Unconventional Techniques for Achieving Oustanding Stereo Imaging

[keyser]

Graaf, apart from if you are right or not, I think it's bad manners to keep repeating the same part ad nauseum, let alone doing it in such a big font.

 

[graaf]

Graaf, apart from if you are right or not, I think it's bad manners to keep repeating the same part ad nauseum,

I will keep repeating until I can see content-related responses

repetitio est mater studiorum

not to mention the fact that it is bad manners to ignore content-related posts in discussion, isn't it?

let alone doing it in such a big font.

I think You should mail the administrator and ask to disable the big fonts, as long as this editing function is available I will use it - why shouldn't?

 

[DBMandrake]

I will keep repeating until I can see content-related responses

In which case your obnoxious large font all caps ad-nauseum repeats of the same point will continued to be ignored by many people.

not to mention the fact that it is bad manners to ignore content-related posts in discussion, isn't it?

How is it bad manners for someone not to respond to every single point of an article that has many points and conclusions in it ? Just because you have seized upon a single point in the article as "proof" of your beliefs, doesn't mean that everyone else agrees with that, or sees it as the most important or interesting part in the article.

It's bad manners of you to keep trying to ram one point down everyone's throat and get upset when people don't respond to your large all caps repeats of the same point which contain no new information.

THE NATURAL CONCERN THAT WIDE DISPERSION AND THE ATTENDANT STRONG EARLY REFLECTIONS "WOULD LEAD TO DEGRADED STEREO IMAGING WAS NOT CONFIRMED BY THE EXPERIENCED LISTENERS

And despite this, half of these same experienced listeners still had a preference for a drier more reflection free sound ? What does that tell us ? (Hint: there is more than just stereo image localization to be considered when comparing different direct to reflected ratios)

Or are you only taking notice of the beliefs of the 50% of experienced listeners who preferred the highly reflective sound, and discarding the rest ?

I think You should mail the administrator and ask to disable the big fonts, as long as this editing function is available I will use it - why shouldn't?

There is nothing physically stopping you walking down a crowded street shouting your beliefs at the top of your voice either, apart from common courtesy

 

[markus76]

There is nothing physically stopping you walking down a crowded street shouting your beliefs at the top of your voice either

Not in real life but here, the ignore function is pretty effective. I can recommend using it - oh I already did

 

[graaf]

Some thoughts why i proposed that

...

Interaural cross correlation will tend to be lower, thereby also lowering the perceivable contribution
of the listening room's "small room reverb", which again is - even if beneficial in some respects - an
artefact.

...

Decorrelation (in highs) may contribute to giving all phantoms (center and side) a more consistent amount
of "virtuality" resulting in a more homogeneous presentation of the sound stage.

yes, yes, yes, most probably, and yes - but how to achieve that?

I believed that flooder or Elias "stereolit" can achieve exactly that but I have been told that these two are bad solutions and I have to tell You that after so much bashing I started to consider the possibility that indeed something rather must be wrong with my hearing... and Elias' hearing, and el'Ol's, and tinitus' and so on...

 

[graaf]

At 120 degrees the extreme toe out, the image was enormous. It grew the size of the room. It was more defined at the edges and somewhat blurry in the center. Sound clarity was OK but not optimal. Instrument separation was the best in this configuration. It is enjoyable for the short term but I probably won't keep it permanently.

------------
When it comes to personal preference I like 60 and 120 the best but they are different. When toeing out speakers the sides of the image become more clear while the center blurs and when toeing in the center improves but the side image deteriorates.

underlines mine

Hey Boris! I think that You really have to check out the stereolith thread and explore this toeing out thing a bit further, I think You may like it:
http://www.diyaudio.com/forums/multi-way/10962-stereolith-loudspeakers-question.html

BTW toeing-out as method of conventional speaker placement in room has been recommended for long time by Von Schweikert, for narrow listening rooms

I find that:

1) Long distance to the close sidewall is desirable.
2) Stronger close side wall reflections are preferable to far wall ones for correct image.
3) Reflections intensity should be minimized or eliminated for anything other than side walls when possible.
4) Side wall reflections should maybe come at different times than ceiling, front wall and be not be clumped together on the time scale.

