Bass is also coming from the same driver that's producing midrange. The forces cancel exactly.
Displacement for an 8" driver to produce 100dB @50Hz: 7mm one-way.
Same driver at 100dB @500Hz: 0.076mm one-way.
The positions of the drivers at any given point are so similar that your point is mute.
Also, if my maths is meaningless, please bring some of your own. Perhaps it can help illustrate your point where words appear to fail.
Might I suggest that you fellas do a little reading to help you understand this phenomenon better.
Buckle ups kids, this is real math.
Modulational instability - Wikipedia, the free encyclopedia
Buckle ups kids, this is real math.
Modulational instability - Wikipedia, the free encyclopedia
Because it's the same math.
The frequencies are different, there are more peaks and dips that pass over a given point in time with higher frequencies. That's why we call it frequency, not speed.
So what happens as some of those peaks will line up with and combine with, the lower frequency peak and create a new, completely new waveform.
The frequencies are different, there are more peaks and dips that pass over a given point in time with higher frequencies. That's why we call it frequency, not speed.
So what happens as some of those peaks will line up with and combine with, the lower frequency peak and create a new, completely new waveform.
That's not what we're suggesting...
Are you being deliberately disingenuous? You keep on coming back to the same argument, providing no math, no measurements, no data to back up ANY of your assertions, and then you come up with a patently ridiculous example which is CLEARLY not what has been proposed.
NOWHERE in the multiple responses to your posts has ANYONE suggested using an open backed midrange driver in a shared enclosure with a woofer.
What IS being proposed is using two MID-WOOFERS and rolling one off at about 1KHZ and the other at 200 Hz. The phase shift created by the differing roll-off allows for more relative output of deep bass vs mid-bass. How the drivers will interact with each other is fairly well understood, and has been verified by many. There are a lot of speakers using the staggered crossover points in 2.5 or 3.5, and many of them are extremely well reviewed.
Ahh, but perhaps you have super-human hearing and can detect things no one else can. NOT LIKELY!! Looks like you are alone in your contention.
For the sake of clarity, let's address your objection: OF COURSE an open backed mid-range would be modulated by the pressure waves in the box. BUT THAT IS NOT WHAT IS BEING PROPOSED.
Back to what has been proposed by the OP, I've tried it both ways, in separate vs single volume and found the differences to be barely perceptible. Zaph has also. Same conclusion. Others here also. It works just fine. QED.
Now, to further refute your theory, Nestorovic and Modaferri devised clever systems where the drivers were different sizes and driven with deliberately different phase angles, and were able to get very deep extended and high quality bass from moderate size boxes. These were VERY high quality systems. No one ever complained about "midrange modulation" there either.
Now let me ask you to tell us all: HAVE YOU ACTUALLY TRIED ANY OF THIS? HAVE YOU ACTUALLY BUILT AND COMPARED BETWEEN THE TWO? Or is this just a pet theory that you refuse to let go of?
Just be honest. Have you ACTUALLY built and compared anything like what the OP has suggested? If not, please just 'fess up, then cease and desist.
Are you being deliberately disingenuous? You keep on coming back to the same argument, providing no math, no measurements, no data to back up ANY of your assertions, and then you come up with a patently ridiculous example which is CLEARLY not what has been proposed.
NOWHERE in the multiple responses to your posts has ANYONE suggested using an open backed midrange driver in a shared enclosure with a woofer.
What IS being proposed is using two MID-WOOFERS and rolling one off at about 1KHZ and the other at 200 Hz. The phase shift created by the differing roll-off allows for more relative output of deep bass vs mid-bass. How the drivers will interact with each other is fairly well understood, and has been verified by many. There are a lot of speakers using the staggered crossover points in 2.5 or 3.5, and many of them are extremely well reviewed.
Ahh, but perhaps you have super-human hearing and can detect things no one else can. NOT LIKELY!! Looks like you are alone in your contention.
For the sake of clarity, let's address your objection: OF COURSE an open backed mid-range would be modulated by the pressure waves in the box. BUT THAT IS NOT WHAT IS BEING PROPOSED.
Back to what has been proposed by the OP, I've tried it both ways, in separate vs single volume and found the differences to be barely perceptible. Zaph has also. Same conclusion. Others here also. It works just fine. QED.
Now, to further refute your theory, Nestorovic and Modaferri devised clever systems where the drivers were different sizes and driven with deliberately different phase angles, and were able to get very deep extended and high quality bass from moderate size boxes. These were VERY high quality systems. No one ever complained about "midrange modulation" there either.
Now let me ask you to tell us all: HAVE YOU ACTUALLY TRIED ANY OF THIS? HAVE YOU ACTUALLY BUILT AND COMPARED BETWEEN THE TWO? Or is this just a pet theory that you refuse to let go of?
Just be honest. Have you ACTUALLY built and compared anything like what the OP has suggested? If not, please just 'fess up, then cease and desist.
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That was you?
Hi Jack,
It seems much more of a compromise than a design goal. The logic of asking different drivers to produce the same frequency escapes me.
