Qms affects impedance shape, Qts affects response shape. Impedance can affect response if you have a high output impedance amp.
Excursion (and box resonance) is intimately related to the box volume and the ratio of Vas to Vb. In my response above, I don't mean to imply that cone mass is not important, just that it is already accounted for in T/S parameters.
I put that equation on wikipedia some 11 years ago
Excursion (and box resonance) is intimately related to the box volume and the ratio of Vas to Vb. In my response above, I don't mean to imply that cone mass is not important, just that it is already accounted for in T/S parameters.
I put that equation on wikipedia some 11 years ago
Qms affects impedance shape, Qts affects response shape. Impedance can affect response if you have a high output impedance amp.
Excursion (and box resonance) is intimately related to the box volume and the ratio of Vas to Vb. In my response above, I don't mean to imply that cone mass is not important, just that it is already accounted for in T/S parameters.
I put that equation on wikipedia some 11 years ago
You are a nice contributor
The mass seems to be included in the VAS parameter !
This is the equivalent air volume of the moving mass suspension... if i put a loudspeaker driver in a closed box with a volume equivalent to the VAS, the membrane is in equilibrium (critically damped).
In this case the loudspeaker driver is electrically damped above his resonant frequency and mechanically damped (by the air volume) under this resonant frequency ?
A better equation for Vas is: Vas=Cms*rho*c^2*Sd^2
Vas is really independent of mass. IF you add or subtract mass from a driver Vas does not change.
If you put a driver in a box equivalent to Vas, resonance goes up by 1.414 times, Qts goes up by 1.414 times. Fc/Fs = Qtc/Qts = sqrt(Vas/Vb+1)
The air in the box acts as a spring, not a damper. Damping action from amplifier is most significant near resonance.
Vas is really independent of mass. IF you add or subtract mass from a driver Vas does not change.
If you put a driver in a box equivalent to Vas, resonance goes up by 1.414 times, Qts goes up by 1.414 times. Fc/Fs = Qtc/Qts = sqrt(Vas/Vb+1)
The air in the box acts as a spring, not a damper. Damping action from amplifier is most significant near resonance.
Vas is independent of mass - but mass is not independent of Vas.
If you alter the value of Vas, Mmd changes (along with Bl, Cms and Rms).
It all depends on whether you are holding other parameters constant or not, and whether those parameters are fundamental parameters or combination /derived ones like Fs, Qts, Qms, etc... By your example, Mmd and Vas are independent (in either direction) unless you are trying to fix Fs, or any of the Q's. ...but this is all rather pedantic, LOL
If Vas=Vb, Fb=sqrt(2)Fs? why?
I mean "compliance" the ability to a thing to pair with... the other thing.
Vas "measure of the 'stiffness' of the suspension"
https://en.wikipedia.org/wiki/Thiele/Small
Mean the ability to apply a force to the cone in order to keep it a neutral position ?
Cms "the compliance (ie, the inverse of stiffness) of the suspension"
https://en.wikipedia.org/wiki/Thiele/Small
Mean the abilty to absorb a force and convert it into "losses" ?
I was thinking that the air was "viscous" at certain frequencies like a very low viscosity fluid and therefore causing losses.
"Mmd is the cone/coil mass without the acoustic load"
https://en.wikipedia.org/wiki/Thiele/Small
This is the weight of all moving parts... without the air load.
The Vas and the Mms are linked by the air contact load.
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If you have two springs and put them in parallel, they are stiffer, so Fs rises In this case the two springs are Vas and Vb (or Cms and Cmb) which represent the same thing. The trouble with wikipedia is anyone can edit it.
Vas is the "volume equivalent compliance" Really proportional to Cms for the same diameter, but...difficult to explain without spending hours and drawing out circuits since every answer seems to bring out 3 questions at this point.. You might look to a book or read the papers by Thiele and Small to get a better handle.
Damping is represented by Rms.
Vas and Mms are not at all related, through air load or anything else. If you want a really low Vas with a low Fs, you will need a high mass, which is why you see car subs with cones that weigh almost a pound.
If you have two springs and put them in parallel, they are stiffer, so Fs rises In this case the two springs are Vas and Vb (or Cms and Cmb) which represent the same thing. The trouble with wikipedia is anyone can edit it.
Vas is the "volume equivalent compliance" Really proportional to Cms for the same diameter, but...difficult to explain without spending hours and drawing out circuits since every answer seems to bring out 3 questions at this point.. You might look to a book or read the papers by Thiele and Small to get a better handle.
Damping is represented by Rms.
Vas and Mms are not at all related, through air load or anything else. If you want a really low Vas with a low Fs, you will need a high mass, which is why you see car subs with cones that weigh almost a pound.
