nspindel
1000+ Head-Fier
- Joined
- Oct 12, 2005
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Hopefully this catches Tyll's attention....
About 12 years ago or so, Polk Audio stopped manufacturing what I always thought was one of the greatest consumer-audiophile lines of speakers I had ever heard. By consumer-audiophile, I mean speakers in the $1000-$5000 per pair range. Above the amount that would be considered consumer, but not priced so far into the stratosphere that only the most serious audiophiles would be compelled to buy them.
This line of speakers used a technology called SDA (Stereo Dimensional Array). These speakers were very unique in that there was a distinct left and right speaker, they were not meant to be interchanged. The back of the speaker actually said "Left Speaker" or "Right Speaker". Most notably, in addition to the cables between the speakers and the amplifier, these speakers had another cable that ran between the two speakers.
The purpose of this wire was to facilitate each speaker putting out an inverted signal of the opposite speaker. I purchased a set of these speakers back in 1989, and I can still remember the discussion that I had with the salesperson who handled the Polk line in the store where I bought them. He described the fact that when a person listens to loudspeakers, the left ear can hear the sound from the right channel, and vice versa. The salesman used the specific comparison to headphone listening - "When you listen on headphones, only the left channel reaches the left ear and only the right channel reaches the right ear - SDA is meant to make the speakers sound more like headphones." The SDA technology sought to eliminate that crossover, with each speaker putting out a cancellation signal of the opposing speaker. I'm not a scientist by any means, but what I can say was that the resulting imaging that these speakers put out was absolutely stunning, unlike anything else I could find in that price range. The soundstage extended much wider than the two speakers, and you clearly perceived a depth to the music as well. You could detect that the drums came from behind the guitars, for example.
Here is how the Polk manual described this technology: "SDA, TRUE STEREO TECHNOLOGY: HOW DOES IT WORK? SDA Technology is a means of reproducing a much larger and more realistic sound stage than can be achieved by conventional speakers. The way that this is accomplished is to make sure that only the original recorded signal reaches the listener's ears. The original recorded signal is entirely contained in the direct sound of the left signal reaching the left ear and the direct sound of the right speaker reaching the right ear. Normally when a person listnes to a conventional pair of stereo speakers sound from each speaker reaches each of the person's ears. The extra signals, crossing the listener's head to reach the ear on the opposite side, can be thought of as distortion which causes the sound field to be constricted and shallow. SDA Technology uses the acoustically inverted dimensional signal to cancel the extra signals without affecting the original recorded signal reaching the listener's ears directly. The result is that only the correct original recorded signal reaches the listener's ears and the full width and depth of the sound stage are accurately reproduced."
Obviously, this technology is in complete opposition to the Crossfeed technology employed in the HeadRoom amplifiers. The Crossfeed, in layman's terms, is designed to blend a little bit of left signal into the right ear and a little bit of right signal into the left ear, in order to make the headphones sound a bit more like conventional loudspeakers.
The HeadRoom documentation says the following:
"Imagine you are listning to a pair of speakers. If you turn off the left speaker, both ears hear the sound from the right speaker. But because the left ear is slight farther away than the right ear, it hears the speaker's sound slightly after the right ear; about 300 miliseconds. This time difference is called the 'inter-aural time difference' and it is the main thing your brain listens for in order to tell where to place sound left-to-right."
"But in headphones if you turn off the left channel, only the right ear hears the sound. In headphones, if there is any sound that is only in the left channel, or only in the right channel, then only that ear hears the sound. This is not natural, and you brain becomes fatigued trying to figure out where the sound is coming from when only one ear is hearing it. This tends to create an audio image that is a blob on the left, blob on the right and a blob in the middle."
"HeadRoom amplifiers cure the problem by allowing you to cross-feed a little of the left and right channels across to each other through a short time delay using the crossfeed switch. The usefulness of the circuit varies depending on what type of recording you are listening to; mono and binaural recordings need no processor at all. Old studio recordings that have instruments panned hard left or right, benefit greatly from the processor. Live and classical recording miked from a distance benefit somewhat less, and can often be listened to without the processor quite comfortably."
It's interesting to me that HeadRoom describes this technology as a cure for the "problem". This would suggest that, at least in HeadRoom's opinion, Polk had things all wrong. I'll leave the opinions to the experts, but what I can say with 100% certainty is that if I were to disconnect the SDA cable with the Polk speakers, they did not image anywhere near as well. The sound stage would only be as wide as the distance that speakers were apart from each other, and there was no depth to the music at all.
