Christian.
By the way, it was easy to stop the problem by placing a pillow on the wall.
This stopped the offending lobe reflection.
I would have thought for PA work these side lobes would have been handy for audience coverage ?
Steve.
By the way, it was easy to stop the problem by placing a pillow on the wall.
This stopped the offending lobe reflection.
I would have thought for PA work these side lobes would have been handy for audience coverage ?
Steve.
Pillow or acoustic treatment is not in my options. The loudspeakers are in rooms we live in not a specific one. They have in addition large windows.
For PA is probably an other story. In non professional events I can go, the low coverage (and the too high on axis level) in HF is often a problem
Christian
Hello Christian.
Yes it would be very bad to have those side lobes in a very reflective room like yours.
The panel that was very bad was the 1inch very high density eps.
Steve.
Yes it would be very bad to have those side lobes in a very reflective room like yours.
The panel that was very bad was the 1inch very high density eps.
Steve.
Christian.
Having the sides of the panel facing you was interesting listening to.
But I would personally not use this orientation.
It was a similar experience to using GA Briggs method of using upwards firing cone mid tweeter combination.
It sounded fantastic when listening to classical music but with rock music it sounded like the guitarist was doing his guitar solo in the next room or two away.
The sound seems to drift towards you.
I used to get around this by toeing the panel speakers out a little to get more direct radiated sound directed at me.
With The Briggs upwards units I used to tilt forward towards me to get the same thing .
The sound from the front of the panels is usually always louder.
Steve.
Having the sides of the panel facing you was interesting listening to.
But I would personally not use this orientation.
It was a similar experience to using GA Briggs method of using upwards firing cone mid tweeter combination.
It sounded fantastic when listening to classical music but with rock music it sounded like the guitarist was doing his guitar solo in the next room or two away.
The sound seems to drift towards you.
I used to get around this by toeing the panel speakers out a little to get more direct radiated sound directed at me.
With The Briggs upwards units I used to tilt forward towards me to get the same thing .
The sound from the front of the panels is usually always louder.
Steve.
For the way I use them I prefer two lobes to the side instead of one lobe to the front. But especially indoors and for typical concert setup I think it can be tricky to place them so both lobes actually cover the audience instead of causing extra reflections.
Hello everybody, I am testing a concentrator on the xt32 and when mounting it without mounting the exciter+concentrator on a panel I get a huge boost at 7khz. I think it's mainly caused by the venting hole, can anybody confirm or deny this? I will do some experiments this weekend to optimize my design and then I will let you know
Christian,
Here are some front and back measurements of a panel. This a carbon fiber/balsa panel on a butyl rubber surround.
First plot is with the default 500 ms window, and below with a 5 ms window. Solid is back of panel, dashed is front. In this comparison, windowing to 5 ms didn't increase the difference at 2-3kHz, but did in the 4-5Kz region.
Hello,
I haven't posted about concentrator tests for now because it is a bit difficult to draw a picture of those tests... One thing that happens on my 10mm EPS test panel is the concentrator is a revelator of its coincidence frequency (more visible with the lightest of both I tested). My current hypothesis is when mounted with a ring, this create a low pass filter that hides the coincidence frequency.
This is visible with directivity measurements.
If you can't do such measurements (need some space and time), there is an indication in the on axis FR (see below at 4ms) : as the coincidence frequency is an emission in HF at high angle, it is reflected by the walls creating an image of the main IR, image which is not in the "without concentrator" panel. It suppose the original to be in condition of no reflection at this time so measurements far from walls (> 1.5m? for all the walls and the ceiling) and absorption of the floor reflection).
For now, I have no evidences of strong emission from a venting (I don't say it doesn't exist). *If it is the source, the effect would be mainly visible from the back side probably over a wide angle.
The coincidence frequency is visible at high angles (let say above 60°?) on both side.
