SDa/M SRS... Can we do it?

[nooshinjohn]

Let me begin by tipping my hat to everyone here that has given their time, talent and skill over the years to maintain and improve the SDA speakers. This forum has the most amazingly skilled and dedicated bunch of audio- artisans of any forum on the web and I am proud and honored to be a part of it.

The purpose of this thread is to explore opportunities to make these speakers even better than they already are by building a state-of-the-art cabinet to replace the "coffins" of thirty years ago. My vision is to combine the Srs front baffle exactly as it is with the sophisticated assembly techniques and handsome good looks of the current LSiM 707's. I understand that others have tried to build SDA's from scratch to varied degrees of success/failure, and hopefully this project will turn out differently. I intend to stay faithful to the originals I terms of all critical specs,( cabinet volume, crossovers, drivers etc)

This threads to discuss what would be the best way to go about building these new speakers, and to discuss what features or improvements can made in the speaker that cannot be accomplished by the known mods that are currently documented.

Thanks for the input guys!

[michael1947]

I'm in, I'll help any way that I can. I'm an advanced woodworker with a complete shop and 3 sets of SDA's. I am ZIPPO, NOT NADA with those little electronic do-dads and my soldering is quite good with copper pipe. Willing to learn.

[PolkMaster1]

I'd love to hear a new generation of SDA-SRS' with a high end SanSpeak Tweeter, a new set of todays high-end midrange woofers and passive radiators.

I'd be willing to assemble one myself if someone would be willing to offer a DIY kit. Just ship me the cabinet built with the schematic diagram, and tell me what drivers and tweeters I can use according to each schematic built (if it is possible for someone to test numerous drivers and tweeters for possible combinations). All parts sourced can be assembled into the cabinet, and with our soldering skills, we would have options on what caps, resistors, and inductors we would like to use on the crossover boards.

It would be our dream Polk SDA Speaker that would exceed the vision that Mathew Polk started.

[Schurkey]

There's a heap of info about speaker building in general in books, magazines, and on the internet. So much so that I can't wade through it all.

I considered building SRS 2 pin/blades; made an offer on the drivers, harness, and crossovers with the idea that I'd make cabinets. The deal fell through fairly quickly. My thought was to use MDF glued 'n' screwed to fireproof (concrete) wall board for the various panels. Like Polk, I'd fill the interior seams with hot-melt glue or epoxy. Fabric on the outside, cheaper than veneer but not as nice to look at. I suspect but don't know that this would end up pretty "dead" from a resonance standpoint. No doubt also hard to work with, and extraordinarily heavy. I'd have explored how to keep the interior volume the same as OEM while building the cabinets in more of a triangular shape--no parallel panels except top and bottom.

But what do I know--I've never built a speaker cabinet before.

[nooshinjohn]

Not looking to re-invent the wheel, so to speak, rather to re-invent how the wheel looks, and hopefully improve the sound. I am hoping we can do something here that uses the original style drivers and captures the spirit of the original while taking performance to a much higher level. Anybody here a wiz at CAD?

[naturallight]

You want to build a cab from scratch, so you can have some curvy corners and stuff like the 707's?

Sounds like ALOT of work. You would have to keep all the dimensions the same, inside baffles, bracing, whatever is in there. If you change things, not sure it's going to sound the same.

Maybe think about modding the existing cab with moldings or something?

[Mr. Bubbles]

Lots of thoughts here already. I have entertained this idea since I first got the Polk bug. My back ground and strong point is primarily cabinet design and building. Where others are stronger on the electronics. The primary improvement to sound could be garnered by a deader cabinet with fewer internal reflections and a smoother narrower (where possible) baffles with more rounded edges. The latter addressing diffraction where it was not addressed in the original designs.

keep in mind any change in shape of the cabinet will change they way the rear wave reacts with the PR and therefor will effect the sound (possibly negative). Look at the internal differences between the SRS and the 1.2TL. Any major changes would alter the sound to a degree that the original designers probably would not have been satisfied. They did a lot of testing and development on these speakers. However there are elements to speaker design that were little known at the time, but are commonplace now.

