View Full Version : Questions on SDA, SH and the like...
08-23-2002, 10:07 AM
I've followed the discussions here on SDA and SH and I understand the concepts. I have a couple of questions/comments, however.. and I realize that I may be missing something basic....
I'm imagining a concert hall, maybe an orchestra is playing, or maybe its AC/DC... you're sitting 7th row center with your two ears on their respective sides of your head... you're going to be hearing direct sound in each ear from that respective side of the stage, and also sound in each ear from the OTHER side of the stage, as well as all the reflected sound... now, if you placed two microphones at that location, and recorded the music live in 2-channel, the microphones would also pick up a combination of direct sound from across the entire stage, as well as the reflected sound.
If SDA cancels out some of that information ... isn't it producing an artificial soundstage and artificial separation? I know not to this extreme.. but listen to old Beatles songs (for example) that are mixed to the point that a particular guitar (for example) comes out of ONLY one channel. Now, that is false stereo imaging.. no way you'd hear it that way live.
Used to be that speaker manufacturers advertised their speakers as being able to reproduce "live" music... and I'd think still that the ultimate speaker would produce not only from below 20Hz to above 20kHz at +/- OdB, but would also place the instruments accurately across the soundstage... If SDA cancels out some of the information....
What am I missing here? I understand that it can produce a more distinct "stereo" image... but is the image it produces accurate compared to what you'd hear live??
08-23-2002, 01:47 PM
I'm not sure of the specifics but...
Live vs SDA's is much closer than live vs non-SDA's given the same quality of components. Actually, the Beatles stuff is really great. That guitar coming out of one speaker with non-sda's turns into that guitar coming from that side of the stage. Really cool!
08-23-2002, 02:47 PM
For folks who don't own any SDA speakers, but would like to understand more of what the sonic improvement is, here's a little demonstration. I warn you, other family members may think you've finally gone "round the bend" and you might be encouraged to "take long walks, to relax" it can be interesting. The goal of the SDA technology is to reduce intra-aural crosstalk, sound of one channel "leaking" into the opposite ear and diluting the stereo image capability. Here's the experiment, with just the two front main channels playing some well recorded stereo music take one of your hands and placed it vertically in front of your face, along the bridge of your nose. Kind of imagine a funny salute where instead of placing your hand at the corner of your eye, this salute goes between your eyes. In effect diving your face down the middle, then take the other hand and place it against the first hand, so the division of your face extends further outward. Now you know why I warned you, you're sitting there, listening to music with both hands, one-in-line with the other dividing the two vertical "halves" of your face. But, what you'll hear is how by providing this kind of barrier keeping left and right sound channels more isolated from opposite sides the stereo image in strengthened.
If this seems interesting, I've read of listeners who have made, out of cardboard, a divider that goes from forehead to chin extending outward a foot or so. They cut out the shape of their facial profile in the cardboard so they get a good fit against the contour of their face. Here again, reassure your friends and family that this is perfectly normal for dedicated audiophiles and this is just "science".
Have fun, Ken
08-23-2002, 02:55 PM
That sounds like a fun exercise...
I don't think the wife will think its strange...not for me at least.
08-23-2002, 03:53 PM
I read on the net somewhere, where a guy did the cardboard barrier from the speaker centerline out to where he was sitting, moved the speakers really close to the centerline and did this with a pair of radio shack bookshelf's, anyway the guest reviewer was blown away with the imaging.
08-23-2002, 04:20 PM
I understand the better imaging.. but that doesn't answer the question of whether the "better" imaging is *more accurate* compared to the original source... does it?? I mean, headphones are, I suppose, the ultimate "SDA" speaker... but is the imaging you get accurate compared to the original source (i.e. hearing it live)? You could build a wall down the middle of your listening room from front wall to listening position - right to your face - and achieve the same effect.... but is that the way it is "supposed" to be if your goal is accurate reproduction??
08-23-2002, 04:25 PM
here is the link
08-23-2002, 04:29 PM
SDA is "suppose" to be more acurate imaging than non-SDA speakers, yes like headphones. Keep in mind it is limited to the source material.
