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Multi-Way Conventional loudspeakers with crossovers

An exercise in converting a speaker to time-phase coherent
An exercise in converting a speaker to time-phase coherent
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Old 27th November 2019, 08:18 AM   #21
TNT is offline TNT  Sweden
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Andy, you never defined your used terms. I'm not sure they are "industry standard". Maybe you would like to state them. They seem a bit overlapping to me... as they both use "time"..

# Time-Phase Coherence
# Time coincidence

//

PS. Aha, maybe Duelund was at B&O at the time?
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Old 27th November 2019, 02:33 PM   #22
john k... is offline john k...  United States
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Quote:
Originally Posted by andy2 View Post
I've been doing some simulation on how to convert a regular speaker to time-phase coherent. The software is Xsim which has enough basic stuffs for basic simulation.

But first let's get some terminology out of the way. The definitions use freq. and phase response so there won't be any ambiguity. I am sure different people might have different terminologies but with respect to what I did, here are three types of first order speaker, from easiest to hardest.

Here are three:
1. First order/No Time-Phase coherence: this speaker will use first electrical order, but there is no time-phase coherence. It will not be able to produce a proper step response. It's more or less conventional with the exception that it uses first order filters.

2. First order/Time-Phase Coherence, BUT NO "Time coincidence"
(which will be explained in #3).
This speaker will be able to produce a proper step response, BUT and an important BUT. It may not be able to produce an excess phase of 0 degree from say 50Hz to 20KHz. This means that the speaker, for example, may have a phase shift of 50 degree or more or could be a full 360 degree at 15KHz, but only 5 deg at 500Hz. That is its excess phase will vary especially at higher frequencies as the tweeter approaching 20KHz. John Atkinson would agree this speaker meets his definition of "Time-Phase Coherence" since it could produce a proper step response. My guess is most speakers that were measured by John Atkinson would fall into this category. I've seen some measurements done on Vandersteens speakers and I was like ... hmmm... I am not quite sure. But the most stringent definition is reserved for #3.

3. First order/Time-Phase Coherence AND Time-coincident: this is the most difficult definition for any speaker to meet. That is it has to be able to produce a proper step response like in #2, BUT it also has to be able to have a 0 degree of excess phase from 1Hz - 20KHz. In reality, no speaker will have absolutely 0 degree, but the variations should be very small. I believe Thiel claims that their speakers excess phase shift is only a few degrees (less than ten). To be honest, I am not sure many speakers in the entire history can meet this definition.

So to summarize, you have three distinct possibilities from easiest to hardest:
1. First order/No Time-Phase coherence
2. First order/Time-Phase coherence BUT NO "Time coincident"
3. First order/Time-Phase coherence AND "Time coincident" (the most stringent)
Excess phase is a manifestation of a pure time delay. It is irrelevant since once the wave form is launched bt a speaker there will be a propagation delay to the observation point (mic, listener, etc).

A truly Time and phase coherent speaker, DC to light, will have an excess phase response given as Phi(f) = 2Pi x f x Td where Td is the time delay between source and observation point.

Time coincident is meaning less. It appears to mean zero phase. If a speaker is time and phase coherent then it must be either linear phase or zero phase, relative to some reference position. Any linear (excess) phase component can be removed by changing the reference point rendering it time coincident. Thus, any time and phase coherent speaker must also be time consistent relative to some reference point. That reference point is the effective source of the sound wave.

Regardless of the crossover, the low and high frequency cut offs of the speaker mean that even if the crossover is phase and time coherent, the speaker can not be, as it will, at best, have the minimum phase response associated with the speakers band width once the excess phase is removed. This can only be corrected by precondition the input signal using digital technology.

No speaker can produce a proper step response because doing so requires response from infinity to DC. Lack of response above, say 20k Hz alters the rise time of the step. Lack of low frequency response gives rise tot he typical tail of a speaker's step. Thus the best any speaker can do, even with digital phase correction, is to reproduce those frequency components of the step response within it's band width time coherently. Two speakers being time coherent can, at best, mean that they are equal distance for the observation point. That is, event reproduced by one speaker arrives at the observation point at the same time as the even from the other speaker. I would presume any definition of time coincident used by speaker manufactures is a made up definition.

A better test of time coherency is a square wave since the low frequency components can be limited to be within the speakers band width by choosing the frequency of the square wave to be above the speakers low frequency cut off.

