Hey Steve where do your 1cm thick light (1 lbs/cu ft) eps panels fall in this comparison? Size and low frequency extension? Thanks.
I have mentioned quite a few times over the years, from my observations of the exciter at low frequencies.
It is clear to me that an exciter that is not braced, has two driving forces.
The braced exciter only has one.
Somewhere ,Below 100hz while the coil is still acting like an exciter should.
The magnet starts to vibrate or bounce causing a resonance.
The magnet is acting like a bass shaker and not like an exciter .
I think if it as being like a helmholtz resonator, increasing the low frequency output.
I used to get quite large amounts of low frequencies from my large eps panels with unmounted exciters, but the only problem was that the panels were shaking all over the place, pretty much out of control.
So I used to roll off the response heavily below 50, 60, 70, 80 or 90hz depending on the panel used.
Otherwise, there would be a considerable bass hump below these frequencies.
On the batman the dark Knight cd for instance, the very low and loud frequencies at about 30hz would set off the exciter (shaker) producing large exciter and panel movement.
Mirroring my transmission line speakers measurements but will a slightly narrower peak.
These are my thoughts.
I hope this helps explain the unmounted exciter performance in the low frequency area.
Steve.
Hello moray.
To be honest, I do not pay much attention to the response below 100hz as I never intend to use my panels much below this.
I have posted the frequency response for these panels somewhere on this forum, but I can't remember how low they do go.
But the exciters will vibrate heavily around the 40hz area if pushed but probably without the increased output wanted.
The last thing you want is the panel to start flapping about all over the place out of control.
Steve.
To be honest, I do not pay much attention to the response below 100hz as I never intend to use my panels much below this.
I have posted the frequency response for these panels somewhere on this forum, but I can't remember how low they do go.
But the exciters will vibrate heavily around the 40hz area if pushed but probably without the increased output wanted.
The last thing you want is the panel to start flapping about all over the place out of control.
Steve.
Hello Steve,
You are right to remind there are 2 cases : the fixed magnet (rigid spine) and the free magnet (no spine and probably soft support like a ribbon).
Because of the deformation of the spider over the time, I consider the free magnet situation only for short term use like tests.
I think Eric reported also the action of the free magnet as bass reinforcement (mechanical resonator you describe).
2 additional points let me also a bit cautious : is there a risk of higher distortion because of the possible extra displacement ? and as we are the very beginning of some prediction possibility with simulation, it is a bit like an empirical vent in a bass reflex; how to be sure it is well adjusted regarding the panel modes?
The good point is fixed/free magnet is an option in PETTaLS (not in my Python simulation which is able of only fixed magnet!).
Christian
Hello Christian.
Yes it was very nice of Eric to confirm my previous observations 😀
There are many was to freely mount an exciter so that the magnet can move freely or be more controlled .
I still have some panels with free mounting that have had no problem with sagging and that is after 10years.
Even if they did sagg I would just turn the panel upside-down, the same as I have done many times with cone speaker units.
The use of stiffer magnet support and a way of controlling the inevitable exciter side wobble caused by the imbalance of the wire and connections to one side.
It is probably a good idea to have some form of support for the magnet even if you are not using the exciter down to the exciter magnet resonance to, as you say, prevent sagging.
I am still intrigued with the x19-4 as it only weighs 30grams , and will suite very light eps, and also may be able to support itself for longer without sagging?
It also has a very good spec, if it is to believe?
Steve.
Yes it was very nice of Eric to confirm my previous observations 😀
There are many was to freely mount an exciter so that the magnet can move freely or be more controlled .
I still have some panels with free mounting that have had no problem with sagging and that is after 10years.
Even if they did sagg I would just turn the panel upside-down, the same as I have done many times with cone speaker units.
The use of stiffer magnet support and a way of controlling the inevitable exciter side wobble caused by the imbalance of the wire and connections to one side.
It is probably a good idea to have some form of support for the magnet even if you are not using the exciter down to the exciter magnet resonance to, as you say, prevent sagging.
I am still intrigued with the x19-4 as it only weighs 30grams , and will suite very light eps, and also may be able to support itself for longer without sagging?
It also has a very good spec, if it is to believe?
Steve.
the Dayton Audio DAEXCT19-4 (32 grams each) - provided response is very nice too and so I bought some to experiment with. Further the DAEX19SL-4 is physically lighter (though wider in width than the DAEX19ct-4 but it has even smoother flatter response and its phase and impedance are even better making it very easy for any amp to drive. The 19SL-4 fr (15.5 grams each) response is smoother/flatter and has a bump at either end of its frequency spectrum which I think is useful. The drawback is that its overall output is on the low side but would be excellent for headphones or computer speakers or if positioned physically close to the listening position. Used in a stereo set up it would be fine I think so long as you don't plan on paint peeling levels of playback.
This remind me I have noticed the wires I use have a stiffness that probably modify the magnet resonance during test... Some portion of soft or reduce section wires are required to let the magnet as free as possible and more important to avoid any strength from the wires on the magnet/voice coil position.
