Revisiting "Imaging"

[grumpy]

The way I think about it is this (not intending to be a definition, or even "correct"... much of this has been said already, and I have no horse in this race. Maybe it will resonate... or not):

Imaging can be heard and quantitatively assessed with panned instruments in a stereo recording.

Soundstage includes the realism of the venue (assuming a minimalist mic setup or very well placed mics and effects), sometimes including "depth" or "size" (which can be room/reverb/plates or relative levels) -and- some level of imaging... a coherent preciseness of where a singer or instrument is located adding to the "realism" or "hyper-realism" of the soundstage.

Certainly have been some interesting comments

[Robh3606]

So which do we prefer? My DIY TADs create a more diffuse image that more closely recreates live music, my point source Meyer speakers create the holographic audiophile type image. I like them both.


Widget

So the best of both worlds! Always nice to have a second system that's a bit different where you can try things out.

Rob

[Mr. Widget]

So the best of both worlds! Always nice to have a second system that's a bit different where you can try things out.

Rob

Yes, and I appreciate how lucky I am to have two very satisfying systems.

I believe the impetus for my starting this thread was having moved to this new house and giving up my beloved Everests, I was once again using the 1400 Arrays as my primary speakers. The 1400 Arrays while not quite as holographic as the Meyers, were way beyond what the mighty Everests were in the imaging department. Subsequently the 1400 Arrays moved on and the 2007 DIY TADs made their comeback. They image more like the Everests, but on the continuum, they are closer to the 1400 Arrays.

If it was 20 years ago I would play around with them a bit more to learn more about the effects of baffle size, time alignment, etc. but these days, I'd rather just cue up some music and enjoy it.


Widget

[1audiohack]

To which:

The responses on the Wilsons have always "baffled" me. They go to extensive steps to line up the acoustic centers and aim them all at the receptor location. But the the step responses still show three distinct driver signals arriving at the mic. If things are time aligned, shouldn't the signal from three drivers hit the mic simultaneously??? What am I missing here?

Hello Todd.

My memory sucks these days, as my days of rigorous studies are far behind me, there may be anything form oversimplifications to outright errors in this. Keeping it simple and short is my goal.

Each speaker device has a delay of its own. They are time invariant devices so different frequencies experience different levels of delay. Every speaker element has an acoustic origin that floats a little or a lot, front to rear over a given frequency range.

There are of course additional and sometimes large delays caused by the dividing network.

Impulse response measurements are dominated by the high frequency in the measurement as there is simply more information there per sample than at low frequencies. Impulse measurements look for peak energy. If the passband of the device under test is band limited, the impulse peak may center on the loudest portion of the received signal and not the highest frequency. Nothing seems certain in audio.

In practice I believe that using the impulse peak response for time alignment is the first rough tool used to get one somewhere in the ballpark. Whether the use of signal delay, physical manipulation or both, of the individual driver units are used to align the impulse peaks, one will undoubtedly end up moving them, in time and or space to get them properly integrated. The HF is going to get moved farther and farther back as compared to the LF.

To my understanding and experience, to achieve anything like the impulse measurement shown on post 154, the drivers must all be operating well within their linear range, the filters gentle, and the mid and low frequency drivers must be critically damped and obviously the drivers are not on the same plane. I am in fact unsure of how you get an impulse response that tight with the LF portion of the speaker in operation. I am not for a minute inferring that the measurement is bogus.

I assume that the Dunlavs are passive? I am going to read up on them a bit.

All the best.
Barry.

[toddalin]

As I noted before, if you listen to Emerson, or lots of piano pieces, you hear the strings laid out infront of you and you hear the notes "bounce" from string to string left to right infront of you. This is never something you would hear in the rear world, but this is what the mics hear, and this is what I want to hear. I don't want to just hear someone playing the piano infront of me as in a piano bar.

[Ian Mackenzie]

OK so basically JBL is not in the time alignment camp like most other manufacturers. You just admitted it in your explanation.

Like I said in my original post. As long as the design meets the B+L graph I originally posted. That means below the curve not at 2.5 Msec at 750Hz where it becomes audible.

Like the 3 systems graphed that are below the threshold.

Those are Stereophile step response graphs buy the way.

Why don't you just admit the 1400 is not time aligned/coincident as in the review? What's the big deal?