Thx, Ok, i will read the papers by Thiele and Small as soon as i find them somewhere
The common point in the wikipedia text was "in free air"... wich seems to mean nothing in term of relation here
These two "compilances" are parallelized and the summation will raise the total resonant frequency.
So incorrect things are :
https://en.wikipedia.org/wiki/Thiele/Small
Mms NO
Measured in grams (g) or kilograms (kg), this is the mass of the cone, coil and other moving parts of a driver, including the acoustic load imposed by the air in contact with the driver cone. Mmd is the cone/coil mass without the acoustic load, and the two should not be confused. Some simulation software calculates Mms when Mmd is entered. Mmd can be very closely controlled by the manufacturer.
Vas NO, it involve the acoustic load imposed by the air in contact !
Measured in litres (L) or cubic metres, is a measure of the 'stiffness' of the suspension with the driver mounted in free air. It represents the volume of air that has the same stiffness as the driver's suspension when acted on by a piston of the same area (Sd) as the cone. Larger values mean lower stiffness, and generally require larger enclosures. Vas varies with the square of the diameter. A typical factory tolerance for Vas spec is ±20–30%.
Neither of these descriptions (omitting your emphasis) is incorrect. A clarification might be made by stating that Vas is an inverse measure of the 'stiffness'...
If stiffness is K, compliance (Cms) and Vas are proportional to 1/K.
I have already tried to discourage the notion that Vas has anything to do with the 'air load'.
You can read some of the salient articles here, about halfway down the page:
http://www.readresearch.co.uk/articles.php
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Vas = rho * c ^ 2 * Sd ^ 2 / ((2 * Pi * fs) ^ 2 * Mms)
Where Mms (total moving mass) = Mmd + air load
Thanks, i'm going to read these soon !
At first i was thinking that the T&S choice of measuring the loudspeakers in the air instead of the vaccum was the presence of encapsulated air in the paper of corrugated suspensions of loudspeakers drivers.
So, i was also thinking that they had decided, due to this material issue to perform their experimentations in a "unperfect" environnement and use their "immagination" to restore this perfect environement by extracting their parameters and by correlating their measurements.
Paper is just small bubbles of air encapsulated in a cellulosic fibers matrix... if you remove the air, the paper is becoming translucid.
I'm reading the documents linked by Ron E, there are a lot of parameters and i can't perform any CTRL+F
All you did here is substitute for Cms in the equation for Vas that I already posted. where Cms = 1/ ((2 * Pi * fs) ^ 2 * Mms)
I stated earlier that mass and Vas are independent unless you are trying to fix some other dependent parameter, which is what you are doing here by making Fs a parameter.
So thanks for backing me up, dude Should it not follow, then.........
Great thread.
I say this, because even though I kind already "knew this" I had not put it into proper perspective.
The vent "loads' the woofer cone at the tuning frequency, thus reducing excursion. Should it then follow, that the port(s) themselves need to be able to propagate the same, if not more, amount of air as the cone ?
Often times I have seen ports (vented ducts, etc.) too small to get the job done. My audio buddy who is also a math professor, and champion of many car audio SLP contests, maintains the port diameter should be at least equal to 1/2 the radiating area of said woofer, with 1:1 being ideal, but not practical in many cases. On a related note, I have seen a formula listed to determine is a given vent size is adequate to avoid compression/chuffing.
Great thread.
I say this, because even though I kind already "knew this" I had not put it into proper perspective.
The vent "loads' the woofer cone at the tuning frequency, thus reducing excursion. Should it then follow, that the port(s) themselves need to be able to propagate the same, if not more, amount of air as the cone ?
Often times I have seen ports (vented ducts, etc.) too small to get the job done. My audio buddy who is also a math professor, and champion of many car audio SLP contests, maintains the port diameter should be at least equal to 1/2 the radiating area of said woofer, with 1:1 being ideal, but not practical in many cases. On a related note, I have seen a formula listed to determine is a given vent size is adequate to avoid compression/chuffing.
The usual 17m/s velocity limit recommendation reduces objectionable noises, but port compression still happens. Back in the day, they used to recommend port and cone area to be the same, but that won't work in small boxes tuned to low frequencies. Bigger in diameter is better, but another thing to consider is port self-resonances. The longer you make a port, the lower the unwanted self resonant frequencies are.
For car audio SPL contests I would guess they tune higher than optimal to get a peak at the tuning frequency excursion minima. This would allow you to both get more sound and pump in more power. Example: Tuning a 2 cubic foot box to 70Hz you could put in a 10" diameter port quite easily - roughly 14" long.
In that case, you should have no trouble in calculating the value of Mms given the following Thiele-Small parameter values:
Sd = 100 cm^2
fs = 50 Hz
Qes = 1
Qms = 1
I look forward to seeing what value you come up with.
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