Crossover Mod for Monitor-40

bkeane1259

I have a pair of Monitor-40's that I use as near field monitors for my workstation setup. I am extremely happy with their sound (especially for what I paid).....however, I know they can really sing with the proper crossover mod. To wit, I have already swapped out the stock tweeter caps with Jantzen Superior Z's, but now I want to rebuild the whole corssover (likely to be an external mount). Has anyone done this already?

JimAckley

Welcome to Club Polk!

To get straight down to business, your 40s weren't an extremely high-end speaker to begin with, so practically speaking, to go the lengths to make an external crossover for it is probably a bit much. If you really wanted to modify them, perhaps some Sonicaps and Mills resistors on the OEM crossover would do the trick. That's as fancy as I would get, personally.

Externals are practical in a situation where the new crossover components won't fit on the original x-over board, are too large to contain within the speaker, or drastically change the interior volume of the speaker.

Don't get me wrong, I'm all for modding. I'm in the process of collecting new capacitors and resistors for a complete redo of my LSis. On the other hand, the LSis are a platform whose potential is greatly limited by the usage of lower-grade components in the crossovers. The Monitors are designed to function at a much lower price point, so their drivers, while still a great set, are probably not designed as well.

I'm not one to stop you from your dreams though. If you really want to make external crossovers, go for it. Make them as kick **** as can be. Audio is an adventure that we each have to experience our own, with the occasional guidance of others along the way. Parts express, Madisound, and Parts Connexion should have all of the parts and components you would ever need to make externals. Good luck! If it's something you really want to do, there are a few guys around here who have the know-how and experience to help you get it done. I'd also look into projects on other sites like hometheatershack.com, and other AV forums. Google will become your best friend when it comes to finding the threads with the information you need.

Cheers!

bkeane1259

Thanks for the info/comments. Initially I was concerned that the size of the modded network would change the box volume and since it's a ported system, I didn't want to screw that up. However, if I only swap resistors and caps, that shouldn't be an issue, and I should easily be able to utilize the underside of the current board for the extra components. In fact, that's where the single Jantzen sits.

I am definitely doing this, but I'm in the middle of a Minimus-7 crossover mod, so this will get full attention as soon as I'm done fiddling with the Old Skool Radio Shack project. Seriously though....the Minimus-7 speakers are worth a look. I got a pair in excellent condition for about $32 delivered thru ebay, and they are going to be drastically improved with new crossovers.

I really believe crossovers are totally underdone by most major manufacturers, so this will be a fun and rewarding project....heck I might even learn something in the process. More later.

bkeane1259

Awhile back I swapped out my Monitor 40 tweeter caps with Jantzen Superior Z's and in the process, I ditched the original mylar bypass caps. Polk will not provide a schematic for the Monitor 40 crossover (why, I don't know), so....does anyone know the value of that component?? I wanna say it was a 0.47uf, but I'm old and my memory is crap. Any help out there?

Face

If you replaced the original tweeter caps with high quality film caps, you do not need the bypasses. IMO, they would degrade the sound of your Z's.

bkeane1259

I replaced the original tweeter caps with these: JANTZEN Z-cap SUPERIOR

Impressions: Immediately I noticed more detail in the high end and more presence in the midrange. Cymbals were much more detailed and clear and sounded "real." I believe after running these caps for about a month now, they are sounding a bit smoother. Initially I thought that while there was marked improvement, some of the tweeter silkiness was missing. Note that I am NOT any sort of audiophile, so take it FWIW. I have decent ears though.

Next step: Bypass the Jantzens. I'm going to try the following bypasses:
VISHAY-RODERSTEIN MKP-1837

Dayton Audio DFFC-0.01 0.01uF 400V By-Pass Capacitor

Anyway, I am going to eventually rebuild the entire crossovers with the existing Jantzen tweeter caps, Jantzen inductors and Mills resistors. I'm not expecting my economical 40's to sound like $2000 speakers, but I'm expecting an improvement, and it will be a fun and educational trip as well.

I plan to document my project in this thread, good or bad outcome. Suggestions and comments more than welcome!!

Face

I wouldn't bother replacing the tweeter shunt inductor. As for the woofer's inductor, make sure the DCR is within 10%, preferably 5%.

I still wouldn't bother with the bypass, even if it was a Duelund CAST.

