phase/time alignment

rblnr

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May 3, 2010
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#1
Some speaker companies such as Vandersteen place heavy emphasis on time aligning the drivers so the signal from each arrives to the listener at the same time. Others, such as Revel, use a flat front baffle. There seems much less concern about lining up the voice coils/time alignment.

What are your thoughts/experiences on this?
 

JackD201

[WBF Founding Member]
Apr 21, 2010
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#2
There are some speakers with flat front baffles that are time aligned electrically via the crossover networks. I owned a pair of Von Schweikert VR-4 Gen IIIs that were done this way. The later generations with the sloped cabinets use mechanical time alignment. According to their designer going from electrical to mechanical added to transparency. Makes sense. Less parts in the way.
 

Gregadd

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Apr 20, 2010
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#3
Although the speed of sound varies it is about 13,200 inche or 1100 feet per second. At an average listening distance of 10 feet it would be a very small difference in arrival time. I am sure there is some research on the subject.
 

rblnr

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#4
Don't know any research specifically, but seem to recall some manufacturers such as Harman citing your argument in downplaying the importance of it. Other manufacturers however insist on the importance of time coherence. Off the top of my head KEF, Tannoy, Vandersteen, Ascendo, Reference 3A, Thiel, et al. Ascendo and some others allow for forward/back adjustment of the head unit to compensate for listening distance. Matters too whether the drivers are wired in phase.

I will say that in reviewing some passive ATC speakers and comparing them to my active ATC 20-2s that are time phased electrically, there certainly seems to be more soundstage depth w/the actives. Obviously, I can't isolate the reason for this.

On another note, single driver speakers almost always image well and have great timing. Again, this could be because of a number of reasons.
 

ggendel

New Member
May 26, 2010
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#6
I did some experiments with phase and time alignment many years ago. I built a pair of "pot-bellied" speakers so the voice-coils were in alignment. I loved the sound from these so much that they were my mainstay speakers for 20 years (living through two woofer upgrades). I also tried a phase alignment using fill-in speakers from B&O technical papers. These were put into a tower with a side-firing woofer. Bottom line was they stayed in my workshop because I never could get them to sound better than mediocre. The B&O speakers that I used as a reference would always blow them away, so it was probably my choice of components rather than basic concept.
 

DonH50

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Jun 23, 2010
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#7
Hey Gregadd -- the link did not work for me? I wanted to read it before commenting as I'm getting tired of pulling my feet out of my mouth. ;) - Don
 

Gregadd

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#8

RBFC

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Apr 20, 2010
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#9
Unity Audio used a capacitative network in their speaker crossovers to actually time align the various frequencies that propogated from each individual driver. Apparently, in a driver's bandwidth, the lowest frequencies arise from the periphery of the cone and the higher frequencies are emitted toward the center. So, in a cone configuration, there is time domain smearing from an individual driver. On top of this, the alignment of multiple drivers is the secondary (and possibly overlapping) source of misalignment. Imagine that a single frequency near the crossover frequency is played by both the midrange and the woofer (for example) so that there is smearing of the same note from two drivers.

Time domain smearing can be a complex problem, indeed.

While I don't know the exact science or implementation behind the crossover design in the Unity Audio PARMs I had, they sure sounded coherent. They also received rave reviews at CES, etc. Unity Audio founder Bob Grost, who now heads Cerious Technologies, was an engineer for sound cancellation in Corvettes for GM, if I'm correct. He's a good guy, and I hope he comes out with some statement projects for our community to examine.

Lee
 

DonH50

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Jun 23, 2010
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#10
Thanks!

Glad I kept my mouth shut. I never would have guessed 6 us was the threshold! Now, I suspect the culprit is the impact on the time response (which could also be expressed in the frequency domain) that in turn causes significant distortion. If you think about it, 6 us is a goodly amount of jitter, and in this case might it be loosely (OK, very loosely) compared to having a deterministic (signal-dependent, and coherent) jitter of that level? Actually, I would model it as a non-linear group delay (or phase error). Might have to piddle with that a bit.

Helps explain why planar speakers do well in tests, and why so many companies spend so much effort time-aligning the speaker systems (including the crossover networks) to maintain a coherent wavefront to the listener.
 

DonH50

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Jun 23, 2010
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#12
Listened to many, owned none (store I worked at carried them, but I stuck with my Maggies). It was an interesting attempt, and certainly offered one possible solution (physically placing the drivers to effect first-order time alignment, sort of). It's greatest gift may have been tohighlight and address the problem, leading other manufacturers to work on it (though many already were).
 
#13
I purchased mine from my Audio Store owner (they had been the owner's) back in 1977. About 1993 we set them up as bi-wire speakers (added a 2nd pair of terminals, changed the crossover, etc.). About 5 or 6 years ago they were totally rebuilt; I removied the super tweeters, and replaced all of the drivers with Dynaudio, Peerless, and a Proprietary woofer. Also, the crossovers were totally rebuilc, rewired the speakers, and replaced all fiberglass stuffing, resealed the woofers to the cabinets, etd. All 3 drivers in the upper cabinet were mirrored and placed on a single Masonite Board. I will finally be taking them out of the system as the main speakers in about 2 or 3 weeks.

Rich
 

rblnr

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May 3, 2010
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#14
Finally got to this -- helps confirm my experiential findings. Directed a bunch of commercials for USC over the years and think I might have ran into the author btw.

Many years ago in NYC, I auditioned nearly 20 pairs of speakers around NYC -- my first 'serious' search for keepers. 2K worth of bartending money on the line. Didn't know it then, but the three finalists had one thing in common -- first order, phase coherent slopes, all drivers wired in phase, and 1 of 3 were time aligned. Around that time owned a pair of Spicas TC50s too -- slanted baffle/time aligned/phase coherent -- and they imaged like almost nothing else out there. In fact, they were the component that intro'd me to the concept of imaging. Too bad they had no bass and the sub didn't work!

I wonder what a company like Revel, which seems unconcerned with time alignment, would make of the test. Would they find a problem with the methodology?

Most disappointing speakers I ever owned were Waveform Mach Solos. Flat frequency response on- and off-axis. Flat sounding too although the got some great reviews. Fourth order (not phase coherent) slopes and not time aligned.
 
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rblnr

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May 3, 2010
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#16

rblnr

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#18
I'll check that out.
 

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