If you wire two woofers with the same polarity, but face them in opposite directions like back to back, what is the summed output for low frequencies on the woofers' axis? Would it be close to 0, because the woofers are moving in opposite directions? Would the 3D polar response be like ---8---, something like a donut?
Below the baffle step the speaker is essentially omni-polar, they act as if they were one big driver. At a frequency determined by the depth and width of the cabinet there is a dip (less deep if the cab is wider than deep), and above that you have a bipolar response.
dave
dave
My question is why would you want to do it?
If you face woofers back-to-back and wired them with opposite polarity, that would halve the Vas* so you could use a cabinet just over half the size. Now that is a tangible benefit.
The setup proposed gives no benefit, afaik.
Frank
* Dickason V. Loudspeaker Cookbook
If you face woofers back-to-back and wired them with opposite polarity, that would halve the Vas* so you could use a cabinet just over half the size. Now that is a tangible benefit.
The setup proposed gives no benefit, afaik.
Frank
* Dickason V. Loudspeaker Cookbook
Too much confusion
ISOBARIC loading is the type of loading that creates 1/2 VAS.
Loading 2 woofers in a common enclosure, magnet facing magnet, wired in phase acoustically, doubles the Vas. This can be a good thing if you can couple the drivers structurally, as it cancels vibration. An associated problem is, unless they are also very close to each other, there will be time delay smearing depending also on the frequency range covered.
As far as the OP's question- the answer is that the outputs cancel.
So again, why would you want to ?
ISOBARIC loading is the type of loading that creates 1/2 VAS.
Loading 2 woofers in a common enclosure, magnet facing magnet, wired in phase acoustically, doubles the Vas. This can be a good thing if you can couple the drivers structurally, as it cancels vibration. An associated problem is, unless they are also very close to each other, there will be time delay smearing depending also on the frequency range covered.
As far as the OP's question- the answer is that the outputs cancel.
So again, why would you want to ?
I think he just wants to know the radiation pattern that results from pushing or pulling the air in opposite directions at once. Beaming in both directions at higher freq, omni pressurizing the room at lower freq. Not "0" not "8" not donut.
Yes, Scott, Francec is describing isobaric.
But re: the original question, it's unclear whether he's asking about two dirvers in free air or connected with a box or tube. back-to-back is not clamshelled... I was assuming some box or tube between. But with both in free air, yes as soon as it got low enough not to beam it would cancel around each driver.
But re: the original question, it's unclear whether he's asking about two dirvers in free air or connected with a box or tube. back-to-back is not clamshelled... I was assuming some box or tube between. But with both in free air, yes as soon as it got low enough not to beam it would cancel around each driver.
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Wired like that you end up with a complex to build dipole (ie OB) without the no box benefit of an OB and twice the driver cost. Bass would be determined largely by the box width convolved with the IB FR.
You may well be thinking an isobarik pair. Not the question.
There are very large benefits to a push-push woofer, one of which is active force cancellation dramatically reducing the energy input into tha box. Everytime i can, i use woofers in this configuration.
dave
And depending on how far away you can position the loudspeakers from the rear wall, placing one driver on the front and one on the rear will compensate for baffle-step losses.
IE below the step the drivers act together as an omni source, reinforcing one another. Then, as frequency increases, the width of the cabinet 'prevents' the higher frequencies from the rear driver from meeting the front so there is no reinforcement. Of course in a real room the walls will reflect sound all over the place, so quite how effective this 'using the loudspeakers cabinet as the acoustic filter' would be in practise I do not know.
IE below the step the drivers act together as an omni source, reinforcing one another. Then, as frequency increases, the width of the cabinet 'prevents' the higher frequencies from the rear driver from meeting the front so there is no reinforcement. Of course in a real room the walls will reflect sound all over the place, so quite how effective this 'using the loudspeakers cabinet as the acoustic filter' would be in practise I do not know.
correction ( i have sumtimerz )
I have thought about this further: The outputs would not cancel completely.
As mentioned above, it would be a complicated di-pole.
If two drivers were in separate boxes, faced each other, and wired out of phase, the outputs would cancel.
Fun thread, yes ?
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I have thought about this further: The outputs would not cancel completely.
As mentioned above, it would be a complicated di-pole.
If two drivers were in separate boxes, faced each other, and wired out of phase, the outputs would cancel.
Fun thread, yes ?
Here is a simplified illustration of what (i understand) we are talking about.
Wired in phase there is no substantial difference in base performance (<< baffle-step) no matter what faces you put the woofers on. ie same as 2 woofers in phase on the front. Omnidirectional.