My thoughts would be a cabinet with the same basic internal dimensions as the original with slight tapering forward to narrow the baffle area compared to the rear panel. This would keep the primary considerations the original designers were concerned with and the major rear wave movement within the cabinet the same except it WOULD create less of a chance for standing waves to create problems. I would then double all wall thickness. This would allow even further damping of the cabinet by allowing the builder to try any number of methods like grooving the panels, using damping materials as a layer between the panel layers or different materials sandwiched together. This not only strengthens and deadens the cabinets but makes them heavier. (think Focal, Sonus Faber, Wilson). The heavier cabinet will them couple to its foundation better and resist cabinet movement in opposition to driver movement better, creating tighter/ quicker sound with less distortion. One last this the thicker cabinet would do is allow the ability to generously round the corners and edges to reduce diffraction induced distortion. Mount crossovers externally, and use some material on the front to further reduce diffraction issues.

Of course all these things should be tested with proper equipment and extensive listening while comparing the changes to the constant (the original design). My ideas could be tried in stages beginning with a single layer cabinet with the slightly different shape and these other things could be added one step at a time to determine any benefits or negative effects.

[Mr. Bubbles]

forgot to add that you definitely don't want to angle or lean the baffle in any way as many modern designs have done. the rear panel could be slightly angled or leaned to aid in standing wave control.

[Mr. Bubbles]

On non SRS models where the tweets are non integrated in the panel between the MB drivers the panel could possibly be stepped to aid in time alignment , but this also would effect the crossover design somewhat (assuming the original designers adjusted for time alignment originally).

[seabeerob213]

Not looking to re-invent the wheel, so to speak, rather to re-invent how the wheel looks, and hopefully improve the sound. I am hoping we can do something here that uses the original style drivers and captures the spirit of the original while taking performance to a much higher level. Anybody here a wiz at CAD?

not a whiz, but familiar with rhino, i dont have the software though. i can talk to my old shop teacher and see if i can hop on a couple hours a day while im home next month though. i could get you a general design for the outer, such as shape and size, and placements, inners and bracing and such i dont think i could get into

[Toolfan66]

[nooshinjohn]

What are you up to Larry?

Inquiring minds must know.

[Drenis]

Have you considered just stripping the existing cabinet of all the side panels including the top and bottom caps then build a new shell over the existing cabinet?

[SDA1C]

If this works they will be huger than the originals. Not sure there is a big plus from that direction. Just building cabinets from MDF rather than particle board would likely yield improved performance. Trying to bend the sides like the 7's while maintaining the original equipment parts list is going to be a nightmare.

JM .02

I'm in! What can I do to help? A CNC router is going to be this projects best friend. Who's the CNC programmer of the crowd?

[Mr. Bubbles]

Have you considered just stripping the existing cabinet of all the side panels including the top and bottom caps then build a new shell over the existing cabinet?

I can't speak for the OP but I would not recommend this. several reasons why;

you would loose your constant for comparison.
this would not allow you to address some of the original cabinets deficiencies.
MOST Importantly; this would not allow you to go back to the original if you either totally screwed up or just wanted to for some reason.

[Drenis]

I can't speak for the OP but I would not recommend this. several reasons why;

you would loose your constant for comparison.
this would not allow you to address some of the original cabinets deficiencies.
MOST Importantly; this would not allow you to go back to the original if you either totally screwed up or just wanted to for some reason.

Well sorry to rain on the parade but what would YOU suggest? He modify the original cabinets? This is about leaving the speakers alone and changing the appearance of them. How do you go backwards on the OEM cabinet when you're only removing the additional panels (Top/Bottom caps, side clothed panels) These components are NOT part of the original cabinet structure.

If anything, John should refrain from making ANY mods to the cabinets as it will affect everything down the chain. It's never how it was designed. I actually think my suggestion will allow him to get the eye candy he wants while retaining the sound signature of the speakers since the OEM cabinets will not be modified in any way.