Comments please?

ad 1) long distance of speakers or of the listener?
ad 2) yes
ad 3) and ceiling
ad 4) yes

 

[graaf]

Asymmetry is one of the most detrimental factors on imaging to me. The little board I've installed does tremendously improve localization within the left side of the sound stage.

congratulations on Your new discovery Markus!

 

[graaf]

what is this thread about?

 

[markus76]

That range of dB is quite close to correct par and parallels my findings. But I also find out the level can be quite critical too and thus the system can be challenging to tune.
Nevertheless, it rules out high directivity speakers with toe in, if spaciousness is required.

- Elias

It rules out any conventional design. A 120° constant directivity design with toe-out might be an exception. This might be desirable (it also "fixes" the sweet spot problem):

An externally hosted image should be here but it was not working when we last tested it.

 

[graaf]

A RFZ design cramps an orchestra into a even smaller space, the space between the speakers.

this plus no realistic images:

Any RFZ design will lack early spatial impressions.

and yes, Markus is also right in that:

There's nothing wrong with it, it is part of the art. It's a cultural phenomenon just like concert halls are.

but concert halls? very unlike phenomenon I would say

OTOH conventional stereo is much more a cultural phenomenon like Big Mac and so on
of course nothing wrong with it, afer all it is just crap, and crap is not anything evil or something, it is just crap


but I would say that worshipping crap IS definitely something wrong, not necessarily evil but definitely harmful to human beings

 

[graaf]

Hi Guys
In several earlier posts I have suggested an experiment where you take your system outdoors (if you can) and set it up with the same or similar geometry as in your home. The reason is what Earl points out, that the research being cited did not include a test involving very low levels of reflected sound.

To me, I don’t see how one can say X doesn’t matter if you never have the chance to judge with and without X and lacking speakers with significant directivity, the next best thing is normal speakers with no walls or ceiling to cause reflections. THEN one can hear the “without” case and decide how valuable close reflections are for a stereo image. .

... in case of this particular stereo speaker and setup exclusively

therefore I am with Markus:

There's an easier way to perceive direction, detail and dynamics of a recording: use headphones.

even better - earphones - I use Shure E2c (also Linkwitz's recommendation)

I too don't believe that a conventional wider dispersion design has any advantage over a RFZ approach but things change when a design is capable of creating very strong ipsilateral reflections (-5dB and higher). This adds a spatial sensation which is absent in "normal" stereo.

yes indeed - wide dispersion is not enough, one needs some exotic - not right - designs like a flooder or a back-to-back

 

[graaf]

It rules out any conventional design.

amen

A 120° constant directivity design with toe-out might be an exception. This might be desirable (it also "fixes" the sweet spot problem):

An externally hosted image should be here but it was not working when we last tested it.

ehm... isn't it Ted Jordan's stereolith-like setup, not far from Elias' and also mine?


check out this one as well, it has even a bit of a flooder in it:
http://www.diyaudio.com/forums/multi-way/196434-e-j-jordan-delay-line.html

 

[graaf]

You are actually precisely referring to the speaker you have built

handsome speakers! quite intimidating to know that Dave S. was da man behind

and here two other handsome speakers designed with this What is the ideal directivity pattern for stereo speakers? question in mind

interesting are those stereolit-like side-firing speakers in Ken Kantor's MGC-1 and flooder-like up-firing speakers in dbx Soundfield V

An externally hosted image should be here but it was not working when we last tested it.

 

[graaf]

I did some tests on the pink noise samples Markus posted.
...
3) Stereolithic back-to-back

Unfiltered pink noise:
Low freq image is very good in the center. Quess what, the speaker is there too At Very high freqs the image is split in two located far behind the side walls in very wide angle, maybe 120++ degrees.

Then I low pass 24dB/oct at 6kHz:
Almost ok ! No side wall images anymore, and low freq image in the center. A good starting point !

