Crossover Design Choice

jimiles

In the process of rebuilding the crossovers in my RTA-15TLs, one question lingered in my mind:

In the tweeter network of the 15TLs (and many other Polk speakers) there is a resistor (2.5 ohm) and capacitor (12uF) in parallel ahead of the other elements filter elements.

1) What is the purpose of those components? My guess is that it shapes the response of circuit to attenuate the lower range of the tweeter's output.

2) Is there a comperable parallel network that would shape the response similarly, thus reducing the number of components in series with the tweeter?

Those of you with more crossover design knowledge, please jump in and set me straight

Thanks!
Jake

Polksaladanni

1) What is the purpose of those components? My guess is that it shapes the response of circuit to attenuate the lower range of the tweeter's output.

2) Could be a Zobel network depending on the mh value and other cap in the curcuit

3) Could be a "trim" curcuit to fine tune the response curve.

4) Might be a series curcuit which Polk used for many years in the Monitor Series. It's actually genius. Because as you said it reduces the number of XO components yet still acheives a very flat Frequency Response.

Here is my Monitor 4 Series2 XO and it is a total series curcuit, plus both drivers sharing the same coil. I guess it would be a puesdo 1st and 2nd order XO in parallel form by the number of parts. The driver parameter differences are easier to compensate and design in a parallel XO.

http://www.polkaudio.com/forums/attachment.php?attachmentid=18764&d=1155784608

Here's a good read on the differences

http://www.polkaudio.com/forums/attachment.php?attachmentid=18764&d=1155784608

I don't know though because I haven't looked at you schematic only the ones for my sets. Hope I helped some instead of hurting.

Paul

jimiles

Thanks Paul! I agree that it looks like a trim circuit. I really need to get some software installed and model the network.

I rebuilt the crossovers once with Solen/Mills and liked it. Then I swung for the fence and rebuilt again using Jantzen Z-Superior caps, Obbligato caps, Duelund resistors, Neotech wire, and Cardas posts. That rig does not disappoint! :cool:

But...before jumping into the land of > $200 caps, I want to make sure I'm building the ideal network for these drivers. Like any commercial product, the RTA15 was designed to a budget, albeit a generous one. Are there features like a zobel, or an entire different filter topology in general, that didn't make the final design cut because of space/budget constraints? I've already gone pretty far down the "parts quality" road, so now I wonder if there are improvements to be had following the "parts count" path.

So...if any of you made radical changes to the topology of your crossovers, I'd love to hear about it!

Party On
Jake

Polksaladanni

Nope. Just cap replacements. The other parts usually never go bad and I feel there is minimal benifit with coils and resistors. Mainly use Dayton MP or FF's (Bennics) and love Jantzens when i can get the correct values. I had bad luck with the Solens once. Maybe it was just a bad cap... I really don't have the time at the moment to redesign an XO and, like you, don't have or can spare the nickel to get software for testing the drivers. Some day I will build some from scratch when the garage is not a train wreck. My wife and friends say I have too much "stuff"

Auditioning some RT55's found locally, EBayed some new RTi6's. Investment for both pairs $330.00 8^)and now, Geez, I think I want to look into some RTi8s because I like the 55's dual 6.5's sound and everyone raves about the 8's cherry boxes.

I am knee-deep in remoldeling the house we bought a few years back. (We are really moving in now) I'm racking the equipment in one of the adjacent master closets. TV's and speakers on the patio, kitchen cab, office and M Bed&Bath. All tied together with IR repeater systems and on-screen display for the cd changers, XM satilite blah, blah. All the while, I'm apessing the wife with paint and molding, full tile bath and soon door replacement through out the house. Just finished a rebuild of the laundry room. Pipes were leaking. Every damn shut-off valve leaks if you give them an angry look.

It sucks to be me right now.

My thoughts with speakers are Mr. Polk has got much more time, money and John Hopkins U to design speakers I just mod them to my taste. Like Cross bracing or more/less dampners and definately ditch the electrolytics on the XO.

Paul

heiney9

Polksaladanni wrote: »

Nope. Just cap replacements. The other parts usually never go bad and I feel there is minimal benifit with coils and resistors. Mainly use Dayton MP or FF's (Bennics) and love Jantzens when i can get the correct values. I had bad luck with the Solens once. Maybe it was just a bad cap... I really don't have the time at the moment to redesign an XO and, like you, don't have or can spare the nickel to get software for testing the drivers. Some day I will build some from scratch when the garage is not a train wreck. My wife and friends say I have too much "stuff"

Auditioning some RT55's found locally, EBayed some new RTi6's. Investment for both pairs $330.00 8^)and now, Geez, I think I want to look into some RTi8s because I like the 55's dual 6.5's sound and everyone raves about the 8's cherry boxes.

