Revisiting "Imaging"

[Ian Mackenzie]

Hi Eso,

Can you advise the angle of your mid -hf corns? Are they conical (straight)?

Also what listening distance works best for you?

[toddalin]

I'd love to take you up on that some time. I'm in Long Beach. Conversely, you could have a listen to my system as well.

Regarding your comments about processing for time aligning horns I'll disagree though. The design I put together for the full Cogent systems I built with Rich and Steve has all of the drivers very close to physical alignment and the hardware is such that they are to be fine tuned to their room. Both physical alignment and focus can be adjusted for any listening distance. In my own installation the built-in bass horns are a 5-6 msec behind the midbass, but most people would never notice that in the bottom octave. My system was always designed for full analog so digital correction has never been an option.

When properly adjusted they disappear and create a great image. My own room is small but well treated: not fully dead but enough diffusion and diffraction for really crisp clear sound.

One this I haven't seen mention of as I've scanned this thread is soundstage extending beyond the speakers. If a signal is sent equally to both speakers in phase it will be centered. If phase is reversed in one channel the resulting phase cancellation will shift the image outside on the speaker with the correct phase. If can happen naturally in well engineered live recordings just from the natural room interactions, but it can also be done in the studio.

eso

Nice set-up. I'll have to try to get over there sometime. If the drivers are close to physical alignment, that is time alignment. As Stereophile notes, it is better to be close than far. BTW, one gent on the other forum noted that he had tri-amped Klipsch and when he used a processor to time align the signals, the imaging dramatically improved.

As far as extension of soundstage, yes, mine goes out well past the speakers, and sometimes, past the room. The other day I was listening to the Dave Mathews Band and the flute was behind me over my right shoulder.

[eso]

Hi Eso,

Can you advise the angle of your mid -hf corns? Are they conical (straight)?

Also what listening distance works best for you?

The horns are conical and are based on a design from Bill Woods. Both the mid and midrange horn original designs are the same as used by ΩMA in their system with a Cogent mid range.

However Rich and I modified the mid horn. We shortened it a little while maintaining the mouth diameter. This opened the angle of the horn to match part of the most extreme internal geometry of the Cogent phase plug. The result was improved clarity. The drivers are so powerful we weren't looking for compression to increase sensitivity. The resulting horn is a 52˚ 12-sided conic.

My own room is small and I'm ~12' from the voice coils in the main arrays. It's a giant pair of headphones, but it works great for my listening. Further in a bigger room could be better.

eso

[Mr. Widget]

Nice set-up. I'll have to try to get over there sometime. If the drivers are close to physical alignment, that is time alignment. As Stereophile notes, it is better to be close than far. BTW, one gent on the other forum noted that he had tri-amped Klipsch and when he used a processor to time align the signals, the imaging dramatically improved.

Hmmm....

Nice set-up.

Yes!

I'll have to try to get over there sometime.

A bit of a road trip for me, but I'd love to.

If the drivers are close to physical alignment, that is time alignment.

But with a vertically staggered array unlike a concentric speaker it can only be time aligned for one listening position. Meaning a lower or higher seat or standing will no longer be time aligned... also the drivers need to have their acoustic centers aligned, not necessarily the voice coils.

As Stereophile notes, it is better to be close than far.

They say a lot of things that are absolutely false. Stereo is designed to be an equilateral triangle, plain and simple... though I agree that sometimes a system sounds better if we deviate from that sightly. I wouldn't generalize though.

BTW, one gent on the other forum noted that he had tri-amped Klipsch and when he used a processor to time align the signals, the imaging dramatically improved.

I'm sure he believes that. I would be shocked if it was confirmed in a blind test.


Widget

[toddalin]

But with a vertically staggered array unlike a concentric speaker it can only be time aligned for one listening position. Meaning a lower or higher seat or standing will no longer be time aligned... also the drivers need to have their acoustic centers aligned, not necessarily the voice coils.

Widget

Right. Only one person listens at my house. Note how the Heils are aimed down to my ears.

Right. And this is why I use an RTA at the sweet spot to determine the smoothest response regardless of how they actually stack forward/rearward.

[Ian Mackenzie]

Hmmm indeed.

Excuse me gentlemen while l interject.

If we going to challenge or question each others views being expressed please include your reasoning or evidence with your view or your challenge. See below an example:

In theory there can only ever be one spot don you think?

Dave Wilson was a pioneer in adjusting time aligned systems.

My understanding is that timing can influence localisation. See the quote from research below. If the harmonic structure of an instrument isn’t time aligned with the fundamental or the harmonics and overtones then there is a problem with some staggering of the arrival timing and the phase shifting during the time domain.

For example listening to a crash cymbal after its struck till when it ultimately fades.

This is about precision and as noted by Andrew Jone it’s where the cost goes up in more elaborate loudspeaker systems.

[Quote]

https://www.sciencedirect.com/topics...rmak%2C%202015).

“ Sound Localization and Binaural Sound Lateralization Tests.
Sound localization is based on binaural cues (interaural differences), or differences in the sounds that arrive at the two ears (i.e., differences in either the time of arrival or the intensity of the sounds at the right and left ears), or on monaural spectral cues (e.g., the frequency-dependent pattern of sound filtering caused by the angle of incidence of the sound with the external ear). Interaural differences are used mainly for left-right localization, whereas spectral cues are used for vertical and back-front localization.”

[Ian Mackenzie]

Right. Only one person listens at my house. Note how the Heils are aimed down to my ears.

