For those of you who have been following the various threads regarding Southbound's favorite speaker mod:

If any of you have doubted his accuracy or methods, simply do a search on the web for "Zobel Circuit" or "Zobel Network". This is a widely accepted practice among crossover designers.

Here is an excerpt from one of the many web sites that I have seen:

"One other thing to consider when designing passive crossovers is the fact that most passive crossovers are designed based on the speakers' nominal impedance. This value is NOT constant, as it varies with frequency. Therefore, the crossover will not work as it has been designed. To combat this problem, a Zobel circuit (also known as "Impedance Stabilization Network") should be used. This consists of a capacitor and resistor in series with one another, in parallel with the speaker."

"To calculate these values,
R1 = Re (in ohms) x 1.25, and C1 = (Lces {in henries} / Re^2) * 10^6.

Note: "Re" is the Driver DC resistance (voice coil, mainly), in ohms and Lces is the electrical inductive equivalent of Cms, in henries. R1 will be in ohms, and C1 will be in uF (micro- farads).

As an example, an Orion XTR10 single voice coil woofer has Re = 3.67 ohms and Lces = 0.78 mH.

So, R1 = 3.67 * 1.25 = 4.6 ohms. C1 = ( 7.8E-4 / 3.67^2 ) * 10^6 = 57.9 uF (be careful with units -- 0.78 mH = 7.8E-4 H)"



These networks are included in some home speaker systems, but not in car speakers. The only reason I can think of is that the manufacturers have cheaped out of installing a couple more components, figuring the average listener won't know what they're missing...

If you want to verify the above quote, follow this link:
http://www.audiowarehouse.sk.ca/steves/


The mod works, so stop doubting, and TRY IT!!!! (and, NO: Southbound DID NOT ask me to back him up.)

As long as you take the proper precautions to prevent shorting to the door frame, you've got nothing to lose (except about 5 bucks worth of parts, and a little time). If you don't like the way it sounds, just remove the mod. Everything is reversible, so there's no risk.

 

Hey Sask,
I don't know how in the heck you stumbled onto this information, but I'm totally amazed that it exists!

HONESTLY, All of my research and work on the subject has been mine and mine alone. It was all done before the age of the internet, so I guess it was a lot easier to not know that someone else had been doing the same sort of thing back then...

Still, it does help to add some credibility to my terminator mod. If you study the values used in the "zobel network", it's obvious that they were also interested in presenting a stable impedance to the amplifier at VERY HIGH ULTRASONIC FREQUENCIES. And if that's the case, the one thing they fail to address, that I keep harping on, is that up at those frequencies, the characteristic impedance of the speaker wire ALSO comes into play. That is why I chose my resistor value of 100ohms. I calculated ZIPCORD speaker wire to have an impedance of around 102/103ohms.

My whole concept was designed around a compromise of giving the amplifier a more stable resistive load and terminating the speaker cable in its characteristic impedance. You must realize that as the frequency goes up into Megahertz land, not only does the impedance of the speaker rise, but so does the amplifier's output impedance. So a 100ohm RESISTIVE load makes an amp very happy as compared to an infinite inductive load.

If the amplifier was DIRECTLY connected to the speaker, then the amplifier's load and the "zobel network" solution would be the only considerations to deal with. However, THERE IS SPEAKER WIRE between the amp and speaker, which will ALSO cause ill effects to the HIGH FREQUENCY signal in the form of reflections, etc. Therefore, my values were derived to compensate for both of these issues.

You've gotta tell me how you went about finding out about the "Zobel network"??? I guess the internet search engine is truly remarkable. I really had no idea that any speaker manufacturers were addressing this phenomenon... I'm glad you went through the effort to try it out and to actually find further research to back up the theory. HOW WOULD YOU DESCRIBE YOUR A-B TESTS? What kind of improvement did you notice? I'm sure it varies with different amps and different types of speaker wire, especially with LONG runs of wire. I would be willing to bet that it works better on modern amps that are supposedly stable to drive 1ohm and 2ohm loads. I don't care what they say, NO AMP is truly stable with that heavy of a load.

THANKS FOR THE UPDATE AND REPORT! I can't help but wonder... What happened to Sniper??? Haven't heard him report in with any results, yet. Maybe he doesn't like crow.... LOL

GREAT RESEARCH!!! I guess I wasn't as crazy as some people probably thought...

Southbound

 

I was converting a really good article that covered a wide range of car audio topics from Word format into HTML, and came across a section dealing with zobels. After thinking about it, I remembered a couple of articles in SpeakerBuilder Magazine from a long time ago. I rummaged through my collection of back-issues, and found the article. Since these articles almost pre-date the World Wide Web, I decided to do a search on dogpile.com, and found a few other hits, including a simple javascript Zobel calculator.

