SDA2b life support

jcandy

F1nut wrote: »

Why are you obsessed with a flat frequency response? It is not the end all that some think it is. I recall one of the better speaker designers mentioning that he built, with the help of test equipment and modeling programs, a speaker with a perfectly flat frequency response. He stated that it sounded like ****.

Was this before he earned the reputation as one of the better designers?

I am not obsessed with a flat response, I am obsessed with facts. The frequency-response curve provides an important yardstick. The polar response, and the power response are also critically important depending on application. If we were talking about a center channel I'd have asked for polar response plot by now. Some people think the phase-response is also important, but in fact studies demonstrate that people are not sensitive to it. If you have a very reflective room, for example, what the flat FR curve tell me is that the speaker is probably going to sound bright unless you're over 50 and went to lots of Ted Nugent concerts in the 70s. My listening room is not very reflective so a flat SPL sounds good.

So, what I would do if I designed an improved crossover is offer a version with flat anechoic response, with instruction on how to progressively slope the tweeter response downward to suit the room characteristics by making simple changes to the shunt/series resistances.

mmadden28

jcandy wrote: »

Are there FR plots showing "before" and "after" the modification?

If I understand correctly, the 'TL' mod was a Polk Engineered design change which was applied to other models with the same crossover design-this wasn't something everybody just did.

Suggestions were made to you on what is generally accepted as the best sounding revision and since you had to buy new tweeters anyway it was suggested that you get the RD0-198s which would be the same cost as new RD0-194s and the only other addition is a 5.8µF cap (choose your poison).
All the other upgrades/improvements are simply recommendations for additional improvements that's all. Many still have their 2B's stock and love them.

You came here asking for advice as to what to do next, then you rebut with engineering this and that. So be it if you want them to remain stock, no need to be demanding FR plots and all that from the people trying to help you out based on what their ears hear. Sheesh.

mmadden28

jcandy wrote: »

Does somebody have a measurement of the original versus the modified 2B? Seriously guys :mad:

Here is a measurement of what I just A/B tested the SDA2Bs against to verify that they do not have a flat frequency response.

Did you perform that measurement in an anechoic chamber?

jcandy

mmadden28 wrote: »

If I understand correctly, the 'TL' mod was a Polk Engineered design change which was applied to other models with the same crossover design-this wasn't something everybody just did.

Suggestions were made to you on what is generally accepted as the best sounding revision and since you had to buy new tweeters anyway it was suggested that you get the RD0-198s which would be the same cost as new RD0-194s and the only other addition is a 5.8µF cap (choose your poison).
All the other upgrades/improvements are simply recommendations for additional improvements that's all. Many still have their 2B's stock and love them.

You came here asking for advice as to what to do next, then you rebut with engineering this and that. So be it if you want them to remain stock, no need to be demanding FR plots and all that from the people trying to help you out based on what their ears hear. Sheesh.

I appreciate the help and suggestions. I think I have rebutted only the boutique capacitor assertions (Sonicaps are 7 times better!), which seem implausible. Maybe its wasn't clear, but these are not my speakers, they belong to my uncle who's had a stroke and must sell them. For this reason I am not anxious to hack up the present crossover.

On the other hand, I've learned alot about the SDA series in the last few days and might acquire my own pair (for ethical reasons I don't want to keep these ones). In that case I'd consider more invasive modifications.

Thanks to those who offered advice. I really do appreciate it.

jcandy

mmadden28 wrote: »

Did you perform that measurement in an anechoic chamber?