08-23-2002, 04:55 PM
Man I have reread you first post, here is somemore thoughts
"you're going to be hearing direct sound in each ear from that respective side of the stage, and also sound in each ear from the OTHER side of the stage, as well as all the reflected sound... now, if you placed two microphones at that location, and recorded the music live in 2-channel, the microphones would also pick up a combination of direct sound from across the entire stage, as well as the reflected sound." I agree
If SDA cancels out some of that information ... isn't it producing an artificial soundstage and artificial separation? Nope
Each SDA speaker will play the information from the source as it was recorded, just like you said above,
So the LEFT speaker is playing direct sound from the LEFT side of the stage and reflections from the right side of the stage, just like all speakers do (because this is in the recording can't take it out)
But here is the SDA trick
The SDA speaker's crossover is also sending this LEFT ch speaker signal over to the outside drivers (SDA array speakers) of the RIGHT ch speaker and it is out of phase. Now you are sitting there in the sweet spot, you hear this LEFT speaker playing the sound, then .5-7milli seconds later your right ear WOULD HAVE heard this same sound from the LEFT speaker, BUT the out of phase LEFT ch signal coming from the right speaker's SDA array of drivers got to your ear at the same time, so the in phase left ch signal + the out of phase left ch signal = no signal, your right ear will not here what the left speaker is playing.
Any closer to understanding?
08-23-2002, 05:21 PM
Any closer to understanding?
You can explain it all day long. Until they here it though.....something I think you just have to here for yourself...:D
08-23-2002, 05:29 PM
As George put it, "Yes, headphones can be excellent examples of SDA. Except for a little conductivity through your jawbone, the left ear only hears the left channel, and the right ear only hears the right channel".
As George put it "Nothing can improve on the original performance."
08-23-2002, 06:23 PM
Some good questions and excellent answers....you've really got to hear them.
08-24-2002, 06:59 PM
"I've read of listeners who have made, out of cardboard, a divider that goes from forehead to chin extending outward a foot or so. They cut out the shape of their facial profile in the cardboard so they get a good fit against the contour of their face."
So we pay extra for SDA speakers when all along we could have been wearing this funny face hat. I guess good sound won't help after your friends and family put you in the loony bin! Great post.
08-25-2002, 08:48 AM
I read all the above.I also have listened to Sda type speakers,my own and others.I think it was a good idea thinking outside the box.My question is why isn't it used anymore??The Srt's where the last of it's kind????????Sda array?
Here's my thoughts .......experience with soundstage,Imaging,and depth.It's all in the positioning of a given pair of speakers.After you pain through the amps,pre amp, wire and sources,positioning is the last beall end all of good sound.This is where you can make or break any system.
The relationship between your system and the room it lives in also will change the sound.
I owned the Sda-2b's and I really didn't think they where all that.They where a good sounding speaker don't get me wrong, but I just couldn't get attached to them.
It would be cool to see Polk make a comeback with the older speakers with todays thinking.
08-25-2002, 01:33 PM
When listening to your home system some of one channel is heard in the opposite ear (25%). This is the same as a live performance. The problem is that most recordings already have this channel transference(25%). It is essentially doubled(50%). SDA reduces the transference found in home environments. Of course the 25% is totally arbitrary and only used to make a point. At least in concept this makes for a much *more accurate* reproduction of the original source.
This is basically the same thing hoosier21 is saying.
Speaker positiong accomplishes much of this. Of course near-field monitors in a large room at low volumes would give similar results, but.....
08-27-2002, 04:36 PM
If any Forum member would like a copy of the classic June 1984 Audio Magazine article "Polk's SDA Speaker, Designed-In Stereo" by Matthew Polk, please send me an email at email@example.com and give me your name and address and I'll be happy to send it, at no charge.
Regards, Ken Swauger
08-30-2002, 01:12 PM
Can you post the article?
08-31-2002, 12:43 AM
I just received the article, thank you! I'll admit that after the first read I probably understood about a third, but found it to be interesting and will re-read it somemore to see if I can get a better understanding.
max, it's rather long with lots of diagrams. You might just want to send for a copy.
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