Text from the Array Review

"In the time domain, the 1400 Array's step response on the tweeter axis (fig.8) indicates that all three drive-units are connected with positive acoustic polarity, and that the tweeter output arrives at the microphone half a millisecond before that of the midrange, which in turn arrives half a millisecond before that of the woofer.

This is definitely not a time-coincident design, though the fact that the ear/brain does integrate arrivals over a longer period than 1ms should mean that this won't matter much.

LG was impressed by the stability and accuracy of the JBLs' imaging, which you'd think might be adversely affected by the lack of time coincidence.

But as far as the lower-frequency units are concerned, the 1400 Array's step response is at least time-coherent, in that the overshoot of the midrange unit's step smoothly leads into the woofer's step.

This suggests an optimal crossover implementation."


The Key is optimal crossover implementation which again I said in my post. Smooth driver integration and good polar response being the main focus.

Essentially all well designed systems are time-coherent. There is a difference they are not the same.

Rob

Hi Rob,

I think don’t appreciate the reasoning behind my previous posts.

Cool your jets, slow down and read my response below:

To explain:

In your earlier post you referred to the BL curve which l think is a good reference for audible thresholds of group delay. What l in fact posted was in the extracts referring to “Time behaviour” if you care to look at that more closely.

So let’s use that BL curve as a baseline for a practical loudspeaker. That is why l did the walk through on the Array 1400.

In my lengthy post l went to some trouble to explain that the acoustic centres of the Array 1400 drivers fall well within the BL threshold.

So what does that mean? It means that a human being won’t detect any group delay errors within the BL curve. Therefore the Array 1400 it’s meets time alignment from an auditory scientific point of view based on my walk through. I’ve actually proved this.

Your line of think seems to be hooked on those step responses tests published in Stereophile.

I quickly read a bunch of the Stereophile reviews. That impulse test is only an indication of what driver arrives first and if the other drivers are in or out of phase. It’s not actually referred to as a time alignment test by John Atkinson. He briefly discussed the impulse tests.

But more importantly there seems to be a consensus that the Project Array systems image very well. No it’s not by the definition of a step response perfectly aligned. I would suggest that as a pointer to imaging isn’t the answer. As far as Stereophile goes they are there to make money and they want to keep you curious so that you continue to subscribe. They know what graphs are attention grabbers. They have got your attention (respectfully). Correct.

So l am not the person getting upset here. It’s about reaching a moment of truth. The Array 1400 is the moment of truth. No it’s not a theoretically time aligned system but it sure a fuck images very well. The proof is in the listening.

There are no absolutes in terms of a right or a wrong. It’s about reaching understanding!
That is where l am coming from.

Where to from here? I think that as far as imaging goes there’s a whole cookbook of things that go towards making it work. It’s about figuring it out.

[1audiohack]

As I noted before, if you listen to Emerson, or lots of piano pieces, you hear the strings laid out infront of you and you hear the notes "bounce" from string to string left to right infront of you. This is never something you would hear in the rear world, but this is what the mics hear, and this is what I want to hear. I don't want to just hear someone playing the piano infront of me as in a piano bar.

Hello Todd;

Don’t you think that depends on where you are listening from? The polar responses of instruments are sometimes predictable but not always.

If you are at the keys, if the lid is open and the music rack is laid down you will certainly hear the piano low left to high right, just as you describe. I quite like that too.

In my youth I (kinda) played trombone, percussion and piano. I would way rather hear a trombone from the mouthpiece than the front. At least up close. (:

Barry.

[1audiohack]

Hi Rob,…So what does that mean? It means that a human being won’t detect any group delay errors within the BL curve. Therefore the Array 1400 it’s meets time alignment from an auditory scientific point of view based on my walk through. I’ve actually proved this….

Hello Ian;

This is where we get into trouble. You contending that the 1400 ARRAY can be scientifically considered to be perceptually time aligned verses the standard measures showing that it obviously is not, is going to be disputed. I understand your point.

Barry.

[Mr. Widget]

Hello Ian;

This is where we get into trouble. You contending that the 1400 ARRAY can be scientifically considered to be perceptually time aligned verses the standard measures showing that it obviously is not, is going to be disputed. I understand your point.

Barry.

