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tschopp

Just wanted to introduce myself and say hi. I've been a polk fan for a long time. I have owned a set of 10B since the late 80s. At that time I got a chance to hear a set of SDA SRS, but the price was way over my budget. I recently picked up a set of 5Jr off ebay for use as either rear speakers or maybe a center, but my daughter installed them in her room. So I then picked up a set of SDA 1C. All I can say is wow!!

The top caps had some issues, I sanded them and put a couple of coats of urethane on them. I am really happy with how the caps look now. The SDA cable was missing so I put in new binding post for the SDA signal and made a 12Ga sda cable. Also made some new speaker cables while I was at it.

I have been looking over the crossover schematics for a bunch of the SDA speakers. I think I have a pretty good understanding of the low frequency section. I will need to spend some more time before I have a good grasp of the high frequency section. Changing out the electrolytic caps seems obvious. It looks like the symmetry could be improved between the stereo and the dimensional drivers. On the 1C (and most early SDA) the wire gauge of the stereo inductors is the same as the dimensional inductors. This causes the dimensional circuit to have a higher DCR than the stereo circuit. In the later TL series the dimensional inductor used a heavier gauge than the stereo correcting this issue. I noticed the TL series also used a higher cutoff frequency for the low pass filter, I need to look at the tweeter sections before I form any opinion on that.

I'm probably not as critical a listener as most hear, hopefully I will be able to hear the difference when I get around to modding the crossover.

I feel myself entering the rabbit hole, already on the lookout for a set of SRS 1.2.

Steve

parnold

welcome Steve!

Libertyc

Welcome! Hide your wallet!

drumminman

Welcome to CP steve. If you haven't already looked there's lots of diy info on modding Xovers, + doing other effective mods to get the most out of your speaks.

Buying the 1C's is only the beginning :loneranger:

Mr. Bubbles

welcome.

GlennDog

Hi, Steve . . . welcome to the addiction

G

fossy

welcome Steve........this is the best forum around .....:exclaim:

gimpod

Welcome to the rabbet hole and definitely hide your wallet! because were real good at spending other peoples money around here.

Somethings about your original post, I don't think you have as good of an understanding of the low pass section as you think.

tschopp wrote: »

It looks like the symmetry could be improved between the stereo and the dimensional drivers.

I have no idea what this means but in the context of your post it gives the impression that your thinking of changing the inductors with ones of a different DCR. If this is the case it's a bad idea as you'll end up changing the voicing of the drivers most likely in a bad way. If you want to change them for better quality ones like Jantzen or Solen perfect lay inductors just make sure there the same gauge, mH's and DCR of the original ones. Most likely you'll have to custom order them as nobody stocks these, Good luck with this.

tschopp wrote: »

On the 1C (and most early SDA) the wire gauge of the stereo inductors is the same as the dimensional inductors. This causes the dimensional circuit to have a higher DCR than the stereo circuit.

For the 1C's and other single board style crossover non TL SDA's this statement is actually backwards and here's why. Even though both inductors may have the same gauge wire the dimensional inductor (L2) is half the mH's of the stereo inductor (L1). Less wire = less resistance. In the case of the 1C's L1 is a 22ga 2.5mh with a nominal DCR of 1.8 ohms and L2 is a 22ga 1.25mh with a nominal DCR of 1.2 ohms (These were measured with my crappy DMM that only go's down to 0.1 ohms at +/- 1%). I believe the only reason Polk changed the wire gauge there by changing the DCR in different model SDA's was to voice the different drivers used, not to correct some perceived issue.

tschopp wrote: »

In the later TL series the dimensional inductor used a heavier gauge than the stereo correcting this issue.

No this was to voice the different drivers used to match the SL3000 tweeters, again not to correct some perceived issue.

Just my $0.02 and again welcome to Club Polk.

tschopp

gimpod wrote: »

I have no idea what this means but in the context of your post it gives the impression that your thinking of changing the inductors with ones of a different DCR. If this is the case it's a bad idea as you'll end up changing the voicing of the drivers most likely in a bad way. If you want to change them for better quality ones like Jantzen or Solen perfect lay inductors just make sure there the same gauge, mH's and DCR of the original ones. Most likely you'll have to custom order them as nobody stocks these, Good luck with this.

Sorry for the symmetry talk, as a physicist that just the way I think. If you look at the left speaker, right speaker, and SDA cable as a single circuit (and I think you need to since they are all connected) you can see a lot of symmetry in the values of the components. In the 1C for the stereo there is a 2.5mH and 20uF that setup a low pass filter. The dimensional has (2) 1.25mH in series and (2) 40uF in series, this yields an effective 2.5mH and 20uF low pass filter that matches the stereo side. But the DCR is higher in the dimensional side. As you pointed out the 1.25mH are 1.2 ohms and the 2.5mH are 1.8 ohms. Since you have the 2 1.25 in series the total inductor DCR in the dimensional side is 2.4 ohm vs the 1.8 ohm for the stereo. This is why I believe the later versions used a heavier gauge inductor in the dimensional. The frequency of the low pass filter changed for the TL and I suspect this was due to the tweeter change, going to SL3000.

