Understanding Loudspeaker Coherency

[Big Daddy]

Ontario, Canada is the center (or centre) of many speaker manufacturing companies. Although many of us have heard of Paradigm, PSB, Axiom, Energy, Mirage, etc, there are a few much smaller boutique speaker companies. One such company is Reference 3A. All the speakers from Reference 3A are phase coherent. No crossover is used for their midrange drivers for phase coherency. The drivers are also angled for correct time alignment. If you are in the market for very good high-end speakers, Reference 3A is highly recommended.

Episode:
http://www.reference3a.com/episode.htm

A two way design utilizing our own directly coupled (no crossover) hyper exponential 8" (20 cm.) woven carbon-fiber main driver, superb 1" (24mm.) soft textile dome tweeter and a gold coated fine ceramic super high frequency exciter.

Front baffle is tilted back at a critical angle and the drivers are positioned precisely for correct time alignment and sound wave propagation.

Grand Veena:
http://www.reference3a.com/grandveena.htm

New Grand Veena is a tall, slender tower housing five seamlessly integrated unique drivers. The front baffle is tilted back at a critical angle and the drivers are positioned precisely for correct time alignment and sound wave propagation. The multi chamber cabinet provides isolation to avoid interference between the drivers operating at different frequency ranges.

Achieving a coherent phase response has always been an utmost priority for us and a design criterion with all our loudspeakers. Carefully assembling the drivers with correct parameters and choosing a more direct signal-path design option, along with critical placement of the perfectly pair matched drivers allows us to achieve this goal with our Grand Veena. They project harmonically rich, clear and expansive soundstage images and offer fatigueless extended listening sessions.

Our own hand-built 7" (170 mm.) main driver is hyper-exponentially shaped and covers a wide range of the music evenly. Utilising advanced materials and techniques the driver is designed to not require crossovers and it is coupled directly to the amplifier. The potentially harmful effects of crossover components are removed from the path so the musical signal arrives at the driver uninterrupted and intact. Every tiny musical detail is tracked precisely and immediately.

[crazyBLUE]

Beautiful speakers & quite an impressive read on the Grand Veena, They probably cost serious bucks I am sure !

[Big Daddy]

Originally Posted by crazyBLUE

Beautiful speakers & quite an impressive read on the Grand Veena, They probably cost serious bucks I am sure !

These are the list prices. I am sure it is possible to find better deals from dealers.

Dulcet:
$1795, or $1975 in Premium Finishes

MM DeCapo:
$2990 in natural or red Maple, $3289 in piano black lacquer

Veena:
$3495 - Natural Maple, Cherry Red Stained Maple, $3845 Piano Gloss Black

Episode:
$5500 in natural Maple, red Maple or black Maple. $6050 in piano black lacquer

Grand Veena:
$8795 in natural or red Maple. $9200 in piano black lacquer

[jsr]

Interesting read. A couple of questions...

1. Why does placing the higher frequency drivers further away (relative to lower frequency drivers) help with phase/time alignment?

2. Why does angling the drivers upward help with phase/time alignment?

[rpatt]

When I get my PT800s & PS1400s docked, they will become four way biamped, time aligned towers.

[rpatt]

Originally Posted by jsr

Interesting read. A couple of questions...

1. Why does placing the higher frequency drivers further away (relative to lower frequency drivers) help with phase/time alignment?

2. Why does angling the drivers upward help with phase/time alignment?

1. The low frequency driver cones are deeper. By moving the high frequency driver cones back, the ends of the voice coils line up vertically and the sound waves reach your ears at the same time.

2. Same as #1.

[jsr]

Thanks rpatt. #1 makes sense, but for #2 I don't see how leaning all the drivers the same angle backwards (pointing upwards) affects relative phase/time alignment. Once their VCs are aligned on the same plane, the leaning would still keep them aligned on that plane so I don't see what leaning contributes. It also looks like it would put the listener more off-axis.

[rpatt]

Originally Posted by jsr

Thanks rpatt. #1 makes sense, but for #2 I don't see how leaning all the drivers the same angle backwards (pointing upwards) affects relative phase/time alignment. Once their VCs are aligned on the same plane, the leaning would still keep them aligned on that plane so I don't see what leaning contributes. It also looks like it would put the listener more off-axis.

Yes, they would still be aligned but on an angled plane. Relative to a vertical plane, the tweeter & midrange would still be farther away from your ears. The correct angle of lean would have to be calculated. It would also make them slightly off-axis.

[jsr]

What does moving the tweeter and midrange further away via angling do for phase/time alignment? I guess the off-axis response may give a more laid-back sound that many like (including myself).

[Big Daddy]

Originally Posted by jsr

What does moving the tweeter and midrange further away via angling do for phase/time alignment? I guess the off-axis response may give a more laid-back sound that many like (including myself).

