A history of Time Aligned Loudspeakers

[gberchin]

The funniest excuse to design bad speakers would be to trust that recordings have some delay errors and manipulations which hide problems of own product.

Schopenhauer's Law of Entropy: If you put a spoonful of wine in a barrel full of sewage, you get sewage. If you put a spoonful of sewage in a barrel full of wine, you get sewage.

 

[DavidR]

Totally agree.
But we can't dismiss them as not nice.

Even Purifi suggests perfectly (their own design) good passive ones for their tweeters for example.
And on top of that, we can't underestimate the set-and-forget, bulletproof factor of non-digital ones.

Since this somewhat off-topic morphed a bit into DSP/active vs. passive, I thought I throw this in. John Kreskovsky published a lot of theoretical papers and used to sell some designs. One of his papers I intend to use as the basis for any systems I make when appropriate. John wrote a paper for a hybrid 2-way system using theoretical drivers for purpose of demonstration. In one page on his the design he sold he used the hybrid approach for the mid-tweeter section. The same principle applies to both.

In short, he demonstrated that an appropriate mix of DSP and passive crossover can have a distinct benefit in both 2-way and 3-way (or more). I won't try to summarize his papers, only post links here. From this it can be debated that use of passive crossovers can still be beneficial even with the use of DSP/active.

Hybrid Design Philosophy: Passive crossovers with active equalization

Figure 9. Lower trace is the response of the active equalization. Red area represents
reduced requirement placed on the amplifier.

Hybrid Design Philosophy applied to the NaO II RS

Figure 3. The grey area shows the amplifier head room retained in reserve through the
use of an active high pass crossover and equalization

 

[Thomas_A]

Passive components have their place to reduce distortion. Already shown in other threads and by others (eg Purifi). Unless you design special drive amps.

 

[Thomas_A]

There have been more modern studies than the 1978 BL curve posted in this thread. I will post a summary of 3 different studies one from 2018.




Are you doing these studies in a real listening room or an anechoic chamber? In a real room any reasonable GD issues, will be further masked by the reverberant field in the room. Making even a borderline system inaudible.



All? How would anyone know? What does requiring a sub have to do with it? We are talking complete speaker systems individually looking at GD for that system. You are worried about sub integration in the modal region of a typical room where the room dominates?



Simply not concerned.

Rob

One can always discuss the <500 Hz GD in multiway speakers or subs. What is the detection limit? Below one cycle at 150 Hz but how low?

 

[DavidR]

Passive components have their place to reduce distortion. Already shown in other threads and by others (eg Purifi). Unless you design special drive amps.

John's papers did not cover distortion. His concern was reduced amplifier requirements and improved headroom. There could easily be beneficial impact on distortion depending on the amplifier and its limits.

 

[Waveform Fidelity]

A violin, a guitar, a double bass, a flute, play in your listening room. Is the sound in phase and temporally coherent? YES.
Why shouldn't the speakers be? I don't understand.

In my opinion, its about practical engineering and cost for passive designs and it all started in history by those first 1970’s ads claiming time alignment and in many respects that in turn came from Heyser’s foundational work on time delay distortion. Fast forward to today, it is straightforward to design out all linear distortion using DSP correction, but there is a massive industry in passive loudspeaker -because of cost, although that gap is narrowing

On your second point, I read in one other threads that Floyd’s work showed that group delay and its corresponding waveform distortion could not be perceived in practice because the room reflections messes everything up…. and it does!

Now imagine you have a solo Violinist that brings her Stradivarius to live presentation, and the organizer says, “look the room is a bit echoey” so the sound of your Stradivarius will get messed up, so here is a regular violin you can use instead - it will be the same! Don’t worry the audience won’t notice either.

Of course this is an absurd example, but it illustrates my point to make the waveform that leaves the loudspeaker as perfect as possible (within cost constrains, of course). Plus, I could be listening outside, which sometimes I do.

 

[robh36062]

One can always discuss the <500 Hz GD in multiway speakers or subs. What is the detection limit? Below one cycle at 150 Hz but how low?

I couldn't tell you. That's a great question and it gets complicated. We are in the modal region of the room so if you did Anechoic test would it hold up in a typical room? Are you sealed or a reflex box? Obviously it will be higher at box tuning but how audible at say 25Hz? That would be 40 msec to meet the 1 cycle "rule" depending on how much GD there is in the box and crossover.

When I set up subs I go for a null as it is much easier to hear and measure. Then reverse polarity under the best conditions you might see a 6db rise from mutual coupling more typically 3db. With a null it can go down 10db easy and deeper depending on how close the phase match is through the crossover. I don't worry about the GD as long I get good summation through the crossover.

The other issue is obviously wavelength. At 80 Hz it's 14ft. So with placement are your subs 14ft away or one cycle? I doubt it. That's why a variable phase control is better than simple polarity switch.