Good question. Its quasi-anechoic. First, one measures the far-field response. The software applies a time window (smaller than the time for the first reflection to reach the microphone) to the MLS impulse to eliminate the effect of reflection, but limiting the validity of the data to about f > 300Hz. Then, the near-field responses of the woofer and port (or passive radiator) are taken and summed to get the complete near-field response. The near-field response is corrected by a numerical cabinet diffraction calculation to convert it to a far-field response (this is the one bit that could be subject to error, but turns out to be very accurate for typical MT and other speakers). Then, the near-field is spliced to the far-field at some joining frequency, usually about 400Hz. If the diffraction calculation was accurate then curves should overlap over a wide region, and if it does overlap you indeed trust that it was. In this case the overlap was great.

inspiredsports

jcandy wrote: »

I appreciate the help and suggestions. I think I have rebutted only the boutique capacitor assertions (Sonicaps are 7 times better!), which seem implausible. Maybe its wasn't clear, but these are not my speakers, they belong to my uncle who's had a stroke and must sell them. For this reason I am not anxious to hack up the present crossover.

On the other hand, I've learned alot about the SDA series in the last few days and might acquire my own pair (for ethical reasons I don't want to keep these ones). In that case I'd consider more invasive modifications.

Thanks to those who offered advice. I really do appreciate it.

OK, now I'm really missing something here.

If you are simply helping your uncle sell them, why not pick up 2 used SL2000's for $40 as I suggested a day or so ago, slap them in, and get them listed on eBay?

You won't improve your chances of selling them, or sell them for more money by modding them with cheap caps. And I certainly can't see why you are so argumentative and insistent about seeing frequency response curves for tweeters you would be putting in these for resale.

And they have immense sentimental value to you, yet you don't feel you can't keep them for ethical reasons?

So at any rate, you've got me really confused.

heiney9

jcandy wrote: »

Its not really about saving money, its more about not throwing it away. There's a significant difference. You see, when I look at (and in) the SDA2Bs, I see a very clever, innovative speaker, but with some problems that cannot be solved with the use of boutique capacitors, such as: inadequate bracing, poor inductor placement, 90 degree baffle edges, large tweeter-mid CTC spacing (which gives rise to lobing). The crossover on the tweeter is only second order which probably does not provide optimal power handling (obviously!). Measurement may uncover further problems. For example, its not clear what the distortion numbers are. This is a critical consideration when starting a new design, and also cannot be cured in the crossover. Instead, you have to start with a low-distortion driver like this one:

http://www.parts-express.com/pe/showdetl.cfm?Partnumber=296-602

This will sound more natural/correct in the critical midrange than the Polk MW6503. Moreover, I do not understand the SDA crossover well enough at the moment to improve it. With something like a monitor 5/7/10 it would be easier.

Anyhow, I now have them up and running with the RDO-194s I picked up directly from the Polk Warehouse in Vista (just north of me). They sound very good (I have other "vintage" speakers from the 90s that sound horrific) but I can tell right away that the FR is not flat. I want to do some measurements to verify this, but have to figure out how to manage that with the SDA effect.

Well apparently you know a WHOLE lot more about SDA's than Matt Polk and the engineers that conceived, built, tested and manufactured these speakers. :rolleyes::rolleyes:. Many if not all of the upgrades that have been done over the years have been suggested or discussed with Matt Polk and others close the SDA product at Polk and passed on, so it's not like all these suggestions are just wild hit and miss things.

For a more technical analysis I suggest you read these two articles and head to the library and read the "original" SDA white paper in the June 1984 Audio Magazine.

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

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

Incorporating the newer silk dome RD0 tweeter gets rid of the steep resonant peak at about 13kHz the original sl2000 exhibits. There has been a discussion from Matt Polk about inductors in the SDA's so search for it. Additionally the SDA's can handle lots of power, where most people have issues is when they under power them. In fact if you read the test articles you'll see the 1C's could have taekn more power except the amp they were using at the time ran out of power before the speaker distorted around 800 watts give or take depending on the frequency. They are also flat +/- 5dB 20Hz - 18Khz if those measurements are important to you.

H9

jcandy

inspiredsports wrote: »

OK, now I'm really missing something here.

If you are simply helping your uncle sell them, why not pick up 2 used SL2000's for $40 as I suggested a day or so ago, slap them in, and get them listed on eBay?

