To put it more proper terms, the Qts is the "combined effort" from both damping characteristics.
Mathematically, it is the parallel combination that can be expressed in two seemingly different yet identical forms:
Qts =(Qms x Qes)/(Qms+Qes)
Or
Qts = 1/((1/Qms)+(1/Qes))
It's all hidden in things called books.
Mathematically, it is the parallel combination that can be expressed in two seemingly different yet identical forms:
Qts =(Qms x Qes)/(Qms+Qes)
Or
Qts = 1/((1/Qms)+(1/Qes))
It's all hidden in things called books.
Yeah, I know. I'm not averse to reading books, and in fact I'm pretty much always reading some text or other as part of the research component of my own work. As desirable as it might be, I haven't yet figured out how to get the time to develop a level of expertise across a range of very diverse fields of study.It's all hidden in things called books.
I would respectfully argue that a driver with low Qts has an EARLIER rolloff with respect to frequency, rather than a steeper rolloff. I guess it all just depends how you're used to modeling things.
However, he does mistake microhenries for millihenries. mH=millihenries=thousandths of a henry (not millionths).
Q is something that pops up in all fields of engineering. All that Q is, which stands for Quality Factor, is the measure of how readily something can be excited and stay excited. The best analogy is a bell or gong. When you ring a bell, it resonates and resonates until eventually it tapers off. The reason it tapers off is due to losses in the system. The higher the Q, the lower the losses OR the higher the ability for the device to overcome its losses.
For the bell analogy, a bell with an infinite Q would ring absolutely on forever and ever. This of course, doesn't happen. Whenever you introduce any sort of damping or resistance, the Q falls. Think of it like this: you have a small sleigh bell, and you have a church bell. Which one, if struck once, is going to resonate for longer? The church bell. Why? Mechanical Q is directly related to mass. Higher mass = higher Q. That iron church bell, once excited is only going to stop ringing (assuming the metal is lossless) due to the resistance of the air around it.
That tiny sleigh bell, however, is much more strongly affected because the ratio of its own mass to the amount of air around it is much, MUCH lower. Another analogy is a gong. The larger the gong, the longer it takes for it to stop ringing. These items are high Q items. However, if you hold your hand on any bell or gong as you strike it, you have introduced an extreme amount of damping, and the resonance stops almost immediately. They are now low Q items.
For a loudspeaker, mechanical Q, Qms, is related to moving mass, and inversely related to resistive loss, Rms. That is: much like a heavy church bell, the higher the diaphragm mass, the higher the Qms, and much like holding on to the gong, the higher the damping, the lower the Qms. Think of Qms as if you were to just take the moving components as is, how easily would they come to rest. Suspension comes into play also: higher stiffness yields lower Qms. This is because Qms = 2pi * (Fs * Mms)/Rms.
Now, electrical Q, Qes, is a bit tougher. The same principle applies here, with the dominating factor being the motor. How quickly the driver can accelerate is directly a function of the force applied to the cone via F = ma. F is BL * i, where i is the current in the voice coil. m in this case is Mms. The higher the BL, the greater the ability for the cone to accelerate and decelerate. A high Q electrical system however, would accelerate and then take a long time to decelerate to zero because the motor can't apply the force it needs to control it.
For this reason, higher Qes drivers are usually put into sealed boxes where the added stiffness of the enclosure helps to control cone movement. While Qes is again directly related to Fs and Mms, it's inversely related to (BL)^2. To iterate again: the motor is king here. Qes therefore is the ability for the electrical components of the driver to control the cone motion, while Qms is the ability of the mechanical components to control cone motion. These abilities are affected by the losses in the system, so the higher the Q, the greater the ability to overcome losses OR the lower the overall loss in the system (call it damping, resistive loss, whatever you wish).
Higher vs. lower Q preference is entirely dependent on the setup, so do not get stuck in thinking ultra low Q = super controlled bass!
