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What is Time-Alignment
What is Time-Alignment
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Old 3rd January 2018, 04:14 PM   #141
scottjoplin is offline scottjoplin  Wales
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Pretty concise description only doesn't phase alignment simply mean that two or more waveforms are in phase, the frequency doesn't change? I think this is what you meant but it didn't quite come out like that . Having re-read your post with a different emphasis I see this is what you are saying more clearly. I was tempted to delete this post, but, what the hell, someone else may have made the same mistake as me
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Old 3rd January 2018, 04:38 PM   #142
ernperkins is offline ernperkins  United States
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You could certainly add Duelund and John Kreskovsky (user johnk here, see his musicanddesign.com website) to that list. John spent a lot of time pursuing transient perfect passive crossovers and produced several different passive topologies to implement them.
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Old 3rd January 2018, 05:27 PM   #143
wesayso is offline wesayso  Netherlands
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Well, I get the impression Michael did not pursue a transient response here. He was facing a problem and got himself a solution by finding the crossover topology that best solved the time difference between both drivers.
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Old 3rd January 2018, 05:48 PM   #144
kimmosto is offline kimmosto  Finland
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Quote:
Originally Posted by ernperkins View Post
...transient perfect...
Yes, that too. We have several possibilities to make quite close to timing properties of acoustical 1st order. For example with Bessel style low pass combined to lower order high pass. Simulator with optimizer makes adapting by f, Q and delay in few seconds without extreme math skills, design tables or white papers. Directivity and power response problems could increase, but that's one thing to control while designing crossover. Timing is not everything.
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Old 3rd January 2018, 06:49 PM   #145
Michael Chua is offline Michael Chua  United States
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Quote:
Originally Posted by wesayso View Post
Well, I get the impression Michael did not pursue a transient response here. He was facing a problem and got himself a solution by finding the crossover topology that best solved the time difference between both drivers.
I appreciate everyone's input.

Hi wesayso

It was never my intention to work on the transient response. My take on that is without DSP, there's very little one can do about it. Transducers are not like transistors where the reaction is instanteous. Perhaps one can work on the crossover to improve the transient but that's likely at the cost of something else.

I was focusing solely on the concept of time alignment. Before the age of DSP, time align means the sound from the woofer and the tweeter reach the mic at the same time. This happens at the acoustic crossover point where it is not only phase aligned but no time delay between the woofer and the tweeter. This crossover can be any freq. Unless I'm mistaken, that's what time-alignment means.

Conventional methods of achieving that is by vertically aligning the acoustic centers of the drivers, using a step to displace the woofer or tilting the front baffle. I did not use any of these methods but I believe I achieved the same objective.
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Old 3rd January 2018, 07:04 PM   #146
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What is Time-Alignment
Quote:
Originally Posted by Michael Chua View Post
the transient response. My take on that is without DSP, there's very little one can do about it.
Build a WAW (formerly a FAST). Fairly easy to choose drivers with extension well beyond the XO, arrangement so that no centre-to-centre is greater than a quarter wave-length, and use a 1st order XO. XO is fairly low (150-400 Hz typically), with a more equable distribution of octave-to-octave duties.

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Old 3rd January 2018, 07:12 PM   #147
scottjoplin is offline scottjoplin  Wales
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Quote:
Originally Posted by Michael Chua View Post
Conventional methods of achieving that is by vertically aligning the acoustic centers of the drivers, using a step to displace the woofer or tilting the front baffle. I did not use any of these methods but I believe I achieved the same objective.
I think the conventional method is by including a phase shift at the crossover frequency
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Old 3rd January 2018, 07:32 PM   #148
wesayso is offline wesayso  Netherlands
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Quote:
Originally Posted by Michael Chua View Post
Click the image to open in full size.
FR of Speaker
The above FR plot shows a lot of room influence. This would make it pretty hard to show the phase result without using some form of gating.

I'd love to see this same plot with a frequency dependent window of about 6 cycles on it, which also shows the phase. Not to look at the FR, but to see trends in the phase.

Another (more traditional) way of viewing what's happening could be to set gating at 3 ms, or just before the first clear reflection (would be close to that 3 ms, judging some earlier zoomed out plots).

Quote:
Originally Posted by Michael Chua View Post
Click the image to open in full size.
Impulse of Speaker
The impulse shows a negative peak before moving to the positive side. It could indicate the high frequency part is inverted, could you tell us the polarity of the drivers? If it isn't inverted we would need a harder look to see what that's causing that negative spike. All I can tell you, it isn't REW that's causing it. First arrival of energy is inverted. Sometimes something else in the signal chain can cause weird looking IR's, even if it is only affecting frequencies up high. Knowing the true polarity of the drivers would help.

