How does SDA work with a pin/blade IC?

nonobaddog

I haven't been able to find this info anywhere. The SDA principle works by sending part of the right channel signal to the left speaker and part of the left channel signal to the right speaker. I see how this could work with the blade/blade IC because there are two conductors between the speakers. How does this work on the pin/blade ICs when there is only one conductor between the speakers?

F1nut

Magic

[Deleted User]

Hello,
Magic plus the common ground connection of the common ground compatible amplifier make the circuit work. This was done to prevent the speaker from shorting out the amplifier if it wasn't compatible. In previous SDA designs a non-common ground amplifier would face a possibly harmful shorting. With the pin/blade design all that would happen was that there wouldn't be any SDA information when connected to a non-common ground amplifier.
So, the pin connection plus the amplifier itself made the necessary circuit.
Regards, Ken

nonobaddog

Lets assume it is using a common ground amplifier. I understand the common ground amplifier supplies the ground connection for both channels. Then one wire in the blade/blade IC would allow the signal from the left channel to go to the right speaker SDA driver(s) and the other wire would allow the signal from the right channel to go to the left speaker SDA driver(s). I don't see how this can be accomplished with only one wire like in the pin/blade IC.

Unless the signals from both channels were blended together for the SDA drivers or something and I would think that would have a reduced SDA effect in the pin/blade style speakers. If that is what is done it would make the blade/blade speakers better at the SDA effect.

[Deleted User]

I think I can explain. The SDA signal each speaker reproduces is the difference information between the two channels. If you took two wires and connected one to your left speaker's positive and the other to your right speaker's positive and then connected the other ends of these wires to a regular speaker the sound produced by this speaker would be whatever happens to be different between the two channels at that moment. If at that fraction of a second your program source were monophonic (meaning the same sound coming from both channels) then there wouldn't be any difference between the two channels and so nothing would be coming from our "extra" speaker. But let's say the recording had hardly any sound coming from the right channel but the sound of a piano coming primarily from the left channel. Then our "extra" speaker would produce this sound since it is very different from the right channel. So, every second this "extra" speaker would produce whatever sound happened to be different between the two channels. You could think of this information as left-minus-right and right-minus-left channel derived sounds produced by the random blending of what the recording microphones produce.
Now this difference information can be used to strengthen how we perceive sounds produced in front of us. If we had two of these "extra" speakers and carefully controlled what frequencies they produce and optimize the strength of these signals compared to the regular right and left channels and placed them to the outside of our regular speakers and inverted their relative polarity we could hear some interesting results. If at a split second there was a sound intended for our right hearing mechanism and simultaneously our left hearing mechanism were to receive a properly controlled opposite polarity version of that same signal we would interpret this as a reinforcing of the sound in our right ear. This happens because our left channel hearing mechanism would normally get a version of the right channel information and as a result not register the sound quite as unique to the right channel. But this effect is somewhat reduced by the opposite polarity difference signal being projected to the left ear. Think of a noise canceling speaker that helps us hear the other channel better by canceling the sound that has drifted into our opposite ear.
Just like "regular" left and right sound there is constant changes between what one channel does compared to the other, the difference information produced by each of these "extra" channels is changing. Going from nothing (monophonic) to large amounts of data (one channel producing everything compared to the other channel) and an infinite amount in between.
So, there only has to be a single positive and negative electrical connection between these "extra" channels. Sometimes they are producing altered right channel information and sometimes altered left channel information depending on the nature of the balance.
Regards, Ken

nonobaddog

Thank you very much. That helps but I still don't completely understand. Sorry, I'm probably being slow today but I'm old so I'll use that as my excuse.
What if the stereo signal is different on each channel, lets say a piano note on the left channel only and a guitar note on the right channel only. Then the main driver on the left side would play the piano note and the main driver on the right side would play the guitar note.
To me, in the ideal SDA world, the right side "extra" or SDA driver would play a phase inverted piano note and the left side "extra" or SDA driver would play a phase inverted guitar note. I see how you could do this with two "extra" channels and two wires but I still don't see how to do it with one. But this may not be what is really going on anyhow.
Now please explain what they would really be playing, I think that will help me get it.

[Deleted User]

You are correct, that's not what's happening. Instead of thinking of four channels: (left, right and inverted left and inverted right; which would require four positive/negative wires to happen) there are three channels: left, right and difference channels (three positive/negative wire pairs). This difference channel is produced by whatever differences in voltages are occurring each split second of listening. If the sound is mono then there's no voltage differences so nothing is produced. If the left is producing slightly more voltage than the right then this difference in voltage is produced in the difference channel.
Seriously, try running a wire to your left positive and another wire to your right positive connections on your amp or receiver, okay? Then connect this wire to a speaker, any speaker. Don't have any other speaker connections to your amp or receiver. Now play some music. If you had an AC meter connected instead of the speaker you would see, on the meter, any voltages present as differences between your left and right channels. If you had a speaker connected there then these voltages would be converted to sound.
The sound will be kind of "back of the auditorium" sounding with some of the instruments very low in volume and others a bit louder but somehow distant. This sound is being produced with only a positive/negative pair of wires and could easily power a second identical speaker. Manipulate this (Matthew Polk's magic) and you have SDA.
In fact this wire to each positive terminal is part of how you test a pair of SDA speakers.

