SDAs unplugged

[John in MA]

Many think the cable just sends a low level signal from the opposite channel. Not true so you are missing fundamental frequencies and it will cause you to try an compensate with tone controls, etc.

Can you provide a proper technical description? There've been threads about this in the past, including going over schematics and guys ohming out their speakers with multimeters. Seems like the result is always the same. At least in the big x.x series, the SDA drivers provide no positive signal above the low-frequency crossover point (below which they work in concert with the main drivers, even if the cable isn't connected.)

[hearingimpared]

Running SDA's without the cable is like having sex with your sister. It is still sex, but it just ain't right.

I love you Bro, but YOU ain't right!!!:p:D

[heiney9]

Yes, I was generalizing which I normally don;t like to do. My statement pertains to earlier SDA's rather than later. Later models and the big boys are more like you describe.

http://www.polksda.com/sda1creview.shtml

Refer to the above link pp 42, left and middle columns.

H9

P.s. The OP has 2B's which are "later" models. Earlier 2's and 1's are as I described, for confirmation see the above link.

[hearingimpared]

I notice the opposite. Tonal balance seems off to me when running w/o the cable. Vocals are recessed, highs are muted and things seem to sound unnatural. Flat, dry, lifeless, uninspiring, flaccid, tepid, vapid, choked, constrained, etc.

H9

Without the SDA cable you have to toe in the speakers to get the right sound which btw with the pair of SDA/SRS I once owned was a real PITA.

[F1nut]

The SDA drivers work up to 1000Hz, with the cable disconnected they only work up to 100Hz, in concert with the stereo drivers. Therefore, H9 is correct in that you are losing some of the frequency range produced by the SDA drivers.

[Schurkey]

The SDA drivers work up to 1000Hz, with the cable disconnected they only work up to 100Hz, in concert with the stereo drivers. Therefore, H9 is correct in that you are losing some of the frequency range produced by the SDA drivers.

With specific regard to the 1Bs in the first post:

The + terminal of the dimensional drivers gets EXACTLY the same signal from the crossover as the stereo drivers. Unlike some other SDA models, the dimensional + circuit is a carbon-copy of the Stereo circuit--same resistors, same inductors, same drivers, same cabinet volume. The only things that make the dimensional driver signal different from the stereo driver is that:

1. The - side of the dimensional drivers has the SDA signal from the other channel; the SDA signal delivered to the crossover is a full-range, full-amplitude version of the opposite-channel signal. This full-range, full amplitude signal is then processed by going through ~185uf of capacitors before being routed to the ground side of the dimensional drivers, and

2. There's a fairly huge inductor in the ground path of the dimensional drivers. This inductor is in the circuit whether or not the SDA cable is connected; disconnecting the cable doesn't disable the inductor.

Depending on program material, there is nothing to prevent the dimensional driver from producing essentially the same frequency response as the stereo drivers--except the inductor in the ground path.

I don't understand how pulling the SDA cable can cut the bandwidth of the dimensional drivers to 1/10 of what it is with the cable connected. Can you explain?

To my ears, the 1Bs have similar (not identical) response whether or not the cable is connected. The cable dramatically expands the soundstage when connected; but not so much effect on the tonal characteristics. This assumes a true "common ground" amplifier; put some resistance between the negative terminals of the amp and the sound quality of the midrange/vocals will go straight to hell with the SDA cable connected. 20 ohms is unlistenable; I haven't experimented, but I'm going to guess that 10 ohms will be "bad" and 5 ohms is "noticeable". I don't know how little resistance between the negative terminals it takes to be "acceptable". With "0" ohms, having the SDA cable connected or disconnected makes little difference in the tonal balance.

This then becomes my advice to the original poster: Measure your amp for resistance between the negative terminals. Maybe even build a jumper wire--it's cheap and easy--and see if that "fixes" your midrange issue. The jumper wire was nothing less than a miracle cure for my system!

Other SDA models are sure to be different. (That's material for another entire thread that I don't have time to start right now--SDA signals are handled in several different ways; and I'm thinking that the "strength" or audibility of the SDA signal is bound to be different depending on the speaker model. So my thread topic will be: which model has the most obvious/strongest/"best" SDA effect???)

