A theoretical model for stereo imaging

[RexrothPigeon]

I don't know what Gary's investigative process was, but his ideas have been subjected to controlled blind testing evaluation.

ok so not exactly
a speaker he made according to his theories beat out (A) a linkwitz orion with no sub or EQ (lol) and (B) a terrible Beringer speaker in a test with 13 listeners. I'm no expert, but it seems to me they did a commendable job trying to produce a controlled test, so that's good.

The test unequivocally can't support this claim, however. And that's what I was asking about.

he finds that a bipolar or dipolar pattern works best, but with the rear-firing radiation about 6dB louder than the front-firing radiation

 

[Flaesh]

I agree with Earl, the test procedure and criteria are not very convincing.

 

[kyuu]

The notion that playing around with reflections somehow negates the importance of the on-axis response doesn't jive for me. Unless the point really is to just replicate the Bose 901 experience of a very diffuse mess.

Also given that most people's rooms are not rectangles with perfectly and evenly reflective walls, and the notion of pulling the speaker out from the wall by some feet isn't going to fly in most setups (hell, mine are inside the wall) makes this difficult to translate even if we take it at face value.

 

[Duke]

The test unequivocally can't support this claim, however. And that's what I was asking about.

It sounds to me like you have objections.

Are you objecting to Gary's approach because it has not been proven to your satisfaction, or are you objecting because you have reasons for believing that it will not give good results?

Or, have I misunderstood you?

 

[Bwaslo]

Having to locate the speakers very near to the front wall is one of the motivations for using directional splash drivers behind them here, as otherwise envelopment was hard to come by. Works remarkably well for me (but might not for others).

Speakers placed out into the room more or less defines that room as a hifi installation and not as welcoming for other casual uses or for people who aren't concerned about sound reproduction quality. I don't have or even want a "listening room", so the goal becomes getting the system to work within the restraints of a living space.

 

[Keith_W]

One local audiophile (who recently died suddenly, relatively early) installed his Lowthers in his attic, rear-facing.
Another local audiophile had been ranting online for years about the benefits of reflected sound, I advised him to install his speakers rear-facing; this guy also recently died of old age .

That's no good. I didn't know that rear facing speakers were so bad for your health.

 

[Flaesh]

mine are inside the wall)

Previously, I had speakers in the wall, then I replaced them with 45º toed in corner speakers and on wall-mounted DBA subwoofers. But I always value articulation and freedom of the listener's position more than envelopment and ASW.

 

[RexrothPigeon]

Are you objecting to Gary's approach because it has not been proven to your satisfaction, or are you objecting because you have reasons for believing that it will not give good results?

No objections at all, just factually that particular test can show something, but it can't show that particular claim. It's not even testing that claim, in fact.

 

[Juhazi]

The ASW preference is very personal and recorded stereo music is recorded and mixed in many different ways and tastes. IMO it is total BS to rate them. And there is no need to agree and make ASR consensus statement!

Being a stereo dipole fan for 12 years, my setup is basically 5.0 and my AVR Yamaha can do also Dolby ProLogic II Music which I sometimes use for classical. Real multichannel recordings/mixes are rare but increasing in popularity now that Atmos has those height channels. But remember that even fanboy Toole doesn't have that in his new smaller apartment... Only stereo with wide dispersion Revels!

 

[Duke]

No objections at all, just factually that particular test can show something, but it can't show that particular claim. It's not even testing that claim, in fact.

Note that I may be incorrect in my understanding that Gary finds a dipole or bipole to work best; the speakers he provided for the blind listening test may have had a more complicated radiation pattern than either of those.

@geickmei, I have two questions about that test: First, if it's not a trade secret, can you give a brief description of the radiation pattern of the speakers you provided?

And second, by any chance do you recall whether those Orions had rear-firing tweeters? My understanding is that early Orions did not, but later ones did.

 

[pma]

Bipolar speakers are rare, and additional rear drivers are occasionally used.

This is the real life example:

 

[Keith_W]

This is the real life example:

According to @geickmei the speakers need to have aimable rear drivers and variable loudness control. I can not think of a single commercial speaker like that. Maybe prototypes and DIY versions exist.

 

[pma]

Like the whole commercial audio, it is about individual preferences and the room used for listening.