...

Schupbach (stereolith) has also a personal theory about this limit for stereo imaging, explaining why he goes with a single tweeter.
Hummmm...

I think Schupbach may have a small genious inside. Maybe he hears like us, who knows.

my thoughts exactly

 

[graaf]

Yes, that probably had an important role to play. But if it were all that dominant, I think that a lot of the "virtual space" we heard would have been similar.

but why? is there any science behind it or is it just a conviction? Moulton strongly asserts to the contrary

I wasn't, it changed from recording to recording - often drastically. From recording studio to night club to concert hall to cathedral to immense cave. What was so mind boggling was the very large spaces. We all commented on it, there were lots of looks of disbelief and head shaking. How could those immense spaces fit inside that little black box theater?

with flooder in much smaller room I have also experienced all kinds of listening spaces and walls disappeared, surely I don't think it was as spectacular as at Kiron nevertheless there was certainly nothing like superimposition of my room acoustics on the recorded acoustics, quite the contrary

I knew that acoustic space well, by that point I had spent 1000s of hours working in it. It only sounded like that during the demos. The big take away for most of us wasn't how great the system was, but how much info is hidden in recordings.

I believe that the effect was also due to the speakers and a very fortunate speaker-room interface

 

[Elias]

Humdinger, Just want to check are you from this planet ?!?

You got:
cross talk cancelling
dipole line arrays
wide directivity tweeters


Wow! That is my concept exactly


Maybe the exploded nerdometer explains few matters..


By the way, I come to think about the single mono speaker for direct sound again as I came accross these cute pics of mono and stereo fields:

No need to say which field is more natural in terms of direct sound !

But single mono speaker do not envelope you with sound. Need to add decorrelated surround speakers !

Did you try with more than 2 surround speakers? And other locations than at the back?

Since I read some vise men wrote IACC is minimised if source is in frontal hemisphere at about +/-55 degrees. There were some other benefits too (forget what). Anyway, in a real acoustic event most of the sound is coming from the frontal hemisphere. Also most of the 'surround'. So, should be logical to put at least some of the surround speakers in front. Maybe at least 4 surround speakers is enough.


- Elias

P.S. and yes the 4 surround speakers do not mean added media channels, but they can be generated from the two stereo channels.

I feel "I am there" when I have minimal playback listening room reflections, the inter-aural cancellator is engaged, and there is reverb embedded in the recording. Best case is with Binaural recordings, but many non binaural are pretty "transporting" too. Synthetic image synthesis has gotten pretty impressive. The further you go away from that, the more it becomes more like "they are here" to my way of thinking, not that that is necessarily so bad. I suspect that only a full nerd like me would appreciate the elevated clarity of imaging at the sweet spot. Only a fool like me wants to completely escape this screwed up world, and step through the looking glass altogether. For most others I'd expect them to be happier with speakers that have 150 degrees horizontal consistent over most frequencies radiation; so there's a good frequency response out of both speakers at most places in the room. Although the DBX Soundfield speaker was exceedingly enjoyable to my ears (4 ft. away from any walls), it did scramble most of the real imaging info in the recording, and replace it with listening room effects. Controlled directivity on the vertical axis makes real good sense in either case, to avoid ceilling and floor bounce, which typically causes -12dB cancellation notches all across the spectrum starting around 500HZ (based on my 1st hand measurement experience).

My appreciation of vertical line arrays keeps growing. Up to 6-7kHZ that might work best with typical listening room acoustics. It inherently has limited vertical dispersion so minimal floor and ceiling bounce cancellations. It works well with room reflections in general because any cancellations are more likely to be filled in (in more locations in the room) by so many other physically displaced sound sources putting out the same thing at the same time. Especially in the lower mid and bass freqs., where the cancellations are typically further apart and only a few effective reflections exist with one or two drivers, so little or no fill-in down there. Above 6-7kHZ, I still think very wide dispersion will sound best, part because most speakers get real narrow in this range (so off axis and power response get bad), and because we don't use that freq range for imaging clarity in the same way as the ranges below it.