We also see some pretty early secondary spikes after the positive peak scaled to 100% by REW.

Quote:
Originally Posted by Michael Chua View Post
Click the image to open in full size.
Step of Speaker
The STEP supports what we see in the IR. I've never looked at this combination of filters before to know what an ideal IR and STEP should look like. I'd first like to know the polarity of the drivers used, maybe see the IR from each driver separately (with filters on) would help too.
Especially the tweeter with filters on.

We will need to get this graph in here too, showing the acoustical slopes of the separate drivers.
Click the image to open in full size.

The tweeter shows a dip, at 10K in every plot we've seen so far. That's why I'd like to see it separately, with phase and an IR.
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Last edited by wesayso; 3rd January 2018 at 07:58 PM.
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Old 3rd January 2018, 08:16 PM   #149
wesayso is offline wesayso  Netherlands
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Quote:
Originally Posted by Michael Chua View Post
I appreciate everyone's input.

Hi wesayso

It was never my intention to work on the transient response. My take on that is without DSP, there's very little one can do about it. Transducers are not like transistors where the reaction is instanteous. Perhaps one can work on the crossover to improve the transient but that's likely at the cost of something else.

I was focusing solely on the concept of time alignment. Before the age of DSP, time align means the sound from the woofer and the tweeter reach the mic at the same time. This happens at the acoustic crossover point where it is not only phase aligned but no time delay between the woofer and the tweeter. This crossover can be any freq. Unless I'm mistaken, that's what time-alignment means.

Conventional methods of achieving that is by vertically aligning the acoustic centers of the drivers, using a step to displace the woofer or tilting the front baffle. I did not use any of these methods but I believe I achieved the same objective.
I think more speakers have been created without a stepped or slanted baffle that with one of these features. That does not mean their developer did not watch the hand over between the drivers. Looking for phase alignment between the drivers at it's crossover point. This is where most "named" crossovers originate from.
As kimmosto said, if we take the response of each driver (with proper timing) into a capable simulation package we can choose the best crossover point and slope and make sure there is phase overlap between the drivers at the crossover. Sometimes this takes inverting one of the drivers, it all depends on the choices one makes.

The frequency response is the first factor, responsible for what we hear by far. However the power response does play a big part to, as we won't hear direct sound only, at our listening spot in the most common places they are used. (like a living room)
Each choice we make in the crossover will determine several factors. For instance, I've already posted a picture showing the difference of a speaker, measured at tweeter height at half a meter compared to a hypothetical listening distance of 2.5 meter.
If we would pick our design axis between the tweeter and woofer, concentrate on getting it right on that axis, it would still hold up better at larger distances. Why? because we wouldn't change the geometry between those two positions as much as we do by keeping that design axis on the tweeter level. So the closer the tweeter and woofer are, the less difference we would get between ear to tweeter and ear to woofer, makes sense?
So even little details like this has an influence on the end result we get at our listening spot.
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Last edited by wesayso; 3rd January 2018 at 08:20 PM.
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Old 3rd January 2018, 11:42 PM   #150
Michael Chua is offline Michael Chua  United States
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Quote:
Originally Posted by wesayso View Post
The above FR plot shows a lot of room influence. This would make it pretty hard to show the phase result without using some form of gating.

I'd love to see this same plot with a frequency dependent window of about 6 cycles on it, which also shows the phase. Not to look at the FR, but to see trends in the phase.

Another (more traditional) way of viewing what's happening could be to set gating at 3 ms, or just before the first clear reflection (would be close to that 3 ms, judging some earlier zoomed out plots).
Is this what you meant. It's at 3ms with Minimum Phase.

Click the image to open in full size.

Quote:
We will need to get this graph in here too, showing the acoustical slopes of the separate drivers.
Click the image to open in full size.

The tweeter shows a dip, at 10K in every plot we've seen so far. That's why I'd like to see it separately, with phase and an IR.
My tweeter is presently surface mounted. The dip at 10k on the tweeter is due to edge diffraction between the tweeter faceplate and the baffle. It will disappear when I flush mount the tweeter.

I'm afraid I may not be able to respond as quickly as I would like. My internet line is affected by the coming storm. To make matters worse, my pc is still mis-behaving. Nonetheless, I shall try my best. I appreciate your help.
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