F1nut

I still wouldn't bother with the bypass

Agreed. Waste of money and time not to mention it will not sound right.

bkeane1259

I have these in mind for the low pass section:
Jantzen 1.0mH 15 AWG P-Core Inductor

You're saying that replacing the tweeter inductor isn't necessary?....that will save me about $10....Thanks. I can try the rebuild without swapping those. Now that I think of it, a project that I just completed didn't replace the tweeter inductor either....and that was in a pair of Realistic Minimus-7's.

Face

bkeane1259 wrote: »

I have these in mind for the low pass section:
Jantzen 1.0mH 15 AWG P-Core Inductor

Those are ok, but do you know the OEM inductor's DCR?

bkeane1259

Face wrote: »

Those are ok, but do you know the OEM inductor's DCR?

I believe 0.21 ohms.

So now I'm wondering if the DCR improvement afforded by the Jantzens (0.13 ohms vs. OEM 0.21 ohms) is worth it?? Both inductors are steel cores. Now I'm going to really sound ignorant....

Should I consider paying twice as much for an air coil that has a DCR of 0.21 ohms (same as OEM) but a much lower distortion profile? Like these - Solen Perfect Lay Inductors

Is this where I'm going to really NOTICE a difference?

Outfitter03

1.2 mH for the mids, DCR 0.25 ohms.

These work:

http://www.erseaudio.com/Products/XQCoils14Gauge/EAV75-14-1200

Face

You have to keep the DCR as close as possible to the original design, otherwise you'll offset the balance of the speaker, possibly change the driver's roll off, and more. Since the Solen inductor has the same DCR, it would be compatible with your speakers. Being an air core inductor, it would be an upgrade over the cored OEM inductor. It won't be as obvious of a difference as the cap swap, but will still be an improvement.

FTGV

bkeane1259 wrote: »

.

So now I'm wondering if the DCR improvement afforded by the Jantzens (0.13 ohms vs. OEM 0.21 ohms) is worth it?? Both inductors are steel cores.

While the percentage of DCR drop is large in the grand scheme of things an .08 ohm reduction in DCR willl not affect driver Q and sensitivity to a significant degree(IMO).If the stock coils core is prone to saturation at higher power levels then replacing it with the Jantzen or air core would be worthwhile.

Outfitter03

The DCR should be 0.25 ohms. The Erse inductors listed above have a DCR of 0.243 so are only 0.007 different. Erse has a 1% tolerance also.

bkeane1259 how did you come up with the DCR specification of 0.21 ohms.

bkeane1259

Outfitter03 wrote: »

The DCR should be 0.25 ohms. The Erse inductors listed above have a DCR of 0.243 so are only 0.007 different. Erse has a 1% tolerance also.

bkeane1259 how did you come up with the DCR specification of 0.21 ohms.

I was going by what I found out thru my internet research and that is obviously wrong - crap, I'm glad I was at least remotely close. Unfortunately, I have been unable to obtain a factory crossover schematic. :mad:

BTW - The ERSE air core looks perfect!! By not swapping out the tweeter inductors, I can apply the savings towards the better quality ERSE inductors for the low pass filter.

I have not actually purchased anything yet (other than the Jantzen Z's) -- still in the early stages of DD for the rest of the mod.

ben62670

Take an ohm meter and measure the DCR. It's that easy.

Outfitter03

bkeane1259 make a couple more posts and then you can read and reply to my PMs. I can help.

ben62670

Can't help here where others may benifit from what you have to say?

bkeane1259

ben62670 wrote: »

Take an ohm meter and measure the DCR. It's that easy.

I do have a multi-tester. Just a question though and this might be an extremely stupid one. Isn't there DCR in the test leads? If that's the case, then would I have to subtract the "no load" reading on my meter from the reading I get when hooking up the coil?

bkeane1259

Outfitter03 wrote: »

bkeane1259 make a couple more posts and then you can read and reply to my PMs. I can help.

Check your email and thanks for the clarification on the inductor value.

bkeane1259

Here is what I am thinking for now:

HIGH PASS SECTION - Jantzen Super Z Cap (8.2uF), Mills resistor (1.2ohm), OEM air core inductor (1.5mH).

LOW PASS SECTION - PE Perfect Layer Inductor (1.2mH 14 AWG), Mills resistor (1.0ohm), Solen Poylpropylene Cap (9.1uF).

