How much does a Zobel network and its components affect the sound of speakers?


Regardless of amplification, my Merlin Audio MMI monitors have always sounded bettter using the Merlin RC Master (Zobel) Networks consisting of a Dueland capacitor and a Caddock resistor in series bringing the tweeter terminals. I've heard that some have replaced the networks using Jupiter capacitors and Vishay resistors and different wires and spades. My question is, How much do the networks and their components and associated values affect the sound? At times my speakers, while having superb resolving ability, can occasionally sound edgy, particularly noticable with voices at higher volumes.
pmboyd
I would avoid playing with those values unless you understand what it's doing.  Especially lowering the resistor value can greatly reduce the effective driver impedance, which can be bad. :) 

If you find edgy sound, a good place to start looking is the acoustics behind and beneath the speakers. The floor and stands in between are places to try padding. Pillows and blankets work. 
" At times my [6.5" two-way] speakers, while having superb resolving ability, can occasionally sound edgy, particularly noticable with voices at higher volumes. "

Here is what might be happening:

In the octave or so north of the 2.2 kHz crossover the tweeter has a very wide radiation pattern, so there is an abundance of off-axis energy in this region. This happens to be the region where the ear is most sensitive. Some designers intentionally put a dip at the bottom end of the tweeter’s response which restores timbral balance at the expense of some clarity, as now the upper harmonics in that region are under-represented in the first-arrival sound. 

Your comment that your speakers have "superb resolving ability" makes me think their on-axis response is pretty close to flat, which implies the presence of excess off-axis energy at the bottom end of the tweeter’s range.

You might try this: Turn them up a bit louder than normal and listen through an open doorway from outside the room, with no line-of-sight to the speakers. All you will hear will be reverberant sound, whose spectral balance will be dominated by the off-axis energy. If you hear that edgy signature from outside the room, it may well be due to an excess of off-axis energy at the bottom end of the tweeter’s range.

If this is indeed the case then you might try listening nearfield, to minimize the loudness of the reverberant field relative to the direct sound.

Duke
I have built many speakers and on at least 40 to 50 occasions,  I have compared sound with and without impedance compensation.  I have never found a negative result in listening, in fact 90+ percent of the time it only improves many aspects.  I have also found that if the zmin is high enough (above 4 to 5 ohms minimum) it will improve the sound of tube amps on those speakers across the board. 
Correction: BRIDGING the tweeter terminals
I'm less interested in playing with values than playing with components. I am hoping for some insight into what impact it might have.
Fyi, I'm currently running a ss integrated.
Dive in and tell us :-)
Anybody out there replaced their Merlin RC networks with something else?
A zoebel circuit is used to flatten the impedance of a driver and is not a crossover per se or doing any filtering. they are typically wired in parallel (you say in series "bringing" the tweeter terminals, which is likely in parallel) and as long as the parts are of good quality and their electrical values are within specification it is unlikely that higher quality parts will have a big impact on the sound quality- such that premium crossovers can do.  
The parts are wired in series, the network itself is wired in parallel,  "bridging" (as corrected) the tweeter terminals. If they impart no sound character, why have some people commented about an improvement in exchanging components of the same values? 
Moreover, why has Merlin Audio (now defunct) experimented with their network components, before settling on the Dueland/Caddock combo?

If you want to pay the shipping, Danny Richie of GR Research actually lets you send him your speakers, which he then measures and checks out the cross-over of. If he sees a way to "correct" some engineering "mistakes" (or compromises) for a reasonable price, he will redo the x/o.

It's sort of like how Mike Holmes on his HGTV show Holmes On Holmes comes in to a house that has been poorly built, and fixes what needs fixing. For a glimpse into the above, watch Danny's GRR Tech Talk Tuesday videos on You Tube.

A zobel affects the behavior of the filters. So while it is not a high or low pass filter per se, it may be needed to ensure the behavior of the surrounding components.


