What are you experiences with imaging and sweet spots?

[paulspencer]

I recently heard a horn system which made me question what is it that makes for good imaging and a broad sweet spot?

The speaker in question has a CD in a large 200 Hz horn on top of a vented 15" pro driver. I'd call the sound "direct." I've heard it said that wide dispersion puts the musicians in the room and narrow dispersion gives a window to the musicians. I think that would describe what I heard.

So I'd like to hear what you guys have experienced - what speakers you have heard and what kind of imaging and sound stage they created as well as the sweet spot.

This is what I've experienced:

* Tannoy - fairly recent dual concentric with 6.5" midbass drivers (vented bookshelf)

Imaging appeared to be good, despite the room being much like a garage with carpet and a couch acoustically.

* My mains - MTM with dome tweeter and 6.5" midbass

They can image quite well as previously mentioned. The sweet spot is such that you can sit off centre without the image collapsing into one speaker - a centre speaker isn't needed for home theatre.

* My mains on an open baffle panel

Noticeably bigger sweet spot, which was welcomed. The sound stage was bigger and the overall sound more appealing. When I put the drivers back in their boxes again, the sound stage was suddenly smaller.

From memory I'm not sure if the imaging is better or not as I didn't pay specific attention to that aspect, but the sound was more transparent, creating a more real illusion of the musician being in the room.

* Adire HE10 (coax 10")

Imaging did appear to be good but the treble harshness made it hard for me to really evaluate.

* CD horn

See previous comment at start

I've heard a great deal many more speakers, but these are the ones where I paid some attention. I've heard some omnis and I can't say their imaging was actually any different to conventional hifi speakers from memory. It was a surprise at the time, as I felt an omni was the worst possible design from an imaging point of view.

A more theoretical question:
How does one achieve a large sweet spot?

I'd like to experiment with horns and dipoles quite soon as an upgrade, I just wonder if I will be happy with the sweet spot and imaging of horns and if I should design any horns to have dispersion as wide as possible. One of my current ideas is a 3 way with a large mid horn (either CD or cone mid driven), concentric supertweeter and 12" pro mid on open baffle.

[SY]

How does one achieve a large sweet spot?

IME, a rather large room and omnidirectional radiators.

[bjorno]

what is it that makes for good imaging

Sy, good answer!

A short answer and leaving out driver qualities and filter requirements for the moment:
A speaker stereo (?) or multi-channel set-up that minimizes phantom localisation errors, vertical and horizontal together with a physical layout that maximizes phantom sharpness, minimises time/intensity trading smear/blur effects by either layout of the physical drivers if using minimal baffles and/or smoothing them out buy intelligent choice of baffle layouts.

b

[medum]

Originally posted by SY


IME, a rather large room and omnidirectional radiators.

I rather agree with SY, ..... BUT:

In my opinion you will always have a "problem", if you don't have the same distance to your speakers - no matter what kind of speakers - because you will have a phase problem. Almost all sounds from your stereo comes from two points, and unless you have the same distance to these points (speakers), the sound are out of phase, right?
So stick to your sweet spot for serious listening

[paulspencer]

I plan on sticking to the sweet spot, but I'm interested in how to make it bigger! So at least 2 people can sit in the sweet spot. Enjoying audio isn't always a solitary affair!

[bjorno]

So stick to your sweet spot for serious listening

Medum, No contradiction at all but a sharpen up the general requirements of the thread owner’s wish: broad sweet spot and entering the lower level where imaging can be discussed?

b

[medum]

Originally posted by bjorno


Medum, No contradiction at all but a sharpen up the general requirements of the thread owner’s wish: broad sweet spot and entering the lower level where imaging can be discussed?

b

of course - If you want a broader "sweet spot" - go for the reflections from the walls. My Marin Logan Clarity speakers have a rear mounted tweeter, that can be activated for "party-listening" - maybe that could be a solution. But I must say that it is not really a sweet spot. Unless you have the same distance to the speakers, you are not in the sweet spot.

[bjorno]

If you want a broader "sweet spot" - go for the reflections from the walls.

No offence Jørn, but now the subject is expanding into including room effects and I find it hard to stay focused at the original question.

There is no indication that the room effects should be counted as I can see. I’m hesitating to further follow this thread because the risk that this matter is divergating too much for my taste.

But maybe this picture can be used as good starting point if a discussion of pros and cons of the sweet spot; sweet spot area is essential for the thread owner?

Look at:Post#2

Aww Jeez, another moronic post (pls forgive me but)...


b

[phase_accurate]

you will have a phase problem

Primarily you generate a delay problem but this will lead to a phase problem as well of course.
But the delay part is the one that spoils imaging.
The phase problem will lead to frequency-response aberrations.

Regards

Charles

[dlneubec]

FWIW, my experience has been similar. My first DIY's were an MTM. They sounded good, had good imaging, but the soundstage was not particulary big and was sort of flat front to back, nor were they forgiving of listener position.

My second major DIY was the NaO Mini, open baffle MTM. The soundstage was much bigger and deeper. The imaging was still very good and more forgiving of listener position. You get a real sense of 3d space around them.

My latest project is a hybrid omnidirectional design. Each speaker has a downfiring 12" sub for 100hz down, an up and down firing midwoofer covering from about 100hz up to 1450hz. Then there is a front firing tweeter that covers from 1450 up to 21khz or so. It has a much bigger and deeper soundstage than even the NaO and for the first time, I seem to be able to hear the size of the recording venue, for example one recording sounds like you are in a small nightclub and another sounds like the soundstage is well outside the walls of the room you are in. Instruments can sound like they are way behind the speakers. However, I think becuse of the direct firing tweeter, they still have good imaging and are very forgiving of listener position, IMO. YMMV.

When I was building and testing the omni prototype, I was able to compare a single speakers sound from each of these types. It was eye opening to me, but sort of hard to describe. Here is the best way I came up with to describe it. You know how a single box MTM sounds so much smaller than a pair of stereo boxes? I could describe the single box MTM as having about 1/4 of the soundstage as two of the box MTM's in stereo. Compared to the box MTM, a single open baffle NaO mini could be described as having 1/3 of the sound of the pair of NaO's. Compared to the others, the hybrid omni had more like 1/2 the sound of the pair of omni's. A single omni almost sounded like it could be as big 3/4 of the soundstage as the two boxes. Here is a photo of the hybird omni: