SDA SRS 2.3TL Schematic vs. earlier 2.3

SciFiTom

Gents,

I bought these things on the strength of having owned a pair of Monitor 7s since they were new, the comments, and enthusiasm of this forum, and a desire for stronger bass than my Maggies were doing in the room I have.

It occurs to me that I've only heard the 2.3s *I* have with the 25+ year-old electrolytic caps. From that viewpoint, the speakers could use a substantial increase in the tweeter output, and a lot more bass definition. More than likely, you are mostly familiar with these speakers in prime shape, which would give you a game-changing perspective.

Technically, when I first looked over the schematics, I mainly considered energy transfer, not the corner frequencies of the filters (not to mention my mis-reading of some values), with the notion that Polk knew the rest. I don't know much of anything about the relationship in operating characteristics between the tweeters under consideration, which if I'm going to re-design the speakers, I ought to know a lot more about. That said, my experience has been that ears are much more important than data when it comes to listening enjoyment. When I look at DarqueKnight's plots, these speakers don't come off very well in comparison to others - even my old Design Acoustics D-12s, are supposedly ±2dB up to about 17kHz. 5+dB deltas across the audio spectrum would be considered extreme now, but they DO sound pretty good. I'd also point out that the venerable Klipschorns also have about a 5dB delta across their range, and a lower top-end, but they, too, have quite a following.

Were I to make these changes scientifically, as DarqueKnight has taken great pains to do, I'd need to go out and get a sweep generator, an audio spectrum analyzer (now where DID that Tek 5L4N go?), and a calibrated microphone, then evaluate before and after with consideration of the rest of the audio chain. All that could happen. I've obviously done stranger things, but likely not.

I am dis-inclined to mess with the bottom end (past replacing the caps) in terms of moving to all 6510s, and replacing the PR, as I tend to concur with Cincycat's comments. Many have suggested I need the rings for them, and I'm good with doing those. Certainly can't hurt, if I can get them.

Informationally, like many, I'm sure, I have a hodge-podge of equipment, because I didn't whip out the checquebook and buy all at once. For the amusement of those who might want to deride my choices: At the moment, (with a couple of pairs of Magnepans sitting off to the side), I am using a Crown XTI-2002 for the front L-R Polks, an Emotive XPA-5 for the Magenpan 1.7 centers -a pair pointing far inward, each with its own channel of the XPA-5, Mirage OMD-15 surrounds, also powered by the XPA-5, an Emotiva UPA-2 driving the aforementioned D-12s as the rear surrounds. All that is fed from an Oppo BDP-103, through an Integra 80.2 pre-pro. This in an 800 sq. ft. room, roughly half of which is the listening area. As I said earlier, the room affects the outcome of all I do, since there's no wall to bounce off of on the right side.

Maybe this would all be easier if I just rebuilt the room, huh? Ain't being an audio nut wonderful?

SciFiTom

Toolfan66 wrote: »

I'm trying to get the time to run some more rings, I have the passives, I just don't have any driver rings or tweeter brackets..

I'm going to echo what I said earlier, leave them as 2.3's, don't try and make them a TL version. If you do try and do it remember your left speaker will become your right speaker, and your right speaker becomes your left speaker...

I'm telling you the 2.3's are awesome speakers, no need to go down that road..

Ah, Dr. Larry, I presume. When you get the time, I would indeed be interested in your product. Kindly let me know when that occurs.

It would seem that I was composing may latest response when you posted this. I understand about the TLs swapping sides, that's part of why I didn't want to go whole hog, and do the bottom end, as well. There seems, perhaps to have been a mis-communication, based on my sloppy language. I'm not trying to do the TL mod in its entirety, I am considering an unusual tweeter update. My apologies to all for presenting that misinformation.

TennMan

SciFiTom wrote: »

Gents,


Were I to make these changes scientifically, as DarqueKnight has taken great pains to do, I'd need to go out and get a sweep generator, an audio spectrum analyzer (now where DID that Tek 5L4N go?), and a calibrated microphone, then evaluate before and after with consideration of the rest of the audio chain. All that could happen. I've obviously done stranger things, but likely not.

I am dis-inclined to mess with the bottom end (past replacing the caps) in terms of moving to all 6510s, and replacing the PR, as I tend to concur with Cincycat's comments. Many have suggested I need the rings for them, and I'm good with doing those. Certainly can't hurt, if I can get them.

This is just my opinion. If you start listening to your speakers with charts and graphs instead of your ears you will never be satisfied with your speakers. The charts and graphs have their place in this hobby but the most enjoyment you will get from your SDAs is when you get immersed in the music and forget the speakers are in the room. Making the speakers disappear is where the SDAs excel. They do that by expanding the sound stage outside the boundaries of the speakers and by adding depth. I'm always amazed at how they can do that while maintaining the positions of instruments with pin point accuracy.

Here is my take on upgrading your speakers... Upgrade your crossovers with quality caps and resistors. Go with the RDO-194s and forget the TL upgrade. I have owned both RDO-194s and 198s. There is not enough difference in them to go to all the extra work that you will have to in order to use the 198s. Take the money you will save and upgrade the dimensional inductors. I used Erse Super Q steel laminated core inductors and it made a huge difference in the bass of my 2Bs. Some people say the high dollar air coil inductors are even better. My 2BTLs have the 198s and Erse inductors and I'm happy that I was able to do both at a reasonable cost. However, if I had to choose between 198s with stock inductors, or 194s with Erse inductors, I would go with the 194s and Erse inductors. In your case that would be the best bang for your buck.

SciFiTom

TennMan wrote: »

If you start listening to your speakers with charts and graphs instead of your ears you will never be satisfied with your speakers. The charts and graphs have their place in this hobby but the most enjoyment you will get from your SDAs is when you get immersed in the music and forget the speakers are in the room.

I concur. I tried to say so in the bottom half of the paragraph above the one you quoted.

TennMan wrote: »

Here is my take on upgrading your speakers... Upgrade your crossovers with quality caps and resistors. Go with the RDO-194s and forget the TL upgrade. I have owned both RDO-194s and 198s. There is not enough difference in them to go to all the extra work that you will have to in order to use the 198s. Take the money you will save and upgrade the dimensional inductors. I used Erse Super Q steel laminated core inductors and it made a huge difference in the bass of my 2Bs. Some people say the high dollar air coil inductors are even better. My 2BTLs have the 198s and Erse inductors and I'm happy that I was able to do both at a reasonable cost. However, if I had to choose between 198s with stock inductors, or 194s with Erse inductors, I would go with the 194s and Erse inductors. In your case that would be the best bang for your buck.

Sound advice. Excellent information on the perceived differences of the two tweeters, thank you. I have had an eye on the inductor you mention, and have looked at the Erse site, though I didn't find the iron-core inductors there. I've been leery of iron in the audio chain, because of the possibility of saturation if the manufacturer didn't account for the intended amplifier power. I do note that the DCR of the iron-core variety would be lower than the air-core, which should be the right direction for that inductor in-circuit, at perhaps the expense of the "happiness" of your amplifier (less a problem these days, than when these speakers were conceived, admittedly).

A WARNING TO ALL: I bought some resistors claiming to be Mills, but they are made in Mexico, and look very suspiciously like Vishay-Dale work. One of the hallmarks of the original Mills resistor was the care taken with the end bells, which I do not expect goes into the Vishays. Both are supposed to utilize the Aryton-Perry winding, which is how they get to be non-inductive, but the quality is suspect. Note the brown resistor at left, versus the black ones at right.

Respectfully,
Tom

TennMan

I purchase the Erse Super Q inductors from Parts Express. I purchased the 17mh, 16awg inductors and used my meter to unwind enough turns off of them to bring them down to 16mh required for my 2Bs. I actually went down to 15mh and then settled on 15.5mh because I preferred how they sounded there the best. Like you, I like to experiment.

BobMcG

Alright, very good, carry on gents.

Just checking in to make sure SDAs still aren't dead.

Hi Jesse.

F1nut

Hi Bob.

drumminman

SciFiTom, while you're refreshing your Xovers I recommend that you change out the board mounted inductors as well. I bought mine from VR3 here on the forum, Jantzen air core, and I was surprised at the improvement they brought in my 2.3TL's.

You'll find some of the values here on Gimpod's chart ; http://www.polkaudio.com/forums/showthread.php?138234-Inductor-DCR-Insanity-For-SDA-s

SciFiTom

drumminman wrote: »

SciFiTom, while you're refreshing your Xovers I recommend that you change out the board mounted inductors as well.

Sir, if you look at the pic I took to demonstrate the resistor issue (back about 5 replies), you'll find that the inductors for the tweeters are quite a bit bigger than stock. I did that because I wanted to replicate the entire tweeter section such that I could return readily to stock, if I hate it. The down-side there is that reducing the DCR may make the output hotter. I considered adding half an ohm more at the input, but decided to stay put, and add it back externally, if desired. I think the biggest bang-for-the-buck would come from replacing the 16mH inductor on the interconnect, as suggested by TennMan, below, but I think I'll wait to consider that until after I've gotten a set of Larry's rings. It would seem that an upgrade to the IC cable at the same time would make sense.

BTW, folks, IF I did the math close to right, the difference between the 2.3 schematic, and the TL schematic (for the tweeters, alone) differs by about 1/10 ohm after accounting for the impedance of the SL2000 vs. RDO-198s, so I'm really not expecting a huge change there.

