prochobo
10+ year member
Sedan Sleeper
bcae1.com
What do you wish to know about them? What they describe? How they are calculated? How it relates to a speaker's sonic footprint? Expand a bit here and I'll do the same, in turn, for you.
- Thread Starter
- #4
Actually, I'd like to learn or at least read about all of that. But first lets start with what they describe. Thanks!
- Thread Starter
- #5
Thanks
- Thread Starter
- #7
Direct copy of the information on Eminence's site. I am looking for a little more than that. Thanks though.
The physical interpretation is instructive.
in free air, the motion of the cone is defined by the following:
Mass
Compliance (springiness)
losses.
notice that a moving mass wants to stay moving forward.
notice that a stretched spring wants to move backward (toward rest position)
notice that losses just want to stop things.
so lets say i push the cone all the way in, and let it loose. To do this, I've stored energy in the compliance -- it acts a spring and will force the cone toward rest.
So the spring starts transfering energy to the mass (to make it move). the cone accelerates. It reaches the rest position. but the cone is moving too fast! the moving mass keeps the cone moving, and transfers energy back into the compliance, to stretch the spring from its rest position.*
how long does this happen? from the above, no energy is lost, so the cone would wobble around forever. but there are losses in the speaker, so on each pass, energy will be removed.
this is the foundation of "Q", which is the "Quality" of a resonator. the above example would be a high-quality resonator -- the cone never stops resonating.
a low Q system is one where there is significant loss.
In a speaker, the mechanical Q is high -- the speaker acts a resonantor fairly well. The electrical Q is low though. Because energy is "transduced" from electrical to mechanical, the electrical system can generate losses that in turn damp out the wobbling, providing a higher amount of control over the cone.
* knowing mass and compliance allows one to determine the rate at which this happens, or Fs.
edit -- the remaining specs of interest are Qts, which is a combination of electrical and mechanical Q, as well as Vas, which allows one to determine how box size will affect compliance, and how Qts and Fs will scale as the speaker is placed into a box that is smaller than a field.
this is not the rigorous version, there is of course a fair bit of math behind this.
in free air, the motion of the cone is defined by the following:
Mass
Compliance (springiness)
losses.
notice that a moving mass wants to stay moving forward.
notice that a stretched spring wants to move backward (toward rest position)
notice that losses just want to stop things.
so lets say i push the cone all the way in, and let it loose. To do this, I've stored energy in the compliance -- it acts a spring and will force the cone toward rest.
So the spring starts transfering energy to the mass (to make it move). the cone accelerates. It reaches the rest position. but the cone is moving too fast! the moving mass keeps the cone moving, and transfers energy back into the compliance, to stretch the spring from its rest position.*
how long does this happen? from the above, no energy is lost, so the cone would wobble around forever. but there are losses in the speaker, so on each pass, energy will be removed.
this is the foundation of "Q", which is the "Quality" of a resonator. the above example would be a high-quality resonator -- the cone never stops resonating.
a low Q system is one where there is significant loss.
In a speaker, the mechanical Q is high -- the speaker acts a resonantor fairly well. The electrical Q is low though. Because energy is "transduced" from electrical to mechanical, the electrical system can generate losses that in turn damp out the wobbling, providing a higher amount of control over the cone.
* knowing mass and compliance allows one to determine the rate at which this happens, or Fs.
edit -- the remaining specs of interest are Qts, which is a combination of electrical and mechanical Q, as well as Vas, which allows one to determine how box size will affect compliance, and how Qts and Fs will scale as the speaker is placed into a box that is smaller than a field.
this is not the rigorous version, there is of course a fair bit of math behind this.
- Thread Starter
- #9
Aw, yes. I'm familiar with the basics (basic basics!) of oscillating systems, but never quite knew it related to woofer Q. Thanks!
I'm kind of on the run so I'll try to get through this quickly.
First thing that is critical in understanding is how they are derived mathematically. Note that there are only 5 basic thiele/small parameters that all others are derived from; these are BL, Cms, Re, Sd, and Mms. So...
Qms = Sqrt(Mms)/(Rms*Sqrt(Cms))
Qes = Re*Sqrt(Mms)/(BL^2*Sqrt(Cms))
Qts = Qes*Qms/(Qes+Qms)
First thing that is abundantly clear is how Qes dominates the total Q of a driver. Obviously changes in the Qes will have the greatest impact on Qts.
Looking at the equation for Qes, it's very easy to define. A lot of people use Qes as a method of describing motor strength (ie. low Qes means high motor strength) but that is simply an inaccurate statement. Yes, low Qes *may* indicate high BL (as seen in BL^2 as a divisor) but it may also indicate very low Mms. Realistically, it represents the electromagnetic ratio of energy stored vs. power dissipated. Again, the equation clearly demonstrates that:
A doubling of Re will result in a doubling of Qes.
A quadrupling of Mms will result in a doubling of Qes.
A doubling of BL will result in a quartering of Qes.
A quadrupling of Cms will result in a halving of Qes.
Looking at the equation for Qms, it is equally easy to define. We can see that:
A quadrupling of Mms will result in a doubling of Qms.
A doubling of Rms will result in a halving of Qms.
A quadrupling of Cms will result in a halving of Qms.
Qms and Qes are valuable only in that they provide you Qts. In my opinion, they don't really hold their own inherent importance as they only relate to half of the total damping characteristics of a driver. Using Qts, it is easier to identify an ideal enclosure for a driver, in terms of both enclosure orientation (ie. sealed, bass-reflex, etc.) and in terms of the size of the enclosure.