 

[SSS]

The BOSE 901 at those old times was not bad but also not perfect as far I remember. The backfired speaker sound depends much on the back surfaces whether damped or reflective. So the sound was not perfect compared with todays high quality speakers. For me to broaden the acoustical scene the distance between the stereo speakers can be increased without the need of early reflections. But anyway this all is subject for personal taste.

 

[Curvature]

I read the original 1989 AES paper and this 2025 article. Before reading, I was also familiar with image modelling and ray tracing techniques from architectural acoustics.

@geickmei I think these are interesting and pull together the right sources, but I don't think the theory works for three reasons.

1. Image modelling only applies to the statistical region of small rooms, above transition and modal. In the transition region, what we hear is the result nonminimum phase response of wavelengths that approach the dimensions of the room, while the modal region comprises a spatial map of minima and maxima due to wavelength being much larger than the room dimensions. From an image perspective, it is as if the images in the transition and modal regions are partial, broken and forced both inside and outside the room.
2. True radiation patterns of physical instruments are incredibly complex, while synthesized sounds are a-spatial... in the sense that they are typically not modelled with a radiation pattern in mind. Digital and hardware reverberation in a studio context makes no assumptions about radiation patterns and are used ubiquitously along with other processing tools, not to mention the how panning has been traditionally used. Normal microphones record only the pressure (or velocity, or a combination of both) at a specific point in a live stage, but they do not act as spatial samples. In fact spatial sampling of a physical soundfield requires 2*f samples per wavelength, the same as digital audio requires 2*f samples to capture the highest frequency. I'm sure for space this number can be rigorously reduced using a psychoacoustically-correct mathematical model, like we have seen successful in audio compression algorithms.
3. The requirements to have significant space behind and around the speakers (outside of creating trouble with SBIR) is highly impractical, either at home, a studio or most performance venues.

As a sort of related side note, there have been past attempts to use speakers in place of instruments in an orchestra. Two come to mind, the most famous being the Acousmonium by Francois Bayle of the Group de Recherches Musicales in France (I believe the stage was called a performance or projection area for sound) and other by Tapio Lokki in Aalto University in Finland. Both were for research, the latter hard science, while the former concerned composition and humanistic study.

The key undeveloped aspect of the texts that inform stereo theory, for me, is why stereophonic sound is so perceptually satisfying when circumstances are right despite presenting so many flaws under investigation. Stereo's requirements are also fairly low and resilient compared to more the complex multichannel, binaural or immersive audio. One of the consequences of having no perceptual model is that we don't have clear guides on assessing or optimizing rooms or speakers. Lots of really good advice, but filled with divergences and contradictions (stereo vs. mono bass, narrow vs. wide vs. multipolar speaker radiation, absorptive vs. reflective room design).

 

[Duke]

This is the real life example:

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Beautiful!

What is your impression of how they sound? What are your thoughts on the bipolar configuration?

 

[Bwaslo]

Our latest iteration is independently aim-able which indeed enables "splashing" off other surfaces besides the ceiling. But it sounds like you already figured out that, and more, on your own!

Sounds interesting, Duke, I hope you're able to demonstrate this method to numerous listeners at shows. I really believe this kind of thing is the solution to getting live sounding music in practical home living spaces.

 

[Curvature]

Sounds interesting, Duke, I hope you're able to demonstrate this method to numerous listeners at shows. I really believe this kind of thing is the solution to getting live sounding music in practical home living spaces.
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I wanted to do something similar after seeing @Duke's designs. Like a small Genelec speaker, highpassed at 1kHz and reduced in level, tilted up.

 

[Bwaslo]

I wanted to do something similar after seeing @Duke's designs. Like a small Genelec speaker, highpassed at 1kHz and reduced in level, tilted up.

Mine is a 3D printed waveguide (designed by "augerpro" at diyaudio) with an SB26ADC dome as driver. I run them from 1100Hz and up, to fill in about where the C6B directivity limits the room fill.

 

[pma]

Beautiful!

What is your impression of how they sound? What are your thoughts on the bipolar configuration?

The photos are from 2017 Hi-Fi exhibition. They sounded fine, however it is difficult for me to make any judgement, as I did not have time enough to listen to them carefully. The guy who designed them is a very talented designer of amps, DACs and speakers. I thing in a proper space it might be an interesting alternative solution.