SciFiTom

TennMan wrote: »

I purchase the Erse Super Q inductors from Parts Express. I purchased the 17mh, 16awg inductors and used my meter to unwind enough turns off of them to bring them down to 16mh required for my 2Bs. I actually went down to 15mh and then settled on 15.5mh because I preferred how they sounded there the best. Like you, I like to experiment.

Thanks for the info. Interesting notion. I will consider that when I've gotten the rings. Are those inductors wire, or foil? Did you pick 16AWG out of concern that lowering the DCR much more might cause your amp to cough up blood?

TennMan

SciFiTom wrote: »

Thanks for the info. Interesting notion. I will consider that when I've gotten the rings. Are those inductors wire, or foil? Did you pick 16AWG out of concern that lowering the DCR much more might cause your amp to cough up blood?

The inductors I bought from Parts Express are wire wound. I bought from Parts Express because I needed to order other things they had in stock at the same time. You can buy directly from Erse but as far as I know there is not a 16mh inductor, steel laminated core available. If I remember correctly your choices for inductors Erse has in stock are 17mh, 16awg or 15mh, 14awg. I think westmassguy has used the 15mh, 14awg and was very happy with them. He will probably chime in and give you his thoughts about that. I read here on the forum that Erse will unwind a 17mh down to a 16mh for an additional $10 over the normal price.

A good high current 2 channel amp should handle a 16awg or 14awg inductor without problems. I wouldn't want to use an AVR with them.

westmassguy

SciFiTom wrote: »

Sound advice. Excellent information on the perceived differences of the two tweeters, thank you. I have had an eye on the inductor you mention, and have looked at the Erse site, though I didn't find the iron-core inductors there. I've been leery of iron in the audio chain, because of the possibility of saturation if the manufacturer didn't account for the intended amplifier power. I do note that the DCR of the iron-core variety would be lower than the air-core, which should be the right direction for that inductor in-circuit, at perhaps the expense of the "happiness" of your amplifier (less a problem these days, than when these speakers were conceived, admittedly).

I'll chime in here, since I did a lot of research on the subject before purchasing the Erse SuperQs. They are not Iron or P core, which do saturate easily. Erse uses a very unique assembly process with alternating grain, laminated steel. Both models are rated up to 20 amps, 500 watts for the 16 gauge, and 600 watts for the 14 gauge, before saturation. This particular Inductor is part of the "Full Compliment, Sub-Bass Drive" circuit. I refer to it as the Dimensional Inductor for simplicity (read the SDA Handbook for a full description of this circuit). It's doubtful you'll ever approach saturation, even on the largest SRSs. The reason is rather simple. This Inductor's sole purpose is to provide a low resistance path to ground for the Dimensional Woofers, below 150 Hz. Your 2.3s have two Dimensional Woofers. It's highly unlikely those two woofers will ever see 500 or 600 watts, before something else burns up, or you go deaf in the process. Would I prefer a Custom, Large Gauge, Air Core Inductor? Probably, but I don't have that kind of discretionary income, so the SuperQ was the only clear choice.

SciFiTom

westmassguy wrote: »

I'll chime in here, since I did a lot of research on the subject before purchasing the Erse SuperQs. They are not Iron or P core, which do saturate easily. Erse uses a very unique assembly process with alternating grain, laminated steel. Both models are rated up to 20 amps, 500 watts for the 16 gauge, and 600 watts for the 14 gauge, before saturation. This particular Inductor is part of the "Full Compliment, Sub-Bass Drive" circuit. I refer to it as the Dimensional Inductor for simplicity (read the SDA Handbook for a full description of this circuit). It's doubtful you'll ever approach saturation, even on the largest SRSs. The reason is rather simple. This Inductor's sole purpose is to provide a low resistance path to ground for the Dimensional Woofers, below 150 Hz. Your 2.3s have two Dimensional Woofers. It's highly unlikely those two woofers will ever see 500 or 600 watts, before something else burns up, or you go deaf in the process. Would I prefer a Custom, Large Gauge, Air Core Inductor? Probably, but I don't have that kind of discretionary income, so the SuperQ was the only clear choice.

Yup, you didn't even mention ferrite cores [grin]. I hadn't seen the ratings on these, but it looks like enough steel not to cause saturation problems. So far, I've not found an air-core above 10mH, so perhaps these are a way to go. You're suggesting eddy-current losses, and all the rest aren't problematic at the frequency range of interest, or it's just, "This is what there is." Is the inductor that's in there now an air-core? I haven't taken the whole thing apart, yet.

zane77

I'm pretty sure Solen makes two different 16 mH air core inductors that are designed for audio.