Rob

 

[Keith_W]

Schopenhauer's Law of Entropy: If you put a spoonful of wine in a barrel full of sewage, you get sewage. If you put a spoonful of sewage in a barrel full of wine, you get sewage.

Suslick's Corollary to Schopenhauer's Law of Entropy: if you put a spoonful of science in a barrel of politics, you get politics. If you put a spoonful of politics in a barrel of science, you get politics.

 

[KL....]

A loudspeaker driver itself already behaves as both a high-pass and low-pass acoustic filter. Once you add even a single capacitor (a 1st-order electrical filter), the resulting acoustic slope is, in the best-case scenario, effectively 2nd order.

So the idea of a “true 1st-order acoustic high-pass loudspeaker” is largely theoretical and practically nonexistent in real-world driver behavior.

Thank you, @LSPhil, perhaps (rarely seen or used or available) consider the Avantgarde CPC circuit....

• 2nd order behaves like 1st order/In Phase, Eliminates Crossover Distortion, etc....

THE CPC TECHNOLOGY.... CPC UPCONVERTION OF MUSIC SIGNAL The permanent change of direction of the field in a capacitor, a phenomena called “dielectric memory effect, causes distortions which get worse the closer the signal passes through the zero point and are at a max just when the electric field changes its direction. The following pictures show these distortions of capacitors at different frequencies. To avoid these distortions Avantgarde Acoustic uses with the CPC, Capacitor Polarisation Circuit. Different to conventional capacitors the CPC capacitor has multiple conductor foils connected with a special electric layout shown in the following graphics. The CPC module up-converts the music signal to the required voltage to bias the conductors. Only the inner conductor is biased with DC. In the CPC module a voltage cascade through a network of diodes increases the voltage of the music signal to a multiple. This high direct current is than fed into the inner conductor. Furthermore is the diode circuit electrically decoupled through a very high impedance transformer to avoid any backlash to the music signal. Already a view moments after turning on the music the CPC module has generated the required direct current to bias the capacitor. As the CPC diode cascade can build-up voltages by far beyond allowable levels, Avantgarde Acoustic has included a protective circuit to avoid overloading the capacitor.

 

[kimmosto]

Edit: I posted this before, but FWIW a paper for Liski (2020) that gives a short overview of earlier studies, too.

https://acris.aalto.fi/ws/portalfiles/portal/66449704/Audibility_of_Group_Delay_Equalization.pdf

I've had related study in my archives for few years. That uses HD650 and focuses to typical XOs of 2- and 3-ways. Audibility limit at LF is too high probably due to test signals, LF is partly invisible in the graph(s) and it does not tell directly what kind of subwoofer XOs would be inaudible - if any. As already mentioned, all typical IIR XOs (24 dB/oct or steeper below 200 Hz) are clearly audible also with headphones. So audible that even tactile sensation is not yet required to confirm the difference. Subwoofers are apparently considered essential, so the issue is neatly ignored.
I don't mind about disagreement in this because timing so old case. Just surprised how eagerly, in a forum that supposedly is objective, people cling to small opportunities to downplay the potential impact.

 

[Suono]

On your second point, I read in one other threads that Floyd’s work showed that group delay and its corresponding waveform distortion could not be perceived in practice because the room reflections messes everything up…. and it does!

No one denies that the room can make it inaudible, but this applies to any type of distortion.
Regarding your example of the Stradivarius, I don't find it very relevant. The violin is present and plays. It doesn't matter to the listener whether it's a Stradivarius or a cheap one. In stereophonic reproduction, there's nothing real; there's something that's recreated in our brain. Time and coherence allow a sound to be transformed from 180° to 360°, or rather, the holography of reproduction.

 

[gnarly]

Very good, almost perfect for an active system! When the project is "under the hat" of a subtractive crossover or DSP processing - then phase-time problems disappear! You can also see large horns - which is a perfect solution! What are the drivers called and where are the slope frequencies?

Thanks. The drivers are a BMS 4694HE coaxial compression driver, and two Faital 10" 10PR330's.
Xovers are at 6500Hz between the CD sections, and 500Hz CD to 10"s. 96dB/oct linear phase.

You might like this one, a more ambitious project.
B&C coaxial CD (or alternatively the BMS above), four 4" B&C 4NDF34's, two Faital 12" 12PR320's, and two BMS 18" 18N862's....
A 5-way, all in this one horn/box.

Xover's are at 100, 375, 900, and 3400Hz. All 96 dB/oct lin-phase (HPF at 43Hz.)
Individual section impulses and mag response shown. As per the flat mag and phase in bottom panel, summed impulse and step are near textbook.
If a hack like me can use DSP to tie a friggin 5-way together with time and phase alignment....what could manufacturers do, that move into sound counts more than marketing arena. Lol.
Oh, and this guy is designed for use with a sub, so a 6-way time and phase aligned system in all.