He obviously doesn't want to take a step back as he is already committed to doing this. What original deficiencies do you talk about? If minor, could they not be addressed BEFORE building the new shell over the cabinet? Finally, I fail to see how he would lose constant compression. Please elaborate on this for me.

Thanks.

Plain and simple, if you want to retain the original speakers performance and sound signature but change the look, I don't see any other option. But feel free to correct me. I'm certainly no scholar.

[nooshinjohn]

[QUOTE=Drenis;1875835]Well sorry to rain on the parade but what would YOU suggest? He modify the original cabinets? This is about leaving the speakers alone and changing the appearance of them. How do you go backwards on the OEM cabinet when you're only removing the additional panels (Top/Bottom caps, side clothed panels) These components are NOT part of the original cabinet structure.

If anything, John should refrain from making ANY mods to the cabinets as it will affect everything down the chain. It's never how it was designed. I actually think my suggestion will allow him to get the eye candy he wants while retaining the sound signature of the speakers since the OEM cabinets will not be modified in any way.

He obviously doesn't want to take a step back as he is already committed to doing this. What original deficiencies do you talk about? If minor, could they not be addressed BEFORE building the new shell over the cabinet? Finally, I fail to see how he would lose constant compression. Please elaborate on this for me.

Thanks.[\QUOTE]


Not looking to mod or change the stock cabinets in any way. Beyond restoring them to their original state. What I am looking to do is build an entirely new cabinet using the "known" data we have from the original SRS cabinet and transfeing that knowledge to an all new design. Unaltered would be the demention and layout of the front baffle, driver complement, and internal volume of the original boxes. Everything else is up in the air. I am assuming the hot rodded crossovers we are currently using would be pretty close to what the new cabinets need. As soon as I've got Internet at home, I will post up a few sketches of what I have in mind, but if you think about a giant version of the LSi/M and 1.2's combined with B&W 802 nautilus build quality, you will start to get what I am thinking of.

[Goth child]

Hi guys,I have a couple of questions Ive been pondering on for a while,related to this topic.The passive radiator is "driven" by the pressure created by the active drivers in the sealed cabinet(?)
In my mind having 8x 6.5" drivers in such a big rectangular sealed cabinet is bound to create all sorts of issues with standing waves etc.
What would happen if we sealed off the passive radiator and substituted it for an active one?
Could we then seal off the SDA driver compliment,effectively turning each cabinet into 3 seperate cabinets?
Wouldnt/couldnt that make each bank of drivers perform more accurately as they wont be affected by the waves in the cabinet caused by the other drivers?
How would that affect the capacitor values used on our crossovers?
Do the 6.5" drivers need the total internal volume to work correctly,or is that just required to get the passive radiator working?
Not that any of this really matters to me,as the only thing thats going to make my wife let me spend any more money on audio gera is if you can come up with a way to make them smaller!

[TennMan]

Goth child, To do what you suggest you would be better off starting with a speaker that has a three-way crossover and an active bass woofer. No use in trying to reinvent the wheel.

Buy a pair of CRS+ SDAs is the way you make them smaller. :)

[Goth child]

Just throwing some ideas out there!Its kind of already been done by Polk when the released the srt system,the SDA speakers sitting on top of the subs.
A lot of modern speaker designs go to great lengths to isolate the different drivers ,so they dont interact /influence each other.
For the record I actually like the way the 1.2s look!
Kind of sexy in a way....

[Mr. Bubbles]

Drennis,

You apparently did not read my posts thoroughly as I did not recommend that he modify the original cabinets in any way ( I actually suggested the opposite as a response to your post). I also stated that keeping the original cabinets is the only way to verify any improvement in sound, as that also was part of the idea presented. And I have already described where I would personally start such a project earlier in this thread, and in so doing described some of the perceivable deficiencies with the original design.

[Drenis]

Drennis,

You apparently did not read my posts thoroughly as I did not recommend that he modify the original cabinets in any way ( I actually suggested the opposite as a response to your post). I also stated that keeping the original cabinets is the only way to verify any improvement in sound, as that also was part of the idea presented. And I have already described where I would personally start such a project earlier in this thread, and in so doing described some of the perceivable deficiencies with the original design.

