A history of Time Aligned Loudspeakers

[LSPhil]

18,Il Maestro die Scuola

 

[JPA]

These speakers are excellent examples of misplaced priorities in audio. If you stagger your speakers on a baffle like that, you will ruin vertical directivity and possibly horizontal directivity as well, if not done properly. Bear in mind, sound travels 343mm in 1ms. So if the baffle is stepped by 34mm, it will provide 0.1ms of time alignment. Which do you think is more audible? A 0.1ms time alignment, or poor vertical directivity?

Please send your observations to Wilson Audio. Maybe they'll hire you to teach them how to correctly design speakers.

 

[MattHooper]

In general, there is logic in your line of thought. Sometimes, as a special case - we can be impressed and like a speaker that does not have good Transient Precision! Who is the model of yours Thiel ?

Thiel 3.7 and 2.7 speakers, as I mentioned here earlier in the thread with some photos.

Jim Thiel’s last great design, where he further perfected his coax design employing his new flat/corrugated midrange. They were even more coherent than the bigger Thiel CS6 I had for a while years earlier. The CS6 had slight destructive interference in the drivers/crossover which caused a slight hollowness to the mids and a loss of richness, depending on one’s head position.

The 3.7 and 2.7s didn’t have that to any noticeable degree and sounded lush and full and natural, with little perceived tonal change over a fairly broad listening window. I’m not a fan of head-in-vice designs. And the 3.7 is still the most boxless and top to bottom coherent sound I’ve heard from a box speaker.

I might also mention that I still own Thiel Model 2 speakers that I’ve had for decades.
They were a relatively cheap large stand mounted two way Thiel produced in the late 70s/early 80s, before they went for phase coherent designs. They remain one of my favourite speakers and… surprisingly… one of the things I like about them is the density and solidity of the sound! And they are not time/phase coherent. Although they don’t image with quite the precision and soundstage vastness of the later Thiel models

 

[Trifonov Audio]

Thiel 3.7 and 2.7 speakers, as I mentioned here earlier in the thread with some photos.

Jim Thiel’s last great design, where he further perfected his coax design employing his new flat/corrugated midrange. They were even more coherent than the bigger Thiel CS6 I had for a while years earlier. The CS6 had slight destructive interference in the drivers/crossover which caused a slight hollowness to the mids and a loss of richness, depending on one’s head position.

The 3.7 and 2.7s didn’t have that to any noticeable degree and sounded lush and full and natural, with little perceived tonal change over a fairly broad listening window. I’m not a fan of head-in-vice designs. And the 3.7 is still the most boxless and top to bottom coherent sound I’ve heard from a box speaker.

I might also mention that I still own Thiel Model 2 speakers that I’ve had for decades.
They were a relatively cheap large stand mounted two way Thiel produced in the late 70s/early 80s, before they went for phase coherent designs. They remain one of my favourite speakers and… surprisingly… one of the things I like about them is the density and solidity of the sound! And they are not time/phase coherent. Although they don’t image with quite the precision and soundstage vastness of the later Thiel models

Very good Step Response - typical for first оrder crossovers. The latest models of J. Thiel (in memoriam) - deserve admiration! Your choice too - bravo!

 

[Duke]

My understanding, drawing from the research of David Griesinger, is that there is merit in preserving the phase relationships of the harmonics north of 500 Hz or so, emphasis mine:

"The information content of speech is (almost) entirely in frequencies above 500Hz. For all people, even children, this means that information – at least the identity of vowels
– is encoded in amplitude modulations of harmonics of a lower frequency tone. This method of encoding is universally used by almost any creature that wishes to communicate, from insects to elephants. Why? Because harmonics have a unique property – they combine to make sharp peaks in the acoustic pressure at the frequency of
the fundamental frequency that created them. It is the presence – or the absence – of these peaks that enables the perception of ‘near’ and ‘far’. The sharp peaks also facilitate separating the signals from noise, and with the appropriate neural network the peaks from one sound source can be separated from another."

Imo one implication seems to be that preserving the phase relationship of the harmonics (and therefore preserving the aforementioned sharp peaks) north of 500 Hz can contribute to conveying depth information - "the perception of 'near' and "far'.

Another implication seems to relate to clarity and/or dynamic contrast, as the sharp peaks which occur when the harmonics are correctly aligned "facilitate separating the signals from the noise", as well as facilitating the separation of one sound source from another.

There are few free lunches in loudspeaker design, so imo these benefits should be weighed against whatever tradeoffs are imposed in order to get them, and different designers have different priorities.

In @robh36062's post #74, you can see what I believe is a good representation of the "sharp peak" Griesinger describes when the harmonics line up, versus the absence of this peak when they do not.

 

[Holmz]

It’s frankly been a long time since I paid close attention to this stuff, but …

So the purported (debated) sonic benefits of time phase coherence are:

1. Image precision
2. Transient precision (definition of the leading edge of notes).
3. Maybe precision in reproducing instrumental timbre?

Have I got that right or have I missed anything?

Those are all things that I found my Thiels excelled at, whether that had to do with time phase coherence or not.
…
Again, just anecdotal stuff… but it’s the type of qualities often purported to time/phase coherence that I perceived in the Thiel sound that led me to favour them over so many other speakers. (again, whether what I was hearing was do strictly to time phase coherence, or perhaps those came from other aspects of the Thiel design).

Maybe it had to do with Thiel’s time & phase coherence?

…
It reminds me of comparisons with another one of my favourite loudspeakers, the Waveform Mach 17 and the smaller Mach Solo floor standing speakers that I once reviewed a long time ago.

View attachment 534392

Just to grab a relevant quote from the review in which Otvos downplays importance of time/phase:

“John Otvos feels that designing speakers for perfect time alignment (for instance, achieving an impeccable square wave response) is not nearly as sonically meaningful as achieving wide, evenly radiated power response. Thus they eschew first order crossovers, which require drivers to operate outside their optimal pass band. Instead the Mach Solo, like the Mach 17, employs a 24-dB/octave Linkwitz-Riley crossover. Waveform claims that this maximizes transient response and power handling, and minimizes intermodulation distortion between the drivers.”
…

One part of that is true.

…
That seems to make sense to me.

Which part?

 

[Holmz]

…
There are few free lunches in loudspeaker design, so imo these benefits should be weighed against whatever tradeoffs are imposed in order to get them, and different designers have different priorities.
…

^Sure^
One big problem is cost of the drivers.
So that cuts into the profit.

It seems easy to chuck out frequency response curves and show it is within so-n-so dB.
Or directivity.
One sort of needs all the nuance plots-n-graphs to make more complete sense of the whole damned thing.

But let’s say, for example, that some actual sound had the same behaviour as the step response.
Woud not the most natural sounding reproduction of that be the speaker that produces the same sound pressure as the micrphone that recoded it?

 

[Duke]

But let’s say, for example, that some actual sound had the same behaviour as the step response.
Woud not the most natural sounding reproduction of that be the speaker that produces the same sound pressure as the micrphone that recoded it?

If the ear/brain system perceives the exact same way as microphones pick up sound pressure, then YES.

If not, then MAYBE.

In my opinion.

 

[Holmz]

If the ear/brain system perceives the exact same way as microphones pick up sound pressure, then YES.

If not, then MAYBE.

In my opinion.

Replicating the pressure field sort of has nothing to do with the ear/brain.

The converse is usually argued, and done so quoting sections of Floyd’s book.
And that is something like “despite the phase being wrong. The ear/brain perceives it as the same.”

So the step function plot removes option and subjective “analysis” in favour of objective fact.

But maybe it can be somewhat similar to harmonics distortions, in that a perfect distortion free amplifier measures good, but a lot of people really like distortions and prefer that subjectively.

 

[Duke]

Replicating the pressure field sort of has nothing to do with the ear/brain.

Imo when you wrote "Woud not the most natural sounding reproduction of that be the speaker that produces the same sound pressure as the micrphone that recoded it?", emphasis mine, you were implying the participation of the ear/brain. Thus my response included the participation of the ear/brain.

The converse is usually argued, and done so quoting sections of Floyd’s book.
And that is something like “despite the phase being wrong. The ear/brain perceives it as the same.”

So the step function plot removes option and subjective “analysis” in favour of objective fact.

Ah, I should have gone into more detail.

My reason for thinking that there can be a disconnect between the step response measurement made by a microphone and human hearing perception is more about loudspeaker radiation patterns and reflection arrival times than about "despite the phase being wrong, the ear/brain perceives it as the same". (The step function plot tells us nothing about the radiation pattern nor the resulting reflection arrival times.)

I think that, in general, the ear/brain system is more forgiving of "the phase being wrong" than of the amplitude response being wrong, but I do not think "the ear/brain system [necessarily] perceives it as the same."

 

[Holmz]

Yeah 100% @Duke - that is also part of the compromises.
As I think Toole’s works pointed out, FR and radiation pattern, and time and phase is probably lower down.

Or I like to think of it as FR and radiation being for cellos and french horns, and time and phase being for drums, cymbals, bells and the percussion.

Ideally/optimally it’s all perfect.

Time aligned and time/phase aligned may intentionally be trading off FR and radiation pattern for the timing attributes.

 

[Keith_W]

Please send your observations to Wilson Audio. Maybe they'll hire you to teach them how to correctly design speakers.

