Like I said in my other post I dont know if its comb filtering or another type of effect but there is something interfering when there is more then one exciter on the same panel. I mean dont you all hear the difference when compared side by side? Or can only Spedge and I hear it?
Again, I don't have measurements on the same plate with different configurations, and I'm not sure how far they can go really. At those levels is it not so easy to test since it is reacing the limit of what most microphones can capture, and you need to find a remote outdoor space to do it.
But measuring the sensitivity should tell you if the exciters cancel out each other at all, and you can extrapolate max SPL from that.
I just know that I would have clearly noticed a 4x reduction in sensitivity as you suggest you experience when you say your 4x exciter panels doesn't go louder than your single exciter. If it would be a large difference I would have noticed it even if I did not look for it, but I really doubt there is even a marginal difference.
Since you claim multiple exciters reduce efficiency I would hope that you have some data, or experiences you can describe a bit more detailed, that is supporting that.
Leob.
once again you are miss understand and miss quoting me.
these are not random peaks and troughs throughout the panel , but are a pattern of waves that move up and down in frequency as you move the microphone between the exciters and away from the exciters.
This does not happen with a single exciter panel.
It is easily seen using a microphone and pink noise.
This you can do yourself .
I do not really want to have to glue on another exciter again and do a three second video just to prove this.
Or set up a YouTube account for a longer video.
If I did show this response, I am still not sure you would actually believe my results?
Steve.
Ok, I don't know what your definition of much is, but the point is that 4 exciters should give a very noticable increase in volume if you apply 4x the power. If you experince the difference as "not much" you either have an odd definition of what a significant increase in SPL is, or you have gotten something wrong.I said the 4x exciters are not much louder then the single exciter. I never said they dont go louder.
What is your definition of much? It is a noticeable increase in volume if it wasnt I wouldnt notice it
. What is your definition of a significant increase in spl? What have I gotten wrong?Hello Leob
Thank you to point on the relation between DML/piston and hearing.
Some months ago, I posted #7259 a patent about the Measuring and optimising diffusivity of acoustic output of loudspeakers. Diffusivity being one of the main characteristics of DML.
After more than 2 years with DML now, I can say (and I will not be alone I think) that they have "something special" (read different from standard loudspeaker) that makes them really music and room friendly even in the most simple or "not optimized" realizations. Which means it is intrinsic to their nature. It is also challenging from a design point of view as the goal seems to have no stable phase relation between the FR components according to the direction.
For the possibility of comb filtering... well we should at least classified in different situations :
- internal to a panel due to multi exciter design
- between panel of a stack playing the same signal
- created by the panel/room interaction.
Hello all
About the effect of multi exciter, you can refer to my post #5270 (about one year ago! Time flies?) where there are some FR with one and two exciters. I haven't pushed more the topic staying on the secure opinion that one exciter is enough in room applications, if 2 are needed a work around IF there are some consequences in HF is to shunt one of the exciter with a capacitor.
From measurements point of view, it seems there is a difference between one or two exciter, not visible using a long time window but visible when using a frequency dependent window (which would lead to say the energy is arriving later?) No conclusion on the fact if we can here it or not. We'll see in the coming time if I will have more conclusion : the idea of doing a dual exciter DML being in my mind for the next month (music in the summer evenings?). I think also DML behavior is too complex and the wave speeds in HF too unusual to make the conclusion on comb filtering. More technical input needed.
Christian
"Not much" increase in SPL would be 1-3 dB perhaps. Anything about that is significant. But since you use a phrase like that instead of the actual difference you have measured in dBSPL, I assume that you made a subjective judgement to come to the conclusion that there are significant cancellation causing adding multiple exciters only resulting in "not much" increase.What is your definition of much? It is a noticeable increase in volume if it wasnt I wouldnt notice it
You have not given any details whatsoever about what you base your conclusion on. What panels, what exciters in what configuration, what amp, how did you measure SPL, etc. So it is impossible for me to say what you have gotten wrong.
I would say that the comb filtering is what happens one a DML plate, also with one exciter. The frequencies emitted from the plate are emitted from several points at the same time, which I would think must cause some comb filtering. However since there are many points on the plate acting as sources of a frequency at the same time, you will not see that pattern in the example, but a bunch of comb filters overlayed. That would result in them being less easy to identify in a FR, and many times even masked by our hearing.
Ok, thanks for your valuable contribution!Exactly you dont know, and you never will.
I was doing A/B comparisons between my single exciter panel and the 4X exciter panel and I noticed even the bass is cleaner sounding with the single exciter. The 4X exciter has more bass but the bass sounds a bit more muddy which again could be from comb filtering or some other type of interference between the 4 exciters spaced 2 inches apart when measuring from voice coil to voice coil.
Again I am not saying the 4X exciter panel does not sound good as they sound really good but they just lack a bit of that coherency and fine detail of a single exciter panel.
Its almost like comparing a full range driver and or a coaxial driver in which it sounds more coherent then most 2 ways because all the sound is coming from a single point with no interference be it comb filtering, time alignment or what ever.
Again I am not saying the 4X exciter panel does not sound good as they sound really good but they just lack a bit of that coherency and fine detail of a single exciter panel.
Its almost like comparing a full range driver and or a coaxial driver in which it sounds more coherent then most 2 ways because all the sound is coming from a single point with no interference be it comb filtering, time alignment or what ever.
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