Even in the best case, the mutual coupling between the coils is unlikely to be excellent. One might just be able to get some signal with some correlation and galvanic isolation.
I think the thought has passed many thinking minds.
In all simplicity it is just a 4 layer coil split to 2 connections.
So your losing half the coil it was designed to have.
In high SPL situations cone area can get doubled.
Going opposite for low level.
Just the old trick of using 2 woofers seems feasible to reduce distortion.
Not including the quality of drivers theses days.
Is it really that bad?
But admit the theory or idea sounds nice if it worked
In all simplicity it is just a 4 layer coil split to 2 connections.
So your losing half the coil it was designed to have.
In high SPL situations cone area can get doubled.
Going opposite for low level.
Just the old trick of using 2 woofers seems feasible to reduce distortion.
Not including the quality of drivers theses days.
Is it really that bad?
But admit the theory or idea sounds nice if it worked
Yeah the "using the second coil" idea is definitely up in the air at this point. For ***** and gigs, I would like to at least see what the signal looks like from the second coil if I only drive one of them (hence the o-scope).
@bentoronto
So called HIFI is about a majority that buy's stuff. As long as people do not know how good music sounds. reproduced from good speakers, they will buy what the industry serves them. Marketing is not about giving true information and educating consumers, but all about selling cheap build low quality stuff for the higest price possible.
High End is something else. It is an island of really high quality sound reproduction, swimming in a sea of snake oil. Most people here try to not get their feet wet 🙂 , even if that is not easy.
If objectively best sound quality would win, MFB would be a standard for any low frequency driver.
You even can control the cone movement of high frequency drivers, as Backes&Müller did in the 80's.
Marketing has been able to convince the majority of listeners that sound doesn't matter, maybe not even exists. Some ear pods and an iPhone is all you need. If you visit a life concert of the newer artists, you may get the impression the sound engineer ist 100% deaf. The kids don't care. They think the sound has to be this way, with bloated bass, not even syncronized to the music.
There is another human factor, which play's into the industries hands and makes people ignore good sound.
Good sound needs knowledge, some work and money. Most don't want to learn anything, don't want to work and are unable to spent money. So instead of commiting to be stupid, lazy and poor (the new holy trinity), they just promote the idea that sound quality above ear pod level is not neccesary or even existing.
Something that recently gave me a little hope. I just finished to repair an old car audio installation. The once extremely expensive Pioneer PR-88RS head unit, with 3-way, DSP- microphone corrected active x-over, broke down and the woofer made ugly noises..
I was quite surprised to find a new head unit, even from Pioneer, only missing the automated equalizing, but with 3-way x-over and time alignment, telephone, digital radio and any gimmik you can think of, for just 150€ new. Just about 1/10 the price of the old one, with many more functions and really good sound. The defective 12" woofer was replaced by an Alpine produkt, for 90€. Steel basket, but perfekt TSP and high linear excursion. So there seems to be a tight corner where high quality at fair prices still exist.
So called HIFI is about a majority that buy's stuff. As long as people do not know how good music sounds. reproduced from good speakers, they will buy what the industry serves them. Marketing is not about giving true information and educating consumers, but all about selling cheap build low quality stuff for the higest price possible.
High End is something else. It is an island of really high quality sound reproduction, swimming in a sea of snake oil. Most people here try to not get their feet wet 🙂 , even if that is not easy.
If objectively best sound quality would win, MFB would be a standard for any low frequency driver.
You even can control the cone movement of high frequency drivers, as Backes&Müller did in the 80's.
Marketing has been able to convince the majority of listeners that sound doesn't matter, maybe not even exists. Some ear pods and an iPhone is all you need. If you visit a life concert of the newer artists, you may get the impression the sound engineer ist 100% deaf. The kids don't care. They think the sound has to be this way, with bloated bass, not even syncronized to the music.
There is another human factor, which play's into the industries hands and makes people ignore good sound.
Good sound needs knowledge, some work and money. Most don't want to learn anything, don't want to work and are unable to spent money. So instead of commiting to be stupid, lazy and poor (the new holy trinity), they just promote the idea that sound quality above ear pod level is not neccesary or even existing.
Something that recently gave me a little hope. I just finished to repair an old car audio installation. The once extremely expensive Pioneer PR-88RS head unit, with 3-way, DSP- microphone corrected active x-over, broke down and the woofer made ugly noises..