Hopefully this helps some, and if not, let me know and I'll try to clarify.
For the bell analogy, a bell with an infinite Q would ring absolutely on forever and ever. This of course, doesn't happen. Whenever you introduce any sort of damping or resistance, the Q falls. Think of it like this: you have a small sleigh bell, and you have a church bell. Which one, if struck once, is going to resonate for longer? The church bell. Why? Mechanical Q is directly related to mass. Higher mass = higher Q. That iron church bell, once excited is only going to stop ringing (assuming the metal is lossless) due to the resistance of the air around it.
That tiny sleigh bell, however, is much more strongly affected because the ratio of its own mass to the amount of air around it is much, MUCH lower. Another analogy is a gong. The larger the gong, the longer it takes for it to stop ringing. These items are high Q items. However, if you hold your hand on any bell or gong as you strike it, you have introduced an extreme amount of damping, and the resonance stops almost immediately. They are now low Q items.
For a loudspeaker, mechanical Q, Qms, is related to moving mass, and inversely related to resistive loss, Rms. That is: much like a heavy church bell, the higher the diaphragm mass, the higher the Qms, and much like holding on to the gong, the higher the damping, the lower the Qms. Think of Qms as if you were to just take the moving components as is, how easily would they come to rest. Suspension comes into play also: higher stiffness yields lower Qms. This is because Qms = 2pi * (Fs * Mms)/Rms.
Now, electrical Q, Qes, is a bit tougher. The same principle applies here, with the dominating factor being the motor. How quickly the driver can accelerate is directly a function of the force applied to the cone via F = ma. F is BL * i, where i is the current in the voice coil. m in this case is Mms. The higher the BL, the greater the ability for the cone to accelerate and decelerate. A high Q electrical system however, would accelerate and then take a long time to decelerate to zero because the motor can't apply the force it needs to control it.
For this reason, higher Qes drivers are usually put into sealed boxes where the added stiffness of the enclosure helps to control cone movement. While Qes is again directly related to Fs and Mms, it's inversely related to (BL)^2. To iterate again: the motor is king here. Qes therefore is the ability for the electrical components of the driver to control the cone motion, while Qms is the ability of the mechanical components to control cone motion. These abilities are affected by the losses in the system, so the higher the Q, the greater the ability to overcome losses OR the lower the overall loss in the system (call it damping, resistive loss, whatever you wish).
Higher vs. lower Q preference is entirely dependent on the setup, so do not get stuck in thinking ultra low Q = super controlled bass!
Hopefully this helps some, and if not, let me know and I'll try to clarify.
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Yeah basically,
and because the volume of the air, and whether or not its ported/sealed will depend on the electrical and physical properties of the driver you're using
THANK U!
So at a glance is it possible to eliminate some drivers from consideration just because their listed Qts is too low or too high? If a Qts is about 0.4 vs 1.5, would this driver be more at home in a small vented or sealed? Or large enclosure, say over 2 ft3 for sealed and 4 ft3 for vented? I know this has been talked about before, but my searching came up with nothing.
So at a glance is it possible to eliminate some drivers from consideration just because their listed Qts is too low or too high? If a Qts is about 0.4 vs 1.5, would this driver be more at home in a small vented or sealed? Or large enclosure, say over 2 ft3 for sealed and 4 ft3 for vented? I know this has been talked about before, but my searching came up with nothing.
Well, some folks rely on a driver's EBP, though doesn't work too well for TL, horn variants IME: https://www.diyaudioandvideo.com/Calculator/SealedVsPortedSpeakerBox/
GM
GM
The Rice-Kellogg type driver is actuated by motion rather than position. Therefore it has its own spring to restore its position to neutral. Sounds like stupid engineering but there you have it in 1924 before servo theory or servo components.
With a spring you have bounce. Since there is no feedback around the driver (stupid again, eh) you need damping. And to make matter worse, the oscillation frequency of the these woofer drivers the way they are built today is right smack in the audible woofer range (like 35 Hz, for example). Stupid again, eh.
