Here you go: this was one early variation, which Peter Bouwer called 'Bi-Amplification'. It's the more complex implementation I described above, but many of the ideas floated across into [much] simpler width stereo implementations as you discovered, which in practice can produce similar results.
There's an interesting thing about the Polk Audio speakers >
If you remember 'Getto-Blasters' that had a 'stereo wide' switch (often called Matrix),
they achieved sounds apparently coming from a wider place than the speakers. (central listening was key)
They achieved this by sending a small amount of (filtered) Left Ch. out of phase to the Right Ch. and
correspondingly, a small amount of filtered Right Ch. out of phase to the Left Ch.
The reason for the filtering was 1. to prevent bass cancellation & 2. to keep a Right Ch. cymbal/HiHat on the Right.
The Polk Audio speakers actually used a dedicated driver connected to the opposite channel of the amplifier (band filtered)
to achieve this 'wider than speakers' spatial effect.
This of course was not strictly HiFi (by the book) , but still enticed & pleased multitudes of people seeking a WIDER STAGE. 🙂
(this 'inter channel off phase feeding' is widely used in the mixing of modern music)
Cool to know. My mums Phillips radio had a Spatial Stereo knob. Should be useful for a bluetooth speaker.
Cheers!
Cheers!
Good old days, was a kid, but remember the more a ghetto blasters had lights and knobs and switches, the better it was 😀
Additional difference with Polks way doing it having two speakers in one basically, is to have physical delay to the other and some crosstalk cancellation.
My immediate thought on the subject is that it cannot sound good, too much interference, improve something and make something else worse. Even though concepts like this seem weird I gotta remember that we have the secondary sounds anyway, nearby objects and boundaries, a lot of interference anyway, so why not do it purposely like so? it could work, especially if sound improves 🙂 I need to listen them some day, perhaps make some simple experiment with small fullrange drivers.
+1 on the increased area of the woofer(s). Additionally, putting two or more woofers close together (within a 1/4 wavelength at the noted frequencies) will increase their efficiency.
+1 on the "side by side" that increases the higher frequency apparent source width (ASW in Floyd Toole's book).
Increased clarity that you reported is probably heard at levels at or above ~80-85 dB at the loudspeakers. Modulation distortion is quite prevalent in these "little loudspeakers on a stick"...and for direct radiating loudspeakers in general. If you look at a relatively simple change in front baffle configuration...
...that increases the efficiency of each of the drivers by ~10-20 dB (between 10 and 100 times on acoustic power, and between 3 and 10 times in amplitude...SPL)--this effectively mitigates the disadvantages of direct-radiating flat-baffle multiple-way loudspeakers . Putting two woofers close together approximates a 180 degree horn baffle at lower frequencies. This pushes modulation distortion sideband levels down by 20-25 dB relative to using the same drivers in direct radiating mode. This effectively eliminates audible modulation distortion sidebands, thus producing exceptional clarity of presentation.
The effect of more randomized phase response of the combined loudspeakers (that is, taken in pairs, triplets, etc. within each channel of the stereo image) will reduce the sudden shifts in phase response around each loudspeaker's IIR (nominally passive) crossover filter frequencies. It's this increase in phase shift induced by the electrical filters and the physical offsets of the acoustic centers of the acoustic drivers that gives rise to the effect of "loudspeaker localization" (i.e., flat phase loudspeakers will also produce a sound image that defies being able to point at the loudspeaker). Two dissimilar passive-crossover loudspeakers with different crossover frequencies will combine to have a smoother phase response due to the effect of "randomized" phase response (closer to a linear phase change vs. frequency). More dissimilar loudspeaker types will increase this diffusion--at the distinct loss of good imaging performance, however). Additionally, the polar radiation pattern of the combined array will experience large off- and on-axis nulls due to dissimilar spread-source radiation patterns.
The increased size of the soundstage is, in my experience, a function of the controlled full-range directivity of the loudspeakers. Having two loudspeakers spaced apart (side-by-side) will by itself increase the horizontal directivity of the combined acoustic image, effectively keeping the acoustic energy off the near field acoustic reflectors just around the loudspeakers, producing a higher direct/reflected acoustic energy ratios at the listener's position(s).
Chris
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An extreme example of such a setup of multiple loudspeakers as described by the op is the 'Acousmonium' a kind of loudspeaker's concert with multiple of them ( last one i experienced was something like 70 in a very big hall*) played by a 'conductor' at desk choosing group of them to give different kind of effects ( close to multichanel rendering).
The initial idea was developed by Francois Bayle in 1974 and used by P. Schaeffer and other guys members of Ircam.
https://inagrm.com/fr/showcase/news/202/lacousmonium
* http://www.cahiersacme.com/article-3064162.html
The initial idea was developed by Francois Bayle in 1974 and used by P. Schaeffer and other guys members of Ircam.
https://inagrm.com/fr/showcase/news/202/lacousmonium
* http://www.cahiersacme.com/article-3064162.html
Although a little off topic,
Does anyone know what 'stand alone' speaker(s) were/are considered to be the flattest phase of all ???
I can see the draw toward such a conclusion, but I'm not aware of a direct connection between these things.
In a symmetrical listening position, the phase response of a speaker should make no difference
to the stereo image & 'apparent' speaker location, providing the speakers (mirror image) are the same.
However, there is still debate regarding phase response vs. fidelity, and even 'absolute phase'.
to the stereo image & 'apparent' speaker location, providing the speakers (mirror image) are the same.
However, there is still debate regarding phase response vs. fidelity, and even 'absolute phase'.