Hi
Direct relationship for cms would be - thinking along these lines , Cms = compliance of the suspension = how much the cone moves per unit of force
we need to measure the air pressure to move the test cone - 1mm, 2mm, 3mm, 4mm, 5mm to xmax.
the cms will be = movement / P x A, and we can do a few calculations and get the average cms the movement.
Direct relationship for cms would be - thinking along these lines , Cms = compliance of the suspension = how much the cone moves per unit of force
we need to measure the air pressure to move the test cone - 1mm, 2mm, 3mm, 4mm, 5mm to xmax.
the cms will be = movement / P x A, and we can do a few calculations and get the average cms the movement.
this will need some controllers controlling the directional valves - if you use solenoids , this will help maintain velocity of the cone. if we can get / solve constant velocity by mechanical means , ie pneumatics here - we will be able to work out the calculations for bl & cms.
And get an idea of the restoring force of the suspension system beyond xmax. -
I have had a little more time to test it and my opinion about the DATS LA has been hardened: The device cannot be used without an additional triangulation laser. The displacement values output by DATS LA are at best close to the measured values. But how do you know that without a laser?
There are also other issues:
Regards
Heinrich
There are also other issues:
- Miserably long storage time
- DATS LA calculates incorrectly with the "Specified Mmd method
- Cms is output with the wrong unit
- Within the "Symmetry Data Export" columns are mixed (Cms - Kms)
- It would be nice to have a Csv export for easier post-processing of the data
- .....
Regards
Heinrich
Here is some good info on the math to calculate the results.
https://klippel.de/fileadmin/_migra...daptive_Controller_with_Current_Sensor_02.pdf
https://klippel.de/fileadmin/_migra...daptive_Controller_with_Current_Sensor_02.pdf
As promised, here is some information and pictures of my DUMAX setup.
The housing is a simple box with a replaceable top and a hose connection. The pump is a 12V air pump that has both a pressure and a vacuum connection. It is powered by an adjustable laboratory power supply unit. The adjustable range of the pump is between 3 and 14 volts.
As the required pressures are so low and the leakage losses cannot be determined, it is not worth planning additional measuring and control units in my opinion. It is easier to set a pressure/vacuum via the pump voltage, wait for the balance between pressure build-up and losses and then measure the excursion and impedance.
The following is an example of how well the excursion control works by regulating the supply voltage of the pumps.
Regards
Heinrich
The housing is a simple box with a replaceable top and a hose connection. The pump is a 12V air pump that has both a pressure and a vacuum connection. It is powered by an adjustable laboratory power supply unit. The adjustable range of the pump is between 3 and 14 volts.
As the required pressures are so low and the leakage losses cannot be determined, it is not worth planning additional measuring and control units in my opinion. It is easier to set a pressure/vacuum via the pump voltage, wait for the balance between pressure build-up and losses and then measure the excursion and impedance.
The following is an example of how well the excursion control works by regulating the supply voltage of the pumps.
Regards
Heinrich
So I am guessing if you want vacuum of pressure you are simply switching inlet for outlet. One is vacuum and one is pressure. Nice to use a lab power supply.
Which LASER do you use? I see Baumer OADM but the number is out of focus.
Yes! Most loudspeakers are not air tight. So to get perfection is not going to happen. If you start sealing and playing with them you have mass added, or stiffness. And that will not be a common characteristic in the other loudspeakers.
So that box on the side of the pumps is the power supply?
Again a guess, you have two pumps for required volume change in a reasonable time period? I see they are piped in parallel.
The type is: OADM 20I6441/S14F. You can find more information about the laser here: https://artalabs.hr/AppNotes/AN7-Estimation_of_Linear_Displacement_with_STEPS.pdf
So I am guessing if you want vacuum of pressure you are simply switching inlet for outlet --> Yes
So that box on the side of the pumps is the power supply? --> No, this is an AD converter with which I record the displacement signal
Again a guess, you have two pumps for required volume change in a reasonable time period? --> With very hard suspended loudspeakers, a pump may not be sufficient. And with very softly suspended speakers, you may need a smaller pump.
Regards
Heinrich
So I am guessing if you want vacuum of pressure you are simply switching inlet for outlet --> Yes
So that box on the side of the pumps is the power supply? --> No, this is an AD converter with which I record the displacement signal
Again a guess, you have two pumps for required volume change in a reasonable time period? --> With very hard suspended loudspeakers, a pump may not be sufficient. And with very softly suspended speakers, you may need a smaller pump.
Regards
Heinrich
Thanks a Lot ! , requesting you to share your thoughts on relationships for mathematical modelling
Best Regards
This is one of my current test rigs. Very solid measurements. And not to hard to integrate a LASER into the measurement.
I'm just starting to read the ARTA Application note. Well written!
I think this discussion may receive more inputs and participation if it was moved to the Software & Tools section. There is a discussion on Klippel replacement there my personal opinion is - we have gone further here discussing a practical and do-able approach.
Hi Boden,
Granted it is not exactly a build-it-yourself DIY measurement system, but like the previous generations of DATS, the new DATS LA system is designed for both professional and DIY/hobbyist use.