You should follow this link, and check it out. It's a web page now, meaning that search engines will be able to see it...

Audio Warehouse Car Audio Page

One of it's major weaknesses is the lack of graphics. Slowly but surely I've been generating images to go with it, but there's a lot of really sound information (I know... bad pun).

As for the tests, I used a friend's home surround system (identical speakers for front and rear). After opening one of them up to confirm that the manufacturer hadn't built it into the crossover, I did the mods to the front pair. We then moved the wires from the rear pair to Speaker B. Slapped a Steely Dan audiophile CD into the DVD player, then simply switched between speakers A and B.

He's really happy that I use his speakers for my guinea pigs. I have swapped out all of the crappy electrolytic caps with Metallized Polyesters, swapped out the crappy iron-core coils with air-cores, moved the coils far away from each other to reduce interference, etc...

Each time I try a mod, we do the same A-B tests before modifying the second pair. I would love to have an original pair to compare the sum total of all the mods, but we have heard a noticeable difference each time. His speakers are about 15 years old now, and I suspect they'll be due for re-coning soon...

Bwa ha ha haaaaaa....

 

got the components by the way yesterday.... will be testing tommorow...

 

SB -

Any sense making this mod on a sub? My home theater system utilizes a rack mounted mono sub amp with 4' - 5' of zip cord to the sub. Or are the frequencies too low to matter?

Also, is there a decent mail order electronics place that has the right caps, resistors, and 5W resistors for my DX6s all at one easy place?

 

Sask,
Sounds like you had a nice A-B setup. I doubt that you could hear any difference by a quick switch between A and B speakers. But if you listen to one pair for a couple of minutes and then pause the music, switch the speakers, and then play the same passage over again, you'll be sure to notice an improvement. You mentioned your set-up, but didn't really report your listening results. How much difference did you notice and how would you describe it? Is that website link in your last post yours? Nice job, in any case. Very informative site. You have done all the correct crossover mods to your friend's speakers. Hope you have some of your own to tweak. Thanks for the updates.

Sniper,
Glad you are still in the loop. Hope you have similar positive results. I'm sure you've been restless to find out one way or the other. Hopefully it will leave you pleasantly scratching your head

heyrandy,
In one of my long winded posts, I did report results of putting a 100ohm/2watt resistor directly across the subwoofer in the TLS. I found it to help out the bass a bit. It was definitely grittier before the mod. The terminator seemed to actually smooth out the bass. It was easy to A-B the mod. I just hooked a couple of clip leads to the subwoofer terminals and let them dangle in the trunk. Then I would listen to a music passage with and without a resistor clipped between the leads. I found it more noticeable with the fader control all the way to the rear to favor the bass output. I could get away without using the cap in series because the TLS subwoofer is only 1/2ohms and has very little voltage sent to it and then only at bass frequencies. In a HOME subwoofer system, I would put the cap back in series with the resistor, or you would most likely fry it. However, you could increase the cap to a .1uF in this case, since the subwoofer doesn't see the full range of audio frequencies. After you've tried the mod out on the main speakers, what the hell, give it a try on the subwoofer. I don't have a subwoofer or surround system in my home But the mod did seem to help out the bass in the TLS. Again, it can't hurt anything to try.

I believe sniper found his components from my referral of "NTE ELECTRONICS". Go to their website at www.nteinc.com and then you can look up dealers in your area. I believe sniper had luck pursuing that route, after not being able to locate any local stores that carried the caps. I believe he mail ordered from one of the dealers listed on the NTE website. If you live in a big area, chances are you may be able to go to one of the dealers in person and buy them that way. If not, try the mail order routine with them. NTE should make ALL of these parts. I believe they list the .05uF "ceramic disc" cap as 50,000pF, (same thing) So just watch out for that. Get the 1KV version. Everything else should be standard stuff. They sell flameproof 1watt resistors, and 5watt wirewound power resistors.

Thanks for the further octane clarifications. I may pour a can of Chevron injector cleaner in every once in a while as long as you don't think it could ever hurt anything?

Hope some of this helps. Good luck!

Southbound

 

SB

Thanks for the info. Electronics Supply in KC seems to carry their full line. I've been there a couple of times when I networked my house. I'll have to make a shopping list before I go (7 home theater speakers plus sub, 4 car speakers plus sub, etc.). I have a new soldering iron so watch out!

While I don't think that fuel injector cleaner will screw anything up, it's one of those things to use only as needed IMHO. Kind of like antibiotics. I used Gumout as a kid working on cars and now I wonder where all of the crap went. Probably to the intake valves. I'm sure the Chevron stuff is much milder but I wouldn't think you would need it with the required additives in CA gas.