The bottom line is that speakers have two kinds of phase, nonlinear phase and excess phase. Excess phase can always be reduced to zero leaving only the speakers nonlinear phase. The goal of achieving a perfect speaker is to eliminate the nonlinear phase.
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Last edited by john k...; 27th November 2019 at 02:38 PM.
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Old 27th November 2019, 09:34 PM   #23
andy2 is offline andy2  United States
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I did a quick measurement of one version of the time-phase coherent. Attached are the simulated results and measurements. There is a bit of a dip on the step response at the initial spike up. Probably due to the diffraction at around 5.5KHz. It's also there on the simulated step response. Notice the min. phase is at about +30 degrees worse case at around 5.5KHz. Will probably need to optimize the baffle to minimize the diffraction. Maybe it's better to not use step baffle, but have the baffle tilted to align the driver acoustic centers.
Attached Images
File Type: jpg setupPic.jpg (203.5 KB, 252 views)
File Type: png simulated.png (57.1 KB, 252 views)
File Type: png Freq_Phase_Measured.png (33.9 KB, 250 views)
File Type: png Step_Measured_1.png (30.4 KB, 249 views)

Last edited by andy2; 27th November 2019 at 09:41 PM.
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Old 27th November 2019, 11:52 PM   #24
andy2 is offline andy2  United States
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Here is a 2-way setup but the tweeter is inverted polarity while the woofer polarity is positive. The step response shows at first the tweeter goes negative with respect to the woofer. Also on the freq/phase plot, you can see the phase shift at 20KHz is -180 degree with respect to, say at 200Hz, because the tweeter is inverted polarity. On a time-phase coherent speaker, the phase shift should be very close to zero.
Attached Images
File Type: png Simulated_InvertedTweeter.png (53.6 KB, 244 views)
File Type: png StepResponseInverted_Measured.png (21.2 KB, 64 views)
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Old 28th November 2019, 12:35 AM   #25
john k... is offline john k...  United States
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You might be interested in this project I did back around 2001.

TP3-project1

Later, in 2004, I redesigned the speaker using PC based digital crossovers.

TP-3W-D-1
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Old 28th November 2019, 12:36 AM   #26
andy2 is offline andy2  United States
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Here is the reason the proponents of time-phase coherent/time-coincident think there is an advantage over conventional speakers with drivers having different polarity.

Below is a simulation of a three-way, with the tweeter and woofer in positive polarity, but the mid is inverted polarity. You can see from the phase plot, at 20KHz, the tweeter is a full 360 degree ahead ( 360 degree phase leads) of the low frequency. The step response shows that the initial high frequencies arrive at your ears ahead of the low frequencies in the time domain.

For example, when the drum is hit, the high frequencies arrives at your ears first, then the low frequencies arrive later. In the real world, they should arrive at your ears at the same time.

The question is can our hearing notice the phase shift at 20KHz? For example, at 20KHz, the 360 degree phase shift equates to about .05milli second. Could you hear that the drum high frequencies arrive at about .05msec ahead of the drum low frequencies? Some people think we could. People have told me that they can hear the difference in time-phase coherent speakers especially in the treble region. I suppose this question will be debated and different people will have their own opinions.
Attached Images
File Type: png ThreeWayInverted.png (53.6 KB, 70 views)
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Old 28th November 2019, 01:38 AM   #27
andy2 is offline andy2  United States
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Quote:
Originally Posted by TNT View Post
A very clever design. Does anyone have a xover schematic of an actual "Uni Phase design"? It seems like it has the advantage of using a 2nd order electrical filter which does not stress out the drivers, but having the advantage of no overall system phase shift.

The "B&O" still fundamentally uses 2nd order filters which have a different time-domain response vs first order filters, therefore the "B&O" will probably "excite" the drivers differently vs. a first order filter and hence the resulting non-linear distortions. Anyway, it's getting a bit too theoretical from here though.

Last edited by andy2; 28th November 2019 at 01:51 AM.
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Old 28th November 2019, 02:09 AM   #28
andy2 is offline andy2  United States
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Here are a series of square waveform being simulated from the xover.
Attached Images
File Type: png System.png (60.5 KB, 68 views)
File Type: png At500Hz.png (9.4 KB, 41 views)
File Type: png At700Hz.png (8.6 KB, 26 views)
File Type: png At1000Hz.png (9.1 KB, 26 views)
File Type: png At1500Hz.png (9.0 KB, 24 views)
File Type: png At2000Hz.png (9.7 KB, 21 views)
File Type: png At3000Hz.png (9.2 KB, 16 views)
File Type: png At5000Hz.png (9.4 KB, 22 views)

Last edited by andy2; 28th November 2019 at 02:16 AM.
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Old 28th November 2019, 02:25 AM   #29
andy2 is offline andy2  United States
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FYI, here's the xover of the Thiel CS2.4 which is a first order, time-phase coherent design.
Thiel CS2.4 xover schematics
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Old 28th November 2019, 03:09 AM   #30
AllenB is online now AllenB  Australia
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Quote:
Originally Posted by john k... View Post
You might be interested in this project I did back around 2001.
I was doing similar in the '90s. At one point I was using your site for inspiration
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