[John in MA]

The SDA drivers work up to 1000Hz, with the cable disconnected they only work up to 100Hz, in concert with the stereo drivers. Therefore, H9 is correct in that you are losing some of the frequency range produced by the SDA drivers.

Yes, but at least in the later big boys their 100-1K range is the reversed-phase signal.

[jrgoswick]

Running SDA's without the cable is like having sex with your sister. It is still sex, but it just ain't right.

WTF MATE???????? That's just wrong. TRUE but ultimately wrong.

[John in MA]

WTF MATE???????? That's just wrong. TRUE but ultimately wrong.

Depends, are we talking step-sister, half-sister, or real sister?

[hearingimpared]

Depends, are we talking step-sister, half-sister, or real sister?

Who, how, when, how, where? . . . I don't know but your post has me cracking up. Sick pups!:p:D

Ben you're still a perv for that one!:p:D

[FTGV]

.... there is nothing to prevent the dimensional driver from producing essentially the same frequency response as the stereo drivers--except the inductor in the ground path...I don't understand how pulling the SDA cable can cut the bandwidth of the dimensional drivers to 1/10 of what it is with the cable connected. Can you explain?

It appears that the signal from the stereo array(SA) is fed to the dimentional array(DA) through the big inductor.Therefore the signal sent to the DA will be low pass filtered so only the low bass will be shared between the SA and and DA sections.

[hearingimpared]

Fred could you make that a little more clear, I'm finding it hard to understand for some reason? Thanks!

[ben62670]

The signal goes to ground through the big inductor to ground so the lower bass doesn't cancel. The signal doesn't pass through except to ground. The mids are what get canceled from about 80hz to 2k or 2.5k via the IC cable.

[FTGV]

Fred could you make that a little more clear, I'm finding it hard to understand for some reason? Thanks!

The big coil only allows the low bass from the SA section to be sent to the DA section. Does that help Joe?

[falconcry72]

I noticed on my 2B's (pin/blade) that when the interconnect is not connected they leak a significant amount of air out of the empty sockets when the passive is pressed in.

[MillerLiteScott]

I was unplugging my IC the other day while a song was playing and I felt air blowing out of the pin IC receiver in the cabinet.

For the record I always run with the interconnect connected but I just wanted to hear the difference because the sound stage was just so enveloping on that particular song and I just wanted to see how compressed it was without the interconnect connected.

Scott

[hearingimpared]

It appears that the signal from the stereo array(SA) is fed to the dimentional array(DA) through the big inductor.Therefore the signal sent to the DA will be low pass filtered so only the low bass will be shared between the SA and and DA sections.

The signal goes to ground through the big inductor to ground so the lower bass doesn't cancel. The signal doesn't pass through except to ground. The mids are what get canceled from about 80hz to 2k or 2.5k via the IC cable.

The big coil only allows the low bass from the SA section to be sent to the DA section. Does that help Joe?

Gotcha, I read to much into the first post, thanks guys.

[ben62670]

The big coil only allows the low bass from the SA section to be sent to the DA section. Does that help Joe?

The big coil lets the bass go to the amps ground. The higher frequencies are sent to the negative of the opposite channels negative canceling the mids in the dimensional array.

[FTGV]

The big coil lets the bass go to the amps ground. The higher frequencies are sent to the negative of the opposite channels negative canceling the mids in the dimensional array.

Looking at the schematic for Shurkey's 1B's here's what I see.The DA and SA sections are essentially connected in parallel the only difference being there is a 9.6 mh coil in series with the negative leg of DA section so it will be only recieving low bass .Being that it's an AC signal the coil will function the same whether it be in the negative or positive side of the signal path. (With the IC disconnected the paralleled 50uf and 130uf caps are out of the circuit.)

An easy test to see if the above is correct would be to try the 1B's
sans IC and see if the DA section drivers are reproducing low bass only.

[ben62670]

That coil is not in series with any driver on most SDA's. The Blade Blade it is in series in some speakers as in his 1B's.

[heiney9]

I once asked Nelson Pass about my Aleph 30 and its compatibility with my 1C's. I sent him the schematics as well as a wiring diagram of the SDA 1C's. His response was that the Aleph 30 used a common ground but he mentioned it looked like the SDA's put stress on the negative side of an amplifier because of the interconnect. He also suggested a recommendation of a step down transformer for non-common ground amps like his X series and gave almost the exact spec of the AI-1. Reading between the lines; you need to have a stout amplifier to run the SDA's properly because it can stress the negative side of an amplifier.