I was hoping to solicit some informed opinions as to the validity of one theory vs. the other. Now I'm going to rest my weary hands.....
About 12 years ago or so, Polk Audio stopped manufacturing what I always thought was one of the greatest consumer-audiophile lines of speakers I had ever heard. By consumer-audiophile, I mean speakers in the $1000-$5000 per pair range. Above the amount that would be considered consumer, but not priced so far into the stratosphere that only the most serious audiophiles would be compelled to buy them.
This line of speakers used a technology called SDA (Stereo Dimensional Array). These speakers were very unique in that there was a distinct left and right speaker, they were not meant to be interchanged. The back of the speaker actually said "Left Speaker" or "Right Speaker". Most notably, in addition to the cables between the speakers and the amplifier, these speakers had another cable that ran between the two speakers.
The purpose of this wire was to facilitate each speaker putting out an inverted signal of the opposite speaker. I purchased a set of these speakers back in 1989, and I can still remember the discussion that I had with the salesperson who handled the Polk line in the store where I bought them. He described the fact that when a person listens to loudspeakers, the left ear can hear the sound from the right channel, and vice versa. The salesman used the specific comparison to headphone listening - "When you listen on headphones, only the left channel reaches the left ear and only the right channel reaches the right ear - SDA is meant to make the speakers sound more like headphones." The SDA technology sought to eliminate that crossover, with each speaker putting out a cancellation signal of the opposing speaker. I'm not a scientist by any means, but what I can say was that the resulting imaging that these speakers put out was absolutely stunning, unlike anything else I could find in that price range. The soundstage extended much wider than the two speakers, and you clearly perceived a depth to the music as well. You could detect that the drums came from behind the guitars, for example.
Here is how the Polk manual described this technology: "SDA, TRUE STEREO TECHNOLOGY: HOW DOES IT WORK? SDA Technology is a means of reproducing a much larger and more realistic sound stage than can be achieved by conventional speakers. The way that this is accomplished is to make sure that only the original recorded signal reaches the listener's ears. The original recorded signal is entirely contained in the direct sound of the left signal reaching the left ear and the direct sound of the right speaker reaching the right ear. Normally when a person listnes to a conventional pair of stereo speakers sound from each speaker reaches each of the person's ears. The extra signals, crossing the listener's head to reach the ear on the opposite side, can be thought of as distortion which causes the sound field to be constricted and shallow. SDA Technology uses the acoustically inverted dimensional signal to cancel the extra signals without affecting the original recorded signal reaching the listener's ears directly. The result is that only the correct original recorded signal reaches the listener's ears and the full width and depth of the sound stage are accurately reproduced."
Obviously, this technology is in complete opposition to the Crossfeed technology employed in the HeadRoom amplifiers. The Crossfeed, in layman's terms, is designed to blend a little bit of left signal into the right ear and a little bit of right signal into the left ear, in order to make the headphones sound a bit more like conventional loudspeakers.
The HeadRoom documentation says the following:
"Imagine you are listning to a pair of speakers. If you turn off the left speaker, both ears hear the sound from the right speaker. But because the left ear is slight farther away than the right ear, it hears the speaker's sound slightly after the right ear; about 300 miliseconds. This time difference is called the 'inter-aural time difference' and it is the main thing your brain listens for in order to tell where to place sound left-to-right."
"But in headphones if you turn off the left channel, only the right ear hears the sound. In headphones, if there is any sound that is only in the left channel, or only in the right channel, then only that ear hears the sound. This is not natural, and you brain becomes fatigued trying to figure out where the sound is coming from when only one ear is hearing it. This tends to create an audio image that is a blob on the left, blob on the right and a blob in the middle."
"HeadRoom amplifiers cure the problem by allowing you to cross-feed a little of the left and right channels across to each other through a short time delay using the crossfeed switch. The usefulness of the circuit varies depending on what type of recording you are listening to; mono and binaural recordings need no processor at all. Old studio recordings that have instruments panned hard left or right, benefit greatly from the processor. Live and classical recording miked from a distance benefit somewhat less, and can often be listened to without the processor quite comfortably."
It's interesting to me that HeadRoom describes this technology as a cure for the "problem". This would suggest that, at least in HeadRoom's opinion, Polk had things all wrong. I'll leave the opinions to the experts, but what I can say with 100% certainty is that if I were to disconnect the SDA cable with the Polk speakers, they did not image anywhere near as well. The sound stage would only be as wide as the distance that speakers were apart from each other, and there was no depth to the music at all.
I was hoping to solicit some informed opinions as to the validity of one theory vs. the other. Now I'm going to rest my weary hands.....