Dark Mower said:
Hmm... Relative to what?
If one compares the sensitivity of two drivers side-by-side* with a single driver in half the box volume it is + 6 dB for parallel connection and 0 dB for series coonnection.
There has been several threads on this in the past, and it is a bit counter-intuitive, but it comes from that the efficiency actually increases when two drivers are mounted close to one another (compared to the wavelength).
*non-isobaric, either normal monting or push-pull.
Svante said:
I've though of includeing BL and Le nonlinearity but it really won't change the result qualitatively. If the drivers were perfectly linear then you would still have the air compliance nonlinearity and it won't go away with PP mounting. The only way to get rid of the air nonlinearity is to load both sides of the driver identiaclly, i.e. no box.
I haven't seen measurement of any of this. Just statements based on the push-pull nature of the systems and conjecture to push-pull amplifiers. But the point I am making is that two identical woofer with the same BL, Le and Cms nonlinearity will only have cancellation of even order HD when mounted in PP format if there are no other sources of nonlinearity that won't "flip" with the PP mounting. With the advent of large excursion woofers in small boxes where air nonlinearity is a factor it doesn't work.
The premise is two identical nonlinear transfer functions which are summed. The basic compound woofer system comes close, provided air compliance is nearly linear (Sd * Xmax is very small compared to Vbox). But the isobaric case isn't even that as it is not a sum of two TF's. It's one nonlinear system coupled to another nonlinear system and the coupling is through a nonlinear element.
My dumb questions....
I have questions about push pull subwoofers when the woofers are mounted on opposite sides of the box. There are 2 scenarios as I see it for the cones to operate facing outward:
1. When the front and back woofers to work in electrical phase; i.e., when the front woofers are moving outward the back woofers do the same, thus resembling a monopole.
2. The front- and rear-firing woofers are working in opposite phase with each other; when the front woofers move outwards, the rear woofers move inwards. In this operating mode, the whole system works (sort-of) as a dipole system
What are the inherent advantages to each? With scenario 1 I can see force cancellation via opposing forces and lessening box coloration, though I do not think scenario 2 provides the same advantage.
I am having a hard time finding commercially available products like scenario 2, but it seems like a good option for mating with open baffle mids.
Any help is appreciated,
Chris
I have questions about push pull subwoofers when the woofers are mounted on opposite sides of the box. There are 2 scenarios as I see it for the cones to operate facing outward:
1. When the front and back woofers to work in electrical phase; i.e., when the front woofers are moving outward the back woofers do the same, thus resembling a monopole.
2. The front- and rear-firing woofers are working in opposite phase with each other; when the front woofers move outwards, the rear woofers move inwards. In this operating mode, the whole system works (sort-of) as a dipole system
What are the inherent advantages to each? With scenario 1 I can see force cancellation via opposing forces and lessening box coloration, though I do not think scenario 2 provides the same advantage.
I am having a hard time finding commercially available products like scenario 2, but it seems like a good option for mating with open baffle mids.
Any help is appreciated,
Chris
Push-pull info
I've compiled some information about push-pull drive over the years. Here are a couple posts with links, test data, etc:
I've compiled some information about push-pull drive over the years. Here are a couple posts with links, test data, etc:
Wayne, I've read the links and am interested in your views on PP for midbass, say 50-250 as I'm working on a HE, hifi design and am trying to select drivers. I can get some competent Eminences (3015) in pairs for the same price as another quality brand driver of the same size that has a single shorting ring. The PP would work into a small manifold (as small as I can make it) where the single driver would of course be baffle mounted. I'd simply buy and test, but I'd have no use for the loser. The PP will require a bit bigger box, but still possible.
Just looking for another data point.
djk, if you're reading, I'd be interested in your opinion too.
Just looking for another data point.
djk, if you're reading, I'd be interested in your opinion too.
Push-pull at various frequencies
Push-pull becomes less and less effective as frequency rises. The distortion reduction happens in summing, so coupling is important. Once you get above 100-200Hz, shorting rings start working so that might be a better option from midrange frequencies up.
But the bottom line on push-pull is coupling is your friend and asymmetry is not. You want the two drivers as close as possible. You also want the forward-facing air loads for the two drivers to be equal and the rear-facing air loads for the two drivers to be equal. Whatever configurations you can come up with that do this most effectively will work best.
Push-pull becomes less and less effective as frequency rises. The distortion reduction happens in summing, so coupling is important. Once you get above 100-200Hz, shorting rings start working so that might be a better option from midrange frequencies up.
But the bottom line on push-pull is coupling is your friend and asymmetry is not. You want the two drivers as close as possible. You also want the forward-facing air loads for the two drivers to be equal and the rear-facing air loads for the two drivers to be equal. Whatever configurations you can come up with that do this most effectively will work best.
Hi Parham
I have just finished to read about shorting rings. but i know that
the original drivers don't have it. i had know about faraday rings
in the scanspeak drivers. i don't know it works as the same.
Parham sometime i will design my isobaric speaker.i'm still use the drivers are not have the shorting rings. is it oche?(okay)
i will build like you said "close as possible" it's still be good.
I have just finished to read about shorting rings. but i know that
the original drivers don't have it. i had know about faraday rings
in the scanspeak drivers. i don't know it works as the same.
Parham sometime i will design my isobaric speaker.i'm still use the drivers are not have the shorting rings. is it oche?(okay)
i will build like you said "close as possible" it's still be good.
Attachments
Symmetry and coupling
You will get more benefit from push-pull drive when two identical speakers without shorting rings are used. Shorting rings reduce distortion, so drivers without them generate more distortion to remove. That's not to say having two distortion reduction mechanisms is a bad thing though.
The important things for push-pull drive are symmetry and coupling. You want both drivers to be matched and have the same acoustic load on their forward-facing sides and also the same on their rear-facing sides. You also want them to be as close as possible, within 1/4 wavelength at most.
You will get more benefit from push-pull drive when two identical speakers without shorting rings are used. Shorting rings reduce distortion, so drivers without them generate more distortion to remove. That's not to say having two distortion reduction mechanisms is a bad thing though.
The important things for push-pull drive are symmetry and coupling. You want both drivers to be matched and have the same acoustic load on their forward-facing sides and also the same on their rear-facing sides. You also want them to be as close as possible, within 1/4 wavelength at most.
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