying but the drivers should be wired like this in the Orion where each driver gets its own amp. Both drivers move the same direction relative to the listener. Excuse the crummy ascii art.

+______________+
amp1 ----- forward facing woofer
-______________-


+______________-
amp2 ----- rear facing woofer
-______________+