For some reason, manufacturers haven't explored mechanical damping much. You think you could add some magnetic goo to the driver or maybe an oil dashpot like the dual SU carbs my 1960 Jaguar had? Today, power is cheap and efficient. But driving a speaker from an amp that acts like a dead-short maximizes the damping effect of the voice coil and is universally used* except for those of us with negative output impedance amps (an obvious consequence of motional feedback) which work vastly better.
Since that is the case, you need to address the springiness or your speaker will boom terribly. That's why some smart manufacturers have tried motional feedback: still tricky to manufacture but clearly the future for Rice-Kellogg drivers.
But back to your question.
If you plot the motion of the cone (AKA frequency response) you can see plain as day the oscillation bump. "Q" is simply a description of the height of the bump relative to the width, either (a) without electrical connections, (b) with a dead short on the voice coil, or (c) total (and they add in parallel as I am sure you know). I could have the definition off, but that's the concept. A lower Q means a low, flat, and/or wide bump and a higher Q mean peaky and boomy.
Anybody can see that you want your speaker to have no character of its own. After all, its job is to "reproduce" music not to "produce" sound of its own. Therefore, you want the tiniest Q possible. The notion of "critical" damping is just a propagandistic play on the swell word "critical" (meaning, just one bounce). Nothing particularly desirable about "critical" damping in a speaker.
In practice, people are prepared to live with a bit of Q in exchange the bit of boost it gives the output. But you can make that choice yourself.
Ben
*Electrostatic speakers have a different situation.
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Because there isn't really much need too. Once it's connected to a powered up amplifier with its typically low output impedance, the current that flows through the driver's coil as soon at is moves (because it's sitting in a magnetic field) provides a significant amount of damping (that's what the Qes component in the t/s parameters refers to). Usually more than enough for its use.
Even more interesting, in control systems terms (one of the engineering fields I studied too many years ago), any system with a "Q" of less than 0.5 is actually considered to be over-damped, i.e. *** takes too long to return to its rest position when disturbed *** . As this describes a significant amount of bass drivers available (Qts<0.5), one could argue that many of them are actually TOO damped until they are put into an alignment that drives that "Q" up.
Damping per se isn't the issue. "Q" and the frequency location of oscillation are the issues. But the basic issue is stupid engineering.
With automobile suspension, you have to face a vast broad frequency range. Currently cars are moving to active suspensions and whole lot faster than speaker development is moving. Seems to me that the challenge is not nearly so great with audio where you can divide-and-conquer the audio range.
If the Rice-Kellogg model is best we can do today, maybe audio enthusiasts should aim for subwoofers with sub-subwoofers? Might solve a lot of design riddles.
Ben
Ben
With automobile suspension, you have to face a vast broad frequency range. Currently cars are moving to active suspensions and whole lot faster than speaker development is moving. Seems to me that the challenge is not nearly so great with audio where you can divide-and-conquer the audio range.
If the Rice-Kellogg model is best we can do today, maybe audio enthusiasts should aim for subwoofers with sub-subwoofers? Might solve a lot of design riddles.
Ben
Ben
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Interesting connection you made there Ben, looking forward to 'damping bypass adjustment' on subwoofer drivers.
And the answer is: motional feedback.Interesting connection you made there Ben, looking forward to 'damping bypass adjustment' on subwoofer drivers.
Having an intuitive grasp about car and bike suspensions can bring insight into speaker building. All the same concepts albeit in different perspectives. And as USRFobiwan says, maybe there's a knob missing on speakers?
I'd compare the sophistication of a modern Koni suspension to a modern cone woofer. Both embody cumulative minor improvements compared to maybe 1950.
So in light of USRFobiwan's critique, what "knobology" would members of this forum speculate to have to control their speakers more to their liking or to the music source?
Anybody want to try? If your answer is "none", why do you think so?
B.
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