Advanced tweaking of Polk SDA's...

daifanshi

GV#27 wrote: »

If you want an active speaker then why not buy some good drivers from Madisound or PE and design your own.With carefully selected drivers and crossover slopes and frequencies etc. you will have a very good chance of achieving excellent results.I believe that active speakers have some real performance advantages and I'm current using a fully active setup myself.However as others have mentioned,SDA's because of their unique design are IMO likely very poor candidates for converting to fully active.

I've already done the above. It's just that I recently aquired a pair of Polks and I think they can be made better because they are good starting point. I believe all passive speakers can benefit from active equalization or conversion to active crossovers.

If my experiments fail to make any improvement. I still gain by learning something. There's nothing wrong in doing something for the sake of knowledge.

Systems

daifanshi wrote: »

50 bucks a tweeter is a lot. If you use moderately price op-amps you can probably do the simple notch filter + PS for less than $30 for both speakers. (

Or for even less $ you can build a passive notch filter .Just a small air core coil (approx 1mh) and a small cap (approx.47-1uf).

Systems

daifanshi wrote: »

I still gain by learning something. There's nothing wrong in doing something for the sake of knowledge.

No there certainly isn't.:D

daifanshi

GV#27 wrote: »

Or for even less $ you can build a passive notch filter .Just a small air core coil (approx 1mh) and a small cap (approx.47-1uf).

There are couple of disadvantages to passive notch filters. The biggest one is sensitivity to source and load impedance. It's also harder to tune them because of the big choke. As you know, "active inductors" only have caps, resistors and op-amps. And you can isolate the loads with input and output buffers.

Face

daifanshi wrote: »

I've already done the above. It's just that I recently aquired a pair of Polks and I think they can be made better because they are good starting point. I believe all passive speakers can benefit from active equalization or conversion to active crossovers.

If my experiments fail to make any improvement. I still gain by learning something. There's nothing wrong in doing something for the sake of knowledge.

How do you plan on experimenting with SL2000's when you claim to own a pair of 2.3TL's?

Systems

daifanshi wrote: »

There are couple of disadvantages to passive notch filters. The biggest one is sensitivity to source and load impedance. It's also harder to tune them because of the big choke. As you know, "active inductors" only have caps, resistors and op-amps. And you can isolate the loads with input and output buffers.

Regardless of which type (passive or active) notch filter is used, accurate frequency response measurements are going to be necessary to optimize the notch and to verify that has the correct Q and freq.Both types can be very effective if designed correctly.

daifanshi

Face wrote: »

How do you plan on experimenting with SL2000's when you claim to own a pair of 2.3TL's?

If I can't get an SL2000 cheap. I was going to present a schematic to the group and hope somebody can build and try it. Or if that doesn't happen I can send a ready built board that some willing participant can try out.

But what I really need is the frequency response plots of the tweeter alone to get started.

ben62670

daifanshi wrote: »

Harshness and other qualities are often difficult to quantify. If the SL2000 are as poor as people say they are, I wonder why Polk even used them in the first place...

I have had one pair of SL2000's that actually sounded good. The problem is that SL2000's age more like Milk than whiskey. They were decent when new, but they age very poorly. To try and fix the XO to improve the tweeters short comings is a waste of time. I still don't understand why you would be so interested in fixing something you don't have

DarqueKnight

daifanshi,

I know you are currently fascinated about the technical challenge of "fixing" the SL2000. Can you digress a moment and tell us about your audio rig (amps, source components, etc.) where the 2.3TL's are set up?

What are your sound stage dimensions and how do you feel about the quality of images within the sound stage? What kind of room do you have your 2.3TL's in?

Jesse (F1nut) has a pair of (modified) 2.3TL's hooked up to some exceptional electronics. I sense that he is tickled to no end knowing that he has another kindred spirit to chat with...about 2.3TL's.

Systems

daifanshi wrote: »

Or a Helmholtz oscillator maybe?

hummm perhaps you meant helmholtz resonator?Can't see how that would apply to a tweeter, as it is the principal of operation of a bass reflex port .

DarqueKnight

You guys are talking way over my head with all this technical/electronics terminology. I'm gonna go listen to some tunes 'til my head stops spinning.

daifanshi

GV#27 wrote: »

hummm perhaps you meant helmholtz resonator?Can't see how that would apply to a tweeter, as it is the principal of operation of a bass reflex port .