Go back and read Posts #1 and #2 again. The explanation is there.

The idea behind this is to mount the drivers in the cabinet so that each is the correct distance from the listener. The individual drivers (tweeter, midrange, woofer) have to have their acoustic centers aligned so that their outputs arrive at the listener's ears at exactly the same time. Time-alignment is done to simulate a single plane radiation source.

Sometimes the differences in phase response at frequencies shared by different drivers can be corrected by adjusting the vertical location of the smaller drivers (usually backwards), or by leaning or stepping the front baffle, so that the wavefront from all drivers is coherent around the crossover frequencies. The center of the drivers determine the amount of rearward offset to time-align the drivers.

This is from Wilson Audio's Maxx Series 3 Website:

In conventional systems, drivers are mounted in a flat baffle such that each driver is positioned at a different distance in relation to the listener. Thus, energy from the tweeter arrives at the listening position in advance of the midrange, which in turn arrives before bass generated by the woofer. The problem of achieving both time-domain coherence and optimal driver dispersion is only exacerbated by larger speaker systems. Most speaker designers simply ignore this measurement. The fact is, misalignment of the drivers by small fractions of an inch will audibly degrade transient performance, soundstage height, width, and depth, as well as introduce tonal anomalies that destroy the otherwise convincing "presence" of an instrument or a singer's voice.

The key to solving this problem lies in the vertical alignment of the various drivers in an adjustable modular array so that each driver's waveform propagation "matches up" with its neighbors' in such a way as to create the sonic equivalent of a single point source. Wilson's patented Adjustable Propagation Delay has long set the standard for precise driver positioning in order to ensure correct propagation alignment for a wide range of listening locations. MAXX takes this technology a step further with its Aspherical Propagation Delay. MAXX's driver modules not only adjust forward and back (in the time domain), but also rotate on their vertical axis in order to achieve optimal driver dispersion for nearly any size room and for multiple listening positions. The Alexandria and now the MAXX Series 3 are the only loudspeakers to utilize these combined innovations.

[crazyBLUE]

Vary interesting Big Daddy

[callas01]

Originally Posted by Big Daddy

The important thing is to push the higher frequency drivers back. If the crossovers in your speakers are first order (6dB per Octave), they are time and phase coherent. If the crossovers are higher order, they may not fully satisfy the rules of phase coherence, but I would still give Boston a lot of credit for being innovative.

In this case BD, all Dynaudio speakers use 1st Order 6 db/octave crossovers. You should add them to the list in the first post.

High quality 1st order crossovers
Only the highest quality components, selected for their sonic properties, are utilized in Dynaudio crossovers: carefully wound pure OFC (oxygen-free copper) air-coils, select capacitors, and temperature-stable ceramic resistors. A Dynaudio crossover features pure 1st order filters (6 dB/octave), which enable a superior transient response and can only be effectively used with the ultra-linear frequency response of the Dynaudio drivers. Another Dynaudio area of expertise is impedance correction, making a perfect combination possible with virtually all amplifiers

[BigAl87]

Originally Posted by callas01

In this case BD, all Dynaudio speakers use 1st Order 6 db/octave crossovers. You should add them to the list in the first post.

Don't forget rule number 2 Steve. If Dynaudio meet the specs with all their speakers then the Hawk has to be there which brings me to if my ears are directly beween the Midbass driver and the tweeter I technically have a perfectly coherent speaker persay.

So the Hawk could qualify as a coherent speaker.

[callas01]

Originally Posted by BigAl87

Don't forget rule number 2 Steve. If Dynaudio meet the specs with all their speakers then the Hawk has to be there which brings me to if my ears are directly beween the Midbass driver and the tweeter I technically have a perfectly coherent speaker persay.

So the Hawk could qualify as a coherent speaker.

whats interesting is that the part I bolded states, that not only does each speakers drives reach the listener at the same time, they also retest to make sure each PAIR of speakers are time-phase aligned.... another reason why dynaudios are so well built.

Dynaudio directivity control
The distinctive driver symmetry with two mirrored drive units is an unmistakable characteristic of the Dynaudio directivity control (DDC) technology. After years of development experience with Dynaudio professional studio monitor loudspeakers, it became clear that many recordings are of superb quality but, due to listening room acoustics, the potential of these recordings could not be fully experienced. In particular, reflections from floor and ceiling boundaries interfere with a faithful, realistic sonic reproduction because of distortions and added time delays. With DDC, Dynaudio has created a technology that effectively reduces these effects. The vertical symmetrical drive unit array and elaborate crossover topology reduce the energy dispersed to the floor and ceiling by approximately 75 percent. The controlled vertical dispersion makes the loudspeaker far less dependent on the room and much less influenced by positioning as compared to conventional designs. DDC isn’t simply arranging the drivers in a symmetrical array. For DDC to succeed, every single detail – from each drive unit to the crossover – must be individually tailored and optimized for this concept. With two tweeters, two mid-range drivers and, depending on the model, two or four woofers, each drive unit complements its identical counterpart in frequency response and phase relationship in such a manner that a carefully defined dispersion characteristic is achieved. This intricate matching is repeated once again for each loudspeaker pair to work together in tandem. DDC is an impressive example of the innovative Dynaudio methodology for loudspeaker design and is truly without equal.

[BigAl87]

Originally Posted by callas01

whats interesting is that the part I bolded states, that not only does each speakers drives reach the listener at the same time, they also retest to make sure each PAIR of speakers are time-phase aligned.... another reason why dynaudios are so well built.

Yes each of the speakers are time phase aligned and not ech of the drivers in each speakers, look at the figure with the Wilson Audio to really understand what they meant.

Any how I know totem does the same they test tone the drivers to pair them together properly and then the built the cabinets with the wood grain that has the closest possible match and retest to make sure the end result is as good as it was originally tested which is one of the reasons Totem have such strong imaging.


Anyhow does not mean because a speaker is not perfectly coherent it's soes not sound fantastic, in a perfect world you would always have to sit in the perfect spot with your ears at a pefect hight to reach perfect coherency. Nearly impossible if you ask me, as if you ear are 2 inches higher than me when you sit and I actually have perfect coherency than you are off.

[Big Daddy]

Originally Posted by callas01

In this case BD, all Dynaudio speakers use 1st Order 6 db/octave crossovers. You should add them to the list in the first post.

I did not intend to list every phase coherent speaker in post #1. I just used a few examples to help people understand phase coherency. I also added a few more to post #2. Unfortunately, there is a limited number of characters that you are allowed to include in one post. If you need additional room, you need to make another post.

The fact that you mentioned Dynaudio is good enough. If you want, you can always add a few pictures.

[Big Daddy]

Rockport Technologies Altair is another example of conherent speakers. They weigh 515 pounds each and cost $97,500 a pair. Their drivers are made by Audiotechnology in Denmark and some of them are made by Dynaudio.

Their Arakis speakers weigh 900 pounds each. They are $165,000 a pair. Most houses will probably collapse if you put a pair of these on the second floor. Each speaker has two(2) 15" subwoofers, two (2) 8" midbass drivers, two (2) 5.25" midrange drivers, and one 1" tweeter. The height is 81", the width is 24:, and the depth is 36.5".

Another speaker that has the curved baffle is the Gryphon Poseidon speakers. They are only $140,000. Their other speakers are also coherent.

[jsr]

Originally Posted by Big Daddy

Sometimes the differences in phase response at frequencies shared by different drivers can be corrected by adjusting the vertical location of the smaller drivers (usually backwards), or by leaning or stepping the front baffle, so that the wavefront from all drivers is coherent around the crossover frequencies. The center of the drivers determine the amount of rearward offset to time-align the drivers.

Gotcha. The leaning is used to accomplish the same task as stepping the baffle.

[prerich]

Originally Posted by Big Daddy

I did not intend to list every phase coherent speaker in post #1. I just used a few examples to help people understand phase coherency. I also added a few more to post #2. Unfortunately, there is a limited number of characters that you are allowed to include in one post. If you need additional room, you need to make another post.

The fact that you mentioned Dynaudio is good enough. If you want, you can always add a few pictures.

Ok BD - I have a question - is there a listening distance where Time-Alignment doesn't serve a function (or that the benefit would be unnoticable)? As most speaker designs are a compromise of some sort, say dynamics for imaging ect. Where would the benefit of Time Alignment be most noticable - when sitting further away from the speakers (since this would mean a farther distance for each indiviual wave to travel before reaching the listener - making the waves more out of time with each other)?

[Big Daddy]

Originally Posted by prerich

Ok BD - I have a question - is there a listening distance where Time-Alignment doesn't serve a function (or that the benefit would be unnoticable)? As most speaker designs are a compromise of some sort, say dynamics for imaging ect. Where would the benefit of Time Alignment be most noticable - when sitting further away from the speakers (since this would mean a farther distance for each indiviual wave to travel before reaching the listener - making the waves more out of time with each other)?

Time alignment and angling of the drivers depends on the height of the ears and distance from the speakers.

As I indicated in Post #1, Richard Vanderseen is the champion of time and phase coherency. He has designed speakers so that you can adjust the backward tilt of the speaker so that all the drivers are perfectly synchronized and their signals converge at the listener's ears. The angle of tilt depends on how far the listener is from the speaker. In their owner's manual, there is a graph that tells you the required amount of offset in relation to the distance of the listening position.

The image is from the Vandersteen 3A Manual.

CoherentSpeakers.jpg