Strange Steve. Like if one receives bass and not the second. How is it wired? role of the capacitor?
... sorry didn't see the second post. The upper exciter is acting like a kind of seismograph?
Christian.
Basically the panel is vibrating heavily in the area of the second exciter.
is it worth tryIng to find a position that does not vibrate, and place the exciter in that position ?
I am thinking that this is going to be a problem for those trying to build a subwoofer dml panel using multiple exciters.
Steve.
Basically the panel is vibrating heavily in the area of the second exciter.
is it worth tryIng to find a position that does not vibrate, and place the exciter in that position ?
I am thinking that this is going to be a problem for those trying to build a subwoofer dml panel using multiple exciters.
Steve.
Yes...bouncing on the spider, and the unloaded exciter mass is affecting the panel vibrations... And when it's powered, I surmise it's bouncing because the driving signal is not in phase with the panel deflection/movement
So yes...multi exciter placement is difficult. Even when all are on a spine, the forces on each coil differ because of the panel deflections
Get it wrong, and some exciters may be 'sucking' where the panel is trying to 'puff' (so to speak)
..tricky stuff
Eucy
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Hey, that’s neat Christian. A lot of the peaks do seem to coincide. There are fewer really big clear peaks in the tap test. Probably you would need to move the microphone around to different positions in the tap test to capture all the same natural frequencies that the impedance test picks up.
Hey Steve, as Christian asked, what was the role of the capacitor?
Sorry, if you already answered and I missed that.
Christian, now I’m wondering if the impedance test doesn’t also give a good way of assessing damping? It would be interesting to see if different perimeter treatments with significantly different known levels of damping result in different size peaks in the impedance test.
I don't think so.. that would indicate the second one being completely out of phase with the first
I think it's inevitable that the woofer panel will need a stiff panel with spines and act in a largely pistonic manner...some bending wave action may be possible with clever design. The result will hopefully be a panel that looks like a DML panel and can be integrated with a mid/high dml panel, but act in a hybrid pistonic/dml manner
Eucy
When using more then one exciter per panel the second exciter regardless if its running or not will act as a WEIGHT. Placement of two exciters is also important as if not placed right one can cancel and or amplify the other.
On another note I've also noticed through my years of experience is that some exciters voice coil is not as stiff as others and I am not talking about the break in period.
On another note I've also noticed through my years of experience is that some exciters voice coil is not as stiff as others and I am not talking about the break in period.
Ok , I did not understand what Christian was talking about.
The capacitor is wired out of circuit, it is kept there in case I need to use it.
Steve.
I'm not sure what you mean by this?
The panel will be varying between fully positive and negative all over the panel at the same time.
The exciter could without knowing be placed on a fully + or fully - or anywhere inbetween these two peaks.
I expected ,as the exciters are very closely mounted, that there would be a mutual coupling.
But obviously not in this case.
It is something to be aware of.
steve.
Node and anti-node locations vary all over the panel with frequency, and also super-impose so there are very complex wave patterns occurring, but if you take a single frequency with one exciter, and find a 'stationary' spot - ie a node, and place a second exciter there and then energise it with the same signal as the first, it obviously won't want to be a node any longer at that frequency and will conflict with the first exciter. That's what I meant by out-of-phase. Depending out how far apart they are, at other frequencies, they may reinforce one another - either way, multiple exciters can be expected to distort the frequency response over that of a single exciter.
If they're very close together, a combined bending wave pattern would be expected, and the hf may be dulled by the 'contact spreading' effect , ie - it would be like having a large diameter single voice coil.
In this case, the anisotropy of the panel may further complicate the effects
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Yes ! exactly so, and no matter how careful the placement is, the cancellation/reinforcement effect is probably impossible to overcome across the full frequency range, hence the preference for a single exciter per panel often mentioned in comments on multiple exciter discussions.
This paper discusses multi exciter equalisation - equalisation of the whole panel proved unsatisfactory, so they resorted to equalising each exciter.
https://www.researchgate.net/public...xciter_distributed_mode_loudspeakers/download
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Hello Eric
This my expectation too to get damping data from the impedance. At the peaks, spring and inertia (mass) effect compensate each other, the damping makes the heigth of the peak (over simplified). I am working on that.
Christian
This paper is probably also among the ones showing the best membrane characteristics (bending stiffness, areal mass, FR...) : light, stiff but not too stiff, orthotropic. Does it inspire the most skilled of us in material?
What is "an eight-foot panel coupling"?
Further to the multi exciter discussion, Typical Ben produced this simple test video :
https://www.google.com/url?sa=t&rct...=MHCpcbOnZZw&usg=AOvVaw3ZeVkBjZSbymimr9_rjFwC
He achieved a big boost in the mid bass region by using 4 exciters, and there was a big jump between 3 and 4 drivers. What he didn't test was removing drivers 2 and 3 and leaving 1 and 4. I believe the boost occurred because driver 4 was placed in a location largely sympathetic to driver 1 over those frequency ranges
https://www.google.com/url?sa=t&rct...=MHCpcbOnZZw&usg=AOvVaw3ZeVkBjZSbymimr9_rjFwC
He achieved a big boost in the mid bass region by using 4 exciters, and there was a big jump between 3 and 4 drivers. What he didn't test was removing drivers 2 and 3 and leaving 1 and 4. I believe the boost occurred because driver 4 was placed in a location largely sympathetic to driver 1 over those frequency ranges
Christian, they don't show photos, but I assume each exciter has 8 frog legs to mount to the panel
Eucy
Exciter coupling by the wiring.
Probably something to keep in mind here is if there is an obvious mechanical coupling of the exciters by the panel when there are several exciters used, there is also a possible electrical coupling for the one wired in series. If you have a look to the impedance curve just before, each time there is a peak if an other exciter is feed by the same current, it will be reduce. An interesting measurement would be to have the impedance curves of each exciters in such case to see if the peaks occur at the same frequency. The impedance curve is heavily materiel dependent.
Probably something to keep in mind here is if there is an obvious mechanical coupling of the exciters by the panel when there are several exciters used, there is also a possible electrical coupling for the one wired in series. If you have a look to the impedance curve just before, each time there is a peak if an other exciter is feed by the same current, it will be reduce. An interesting measurement would be to have the impedance curves of each exciters in such case to see if the peaks occur at the same frequency. The impedance curve is heavily materiel dependent.
The problem vibration is below 60hz, that is why I mention it as being a problem for sub use as they would only be interested in this area.
I talked about the problems of using multiple exciters on full range dml panels over 10 years ago, and from my quick testing with the proplex panel , my thoughts have not changed.
For home use at least I see no reason to use multiple exciters.
It just muddied the waters.
Steve.