Here is a typical BL curve:
Yesterday I talked a bit about measuring BL on another thread : diyAudio DATS LA Review
In that response I broached the calculation of speaker cone excursion and thought I would repeat a bit of that here as it relates directly to creating a "BL curve" of a driver. The BL curve we like best shows BL plotted versus X, the cone excursion. So here is a gentle introduction to calculating the excursion of a driver with a given DC Voltage applied.
First we note that the suspension of a loudspeaker is much like a more simple system consisting of a mass attached to a spring anchored to a stationary block. The cone of the speaker behaves like the mass attached to the spring in that the more force you apply the further the cone (or mass) is displaced. In Physics we have a nice simple rule that applies to spring systems It's called Hooke's Law after Robert Hooke who first outlined the law in 1660. It serves as a universal description of the phenomenon we know as "elasticity".
We begin by applying Hooke's Law to determine the force exerted on the cone by the voice coil and K (the "spring" constant) to get displacement of the cone.
Force: F is measured in Newtons (N)
Spring Constant K is called Kms for a speaker and is measured in meters per Newton (m/N).
Displacement of the cone is X and it is given in meters (m).
Compliance of a spring is simply 1/K and is expressed in Newtons per meter (N/m). (For speakers: Cms = 1/Kms)
Starting with Hooke's Law we have:
F = K*X where: F = force; K = Kms = spring constant ; X = displacement, we solve for X and get:
X = F/Kms substituting loudspeaker compliance for K (Cms = 1/Kms) we get:
X = F*Cms next we note that: F = BL * I, where I is the current through the voice coil, and substitute for F
X = BL * I * Cms finally we can substitute: I = V/Re (Ohms law) and add dependence on V to get Beranek's equation:
X = BL(V) * V/Re(V) * Cms(V) where V is the voltage across the voice coil. NON-LINEAR!
Before that last line X it was easy to calculate X as the terms on the right side were all constant. The last line is where the complexity of nature emerges as we note that each of the parameters on the right side is changing with the applied voltage. The solution for X is no longer trivial. I pursued solutions to the non-linear equation for quite some time because it could enable measurements of cone excursion from a series of complex impedance measurements made at a series of cone displacements. Yes, "complex" because impedance is a complex number having both Real and Imaginary parts. As I worked toward a solution the math swamp got deep fast. But after several failed attempts I finally emerged with a precise solution for calculating X from a series of Z (impedance) measurements. The details of the complex non-linear algorithm I developed to calculate excursion (no estimates!) remain proprietary at this time. This is the method DATS LA uses to determine speaker cone displacement.
I look forward to your comments and suggestions.
Best regards,
John
John L. Murphy
True Audio®
The suspension system should not be a simple spring as it needs to provide effective braking at x max. Therefore the suspension is not a linear spring with a mass attached to it - and this is why we are aiming here to get relative accuracy in measurements by diy means , maybe not up to the professional level as that of Klippel but sufficient - for loudspeaker large signal parameters.
Taking the topic back to Dats LA the following comparisons were done, these take time and interest from Ente to get access to both system and provide us a feedback. Please go over page 7,8 & 9 of this tread.
Why we are looking for a approachable measurement system as Klippel is very expensive , how will it benefit , where can it be utilized -
The size and type of magnets is fully standardized, so are the magnet plates. More or less all parts of the motor structure is standardized - and available off the shelf depending on vendors located in each country.
A small variation is always possible to be carried out - for eg increasing magnetic gap, extending the pole , undercutting a pole adding copper sleeve etc - depending on FEA. (adding a magnet and extending the ole all of this mods are done at additional costs by the vendors)
The above is pretty much accessible - and FEA is accessible too. If one has a magnet charger - they can start making speakers as of yesterday - it is not rocket science.
The brainstorming starts - with the various options of speaker baskets & hundreds of options of suspension & cone - to voice coil type & height. Optimizing this - "Separates the men from the boys."
The best engineering combination - to maximize cost efficiency and achieve a desirable quality, reliability, spl & distortion - is <> where the measurement system we are trying to develop here will help a lot.
Those speaker makers that have been able to get at least VC & Cone manufacturing in house - "That’s when leaders emerge."
And those that have been able to vertically integrate as many of the speaker component manufacturing inhouse to control end to end - "true character is revealed." (and profitability achieved).
Best Regards
Suranjan
I would say not a single loudspeaker is airtight.
On the other hand, I would also call this barely vacuum on the scale of being vacuum.
That sounds good in theory, but if anyone who does all of these things deviates their designs away from the same ol' thing that Forum Expert™ narrative has dictated for the last 40 years, you will still get told you don't know what you are doing. I've had Experts™ on this forum call my designs "mud pumps" while the design is literally going into production as a high end hifi product, just because it's different than the thing they have known for the last 3 decades.
I am actually working on a open source alternative.
Don't wanna share to many details just yet (unless you're a good open minded coder, still looking for one)
The more I thought about it, the more I have to agree. A few coats of polyurethane on the inside and outside you should be fine. Much easier to make a box too! The vacuum will be relatively small.
By now you should know whom to approach. Only some 85 kms away for your home. The family name both starts and ends with a T.😉