Christian
Last edited:
Hello Eric,
Would that mean the Gremlins is playing for you at 4.5kHz? Is it a stressed Gremlins? ;-)
For now, my tests don't show a possible cavity resonance as unique cause... In some cases with a concentrator, there is a reduction of the SPL, a change in the shape. In addition the concentrator seems to create new things... Not easy.
The frequency of the peak is not the same for all the panel despite the exciter is the same model. let say from 1.5 to less than 3k for me. To be detailled. I am currently testing much larger panels to see if there is relation to the panel dimensions.
What is strange in addition in your test is the almost constant difference rear to front between 2 to 3k.
Which exciter is it? What are the panel dimensions?
Christian
I've 3D printed several concentrators too. Here's the latest one. The center ring in contact with the panel has an OD of 12 mm and an ID of 6 mm. It weighs about 2 grams. I attached it to my plywood panel with a tiny M2 bolt and nut. The exciter is attached to the concentrator with double sided tape.
Here is the result compared to the exciter alone (25FHE-4) with no concentrator. The concentrator gave a little boost to the response between about 1 to 12 kHz, then had a bit dip 16 kHz, where the exciter alone had the big peak.
I also tried cutting a hole in the panel at the exciter location. The hole diameter is about 18 mm, so just a bit smaller than the 21 mm ID of the exciter foot. Sadly, my hole was pretty ragged! Embarrassing! In any event, the hole had a pretty similar effect on the frequency response as the concentrator did, except above 12 kHz, where the peak remained, but not so big as with the exciter alone with no hole.
See also below the impulse response plots for the three variations. It's pretty nasty for all three, but the standard exciter is the least nasty, and the concentrator the worst. I don't really know why that would be, but it has happened with all the concentrators I've tested so far. This one actually had the cleanest impulse response of the three or four variations I've tried.
So far, I'm no too excited about either the concentrator or the hole. Mainly I suppose because the biggest impact is above about 12 kHz, which I can't hear anyway!
Eric
Here is the result compared to the exciter alone (25FHE-4) with no concentrator. The concentrator gave a little boost to the response between about 1 to 12 kHz, then had a bit dip 16 kHz, where the exciter alone had the big peak.
I also tried cutting a hole in the panel at the exciter location. The hole diameter is about 18 mm, so just a bit smaller than the 21 mm ID of the exciter foot. Sadly, my hole was pretty ragged! Embarrassing! In any event, the hole had a pretty similar effect on the frequency response as the concentrator did, except above 12 kHz, where the peak remained, but not so big as with the exciter alone with no hole.
See also below the impulse response plots for the three variations. It's pretty nasty for all three, but the standard exciter is the least nasty, and the concentrator the worst. I don't really know why that would be, but it has happened with all the concentrators I've tested so far. This one actually had the cleanest impulse response of the three or four variations I've tried.
So far, I'm no too excited about either the concentrator or the hole. Mainly I suppose because the biggest impact is above about 12 kHz, which I can't hear anyway!
Eric
Hi everyone -
A new video has been posted showing off some of the new things I've added to PETTaLS - mostly just adding Dayton Audio exciter models right now. Let me know what you think, because I'm getting closer to making it available, and I'm still happy to incorporate changes!
For those of you working on the couplers, is it possible to post impedance measurements with and without the coupler? I wouldn't be surprised if Eric's already asked for this or done this himself, so sorry if this is a repeat question. I'm interested to see what effects are visible in the impedance measurement.
A new video has been posted showing off some of the new things I've added to PETTaLS - mostly just adding Dayton Audio exciter models right now. Let me know what you think, because I'm getting closer to making it available, and I'm still happy to incorporate changes!
For those of you working on the couplers, is it possible to post impedance measurements with and without the coupler? I wouldn't be surprised if Eric's already asked for this or done this himself, so sorry if this is a repeat question. I'm interested to see what effects are visible in the impedance measurement.
Haha, that's the one thing I usually do, but have not done yet with the concentrator. Maybe tonight. Though I'm still not sure my execution of the concentrator concept is good or not.
