Time alignment

Jeff Fritz

[Industry Expert]
Jun 7, 2010
433
0
0
#1
Hi guys,

I often see mention on the forums about various speakers being time aligned due to slanted baffles, adjustable modules, etc. Most of these speakers are anything but time aligned.

To verify if a speaker is time aligned, you want to look at the step response. For instance, look at this Dunlavy:

http://www.stereophile.com/content/dunlavy-audio-laboratories-sc-iv-loudspeaker-measurements

The output of the drivers arrives at the microphone simultaneously -- it is a time-aligned design. Stereophile uses an impulse response to derive the step response and therefore is a good source for verifying this information.
 
Aug 25, 2010
949
0
16
Destiny
#2
Hello Jeff

OK that's true very few speakers are time aligned. The real question is does it matter??

Rob
 

rockitman

Member Sponsor
Sep 20, 2011
6,872
1
38
Northern NY
#4
Wilson X-2's and Maxx 3's are time aligned. I would imagine so is Alexia. It does make a difference as these wilson speakers can be adjusted optimally for distance back and ear height. Most speakers can not be adjusted in this way.
 

cjfrbw

Active Member
Apr 20, 2010
2,145
1
38
Pleasanton, CA
#5
Can't remember exactly, but I think it was Linkwiz who stated that if he had his druthers, he would choose phase coherence over strict time alignment.
 

Mark Seaton

WBF Technical Expert (Speaker & Acoustics)
May 21, 2010
319
2
18
42
Chicago, IL
www.seatonsound.net
#6
Hi guys,

I often see mention on the forums about various speakers being time aligned due to slanted baffles, adjustable modules, etc. Most of these speakers are anything but time aligned.

To verify if a speaker is time aligned, you want to look at the step response. For instance, look at this Dunlavy:

http://www.stereophile.com/content/dunlavy-audio-laboratories-sc-iv-loudspeaker-measurements

The output of the drivers arrives at the microphone simultaneously -- it is a time-aligned design. Stereophile uses an impulse response to derive the step response and therefore is a good source for verifying this information.
Claims related to "time" are most certainly some of the biggest abuses and loosest definitions. Figure 5 in the linked Dunlavy measurements is the most telling. IMO the arrival of the sound at/through the crossover is what matters much more as it also can play out in the spacial response. Put another way, the time discontinuities at crossover and then the phase response/group delay are what really matter. Of course you will get different sets of priorities from different designers.

In the past it was common to talk about "time alignment" in terms of aligning voice coils. Unfortunately this approach is thrown out the window once you add anything more than a 1st order crossover any low pass filter delays a driver. In most cases it simply made predictions with textbook crossovers easier as you were equidistant from the drivers. The fore-aft adjustment does certainly change interactions, but simple visual alignment is rarely optimized.
 

ack

VIP/Donor & WBF Founding Member
May 6, 2010
5,152
7
38
Boston, MA
#7
Isn't time alignment only meaningful at the listening position, and for which the drivers may have be adjusted back or forward, a la Ascendo, Wilson and some others?
 

Mark Seaton

WBF Technical Expert (Speaker & Acoustics)
May 21, 2010
319
2
18
42
Chicago, IL
www.seatonsound.net
#8
Isn't time alignment only meaningful at the listening position, and for which the drivers may have be adjusted back or forward, a la Ascendo, Wilson and some others?
What arrives at the listener's ears is what matters, although the terms often thrown around use no qualifications until a salesman has to make them up on the fly when asked. :rolleyes:
 

Mike Lavigne

Member Sponsor & WBF Founding Member
Apr 25, 2010
7,094
24
38
#9
when asked about time alignment relative to my MM7 main towers and bass towers here is what my speaker designer said;

While it is true that the lower frequencies have much larger waves, getting them to integrate in phase with the main tower is really not much of an issue when it comes to room placement, meaning you will not experience much if any wave cancellation. However, the wave launch, when having the towers perfectly time aligned to the listening chair is needed to provide a tighter presentation with greater impact, and also to align the harmonic series from top to bottom to produce a seamless and tonally lifelike presentation. This is not to say that you can not move the towers around, because you can.
so for him optimally you would have perfect alignment; but it's not essential, simply desired. there are other issues which may be more important in particular situations.
 

Jeff Fritz

[Industry Expert]
Jun 7, 2010
433
0
0
#10
Wilson X-2's and Maxx 3's are time aligned. I would imagine so is Alexia. It does make a difference as these wilson speakers can be adjusted optimally for distance back and ear height. Most speakers can not be adjusted in this way.
http://www.stereophile.com/content/wilson-audio-specialties-maxx-series-3-loudspeaker-measurements

http://www.stereophile.com/content/wilson-audio-sasha-wp-loudspeaker-measurements

On the other hand, this is:

http://www.stereophile.com/content/quad-reference-esl-2805-loudspeaker-measurements
 
#11
Hi guys,

I often see mention on the forums about various speakers being time aligned due to slanted baffles, adjustable modules, etc. Most of these speakers are anything but time aligned.

To verify if a speaker is time aligned, you want to look at the step response. For instance, look at this Dunlavy:

http://www.stereophile.com/content/dunlavy-audio-laboratories-sc-iv-loudspeaker-measurements

The output of the drivers arrives at the microphone simultaneously -- it is a time-aligned design. Stereophile uses an impulse response to derive the step response and therefore is a good source for verifying this information.
---- Hi Jeff,

You just pointed out a very good observation and fact. ...John Dunlavy was a smart man when designing loudspeakers.
It is sad that he had to give up because of economics.