I am thinking of changing the inductors, mostly for better quality. I am considering lowering the DCR in the dimensional side to match the stereo. This would slightly increase power to that section and slightly increase damping.

Mostly just trying to figure out what mods I want to try first. What do you think has the most bang for buck (tightly guarding wallet)?

drumminman

IMHO the most bang for the buck if no mods have been done and all drivers are original is to swap out the tweeters for new RD0-194 (or RD0-198 - not sure which would be appropriate for the 1C's). Only one of these will work due to the Xover design; a search will tell you which one. They're $48 each if you tell Polk you're a member of CP.

Other cheap and effective mods are to damp the MW and passive radiator baskets with Dynamat Extreme or the equivalent. This stops the stamped metal baskets from ringing and removes a bit of mid range congestion. Also effective is making new gaskets for all drivers and PR. You can use Armaflex or moretite (rope Caulk). I've had good success with both, though the former is easier and less messy to use.

The next thing I would do is rebuild the Xovers with film caps and better resistors. Members here have had good results with several different brands of each.

There other proven tweaks but this should be enough to get you started.

It appears you may be standing at the edge of the rabbit hole, trying to determine just how deep it goes. It goes deep my friend! :cool:

audio_alan

Since you're already on the lookout for 1.2's, I'd say you've already entered the rabbit hole...

Enjoy your trip, and welcome Steve!

gimpod

What your thinking of doing is a bad idea, it's been tried before with less than favorable results. Check this thread out by fellow member DarqueKnight Improvements To Modified SDA SRS 1.2TL Crossover, actually any of his threads regarding SDA mods IMO are a must read as they contain a lot good information and are well documented.

Also here's a couple papers that you should read that will give you a better understanding of the SDA Technology.

This paper is about the SDA Surround Technology used in Polks SoundBars but also covers the original SDA Technology.
SDA White Paper.pdf

The inductor there referring to in this one is the big round inductor the crossover mounts to.
Inductor Upgrades For SDA.pdf

Happy reading.

As far as what mod has the most bang for your buck, I'd have to agree with drumminman tweeters the RDO-194's the RDO-198's won't work with the 1C crossover. With crossovers second only because of costs.

Now if you still want to lower the DCR of those 1.25mH inductors go for it I don't think you'll like the results but after all there your speakers.

tschopp

gimpod wrote: »

What your thinking of doing is a bad idea, it's been tried before with less than favorable results. Check this thread out by fellow member DarqueKnight Improvements To Modified SDA SRS 1.2TL Crossover, actually any of his threads regarding SDA mods IMO are a must read as they contain a lot good information and are well documented.

Thanks gimpod, I had read that, but missed the part about the lower DCR inductors being pulled out and replaced with the stock originals. I also read a latter thread where the the stock were replaced with perfect lay inductors, but the same DCR and that was an improvement.

I may need to adjust my thoughts on how refined these crossover designs are. All designs involve compromise. I would have guessed that the DCR of the original was an acceptable compromise relative to cost. I am a bit surprised that that a slight increase in power to the low section would require a rework of the overall design to put things back in balance. By design compromise I mean Polk had more options than we have as you throw more money at it. For example, to get more bass, instead of spending the money on a lower DCR 16mH, they could add more drivers and a 15" PR instead.

I will start with the well proven mods and if I do anything untested I would mod one thing at a time to figure out what works and what doesn't.

I think I got my foot stuck in the rabbit hole over 20 years ago when I heard some SRS. The wife acceptance of the 1C was better than expected, this got me thinking I need to keep a lookout for 1.2s. I explained that the 1C was just a bit taller than the 10, the footprint is basically the same. Now the 1.2 is just a bit wider and taller than the 1C, should be fine, right.

helipilotdoug

tschopp wrote: »

The wife acceptance of the 1C was better than expected, this got me thinking I need to keep a lookout for 1.2s. I explained that the 1C was just a bit taller than the 10, the footprint is basically the same. Now the 1.2 is just a bit wider and taller than the 1C, should be fine, right.

Perfect reasoning!! Hope the Wife agrees
Welcome to CP Steve.

rromeo923

I second the idea of swapping the tweeters for the RDO's first. This was a big upgrade when I did it to my 1C's. Very easy to do and the smile factor was huge after it was done.

whereas

Welcome, Steve!

charley95

Welcome tschopp! If you don't find some 1.2's, I have some 2.3's in the "for sale" section.
I'm an hour and a half up the road from you in Peoria.

TNHNDYMAN

Hi and welcome to Club Polk.