 

[NTK]

Schopenhauer's Law of Entropy: If you put a spoonful of wine in a barrel full of sewage, you get sewage. If you put a spoonful of sewage in a barrel full of wine, you get sewage.

Curious. Wine or something else?
https://www.gencowinemakers.com/docs/To Sterilize or Just Clean.pdf

 

[gnarly]

Audiophile claims that cable differences are audible are met with skepticism on ASR because they are not measurable.

Engineering measurements of errors in time-alignment are met with skepticism on ASR because they are not audible.

The irony is delicious.

irony indeed

Folks often forget that what is deemed science,..... is very, very often under the effectively political influence, of those deemed in the know.

 

[LSPhil]

irony indeed

Folks often forget that what is deemed science,..... is very, very often under the effectively political influence, of those deemed in the know.

Oh, don't cry so much — just tilt your speakers back a few degrees and you'll have time alignment.

 

[kimmosto]

Audiophile claims that cable differences are audible are met with skepticism on ASR because they are not measurable.

Engineering measurements of errors in time-alignment are met with skepticism on ASR because they are not audible.

The irony is delicious.

Few words if I may.
Many parameters / differences in cables are measurable.
Time-alignment is just mechanical or electrical delay adjustment which does not eliminate excess phase without suitable crossover. Adequate timing error is measurable and audible and also perceivable with tactile sensation. If some of you believes it's measurable only, show valid studies which indicate it. I'm aware of one very limited study: Perception of Time Distortions Caused by Loudspeaker Crossover Filters by Mwambakale and Hipperson 2023, which focused to "2-ways" with GD step of 0.54 - 0.59 ms and used headphones. World of audio is probably a bit larger so difficult to see why that study even exists. Maybe they had to do and publish something to avoid lay off.

 

[Canuck57]

I've had a pair of these for many many years. They are the daily drivers for my video system (I'm old school and prefer stereo to surround for home movie watching). They've never let me down! https://www.hifi-classic.net/review/thiel-cs2-124.html

I had a pair of those as well that I purchased used. Excellent speakers.

 

[Trifonov Audio]

Thanks. The drivers are a BMS 4694HE coaxial compression driver, and two Faital 10" 10PR330's.
Xovers are at 6500Hz between the CD sections, and 500Hz CD to 10"s. 96dB/oct linear phase.

You might like this one, a more ambitious project.
B&C coaxial CD (or alternatively the BMS above), four 4" B&C 4NDF34's, two Faital 12" 12PR320's, and two BMS 18" 18N862's....
A 5-way, all in this one horn/box.

View attachment 535040


Xover's are at 100, 375, 900, and 3400Hz. All 96 dB/oct lin-phase (HPF at 43Hz.)
Individual section impulses and mag response shown. As per the flat mag and phase in bottom panel, summed impulse and step are near textbook.
If a hack like me can use DSP to tie a friggin 5-way together with time and phase alignment....what could manufacturers do, that move into sound counts more than marketing arena. Lol.
Oh, and this guy is designed for use with a sub, so a 6-way time and phase aligned system in all.

View attachment 535045

O-oo, I personally know the chief designer of BMS. A brave, ultra-innovative inventor!
The idea with many drivers to one horn is awesome!!
Bravo, congratulations!!

 

[Thomas_A]

John's papers did not cover distortion. His concern was reduced amplifier requirements and improved headroom. There could easily be beneficial impact on distortion depending on the amplifier and its limits.

I was merely pointing to the effects of distortion and the use of passive components. Active solutions seldom take that into the equation.

Low Distortion Filter for PTT6.5X04-NAA

purifi-audio.com

 

[KL....]

Thanks. The drivers are a BMS 4694HE coaxial compression driver, and two Faital 10" 10PR330's.
Xovers are at 6500Hz between the CD sections, and 500Hz CD to 10"s. 96dB/oct linear phase.

You might like this one, a more ambitious project.
B&C coaxial CD (or alternatively the BMS above), four 4" B&C 4NDF34's, two Faital 12" 12PR320's, and two BMS 18" 18N862's....
A 5-way, all in this one horn/box.

View attachment 535040


Xover's are at 100, 375, 900, and 3400Hz. All 96 dB/oct lin-phase (HPF at 43Hz.)
Individual section impulses and mag response shown. As per the flat mag and phase in bottom panel, summed impulse and step are near textbook.
If a hack like me can use DSP to tie a friggin 5-way together with time and phase alignment....what could manufacturers do, that move into sound counts more than marketing arena. Lol.
Oh, and this guy is designed for use with a sub, so a 6-way time and phase aligned system in all.

View attachment 535045

Thank you, @gnarly, what are the Box Dimensions....