Yes, once we enter the "perceptual" domain all hell breaks loose. What can the average person perceive, what can a trained listener perceive, what can an individual listener perceive...
On top of that, there is the whole question of how important time alignment at all. In gross terms, thinking of the original massive Altec theater systems where the HF horns were on sleds to reduce the delay between the woofer/tweeter, there is no question that alignment is important, but when we are discussing "time alignment" in the modern sense, there is a lot of potential debate on the topic.

In my opinion a speaker is either time aligned or it is not... kinda like being partially pregnant, it isn't a thing.


Widget

[Robh3606]

Morning Ian

Just echoing the previous posts once you get into perception it's psychoacoustics and it get's complicated. You have the step responses that are derived from the impulse response and then you have a delay table the B+L laws which are perceptual.

That's Widgets speakers on skids where they are physical moving things around to make sure the physical offset's, which are offsets in time ultimately, are under the line in the B+L table so they are not audible.

Take a look at the 3 systems graphed there. The worst offender is the 4331 and that is because of the long horn used that shifts the acoustic center of the tweeter. After the hump you can see a constant offset where the other two systems have much less delay over the same frequency range.

The kicker is all 3 systems don't have audible group delay even though we can clearly see the delay in the measurements.

What you posted about Greg's efforts I have no doubt definitely contributes to why the 1400's image like they do. That's rooted in his experience and understanding in the balance of measurement and psychoacoustics and what in his experience should be emphasized.

He hit a homerun with that system

Rob

[Robh3606]

Hi Rob,

I quickly read a bunch of the Stereophile reviews. That impulse test is only an indication of what driver arrives first and if the other drivers are in or out of phase. It’s not actually referred to as a time alignment test by John Atkinson. He briefly discussed the impulse tests.

Where to from here? I think that as far as imaging goes there’s a whole cookbook of things that go towards making it work. It’s about figuring it out.

Hello Ian

Atkinson is correct you don't use the impulse to determine the offsets you use the Step response. The Step is derived from the Impulse. The Step response shows you the actual alignment offsets in Msec.

You have a measurement system you don't have a Step Response choice in your system??

There is so let's keep the conversation moving forward.

Rob

[toddalin]

Hello Todd;

Don’t you think that depends on where you are listening from? The polar responses of instruments are sometimes predictable but not always.

If you are at the keys, if the lid is open and the music rack is laid down you will certainly hear the piano low left to high right, just as you describe. I quite like that too.

In my youth I (kinda) played trombone, percussion and piano. I would way rather hear a trombone from the mouthpiece than the front. At least up close. (:

Barry.

The difference being that close miced, the strings are sonically further apart providing much more separation. Yes, opening the lid and sitting at the keyboard you hear the left/right movement, but you can't "place each string" within that movement.

[toddalin]

Who says that JBL never got into time alignment? Isn't that partially the concept of the 4430? Doesn't the 2425 line up with the 2235?

While my 4430s were not the last word in soundstage and imaging, they were far superior to the L200/300s.

https://www.lansingheritage.org/imag...986_pro/a1.jpg

[Robh3606]

Who says that JBL never got into time alignment? Isn't that partially the concept of the 4430? Doesn't the 2425 line up with the 2235?

While my 4430s were not the last word in soundstage and imaging, they were far superior to the L200/300s.

https://www.lansingheritage.org/imag...986_pro/a1.jpg

I would say no. They are close and you can see that in the B+L curve where the 4430 is graphed. If you go through the Improvements in Monitors paper you will find they have a deliberate offset to tilt the listening axis up when floor mounted. They use a phase delay to tilt so there will be some offset.

I would like to see the step response on that system!

It's a good idea to read it as it addresses the B+L laws directly and as a user of the system it goes through why they image so well in comparison.

Has much more to do with the 2344 horn and directivity than T/A

Remember Time Alignment was Urie's claim to fame. If JBL came out with a T/A system I would think marketing would have been all over that.

There is a lot of information in the B+L table. If you look closely and read the captions the COAX is a UREI system. Look at the group delay through the crossover of the coax and the 4430

Again would like to see a Step on both not sure exactly what's going on.

https://www.audioheritage.org/vbulle...peaker-Systems

[Robh3606]

Here is an Impulse response and the derived Step Response on my Array 1400 clone. I also included a flipped version because I screwed up the polarity when I did the measurement.

The Flipped is so the Stereophile and my step can be viewed in the same polarity and not confuse anyone.

Impulse first

Step Response

Flipped polarity Step

As you can see there is a significant difference between the 2 views of the Impulse response,

Rob