 

The results were a little smoother, but I've already modded the hell out of the speakers. I imagined that any further mods would result in diminishing gains, and I was right. If the mod were installed in a pair of absolutely stock speakers, the difference would be quite noticeable. Kind of like installing a better intake manifold after installing a NOS system. Yes, it works better, but compared to the previous change...

As for the A-B tests, I have used the same CD for EVERY demo I have ever done, and have listened to some of the tracks literally hundreds of times (Steely Dan - Aja). I know every note, breath intake, cymbal strike and guitar string scratch on these songs. The listening method you described is what I do. Listen to the entire song, switch, listen to it again.

As for the site, the only credit I can claim is the HTML conversion of the tips file, and the graphics in that file (plenty more to come). I will be submitting some changes and additions to the file to make the information more user-friendly, and to add some more source material. My web page will look considerably better. Audio Warehouse paid a web developer to design the site, and finances were limited. One of their employees maintains the site, but again, he is on salary, and the store can't afford to pay him to make the page really sexy. I don't have that problem, and I have the luxury of time to fine tweak everything. Because of that, I have no idea when my page will be online...

By the way, I have NO IDEA who "Steve" is. I just know that the original file had a pile of good information but it was very badly organized, and was in the form of a WORD document and a Wordperfect document, using crappy ASCII character graphics, and it was zipped up.

 

Just solder these pups across your speaker leads or crossover inputs and off you go. I got my fronts done last night and will do the backs tonight. I'll let ya all know what I think when I've had a chance to "road test" them.


-----------------------------------------------------------------------------------
2002 WDP TL-S w/nav
OEM body kit, rear spoiler, fog mod,
9006ST fogs, 3A exhaust tips.......Stereo in progress

 

Yep, That's the right components and the way to put them together to tie across the speaker terminals, or in the case of a component system, across the crossover inputs. NTE has 1KV caps and flameproof metal film resistors. They have distributors All over the U.S. Just go to their website at www.nteinc.com to search for a dealer near you. These are the exact parts that I have been using.

Iggy,
I hope you are able to give the mod a fair A-B listening test. I know you should be able to lift one side of the mod on your crossover to perform listening tests before and after. It's a hassle with just speakers or systems with the crossover mounted behind the door frame. But in your case you should be able to listen to a good tune for a couple of minutes and then connect or disconnect the mod and re-listen again. Do this back and forth a few times, and I think you'll be convinced of its worthiness. The rear speakers are a bit more of a hassle to do. I attached the mod (carefully) with clip leads on my speakers and then kept taping the speaker back in place while I kept pulling it back out to reconnect or disconnect the mod. By the convenient placement of your crossover, You should be able to perform a fair comparison relatively easy with your front speakers. If you just simply solder the mod in place and then button things up and then wait overnight to listen, I doubt that you will be able to tell a whole lot of difference. The ears and brain can't retain that subtle of a change for that long of a time. Now that I'm used to my speakers with the mod, and if it were secretly removed, I don't know that I would go out in the morning and start up the car and say "Who took my terminator mod out overnight?" But then again, if you are REALLY used to the way your system sounds, you might just be surprised that you would notice right away. It depends a lot on your system and your particular set of ears... But a good and proper A-B test should prove to you that you've done the right thing whether or not you've forgotten about it months down the road. You will get used to it and always want better, BUT YOU CAN NEVER GO BACK!

Good luck, I've printed your bypass schematic just for my future reference, even though I don't think I'll ever forget the routine.... Thanks for posting it!
Southbound

 

It also wouldn't hurt to slap a piece of heat-shrink tubing over as much as possible to prevent any shorting to the door frame. You won't get it over the cap, but should be able to cover the resistor and most of the leads...

 

Well it's in and I went for a 45min drive to nowhere just listening to tunes. I believe the mod does work! It seems to smooth things out and reduce the harshness. I give it a thumbs up.

I decided not to shrink wrap the cap and resister because they tucked into the speaker nicely. besides with all the cascade material I have in the area they aint gonna be touching any metal.


Iggy

 

for the insanely lazy ... here's direct links to electronics plus for those parts that iggy posted

I went hunting for an online store and after like FIVE tries.. I finally found this one that had it. right descriptions and everything. figure this might help other ppl attempting to buy online.

thanks iggy, with those pics, I was able to get exactly what I was looking for. no guesswork

50,000 pf 1Kv CERAMIC DISC CAPACITOR

http://www.electronics-plus.com/Merc...uct_Code=90350


100ohm/1watt resistor

http://www.electronics-plus.com/Merc...uct_Code=1W110

 

For those that add this mod, I would agree with Sask and also suggest that you put some sleeving on the two outside leads of the network. I'm sure Iggy, put things back in carefully and made sure of his clearances, etc. BUT if you're not careful the leads can hit the bottom of the door hole cutout or they can get bent by the adjacent speaker wires during the final install and screw down procedure. This could cause an unexpected short either to the door frame or it could short out the cap, in which case the resistor would end up getting hot. Just strip some insulation off of a couple of pieces of wire and slip them over the leads. I also taped the center junction with a couple of wraps of electrical tape just to be safe in my case. The stock head unit can sustain a short circuit. It just shuts down ALL four door speakers if it detects a short on one of the lines. Who knows how well protected an aftermarket amp would be?