Yeah. I've heard it called both. But you're right technically resonator is more accurate. For a 13khz spike like that the resonating structure would be pretty tiny. Like a gap between the tweeter diaphram and surround or something involving the faceplate. I think I read somewhere that the diffuser on old Wharfedale tweeters from the early 70's actually had this type of problem from air being compressed between the diaphragm and diffuser during operation.

I'm just guessing but for that spike to be 6dB above the nominal response it must be a pretty hi Q resonance. Like a breakup mode of the dome material. Maybe somebody here more familiar with tweeter design can chime in.

daifanshi

DarqueKnight wrote: »

You guys are talking way over my head with all this technical/electronics terminology. I'm gonna go listen to some tunes 'til my head stops spinning.

Really it's not complicated. I'm sure you've created a Helmholtz resonator in your lifetime. Next time you're downing a bottle of your favorite lager, blow across the top of the bottle. Instant Helmholtz resonator!!!

It's just a fancy name...

ben62670

ben62670 wrote: »

I have had one pair of SL2000's that actually sounded good. The problem is that SL2000's age more like Milk than whiskey. They were decent when new, but they age very poorly. To try and fix the XO to improve the tweeters short comings is a waste of time. I still don't understand why you would be so interested in fixing something you don't have

Third time a charm?

heiney9

daifanshi wrote: »

I believe all passive speakers can benefit from active equalization or conversion to active crossover.

That's exactly why I don't have any confidence in your ability or opinions. You are saying ALL passive speakers, when obviously you haven't listened to every passive speaker ever made. Blanket statements in audio are dangerous and are many times an indication that one has less actual knowledge than one tends to exhibit.

The statement above pretty much dismisses you as someone who really knows anything about speaker design and theory. You are condemning many speakers before having even spent ample time listening and evaluating.

You didn't answer the question I asked earlier. Have you read and fully understood the "white" paper written by Matthew Polk explaining and proving how SDA's work? If not, start there and quite trying to convince us you somehow know better.

H9

H9

danger boy

why hasn't Candyliquor35M chimed in on this topic? it's right his kazoo.

heiney9

So what you are saying is Polk could have made a few cheap tweaks to fix the sl2000, but instead they embarked on an expensive time consuming R & D to develop a new tweeter to fix the inherent shortcomings of the original tweeter.

Where were you to advise them differently? And then after the process for making the dome material was discontinued they spent even more time and money to develop and R & D (2) new silk replacement tweeters.

Hmmmmmm perhaps you should start your own speaker company since you seem to think you can fix a shortcoming with a few cheap caps and op amps.

ben62670

He reminds me of a newb who joined back in November 06.... Hmmm wait that was me:o Stick around, and get your learn on;)

heiney9

ben62670 wrote: »

He reminds me of a newb who joined back in November 06.... Hmmm wait that was me:o Stick around, and get your learn on;)

Ben, your approach and attitude was a bit different. Look I hate to rag on the guy but if anyone looked in the archives this is a very tired subject. It's been talked about a lot and it always ends the same. That is a notch filter isn't even close to a solution for the sl2000 and active x-overs don't behave in a way that is desirable in SDA's to keep their true nature intact.

H9

bikezappa

daifanshi wrote: »

F1nut,

But for those who might be interested, I was hoping there would be some reasonable discussion about it.

Some people think they know every thing about these speakers, maybe they do, and any DISCUSSION is difficult. Try your idea and tell us the results.

Rock on.

Systems

daifanshi wrote: »

I think I read somewhere that the diffuser on old Wharfedale tweeters from the early 70's actually had this type of problem from air being compressed between the diaphragm and diffuser during operation.

Actually that is the purpose for the phase shield or (diffusor) mounted in front and center of most metal dome tweeters. Apparently metal domes benifit from having the added air pressure placed at the center of their dome to reduce their tendancy to act like a beer can being crumpled.

Systems

heiney9 wrote: »

That is a notch filter isn't even close to a solution for the sl2000 and active x-overs don't behave in a way that is desirable in SDA's to keep their true nature intact.

H9

A properly designed notch filter could actually reduce the nasty peak in the SL2000's response but it would be a band aid solution at best and wouldn't solve any other glaring issues it may have.

heiney9

GV#27 wrote: »

but it would be a band aid solution at best and wouldn't solve any other glaring issues it may have.