Since the RDO-194 was a drop-in replacement and cures some of the SL2000s problems, that made the most sense to me. Replacing the tweeters with the "best" replacement part is not invasive. Since I live relatively close to the Polk warehouse, it was fast and easy for me to just run by and get them. Now the RDO-194s are in and work well. They are excellent speakers.

inspiredsports wrote: »

You won't improve your chances of selling them, or sell them for more money by modding them with cheap caps. And I certainly can't see why you are so argumentative and insistent about seeing frequency response curves for tweeters you would be putting in these for resale.

I am intrigued by these speakers, and they still do hold great sentimental value. I think in the future I would like to try to design a modified crossover for an SDA (on the other hand, a monitor 10 would be easier). And to answer your question in a general way, I just want to know the facts.

inspiredsports wrote: »

And they have immense sentimental value to you, yet you don't feel you can't keep them for ethical reasons

It would look like I'm freeloading! I said I would fix them (they were DoA with side panels off all fallen off) and sell them, and that's what I'll do. Because they have sentimental value I want to sell them to someone who will treat them well. I said I'd sell all that NAD gear, so I have to do that too, but I'm wasting too much time here! Honestly, I've learned alot in the last few days even if it seems I'm just a s--t disturber.

inspiredsports wrote: »

So at any rate, you've got me really confused.

Sorry for that. I've kind of got people jumping all over me by now.

jcandy

heiney9 wrote: »

Well apparently you know a WHOLE lot more about SDA's than Matt Polk and the engineers that conceived, built, tested and manufactured these speakers. :rolleyes::rolleyes:.

When did I say or imply that? I am sure Polk would have done various things differently (bracing for example) had cost not been an issue. Slamming all the inductors together on one board, or omitting complex internal bracing, is something that starts to become very efficient/attractive in a mass-produced speaker, but its not something you need to do if you are building your own, or if cost is no object. Here's an example of a speaker that starts with spectacular drivers (the woofer is hand-made in the USA, the mid in Italy, and the tweeter in Denmark) and uses an enclosure that could withstand a nuclear blast:

http://www.aespeakers.com/phpbb2/viewtopic.php?t=1702

Nearly all of the (numerous) crossover components, however, are Dayton, which on this forum are apparently worse than garbage.

heiney9 wrote: »

Many if not all of the upgrades that have been done over the years have been suggested or discussed with Matt Polk and others close the SDA product at Polk and passed on, so it's not like all these suggestions are just wild hit and miss things.

I believe that many of the upgrades are probably sound. But I have given examples of the more problematic information, like replacing the air-core inductor with an SL, or believing that changing a very good poly capacitor with another very good poly capacitor will "open up the soundstage". I would need to see real proof of that before I could believe it.

heiney9

jcandy wrote: »

I believe that many of the upgrades are probably sound. But I have given examples of the more problematic information, like replacing the air-core inductor with an SL, or believing that changing a very good poly capacitor with another very good poly capacitor will "open up the soundstage". I would need to see real proof of that before I could believe it.

Well, therein lies your problem, unless your ears can see. There is a very, very interesting discussion about inductors in SDA's from Matt Polk himself explaining inductors in SDA's. You could search for it if you are really interested in finding the proper answer.

Actually since i assumed you wouldn't bother to look for Matt and Stu's response I found it for you. This is specifically about the inductors in a pair of SDA SRS's, but I'm sure you can extrapolate the info to other model SDA's.

http://www.polkaudio.com/forums/showpost.php?p=1365585&postcount=5

heiney9

Here's one entire thread on SDA inductors

http://www.polkaudio.com/forums/showthread.php?t=103052&highlight=inductor

jcandy

heiney9 wrote: »

Well, therein lies your problem, unless your ears can see. There is a very, very interesting discussion about inductors in SDA's from Matt Polk himself explaining inductors in SDA's. You could search for it if you are really interested in finding the proper answer.

