Sometimes, it is better to go back to the beginning and read what those guys did. They went through most of the 'ideas' as the topic was hot then. Some of them have gone away, though, but they actually made a pair of speakers.
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Sure, I will, come summer.
The time for sticking an exciter on any random sheet has gone.
Though, I found that the edge exciting works even better under thin glass panels and bottom exciting under thick bottomed glass vases. I cannot atm, fathom why that 10mm thick glass bottom radiates such good sound through vertical 3mm thick 70cm high round glass walls. Actually, the edge exciting works better with practically all sheets. Well, that was known to Georg von Arco (~1924) and Lee de Forrest (~1925), or maybe even before to other people.
Sure, I will, come summer.
The time for sticking an exciter on any random sheet has gone.
Though, I found that the edge exciting works even better under thin glass panels and bottom exciting under thick bottomed glass vases. I cannot atm, fathom why that 10mm thick glass bottom radiates such good sound through vertical 3mm thick 70cm high round glass walls. Actually, the edge exciting works better with practically all sheets. Well, that was known to Georg von Arco (~1924) and Lee de Forrest (~1925), or maybe even before to other people.
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It is not the size that is the problem, it is the way that I am recording that is the problem.
The panels are rolled off at 300hz because the exciters are not braced, the wires are mains cable and will put the exciters way out of balance, causing dangerous wobbling.
I am holding the phone 1m away from the panels, but the subs are another foot or two behind in the corners (time corrected) so that the panel response is being emphasised.
The microphone also rolls off early with nothing going on below 50hz.
When quick recording I have no idea how the sound will be on the recording until I listen afterwards , I can get the mix totally wrong !
The only way to make a perfect recording is to hold the microphone between the two panels in headphone mode ,using the panels in full frequency but at a lower volume.
This is not a problem, but when listening on headphones it does sound like you are listening to headphones not in a room.
I hope this clarifies the recording problems, it is not the panels falt, it is mine 😜
If XO is done properly small panels (even very small panels)sound just as good as and sometimes better than large panels in a normal room size.
Steve.
Further to post #8,780,
The NXT idea of inserted into the radiator panel transducer is quite an interesting idea for the distributed mode sound propagation. This way, the voice coil doesn't move in regard of the radiator, but the magnet system moves instead, and only in to and fro motion, which only allows the 'bending' waves to travel away from the fixed voice coil, that is, only vibrations happen, but not the 'pistonic' motion of the radiator panel. And, in a push pull motion, with only one transducer, exciting both sides, one after the other in a tiny time difference.
If both pistonic motion and the bending motion happens at the same time, then the radiator would be a balanced mode radiator (BMR), but even that has to be blocked at the edges with rubber-like suspension. The distortions/colourations of the free hanging, unsupported radiators are due to that dual motion, easily noticed by the uncontrollable wobbling.
The NXT idea of inserted into the radiator panel transducer is quite an interesting idea for the distributed mode sound propagation. This way, the voice coil doesn't move in regard of the radiator, but the magnet system moves instead, and only in to and fro motion, which only allows the 'bending' waves to travel away from the fixed voice coil, that is, only vibrations happen, but not the 'pistonic' motion of the radiator panel. And, in a push pull motion, with only one transducer, exciting both sides, one after the other in a tiny time difference.
If both pistonic motion and the bending motion happens at the same time, then the radiator would be a balanced mode radiator (BMR), but even that has to be blocked at the edges with rubber-like suspension. The distortions/colourations of the free hanging, unsupported radiators are due to that dual motion, easily noticed by the uncontrollable wobbling.
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The blu-tack method is my least favourite method of preventing problems in the coil area as it adds mass, but it is cheap and effective on heavy rigid panels.
I would not use this method on EPS !
Use as little as possible of the blu-tack, less is more.
You could even experiment offsetting the blu-tack a little to see if this improves things, but you really need to watch this in real time as you are moving the blu-tack around ,it saves so much time.
To start with just place the blu-tack in the centre of the voice coil area.
This will do nothing to prevent cavity resonance but may help damp the sound a little?
Maybe I should do a rough drawing to explain the problem ?