Those 19mm exciters have small magnets. I can't find the weight of a DAEX19CT to compare but the force factor of the XT19 is higher which is good for the efficiency. Even if better than the 19CT is about 40% less than a 25mm...
By curiosity, I just run very quick simulations with PETTaLLS without any fine tuning to compare a DAEX19CT on a 30x50cm light EPS panel to a DAEX25VT on a 3mm plywood of the same dimensions. Both with exciters at 0.37/0.37, 1W, free magnet, free edges (FFFF). I did that to have an idea of the resulting efficiency (light panel with a low BL exciter, heavier panel with a higher BL)
The simulation shows the global efficiency are about the same.
The output I didn't expect is the roll off of the 19CT has a more important slope... what I can't explain. May be because of the higher stiffness or the lower magnet mass of the 19mm model
This reminds me I observed similar behavior while testing panels with a 13CT at home. I was expected with them a better HF extension than with a 25mm, which was true by rejecting higher in frequency the effect of the voice coil diameter but I was more surprised by the effect on the bass cut off.
Christian
PS: by the way, I would like to encourage all the DML builders to use such a tool. I think it is reaching a very good level even if all the possible configurations, exciters or materials are not available. There are 2 possibilities : its output are confirmed by the experience so we gain in confidence in its use, it is not confirmed so some aspect is maybe not covered or not with an appropriate model. In any case it is part of the learning experience. Thanks again to Dave (@EarthTonesElectronics) for the free availability of PETTaLS (follow the links to download and install) with its clear interface.
Dark blue : DAEX25VT on 3mm plywood, light blue : DAEX19CT on 10mm light EPS
Hello moray.
I found the output from a 2cm thick low grade eps test panel to be quite considerable using this small exciter.
I think it is a 4 or 5 watt exciter.
As long as you do not expect low frequencies from such a low powered exciter.
The xtreme x19-4 , although they advertise it as 10watts , in the spec it says that is 20watts ???
Which is the true true power rating ?
Steve.
I found the output from a 2cm thick low grade eps test panel to be quite considerable using this small exciter.
I think it is a 4 or 5 watt exciter.
As long as you do not expect low frequencies from such a low powered exciter.
The xtreme x19-4 , although they advertise it as 10watts , in the spec it says that is 20watts ???
Which is the true true power rating ?
Steve.
Attachments
Hello moray.
I have this old video of me singing (sorry)😱 to test the panel for microphone use.
I have some playing music but I'm not sure about the copyright.
So this will have to do.
I would suggest putting your fingers in your ears, but then that would defeat the object of the video 😁
I have this old video of me singing (sorry)😱 to test the panel for microphone use.
I have some playing music but I'm not sure about the copyright.
So this will have to do.
I would suggest putting your fingers in your ears, but then that would defeat the object of the video 😁
Hello Christian.
I would have expected the overall output of the eps to be much higher than the ply ?
Eps is so much more efficient.
Strange.
Steve.
I would have expected the overall output of the eps to be much higher than the ply ?
Eps is so much more efficient.
Strange.
Steve.
I'm sure @homeswinghome can answer as well, but the DAEX25VT-4 has a BL (force factor) that's about 5x the BL of the DAEX19CT-4, so that adds about 14dB of sensitivity to the plywood response relative to what it would have been with the smaller exciter.
This is a good test, because it demonstrates that for a certain level of 1W sensitivity on plywood you need a much more powerful exciter than you would on a lighter material like EPS.
Haha, not likely me. To the contrary, I've always found (as I recall anyway) that there is practically no effect of fixing the exciter magnet or leaving it free, at least not in terms of frequency response.
Below are two examples. First a "free" (no frame) poplar plywood panel. Blue line is with the exciter free, green is exciter fixed. Response is identical for all practical purposes (VT25-4 exciter).
And here a "free" EPS panel also with a VT25-4 exciter. Blue curve is with exciter free, orange is exciter fixed. Again, identical response for all practical purposes.
Both of these are examples with free (hanging) panels, but I have found the same to be true with panels mounted on a foam surround. No practical difference in frequency response with magnet free or fixed.
For this case below (acrylic, SSSS boundary), Pettals predicts a slight boost at the magnet resonance for the "free" magnet, but the output in that region is already 20 dB down, so any such boost is of no practical consequence.
Eric
Dayton Audio publish frequency response graphs for their DML exciters. Drivers are all mounted on a 12 inch by 12 inch by 1/2 inch thick panel of low density EPS (expanded polystyrene) which is then mounted into an infinite baffle (would assume a 4' x 4' or a 4' x 8' ft panel). This likely has an impact on frequency response below about 100 Hz. I am curious to know if anyone here with measurement equipment has compared any of these Dayton Audio exciters on the same size and thickness EPS panels alone to compare with the factory response. One would assume that Dayton would hardly go tho the trouble of using an infinite baffle unless it would make the bass response look much better that way. Have any of you done this experiment? Thanks for any feed back.