Schurkey

I thought the whole reason to replace the SDA inductors was to eliminate the air-core units. The ferric (iron/steel) core units need fewer windings to achieve the same inductance. Fewer windings particularly with larger-gauge wire reduces the DC resistance...and I thought the reduction in DC resistance was the whole point of this exercise. Reduced DC resistance improves bass impact, but requires more current from the amp.

Polk used the small-gauge air cores to help boost the overall speaker impedance to a more-reasonably level, and even so their speakers were on the low-impedance end of the mass-market range.



At any rate, I installed ERSE 16-gauge SuperQ inductors ESQ55-16-10000 (10mH, unwound to match the stock 9.6mH) in my 1Bs. Very pleased. The 14-gauge version is perpetually back-ordered, hence the 16 gauge was what I purchased.

westmassguy

SciFiTom wrote: »

Yup, you didn't even mention ferrite cores [grin]. I hadn't seen the ratings on these, but it looks like enough steel not to cause saturation problems. So far, I've not found an air-core above 10mH, so perhaps these are a way to go. You're suggesting eddy-current losses, and all the rest aren't problematic at the frequency range of interest, or it's just, "This is what there is." Is the inductor that's in there now an air-core? I haven't taken the whole thing apart, yet.

All the inductors in the SDAs I've worked on are air core. Since I have no way of measuring the various distortion components common to non air core inductors, I went with the manufacturers stated distortion figures, and the recommendation Stu Lumsden made in the SDA Handbook, that only laminated steel core inductors were acceptable replacements.

westmassguy

zane77 wrote: »

I'm pretty sure Solen makes two different 16 mH air core inductors that are designed for audio.

Several companies make custom value air core inductors, and their custom prices will knock you off your chair.

westmassguy

Schurkey wrote: »

I thought the whole reason to replace the SDA inductors was to eliminate the air-core units. The ferric (iron/steel) core units need fewer windings to achieve the same inductance. Fewer windings particularly with larger-gauge wire reduces the DC resistance...and I thought the reduction in DC resistance was the whole point of this exercise. Reduced DC resistance improves bass impact, but requires more current from the amp.

Polk used the small-gauge air cores to help boost the overall speaker impedance to a more-reasonably level, and even so their speakers were on the low-impedance end of the mass-market range.



At any rate, I installed ERSE 16-gauge SuperQ inductors ESQ55-16-10000 (10mH, unwound to match the stock 9.6mH) in my 1Bs. Very pleased. The 14-gauge version is perpetually back-ordered, hence the 16 gauge was what I purchased.

Correct...
The 18 gauge, 16mh inductor on my CRS+ was around 2.5-2.6 DCR IIRC. I used 14 gauge, 15mh SuperQs to replace them (about 6% lower than the original). It's DCR is 0.34. That's a 7 fold decrease in resistance. The 150 Hz crossover most likely rose to around 180 Hz, but this was not noticeable to my ears. What was noticeable, was the tremendous increase in low bass output from the CRSs which are a bit bass shy to begin with, compared to their big brothers.
As you say, the 14 gauge are always back ordered now, so I order 16 gauge, 18mh now, and unwind them to 16mh with my LCR Meter. My 2A's 5.6mh was available off the shelf in 14 gauge. The original 5.6mh air core was around 1.7-1.8 DCR. The 5.6mh SuperQ is 0.18 DCR. That's nearly a 10 fold decrease. My 2A's low bass output also increased dramatically.
The one giant caveat, is the overall impedance of the speakers will drop substantially. My CRS+s were 6 ohm nominal, and are now 4 ohm. My 2As were 4 ohm nominal (and dropped to 3.5 ohms at certain frequencies), are now 3.5 ohm, and drop well below that in the low bass region. My Carver has no problems driving loads down to 2ohms.
This simple fact must be considered before making the change.

SciFiTom

I was thinking in terms of a larger gauge air-core inductor to avoid both large change in the bass, and the impedance drop. The idea was to drop the DCR by something like a factor of two, or 3. I looked at the Solen site, but didn't see anything there larger than 9.1mH. As Westmassguy said about cost, I didn't want to fool with either multiple inductors, or custom winding. I may try the steel-core in a smaller gauge, say 18, as a split-the-difference approach, though the DCR will still be mighty low. My present amp is stable to 1 ohm, so that part doesn't scare me, but the THD goes way up when it's driven that low.

SciFiTom

I did just see a post by DarqueKnight from 2012:

The 16 mH SDA inductors in my third pair of CRS+'s was replaced with Solen 16 mH, 14 AWG, 0.945 ohm inductors, $67.68, part number S1416.0. The Solen inductors outperformed the Northcreeks and cost 40% less. The Solen inductors were ordered from Parts Connexion.

Note the DCR for the Solen he mentioned is about what I was looking for (18 to 14AWG).

pitdogg2

Now all I need is for "Larry" to pass through here to say, "Here's how you get them."

Post #13 :cool: