Thread: The Audiophile Thread

  1. #2326
    Member Firth's Avatar
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    Quote Originally Posted by rcarlberg View Post
    I'm still confused. If the Polks do not have a small sweet spot -- and speakers that produce sweet spots don't need SDAs -- then what does the Polk SDA do and why is it needed?

    When I was a kid I experimented with putting my speakers facing each other, and sitting in the middle between them. This was like wearing a really big pair of headphones. Effective, but it limited the listening space.
    Polks are not large arrays and don’t have sweet spot, and therefore benefit from SDA.

    This video explains how SDA works:
    Last edited by Firth; 02-22-2020 at 06:48 AM.
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  2. #2327
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    Quote Originally Posted by rcarlberg View Post
    I'm still confused. If the Polks do not have a small sweet spot -- and speakers that produce sweet spots don't need SDAs -- then what does the Polk SDA do and why is it needed?

    When I was a kid I experimented with putting my speakers facing each other, and sitting in the middle between them. This was like wearing a really big pair of headphones. Effective, but it limited the listening space.
    Also, as Iíve stated before, a good 5.1 mix will have information common to front left and front right channels placed in the center channel, and therefore does not have the inter aural distortion mentioned by Polk. The good 5.1 mix approaches the advantage of mono, or the source coming from one voice.
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  3. #2328
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    Quote Originally Posted by Firth View Post
    The good 5.1 mix approaches the advantage of mono
    Okay, I'm done here.

    Quote Originally Posted by Firth
    This video explains how SDA works:
    I'm familiar with the concept. My DAW has a plugin called "channel mixer" which allows you to mix in negative amounts, i.e. out of phase signal, of the left and right channels. I've actually used this plugin to try to widen the stereo perspective on some sub-standard sources, like cassettes.

    I think I've also mentioned before Carver Electronics used to sell a device they called a "Sonic Hologram Generator" which did the same thing electronically.

    It's not a new concept.

    My bottom line is that IAC is not a real thing in a decent listening room. You cannot get to "transparency" by introducing distortions (variations from the source signal).
    Last edited by rcarlberg; 02-22-2020 at 09:14 AM.

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    Quote Originally Posted by clothes pen
    Years ago i actually sold Bob Carver products in the store i worked for, and the holograph was one of the items. It was a fun piece to use and it created some amazing sound affects, including putting voices behind me on the I Robot album (that was so amazing). however, like Paul said, it really botched the sound up overall and we never really sold that many. But it got me to thinking and i created my version of it using two room tunes that are about 4′ tall and 12″ wide. i position them on either side of the listening chair in such a way as to have the left one block the tweeter signal from the right ear and vice versa. While not as dramatic in affect as the Carver, it does a nice job and the sound field is wider and more spacious, and it does not monkey around with the phantom channel at all. A person could build these using almost anything to stop the inter aural cross talk. have fun.
    Source

  5. #2330
    Member moecurlythanu's Avatar
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    I have a Carver pre-amp, purchased in the mid-late 90s which incorporates Sonic Holography technology. It has a button on it to turn the SH on, or let it play "straight." I prefer the SH sound. YMMV.
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  6. #2331
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    Here's a demonstration of BEFORE sonic holography and AFTER sonic holography:


    As Paul McGowan explains, in the link in the previous post (and I've repeated the video below), the PROBLEM with sonic holography is that it cancels out signals that are common to both channels, which is the "center channel" or so-called "phantom channel." Depending on the mix, this usually includes all of the low-frequency elements (bass & drums), as well as anything else mixed to center, most commonly the vocals, and any soloists... in other words the FOCAL POINT of most recordings. To prevent this "vocal eliminator" effect, the out-of-phase signal can be frequency-limited (as it is in the Carver C-9), so the bass & drum are let through but the high hat cymbals and soprano saxes stay out in the wings.



    As you can hear in the before & after video (especially on headphones), the "sonic hologram" effect adds additional width to the high frequencies, while not "holographing" the lower frequencies like the drum machine's kick drum. The problem is, it makes the higher-frequency center-channel content -- in this case the sequenced synthesizer (4:45) and soprano sax (4:59) -- it makes those instruments out-of-phase. They jump out of the mix and no longer fit into the recording.

