Hello Eucy,
For the exciter models I have, with REW:
Christian
For the exciter models I have, with REW:
- DAEX13CT-4 : measured 0.87Tm, spec 1.12Tm
- DAEX30HESF : measured 5.5, spec ?
- DAEX25FHE-4 : measured 3.9 / 4.2Tm, spec 3.6Tm,
Christian
For the BL of exciters in the lite version of PETTaLS, I have:
I am planning to work more on measurements for the squishy, thick plate materials like PES/XPS/gatorboard and try to integrate those better into my models, but I probably won't be able to get to that until the summer months.
- DAEX19CT-4: 1.3 Tm
- DAEX25VT-4: 5.0 Tm
- DAEX32EP-4: 3.5 Tm
I am planning to work more on measurements for the squishy, thick plate materials like PES/XPS/gatorboard and try to integrate those better into my models, but I probably won't be able to get to that until the summer months.
@EarthTonesElectronics
Hello Dave,
2 questions about PETTaLLs :
1/ Is there a possibility to export a curve (ie impedance or SPL) to a text file?
2/ Could you add to the BL information the values of Mms (mass), Cms (compliance), Rms (damping) of the exciter models?
Thank you!
Christian
Hello Dave,
2 questions about PETTaLLs :
1/ Is there a possibility to export a curve (ie impedance or SPL) to a text file?
2/ Could you add to the BL information the values of Mms (mass), Cms (compliance), Rms (damping) of the exciter models?
Thank you!
Christian
@EarthTonesElectronics
Hello Dave,
I have additional questions... Maybe you already answered but I am not able to find the answers in previous posts...
1/ For the on axis SPL, for which distance is it calculated? is there a correction to plot it at a standard distance like 1m? Or to explain the question in other words, it is common to measure a loudspeaker at let say 2m to be in the far field and to plot the result with a correction like if it was 1m.
2/ In the velocity plot (the curve in the same window as the impedance), which velocity is it? In your thesis there is a similar plot which is the "spatially averaged RMS panel velocity". Is it the average value of the RMS speed of each point?
Thank you
Christian
Hello Dave,
I have additional questions... Maybe you already answered but I am not able to find the answers in previous posts...
1/ For the on axis SPL, for which distance is it calculated? is there a correction to plot it at a standard distance like 1m? Or to explain the question in other words, it is common to measure a loudspeaker at let say 2m to be in the far field and to plot the result with a correction like if it was 1m.
2/ In the velocity plot (the curve in the same window as the impedance), which velocity is it? In your thesis there is a similar plot which is the "spatially averaged RMS panel velocity". Is it the average value of the RMS speed of each point?
Thank you
Christian
I'll add this to the list of things I'm working on!
The model that I'm using is more complex than this, but collapsing it down to these components... (as electrical units)
DAEX25VT-4: Mms = 78 mF, Cms = 320 uH, Rms = 0.8 ohm.
DAEX32EP-4: Mms = 124 mF, Cms = 323 uH, Rms = 1.3 ohm.
DAEX25CT-4: Mms = 29 mF, Cms = 45 uH, Rms = 0.18 ohm.
It's at 1m right now. Adding the distance as a variable wouldn't be difficult.
Yes, I do the RMS because the velocity at each point has a magnitude and phase, then take the average over all points on the surface.
Thank you Dave
This is not a request but yes it might be an interesting features to exchange the results with other tools like REW.
In fact, a bit more than 2 years ago, we started different tentative of simulations with Eric and an other contributor Paul. I wrote a python script based on the FDM (finite difference method). At that time it was only for simply supported and clamped edges. Last year I found how to extend to free edges. Some weeks ago I implemented the free edges. Thanks to Eric's help, the script was debugged and shown a pretty good precision on the modes compare to the FEM... at least for the few test cases we ran.
Those tests confirmed the versatility of the FDM approach to implement various boundary conditions beyond the classical ones which is what I would like to explore.
I just implemented the impedance and SPL calculation that I compare to the PETTaLs outputs.
About the model values you posted, it is not the order of magnitude I usually see making the conversion to the mechanical data with a BL² factor (classical loudspeaker like in REW). Am I on a wrong model?
Christian
Thank you Eric. Yes it is a satisfaction to have this FDM script running. It should allow to test different mounting solutions and it is ready to give results for orthotropic materials... at the condition to be able to feed it some material characteristics and to be able to evaluate the results.