The problem with formal qualifications is that they don't teach common sense, and I'm not saying that flippantly.
Any sort of formal qualifications obtained in a subject are also not the end of the matter. Formal study and qualifications are a starting point in a field of study, not the end point. After formal study the real learning begins, and is a lifelong process...and not everyone needs that formal introduction to a subject if they are willing to put in the effort and have a knack for it.
Personally I don't take too much notice of whether someone is formally qualified or not in a field like audio or electronics, I'm more interested in their practical experience and whether they can back up what they say with solid reasoning and facts, and display a good understanding of the subject material.
I'd rather see the facts speak for themselves than people using an appeal to authority fallacy - something that is inherently problematic in a medium like an internet forum where at the end of the day we really know very little if anything about each other...anyone can say they're qualified in something with no way to verify it, so why even worry about it.
Any sort of formal qualifications obtained in a subject are also not the end of the matter. Formal study and qualifications are a starting point in a field of study, not the end point. After formal study the real learning begins, and is a lifelong process...and not everyone needs that formal introduction to a subject if they are willing to put in the effort and have a knack for it.
Personally I don't take too much notice of whether someone is formally qualified or not in a field like audio or electronics, I'm more interested in their practical experience and whether they can back up what they say with solid reasoning and facts, and display a good understanding of the subject material.
I'd rather see the facts speak for themselves than people using an appeal to authority fallacy - something that is inherently problematic in a medium like an internet forum where at the end of the day we really know very little if anything about each other...anyone can say they're qualified in something with no way to verify it, so why even worry about it.
I've deleted a few posts and Alvis has earned himself 7 days in the sin bin.Check the Modaferri patent
Have look at the Modaferri patents, http://www.pat2pdf.org/patents/pat4403112.pdf
This application looks like it could work really well to extend the low bass response in a given enclosure size, more than with traditional size/efficiency sealed or vented enclosure. The price to be paid is that of needing a second woofer and motor structure plus the associated phase shift networks. But it does away with ports and chuffing, or passive radiators etc, etc.
One advantage that looks significant is the much more linear and resistive impedance function in the bass region.
Makes it much easier to drive, especially for low damping tube amps, etc.
It'd be very interesting to actually build a pair of Modaferri variants. I've only built 2.5 types using the 2nd woofer to compensate for baffle lift, but that's using only one large single coil to roll off the mids. I also used staggered filters on a single mid-bass driver using a Focal Kevlar dual voice coil. Worked well up to the limits of the driver's excursion.
I haven't yet tried a more radical phase shift along the lines of what Modaferri showed. I'll get around to that once I've finished up my new OB speakers.
Aside from the extended bass, I'm wondering how the Modaferri approach would do with transient response and distortion characteristics. Regular 2.5 type enclosures seem to perform pretty much like 2 drivers in parallel, but with the more extreme phase shift Modaferri examples, I wonder if it would be suitable for reproducing anything beyond 250Hz or so.
So Modaferri's old patent really looks like an interesting tool in the 2.5 arsenal. And since it's just a matter of tuning the phase shifting network, the OP could play with this variant without incurring too much extra expense or effort.
It's all about extending the low bass - or is it?
Have look at the Modaferri patents, http://www.pat2pdf.org/patents/pat4403112.pdf
This application looks like it could work really well to extend the low bass response in a given enclosure size, more than with traditional size/efficiency sealed or vented enclosure. The price to be paid is that of needing a second woofer and motor structure plus the associated phase shift networks. But it does away with ports and chuffing, or passive radiators etc, etc.
One advantage that looks significant is the much more linear and resistive impedance function in the bass region.
Makes it much easier to drive, especially for low damping tube amps, etc.
It'd be very interesting to actually build a pair of Modaferri variants. I've only built 2.5 types using the 2nd woofer to compensate for baffle lift, but that's using only one large single coil to roll off the mids. I also used staggered filters on a single mid-bass driver using a Focal Kevlar dual voice coil. Worked well up to the limits of the driver's excursion.
I haven't yet tried a more radical phase shift along the lines of what Modaferri showed. I'll get around to that once I've finished up my new OB speakers.
Aside from the extended bass, I'm wondering how the Modaferri approach would do with transient response and distortion characteristics. Regular 2.5 type enclosures seem to perform pretty much like 2 drivers in parallel, but with the more extreme phase shift Modaferri examples, I wonder if it would be suitable for reproducing anything beyond 250Hz or so.
So Modaferri's old patent really looks like an interesting tool in the 2.5 arsenal. And since it's just a matter of tuning the phase shifting network, the OP could play with this variant without incurring too much extra expense or effort.
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I appreciate the link. I am still wondering why one would consider doing this with different drivers. It's hard enough to match two of the same so I can't imagine the headaches in trying to match different units. I realize matching is more important the higher the frequency but I am still sensitive to lower as well and I just see it as starting down the wrong path and then having to try and 'fix' it from that point on.
Anyway, I'm not sure there will be a consensus on this so perhaps we can leave it there.
Cheers.
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