I intend ,when I have finished doing a few more experiments with this panel, to drill a small hole (2mm maybe)in the central area and filling it with blu-tack or even some sort of mastic?
Hopefully this way there will be no extra mass? " Quid pro quo clarice " 😈
Does this help ?
Steve.
I will also be using this panel to try out a new idea of implementing the exciter, which I have tried on very small 4inch panels in the past ,but not shown it on this site (I think)as they only went down to about 500hz ,I think ? Not full range.
But I want to see if lower frequencies are possible, but may have to use a thinner lighter more flexible panel ?
I will probably post this on burnts new exciter design forum ,if it is viable ?
Steve.
But I want to see if lower frequencies are possible, but may have to use a thinner lighter more flexible panel ?
I will probably post this on burnts new exciter design forum ,if it is viable ?
Steve.
A DML is identified by the fact that its radiation is due to uniformly distributed, free vibration in a stiff, light panel and not to pistonic motion.
Because bending waves are dispersive (the wave velocity is a function of frequency), a good approximation is to consider the panel as a randomly vibrating area. In order to achieve this constant velocity with a constant force, the mechanical impedance must be resistive. A panel operating in bending waves meets this criterion.
Because we are considering the DML to be randomly vibrating, the existing motion of the panel will be uncorrelated to any new input being applied therefore it looks like an infinite panel. Additionally, because the panel has low mechanical loss, it is assumed that all energy supplied to the panel had to be dissipated by acoustic radiation.
Because the DML panel is modal, the radiation that arises is diffuse and uncorrelated. Although the impulse response lasts for more than 25ms, it has a random charasteric, with no single frequency that can be picked out. For the DML panel the directivity is substantially independent of frequency.
Because of the diffuse nature of a DML panel there exists a region close to the panel in which the pressure remains substantially constant. When in rooms the DML panel can use the rear radiation to support the front pressure region in such a way as to increase the region where the pressure remains constant. Since the DML panel has diffuse radiation, it also must enjoy diffuse reflections. These two features combine to give a loudspeaker that excites far fewer room modes than a traditional loudspeaker.
A DML loudspeaker is, intrinsically, a broadband acoustic radiator.
Because bending waves are dispersive (the wave velocity is a function of frequency), a good approximation is to consider the panel as a randomly vibrating area. In order to achieve this constant velocity with a constant force, the mechanical impedance must be resistive. A panel operating in bending waves meets this criterion.
Because we are considering the DML to be randomly vibrating, the existing motion of the panel will be uncorrelated to any new input being applied therefore it looks like an infinite panel. Additionally, because the panel has low mechanical loss, it is assumed that all energy supplied to the panel had to be dissipated by acoustic radiation.
Because the DML panel is modal, the radiation that arises is diffuse and uncorrelated. Although the impulse response lasts for more than 25ms, it has a random charasteric, with no single frequency that can be picked out. For the DML panel the directivity is substantially independent of frequency.
Because of the diffuse nature of a DML panel there exists a region close to the panel in which the pressure remains substantially constant. When in rooms the DML panel can use the rear radiation to support the front pressure region in such a way as to increase the region where the pressure remains constant. Since the DML panel has diffuse radiation, it also must enjoy diffuse reflections. These two features combine to give a loudspeaker that excites far fewer room modes than a traditional loudspeaker.
A DML loudspeaker is, intrinsically, a broadband acoustic radiator.
- Wide bandwidth from a single radiator,
- Temporally & spatially diffuse sound radiation,
- Directivity & polar pattern - substantially frequency independent,
- Intrinsic scalability,
- Uncorrelated, constructive rear radiation,
- Power loss versus distance,
- Improved room interaction flat power, with no sweet-spots,
- -Simple resistive load presented to the amplifier
Lordtarquin.Finally dug out the laptop with measurements of the panels for the PA system.
In the rush I had not labelled them too well, but I think this is the correct responses.
Blue is pre-eq and red after.
I think I ignored the very large swings in the mids, since they where sounding really good with some EQ and I was in a hurry, but looking at the curves now it is actually nice to see what a disaster it is pre-eq, considering it still sounds really great
It means there should be plenty of room for improvement when tweaking them to even out the response in 250-600Hz region. I'm hoping I can get decent results by modifying the suspension more, which is very easy to do.