I don't think so. I clearly stated about building around the existing cabinet and you shot it down. SO what's it gonna be? Come on. Answer my questions.

[Mr. Bubbles]

I don't think so. I clearly stated about building around the existing cabinet and you shot it down. SO what's it gonna be? Come on. Answer my questions.

I could really give a crap less if you think so or not. Again, please re read my posts; you suggested building around the original cabinet and my response was plainly that i would not recommend doing that. BUT JUST IN CASE YOU HAVE COMPREHENSION ISSUES LET ME STATE AS PLAINLY AS I POSSIBLY CAN, I DO NOT RECOMMEND THAT ANYONE MODIFY THEIR ORIGINAL CABINETS. Cabinets can not easily be changed back like crossovers, wiring etc. Also without the original cabinet for comparison (in listening as well as taking measurements), there is little to go on to guarantee improvement. If you have further questions please state them plainly and I will gladly give my opinion on how I would address such an issue personally. None of my comments are meant to describe to any other member of this forum that they should do things as I do. Their speakers are theirs and mine are mine. I will do as I wish with mine without giving results to anyone on this forum but will answer questions to any that ask or present ideas.

[TennMan]

... Their speakers are theirs and mine are mine. I will do as I wish with mine without giving results to anyone on this forum but will answer questions to any that ask or present ideas.

Thanks Mr. Bubbles. It brought a smile to my face when I read that. I should have followed your advice about not giving out results. I put my CRS+ crossovers and MWs in my monitor 10B cabinets and caught a lot of flack from some folks here who said it would never work and I screwed up a good pair of speakers. That has been well over a year ago and I still listen to my hybrid speakers every night and fully enjoy them. I have no regrets other than telling about what I had done here on this forum.

[Face]

Why bother? If you don't like the appearance, throw some automotive paint or veneer on them.

IMO, this has nothing to do with the (LSi)M series as they use much more advanced drivers and cabinet design than Polk has used before.

[Face]

If a modern SDA were to be built, I would start with drivers like these:

Tweeter:

http://www.madisoundspeakerstore.com...ring-radiator/

Or

http://www.madisoundspeakerstore.com...-deep-chamber/

Mids

http://www.parts-express.com/pe/show...umber=264-1082

http://www.parts-express.com/pe/show...umber=264-1132

And a separate woofer/PR to take the load off of the mids.

http://www.madisoundspeakerstore.com...1001-04-4-ohm/

http://www.madisoundspeakerstore.com...ate-to-l26roy/

Or go even bigger...

http://www.madisoundspeakerstore.com...s75-12-woofer/

http://www.madisoundspeakerstore.com...sive-radiator/

A narrower cabinet would be possible too. The minimum cabinet width would be dictated by the width of the woofer or side by side mids, whichever is wider.

[PolkieMan]

There is somewhere I read that the stereo and dimensional driver center line distance has to be a certain amount in order for the SDA effect to operate properly that was the reason for the wide fronts on the speakers. This was also controlled also by the diameter of the midwoofer and the reason 6.5 was used as it offered a speaker which could reach low enough for the PR to operate properly and go high enough that a 1" tweeter could be used, all the time keeping the front baffle not too wide.

[F1nut]

What would happen if we sealed off the passive radiator and substituted it for an active one?

Higher distortion levels and less bass.

[westmassguy]

There is somewhere I read that the stereo and dimensional driver center line distance has to be a certain amount in order for the SDA effect to operate properly that was the reason for the wide fronts on the speakers. This was also controlled also by the diameter of the midwoofer and the reason 6.5 was used as it offered a speaker which could reach low enough for the PR to operate properly and go high enough that a 1" tweeter could be used, all the time keeping the front baffle not too wide.

There must have been a lot of wiggle room there. If you compare the early SDAs, and my 2As, the drivers are almost touching, where-as the big SRSs have quite a bit of room between them.

[tophatjohnny]

One of the craziest threads I've read, but at the same time, very interesting.