An other interest is the possibility to loop over a set of characteristics, letting the computer working for example at night and then collecting the results. The condition for that is to define criteria which seems possible (ie the smothness of the FR on a certain frequency range).
The main question in front of us is how it is representative... We have 2 possible observable physical quantities which are the impedance and the response of an open back panel. We already know from Dave there are difference between the simulation in PETTaLS and the measurement of the impedance. I have the feeling that has important consequences : first about the model (need of improvement?), second on the SPL simulation as the impedance plays a role in it (at least in my script). For the SPL of an open back panel, for now it is not an output of a simulator. There is here an additional modelling effort needed... hoping it is possible.
@EarthTonesElectronics
Dave, if you have suggestions of an algorithm to get the SPL of an open back panel, please, let me know.
Christian
PS : other advantage of the FDM, is the possibility to simulate easily adding mass like the one we see on the commercial DML either to balance the panel or to tam some modes
An other interest is the possibility to loop over a set of characteristics, letting the computer working for example at night and then collecting the results. The condition for that is to define criteria which seems possible (ie the smothness of the FR on a certain frequency range).
The main question in front of us is how it is representative... We have 2 possible observable physical quantities which are the impedance and the response of an open back panel. We already know from Dave there are difference between the simulation in PETTaLS and the measurement of the impedance. I have the feeling that has important consequences : first about the model (need of improvement?), second on the SPL simulation as the impedance plays a role in it (at least in my script). For the SPL of an open back panel, for now it is not an output of a simulator. There is here an additional modelling effort needed... hoping it is possible.
@EarthTonesElectronics
Dave, if you have suggestions of an algorithm to get the SPL of an open back panel, please, let me know.
Christian
PS : other advantage of the FDM, is the possibility to simulate easily adding mass like the one we see on the commercial DML either to balance the panel or to tam some modes
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BL wasn't incorporated into those values - I'm assuming that there's a transformer with a value of BL:1 between the voice coil and mechanical components.
Here's a picture of the very basic model (missing quite a few things) - this works okay to model the exciter impedance when it's stuck to a table.
Added masses are part of the PETTaLS model, too, I was just leaving those for the advanced version. This is how I simulated clamped corners, for example - by adding very large masses to the corners.
OK, you are in the analogy force <=> current and speed <=> current on the mechanical side (M, 1/B, 1K)? I would expect then M in the range 1 to 5mF for Mms from 1 to 5g (about) and 1/K 30 to 300µH for Cms in the range 0.03 to 0.3mm/N for the exciter alone.Here's a picture of the very basic model (missing quite a few things) - this works okay to model the exciter impedance when it's stuck to a table.
Maybe the structure of your model is different the one I have in mind...
Christian
When you translate everything back to a purely electrical circuit without the transformer, these values sound right (e.g. there is a factor of BL^2 difference between my values and your ranges).
I'm using RMS (root-mean-square) instead of MS - MS velocity is more related to power rather than velocity itself. Neither is more correct than the other, but they do represent different physical quantities!
Also, apologies that I haven't had much time to check up on the forum or release new changes! A lot of other projects have required my attention lately.
Still planning lots of additional features, I promise!
And it'll be good to have more simulation models out there - this field desperately needs it!
Still planning lots of additional features, I promise!
And it'll be good to have more simulation models out there - this field desperately needs it!
I thought it might be interesting to talk about what the results of a "good" DML design might actually look like in Pettals.
So I am inviting those who are interested to come up with a virtual design that looks good to you, and share it with the rest of us. The idea for the time being is to simply assume that Pettals is perfectly accurate, and find and share a design and response in Pettals that looks like the response you would like to see from your own DML panel. Use whatever material properties and configuration that you want.
The design/response below is my first entry. In the interest of being realistic (or close), I tried to limit myself to:
Below is what I came up with, the second screenshot is the same as the first, but with the impulse response plot selected instead of the Polar response.
Some points:
Eric
So I am inviting those who are interested to come up with a virtual design that looks good to you, and share it with the rest of us. The idea for the time being is to simply assume that Pettals is perfectly accurate, and find and share a design and response in Pettals that looks like the response you would like to see from your own DML panel. Use whatever material properties and configuration that you want.
The design/response below is my first entry. In the interest of being realistic (or close), I tried to limit myself to:
- Designs using one of the three actual exciters in the program (i.e. not point force)
- Material properties that are (hopefully) within the realm of possibility.
- SSSS panel (I'll try FFFF next).