I find using a decent film cap is useful. Be careful going from an electrolytic to film though, as you may be altering the total effective series resistance.
" If they impart no sound character, why have some people commented about an improvement in exchanging components of the same values? "

There are places in a crossover circuit where the characteristics of the components matter more than others. The Zobel is among the less critical locations in the circuit; in contrast, the series capacitors are quite critical.

Just my opinion, but "my speakers... can occasionally sound edgy, particularly noticeable with voices at higher volumes" sounds to me like a much bigger issue than can be addressed by exchanging Zobel parts, especially if their quality is high to begin with.

Duke
The edginess is minor and infrequent and not an issue I'm particularly concerned with. I mentioned it in passing. I brought up the Zobel network as a possible simple and inexpensive performance tweak, like a duplex outlet. The edginess I cited occurs typically with specific recordings and likely is related to transfer or mastering.
Rereading my initial post, I se that it was misleading. If changing the networks could eliminate this minor issue, I would be pleased, but I'm not expecting it. What I'm looking for is a little more body, relaxation and air.
" The edginess is minor and infrequent and not an issue I’m particularly concerned with. I mentioned it in passing. "

I misunderstood and thought that was the issue you were working on; sorry about that.

Duke


Audiokinesis... no, "my bad." Thanks for your input about off axis energy, I'll check it out.
"Moreover, why has Merlin Audio (now defunct) experimented with their network components, before settling on the Dueland/Caddock combo?"

@pmboyd Bobby used a Hovland capacitor in that position before switching to Duelund. He mention to me at an audio show that the Duelund cap in the Zobel was a significant improvement. Its low .01uf value in the Zobel was a relatively inexpensive upgrade and did not much upset the overall price point of the speaker. He also used cryoed Caddock MP resistors and Hovland mylar capacitors throughout in the crossover. If you want to improve the speaker, consider replacing the Hovlands inside with better parts.
I considered that but it's an expensive upgrade, expensive enough to consider replacing the speakers altogether, not least of which because of the time required to open the sealed enclosure and remove and replace the extensive bracing. Instead, I thought it might be worthwhile intestigating replacing the Zobel as a inexpensive alternative. I'm generally pleased with the speakers, but want to get a sense of what the Zobel with its potential components contributes to their sound.
as "AK" mentioned sounding edgy at higher volume could mean a high amount of off axis output but there are many other potential causes.
I review of your speakers mentions the need for precise room positioning and toe-in.  This also implies that the listening position needs to be somewhat nearfield and also dedicated as lots of true monitor speakers require.  
Does it sound edgy while walking about or in different listening positions other than dead center?  They are designed to sound best listening dead center with considerable distance (4 feet or so) from side walls and optimized toe in.  
Getting the speaker and listening positions at their best is important for these speakers.  
I am experimenting with placement, however, this doesn't address my basic question which is, How much and in what specific way does the Zobel network and its component variables affect the sound of the speakers?
To reiterate, the speakers sound better with the Zobel networks engaged. The networks consist of a Dueland capacitor and a Caddock resistor. What if I changed the capacitor, say, to a Jupiter copper foil and/or the resistor to a Vishay Z foil? As long as the values are equal, would this change the tonal characteristic of the drivers or internal crossover, and if so, wouid it be a negligible change or a palpable one?
You definitely need the zoebel and might see an improvement in sound with new parts if the current cap and resistor are out of spec or defective.  
the zoebel is not a critical part of the crossover network that would lend itself to sound quality upgrades with improved quality parts.  
If you have DIY capabilities those parts should be inexpensive all things considered if you are determined to give it a try.  

Caddock MPs are 10W resistors.  Vishay/Texas Components Z-foil are .25W.  If you want to experiment, use 10W alternatives such as Path, Duelund, Mills, or ebayed Russian SSG silver mica.  
A few thoughts about the Merlin RC Networks (or Zobels).

