A history of Time Aligned Loudspeakers

[Waveform Fidelity]

How many loudspeaker companies built these types of loudspeakers? Post or quote your favorite pics or example.

I recall the first ones coming out in the late 70’s here is one by Leak, that used a stepped baffle. Its was all the rage in the 70’s

 

[Chrispy]

Just by baffle position?

 

[Sal1950]

Hummm, what do you think about the DCM Time Windows approach?
Peter had fun with these.

https://akdatabase.com/AKview/albums/userpics/10007/TW_Audio_Critic_Reviews.pdf

A big deal in the 70s

 

[JSmith]

Duntech PCL-3 (Phase Coherent Loudspeaker Model 3) - 1982;

Duntech Sovereign PCL-2001 - 1987;

JSmith

 

[Keith_W]

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?

 

[sam_adams]

Hummm, what do you think about the DCM Time Windows approach?

The 'magic' of the Time Windows was in the crossover. The frequency and group delay plots of the electrical response of the TW-1 crossover circa 1978-1979:

The 'dashed/dotted' plots in Blue and Green are the group delay of the crossover for the tweeter and woofer respectively. Solid Blue and Green plots are the frequency response of the tweeter and woofer respectively. The Red plot is the combined electrical frequency response. The - 6 dB drop in the combined response above ≈ 1 KHz is because the higher sensitivity of the tweeter as compared to the woofer is being compensated for in the crossover. Note the group delay at the crossover frequency of 2 KHz. That's the 'Time' in the Time Windows.

Here's the schematic:

Tweeter crossover filter is a modified Cauer (Elliptical) filter response.

(Made a small edit to get the driver order correct.)

 

[respice finem]

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?

Probably other factors were considered - like having an edge against competition (real or not).
And, in the 70s and 80s, they didn't have today's knowledge.

 

[Bjorn]

Serious edge diffraction issues.

 

[EJ3]

How many loudspeaker companies built these types of loudspeakers? Post or quote your favorite pics or example.

I recall the first ones coming out in the late 70’s here is one by Leak, that used a stepped baffle. Its was all the rage in the 70’s

I have 2 pair of these. When they are on their stands (3.5 degree angle) their time alignment is:

Dahlquist M-905
Quasi-anechoic FFT measurements show an overall group-delay variation of about 0.1 millisecond between 4,000 and 20,000 Hz and 0.5 ms between 1,000 and 20.000 Hz, convincing evidence of the attention paid to the phase characteristics of the M-905.

 

[kimmosto]

Which do you think is more audible? A 0.1ms time alignment, or poor vertical directivity?

0.1 ms is just mechanical part of the job. Phase linearization to achieve actual time alignment to on-axis requires suitable XO slopes too. Agree that 2-way does not really need those tricks due to very short delay so it's mostly just policy to harmonize whole product family. Time alignment starts to pay back with 3...5-ways with symmetrical driver layout such as Duntech Sovereign PCL-2001, but old passives also required close to 1st order acoustical XO slopes and sealed enclosure to produce minimum-phase total. Harsch, Le Cleach, Trifinov XOs etc. reduce excess delay, but don't reach minimum-phase.
I wouldn't take semi-modern multi-way with very steep IIR XO slopes causing terrible timing and lame non-dynamic sound. Strong and bad vertical directivity of WMTMW etc. concepts with minimum-phase timing is better than very bad timing with perfect vertical directivity (assuming that both designs are proper).

 

[smygolf]

Cabasse had Brigantin 372 in the late 60:s (pic 1975 active Brigantin)

Original Brigantin - i think.

And from 1974 isch up to 1995 most Cabasse had stepped baffles.

 

[EJ3]

Cabasse had Brigantin 372 in the late 60:s (pic 1975 active Brigantin)
View attachment 533738

Original Brigantin - i think.
View attachment 533739


And from 1974 isch up to 1995 most speakers had stepped baffles.

I never saw any in person back then (in the USA) with stepped baffles. And I knew people that owned many exotic speakers (for that time) starting in 1974. Acoustat, Maggie, OHM and others. People that had 21" & 24" Hartley subs built into their floors. I knew of stepped baffle speakers. But never saw any in person (until they became "vintage".
Maybe not much of a 'thing' in the Southern USA. But I never saw any in Austria, Germany or Italy back then either. And Graz, Austria is where I got my first inkling of the "Stereo Bug" in 1970 or 71.

 

[KL....]

Hummm, what do you think about the DCM Time Windows approach?
Peter had fun with these.

https://akdatabase.com/AKview/albums/userpics/10007/TW_Audio_Critic_Reviews.pdf

A big deal in the 70s

Thank you, @Sal1950, Yes, my pair (1st Speakers owned) are still working/performing well, to this day, and are over 40yrs old. Grill material still perfect, the Speakers still look in mint condition, but the Boxes/Packageing now looks old but intact :=)

Thank you, @sam_adams,

 

[mglobe]

IIRC time alignment was Vandersteen’s “thing” with the 2C’s when they were introduced in 1980 and continued to be going forward.

