Those are very interesting results. Push-pull usually cancels odd-order harmonics.
I have tried with three different setups. The first was a cheap 10 inch driver one, the second a better 12 inch one, and the third an exemplary pair of 12 inch drivers. With the high quality drivers I noticed no difference.
I have tried with three different setups. The first was a cheap 10 inch driver one, the second a better 12 inch one, and the third an exemplary pair of 12 inch drivers. With the high quality drivers I noticed no difference.
Are you looking for a push/pull or compound woofer (Isobaric) designs? Each is a different.
The push/pull will cancel odd-order problems and significantly reduce driver distortion but the Vas will be twice the volume. You’ll get a +3dB for a parallel setup and -3dB for a series connection. The drivers can be used with sealed and vented boxes.
The compound woofer system will have half the Vas, impedance will be half in a parallel setup, and sensitivity will be the same. The great plus over the push/pull is the box is half the size.
To say it simply, design a speaker system. For a push/pull, double the size if you are going to use a push/pull design and expect twice (3dB) output. For compound woofer, half the size and expect an increase or decrease of 3dB output depending on your connection.
In my compound woofer, I’m not worried about the loss of 3dB because amplifier power is cheap. In reality, it may have gained or exceed the output of a push/pull because my DIY has specifically designed ports and I’ve corner loaded the sub- acoustically coupling two walls and floor. Of course a push/pull placed in the corner would have more output but be very big and noticeable- too noticeable for me.
With my setup, I can get away with using only a 200W amp. It’s designed for a maximum flat output which gives it a very low frequency response and very tight bass. The tradeoff for maximum flat alignment is a slightly larger box. It is more then enough- there is enough bass so I have to drop the output considerably using the controls in the subwoofer amp. The box is very impressive when it makes itself known. When it was first hooked up, it took days to find all the rattling stuff around the house!
Of course the one disadvantage to a push/pull or compound woofer is that you have to buy two woofers to make it work. Because of the extra cost, my friends would never go for it even though it is a noticeably superior sounding system. But my family has enjoyed the tight and low bass sounds from my CW for over 10 years, and still going, so spread the cost of the extra woofer over the years and you’ll see its been cheap and fun sounds.
What are you looking for?
The push/pull will cancel odd-order problems and significantly reduce driver distortion but the Vas will be twice the volume. You’ll get a +3dB for a parallel setup and -3dB for a series connection. The drivers can be used with sealed and vented boxes.
The compound woofer system will have half the Vas, impedance will be half in a parallel setup, and sensitivity will be the same. The great plus over the push/pull is the box is half the size.
To say it simply, design a speaker system. For a push/pull, double the size if you are going to use a push/pull design and expect twice (3dB) output. For compound woofer, half the size and expect an increase or decrease of 3dB output depending on your connection.
In my compound woofer, I’m not worried about the loss of 3dB because amplifier power is cheap. In reality, it may have gained or exceed the output of a push/pull because my DIY has specifically designed ports and I’ve corner loaded the sub- acoustically coupling two walls and floor. Of course a push/pull placed in the corner would have more output but be very big and noticeable- too noticeable for me.
With my setup, I can get away with using only a 200W amp. It’s designed for a maximum flat output which gives it a very low frequency response and very tight bass. The tradeoff for maximum flat alignment is a slightly larger box. It is more then enough- there is enough bass so I have to drop the output considerably using the controls in the subwoofer amp. The box is very impressive when it makes itself known. When it was first hooked up, it took days to find all the rattling stuff around the house!
Of course the one disadvantage to a push/pull or compound woofer is that you have to buy two woofers to make it work. Because of the extra cost, my friends would never go for it even though it is a noticeably superior sounding system. But my family has enjoyed the tight and low bass sounds from my CW for over 10 years, and still going, so spread the cost of the extra woofer over the years and you’ll see its been cheap and fun sounds.
What are you looking for?
Push-pull cancels even harmonics, not odd.
When arranged in a slot similar to the thumbnail sketch shown, some 3hd reduction occurs due to roll-off of the higher frequencies, and some reduction occurs in frequency modulation distortion.
http://www.linkwitzlab.com/images/graphics/d_woof1.gif
"In short, I had originally asked Eminence to investigate the possibility of putting a shorting ring into a subwoofer to reduce harmonic distortion. This would be used as the motor for high-performance subwoofer designs. JBL has been very successful with this technology and even though the distortion reduction works best above 100Hz, they have been able to reduce distortion at subwoofer frequencies as well. So I had hoped Eminence might be able to build an improved subwoofer too.
Eminence found that they were unable to get significant distortion reduction below 150Hz from a shorting ring. The reason is pretty simple - The shorting ring works like a transformer winding, and it has to inductively couple enough energy to create a magnetic field large enough to offset the difference in force caused by flux modulation. As frequency goes down, this becomes harder and harder to do and the size of the ring becomes prohibitively large. The volume displaced by the ring makes magnet size smaller so more magnet has to be added to compensate and the requirements become a vicious cycle. So there just isn't enough "meat" to make a good flux stabilized subwoofer.
Another solution presents itself, and that is the push-pull configuration. There are a handful of ways to do this, and all involve basically running a two voice coils in a magnet or two similar magnets, each going opposite directions but summing to form positive pressure. The idea is that when one drive is made slightly weaker by flux modulation, the other drive is made stronger. The net effect is that symmetrical pressure is generated by a symmetrical drive signal, something that doesn't happen on a single drive unit because of flux modulation.
The easiest way to accomplish this is simply to use two similar speakers, each driven in opposite polarity. Output is then taken from the front side of one and the rear side of the other, so that pressure differentials are generated. What essentially occurs is one driver is stronger on each half-cycle, and the other is weaker. On the other half-cycle, the "strong side" flips to the other driver. The net result is pneumatic symmetry.
This push-pull configuration is easy to implement because it can be accomplished with standard drivers. It works best at low frequencies with drivers physically close together, especially when operated in a common chamber. The further apart they are, the less coupling is provided. So the push-pull arrangement is very well suited to subwoofers whereas shorting rings are better suited for midbass, midrange and higher frequency drivers."
When arranged in a slot similar to the thumbnail sketch shown, some 3hd reduction occurs due to roll-off of the higher frequencies, and some reduction occurs in frequency modulation distortion.
http://www.linkwitzlab.com/images/graphics/d_woof1.gif
"In short, I had originally asked Eminence to investigate the possibility of putting a shorting ring into a subwoofer to reduce harmonic distortion. This would be used as the motor for high-performance subwoofer designs. JBL has been very successful with this technology and even though the distortion reduction works best above 100Hz, they have been able to reduce distortion at subwoofer frequencies as well. So I had hoped Eminence might be able to build an improved subwoofer too.
Eminence found that they were unable to get significant distortion reduction below 150Hz from a shorting ring. The reason is pretty simple - The shorting ring works like a transformer winding, and it has to inductively couple enough energy to create a magnetic field large enough to offset the difference in force caused by flux modulation. As frequency goes down, this becomes harder and harder to do and the size of the ring becomes prohibitively large. The volume displaced by the ring makes magnet size smaller so more magnet has to be added to compensate and the requirements become a vicious cycle. So there just isn't enough "meat" to make a good flux stabilized subwoofer.
Another solution presents itself, and that is the push-pull configuration. There are a handful of ways to do this, and all involve basically running a two voice coils in a magnet or two similar magnets, each going opposite directions but summing to form positive pressure. The idea is that when one drive is made slightly weaker by flux modulation, the other drive is made stronger. The net effect is that symmetrical pressure is generated by a symmetrical drive signal, something that doesn't happen on a single drive unit because of flux modulation.
The easiest way to accomplish this is simply to use two similar speakers, each driven in opposite polarity. Output is then taken from the front side of one and the rear side of the other, so that pressure differentials are generated. What essentially occurs is one driver is stronger on each half-cycle, and the other is weaker. On the other half-cycle, the "strong side" flips to the other driver. The net result is pneumatic symmetry.
This push-pull configuration is easy to implement because it can be accomplished with standard drivers. It works best at low frequencies with drivers physically close together, especially when operated in a common chamber. The further apart they are, the less coupling is provided. So the push-pull arrangement is very well suited to subwoofers whereas shorting rings are better suited for midbass, midrange and higher frequency drivers."
DJK I apologise, it's was a while since I looked at push-pull and it does indeed cancel even harmonics in speakers. It's push-pull output stages that cancel odd-order.
However, I still stand by my own findings that with very high quality drivers the non-linearities are pretty small anyway so the gains offered by push-pull with regard to cancellation are minimal.
However, I still stand by my own findings that with very high quality drivers the non-linearities are pretty small anyway so the gains offered by push-pull with regard to cancellation are minimal.
"It's push-pull output stages that cancel odd-order."
Some quotes from:
http://www.vac-amps.com/no_se_amps.html
"In a... push-pull circuit, there is a natural cancellation of even-order harmonic distortion products. "
"Note that a push-pull circuit has no significant ability to cancel odd-order distortion products. "
"excess 2nd harmonic distortion.... sound(s) somewhat full, mushy, or thick, even on instruments that should be clean and fast."
And some more from Wayne Parham:
"(With) two woofers in use, it makes sense to orient them so they cancel distortion. One could argue that the distortion is euphonic or they could argue that it is not all that audible. We've all heard those arguments about distortion in subwoofers over the years. But if we're willing to compromise ourselves with those kinds of arguments, why bother making improvements at all? We could all have just settled with 1970's gear and called it good."
And from:
http://www.teresaudio.com/haven/subs/subs.html
"A variation I almost didn't try was mounting one of the woofers backwards (with the magnet facing out) and then wire the drivers out of phase. The theory is that woofer cone movement is not perfectly linear. In response to a symetrical sine wave the outward motion of the cone does not match the inward movement. By mounting the drivers front to back and wiring out of phase the non-linearities cancel out. I figured that with a high quality driver and limited excursion that the cancelation effects would not be audible. Boy was I ever wrong! The bass was notably cleaner and controlled with lots of slam. Subjectively there seemed to be a little less bass which is a clear indication of less distortion. After hearing the difference I would never consider any other topology than out-of-phase push-pull. It is more than a little odd looking but it fits with my non-conventional theme. "
Some quotes from:
http://www.vac-amps.com/no_se_amps.html
"In a... push-pull circuit, there is a natural cancellation of even-order harmonic distortion products. "
"Note that a push-pull circuit has no significant ability to cancel odd-order distortion products. "
"excess 2nd harmonic distortion.... sound(s) somewhat full, mushy, or thick, even on instruments that should be clean and fast."
And some more from Wayne Parham:
"(With) two woofers in use, it makes sense to orient them so they cancel distortion. One could argue that the distortion is euphonic or they could argue that it is not all that audible. We've all heard those arguments about distortion in subwoofers over the years. But if we're willing to compromise ourselves with those kinds of arguments, why bother making improvements at all? We could all have just settled with 1970's gear and called it good."
And from:
http://www.teresaudio.com/haven/subs/subs.html
"A variation I almost didn't try was mounting one of the woofers backwards (with the magnet facing out) and then wire the drivers out of phase. The theory is that woofer cone movement is not perfectly linear. In response to a symetrical sine wave the outward motion of the cone does not match the inward movement. By mounting the drivers front to back and wiring out of phase the non-linearities cancel out. I figured that with a high quality driver and limited excursion that the cancelation effects would not be audible. Boy was I ever wrong! The bass was notably cleaner and controlled with lots of slam. Subjectively there seemed to be a little less bass which is a clear indication of less distortion. After hearing the difference I would never consider any other topology than out-of-phase push-pull. It is more than a little odd looking but it fits with my non-conventional theme. "
Commercial Isobarik design
http://www.horninghybrid.com/
Tommy Hørning use 4x8" bas-drivers in Isobarik and gets 30 Hz -3dB in the speaker called Aristoteles.
The bigger system Eufrodite use 8x8" drivers. No frequency response given.
Hørning claims that his bass design using Isobarik is way better than his former bass horns (which by them self sounds fantastic in my experience).
Using WinISD I've simulated a bass system based on Isobarik using 4 cheap 8" Peerless drivers.
I get -3 dB at 31 Hz and around 200 Hz. Cone movement is less than 0.5 mm down to 31 Hz! Very impressive IMO.
http://www.horninghybrid.com/
Tommy Hørning use 4x8" bas-drivers in Isobarik and gets 30 Hz -3dB in the speaker called Aristoteles.
The bigger system Eufrodite use 8x8" drivers. No frequency response given.
Hørning claims that his bass design using Isobarik is way better than his former bass horns (which by them self sounds fantastic in my experience).
Using WinISD I've simulated a bass system based on Isobarik using 4 cheap 8" Peerless drivers.
I get -3 dB at 31 Hz and around 200 Hz. Cone movement is less than 0.5 mm down to 31 Hz! Very impressive IMO.
the simulators are not the problem.
It's us users that can't interpret the results.
It's exactly the same with using computers to calculate anything critical. The user must be able to cross check the result manually to ensure the software is predicting sensible numbers. This is demanded in civil and structural engineering. We don't want any more of our bridges falling down due to incompetent design engineers.
It's us users that can't interpret the results.
It's exactly the same with using computers to calculate anything critical. The user must be able to cross check the result manually to ensure the software is predicting sensible numbers. This is demanded in civil and structural engineering. We don't want any more of our bridges falling down due to incompetent design engineers.
Regarding odd/even harmonic cancellation, these two cases can occur:
1. The transfer function is prefectly symmetric, ie if there is a flaw in the linearity on the positive half, there is an identical flaw on the negative side of opposite polarity. In this case, the non-linearities will generate no odd order harmonics. This is the case with isobaric mounting of loudspeakers, assuming that all nonlinearities originate from the drivers.
2. If the positive and negative half of the transfer function are perfectly linear, but have different gains, the non-linearity will generate no even order harmonics. This type of non-linearity can occur in push-pull output stages of amplifiers, but there are also other sources of distortion. Actually I would say that it is not very typical that the gains in the two halves are significantly different.
These are the two archetypical types of transfer functions that "cancel" odd and even order harmonics, respectively. I suppose that this has lead to the (over-)simplification that isobaric speakers lack even order harmonics and that push-pull stages lack odd order harmonics.
1. The transfer function is prefectly symmetric, ie if there is a flaw in the linearity on the positive half, there is an identical flaw on the negative side of opposite polarity. In this case, the non-linearities will generate no odd order harmonics. This is the case with isobaric mounting of loudspeakers, assuming that all nonlinearities originate from the drivers.
2. If the positive and negative half of the transfer function are perfectly linear, but have different gains, the non-linearity will generate no even order harmonics. This type of non-linearity can occur in push-pull output stages of amplifiers, but there are also other sources of distortion. Actually I would say that it is not very typical that the gains in the two halves are significantly different.
These are the two archetypical types of transfer functions that "cancel" odd and even order harmonics, respectively. I suppose that this has lead to the (over-)simplification that isobaric speakers lack even order harmonics and that push-pull stages lack odd order harmonics.
An externally hosted image should be here but it was not working when we last tested it.
Here's part of the description on Push-Pull drivers from danmarx.org
Compound ~ Push/Pull Dual Drivers
"Two drivers share an acoustic volume of air within a single enclosure. The best way to take advantage of this alignment is to mount one driver facing outwards with the other driver inverted and facing inwards. The drivers are then wired so that they are electrically out of phase while remaining mechanically still in phase with one another. and variations."
My question is ... what is gained by mounting one speaker facing inwards? For the sake of simplicity ... and neatness, why not have both speakers mounted facing outwards, as shown below.
Thanks in advance,
Glenn
Compound ~ Push/Pull Dual Drivers
"Two drivers share an acoustic volume of air within a single enclosure. The best way to take advantage of this alignment is to mount one driver facing outwards with the other driver inverted and facing inwards. The drivers are then wired so that they are electrically out of phase while remaining mechanically still in phase with one another. and variations."
An externally hosted image should be here but it was not working when we last tested it.
My question is ... what is gained by mounting one speaker facing inwards? For the sake of simplicity ... and neatness, why not have both speakers mounted facing outwards, as shown below.
An externally hosted image should be here but it was not working when we last tested it.
Thanks in advance,
Glenn
GlennME said:
The main advantage is that the transfer function for the drivers becomes symmetrical (see my blue curve above), and that this causes even order distortion from the drivers to be cancelled.
I think that the first time I saw this was on Audio Pro's early subwoofers using ACE-bass. This technology is particularly sensitive to non-linearities of the voice coil inductance, and distortion decreased dramatically at high-ish frequencies when one driver was turned backwards.
For normal driving (without the ACE-bass technology) the gain is less, but still there.
I posted this link under a related thread. I'll post it here again:
http://www.musicanddesign.com/Isobaric.html
http://www.musicanddesign.com/Isobaric.html
john k... said:
Interesting simulations...
Do you know if anyone has measured this on a real system? I could imagine that the result depends quite a bit on how the actual nonlinearity is implemented, in particular how well the nonlinearity of the woofer matches and possibly cancels the non-linearity of the air.
Also, it seems as if he puts all of the non-linearity in Cms, in real life also Bl and Le depends on the cone excursion.
... but I agree that the cancellation probably not is perfect, since the two drivers operate under slightly different conditions. The question is if it is still lower than for the single driver.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.