Merlin made two types of RC’s. The “Standard RC” was made with the Hovland cap and the Caddock resistor. The “Master RC” was made with a custom spec Duelund VSF type cap and the same Caddock resistor. The caps used in both networks were the same value (0.01uF as mentioned above), but the Duelund cap costs about 10 times more than the Hovland cap (I know this because I have Duelund make me the exact same parts today as I make new Merlin Master RC networks, exactly as Merlin made them, for customers who want them today). While this makes the Master RC’s much more expensive than the Standard RCs  (which I also can make for folks), the Master RC’s do sound better.

The Merlin Zobel, interestingly, basically comes into play around 1.0Mhz (at 20KHz its impedance is around 800 ohms) and it is basically providing a way for RFI frequencies that appear at the speaker terminals to be dissipated.

IMO, since I find later/last version of Merlins made to have less coloration or noise due to improvements they have in the crossover caps, and internal wiring used - I think the effect/benefit of the Master RCs is more audible.

Duke is correct that the speakers (TSM and VSM models) have a quite flat on axis frequency response, though due to the characteristics of the soft dome tweeters Bobby used the on axis response in the treble is a little rougher on axis. The speakers were recommended/designed to be used as noted in their user manuals At around 10 to 15 degrees off axis as there is where the frequency response was the most smooth/flat. Yes, the speakers have fairly wide dispersion and some attention is generally needed if they are placed near reflective sidewalls for best mid-top frequency performance.  IMO/experience, often any edginess can be corrected with some basic room treatment or proper speaker placement (as discussed in the speaker manual). I do notice in the later models/version (i.e. “Black Magic” edition versions) of the speakers, that the speaker’s upper mid/treble performance is very clean/even/smooth. Clearly better than in older models. I don’t know if the speakers have the exact issue Duke refers to (it is possible), I think I have some off axis frequency response curves somewhere which would give a idea if that is the case or not.

Happy listening,
Rich
Rich, My MMIs are Serial numbers 4168, if that tells you anything. Your information is interesting, but it tells me nothing specific about how the RC networks and their particular components affect the sound, nor anything about how swapping components might do so.
@signaturesound That makes it sound like a worthwhile upgrade to any speaker. Could you also say what value the resistor is in the zobel circuit? I'd be interested in building a pair and trying on my coincidents. 
@pmboyd  - Sorry, hard for me to comment on something I have not tried (trial/error listening of RC Networks with various different part types/designs) as my experience is limited to the Merlin Standard RC network, the Merlin Master RC's. BUT there are other folks making RC network (Zobel) devices. One example I can think of off the top of my head is the Walker Audio High Definition links - these are a Zobel network (which I have heard, but I can't accurately recall the sonic effects they had as it was more than 15 years ago that I encountered them). So, there are other things out there to compare (the Merlin RCs) them to (if you can't DIY your own)... I will say I think that their effect DOES vary from system to system, but generally when you are damping/squashing RF that is at the speaker terminals, you are removing a layer of fuzz/haze from the sound. My thinking (2 cents) is that the resistor type plays some role (as you want something that is non-inductive and acts as a good resistor at RF frequencies) to the sound of the Zobel. The capacitor IMO is the item that has the most impact on the "sound" of the RC network. Apparently a good sounding cap for audio (coupling/bypass) use makes a good cap for a Zobel based on what I hear between the Hovland cap based RC and the Duelund cap based RC (which has a bit more cleaner/natural/organic character in my experience). - Hope that helps some.

@cal3713 The resistor value is 10 ohms (its written right on the part if you look at a pair of Merlin RCs) :-) FWIW, I use old Merlin Std RCs Networks on various speakers from time to time. The magnitude of the effect they have varies (can be very subtle to more obvious), but these days with the amount of RF floating around every home from wireless devices and switching power supplies some amount of that is bound to make its way to one's speaker terminals and it can't hurt to try a Zobel/RC to see if it can help mitigate those effects to some so nice benefit. This does assume the speaker and/or amplifier design you are using does not already have them incorporated into their designs. In my experience, most amplifiers do not have Zobels on their outputs, a few do however which is why Bobby P left the RC networks external to the speakers (doubling up RC/Zobel networks in the amp and at the speakers may make things worse, not necessarily better).

