It depends on the type of crossover. In a first order crossover, both drivers are connected
in positive absolute phase, and the sum is unity. This is not true for most crossover types.
Not sure this answers Pegaso's question.
I think what means is 'Provided the crossover topology demands inversion of one driver why is usually the tweeter inverted rather than the woofer?'.
At least that is how I read his post.
Perhaps nothing more than convention, it could be done either way as long as one driver is inverted relative to the other if the cross-over topology requires it. In some cases it may simply be to maintain compatibility with other speaker systems used in a mixed system? (Not that I haven't run into speaker systems from different brands that were phase inverted relative one to the other, but not a common issue.)
Usually for symmetric 2nd order XO's like LR2 or BW2, one of the drivers needs to be 180deg out of phase for the summation to be flat. Since the woofer moves a lot of air, people think that the compression wave corresponding to a woofer pushing out like a kick drum membrane is more realistic than a rarefaction (suction or creating a low pressure) of the membrane moving away. Supposedly the tweeter can be backwards and less noticeable. For some topologies like 1st order or Harsch (BW4 and BES2 with delay) both drivers are same phase. However, a quasi transient perfect XO like Harsch will sound more realistic with percussion sounds when the tweeter is same direction as woofer.
Yes this is the question, in LR2 is normal to see that be reverse the polarity of the tweeter and I did not know why.
I understand that to have the best sound is better to design a crossover to try to keep the same polarity of both drivers in two ways.
If rarefaction isn't seen as common due to theoretical opposite direction thought processes, then why do we have inverting amplifiers?
FWIW- I've inverted the woofer in cases where I could easier access it than the tweeter. It worked just fine and 'looked' just fine.
The impulse measurement is not inverted this way either.
Later,
Wolf
FWIW- I've inverted the woofer in cases where I could easier access it than the tweeter. It worked just fine and 'looked' just fine.
The impulse measurement is not inverted this way either.
Later,
Wolf
Of course I know this about the impulse. You can flip the polarity of the entire speaker if it vexes you. I was just stating there is nothing wrong with doing it this way.
Wolf
Not saying you did not know, but it vexes me either way as I have, quasi-transient perfect speakers, and for me, they both need to be in the same direction, and positive rising edge to sound realistic. There is a difference, and most people don't know because they have not heard a transient perfect speaker before as they are rare. To hear one correctly reproduce the sound of a plucked guitar, piano, drums (rimshots, bongos), stand up bass, etc. it sounds like the instrument rather than the sound of one played on a speaker. Once you hear the difference, you can't go back. It's like having 120 Hz 1080p HD and being told 60Hz 720i is just as good. It's not.
For many years both JBL and Tannoy woofers were designed to move into the cab with positive voltage. Both claimed that is was so absolute phase is maintained from mic to speaker ie the speaker cone would move the same way as the mic diaphragm.
Both eventually relented in the '80s I think and started making woofers with the same polarity as everybody else.
Maybe so. Absolute phase is audible, for me anyway, particularly on percussion instruments, including piano.
Since the woofer usually covers most of the range, that driver would be best kept correct.
With some crossovers, you will get a deep measured notch at the crossover frequency unless the tweeter
polarity is inverted and that looks bad, even though it's relatively benign to the ear (at least for me) in practice.
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This is an interesting subject. There's no such thing as absolute phase in real life, you could stand on any side of a piano and depending on where you stand you'd be hit by positive or negative waves. IOW, one could say that a drummer always heard his kick out of phase - which is really not. I'm not even sure that studies showed that it can't be detected. But I really might be recalling incorrectly.
The standard (is that AES?) nowadays is that a positive voltage pushes the woofer forward. If the XO puts the 2 drivers 180 out of phase then maybe they swap the tweeter to keep positive voltage pushing out the woofer? Just a hypothesis, IDK.
I think it probably has to do with the impact. The bass notes are big. If you invert that, you'd be creating a situation where you suck first, then blow. From a purely measurement perspective, it makes no difference which you invert, but from which driver makes the biggest impact (literally) it's the woofer so it's the one I'm least happy about inverting.
I don't know of any real research into the subject though.
Sadly, I've also never heard a speaker that was time-aligned make that much of a difference to me. Having great integration however did. The last speakers I heard that were time aligned were the Mundorf kit speakers. Sadly in a terrible room with terrible music and even worse electronics. Before that I listened to Thiel's and some B&W's which are arguably kind of sort of time aligned.
Are the Wilson Sasha's in the category? If so then count those too.
Perhaps I will experiment with this later with my current speakers and a DSP crossover.
Best,
Erik
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A lot of misinformation and conjecture in this thread.
Reversing the polarity of the tweeter simply changes the phase. What is phase? Phase indicates the relative time arrival of frequencies. Note the word 'relative'. If you had flat phase, it means all frequencies are arriving simultaneously. Crossovers introduce phase warps. Higher the order of the crossover, greater the change in phase.
In a typical two-way, you are looking for phase overlap between the two drivers in the crossover region. Remember that the total output at a frequency near the crossover is the vector sum of the woofer and tweeter output. So, if you have the tweeter output 180 degree out of phase with the woofer, you will get perfect cancellation. If it's in phase, meaning the phase responses of the two drivers overlap, you will get a perfect sum. If it's somewhere in between, you'll get non-perfect addition and subtraction as you move through the crossover region.