Actually since i assumed you wouldn't bother to look for Matt and Stu's response I found it for you. This is specifically about the inductors in a pair of SDA SRS's, but I'm sure you can extrapolate the info to other model SDA's.

http://www.polkaudio.com/forums/showpost.php?p=1365585&postcount=5

Thanks for sending me the link. I did look for this but couldn't find it. Both these guys know exactly what they're talking about Its also quite consistent, technically, with what I've been saying. One tricky point is related to the inductor DCR and bass response. Here's what I said earlier:

Yes, I can understand replacing the capacitors because of the tendency to degrade over time. Replacing the air-core inductor with steel-laminate could really be an *error*, since the two will differ significantly in DC resistance. Generally speaking, if you switch from air-core to SL in a low-pass filter, you will raise the level of the low-pass transfer function, accentuating the bass. Maybe this is the "bass slam" people spoke of

and here is what Polk said,

Decreasing the DC resistance will definitely improve the bass response of the system both qualitatively and quantitatively. However, before you rush out to buy those Hi-Q replacement inductors be aware of some concerns.

However, in this case, improve means "raise". Generally speaking, shaping the bass response is an application-dependent exercise. What designers normally do is provide options for bass tuning in connection with intended application. If you are placing speakers close to the wall and excite room modes sufficiently, or if you are using them for near-field monitors, there is not much need for baffle-step compensation (BSC), although there may be a need for tweeter attenuation in a design with a uniform power response. But if you have an open room you might want up to +6dB of BSC. In my most recent design I used two inductor stages to ensure a full +6db of BSC as well as a perfectly flat SPL. I also like the sound of full-BSC designs, which are equivalent to flat anechoic far-field designs.

I guess the point is that just swapping out components is a hit-and-miss approach, which is awfully time-consuming. For this reason, it is extremely important to have an SPL trace of the stock SDA2B before attempting any modifications.

sda2mike

jcandy wrote: »

Nearly all of the (numerous) crossover components, however, are Dayton, which on this forum are apparently worse than garbage.


huh?? my xovers were done to TL standards by the highly-respected ben..he's done lot's of member's xovers...guess what? my xovers have 1 dayton each! the rest are sonicaps. i highly doubt that ben would install something less than garbage.

you might want to stop thinking about graphs and charts and articles and just listen...to the music AND the guys here who know wtf they're talking about.

mike

jcandy

heiney9 wrote: »

Here's one entire thread on SDA inductors

http://www.polkaudio.com/forums/showthread.php?t=103052&highlight=inductor

After reading this over and over, Polk really makes it seem as though the reduced DCR will give unequivocally better low-frequency response because it removes the (unwanted) SDA effect (although the the speaker will have dangerously low impedance). I find it hard to believe. But, I guess its possible. Interesting.

Thanks for the links.

jcandy

sda2mike wrote: »

huh?? my xovers were done to TL standards by the highly-respected ben..he's done lot's of member's xovers...guess what? my xovers have 1 dayton each! the rest are sonicaps. i highly doubt that ben would install something less than garbage.

I assure you the Daytons (which are Bennics) are excellent.

sda2mike wrote: »

you might want to stop thinking about graphs and charts and articles and just listen...to the music AND the guys here who know wtf they're talking about.

But I can't stop thinking about them! I will post measurements of the SDA2Bs as soon as I can. Should be an eye-opener!

heiney9

jcandy wrote: »

I assure you the Daytons (which are Bennics) are excellent.

They are OK, certainly not garbage, but certainly not anything above average.

H9

inspiredsports

heiney9 wrote: »

They are OK, certainly not garbage, but certainly not anything above average.

H9

Great caps don't seem to be as critical in the low pass section, but I can attest that Sonicaps or better DO make a difference up top.

F1nut

jcandy wrote: »

I think I have rebutted only the boutique capacitor assertions (Sonicaps are 7 times better!), which seem implausible.