I see you left most of the rainshield intact on the stock plastic basket. Some of us have found that we got a little better and more solid bass out of the POLKS by cutting the entire back of the basket off down to the rubber gasket. It lets the speaker better port and breath into the door frame. If you're happy with the sound, I wouldn't change it, but if you find the POLKS lacking a bit in volume and punch, you might try cutting the rest of the basket off, leaving you a simple spacer only. I talked to three technicians at POLK and they all said that a rainshield was NOT neccessary on this speaker due to the material that it was made out of. BUT do what makes you happy.

GREAT WORK! BTW, Is there any way that one can reach behind the headunit and remove the connector and make it reach out far enough to do the EQ bypass without taking all of the console and dash apart? Probably just wishful thinking, but that is what's stopping me from jumping on the bypass at this point in time. I need more tips on how to get to the back of the radio... What are the minimum steps that I would have to take?

Thanks!

Southbound

 

Iggy -

I agree with SB. When I first put in my DX6s in the fronts, I cut the rainshields so they looked exactly like yours.

I then had to favor the fronts by 2 clicks on the fader to hear even sound volume.

After following SB's research, I went back in and cut the rainshields to the gasket (and smoothed rough edges out, etc.).

My fader is now centered with even sound all around.

 

Heyrandy,

As much as I hate to pull the door panels again, I may just take you guy's advice and cut down those baskets. As long as I've allready got 50 gagilion hours into this thing another 30 min aint much. I may drop by the dealer today and pick up some new door clips so everything goes back together nice and tight.

Iggy

 

Iggy -

I know what you mean. I'm getting ready to pull my fronts again, add the resistor/cap mod, a tweeter resister and the Ford version of dynamat and then add a pair of Polks to the back doing all of the same stuff.

After you remove the rest of the rain shield, you will then realize how choked off the speaker really was. I used a Dremel to round the edges and to get as close as practical to the gasket.

It was a dramatic change to my ears.

 

heyrandy,

I could'nt stand it any more after you guys talked about giving the the Polk's some "breathing room" so I did mine tonight. Thank god(ya know GOD spelled backwards is DOG) I had a few Becks left over from the other night because this install just seems to have no end , but I can see the light. Once I get the sub replaced I'm DONE

Cheers,

Loren
aka- Iggy

 

Iggy,
I love the way you can't leave well enough alone when you know that there's one more easy thing to do...

Did you notice an improvement? I cut mine back that far from the beginning, just for good practice. So I really don't know how much difference that it actually makes. I know heyrandy was unhappy with the POLK upgrade until he went back in and cut his out. With just the narrow spacer now created, you can at least look at the back of the speaker and actually see some cone. Polk calls for a 5 inch cutout for proper installation. The doorhole cutout is only a little over 4 inches... so It's got to be better for performance.

So while we're in the true confessions mode... how did IGGY come about?

P.S. you know in Engineering what the ENEMY of good is, don't you? "BETTER"

 

Hope this is not too dumb a question. Is it necessary to bridge directly between the inputs to the speakers, or can you just bridge the speaker wire just before it connects to the speakers? I will want to try this mod on my home theater setup that has 5 Klipsch speakers plus subwoofer, and then move on to my 2003 TL-S. Thanks.

 

If you are referring to my terminator mod also known as the "Blackum" box... It is fine to place the network across the inputs to the speaker cabinet. Place the RC network across the terminals at the END of your speaker wire run. NO need to open up the speaker cabinets and place the termination inside of there. You would run across a crossover network shortly thereafter, and you want this network on the amplifier side of the crossover network. BUT DO PUT IT AT THE END OF THE SPEAKER WIRE LINE, NOT AT THE OUTPUT TERMINAL OF THE AMPLIFIER!

I've tried placig it directly across the output terminals of my home amplifier and it's just not as effective as placing it at the speaker end of the speaker wire. That's because this mod works to stabilize the final amplifier output stage when driving an inductive load, as well as compensating for the characteristic impedance of the speaker cable.

Give it a fair A-B test, and I think you'll notice the improvement. If you haven't followed the whole LONG thread of information on this topic, do a search for "terminator mod" or "Blackum" box and there is enough ramblings to keep you pondering for weeks....

Good luck!
Southbound