Eric
Hi Eric, Using a plastic screw in place of the steel, might be a good way to isolate how mass effects the response of the concentrator. Mcmaster-Carr has a good selection. Nice work on this!
Bruce
Dave,
Nice update. I do like having the two versions of frequency response lined up with each other like you have now. And the other displays are great to see too, especially the impedance (of course).
Regarding exciters to include, it would be nice to have the Xcite line of exciters as options. I'm eager to try out the new 19 and 25 mm versions myself, but have not bought any yet.
One other thought for a feature: Could the lower frequency response curve be set up to have as an option to show a slice of the polar response at a selected angle? I could see it working like your surface velocity map (where you select the frequency you want), except instead of selecting a frequency, you select in this case the angle at which you want to see the response. It is a bit redundant since you have the polar response plot already, but I still think it would be a nice feature.
Also, I wonder if you could comment on the following: In the image below from the new video, one can see that there are lobes at each of the resonances of the aluminum plate. And that at higher and higher frequencies, the number of lobes at each resonance increases. Is the number of lobes at each natural frequency directly related to the corresponding mode shape? And exactly how? It almost looks like the number of lobes might equal one of the mode indices. Is that right?
Finally, is you plate model based on a Kirchhoff-Love (thin plate) or Mindlin (thick plate) model? Or other?
Thanks,
Eric
Thanks,
Eric
+ Veleric
And also : When I tried using a m3 steel bolt, (being magnetic?-extra dampig?) resulted in less high frequency, a stainless steel bolt worked better/less bad.
Hans
Hello Eric,
Nice to see tests of concentrators and hole. I am in difficulty like with mine to understand what happens. The concentrator seems to add some complexity.
Questions :
- why do we see 4 curves on the plots (2 measurements of each ?)?
- is it a high ratio panel?
- the peak at 12k in original panel (no hole, no concentrator) is probably from the central area (drum effect) and disappear with this area.
- like you, I see a "degradation" of the IR like if some energy is added lately or some ringing occur. In your tests, it is difficult to analyze them because without knowing what is from the panel (the direct sound) and what is reflections we can't identify the source of what is added.
Orange is the panel with the standard ring mounted exciter.
Green is a 1.9g concentrator
Blue is a 20mm hole
Those measurements are not from the same day so it might be some differences in the reflection time due to a small difference in position in the room
So clearly, the concentrator and the hole have much higher reflections meaning they radiate at high angle.
Then be careful with an FR using a long time window that will take into account those reflections but without information to you about when and from which direction the energy comes.
In addition to that, I don't observe a significant reduction of the rear sound SPL in the 2 to 3k as expected (the supposed cavity resonance).
At the moment I see more drawbacks than advantages to the concentrator (at least with a small diameter) or to the hole... In an other hand, the drum effect is a reality... What is also visible from the directivity plots is a 25mm ring start beaming around 8k which is not so bad. When the central area is reinforced to limit the drum effect, the beaming effect seems a bit more severe.
So for no, I ma in the opinion not to reduce central area rigidity below what the panel gives (no hole) but probably to increase it, not to drive the panel on a diameter below 15mm, maybe 20mm.
And from all of that, no solution for now and even no full explanation to the rear side SPL in the 2/3k or higher range...
Christian
Eric,
For the IR, I generally don't have a look after for sure 50ms or even 30ms which is the starting range of echos for the auditory system and preferably now I zoom on the time horizon of the arrival time of the 1st reflections of the room so the range 5 to 10ms or about.
In my understanding : other. The tool seems for me based on the superposition of the modes (see the effect on the computation time in the last video when the density of modes increases). So the knowledge of the modes and mode shapes is a kind of input for the simulator. Analytical solutions are known for SSSS, CCCC. We made together simulation checks based on that. A mathematical approach (or estimation?) extends to the other boundary conditions.
@EarthTonesElectronics : Dave?
Christian
Neither I am, see post below
I agree I can't hear pure tone in this range. I also remember some complains Eucy had from young hears (the Eucy dome story). I hope my memory is correct...