I am knee-deep in remoldeling the house we bought a few years back. (We are really moving in now) I'm racking the equipment in one of the adjacent master closets. TV's and speakers on the patio, kitchen cab, office and M Bed&Bath. All tied together with IR repeater systems and on-screen display for the cd changers, XM satilite blah, blah. All the while, I'm apessing the wife with paint and molding, full tile bath and soon door replacement through out the house. Just finished a rebuild of the laundry room. Pipes were leaking. Every damn shut-off valve leaks if you give them an angry look.

It sucks to be me right now.

My thoughts with speakers are Mr. Polk has got much more time, money and John Hopkins U to design speakers I just mod them to my taste. Like Cross bracing or more/less dampners and definately ditch the electrolytics on the XO.

Paul

FWIW,

I do advocate replacing the stock resistor(s) with either the Mills non-inductive type or Bennic non-inductive. Both are wire wound and around $2-3 a piece and are a great improvement over stock since they are in the signal path.

One thing I see in a lot of vintage Polks is if the speaker has been abused anytime during it's life many times the resistor gets scorched (sometimes visibly; sometime not) and it's great piece of mind for a couple bucks. Plus since you're already in there, replacing a resistor or two is a no brainer.

H9

ben62670

heiney9 wrote: »

FWIW,

I do advocate replacing the stock resistor(s) with either the Mills non-inductive type or Bennic non-inductive. Both are wire wound and around $2-3 a piece and are a great improvement over stock since they are in the signal path.

One thing I see in a lot of vintage Polks is if the speaker has been abused anytime during it's life many times the resistor gets scorched (sometimes visibly; sometime not) and it's great piece of mind for a couple bucks. Plus since you're already in there, replacing a resistor or two is a no brainer.

H9

Absolutely.

Polksaladanni

Oh man Heiney,

I guess I'm going to have to do a "poor man's" parts option post on Resistors and Caps. Maybe hook-up wire also.

The OE resistors (white ww/ceramic incased for cooling and flame proofing) are wire wound on every single XO I have looked at lately included my old M4's. Almost every resistor made in the world is non-inductive, coils are inductive that is their purpose. Yes, the real cheap R's are, but not the stock ones you see on the board. I just redid my old M4 XO before I turn them over to some deserving sole. The 1ohm R @10% tolerence, 17 years old, measured 9.9ohms

Here's some thought fodder.
I'm not trying to be smug either. Just trying get you to look beyond "marketing"

If standard 2-5% M-Ox resistors are so bad, why are they put in every High End amp and pre amp such as Adcom or Krell?

Get back to me. I'm watchin that hot VP chick, debate tonight.

ben62670

I agree that the stock R's are almost always within spec, but they are 5w. The 12w gives the a little more performance in the high end.
Ben

Systems

jimiles wrote: »

In the tweeter network of the 15TLs (and many other Polk speakers) there is a resistor (2.5 ohm) and capacitor (12uF) in parallel ahead of the other elements filter elements.

1) What is the purpose of those components? My guess is that it shapes the response of circuit to attenuate the lower range of the tweeter's output.

Yes you are correct,its a contour network that compensates for rising response as frequency decreases.

Polksaladanni

Yep,

The Mills is a very very fine product. But you can get this wire wound, non-inductive, flame proof for.......

http://www.partsexpress.com/pe/showdetl.cfm?&Partnumber=017-4

It clearly states in print in the PE catalog/catalogs I have (not online) that it is described per above.

With the manufactoring processes of todays world and what I have actually measure on XO's, and many, many curcuit boards over the years, I'm betting it's dead-**** on for the value.

Think about it. You got a 1ohmR that's off 10%. That=1.1ohms

Idle thoughts

Like I said. I'm gonna post a "Poor Man's" parts post for guys that just don't have the jack for $40.00 Caps and tha like. I've seen speaker cables over the years in magazines/net that I can easily make for $100.00-$200.00 that people "market" for $900 to $3000 bucks. To me it's BS.

To each his own choice.

ben62670

These work well.
http://www.partsexpress.com/dayton-non-inductive-resistors.cfm
Also not everyone uses the expensive caps here. I have done a shootout between Jantzen, Solen, and Dayton. The Dayton's are actually the cheapest, and sound the best out of the three. While the Solen caps are a big improvement over stock I feel they don't work very well in the highs.
Ben

heiney9

Hey man,

Do whatever............I was just giving my experience. I don't buy into marketing. I've used the $3 Mills and really really like them. Your speaks, do whatever. Just having a discussion. If $3.75 a piece too much for your project, well then get the cheap ones or leave the original alone.

Mills are a great sounding and aren't all marketing.

H9

P.s. I used Solens and Mills in my 5B's and spent about $50. If that's too much scratch then perhaps some should reconsider upgrading/refreshing x-overs and just leave them as is. There is a difference in parts and you get what you pay for.

Face

You mean everyone doesn't use Claritycap MR caps and Duelund resistors? :rolleyes:

jimiles, GV is correct, it's a contour circuit. If you play with the voicing of your tweeter, this is the easiest place to start without throwing everything out of whack.