- Sensitivity >90 dB at 1 watt
- Flat-ish response over the widest frequency range possible, with emphasis on 100 Hz to 10 kHz
- Slight downward slope okay/preferred.
- Minimal variation of FR with angle, directivity always positive, or nearly so.
- Clean impulse response without long tails.
Below is what I came up with, the second screenshot is the same as the first, but with the impulse response plot selected instead of the Polar response.
Some points:
- The panel properties are approximately what I get with a carbon fiber balsa sandwich, but for this design I need balsa and cf fabric about half the thickness of what I have made before.
- I chose a thickness that put the coincidence frequency and exciter cut-off frequency at the same value. However, since the panel is not isotropic the prediction of fc is dubious.
- The panel size was made just large enough to get the fundamental frequency (first impedance peak) at around 100 Hz.
- The aspect ratio and exciter location were positioned by trial and error to get the flattest possible response.
- I used a Q of 2. I'm not really sure if it is really possible to get Q quite that low. Using Poron foam on the perimeter with the thicker versions of these panels resulted in a Q of near 3, I think. I don't know if Q will be higher or lower with a thinner panel. Using Q=1 gives an even flatter response, with virtually no cost in output, but setting Q any lower than 1.0 starts hurting output SPL.
- Probably the weakest part of the response is around 1000 Hz, were there is a bit of a dip in the on-axis response, and the DI goes slightly negative, but otherwise I think the simulation looks pretty good.
Eric
@EarthTonesElectronics
Dave,
I just tried this sim of an FFFF plate with the exciter in the center of the X direction. I was surprised to see that the responses at +90 and -90 are pretty different, particularly in the region of 150 Hz to 2000 Hz. Interestingly, in that same frequency region, the surface velocity maps look very symetric, like the one shown at 757 Hz. I have not see anything like this with SSSS conditions.
Any thoughts?
Eric
Dave,
I just tried this sim of an FFFF plate with the exciter in the center of the X direction. I was surprised to see that the responses at +90 and -90 are pretty different, particularly in the region of 150 Hz to 2000 Hz. Interestingly, in that same frequency region, the surface velocity maps look very symetric, like the one shown at 757 Hz. I have not see anything like this with SSSS conditions.
Any thoughts?
Eric
Hmm... something is strange. With the transformer, I wouldn't expect the BL² is involved in this circuit. The resonance frequency of the LC circuit is around 32Hz which is not the typical frequency resonance of an exciter (voice coil side).
Christian
Eric... If customwood (a very dead material) is listed at a Q of 5, I don't think a CF/balsa sambo is going to be 2... What does the graph look like @Q = 5?
Eucy
Great initiative, thank you Eric. Obviously it would be fantastic the day when Pettals designs are actually built, measured and listened to. I am sure this is not too far away. I lurk here with interest.
Eucy,
You are right for sure that the Q of the CF/bala combo itself isn't going to be as low as 2. I can't recall if I tried estimating the Q of a free cf/balsa panel or not, but I would guess it's closer to 50! Cf/balsa itself is far from dead. But what I'm suggesting is that (just maybe) with the incorporation of a strong damping at the perimeter, that a "system Q" or "equivalent Q" of about 2 just might be possible.
Also, I think it's worth noting that (as I understand it) the Q in the model is intended to represent the Q of the material itself, rather than the "System Q". So you can argue that I am "mis-using" the model by trying to include the perimeter damping into the "panel Q". But until Dave incorporates an explicit "perimeter damping" input (i.e. reflection coefficient?), the best way I can think of to include the effect of perimeter damping is to think of the "Q" in the model as the overall system Q rather than simply the Q of the panel itself.
I do wonder how much difference it would make if the damping is inherent in the panel itself vs. coming mainly from the perimeter. That is, say you could make two panels with the same modulus and density, but one with a Q of 2, and the other a Q of 100. Then you mount the Q=2 panel to a frame using something that adds virtually no damping of its own, and mount the Q=100 panel using something that adds loads of damping. Would the resulting response be very similar for the two panels, or not? For now, I'm making the assumption that the difference would be small, but only because Pettals doesn't yet have a feature to model perimeter damping separately.
Eric
I am certainly already using Pettals to inform my next builds. In fact just yesterday I ordered an acrylic panel to try out a Pettals inspired design.
Have you given Pettals a try? If not, give it a go and maybe even share a Pettals result that looks good to you. Or take my design and make it better! I'm disappointed that nobody has shared their own Pettals designs yet.
Eric