Stereophonic Sound from a Single Loudspeaker

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The idea is hardly novel. The electrical circuit is virtually identical to Ralph Glasgal's Stereo Separation control issued as US patent no. 3170991 issued in 1965

System for stereo separation ratio control, elimination of cross-talk and the like

The idea has its genesis in the matrix circuit for the FCC approved Zenith method of frequency division stereo demultiplexing in which the L+R mono signal is added in and out of phase to the L-R signal detected by the multiplex adaptor to obtain 2L and 2R. This is undoubtedly the same circuit used on HT receivers to generate the "wide" mode. (Ambiophonics takes the same principle and uses it for acoustic cancellation by slightly attenuating and delaying each channel and feeding it to the opposite amplifier/speaker. When the two fields arrive at the same point 180 degrees out of phase, your ears if you are precisely in the right location, cancellation of the opposite speaker's field occurs and voila, increased separation.)

You could rewire a single bose 901 speaker to do the same thing and operate it from the three front channels of an HT receiver in the wide mode.

Another attempt at single speaker stereo is JBL Paragon. Side firing single stereo speakers are nothing novel either. All rely at least in part on reflected sound to increase separation. Results strongly depend on room acoustics and speaker placement requiring experimentation to obtain the best effect. Equalization of the side firing speakrs can compensate for differential spectral absorption by the room boundaries otherwise the reflected sound will not have the same spectral transfer function as the front sound.
 
have You considered/measured the effect of the back wave of one speaker superimposed on the output of other two speakers and of the output of each speaker diffracting around the box?
for me it looks like that for frequencies below about 700<1000 Hz the output from each of the speakers is equally all around just with little relative SPL differences plus small time delays

Yes I'm planning to do detailed measurements, but at the moment I'm just enjoying the sound from this prototype :cool: Rarely something this simple sounds so nice.

In theory the idea of this kind of speaker is the directivity pattern is steered according to the stereo input signals L and R.

It may be that conventional measurements do not fully reveal how this kind of speaker is perceived in a room.


- Elias
 
It may be that conventional measurements do not fully reveal how this kind of speaker is perceived in a room.

- Elias
Yes, conventional measurements do not reveal perception.

The console stereo in my parents living room in the 1960's had side pointing Heppner horns, and front facing cone speakers, basically a larger version of what your experiment is.

I have fond memories of music played on that console.
In the mid 1980's they replaced the console with bookshelf speakers, the console went out on the enclosed porch while they tried (unsuccessfully) to give it away.
On a visit, I turned it on again out of nostalgia, it amazed me how awful it sounded.

Perception is quite subjective ;).
 
The console stereo in my parents living room in the 1960's had side pointing Heppner horns, and front facing cone speakers, basically a larger version of what your experiment is.

hm... usually consoles had side firing woofers

or perhaps was it Magnavox Imperial shown in this catalogue?

but in such a case those two horns were toed out to a degree rather than side pointing
plus two woofers facing forward - all this not very similar to Elias' box, wouldn't You agree?

perhaps You parents' console was different, do You know the name of it or can You post any pictures?
 
Those coefficients have so many decimals it must be based on academic research :D Any references ? Gerzon ?

So your three speakers, are they integrated as one, or spread in front in conventional triangle ?


- Elias


Yes Michael Gerzon.. Search Google patents to find details..

And yes single box 3 speakers 1 forward, 2 on sides angled forward. hmm, i did mention 30 deg, but i checked and its only about 15 :eek:

I have tried the lcr triangle. It works well with Gerzon's formulas... However i wanted a simple solution for my den. Hence i tried the single box method.

The LCR method i use atm is so much better than standard stereo triangle. Sweet spot is every where...... Instrument positioning is exact. I dont sit still in my den so i needed a solution that would allow me to move around. It works for me.... Thats what matters....:D

I admit.... It takes a day to get use to the setup.... My brain was not use to having the centre channel at first.... But when i listen on my main system (standard triangle) i miss the stability the LCR setup provides... This will change.... New main system on its way..

I can create some 3 channel songs (2 to 3 channel conversion done) in mp3 format for those that want to experiment. I am working on scripts to do the conversion via commandline atm. So i can just use a 3 channel player or 4 channel 3.1 format (if they exist) to eliminate the PC i use atm.

Cheers,

Optic
 
However, x = 0.5 can be done passively !
This schematic allows comparison between x = 0 (Stereolith) and x = 0.5 (vector steering) by a single switch ! (x = 0 means switch is closed)

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


Using the switch while listening is enlightening !
- Elias

strictly speaking even when x=0 it is hardly Stereolith because in Stereolith the front speaker is high passed at 2.8 kHz

anyway - can you describe the spatial presentation of "X0.5" - nice name BTW, isn't it? :) - vs the spatial presentation of the simplest back-to-back with direct sound blocked (the pillow-ed one)? What are the differences?
 
Yes Michael Gerzon.. Search Google patents to find details..