When as (illustrated) we approach baffle-step frequency, the on-axis FR of a face with a driver has a dip from cancellation, (>> bafflestep) you have the output of the front driver + room reflections of the back driver.
If you measure on axis of a face between the 2 woofers (ie the drivers are side mounted), there is no dip and FR starts falling with the 90+ degree dispersion of the driver (+ room)
dave
Wired in phase there is no substantial difference in base performance (<< baffle-step) no matter what faces you put the woofers on. ie same as 2 woofers in phase on the front. Omnidirectional.
When as (illustrated) we approach baffle-step frequency, the on-axis FR of a face with a driver has a dip from cancellation, (>> bafflestep) you have the output of the front driver + room reflections of the back driver.
If you measure on axis of a face between the 2 woofers (ie the drivers are side mounted), there is no dip and FR starts falling with the 90+ degree dispersion of the driver (+ room)
dave
Attachments
planet10 you got the right picture- almost. I'm planning on putting the woffers in OB, so that the side walls are open. Midrange and tweeter section will be above, and obviously a plank of wood at the bottom for the base. I want to use this on a desk, so no vibrations and minimal cabinet volume. I tried a sealed cabinet, but the dimensions were too big, so therefore OB. Frequencies will be from bass to around 500hz, so baffle effects are negligible. There will be a high pass to prevent over-excursion.
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Teledyne AR9 is built that way with the woofers in phase near the floor and the back wall. With the speakers carefully positioned and equalized they can produce extremely powerful low distortion bass, as good as I will likely ever want or need. Parts express now offeres a similar design.
Dayton Audio RS1202K 1000 Watt Dual 12" Subwoofer Kit 300-766
If I were building a high end system at the moment, I'd start with two of these.
Dayton Audio RS1202K 1000 Watt Dual 12" Subwoofer Kit 300-766
If I were building a high end system at the moment, I'd start with two of these.
12" is too wide on the desk. I was thinking 2 Dayton RS150T-8's on the bottom facing forward and back, and 2 Neo8's on the top. Any suggestions?
Take the sides away from what i'll drawn and all bets are off... you will get better performance from a single driver.
Do note, that if you want any bass, an OB will be "bigger" than a box.
dave
Why better from a single driver?
What does your second statement mean?
2 Dayton RS150T-8's can fit in a ~7" open cube, although they give up on bass pretty early.
What does your second statement mean?
2 Dayton RS150T-8's can fit in a ~7" open cube, although they give up on bass pretty early.
Nice, almost exactly my future sub build.
I would like to use those same subs for a front/back "bipole" style sealed box design with LT equalization. Oh yeah, and make that a stereo pair.
there was a classic KEF speaker that used this method with a port, which produced a cardioid pattern. The 104/2. Good sound.
You can see the speakers through that hole. The advantage is that it removes overall vibration, since the speaker cones' moments of force cancel out. To get optimum results, the speakers' chassis must be coupled, KEF achieved this with a metal pole, which you can also see through the hole.
Used without an enclosure and a port, I'm not sure what a donut shaped dispersion would be called, probably toroidal. I suspect that's what you would get with speakers facing each other.
You can see the speakers through that hole. The advantage is that it removes overall vibration, since the speaker cones' moments of force cancel out. To get optimum results, the speakers' chassis must be coupled, KEF achieved this with a metal pole, which you can also see through the hole.
Used without an enclosure and a port, I'm not sure what a donut shaped dispersion would be called, probably toroidal. I suspect that's what you would get with speakers facing each other.
Yes, good sound but not a cardiod pattern. This gave normal omni LF response.
Drivers where acoustically in phase, meaning positive volts moved both units into the center cavity. This had the cones moving in opposite directions (realative to "up") so the force canceling rod and compliant mounting greatly reduced cabinet vibration. Finally, since one woofer is moving into the magnet structure while the other is moving out, a great deal of even harmonic distortion is cancelled.
David S.
I tried modeling these two cases:
1. cones moving in opposite directions 7" apart
2. cones moving in same direction, 7" apart
and I'm getting a high pass at ~200hz for the first case. Does that really happen? For the second case, it's a flat response.
If I make them closer, the high pass point moves up; farther, and it moves down.
For both cases, polar response is the same at all angles.
Can someone verify what actually happens in real life?
1. cones moving in opposite directions 7" apart
2. cones moving in same direction, 7" apart
and I'm getting a high pass at ~200hz for the first case. Does that really happen? For the second case, it's a flat response.
If I make them closer, the high pass point moves up; farther, and it moves down.
For both cases, polar response is the same at all angles.
Can someone verify what actually happens in real life?
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