H9 was being conservative, IMO. I'd say the Sonicaps are at least 10 times better.

inspiredsports

I'm curious about what you did with your uncle's SDA-2B's, (especially with all that's transpired since several other members and I warmly welcomed you aboard back in September, 2010 as #1 above was your very 1st post).

Does the saga continue here? http://www.polkaudio.com/forums/showthread.php?t=106512

fbm211

If we only knew then what we do now.

jcandy

inspiredsports wrote: »

I'm curious about what you did with your uncle's SDA-2B's, (especially with all that's transpired since several other members and I warmly welcomed you aboard back in September, 2010 as #1 above was your very 1st post).

Does the saga continue here? http://www.polkaudio.com/forums/showthread.php?t=106512

I advertised them on CL a few times, but nothing ever materialized. I was travelling alot during that time, and also coordinating the sale of many other items, so that probably cost me the sale. I turned down a few crazy low-ball offers. I'd rather hold on to them than give them away for $100. At this point they are still in my house, disconnected, but are promised to a friend of a friend -- presumably, as soon as he breaks the new to his wife :frown:

Before they are gone I am going to do an SL2000T versus RDO-194 HD comparison (I promised Face I would do this).

jcandy

inspiredsports wrote: »

I warmly welcomed you aboard back in September, 2010

I have said many times that I received some good tips when I first showed up. I do appreciate any and all honest help I've been given. The accusations of trolling that are continuously thrown my way (by a select few) are just plain weak; they're good examples of the pot calling the kettle black.

inspiredsports

jcandy wrote: »

I have said many times that I received some good tips when I first showed up. I do appreciate any and all honest help I've been given. The accusations of trolling that are continuously thrown my way (by a select few) are just plain weak; they're good examples of the pot calling the kettle black.

I've read the other forums where you starts threaded and the term troll was use in those cases also. Comment?

I've posted elsewhere that you show signs of high intelligence, like Rain Man with the matchsticks. But then you seem to cover your ears when the music is playing.

All work (measurement) and no play (listening) makes J a dull boy.

On3s&Z3r0s

jcandy wrote: »

I advertised them on CL a few times, but nothing ever materialized. I was travelling alot during that time, and also coordinating the sale of many other items, so that probably cost me the sale. I turned down a few crazy low-ball offers. I'd rather hold on to them than give them away for $100. At this point they are still in my house, disconnected, but are promised to a friend of a friend -- presumably, as soon as he breaks the new to his wife :frown:

Before they are gone I am going to do an SL2000T versus RDO-194 HD comparison (I promised Face I would do this).

Part 'em! Actually, I feel dirty just suggesting it, but if the tweeters are shot anyway...

mossbacked

jcandy wrote: »

I am trying to revive my uncle's SDA2Bs that suffer from (at least) the blown-tweeter problem. These speakers have great sentimental value: in fact, I drove them home myself in 1990, in a 1986 Honda Civic hatchback. I lost contact with him in the period 2002-2010, but recently he had a stroke . Now I am helping him to sell some items, and since I am a DIY audio fanatic, I offered to deal with the complete setup (also includes the high-end NAD pre-amp-tuner-cd from that era). The entire system was ridiculously expensive when purchased in August 1990 (seems like yesterday ...), and oddly enough, hasn't really been used for about 10 years. My uncle doesn't really like music!

Over the years, I believe two sets of replacement tweeters were ordered, but all tweeters he can locate are *dead*. I tested a random spare tweeter and this produced a roughly correct SPL, so I know there is a signal to the tweeters. The inner 6.5 driver is making NO sound, but I suspect this is because I don't have the SDA interconnect.

What should I do? Attempt to locate replacement tweeters, upgrade the crossover (I am comfortable with that), just sell them as-is, what

As I googled SDA2B my search landed here and I am wondering if they were for sale and can ship to 60952?