Ideally, you want the phase response of the drivers to overlap through the crossover region, maybe until the drivers are down by 24-30 db. This will give you a nice sum. Of course, as you get off-axis, you might notice a dip near the crossover. This means that at that frequency, your drivers are out of phase. This happens because relative to your measurement point, the drivers center to center distance has changed. For example, if you measure up, then the tweeter is closer than the woofer. This will cause the tweeter frequencies to arrive earlier than the woofer frequencies at this measurement point, i.e., a change in phase overlap.
So, when you reverse the polarity of the tweeter, all you are looking for is whether the phase overlap through the crossover region is better. Flipping the polarity changes the phase by 180 degrees at the crossover frequency -- kind of a crude tool, but a tool to improve the crossover nevertheless. Crossovers and other filters on the other hand can change the phase in smaller increments.
Flipping the polarity has nothing to do with compression and rarefaction of waves. If you experience a better "transient" response by flipping the polarity, what you are really experiencing is a better phase overlap, which results in a flatter response (less undulations through the crossover). If you have excellent phase overlap between the drivers, it can sound really good-- like a single driver -- and it will be almost impossible to tell where the crossover is.
EDIT: A point about waves. Normally, we need several cycles of a frequency before we can tell what frequency it is. Basically, we need to hear the frequency for a while before knowing its identity. When a drum is struck or a piano note is struck, it's not like only a single cycle is emitted. Hundreds of cycles are emitted. For example, you can fit 20 cycles of 20 Hz in one second. With some software one could experiment how many cycles at 20 Hz are needed before one can discern that it is 20 Hz (and not 30 Hz or 40 Hz and so on).
Reversing the polarity of the tweeter simply changes the phase. What is phase? Phase indicates the relative time arrival of frequencies. Note the word 'relative'. If you had flat phase, it means all frequencies are arriving simultaneously. Crossovers introduce phase warps. Higher the order of the crossover, greater the change in phase.
In a typical two-way, you are looking for phase overlap between the two drivers in the crossover region. Remember that the total output at a frequency near the crossover is the vector sum of the woofer and tweeter output. So, if you have the tweeter output 180 degree out of phase with the woofer, you will get perfect cancellation. If it's in phase, meaning the phase responses of the two drivers overlap, you will get a perfect sum. If it's somewhere in between, you'll get non-perfect addition and subtraction as you move through the crossover region.
Ideally, you want the phase response of the drivers to overlap through the crossover region, maybe until the drivers are down by 24-30 db. This will give you a nice sum. Of course, as you get off-axis, you might notice a dip near the crossover. This means that at that frequency, your drivers are out of phase. This happens because relative to your measurement point, the drivers center to center distance has changed. For example, if you measure up, then the tweeter is closer than the woofer. This will cause the tweeter frequencies to arrive earlier than the woofer frequencies at this measurement point, i.e., a change in phase overlap.
So, when you reverse the polarity of the tweeter, all you are looking for is whether the phase overlap through the crossover region is better. Flipping the polarity changes the phase by 180 degrees at the crossover frequency -- kind of a crude tool, but a tool to improve the crossover nevertheless. Crossovers and other filters on the other hand can change the phase in smaller increments.
Flipping the polarity has nothing to do with compression and rarefaction of waves. If you experience a better "transient" response by flipping the polarity, what you are really experiencing is a better phase overlap, which results in a flatter response (less undulations through the crossover). If you have excellent phase overlap between the drivers, it can sound really good-- like a single driver -- and it will be almost impossible to tell where the crossover is.
EDIT: A point about waves. Normally, we need several cycles of a frequency before we can tell what frequency it is. Basically, we need to hear the frequency for a while before knowing its identity. When a drum is struck or a piano note is struck, it's not like only a single cycle is emitted. Hundreds of cycles are emitted. For example, you can fit 20 cycles of 20 Hz in one second. With some software one could experiment how many cycles at 20 Hz are needed before one can discern that it is 20 Hz (and not 30 Hz or 40 Hz and so on).
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If you put negative of amp to positive terminal of woofer, a signal intended to cause driver to push out on kick drum will suck in. This is not how the kick drum feels or sounds. The 180 deg phase flip has everything to do with rarefaction vs compression. If it did not why do we have positive and negative labeled terminals on drivers and amps and signal input cables?
X, absolute polarity simply doesn't matter. There are black and red labels so that the polarity between speakers is the same. You don't want to wire the left speaker one way and the right speaker the opposite way. But if you flip both it will sound exactly the same. Give it a try. Ask someone else to make the change (or no change) and you try to see if you can hear a difference (i.e., do it blind) .
There are many things that happen to the signal since it gets recorded. You are not going to achieve anything by adjusting polarity one way or another.
There are many things that happen to the signal since it gets recorded. You are not going to achieve anything by adjusting polarity one way or another.
Quite possible
I guess I wasn't responding to the OP. Low pass crossovers for woofers usually move the acoustic center of the woofer further back (it's already behind the tweeter, usually) and move the acoustic center of the tweeter forward. So, flipping the polarity would move it backward for the tweeter. I don't think it matters which one you flip. You will get the same result as far as I know.
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