H9

[bigaltx24]

Thanks Schurkey, I knew I wasn't imagining this. I checked my amp, I'm getting .9 ohms between the grounds. I checked the MWs, without the cable all four seem to sound the same. I ran the SDA quick test and they passed with flying colors. Now back to some more A-B testing

[ben62670]

Sorry Fred I didn't realize you were talking about the 1B's.

[comfortablycurt]

Running SDA's without the cable? I've tried it. No thanks.

The magic disappears.

As others have mentioned, these speakers are designed to be run WITH the cable in place. They don't simply function as a normal pair of speakers when the cable is unplugged. They work, yes...but they aren't really designed to be run that way.

[lightman1]

I've been farther than you have...you can bet on that Russ.

I know. It's just fun for me to get a rise from you.


You still have bad ears.


Say sumpin' chump!:D

[lightman1]

I've just read a few of your other posts; when was the last time you had your mouth washed out with soap?

SHUT UP RUSS!:p:D

I can use the F word any way I wish.


except here....

[Schurkey]

Looking at the schematic for Shurkey's 1B's here's what I see.The DA and SA sections are essentially connected in parallel the only difference being there is a 9.6 mh coil in series with the negative leg of DA section so it will be only recieving low bass .Being that it's an AC signal the coil will function the same whether it be in the negative or positive side of the signal path. (With the IC disconnected the paralleled 50uf and 130uf caps are out of the circuit.)

I agree with almost everything you state. The 9.6mh coil will NOT function the same if it were in the positive side of the circuit, because if it were in the positive side, the SDA signal coming from the other channel would go to ground without being blocked/filtered/modified by the inductor. Or, put another way, the inductor will function the same way, but it's in the wrong place with regard to the SDA signal. It's in the negative leg so that it filters/modifies the SUM of the "regular" signal delivered to the dimensional drivers and the SDA signal which is applied to the ground side of the drivers.

I don't fully understand how the SDA signal travels through the wiring of the speaker; it seems to me that there's every likelyhood that it back-feeds through the drivers and crossover network as well as draining directly to ground through the big inductor. And, it doesn't help my understanding that the SDA signal is very changeable due to the program material. I know that if you disconnect the + speaker cable at ONE speaker, with the SDA cable connected, the speaker will still produce sound (program material dependent) at the tweeters due to the SDA signal back-feeding through the crossover. Spooky.

I don't know what else to say except "Thank You". Every time I read about the SDA signal, I'm forced to re-examine what I know about it; and pretty much every time I learn something I didn't know before.

Thanks Schurkey, I knew I wasn't imagining this. I checked my amp, I'm getting .9 ohms between the grounds. I checked the MWs, without the cable all four seem to sound the same. I ran the SDA quick test and they passed with flying colors. Now back to some more A-B testing

Shove a jumper wire into the negative terminals, and see what happens. Worst case: you've wasted ~$5 on two Rat Shack banana plugs and a foot and a half of speaker wire.

Gut feeling: add jumper wire; your midrange/vocal anomaly is g-o-n-e. But what do I know?

[heiney9]

Shove a jumper wire into the negative terminals, and see what happens. Worst case: you've wasted ~$5 on two Rat Shack banana plugs and a foot and a half of speaker wire.

Gut feeling: add jumper wire; your midrange/vocal anomaly is g-o-n-e. But what do I know?

Or he blows up his amp. Why are you insisting on him jumping his negative terminals on his amp? Do you have specific knowledge of his amp? I'm just curious, not being argumentative. Many non-common ground amps can NOT be jumpered or strapped without blowing up the amp. It seems his amp is common ground because of the the very low reading he has when measuring.

H9

[dorokusai]

Heiney brings up a serious point....as you cannot just strap any amp and press play.

[Schurkey]

Heiney brings up a serious point....as you cannot just strap any amp and press play.

I'm getting .9 ohms between the grounds.

If there's less than one ohm between negative posts already...


...how is a jumper wire going to hurt??? The negative posts are already electrically connected; just with a hint more loss than is optimum for the SDA signal.