Systems

Face wrote: »

it's a contour circuit,if you play with the voicing of your tweeter, this is the easiest place to start without throwing everything out of whack.

I'm guessing that the response at the bottom end of the tweet must be bumped up a bit so they used the paralleled RC combo to tame it.
The value of the resistor determines the amount of attenuation and the value of cap sets the frequency range in which the attenuation occurs.I wouldn't alter these values too much as Polk had the advantage of being able to do accurate measurements when they were optimising them.

mmadden28

Polksaladanni wrote: »

Yep,

The Mills is a very very fine product. But you can get this wire wound, non-inductive, flame proof for.......

http://www.partsexpress.com/pe/showdetl.cfm?&Partnumber=017-4

...

Yeah but how big is that thing?
Here's a shot of a 1R resistor upgrade I did with both types next to each other so you can see the size comparison. Note however that the preexisting was a 10W, not 20w which would be even bigger. The Mills is a 12W.

Polksaladanni wrote: »

... Just trying get you to look beyond "marketing"

heiney9 wrote: »

...Mills are a great sounding and aren't all marketing....

I honestly can't say I've ever seen a commercial or anything close for marketing for a Mills product.

heiney9 wrote: »

....spent about $50. If that's too much scratch then perhaps some should reconsider upgrading/refreshing x-overs and just leave them as is. There is a difference in parts and you get what you pay for.

+1

Polksaladanni

Oh for goodness sakes. Don't take it literally. I meant marketing as in techno speak or a glowing discription of a product. Not TV ads. Duly noted on the size. They also offer 5, 10 and 20W.

GV's right.
Looked-up the pdf, it's a trim circuit. Kinda strange they used the same value cap. But Polk has the graph which all the parameters and has much better testing and R&D for drivers than any of us have.

Hey Heiny, Your quote.

Hey man,
Do whatever............I was just giving my experience. I don't buy into marketing. I've used the $3 Mills and really really like them. Your speaks, do whatever. Just having a discussion. If $3.75 a piece too much for your project, well then get the cheap ones or leave the original alone.

Mills are great sounding and aren't all marketing.

H9

P.s. I used Solens and Mills in my 5B's and spent about $50. If that's too much scratch then perhaps some should reconsider upgrading/refreshing x-overs and just leave them as is. There is a difference in parts and you get what you pay for.

Your reply is absolutely right.
I do make my own choices on the many options out there based on my experiences and research of products. Man, just ask my wife she thinks I over research any product. My opinion is just an opinion. No point in putting someone down about how much they need to pay for improvements. It's costing me about the same for the RT55's I am R&Ring. I could spend $600 per speaker if I truly felt there would be a MAJOR audible difference. I have used Mills, Solen, Dayton, Jantzen and Clarity Caps all with great results. I, like Ben, prefer the Dayton’s. (Bennic’s) The new Polk’s I have are all Bennic parts on the XO. My experience says some things are not worth it.

The point missed was the majority of the people here can do some simple and cost effective mods that is well within their budgets and improve the sound of new or aging speakers. That's all...

Everybody should do their own research and after that if someone feels that certain products is superior or fits their needs better then, by all means, purchase it and enjoy.

On you get what you pay for:
Your right. Almost all the time, I choose the "name brand" especially with any type part.
“Cheap” is a bad word that implies it's junk. How about value per dollar on very functional parts.

Here’s a non-electrical example of choice and value per dollar.

1990 Acura NSX-$70,000 1990 Nissan 300ZX Twin Turbo $39,000
Both very fast stock and very easy to drive on the street.

They are both considered "super cars". Yes, the Acura was the first production car with cast aluminum control arms and aluminum body panels. It also sported full independent suspension, rear transverse mount motor like the Porsche and Ferrari and handled extremely well for the wheel/tire options at the time.

The Nissan had a little more power, full multi-link suspension that handled better; even with a front mount engine 54/46 F-R weight ratio.

The Acura entered the 24 Hours of Lemans 3 times never finishing better than 4th place. The Nissan won it three times I believe in the same GTS class. The 300 Z pretty much ruled the tracks from 1989-1994 in Showroom Stock, GTS and GTP class. I chose to buy the Nissan because of the value per dollar and bang for the buck. Plus it's fairly reliable.

heiney9

I don't like Japanese cars. And chill a bit I wasn't intending to put anyone or anything down. Just giving my opinion, no need to act so defensive. I stand by the statement if your not willing to spend a little bit of money then leave it alone and you do get what you pay for, a .59c resistor is just that, a .59c resistor.

YMMV

H9

Polksaladanni

Too bad, some great ones came from that era.Yep, 30mpg normal hwy or a fun 12mpg leadfoot on the track. Just trying to make a point with the comparison.

To be honest I don't use those resistors either it's basically the same as the R on the board of the vintage speaker. I only used it as an example.

I use the Dayton wire wounds. That Ben used as an example or 10w flameproofs that I can get locally from one of my customers.

Paul