 

[DanielT]

This is a classic in Sweden. Qln One from sometime in the 80s. It has a slanting baffle, where I suspect the idea was to get a time alignment between the drivers:

A solid speaker build I must say. I have rounded the baffle corners myself. I don't know if that in itself made any sound improvements, I didn't do any before and after measurements. Mostly done because I think they looked better with rounded corners.
Now with Dayton Audio ND25FW-4 tweeters plus active crossover.

When I fix the spacers I'll pop in my SB15NBAC30 woofers in them.
(With my LR4 and crossover point at 2.5 kHz it gives 1.2 times the wavelength considering the drivers c-c. I hope it will be good, will do measurements this summer)

 

[smygolf]

I never saw any in person back then (in the USA) with stepped baffles. And I knew people that owned many exotic speakers (for that time) starting in 1974. Acoustat, Maggie, OHM and others. People that had 21" & 24" Hartley subs built into their floors. I knew of stepped baffle speakers. But never saw any in person (until they became "vintage".
Maybe not much of a 'thing' in the Southern USA. But I never saw any in Austria, Germany or Italy back then either. And Graz, Austria is where I got my first inkling of the "Stereo Bug" in 1970 or 71.

People had more fun back in the day

And regarding most had stepped baffle, i meant Cabasse

 

[Chris A]

How many loudspeaker companies built these types of loudspeakers? Post or quote your favorite pics or example.

Apparently an originating patent (expired in 1994):

Linear phase response multi-way speaker system

I think the B&O folks addressed the crossover all-pass phase growth with their "Uni-Phase" loudspeakers--apparently from an article that an B&O engineering manager (Erik Bækgaard) addressed in May 1977.

So the technology actually goes back to the mid-1960s (Japan).

More here on designing flattened phase loudspeakers and the listening effects of such loudspeakers in properly treated rooms and placed loudspeakers:

PASSIVE Linear Phase (Quasi Transient Perfect) XO s
"The phase coherence of harmonics in the vocal formant range, ~630Hz to 4000Hz"
Phase link principle

More references can be found. I think it suffices to say that the principle originated in the past 50-60 years of engineering, and loudspeakers were designed using this principle of "linear phase" crossovers and drivers since that time.

EDIT: one more article...

A Unique Loudspeaker Crossover Design with Waveform Fidelity

Chris

 

[EJ3]

0.1 ms is just mechanical part of the job. Phase linearization to achieve actual time alignment to on-axis requires suitable XO slopes too. Agree that 2-way does not really need those tricks due to very short delay so it's mostly just policy to harmonize whole product family. Time alignment starts to pay back with 3...5-ways with symmetrical driver layout such as Duntech Sovereign PCL-2001, but old passives also required close to 1st order acoustical XO slopes and sealed enclosure to produce minimum-phase total. Harsch, Le Cleach, Trifinov XOs etc. reduce excess delay, but don't reach minimum-phase.
I wouldn't take semi-modern multi-way with very steep IIR XO slopes causing terrible timing and lame non-dynamic sound. Strong and bad vertical directivity of WMTMW etc. concepts with minimum-phase timing is better than very bad timing with perfect vertical directivity (assuming that both designs are proper).

Well: whatever Jon Dahlquist and Saul Marantz were doing, they where getting things right:
The close-miked woofer (and port) response is considerably flatter than most speakers, with a very small bass-resonance peak. At the system resonance of 60 Hz, the output is only about 2 dB above its average level in the upper part of the woofer’s range, and even that minor output variation was spread over almost two octaves. When the bass curve was spliced to the room-response measurement, the resulting composite frequency response was flat within about ±2 dB from 26 to 20,000 Hz. The horizontal directivity of the tweeter was only discernible in the room measurement above 10,000 Hz.

 

[gnarly]

I find it very helpful to separate the concept of 'time alignment' from 'phase alignment'.

Time alignment is having the distances from drivers' acoustic centers, to be the same to a listening position / tuning spot.
Either accomplished geometrically via drivers' locations, or electrically with constant time delays.
So whenever I see a stepped or sloping baffle arrangement, I know the speaker designer was working towards achieving time alignment.
Generally, I tend to assume any designer interested in achieving time alignment was also interested in achieving phase alignment.

They are not the same thing. Many designs tout phase alignment (especially two and perhaps simple three ways) without any real concern for time alignment. They often use 'pseudo time', aka group delay between driver sections to achieve 'pseudo time alignment'. The difficulty of making fixed delays with passive circuity is the root of the use of pseudo delay.

Not trying to overcomplicate the thread....just trying to highlight that when discussing time aligned speakers, crossovers alone don't achieve it.
It takes either geometric delays, or fixed electronic delays mimicking geometric delays.

 

[jkasch]

Technics “Linear Phase” series