I was quite surprised to find a new head unit, even from Pioneer, only missing the automated equalizing, but with 3-way x-over and time alignment, telephone, digital radio and any gimmik you can think of, for just 150€ new. Just about 1/10 the price of the old one, with many more functions and really good sound. The defective 12" woofer was replaced by an Alpine produkt, for 90€. Steel basket, but perfekt TSP and high linear excursion. So there seems to be a tight corner where high quality at fair prices still exist.
For MFB speaker, there is a lot of information on this forum. To use one of the two coils of a dual sub is a very bad idea. With MFB you need a lot of power. To half the driving force of a 2-coil woofer, is just plain stupid. Even more on this special woofer principle, which depends on two voice coils.
The best practical ways of MFB are the simple resistor, an acceleration sensor or a pressure detecting microphone in the center of a cone.
You can think of much more complicated options, like a variable capacitor, optical detection or some laser monitoring of the cone movement.
Most solutions are overkill for MFB of a woofer, as the speed of a cone at 10-200Hz is quite low, compared to modern measuring hardware.
Also, the principle has to be robust, easy to adjust and quite cheap.
The best practical ways of MFB are the simple resistor, an acceleration sensor or a pressure detecting microphone in the center of a cone.
You can think of much more complicated options, like a variable capacitor, optical detection or some laser monitoring of the cone movement.
Most solutions are overkill for MFB of a woofer, as the speed of a cone at 10-200Hz is quite low, compared to modern measuring hardware.
Also, the principle has to be robust, easy to adjust and quite cheap.
I guess that means my middle name is moist 🤪
When I go to work, I usually have my Fiio on me with my sennheiser iems. Whenever I have that conversation (and it occurs quite often) I always have evidence to the contrary. It's always the same reaction: eyes wide, jaw dropped, etc. The real shame is, like you said, people don't even know this level of fidelity exists. And yes, you don't always need to spend an arm and a leg. I owned a set of ATH-M50s for almost a decade before I upgraded to my grados. Heck, even grado has some good affordable options for folks who don't want to spend the mad money enthusiasts are willing to spend.
My biggest worry is, while I do like the piratelogic sensors, I'm not quite sure about removing the dust cap of a carbon fiber cone. That's why I've been looking to a few more... exotic options... that and apparently I'm a glutton for punishment lol
Today woofer have evolved to what is physicaly possible, with the downside of huge power demand. Yes, MFB is superior, if you want very small cabinets or very low response from a small woofer. On the other side, you can get great results just by using modern woofers in the right way.
MFB is not the only way for a good low end. You can have excelent results without it.
A twin voice coil woofer can be driven by two amps, because of the low coil resistance it can take a lot of power.
Personaly I would reserve them for very special cases, for example when amplifier voltage is limited. Using them passive reduces them to two coils connected for a civilised 4 Ohm resistance or a very complicated x-over is needed. Which is a costly, complicated thing.
In general, passive speakers with refined x-overs have become some kind of questionable. If you are in DIYS territory a 4-way DSP is cheaper than a copper coil for a bass driver. A small hand full of boutique capacitors costs more than six D-amps with the SMPS powering them.
If you are not ideologicaly blinded, today a well made chip amp sounds better than many high $ amps of the past. It is a bit sad, when I look at my old, heavy amps, but this is a reality.
MFB is not the only way for a good low end. You can have excelent results without it.
A twin voice coil woofer can be driven by two amps, because of the low coil resistance it can take a lot of power.
Personaly I would reserve them for very special cases, for example when amplifier voltage is limited. Using them passive reduces them to two coils connected for a civilised 4 Ohm resistance or a very complicated x-over is needed. Which is a costly, complicated thing.
In general, passive speakers with refined x-overs have become some kind of questionable. If you are in DIYS territory a 4-way DSP is cheaper than a copper coil for a bass driver. A small hand full of boutique capacitors costs more than six D-amps with the SMPS powering them.
If you are not ideologicaly blinded, today a well made chip amp sounds better than many high $ amps of the past. It is a bit sad, when I look at my old, heavy amps, but this is a reality.
Pirate logic IMO makes some mistakes. First they are fixated on small woofer. Second they make things seem quite complicated.
Next, selling unpopulated PCB's is not state of the art any more. Having such a PCB populated, in China, where they are done anyway, is only a few Cent, a tiny fraction of the cost of a parts order at Mouser or the like. For one P-L MFB board, it may not even be half of the P&P any European or US retailer charges.
