View Full Version : Building new SDA's?
05-15-2002, 10:55 AM
I figured out a long time ago that Polk is not going to build any more SDA's. I finally want something different so I am building my own. Picture this, two line arrays of 12 5.25" drivers and maybe a passive radiator and some Vifa tweeters with a hacked up 1.2 crossover. The drivers are due in today and I picked box sizes that require minimal cutting of the wood used. I wish there were a tech person interested in talking design but I will probably have to just take my best shot and see where I end up. This should take awhile. I'm sure some polk engineer is laughing at this one.
05-15-2002, 11:02 AM
I've pondered the same thing, at least you have some 1.2 networks to start with. I envisioned the line array also, but was leaning towards a ribbon, or multiple ribbon tweeters...
Are there any white papers or schematics for ANY sda network? What is that cable doing exactly, sending the opposite channel out of phase?
05-15-2002, 11:45 AM
Somebody posted the 1.2tl schematic here before.
Russ, yes the cable sends the Right channel signal to the Left channel "SDA array drivers" out of phase. It does this only in a narrow bandwidth (midrange only).
Madmax has gone off the deep end, WOW what a project, GOOD LUCK my friend.
Polk may not like you calling them SDA, you might think about a new name like CAS cool as **** or TPD the panty droppers or SSCICBPQMT speakers so cool it can't believe Polk quit making them
05-15-2002, 11:52 AM
That in and of itself doesn't seem hard to to mimic, just requires a little thought. Since I seem to lack in the woodworking skills dept, I just bought some old Rat shack floorstanders on ebay for $20. Those will be my cabs to start experimenting with....
I'll search for the schematic......
Max, what drivers did you purchase for your array?
05-15-2002, 12:05 PM
Here they are
05-15-2002, 02:09 PM
I am using these 5.25" drivers. They are on sale for $6.16 each. As for the tweeters, I was thinking about the Peerless they offer for $27 ea or I may switch to whatever future sale they may offer. The Peerless look just like the SL2000's.
Thanks for the Schematic. That will make it easier to disect the existing xover. I can figure out the xover points as I go.
Physically I am makeing four towers of 12 drivers each. Each side will consist of two towers with the tweets mounted in between somewhere. The towers will each be 6"W x 72"H x 14"D. I am going with separate towers so I can change the distance between the main drivers and SDA function drivers easily. I am not sure if there can be an open space between the two or not. I'll find out. The two towers will eventually be mounted on a base to hold them in place. I am starting with them in a sealed box rather than a ported or passive radiator design because it becomes a crap shoot to determine the box resonance with all the drivers open to each other. Once I figure out the SDA placement then I may play with a PR.
05-15-2002, 02:15 PM
Those look GOOD mm, thats a helluva good price too. High power handling, decent resonant freq....with 12 per side, you'll be upwards of 350wrms power handling, and probably damn near 100db efficency.
Please document the process, if you can, I'm interested in how it goes.....
05-15-2002, 02:26 PM
Stuff like this takes me forever so that should give me time to document it. I have been watching for a good sale like that for a year now. When you start thinking in the range of 48 mid drivers and 12 or so tweeters price becomes a pretty big issue. I actually ordered 50 of these and the price was $330. Not really a lot if you think of the other options. I figure $150 for the cab and $200 for the tweets and I'll still be under $700. I'm sure there are other costs involved. (like screws? QTY: 250 or so...) That reminds me, buy new electric screwdriver!
05-15-2002, 02:33 PM
More like 24 per side, 48 total
Madmax, I thought the spacing of the drivers was a fixed distance. X distance = X ms delay of sound, and that was what made the SDA work??
05-15-2002, 02:49 PM
I believe your right. The question is what is the exact time I need and where to measure to? If I were using the 6.5" drivers I could probably keep the same distance they had. The two towers make it easier for me to build and allow for tweaking. I am only making them 6" wide so I should be able to place them as close together as I need. The other thing is I want to start out with the mains and SDA's isolated from each other. I can always port the two together if I need to. Good tip! I'll have to read all the literature again and maybe save some time.
05-15-2002, 03:25 PM
Have Ken at Polk fax you the Designed in Stereo "white paper".
I think it had stuff like that in it.