Wilson Audio does not design speakers. They design luxury products that produce sound. Everything about the design serves their purpose of marketing. If they cared about objective performance, the best way to achieve that is to forget that antiquated passive XO and go DSP and active. Since it's obvious they are more interested in making money (which they do very well) rather than objective performance, they wouldn't hire anyone who does not serve that purpose.

 

[bmc0]

In @robh36062's post #74, you can see what I believe is a good representation of the "sharp peak" Griesinger describes when the harmonics line up, versus the absence of this peak when they do not.

If my understanding is correct (no guarantees ), it's the phase coherence of harmonics that fall within the bandwidth of a cochlear filter that is important, not the phase coherence of the whole band above 500Hz. Crossover slopes typical of loudspeakers don't generally cause all that much phase rotation over an ERB, so the "bad" step response of, say, an LR4 crossover shouldn't be a big problem regarding the perceptual phenomena Griesinger is talking about. High-level specular reflections, on the other hand, cause large jumps in phase over a narrow bandwidth.

 

[Sal1950]

Wilson Audio does not design speakers. They design luxury products that produce sound.

But Keith, they look so KOOL!

 

[Waveform Fidelity]

Please send your observations to Wilson Audio. Maybe they'll hire you to teach them how to correctly design speakers.

The basics of diffraction might be a good starting point. Plus all those precision gears and mechanics to wind the speaker pods in and out, to time align all the driver boxes, while visually impressive can be done simply with DSP with better precision, so they could learn there too, but its likely they know all this stuff anyway, and their value proposition is that their speakers are “just different” and “exclusive” for the wealthy…..

 

[jareinertson]

Is "time-aligned" and "time-coherent" mean the same thing, in speaker design; or do they have different nuances?

In the case of KEF Uni-Q and MoFi SourcePoint offerings; they are coaxials/concentrics (AndrewJones calls his creation "co-incident").
Both align their acoustic centers but are not exactly time-aligned. Are they?

Me too!
RichardVandersteen was born as a cheap but clever designer. He gave us time-alignment but cut costs by having no cabinetry/woodwork.
View attachment 533941
I was a sucker for a few generations of his model 2C iterations and was perfectly happy.
I am no longer time-aligned since I have become a MoFi SP10MP fanboy of late.

I certainly enjoyed my Model 3’s for several years.

 

[kimmosto]

Conventional phase-matching IIR crossover at low frequency is by far the most audible with continuous transient signals like the following. XO to subwoofer alone makes quite big difference, but 3-way with sub with steep XOs does not have much common with the original. Phase distortion creates kinda extra boom at fundamental.

 

[Sokel]

Wilson Audio does not design speakers. They design luxury products that produce sound. Everything about the design serves their purpose of marketing. If they cared about objective performance, the best way to achieve that is to forget that antiquated passive XO and go DSP and active. Since it's obvious they are more interested in making money (which they do very well) rather than objective performance, they wouldn't hire anyone who does not serve that purpose.

Why so dogmatic?
Neumann KH 420 doesn't have an ounce of DSP but still does really good, so a lot of passive speakers.

All it needs is work by formally educated/very experienced people.
DSP could be the extra step for taste, RC, etc.

 

[Suono]

Yeah 100% @Duke - that is also part of the compromises.
As I think Toole’s works pointed out, FR and radiation pattern, and time and phase is probably lower down.

Or I like to think of it as FR and radiation being for cellos and french horns, and time and phase being for drums, cymbals, bells and the percussion.

Ideally/optimally it’s all perfect.

Time aligned and time/phase aligned may intentionally be trading off FR and radiation pattern for the timing attributes

If your goal is to create a speaker without compromises and a representation of high-fidelity reproduction, you cannot underestimate frequency response, dispersion, or even phase and timing. All musical instruments are in phase and coherent over time without detuning.

 

[thewas]

Take a look at this it's a KEF LS50 you can clearly see the tweeter arrival first. I agree look very good however the second is step is from a time aligned system from Theil. The KEF are very good and time coherent not time aligned.

Rob

KEF LS50 Meta loudspeaker Measurements | Stereophile.com

Sidebar 3: Measurements I used DRA Labs' MLSSA system and a calibrated DPA 4006 microphone to measure the KEF LS50's frequency response in the farfield, and an Earthworks QTC-40 for the nearfield and spatially averaged room responses. My estimate of the LS50 Meta's voltage sensitivity was...

www.stereophile.com

In the same link the "optically superior" of the original LS50 is shown too

and this a good example how few such plots (except in rare very problematic cases) correspond to audibility, as the LS50 Meta is superior in tonality without having audibly worse imaging or "attack", I own both since their releases.