**I'm going to try a couple different bypasses and see what sort of difference it makes. Despite the recommendation to NOT bother, the cost is extremely minimal, and having ripped out and ditched the original OEM mylars and noticing an initial loss of tweeter silkiness, I'm going to toy around with the Vishay's and Dayton's just for yuks to see how/if they complement the Jantzens.

Bypass ideas -
VISHAY-RODERSTEIN MKP-1837 0.01uF
Dayton Audio DFFC-0.01 0.01uF

PRICE LIST --
Jantzen Z-Superior Caps - 2 @ $38.31 ea. = $76.62
Mills resistors - 4 @ $4.25 ea. = $17.00
PE Perfect Layer Inductors - 2 @ $24.85 ea. = $49.70
Solen Poylpropylene Caps - 2 @ $6.15 ea. = $12.30

Bypass Caps: **I'm going to switch between the two (Vishay and Dayton), note the differences, and ultimately only go this route if it sounds better**
Vishay MKP-1837 - 2 @ $0.99 ea. = $1.98
Dayton Audio - 2 @ $0.74 ea. = $1.48

Any thoughts/ideas?? I already have the Jantzen Z's but I want to order the rest of the parts soon and get hauling on this project. I'm fairly confident these components can somehow be stacked on the backside of the existing speaker terminal cup (same place the OEM crossover is located).

ben62670

bkeane1259 wrote: »

I do have a multi-tester. Just a question though and this might be an extremely stupid one. Isn't there DCR in the test leads? If that's the case, then would I have to subtract the "no load" reading on my meter from the reading I get when hooking up the coil?

DCR is just ohms.

F1nut

**I'm going to try a couple different bypasses and see what sort of difference it makes. Despite the recommendation to NOT bother, the cost is extremely minimal, and having ripped out and ditched the original OEM mylars and noticing an initial loss of tweeter silkiness, I'm going to toy around with the Vishay's and Dayton's just for yuks to see how/if they complement the Jantzens.

You don't seem to be grasping the purpose of a bypass cap. When using an electrolytic in the high pass, there is an advantage to adding a better quality bypass cap as it makes the electrolytic sound better than it would on its own. When you upgrade the electrolytic to a superior film/foil cap, the very reason a bypass is used no longer applies. Now, instead of helping, the bypass cap has the opposite effect by causing unwanted artifacts.

The initial loss of tweeter silkiness that you experienced can be put down to a few reasons of which none involve the bypass cap. The new cap may not be burned in yet and/or the sonic signature of the new cap isn't mating well with the tweeter and your ears.

bkeane1259

F1nut wrote: »

You don't seem to be grasping the purpose of a bypass cap.

Fair enuf - thanks. I do believe what you say, and I'm guessing that my Jantzens don't have enough burn-in hours. From what I read, this is common so I have even sweeter highs to look forward to in the future!!

Here's sort of where I got the idea for the Vishay Caps and why I would go thru the trouble of fiddling around with the bypass idea- if you have a moment, would you like to comment on this guy's quote?

Re: Vishay MKP1837
"Verdict: Can't live without them! Use them as bypass cap with any capacitor, they cost practically nothing!"
http://www.humblehomemadehifi.com/Cap.html

ben62670

I have tried bypass caps and I have removed them. I didn't listen to others here that have been around the game longer than I have. I also don't care for the Jantzen caps, or Solen's. The Dayton's are cheap and sound very good for the money. I use SonicCaps almost exclusively for the tweeter circuits. Clarity has been getting good reviews around here too. I think I will be doing a pair of Monitor 7's with SonicCaps and Clarity's on the highs.
Enjoy
Ben

F1nut

Yes, I am quite familiar with that site. I couldn't disagree more with his comment.

Here's a view point from another cap guru that I agree 100% with as I and many others here have experienced the same results.

Bypass capacitors. In addition to the Multicap RTX, I have tried either .1 ?F or .01 ?F bypasses from Sonicap (Gen I and the Teflon? Platinum cap), Hovland, AudioCap, and Wima. In every case the results were similar. Let me digress for a minute or so (depending on how fast you read) and talk about crossovers.