    To some extent I guess this is a philosophy/personal preference discussion. As I mentioned, you can't get to "transparency" by adding this to the signal. If you like the sonic hologram effect, fine. There's nothing wrong with that. But it's not more accurate or transparent: it's actually LESS.

  7. #2332
    Member moecurlythanu's Avatar
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    I would never argue that it's more accurate. There is clearly alteration going on.
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  8. #2333
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    Quote Originally Posted by rcarlberg View Post
    Interesting, would love to hear it !
    But not exactly purist HiFi.

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    The Carver C-9 Sonic Hologram Generator has front panel switches for IN/OUT so you can switch it out of the circuit when playing material where it "really botched up the sound overall" (as Mr. Clothes Pen put it above).

    Do the Polk L800s come with a way to eliminate the SDAs when they're not advantageous?

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  11. #2336
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    Paul actually has some pretty good videos -- like this one on imaging:

  12. #2337
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    Quote Originally Posted by rcarlberg View Post
    The Carver C-9 Sonic Hologram Generator has front panel switches for IN/OUT so you can switch it out of the circuit when playing material where it "really botched up the sound overall" (as Mr. Clothes Pen put it above).

    Do the Polk L800s come with a way to eliminate the SDAs when they're not advantageous?
    Iím guessing not. My friend had a Carver CD player and a Rega CD player which we compared using quality CDs. The Carver won, night and day on his Magnaplanar speakers with huge Crown Amps. I donít how a sonic generator could do what SDA does, but Carver was mostly amplifying the L-R and adding it back in to the Mono (L plus R) signals. That would exacerbate inter aural distortion. That Carver effect was best on vinyl which has weaker separation between L and R. The clear advantage of CD or digital is stereo separation. I want people to compare records on turntables to the CD equivalent, on headphones. You will hear the difference.
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  13. #2338
    Member Firth's Avatar
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    BTW SDA is a spatial and directional cancellation, not a signal cancellation like the C9.
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  14. #2339
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    Quote Originally Posted by Firth View Post
    BTW SDA is a spatial and directional cancellation, not a signal cancellation like the C9.
    Both work by adding out-of-phase signal.

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    Quote Originally Posted by Firth View Post
    Carver was mostly amplifying the L-R and adding it back in to the Mono (L plus R) signals. That would exacerbate inter aural distortion.
    Indeed.

    Adding L-R signal (difference between left and right) to L+R (signal common to both left and right) gives enhanced mono, or if added out-of-phase, a weird hybrid where only the difference signal is played monaurally. That's how "vocal eliminators" work.

    If not frequency limited, they'll take out all the bass & drums too.

  16. #2341
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    The advantage of the Polk approach is that the two mid-drivers (in a speaker) implement a steerable beam in the midband across the horizontal plane. That beam is steered with the appropriate choice of phase between the drivers. The pointing of the narrow beam away from the ear on the opposite side effectively cancels that channels signal at that ear.

    The C9 Hologram screwed with the left and right channels inaccurately. SDA uses multiple speakers in a given channel to cancel the signal at the ear which faces the other channel. Polk Audio founders came from Johns Hopkins Labs which have been significant developers of sonar array technology. Sonar arrays are known for being able to form acoustic beams with transducers in the water.
    Last edited by Firth; 02-23-2020 at 07:29 AM.
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  17. #2342
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    Quote Originally Posted by Firth View Post
    The advantage of the Polk approach is that the two mid-drivers (in a speaker) implement a steerable beam in the midband across the horizontal plane. That beam is steered with the appropriate choice of phase between the drivers. The pointing of the narrow beam away from the ear on the opposite side effectively cancels that channels signal at that ear.

    The C9 Hologram screwed with the left and right channels inaccurately. SDA uses multiple speakers in a given channel to cancel the signal at the ear which faces the other channel. Polk Audio founders came from Johns Hopkins Labs which have been significant developers of sonar array technology. Sonar arrays are known for being able to form acoustic beams with transducers in the water.
    SDAs did a good job of expanding the sweet spot, widening and deepening the soundstage, whereas the Sonic Holographer seemed to color the midrange.