View attachment 1085679
I was looking for leobs sound check video ,but could not find it, but noticed that his panels had a very similar frequency response to your panels.
Steve.
Steve
This could either be a panel mounting phenomenon or a panel material's one.
In other news, I've managed to get real time displays of pink noise out of REW, thanks to Eric's input.
Simon.
Thanks so much for this Eric. I've tried it from my listening position and it works well. With 1/6 octave smoothing and RTA also set at 1/6 octave, I get a better impression of overall balance with pink noise played for 20 seconds or so than with a simple frequency sweep.
The next step is to turn off all the EQ and use the mic at various positions from the panel to determine where the critical peaks and troughs are and to try to address them on the panel rather than solely through EQ.
Hi @pixel1,
One solution is to mount the exciter to a spine that is attached to the frame for the panel Like shown in these pictures.
I typically use a piece of foam with adhesive on both sides between the back of the exciter and the spine, but I don't think the foam is necessary. You can attach the exciter directly to the spine using the threaded hole in the back of the exciter (if it has one), or with double sided tape. Just make sure not to compress the exciter significantly between the spine and the panel. I try to compress it by only about 0.25 mm. Just enough to keep a tiny bit of pressure.
Eric
Lordtarquin.
The method I use is similar to this YouTube video at about 8mins in.
I have my deq set to peak hold not average as in the vidio.
when I am sitting on my couch in the listening position, I move the microphone to the left about 2ft then 2ft to the right and also up and down covering the whole couch area.
Do not move the microphones fast as in the video unless you have a wind shield, I move the microphone slowly anyway.
This will give me an average of the response in this seating area, which is most important.
If I took single point measurements they could be totally different and EQing one point could make the other points worse.
I hope this is of some use.
This is why I do not usually use EQ although I have the option.
Steve.
The method I use is similar to this YouTube video at about 8mins in.
I have my deq set to peak hold not average as in the vidio.
when I am sitting on my couch in the listening position, I move the microphone to the left about 2ft then 2ft to the right and also up and down covering the whole couch area.
Do not move the microphones fast as in the video unless you have a wind shield, I move the microphone slowly anyway.
This will give me an average of the response in this seating area, which is most important.
If I took single point measurements they could be totally different and EQing one point could make the other points worse.
I hope this is of some use.
This is why I do not usually use EQ although I have the option.
Steve.
That right Eric. A white noise with an RTA will give a rising response due too many power while the frequency increase in a fixed width filter. It is the reason of the pink noise to get a flat response.
Christian
This a good method for a room averaged response called "Moving Microphone Measurement". See the post #4488 for notes and links.
Christian
If you use multiple exciters, first try connecting them together with wood brace. You can use double sided adhesive tape to glue the brace on the magnets.
Attachments
The easiest way is with double sided mounting tape. Attach the tape to the frame and then attach the panel to the tape. The mounting tape I like best is 3M Extreme double sided mounting tape. It comes in a strip 1 inch wide but I prefer to use only a 1/4" to 3/8" wide strip. I prefer to use the tape around virtually the entire perimeter, except for a few inches (2 or 3) from each corner. But the only reason for leaving the corners free is because it makes it much easier to separate the panel from the frame later if you want too.
Instead of the mounting tape you can use foam like the gray Frost King window weather stripping, or EPDM foam. Those are typically about 3/8" thick and 3/4" wide. I use the full 3/4" width with those. Also, these usually only have adhesive on one side, so you have to use something else (double sided tape or spray adhesive) to mount the other side to the frame or panel. But which tape or foam works best, and which dimensions depends on the panel material. Finding the best combination is still trial and error for me.
In the images below I attached the foam to the panel first, instead of the other way around. I also used a bigger gap in the corners than I do now, but I think you can get the idea.
Eric
Steve
Just spotted this. I EQ my overall response to an overall 3db drop from about 40hz all the way to 20khz.
I use a fancy Gorilla glue to attach the exciters to the panels. The sticky pads tend to result in poorer energy transfer from exciter to panel.
Simon