Lekha is just prodding with his baton to see who will respond
Haha, no, I don't think there is an equivalent phrase in English, but I like it!
Hi Dave,
The difference between the model and the measurement is significant. What is the Q you are are using for the plate and how did you measure it? Does the exciter have a Q of its own? And does it come from the exciter specs, or measurement? Does the model come any closer if you fudge the panel Q higher?
Also, the double peak below 100 Hz in the measurement, where the model shows only one (in between) seems odd. Is this a clamped plate too? Or other? Which exciter? Does that double peak make any physical sense? Is the exciter magnet resonance in that region? For a clamped plate there are usually no other plate resonances that close to the fundamental.
What are the components of the impedance in the model? For now, the acoustic impedance is ignored (as is common), but what is included?
This is not my area, but I presume the inductance of the coil and the "back emf" caused by the velocity of the coil. Are there other components of the impedance in the model? And for "velocity" used in the calculation of impedance it would be the velocity of the coil minus the velocity of the magnet that matters, right?
Sorry for the barrage, but just thinking out loud.
Eric
lekha,
In your view, do any speakers function by pushing air? Or do they generate the sound by "itself"? Or do some speakers operate by pushing air, while other types generate the sound themselves? If so, which types "push air" and which don't?
Eric
I concur, Leob. I've just about given up on the idea that a single driver will cover 100Hz - 16kHz without too much variation in response.
But also, by the very nature of the DML panel action, cyclical/transverse HFs will never transmit through the air in the same way that the longitudinal waves from a horn driver would, and HF will suffer especially over greater distances.
Dave, those models are impressively close to experimental! Very impressive indeed.
I have tried for a while to write modelling code, but got nowhere close to that level of accuracy.
Hello André,
Do you have element in this way? I see the DML as a loudspeaker with a very wide dispersion (almost 90°), with possibly lobes (coincidence frequency effect and I make also the hypothesis of the dipole effect - for that I am trying to find evidence). At the opposite PA system not well designed have narrow dispersion in HF leading to a too high level in axis and an unbalanced sound of axis.
Christian
It is a common expression here used with and by the children in for example a guessing game. When one player doesn't find the solution, he uses this expression to ask for it saying by the way he gives up. It seems it became popular because used by a famous writer Madame de Sévigné in the XVII century (it was to the dog at this ). The cat appeared in the XIX with Georges Sand... It may come from the idea, "I stop thinking".
#10 is here simply to absorb the sound wave made by the internal surface of the cone, transmitted by the air. The energy of a sound wave is in the air movement.
#1 : it is a bending wave driver as a Manger driver is or a DML is. If there is no global movement of the cone according to its axis pushing the whole surface (except1st mode?), there are local movements perpendicular to the surface (so almost radial, in or out depending of the point and the frequency) pushing (pumping?) locally the air so that the air get a speed which is the origin of the sound wave.
Years ago, I copied a DIY realization of such a Walsh driver. It was made from a standard loudspeaker without its membrane and of a cone made from plastic gift paper. I can say there is local movements you can perfectly feel. Picture #7366
Making the choice of a closed box to absorb the inner wave or a bass reflex doesn't change the presence of bending waves in most of the bandwidth. It is a design choice to reuse or not the energy of the inner wave to extend the response to the low frequencies.
... looking at the drawing, I am intriguing by what is #11... I will have a look... Probably to limit the reflections and diffraction at the exciter level.
To come to the topic, I understand it is your answer to Eric's question even if in my understanding this kind of driver is as all the others "pushing", even if it different from point to point, the air.
I don't understand it is an answer to Bruce's question, which is also mine : what are the advantages of a flat coil exciter compare to a standard one? I have already said I see the possible drawbacks and can add that for now I don't understand it as a solution to the problems I see of the standard exciter. But then, I have a doubt : are you convinced that BOTH can produce bending waves into the membrane?
Christian
Oh, I have not given up on the idea 🙂 Apart from some construction issues with some units of my previous revision, I'm quite happy with the reponse. The reason I like to explore using separate exciters and plates for different ranges is not because using a cluster of exciters is not working out, but a possible optimization in cost and power density.
