Understanding Crossovers

machone

I have owned a pair of SDA-1As since the early 80s.

The experiences of this forums members have helped me tremendously. Thank you all!

I am planning to upgrade my speakers very similar to the SDA-2s that Westmassguy rebuilt. I plan to do all of the mechanical upgrades as well as crossover upgrades, binding posts, IC cable and connectors. I just upgraded the stock stereo tweeters (SL-1000) to RD0194 this week. I have pulled the fuses for the SDA tweeters and have no plan to upgrade them or their circuit.

As I study the schematics for the 1A versus the 2 the only thing that I see different is the 1A has an extra stereo driver in parallel and the coil in the crossover (5.6mh) is exactly half of the value of the 2 at (11.2mh).

I assume that the difference in the coil value is to keep the overall impedance of the speaker system at 4 ohms?

Also does disconnecting the SDA tweeter change the overall speaker impedance?

Why do the specifications for the SDA-1A show crossover frequencies at 50,125 and 2500 and the SDA-2 at 50 and 2500?

machone

Hey guys. During my crossover rebuild I found wire that is corroded so I am preparing to rewire my SDA-1A's. While I am in there I am going to double check everything. I was searching the forum about this and my speakers and found a thread that is confusing. It said that the diagram that I downloaded from this website was incorrect for the 1A and 2. The error was in the bass circuit which shows a single inductor in series with the bass driver(s).

dorokusai wrote: "The final answer is that the xover schematic referred by Dudeman above is incorrect. It's even inside the SDA Compendium but so is the correct one. It has been removed from the list.
There IS a 55uf Capacitor and 7.5ohm Resistor inline with those woofers via 2nd order setup. No Polk loudspeakers work with only an inductor, period. NO first orders."

I just rebuilt the crossovers in these speakers and there was no 55uf capacitor and 7.5ohm in the woofer circuit.

I am going to confirm that my internal crossovers and wiring match the schematic that I downloaded from this website.

I realize that 1A's are not on everybody's hot list but it would be nice to get clarity on this subject. Any help will be greatly appreciated.

pitdogg2

ok I have done all upgrades on my SDA1a's. internal wire 16ga. check. all caps sonicap. check. New binding post yep. check. new interconnect also check...you will not turn these into SDA2 no mater how hard you try. What Dave (westmassguy) did was TL his SDA2a'S so he could use the RDO-198 which I think you can do to the SDA1A's as they already have a resister bypassed with a cap in the circuit. Go ahead and do all the upgrades you will not be sorry it took mine to a whole new level. Better bass better mids better better better. Polk did a lot of stuff on the fly you need to get inside and CONFIRM what is in there before YOU EVER order parts. I think what you are referring to is the 1st SDA1 had a vented box for the upper mid-woofers and a second inductor. In switching to the SDA1A you plugged the ports and REMOVED the second LARGE inductor which was taken out by POLK on all SDA1 signature's (transition model) that went on the become they SDA1A. confused yet? This is what is inside of mine
http://www.partsconnexion.com/wire_hookup_furutech.html

It has tripled in price since my upgrade just make sure you get 3 colors or you will be in for a headache in trying to hook up. Black, White and SDA circuit. This is not the easiest XO to do. Do one side at a time so you can reference but understand it will be mirror image and color opposite so another thing I would do is take detailed pictures of each XO.

TAKE YOUR TIME or you will let all the magic smoke out of your gear.

machone

Thanks pitdogg2. I already upgraded the crossovers with Sonicaps, Mills and there is only a 5.6mh inductor in series with the two woofers; no cap and no resistor. Yes I agree that the cap and resistor is in the SDA 1 but not the 1A. While rebuilding the crossovers is when I noticed the corroded wire. Thanks for the link.

Question to all:

With very similar schematics why do the specifications for the SDA-1A show crossover frequencies at 50,125 and 2500 and the SDA-2 only at 50 and 2500?

Schurkey

machone wrote: »

Question to all:

With very similar schematics why do the specifications for the SDA-1A show crossover frequencies at 50,125 and 2500 and the SDA-2 only at 50 and 2500?

My answer is in your other post.