I'm a big Gerzon fan, I may have read all of his puplications :D If someone mentions Ambisonics I start to drool :p



The LCR method i use atm is so much better than standard stereo triangle. Sweet spot is every where...... Instrument positioning is exact. I dont sit still in my den so i needed a solution that would allow me to move around. It works for me.... Thats what matters....:D

Propably one of the most interesting feature of Gerzon matrixes is the frequency depending decoding, where there is a smooth level shift of about 3dB around 5kHz steered between the center speaker and the side speakers. It must be due to how high frequency phantom image localisation differs from low frequency one, and because of the pinna !



I admit.... It takes a day to get use to the setup.... My brain was not use to having the centre channel at first.... But when i listen on my main system (standard triangle) i miss the stability the LCR setup provides... This will change.... New main system on its way..

Optic

For me the shift from conventional stereo triangle to this single speaker stereo was painless ! It was immediately apparent that something the conventional stereo triangle was lacking is strongly present now !

Of course it is not perfect yet.. My first proto is made of cardboard and 10€ fullrange elements :eek: But if even that can demonstrate the potentiality, it should be the right way to go further ! :cool:


- Elias
 
so what You proposed Elias can be also seen as a kind of one-box trinaural?

Yes the same logic has occured in my mind too ! But, my equation is different for the center speaker ! :D Only for the x = 0.5 seems logically similar.

However, of course they are also different. For example true mono signal is reproduced by Single Speaker Stereo (SSS) from a single location (Natural !), whereas by conventional three speaker spread stereo it is reproduced from three distinctive locations (Not natural !).


strictly speaking even when x=0 it is hardly Stereolith because in Stereolith the front speaker is high passed at 2.8 kHz

anyway - can you describe the spatial presentation of "X0.5" - nice name BTW, isn't it? :) - vs the spatial presentation of the simplest back-to-back with direct sound blocked (the pillow-ed one)? What are the differences?

Yes x = 0 is not exactly the Stereolith product, but the stereo part of it should be based on the same configuration, that is the two sideways aimed L and R signals.

Some of the listening experiences are listed here:
Elias Pekonen Home Page - Stereophonic Sound from a Single Speaker

Maybe some of the biggest differences of x = 0 and x = 0.5 are:
* center image definition is better with x = 0.5
* with x = 0.5 the direct sound is no longer to be considered as an error, but is crucial for the operation (i.e. no pillow trick needed ! :D)
* with x = 0.5 the tonal balance is better especially in the top end, maybe because elements on all three sides.
* overall x = 0.5 works better on more records than x = 0, this means those records that do not sound good with x = 0 now sound much better with x = 0.5, and those records that sound good with x = 0 also sound good with x = 0.5. So an overall improvement !


- Elias
 
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Maybe some of the biggest differences of x = 0 and x = 0.5 are:
* center image definition is better with x = 0.5
* with x = 0.5 the direct sound is no longer to be considered as an error, but is crucial for the operation (i.e. no pillow trick needed ! :D)
* with x = 0.5 the tonal balance is better especially in the top end, maybe because elements on all three sides.
* overall x = 0.5 works better on more records than x = 0, this means those records that do not sound good with x = 0 now sound much better with x = 0.5, and those records that sound good with x = 0 also sound good with x = 0.5. So an overall improvement !
- Elias

thank You Elias but the above is not an answer to my question - I am asking about differences between the X0.5 and back-to-back without front speaker playing and with direct sound blocked - as in Your previous experiments with the cardboard and a pillow
 
* with x = 0.5 the tonal balance is better especially in the top end, maybe because elements on all three sides.

I think tonality is the biggest issue with matrixing in a single speaker stereo concept. For example, at lower frequencies we're looking at a monople. In the x=0.5, full right/left panning case the inverse signal has a high pass filter effect on direct sound and first reflections.
 
I think tonality is the biggest issue with matrixing in a single speaker stereo concept. For example, at lower frequencies we're looking at a monople. In the x=0.5, full right/left panning case the inverse signal has a high pass filter effect on direct sound and first reflections.

I would say that tonality is the biggest issue with matrixing

it is not a (difficult) issue in case of single box stereo concept as such without matrixing
 
I think tonality is the biggest issue with matrixing in a single speaker stereo concept. For example, at lower frequencies we're looking at a monople. In the x=0.5, full right/left panning case the inverse signal has a high pass filter effect on direct sound and first reflections.


Let's not invent problems where there may not be real problems !

The low freq directivity pattern depends on the amplitude and phase of the stereo input signals L and R. It will shift from monopole to cardioid to dipole when introducing a phase reverse. However, in a typical stereo recording there is no phase reversals at the low freqs !

In addition, at high freqs the cabinet and element size affects the directivity more than input signal.

So, I would even say, the tonal issues can be even less serious than with a conventional widely spaced stereo triangle with gross interference field and comb filtering at the listening position !


- Elias