That's what I meant when I stated "isn't even close to a solution for the sl2000"

H9

Systems

heiney9 wrote: »

That's what I meant when I stated "isn't even close to a solution for the sl2000"

H9

cool,I took it as it would offer "no" improvement at all.

daifanshi

GV#27 wrote: »

cool,I took it as it would offer "no" improvement at all.

Your not the only one. :rolleyes:

Anyways, I've completed some simulations of the crossover in the 2.3TL and noticed that the crossover frequency is very low ~1.5kHz for a 2nd order crossover. If somebody can confirm the "correctness" of the schematics posted here I'd appreciate it.

The free air resonant frequency of the SL3000 is not very low. I did a quick test and found that it is around 1kHz. I'm going to do a more detailed test once I take my test amp out of storage. My jury rigged test setup may be flawed. There are some possible implications here that I will keep to myself. Some of you might understand what I mean here. But won't know for sure until later. There are some additional elements in the tweeter array that need to be looked at.

If anybody here has tested the SL3000 electrically, please share what you know. I prefer not to re-do work that somebody's already done.

Thanks.

heiney9

Are you purposely ignoring my question? I'm just curious to know if have read and understood the SDA "white paper"? I'm betting you didn't and don't care too. Which is fine except if you are trying any kind of meaningful experiment it would be best to understand the fundamentals. By the questions and discussions you've had so far it sounds like your shooting in the dark.

H9

heiney9

daifanshi wrote: »

:rolleyes:

Back at you :rolleyes:

daifanshi wrote: »

If anybody here has tested the SL3000 electrically, please share what you know. I prefer not to re-do work that somebody's already done.

Thanks.

Polk has and it's been printed in the SDA compendium and I bet if you called Polk CS and talked to Ken he'd make it available to you. But, in your own words, you say most CS people are hacks.

H9

DarqueKnight

daifanshi wrote: »

Anyways, I've completed some simulations of the crossover in the 2.3TL and noticed that the crossover frequency is very low ~1.5kHz for a 2nd order crossover. If somebody can confirm the "correctness" of the schematics posted here I'd appreciate it.

What software did you use for the simulation?

Why would a forum member need to confirm the "correctness" of the SDA schematics posted here? They all have one or more approval signatures from Polk's engineering department.

Here are a couple of questions I posted earlier that I think you missed:

DarqueKnight wrote: »

daifanshi,
Can you digress a moment and tell us about your audio rig (amps, source components, etc.) where the 2.3TL's are set up?

DarqueKnight wrote: »

What are your sound stage dimensions and how do you feel about the quality of images within the sound stage? What kind of room do you have your 2.3TL's in?

There are lots of SDA enthusiasts here and we love to share information about sonic performance. Some, like yourself, have fairly deep backgrounds in audio electronics.:)

schwarcw

I think Polk engineers realized there were some sonic benefits to using an active crossover. Their SRT system proves they believed there was some merit to the idea. I heard an SRT system for the first time several weeks ago. I was impressed with what I heard. Were they better than the passive SDA's?? I can't answer that for you, but I thought their was a more holographic and deeper sound stage. The electronic that were being used amp, CD, preamp, etc. were fine quality but not over the top.

I've also had curiosities about an active crossover with SDA's. Give it a try, that's what a hobby is for, to have fun. Good luck and welcome to Club Polk!

heiney9

That is true Carl, but also remember the SRT system was intended to be the ultimate home theater system and sometimes the goals/results and compromises are different for 2 channel home audio vs. multi-channel HT. I'm sure Polk did a great job constructing a suitable active x-over. But I'd be willing to bet they had a lot more knowledge at their disposal than the OP in this thread.

I'm not in any way discouraging anyone from experimenting but there are certain basics and fundamentals, IMO, that need to be used as ground work to build on. One of them is having a complete understanding of how the SDA principle was implemented in the fist place. Not sure the OP has any true idea what the process is and how it was painstakingly achieved. There are resources and it appears he's not using them or already feels he knows enough. This information isn't gotten by simply looking at a schematic.

His lack of credibility and his attitude (intended or not) about seemingly knowing more than some of the people here really turns me off. Hence my combative approach.

H9