I am very well aware of his great contributions to the world of 'Sound Coherence'.
...And most people (the vast majority of 'audiophiles') simply ignore this extremely important aspect.
Seldom we see this subject discussed at its true value in audio forums; it is more about ....

Anyway I'm glad that you brought this subject on the table here, and hope it will result in some very positive exchanges in this discussion, this thread. :b

Bob

* As time goes by and that members contribute here; I will eventually provide some great insights into this great and important subject; Sound Coherence.
And a big key word too; crossover.
 
Last edited:

Jeff Fritz

[Industry Expert]
Jun 7, 2010
433
0
0
#14
---- Alright, please, you and Amir, give us the full scoop regarding 'Time Alignment & Sound Coherence'. :b

...In your own words, if possible.
OK, here goes: most designers I've talked with feel that there are other, more important design criteria (low distortion, smooth off-axis dispersion, wide bandwidth, etc.). So, for instance, they would not use a 1st-order crossover due to the power handling issues that would normally cause. And having a driver operate far outside of its comfort zone (due to the low-order crossover) can cause other issues such as beaming, etc.

However, its adherents, such as the late Jim Thiel and the very-much-alive Richard Vandersteen, would counter that it is supremely important. The designs from those companies put time alignment as a primary concern though there is also energy put elsewhere, too. I have great respect for them both. In fact, other than the Dunlavy speakers of yore, and Green Mountain Audio, Thiel and Vandersteen are the only companies that produce dynamic-driver loudspeakers that I can think of that still do this.
 
#15
-- Good points there regarding 'distortion' and 'off-axis response'.

Any type of distortion is a killer for phase coherence.
And the wrong crossover's choosing doesn't help in any way either.

You just brought the 'power handling' issue in correlation with the crossover(s).
So the drivers are really important in their designs; in how they can handle certain audio frequencies better than others, and how you transfer the ones appropriately to their right 'owners'.

....
 

puroagave

Member Sponsor
Sep 30, 2011
1,297
0
0
#16
OK, here goes: most designers I've talked with feel that there are other, more important design criteria (low distortion, smooth off-axis dispersion, wide bandwidth, etc.). So, for instance, they would not use a 1st-order crossover due to the power handling issues that would normally cause. And having a driver operate far outside of its comfort zone (due to the low-order crossover) can cause other issues such as beaming, etc.

However, its adherents, such as the late Jim Thiel and the very-much-alive Richard Vandersteen, would counter that it is supremely important. The designs from those companies put time alignment as a primary concern though there is also energy put elsewhere, too. I have great respect for them both. In fact, other than the Dunlavy speakers of yore, and Green Mountain Audio, Thiel and Vandersteen are the only companies that produce dynamic-driver loudspeakers that I can think of that still do this.
i would put crossover-less designs like totem, epos and reference 3a to name a few, in the same group as speakers with 1st order networks. the theil 3.7s portrayal of depth and spatial cues is exemplary, maybe in part due to the concentric driver along with a 1st order network. the one issue that would stop me from buying a pair is the hot top end - even with tubes.
 

Gregadd

WBF Founding Member
Apr 20, 2010
6,434
1
38
Metro DC
#17
At the prices of todays' speakers, I see no reason why design criteria should be mutually exclusive.
 

TJE

New Member
Nov 13, 2012
30
0
0
#18
At the prices of todays' speakers, I see no reason why design criteria should be mutually exclusive.
Now that is funny. Design process is a constant battle between mutually exclusive goals. You have to ultimately choose priorities and make tradeoffs.

Normally any speaker crossover with a rolloff steeper than 6 dB per octave will warp phase and screw up time alignment. That's not a fatal flaw and most speaker designers accept this in return for the advantages of steeper slopes. There may be a high-tech solution with digital signal processing, but even in the digital realm you typically get the same phase warp as with analog crossovers. There is a software app called "phase arbitrator" designed to reverse the phase warping of a DSP crossover, and probably some other DSP tools with the same goal.
 

DonH50

Member Sponsor & WBF Technical Expert
Jun 23, 2010
3,527
3
38
Monument, CO
#19
Actually, there are plenty of passive filters that provide linear phase, but they are generally more complex and there are other trades, like slower roll-off, ripples in the pass and/or stop bands, etc.. Always compromises and trades...
 

Gregadd

WBF Founding Member
Apr 20, 2010
6,434
1
38
Metro DC
#20
Now that is funny.
Thanks. At least you get my humor. Some people call me names.
DesigYou would agree the more money the less trade offs? n process is a constant battle between mutually exclusive goals.
So you think the two are mutually exclusive?
You have to ultimately choose priorities and make trade offs.
Normally any speaker crossover with a roll off steeper than 6 dB per octave will warp phase and screw up time alignment. That's not a fatal flaw
(But not optimum?)
and most speaker designers accept this in return for the advantages of steeper slopes. There may be a high-tech solution with digital signal processing, but even in the digital realm you typically get the same phase warp as with analog crossovers. There is a software app called "phase arbitrator" designed to reverse the phase warping of a DSP crossover, and probably some other DSP tools with the same goal.
So there is a solution.
As i say man solves one problem and creates another.
Thanks for the education
 

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