Schurkey

Compare the schematics for an SDA 1B (blade/blade) versus the SDA 1C (pin/blade)
https://us.v-cdn.net/5021930/uploads/attachments/1/8/5/1/1/31011.pdf

https://us.v-cdn.net/5021930/uploads/attachments/1/8/5/1/1/31012.pdf


Each 1B cabinet sends a full-range, full-strength, un-modified signal to the opposite speaker cabinet via the conductors in the SDA interconnect. Left channel signal is sent to the right cabinet, right channel info is sent to the left cabinet. The opposite-channel information is filtered by the SDA capacitors (130 +55 = 185uF in each cabinet) and the SDA inductors (9.6mH in each cabinet), and the resulting filtered SDA signal is fed to the negative terminals of the SDA drivers. By supplying signal to the negative terminals, the phase is inverted which is what we want for the SDA audio to work properly.

The 1C is wired more simply in the SDA section. The negative terminals of the SDA drivers in the left cabinet are connected to the negative terminals of the SDA drivers in the right cabinet. Doing this removes any direct grounding of the SDA drivers. The SDA signal has already been filtered by the crossover network in each cabinet, although it's filtered further by the SDA inductors (16mH in each cabinet) which provide the only path to ground. This tying-together of the SDA negative terminals takes only one conductor. Whichever driver set--left or right--has the greatest voltage at that instant will produce current flow to overpower the drivers in the opposite cabinet, creating the reverse-polarity signal needed for the SDA audio to work properly.

[Deleted User]

For those who have a more experimental bent, take this difference information voltage, drop it down to a line level voltage and feed it to a single channel amplifier with some tone control ability. Connect this amplifier to two speakers and you now have the basic principal of the SRT controller. Now you can place two speakers to the left and right of your main speakers, as close as possible and listen and adjust the volume and frequency response of the difference amp and create an SDA-like system out of regular speakers.
Hmmm, use LSiM speakers?
Oh, my!

scotvl

Wow great explanations for someone like me that's never heard any of the Sda line. Thanks

PolkieMan

Ken I would like to try that experiment sounds like fun. How would I drop the signal down to a line level voltage for an amplifier?

Kenneth Swauger wrote: »

For those who have a more experimental bent, take this difference information voltage, drop it down to a line level voltage and feed it to a single channel amplifier with some tone control ability. Connect this amplifier to two speakers and you now have the basic principal of the SRT controller. Now you can place two speakers to the left and right of your main speakers, as close as possible and listen and adjust the volume and frequency response of the difference amp and create an SDA-like system out of regular speakers.
Hmmm, use LSiM speakers?
Oh, my!

[Deleted User]

This would seem to work:

http://www.amazon.com/XANTECH-SLLC1-Converter-Discontinued-Manufacturer/dp/B000P0UE38

Any speaker level to line level converter would operate, you would only use one half of it.

Schurkey

Carver and Soundcraftsmen also sold speaker-level to line-level converter boxes; both are long discontinued but available occasionally on eBay or other sources.

Carver version was called the Z1, with the "Z" representing it's impedance-matching ability.

Soundcraftsmen sold their version as the PC-1.

nonobaddog

I sure want to thank you Kenneth Swauger and Shurkey for the information on how SDA works. That is so great to have experts explain these things. I have several pairs of SDA speakers and now I know what is going on in them. Thank You!

[Deleted User]

You are welcome, I'm glad the information was helpful.

westmassguy

Kenneth Swauger wrote: »

Seriously, try running a wire to your left positive and another wire to your right positive connections on your amp or receiver, okay? Then connect this wire to a speaker, any speaker. Don't have any other speaker connections to your amp or receiver. Now play some music. If you had an AC meter connected instead of the speaker you would see, on the meter, any voltages present as differences between your left and right channels. If you had a speaker connected there then these voltages would be converted to sound.
The sound will be kind of "back of the auditorium" sounding with some of the instruments very low in volume and others a bit louder but somehow distant. This sound is being produced with only a positive/negative pair of wires and could easily power a second identical speaker. Manipulate this (Matthew Polk's magic) and you have SDA.
In fact this wire to each positive terminal is part of how you test a pair of SDA speakers.

Ken, I believe this was known as the "Hafler" circuit back in the 60s, for extracting ambient information from Stereo Recordings. You placed a singe speaker at the rear of the room.

[Deleted User]

Exactly, it became the rear channel information in Dolby pro-logic and the common channel information became the center. The Dynaco was, and still might be, the best sounding approach to multi-dimensional sound. That and what Ambisonics produced.

westmassguy

Poor-mans surround system. Forgot about the Dynaco, they added a L-Pad as I recall to adjust the rear levels.

[Deleted User]

Here it is:

http://www.canuckaudiomart.com/details/649075660-dynaco/images/614104/

westmassguy

Kenneth Swauger wrote: »

Quadpod?

Sounds like a town in Rhode Island

westmassguy

They actually do work well, but as always, depends on the source and how much difference signal is present

Schurkey

That box was "resurrected" by a company that took over Dynaco's assets (Panor) as the "Dynaquad QD-1 II". Stereophile did a review, but it doesn't seem to be on-line.

lawdogg

This is really awesome information to have. This forum is great. I have the 3.1's and have been wondering the same thing.

vmaxer

Good reading..

PolkieMan

I really enjoyed this thread also, thanks!! SDA is not dead it's just waiting

Kenneth Swauger wrote: »

You are welcome, I'm glad the information was helpful.