But like we discussed before, I guess we might just have different demands...you seemed to be getting very good results with a very smooth response. But considering I put on multiple events with decent size crowds, and had incredible amounts of positive feedback, I feel very confident that my previous designs does not have "too much variation". They could for sure sound even better, but seems like almost everyone who hears them think they sound better than any regular high end PA already 🙂
For studio/home use I'm still planning to use a cluster of 4x XT25 or XT19...unless splitting the bands actually improves the response, but I doubt that will be the case, I'm just hoping I can keep it as good.
@lekha
If I remember correctly, in the thread about this large cone driver, there is a picture showing it mounted in an enclosure... here is one : my 14 inch full range speaker! #76. It is used here like a standard full range not like a Walsh no?
Here is a FR : #17
From one link to an other one, here is the source of the speaker I made : http://www.audiodesignguide.com/full/conus1.html (found in OHM Acoustics "Walsh F" Speaker remakes #6)
If I remember correctly, in the thread about this large cone driver, there is a picture showing it mounted in an enclosure... here is one : my 14 inch full range speaker! #76. It is used here like a standard full range not like a Walsh no?
Here is a FR : #17
From one link to an other one, here is the source of the speaker I made : http://www.audiodesignguide.com/full/conus1.html (found in OHM Acoustics "Walsh F" Speaker remakes #6)
Hi Eric -
Sorry to get you going down a rabbit hole. It was just a bug in the code. I, too, thought that there was something I was missing in my model and spent quite a while re-deriving all of the equations.
Here's the new model output. As you can see, some peak amplitudes are still off by a little bit, but that actually makes this a very good way to measure the Q of panel modes and compare them to the model assuming a fixed Q. (I'm assuming Q is 8)
The double peak at the exciter resonance seems to be a function of the wires pulling on the exciter. If I support the wires, the shape of that peak changes. This a Dayton DAEX19CT-4.
Dave
I have suspected the same effect at times also.
Impedance looks much better.
Two thoughts:
- It would be interesting to see what it looks like with a heavier exciter, like the 25FHE or 25VT. Those would separate the magnet resonance from the panel resonance.
- I'm assuming that your test case is with "fixed" edges, as in your recent paper, but I wonder if it wouldn't be better to evaluate the impedance model performance using free edges, rather than fixed. IME it's really hard to get truly fixed edges. First, there is really no perfect clamp, so the panel dimensions are not really well defined. Second, the clamp itself always adds a little damping, but how much? But hanging a panel with a pair of long masking tape strips comes really close to "free" edges, and you don't have to worry about having introducing damping at the perimeter.
In that video of the guy with the exciters on his thick wood planks, when the sound is transferred from the pine plank, into the air, is there any motion of the air involved?
What about here? For this old Soviet speaker, in the transfer of sound energy from the coil to your ear, is there any motion of the air involved?
Eric
+ @EarthTonesElectronics
Yes, fully agree. Measurements start often (for me) with almost no support.
Christian
This is known as trolling. Don't feed the troll.
Christian I think it's a result of the "circular" (?) motion of air molecules at HF at the panel surface that reduces their impact over greater distances. I definitely have to raise the HF (from 4kHz to 12kHz) by almost 12db in outdoor performances to get a balanced sound. This is a common 'fix' I've had to use across all of the composites that I've tried from kevlar-skinned 3mm-thick polystyrene, ditto 5mm and 10mm; Dyneema-skinned, ditto; 22gsm carbon-fibre tissue (fairly low E though, much lower than woven CF), ditto; Naked 5mm twin-wall polycarb (not bad actually), 5mm honeycombed Nidaplast with all of the previous skins in turn; and 3mm Albasia on stretched canvas frames, and all of the other cores in turn.
NONE of the above have resulted in a decent HF that I can use on stage without significant EQ.
Yes, if it's EQ'd properly then the wide dispersion is very nice, and the definition, clarity and instrument separation is incredible. But I want to run the system without EQ. First prize.
But, as Leob says, and I sadly concur, maybe it's time to consider using different elements for different ranges.