In the simple first order high-pass crossovers we are using for this capacitor comparison, the value of the single capacitor, together with the impedance of the loudspeaker driver, determines the crossover frequency. An 8 ?F capacitor with the 4 ohm impedance of the Magnepan quasi-ribbon tweeter gives a crossover frequency of about 5000 Hz (1/2πRC). A smaller value capacitor (for example, 4 ?F instead of 8 ?F) will raise the crossover frequency. If we used only the very small value .1 ?F capacitor without the 8 ?F, we would hear nothing because the crossover frequency is now almost 400,000 Hz. Even a dog would not hear it!

So why use a bypass at all? There are actually components of very high frequencies in some audio waveforms. Some are high order harmonics. If you think of a square wave, the right angles at the top of the wave are extremely high in frequency. Sometimes there are high frequency components in very fast audio sounds, for example, the instantaneous tap of a drum stick on a cymbal. These are the sounds that should be "helped" by including a small-value bypass capacitor in a high pass crossover.

Well, I don't think so. If the 8 ?F capacitor blocks frequencies below 5000 Hz and passes frequencies above 5000 Hz, why do we need what is actually another crossover for the same tweeter, but operating at frequencies already passed by the big cap? I am sure engineers have a very good reason, and a couple of them have tried to educate me on this subject. I respect the science and electrical theory on this subject, and my technical background helps me to understand it fairly well. But there is one small problem: the bypasses all sound bad! They add a quality that at first sounds like an increase in air and detail, but after a couple of hours becomes an intrusive harshness and discontinuity in the upper treble. Remove the bypass: all of the detail is present but without that grating and annoying sound. The high frequencies are cleaner, smoother, and much more enjoyable. It doesn't matter if the bypass cap is Teflon?, polystyrene, or common polypropylene, the results are very similar. And to be avoided.

bkeane1259

ben62670 wrote: »

I use SonicCaps almost exclusively for the tweeter circuits. Clarity has been getting good reviews around here too. I think I will be doing a pair of Monitor 7's with SonicCaps and Clarity's on the highs.

Wow....lots of food for thought now. Perhaps I should invest in another brand of cap for the high pass and do a comparison. I would not mind the expenditure because I do indeed like the Jantzens and could save them for another project.

Let me ask you this...I purposely sort of went cheap on the low pass cap and allocated more funds towards the inductor. Is this a mistake? Should I be keeping the cap brand the same for both high and low pass circuits? Does it matter?

ben62670

I use Dayton's and Solen's in the shunt position on many of the upgrades I do. It is where the cap is inline(series) with the driver that the better caps really shine. I have never heard the 40's so I don't know what cap would be best. There is no "best cap". Different speakers have different sounds and synergy comes into play. Here is a thread I did on some caps a while back. If you skim through it you can get the idea of what tonal characteristics are. Also there is a good link buried in there about another site that did a comparison.
http://www.polkaudio.com/forums/showthread.php?t=61727

pitdogg2

F1nut wrote: »

You don't seem to be grasping the purpose of a bypass cap. When using an electrolytic in the high pass, there is an advantage to adding a better quality bypass cap as it makes the electrolytic sound better than it would on its own. When you upgrade the electrolytic to a superior film/foil cap, the very reason a bypass is used no longer applies. Now, instead of helping, the bypass cap has the opposite effect by causing unwanted artifacts.

The initial loss of tweeter silkiness that you experienced can be put down to a few reasons of which none involve the bypass cap. The new cap may not be burned in yet and/or the sonic signature of the new cap isn't mating well with the tweeter and your ears.

ben62670 wrote: »

I have tried bypass caps and I have removed them. I didn't listen to others here that have been around the game longer than I have. I also don't care for the Jantzen caps, or Solen's. The Dayton's are cheap and sound very good for the money. I use SonicCaps almost exclusively for the tweeter circuits. Clarity has been getting good reviews around here too. I think I will be doing a pair of Monitor 7's with SonicCaps and Clarity's on the highs.
Enjoy
Ben

These two really know their stuff and you could learn a lot from them. Although there're many others who have much wisdom to dismiss their advice would be a mistake.
By the way welcome to club Polk
Ivan

bkeane1259

pitdogg2 wrote: »

These two really know their stuff and you could learn a lot from them. Although there're many others who have much wisdom to dismiss their advice would be a mistake.
By the way welcome to club Polk
Ivan

Thanks. Yes, I certainly am. My little project is in the process of a complete 180.