  18. #2343
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    The SDAs I had needed an additional cable between the two speakers. W/o this cable, they were regular speakers. The SDA was effective, but only situationally, i.e. proper placement, sitting distance, etc. I can't imagine needing SDA in a multi-channel setup.

    Didn't we go down this SDA road before, RCarlberg? Are you thinking about buying a pair? It's not a new thing. SDA has been around since the early '80s.

  19. #2344
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    Quote Originally Posted by 3LockBox View Post
    The SDAs I had needed an additional cable between the two speakers. W/o this cable, they were regular speakers. The SDA was effective, but only situationally, i.e. proper placement, sitting distance, etc. I can't imagine needing SDA in a multi-channel setup.

    Didn't we go down this SDA road before, RCarlberg? Are you thinking about buying a pair? It's not a new thing. SDA has been around since the early '80s.
    According to Polk, they are compatible with multichannel, suggesting that a pair of the L800 towers would be good as rear surrounds. Problem is the the price tag is 6k per pair. One of the first surround implementations which was designed by David Hafler (Dynaco) formed the L-R and R-L for L and R rear channels, but the idea was to amplify audience noise which was decorrelated from the front L and R channels.

    The new SDA design pivots mid-drivers towards and away from the listener, on one side. Or there is a driver facing both ears.
    Last edited by Firth; 02-23-2020 at 10:36 AM.
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  20. #2345
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    Quote Originally Posted by 3LockBox View Post
    It's not a new thing. SDA has been around since the early '80s.
    Or even earlier. In the 1970s lots of people, including me, experimented with adding rear-facing radiation to speakers in an attempt to replicate the bipolar radiation of ribbon tweeters and electrostatic drivers. The effects could emphasize the stereo separation, the way the C-9 does, but always at the expense of accuracy and transparency.

    Quote Originally Posted by 3LockBox View Post
    Are you thinking about buying a pair?
    No. I decided I don't want to add anything to the music that isn't there in the original.

  21. #2346
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    Quote Originally Posted by rcarlberg View Post
    Or even earlier. In the 1970s lots of people, including me, experimented with adding rear-facing radiation to speakers in an attempt to replicate the bipolar radiation of ribbon tweeters and electrostatic drivers. The effects could emphasize the stereo separation, the way the C-9 does, but always at the expense of accuracy and transparency.

    No. I decided I don't want to add anything to the music that isn't there in the original.
    If stereo speakers add a distortion not there in earphones, would it not be worthwhile to at least listen to the new Polk SDA design. And BTW, it’s not just Polk. There is a new collaboration of a group of outstanding engineers that could produce revolutionary designs. This new Polk design is much more accurate than any previous product, even if the L800 SDA isn’t listened to.
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  22. #2347
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    I have no doubt they're good speakers. I'm just not interested in buying a pair.
    Last edited by rcarlberg; 02-24-2020 at 07:10 AM.

  23. #2348
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    Quote Originally Posted by rcarlberg View Post
    I have no doubt they're good speakers. I'm just not interested.
    Your numerous inquiries suggest that you are, unless there's another reason you're asking.

    The SDAs I had were from the mid-80s and those were a different driver layout that Firth is describing. And yes, I believe they did do a good job of spreading the soundstage and sweet spot but it was at cost of mid-bass punch, which is why I only used the cable situationally.

    I played around with a pair of rear speakers in a Hafler configuration but that too, only seemed to work situationally.

  24. #2349
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    "Hafler configuration"? Is that where the rear speakers are wired up to play only the DIFFERENCE between the front left and front right speakers, i.e. using the positive lead from each?
    Last edited by rcarlberg; 02-24-2020 at 09:59 AM.

  25. #2350
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    Quote Originally Posted by 3LockBox View Post
    Your numerous inquiries suggest that you are, unless there's another reason you're asking.

    The SDAs I had were from the mid-80s and those were a different driver layout that Firth is describing. And yes, I believe they did do a good job of spreading the soundstage and sweet spot but it was at cost of mid-bass punch, which is why I only used the cable situationally.

    I played around with a pair of rear speakers in a Hafler configuration but that too, only seemed to work situationally.
    I listened to the Guttenburg review of the Polk L200 which has the same tweeter and midwoofer that the L800 has, but no SDA. He said the L200 had serious clean bass and mid bass compared to the KEFs used as a reference.
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