05-15-2002, 08:08 PM
Good idea, I'll check Mikes polk page also. This is cool, partsexpress.com had some reasonable tweeters on sale. I ordered 8 per side plus extras!!! I like the soft dome tweeters much better than the hard dome ones. This idea better work or I'll end up with 70+ useless drivers!
05-15-2002, 08:09 PM
Let me repost that link. I think it got messed up. Parts express is great!
05-15-2002, 08:12 PM
what an excellent project madmax! good luck, and it would be very interesting to keep us updated with your progress...
05-15-2002, 10:05 PM
So long as it doesn't pose any problem for polk I will post about it. The bad thing is that I'm all hyped up about doing it but I just had a 2 hour listening session with the SDA-SRS's. How does it get any better? I would be pretty bold to think I can get the same sound let alone better. Obviously I would be stealing polks idea for the signal cancelation and would only do so for myself. Must be cool to work for them! Must have been even cooler back in the days of SDA! How can they not continue the best sound advancement of all time??? I guess for now I will be happy with just doing something different. I hope it doesn't turn out to be a $700-$1000 contraption. I must say this is the biggest risk audio project I have ever attempted. I guess I could make a boatload of little two ways and sell them on ebay if I crash and burn with the SDA idea. Hoosier21's signature comes to mind at this point...
"I swear, I thought turkeys could fly" or something like that.
05-16-2002, 12:46 AM
Madmax, I have also thought of such a project. One idea was with two pairs of RTA15TL's One pair would be the stereo pair with the other for sda. The stereo pair would then be able to be angled in. You would then be able to adjust the sda array any way you want. If Matt would just put his foot down and release another bookshelf model with SDA drivers I would be fired up. All they need to do is take the LSI center channel and turn it into an LSI-CRS. They have the box, the drivers and the new tweeter. Throw in a new crossover and SDA cable and you have a winner. Then throw in two 650 subs! SOUNDS LIKE A WINNER TO ME! I am happy with my 1.2tls but they have to be played loud to get alot of feel it in your chest bass. I have often thought about taking a 1c and wiring the two low bass drivers so you could plump up the bass a little without hurting the midrange. If you could adjust the output of those two low bass drivers by themselves I think it would be like having a built in bass managment system. Good luck, Tom
05-16-2002, 01:40 PM
A gentleman on the PE site sent me this white paper on line arrays. It is very informative!
I received the 5.25 inch drivers. They are awesome little drivers for $6 each. From a visual standpoint they look like they should be $40-$55 drivers. Nice rubber surrounds and center caps and a cast frame. The box they came in said "Definitive" and had a part #1144a100.
05-19-2002, 09:50 AM
My Acrobat took a poop on me, so I can't download the .pdfs. I did notice the word Linus. At the Midwest Audiofest I got to hear the Line Arrays. 12 mid/woofs and 6 ribbon tweets per speaker. Real sweet sounding. I couldn't dedicate enough time for a true listen though. Too much time with the Edgarhorns. If these are the ones you're building, the specs (with their drivers) are:
94 dB SPL @ 1 watt
>120 dB dynamic range
6 ohms impedence
>400 watts max power.
You should be able to contact Rick Craig firstname.lastname@example.org for free construction plans.http://home.earthlink.net/~selahaudio/_wsn/page4.html I may have just done a link, wish me luck.
Russman: I may have sent you a sheet on these.
05-19-2002, 10:05 AM
The cabinent is planned around pre-cut pieces. As I said in the first post I plan on two towers per speaker, an SDA tower and a main tower both mounted to a single base. The size of each tower is 6"W x 72"H x 14"D which is enough area for a sealed cab for the given speakers. I'm starting out that way anyhow. For all I know the SDA's and mains may rely on the coupling of the two in the same box. That point is an unknown to me and may cause me to build another cab to make them work.
The Linus is what I was looking at but it is a different set of drivers. I don't know if they are comparible other than each has 12 vertical drivers. I'm not following the Linus design although it looks like it would sound awesome.
05-21-2002, 09:56 AM
I got my box of tweeters last night. By appearence they are not quite SL-2000 quality but a quick powerup yielded a nice smooth sound. They have a soft textile dome which has a pleasing sound to me. The box of tweeters weighed 55 pounds. I think the UPS guy is probably getting tired of me. Oh yea, I found a 4.75" hole saw which should make it much easier to cut out the 48 necessary holes!
