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Multi-Way Conventional loudspeakers with crossovers

What is Time-Alignment
What is Time-Alignment
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Old 28th December 2017, 07:51 PM   #1
Michael Chua is offline Michael Chua  United States
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Default What is Time-Alignment

There seems to be some confusion as to what Time-Alignment is.

Simply put, it is the aligning of the woofer and tweeter acoustic phases at the crossover frequency.

If the two drivers are not aligned, the result is phase cancellations at the crossover region. When the woofer and tweeter are time-aligned, it will eliminate smearing and improve stereo imaging.

All Time-Aligned speakers like Thiel, Dunlavy and others do this. Sometimes, it's called Time-Coherence or Phase-Coherence. They all mean the same thing. A clean handover between the woofer and the tweeter. As an example, the illustrations below show a crossover frequency of 2kHz.

Click the image to open in full size.

Click the image to open in full size.

Time-Alignment doesn't mean 20Khz and 20Hz reach the ear at the same time. That is not possible with inductors and capacitors because one will introduce phase lag and the other phase lead.
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Old 28th December 2017, 08:11 PM   #2
andy2 is offline andy2  United States
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Quote:
Originally Posted by Michael Chua View Post
There seems to be some confusion as to what Time-Alignment is.

Simply put, it is the aligning of the woofer and tweeter acoustic phases at the crossover frequency.

If the two drivers are not aligned, the result is phase cancellations at the crossover region. When the woofer and tweeter are time-aligned, it will eliminate smearing and improve stereo imaging.

All Time-Aligned speakers like Thiel, Dunlavy and others do this. Sometimes, it's called Time-Coherence or Phase-Coherence. They all mean the same thing. A clean handover between the woofer and the tweeter. As an example, the illustrations below show a crossover frequency of 2kHz.

Click the image to open in full size.

Click the image to open in full size.

Time-Alignment doesn't mean 20Khz and 20Hz reach the ear at the same time. That is not possible with inductors and capacitors because one will introduce phase lag and the other phase lead.
That is a highly theoretical conception of "time aligned". In the real world, it's very difficult to get the tweeter and woofer to aligne perfectly. You could get them to "time aligned" at a specific frequency but not at "all frequencies". At the end, you have to compromise.
And by the way, "time aligned" is just one aspect of speaker design. There are all sorts of variables when it comes to the final results. Just having "time aligned" does not automatically mean you have a good sounding speakers.
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Old 28th December 2017, 08:14 PM   #3
globalplayer is offline globalplayer  Germany
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To align them perfectly you will need to know placement and the listening position beforehand.
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Old 28th December 2017, 08:26 PM   #4
nigelwright7557 is offline nigelwright7557  United Kingdom
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A Linkwitz Reilly 24db/octave active filter will give phase alignment.
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Old 28th December 2017, 08:29 PM   #5
Michael Chua is offline Michael Chua  United States
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Originally Posted by andy2 View Post
That is a highly theoretical conception of "time aligned". In the real world, it's very difficult to get the tweeter and woofer to aligne perfectly. You could get them to "time aligned" at a specific frequency but not at "all frequencies". At the end, you have to compromise.
And by the way, "time aligned" is just one aspect of speaker design. There are all sorts of variables when it comes to the final results. Just having "time aligned" does not automatically mean you have a good sounding speakers.
Yes, time alignment is not a guarantee of good sounding speakers. But if you have a pair of good sounding speakers, they will be even better when the woofer and tweeter are time-aligned.

Time alignment refers to aligning the acoustic phases at the crossover frequency. It does not mean all frequencies from 20Hz to 20kHz reach the ear at the same time. To do that, you'll have to use digital technology like FIR filters.
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Old 28th December 2017, 08:42 PM   #6
Michael Chua is offline Michael Chua  United States
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To align them perfectly you will need to know placement and the listening position beforehand.
Yes, it is a single point in space. Usually, time alignment is done on the tweeter axis with the mic on a stand 1 meter away. So, as long as you are exactly on the tweeter axis, you're fine. If you move left, right, up, down, it will not be perfectly aligned.

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Originally Posted by nigelwright7557 View Post
A Linkwitz Reilly 24db/octave active filter will give phase alignment.
It doesn't mean they will align. More often than not, they don't. This is because the acoustic centers of the woofer and tweeter are not aligned.
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Old 28th December 2017, 08:43 PM   #7
nigelwright7557 is offline nigelwright7557  United Kingdom
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Originally Posted by Michael Chua View Post

It doesn't mean they will align. More often than not, they don't. This is because the acoustic centers of the woofer and tweeter are not aligned.
But at least electrically they will align before you start worrying about the physical side. Its easier to work with one variable than two.
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Old 28th December 2017, 08:55 PM   #8
Michael Chua is offline Michael Chua  United States
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But at least electrically they will align before you start worrying about the physical side. Its easier to work with one variable than two.
Time alignment is acoustic time domain. Electrical phase is totally different.

Electrical phase is about power amplifiers. Power amps work best when the load is resistive. Unfortunately, a speaker with a crossover is a reactive load. This causes electrical phase to shift. When that happens, the power amp has to work harder. A speaker with minimal electrical phase shift is a friend to a power amplifier.
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Old 28th December 2017, 09:04 PM   #9
Michael Chua is offline Michael Chua  United States
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This is one of my speakers with good electrical phase. You can see there are no wild fluctuations at the crossover region.

Click the image to open in full size.
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Old 28th December 2017, 09:08 PM   #10
Fernando R is offline Fernando R  United States
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But at least electrically they will align before you start worrying about the physical side. Its easier to work with one variable than two.
Unfortunately, the real world does not know the difference between mechanical and electrical characteristics. In filter theory, they are the same. Therefore when a network such as an L/R is used which is electrically aligned, the mechanical side also needs to be aligned. As I think you are saying, you can treat both issues independently to arrive at your target


Typical asymmetric filters are a good case where two wrongs make a right. The filter's asymmetry compensates for the mechanical misalignment over the narrow crossover zone. You can't separate one from the other.
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