If you really want to fit MFB to this carbon woofer, go for the small "ClingON". There is no need to mount it at a place inside the chassis you can not reach with your fingers. Just glue it on the cone, where it meets the dust cap, drill a small hole to route the connection wire inside (must be a very flexible version) and you are done. Epoxy glue is the best to do this. This way you do not risk to ruin the woofer. You can even use it without MFB, if it fails, the little extra wheigt on the cone is not critical.
Next, selling unpopulated PCB's is not state of the art any more. Having such a PCB populated, in China, where they are done anyway, is only a few Cent, a tiny fraction of the cost of a parts order at Mouser or the like. For one P-L MFB board, it may not even be half of the P&P any European or US retailer charges.
If you really want to fit MFB to this carbon woofer, go for the small "ClingON". There is no need to mount it at a place inside the chassis you can not reach with your fingers. Just glue it on the cone, where it meets the dust cap, drill a small hole to route the connection wire inside (must be a very flexible version) and you are done. Epoxy glue is the best to do this. This way you do not risk to ruin the woofer. You can even use it without MFB, if it fails, the little extra wheigt on the cone is not critical.
I do not see why the idea is "bad". And there is certainly nothing wrong with trying. It won't be an easy straigth road. But if I see other projects here....
MFB was done by Philips. I guess it never was a great succes then because of the need to set up each speaker-filter system individually. Tolerances in speaker manufacturing and analog electronics being what they were/are. And then you have the thing that you can only do this in active systems. Expensive in those days.
MFB was done by Philips. I guess it never was a great succes then because of the need to set up each speaker-filter system individually. Tolerances in speaker manufacturing and analog electronics being what they were/are. And then you have the thing that you can only do this in active systems. Expensive in those days.
Oh definitely doing active. A while ago someone explained to me how my mid and tweeter were 10db more sensitive than my sub. At that point, went active.
I was thinking of doing DSP for a while, but the way I would want to do it is expensive and the learning curve is a but steeper than even what in doing now.
Sub is going to be driven with a TPA3255. Definitely settled on that. Still debating on whether I should just get a dev board or make it myself.
I'm not sure that's going to be a option either. The shape of the cone itself is damn near completely curved. Another reason I ordered a sacrificial woofer was so I could get a better feel for what I'm working with (leaving the good ones packed for now until the final build).
I don't think it was so much that as the fact it just never caught on. Plenty of companies implement it today with great results. @perrymarshall earlier in the conversation was talking about how he was working on them for a company as well. Mainstream companies a lot of times will only pay attention to that sort of thing if it's cost effective.
Thanks for the info 🙂 Lots of good stuff. Two questions: 1) What was your test set up? 2) Were you using them actively or passively?
I used a S&L WT2 to measure impedance.
I used Passive Crossover Designer for the model.
I used the components as a pending future passive xover primer for this woofer.
The initial goal was to see what was required to keep the parallel 2 ohm nominal impedance benign for a 4 ohm stable amplifier, while gaining initial sensitivity and not having to start at an already too low sensitivity point. Since the driver has dual coils, I was trying to take advantage of what it has and make it work for me.
There is no reason you can't use the 2 or 3 components specified for this driver and use the specified box alignment to make it work on a 4 ohm amplifier with lower power requirements than were you to run it wired in series. Therefore, it is still valid.
I used Passive Crossover Designer for the model.
I used the components as a pending future passive xover primer for this woofer.
The initial goal was to see what was required to keep the parallel 2 ohm nominal impedance benign for a 4 ohm stable amplifier, while gaining initial sensitivity and not having to start at an already too low sensitivity point. Since the driver has dual coils, I was trying to take advantage of what it has and make it work for me.
There is no reason you can't use the 2 or 3 components specified for this driver and use the specified box alignment to make it work on a 4 ohm amplifier with lower power requirements than were you to run it wired in series. Therefore, it is still valid.
I don't doubt it. Unfortunately for me, the chip amp I'm going to use for it apparently does not like to be used at 2 ohms (at least according to TI).
It's not a 2 ohm load, even though it is in parallel. The driver is 2 ohms in parallel, but the circuit keeps all but one place above 3 ohms, and that one spot at 2.7 ohms. This should be benign enough for most 4 ohm stable amplifiers. That is what I'm trying to tell you. With the circuit in tow, 4 ohms amps are fine.
I was pretty happy with it. The biggest issue is noise which is manageable but requires close attention. I used it with small high xmax 12” subs in 30 liter boxes. Natural Fb 48hz, extended flat to 18Hz with decreased distortion.