Happy listening,Rich
If they impart no sound character, why have some people commented about an improvement in exchanging components of the same values?
Confirmation bias is rampant in HiFi.

He also used cryoed Caddock MP resistors and Hovland mylar capacitors
Replace the Mylars with PolyPropylene and your problem may likely go away. It still astounds that builders compromise a design for a few pennies. Or is it ignorance?

Additionally, there is space, so you may want to try a felt donut around the tweeter to reduce off axis energy and also ameliorate diffraction effects at the box edges.

The amplifier / cable combo [don't be shy tell us what you have] may not like a certain combination of load and drive request.

There may be a resonance due to cone breakdown.

If the tweeters had ferrofluid, it maybe toast.

If there are any electrolytics in the XO, replace them with PP.

Do you have any room treatment? Or is it a far too typical plaster box?

Finally, some recordings are not playable on systems due to Monte Carlo accumulation of faults in recording, playback electronics, cables, speakers and room.

@pmboyd Another possibility could be to replace the parts with cheap value matched equivalents. Should let you evaluate the impact of part quality while only costing $5. If it makes a big difference, than spring for the duelund cap replacements.
@signaturesound Thanks! 
As I stated, I already have the Dueland networks -- the Merlin Master RCs. Evidently some people have replaced the Dueland caps with Jupiter, however, no one has responded to my queries as yet about the difference in sound. In one instance, a chap used a Jupiter in lieu of a Hovland, but he seems incapable of articulating the improvement he notred in specific terms. 
Another possibility could be to replace the parts with cheap value matched equivalents.
Drivers vary more than can be detected with matching caps.

Additionally, ALL of the PP & PS caps I've bought and tested in past few years far exceed their tolerance spec.
Confirmation bias is rampant everywhere, not just nor especially in HiFi.
@pmboyd Ahh, sorry, missed that. In my speaker (hp) crossover duelund was very superior to Jupiter. My impression across all the cap threads I've read is that that is a pretty strong consensus regardless of where people made the Jupiter-duelund comparison. Please do report back if you try. 
Finally, some recordings are not playable on systems due to Monte Carlo accumulation of faults in recording, playback electronics, cables, speakers and room.

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Wow.... what a Box-o- jumbled metaphors and kinda sorta mathematical iterative NON-SENSE!!!
 Yeah, less than desirable recording - master work, AND, YES, room acoustic interactions.
I'd strip that Zobel junk out of the system except any Zobel network inside the amplifier(s) that are there from designers mfg. all else begs problems.

Said someonenew who never recorded anything in his life and likely has fan-boy comprehension electronics - cables - speakers - room.

English is also a problem. There are no metaphors in the quoted text.

What makes a Zobel in an amplifier which may be connected to a nearly limitless combination of cables and speakers more valid than a Zobel across a speaker to tame its specific impedance curve?

Said someonenew who never recorded anything in his life and likely has fan-boy comprehension electronics - cables - speakers - room.

English is also a problem. There are no metaphors in the quoted text.
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Ah................. obviously YOU must be a gifted audiophile savant.
My gracious genuflection to your advanced understanding!
ALL cynicism genuinely intended.

My system:
Moscode Minuet in A (G. Kaye updated 2019)
AudioNote cd2
Magnepan T-1D (recoiled) mid-range -> Moscode 402AU (amp #1)
Magnepan T-1B bass panels (recoiled) bass -> Moscode 402AU (amp #2)
Sequerra T-2 ribbon tweeters (only pair made) treble -> Levinson ML-9 (amp #3)
Vendetta Research (J. Curl) X-O

Transcendent T-8 6c19p-ev OTL headphone amp
Light Speed passive pre-amp.
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Me:
Retired
electro-hydraulic servo system engineer - designer 36 yrs. 
FAA lic. AP-IA 42 yrs.
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Thats all to say.
Yawn...

Owning a GT40 would not make me Ken Miles.