05-27-2002, 08:15 PM
Just a quick update:
I took one of the tweeters and one woofer and built the recommended sized sealed enclosure. I crossed the tweeter over with a 22uf cap and ran the woofer full range. The enclosure is 6.5"W x 15"H x 5.5"D. I am driving it with my 2x40 watt Sony office stereo.
The sound is very big and reaches really reasonable sound levels fairly easily. It is a very clean detailed sound but very "big" sounding. With my eyes closed I can imagine a tall floor standing speaker. It is hard to evaluate a single speaker but I am VERY impressed with the sound quality. The box is ugly but I may go ahead and build another and use them as office speakers. I think there is something to this speaker building stuff unless I just got lucky this time. For $21 total including cabinent and drivers I have a single speaker that sounds like maybe an LS-70. Certainly better than any of the Infinitys at CC. With a Vifa tweeter and second midbass driver I would be up another class. I think 48 of these midbasses and 16 tweeters is going to knock my socks off!!!
05-29-2002, 05:37 PM
How much power do you think you will need to get all of those drivers working?
05-29-2002, 05:45 PM
I bet you could run them fine with 50 clean watts per channel. I'm sure they will handle more, much more, but in an array design, doesn't efficiency usuall increase?
I'm not sure how the sda/array design will react, but I would think the same....
Can't wait to see pics mm....
05-29-2002, 08:27 PM
I think Russman is right. The efficiency should increase 6db with every doubling of drivers. This means I may get a huge quantity of sound with minimal wattage. The overall distortion is said to be reduced this way as well. The reason I started looking into line arrays is that polk uses them on the larger SDA's. Only four drivers in each array but still an array. The spacing they use between drivers is abnormal for an array (too far apart) and I am not sure why that is. If this works I will be very happy. If it doesn't then I will have two towers of junk. In either case I won't mind moving the sda's around as much any more. Each tower will probably weigh about 250 pounds. I don't think anyone would ever walk off with them!
05-30-2002, 09:22 AM
The distance between the primary array and the sda array is critical. It needs to be the same (approximately) as the distance between your two ears. This creates the delay needed for imaging with the "negative" signal from the other channel.
Regarding polk array being non-standard... I think the drivers are placed reasonably close together. I think you are mistaken. Please elaborate.
05-30-2002, 10:28 AM
I forget the distances but the tweeters especially are very far apart vertically. Something like 6 inches or so. I've read they should be as close together as possible so a reasonable crossover can be selected. A formula of the speed of sound divided by the distance center to center gives you the minimum crossover frequency without having comb filtering. To get it much below 2khz they would have to be much closer. I'm not saying the polks are wrong, just that they don't fit the standards I have read about. They are probably crossed over at different frequencies. I'm sure there is a reason, I just don't know what it is. On my midbass arrays I will place the drivers as close together as I can vertically and for the SDA array I'll start with them the same distance as the SDA's as you suggest (one head-width apart). The tweeters can be easily moved around vertically so I will determine where they are located by test.
06-20-2002, 07:21 PM
What about the passive Radiator? What should the weight be? there are no specs available for the old polk drivers. I am trying to recreate the sda crs+ model. I already have the original crossover design from 1986 and the drivers are ordered but I cannot determine the parameters of the passive radiator since it is no longer available from polk
06-23-2002, 09:54 PM
Good luck! I am making my line array's in a sealed design. Just try to figure the needed weight for a passive! To start with you only include the driven driver? Or maybe both the driven and SDA? Does the SDA driver have anything to do with the passive? Keep in mind the SDA driver may act like a passive given the way it is driven? Maybe not? Whew, test, test, test. The whole design is a cluster fu$k of questions! That is why polk was on the edge in my opinion!!! Good luck.
PS: sorry I have no real answers for you.
02-16-2004, 12:49 PM
max, whatever happened with this?
02-16-2004, 04:25 PM
damn, brought this one back from the dead
02-16-2004, 04:56 PM
Originally posted by Airplay355
damn, brought this one back from the dead
02-16-2004, 09:23 PM
Dang! Can't believe I missed this the first time around!
I've got a boatload of those 5.25" Def Tech woofers..
02-17-2004, 11:42 AM
It's still on the menu...
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