When determining the best enclosure orientation, however, there are many factors to be considered. Quite often, you will here people utilize the EBP of a driver in a process of elimination (EBP is given by Fs/Qes and comparing against empirically suggested values). To me, EBP is a useless extra calculation: the same basic parameters used to calculate EBP are utilized in Qts, thus, if we can determine the appropriate enclosure for a given Qts, there is no need for an EBP. However, as with all things, there is no specific answer and the enclosure is largely application dependent.
In a traditional sense, many people find a high Qts (0.5 or above) indicative of a sealed or infinite baffle enclosure; Qts 0.4 to 0.5 is often considered the middle ground between sealed and ported, while Qts less than 0.4 is often considered most suitable for a bass-reflex or higher order bandpass design. Low Qts in any enclosure utilizing a port is probably a good idea; the driver will see an increase in resonance and the damping provided by a low Qts design is worthwhile. However, low Qts drivers are proving more appealing in sealed enclosures as of late. The 15" Mag from Stereo Integrity is a fine example of this. Likewise, very low Qts designs are proving very appealing in infinite baffle applications, so long as Fs and the inherent low end extension is sufficient.
These are just generalizations and we can probably go into a bit more depth if you'd like. Let me know what you think and maybe provoke some further thinking on my part, if you don't mind. Anything need clarification, correction, or expansion?
First thing that is critical in understanding is how they are derived mathematically. Note that there are only 5 basic thiele/small parameters that all others are derived from; these are BL, Cms, Re, Sd, and Mms. So...
Qms = Sqrt(Mms)/(Rms*Sqrt(Cms))
Qes = Re*Sqrt(Mms)/(BL^2*Sqrt(Cms))
Qts = Qes*Qms/(Qes+Qms)
First thing that is abundantly clear is how Qes dominates the total Q of a driver. Obviously changes in the Qes will have the greatest impact on Qts.
Looking at the equation for Qes, it's very easy to define. A lot of people use Qes as a method of describing motor strength (ie. low Qes means high motor strength) but that is simply an inaccurate statement. Yes, low Qes *may* indicate high BL (as seen in BL^2 as a divisor) but it may also indicate very low Mms. Realistically, it represents the electromagnetic ratio of energy stored vs. power dissipated. Again, the equation clearly demonstrates that:
A doubling of Re will result in a doubling of Qes.
A quadrupling of Mms will result in a doubling of Qes.
A doubling of BL will result in a quartering of Qes.
A quadrupling of Cms will result in a halving of Qes.
Looking at the equation for Qms, it is equally easy to define. We can see that:
A quadrupling of Mms will result in a doubling of Qms.
A doubling of Rms will result in a halving of Qms.
A quadrupling of Cms will result in a halving of Qms.
Qms and Qes are valuable only in that they provide you Qts. In my opinion, they don't really hold their own inherent importance as they only relate to half of the total damping characteristics of a driver. Using Qts, it is easier to identify an ideal enclosure for a driver, in terms of both enclosure orientation (ie. sealed, bass-reflex, etc.) and in terms of the size of the enclosure.
When determining the best enclosure orientation, however, there are many factors to be considered. Quite often, you will here people utilize the EBP of a driver in a process of elimination (EBP is given by Fs/Qes and comparing against empirically suggested values). To me, EBP is a useless extra calculation: the same basic parameters used to calculate EBP are utilized in Qts, thus, if we can determine the appropriate enclosure for a given Qts, there is no need for an EBP. However, as with all things, there is no specific answer and the enclosure is largely application dependent.
In a traditional sense, many people find a high Qts (0.5 or above) indicative of a sealed or infinite baffle enclosure; Qts 0.4 to 0.5 is often considered the middle ground between sealed and ported, while Qts less than 0.4 is often considered most suitable for a bass-reflex or higher order bandpass design. Low Qts in any enclosure utilizing a port is probably a good idea; the driver will see an increase in resonance and the damping provided by a low Qts design is worthwhile. However, low Qts drivers are proving more appealing in sealed enclosures as of late. The 15" Mag from Stereo Integrity is a fine example of this. Likewise, very low Qts designs are proving very appealing in infinite baffle applications, so long as Fs and the inherent low end extension is sufficient.
These are just generalizations and we can probably go into a bit more depth if you'd like. Let me know what you think and maybe provoke some further thinking on my part, if you don't mind. Anything need clarification, correction, or expansion?
- Thread Starter
- #11
Thanks man. I understand everything and would very much like to take are more technical approach to this. If you've got something else to say I'd love to hear it. And feel free to take your time with it as well.
Thanks!
What aspects? are you interested more in the practical use aspects, the physical interpretation, or the signal theory aspects.
keep in mind that T/S is small signal analysis -- valid for small signals. at high power levels, the speaker may behave significantly differently.
keep in mind that T/S is small signal analysis -- valid for small signals. at high power levels, the speaker may behave significantly differently.
How so?
How can you model it?
- Thread Starter
- #14
Quite honestly I'd like to learn about all three, but lets start with practical use aspects, since its.......more practical.
I pose the same questions to you as Flipx99. How do they change, what do they change to, why and what is the end result?
I am sure you are going to get the worst answer for people like me and you....you have to test because it's application specific. I am sure you can model it for chambers, but then they would be worthless as your application would change the results.
I tried to request a model be build about predicting impedance rise, as the factors involed grew, I knew I couldn't model it to predict.
Activity
No one is currently typing a reply...
Similar threads
- Started by ikpthegame
- Wiring, Electrical & Installation
- Started by JustinStone
- General Car Audio
- Started by Thorhadahammer
- Subwoofers
About this thread