 

[boris81]

By the way, I come to think about the single mono speaker for direct sound again as I came accross these cute pics of mono and stereo fields:

Elias,
visual simulations are great for predicting interactions between sound waves and the environment but should not be used to illustrate how we hear. Indeed if continuous, even sinus waves are played in stereo the listener will have no idea what direction they are coming from. Our brains seem to react best to transients when processing sound information and music happens to be rich of those.


We are all aware that stereo is not a perfect technology but the vast majority of music is recorded that way. Until someone revolutionizes the recording industry we are all stuck building speakers to accommodate the stereo format.

By making the tweeter very wide directivity, maybe even close to omni, it will not introduce contradicting cues but will faint away in the backround to allow lower frequencies to enable the imaging.

And because of this, the speaker at lower frequency ranges than treble must have high directivity to allow less room influence.

Ideal directivity pattern for stereo speaker is: high directivity at bass and midrange, and low directivity at the treble.

I am curios about this design view and I am tempted to give it a try in the near future. I find multiple reflections in the midrange and bass to be detrimental to imaging and clarity. Reflections in the highs don't seem to be as offensive. Has anyone build something like this?

 

[graaf]

This quote is not exactly correct (nor is your interpretation of it). For slow moving symphonic music it is generally considered that sound within the first 50ms increases perceived level without degrading musical clarity. For speech the window must be dropped to 30 ms otherwise inteligibility suffers.

are You sure?

because for Leo Beranek ("Concert hall acoustics", Journal of the Acoustical society of America 92, 1992) clarity is about the "adequate ratio between the energy of the first 80ms and that in the next 2s":

"Clarity means the ability of distinguishing successive musical notes and different instrumental groups or the clear detection of words. It seems to be a degree for intimacy. As an objective criteria for music it means the ratio between the energy of the first 80ms and the energy after 80ms."

"For speech applications the same criteria is used but with the limit of 50ms."

...the ear effectively uses a variable time window, short at high frequencies and long at low frequencies. The time window is so short at high frequencies to only let in the direct sound and some nearby cabinet reflections. By the midrange the nearest boundary bounces, such as the floor bounce, will be perceived wile later bounces are excluded. At low frequencies the window is fairly long and most of the room response is perceived.

undelines mine
looks like You have just authoritatively explained why a flooder works - frequency response-wise - thank You

 

[graaf]

Humdinger, Just want to check are you from this planet ?!?

You got:
cross talk cancelling
dipole line arrays
wide directivity tweeters


Wow! That is my concept exactly

yeah, there is a lot in common
Humdinger system is nowhere near conventional stereo

No need to say which field is more natural in terms of direct sound !

But single mono speaker do not envelope you with sound. Need to add decorrelated surround speakers !

for my part I say give a mono flooder another try - this time more serious

You get spaciousness which is lacking in case of conventional stereo
what is lacking in this case is of course left-right aspect of the soundstage

 

[DBMandrake]

Maybe the exploded nerdometer explains few matters..


By the way, I come to think about the single mono speaker for direct sound again as I came accross these cute pics of mono and stereo fields:

No need to say which field is more natural in terms of direct sound !

Cute though your picture may be, it doesn't tell us anything about how sound is perceived by two ears. What it shows is the interference pattern between left and right speakers at one frequency, (which frequency ?) as measured by an omni mic which has 100% channel crosstalk. You are seeing a visual manifestation of the comb filtering that was being discussed a couple of pages back.

As also discussed a couple of pages back, at high frequencies our head dramatically reduces channel crosstalk above ~1-2Khz for speaker separations of ~60 degrees and greater. So the perceptual sound field doesn't look anything like that.

I'd also point out that inverse square law reduction in amplitude doesn't appear to be taken into account in that picture, so it's a rather naive representation of the sound field.

Be careful about drawing conclusions on how something will sound based on a visual representation of data which does not take into account important aspects of our hearing mechanism.