Right. And this is why I use an RTA at the sweet spot to determine the smoothest response regardless of how they actually stack forward/rearward.

Todd,

I have visited your home and l admire your ingenuity & persistence.

If only we had more like you.

[Robh3606]

But with a vertically staggered array unlike a concentric speaker it can only be time aligned for one listening position. Meaning a lower or higher seat or standing will no longer be time aligned... also the drivers need to have their acoustic centers aligned, not necessarily the voice coils.


Widget

Yes one point only within some tolerance hopefully not in inches. If you move outside the window it degrades so with changes to distance and height the driver arc would change. The real question is just how audible this really is. There are very few true Time aligned systems and as long as you stay within the B+L curve for group delay you should be OK.

I played with that once in one of my older systems and depending at what height I measured the speakers at I could get very close to the single spike triangle step response.

The Arrays are not time aligned and yet they manage to image well as an example.

See figure 19 in attached page from Improvement in Monitors

Rob

[toddalin]

More on imaging.

Listen to this track (I'm sure that many have it). You have shrunk yourself down and are standing on the piano just behind the keyboard with the strings laid out infront of you. As each note is played you can hear the sound move to the left/right such that each string is clearly defined in space. This is not something you would hear in the real world standing next to a piano. I'm sure many classical pieces are recorded like this too.

https://www.youtube.com/watch?v=JBchE1PMkg8

[toddalin]

Todd,

I have visited your home and l admire your ingenuity & persistence.

If only we had more like you.

Thanks. You know that you always have a place to stay if you get up to this area.

[Ian Mackenzie]

Hi Rob,

Here attached is far more insightful and relevant information from the Project Array Designer himself.

See the attached documentation

https://support.jbl.com/on/demandwar...20Brochure.pdf


[Quote]
“The final major feature is the capability of the horn to be moved forward or back without creating baffle discontinuities. This allows the horn HF and LF drivers to be lined up in the depth direction to achieve the best time behavior over a large frequency range. This also allows the drivers to be "in polarity" in addition to "in phase" at the crossover point.
The sum total of these main features is a loudspeaker system with the speed and dynamics of a compression-driver system, but with the smoothness and imaging of the best direct-radiator and panel systems.”

So obviously the time behave matters or he wouldn’t have gone to all that trouble with the industrial design.

If you unbolt your Array horn and move it you may not hear the difference but other people might. You might be as deaf as a post or the next person might be. Your own biases may also influence what you hear. All that matters is what you hear on your own system and no one gets hurt.

[Robh3606]

Hi Rob

So obviously the time behave matters or he wouldn’t have gone to all that trouble with the industrial design.

If you unbolt your Array horn and move it you may not hear the difference but other people might. You might be as deaf as a post or the next person might be. Your own biases may also influence what you hear. All that matters is what you hear on your own system and no one gets hurt.

Hello Ian

I think you are missing the point I was trying to make. He made sure that group delay met the B+L curve in the figure I posted. That is the threshold for audibility,

I didn't say it wasn't addressed or not important in the design as obviously it was and is going forward.

Take a look at the impulse response. It's obvious he put summing through the crossover and the polar response before time alignment. He knows what counts and what to emphasize.

You don't need textbook time alignment to make a well engineered speaker that images well.

Also moving the horn front to back only works for the woofer and mid 435Al driver. It does not in any way change the physical offset between the 435Al and the 045Ti tweeter that clearly leads the other 2 drivers.

Here is the step response. First one posted 1400 Array

The step response in a time aligned system on the designed axis is a single triangle with no differentiation visible between drivers.

Also attached is the step response on the Wilson system that takes a rather extreme and brute force approach to time align their speakers by making the baffle adjustable to distance and ear height.

They get much closer to ideal where their emphasis is time alignment. Wilson Speaker post 126

Rob

[eso]

[QUOTE=Ian Mackenzie;446889]Hi Rob,

Here attached is far more insightful and relevant information from the Project Array Designer himself.

See the attached documentation

https://support.jbl.com/on/demandwar...20Brochure.pdf

“The final major feature is the capability of the horn to be moved forward or back without creating baffle discontinuities....

Being fully adjustable was a primary requirement for the Cogent main arrays.

Early on Rich and I worked on locating the balance points of each horn/driver assembly and mounting those assemblies around their balance points while having the drivers physically aligned became the basic layout for the racks.

Zero position was suspending the mid horn and driver at it's balance point with a pivot and struts that allowed a good +/- range on the vertical axis. The midbass assembly is able to move forward or backward to maintain physical alignment with the mid while moving up or down as needed to focus with the mid and the desired distance.

Finally the tweeter needed to be able to move in yet another axis to align with both of the other drivers. Sourcing all of the various hardware took a while, and once we had it Rich's machining know how was needed to adapt everything.

And then other features just help to make a cohesive system. One side of the racks distributed the signal wiring and the other side fed the field supplies. Crossover network mounted in the base of the rack.

I made a variation on these racks for my system here. I needed something shorter

eso

[Robh3606]

Hello eso

Hey they look just like stainless steel turnbuckles used on a sailboat to tension the rigging! Cleaver idea infinitely adjuatable.

Rob

[Ian Mackenzie]

Edit : For those involved or just lurking my endeavour in this thread has been to engage members to express in their own words what they done themselves in so far as the imaging of their system is concerned. There have been some great posts to date.

Keep it coming.