kind of reminds me of Bob James a favorite of mine. So what size is a medium tower? I like the sound of this panel more than the square one. Folks would be interested to know more I am sure after listening to this. Thanks for posting.
Hi Scrapper 4 . I am feeling a bit confused here. I can see if using a relatively thick panel with a soft very low density eps foam would block high frequency transmission from the voice coil on its way to the front of the panel. But if a thin low density eps panel of say 1/4 inch thick is used and the panel is coated to surface stiffen it so it is not floppy the thin soft foam is going to be a lot more transparent to the high frequency reaching the front surface of the panel. A stiff panel coating should also help spread high frequency across the thin light low density panel panel. It would seem to me that a thin yet stiff coating would help with high frequency and yet still be light enough to maintain good panel efficiency.
The higher the panel density the better the transmission of high frequency but the heaver the panel gets for a given thickness so high density panels must be made thinner to maintain good efficiency. So it seems to me that it would seem logical that a good panel should be able to be made with either a very light density panel material or with a higher density panel material and it would seem a matter of the correct balance of thickness and stiffness. In both cases the stiffening coating will also damp the panel from ringing. Have I got the concept correct or am I missing something?
do you find an improvement in mid bass and lower lower end coupling when a rectangular shaped panel is positioned so that the long axis is parallel to the ground? Likewise I guess if you take a square panel and rotate it so a corner to corner (long axis) is parallel to the ground.
How low does this medium tower speaker play down to solid? I realize I am listening on cheap headphones off my computer but theses sound very good to me. I would be feeling quite content with a set of these. Thanks for responding and for engaging in discussion much appreciated.
So the medium tower panel is a 10mm thick 3 lbs per ft3 EPS panel? Hypothetical question; if I were to use a 1.2 inch thick 1 lb eps (or lower density like the foam sols for crafts and packing) but I was to sand the surface skin off smooth and apply a stiffening mater which did not add too much weight and which did not over damp the panel I should be able to find a compromise where I should get a very similar sound quality to the panel with the 10 mm 3 lb EPS? Does that sound like a plausible situation? Obviously the stiffening agent would need to be lighter than PVA and stiffer. In other words there ought to be a number of different combinations possible to reach a similar balance. What do you think should this be the case? Thanks for helping me to figure my way through this.
Moray, nup, nup, nup (imo)
Performance with soft EPS won't be anywhere near the thinner, denser material. You'll lose a lot of hf in that formation.
That being said, you could try that thickness in XPS with the surface treatment you describe. It'll be crisper than soft EPS.
But... Try it out... In the end it's the only way to know.
Eucy
this should have read "if you use a 1/2 inch thick 1 lb eps foam" sorry for the mistake.
Has no one commented on this yet? Very interesting observation. Thanks for posting.
In my opinion the idea that one side sounds different than the other is almost certainly an incorrect deduction. It's far more likely that small changes in exciter placement and mounts when switching sides caused the observed effect. Panels are very sensitive to mounts and exciter placement, and the smallest changes can have a big effect. This makes testing and tuning more difficult. If one was building these in a factory a lot of careful QC and QA would be required to ensure each individual panel was performing as expected.
If the idea that one side sounds different than the other were true, I'd guess it would be caused by variations in the surface treatment and/or variations in density. It is reasonable to think that when the PS is expanded in the factory the force of gravity could cause the density to be very slightly higher on the bottom side, but I would think that the pressure in the mold from the expanding foam would be so high compared to gravity that the the difference should not be measurable. Similarly, with EPS more so than XPS, the foam itself could have some pockets of higher or lower density if the foam is not evenly distributed in the mold and if it is not all hardening at the same time, or if heating and cooling rates are not uniform. I don't think that any of this will be significant enough for us to measure because I expect modern manufacturing techniques to produce very good quality. I could be wrong though.
When you remove exciter, flip panel, reattach exciter, odds are high that the exciter was reattached on the opposite side of the panel. If there was an off-center pocket of higher density foam then that would be like gluing a mass in that spot to a panel of perfect uniform density. We know this can make significant differences in FR. To really test the 'one side sounds better than the other' idea then I'd suggest drilling a small hole perfectly perpendicular through the panel then use a compass to draw a perfect circle so that the exciter can be perfectly aligned in the exact same spot on both sides of the panel. The mounting situation would need the same level of care to ensure that no pressure on the panel is changed in any place between tests.
For most of my panels I have 2" thick XPS that I slice down to 3/4". I do try to take the center region of the 2" thickness because the outside surface appears to be less expanded than the inside. When I slice the first 1/4" off the top of a panel both sides bow after cutting, but that 1/4" slice can really bow quite a lot with the exterior side being shorter than the interior side. The exterior surface is cooled in the mold first while the inside has more time to expand, that's what I'm thinking anyway. It's a lot like a loaf of bread - firm crust with very tiny bubbles in it but in the center of the loaf the bubbles are much larger. The whole thing is a gradient of density with crust being heaviest and center being lightest. For foam this is quite uniform across the thickness though, so if you aren't slicing a panel through its thickness then it will not cause one side to be any different than the other.
If the idea that one side sounds different than the other were true, I'd guess it would be caused by variations in the surface treatment and/or variations in density. It is reasonable to think that when the PS is expanded in the factory the force of gravity could cause the density to be very slightly higher on the bottom side, but I would think that the pressure in the mold from the expanding foam would be so high compared to gravity that the the difference should not be measurable. Similarly, with EPS more so than XPS, the foam itself could have some pockets of higher or lower density if the foam is not evenly distributed in the mold and if it is not all hardening at the same time, or if heating and cooling rates are not uniform. I don't think that any of this will be significant enough for us to measure because I expect modern manufacturing techniques to produce very good quality. I could be wrong though.
When you remove exciter, flip panel, reattach exciter, odds are high that the exciter was reattached on the opposite side of the panel. If there was an off-center pocket of higher density foam then that would be like gluing a mass in that spot to a panel of perfect uniform density. We know this can make significant differences in FR. To really test the 'one side sounds better than the other' idea then I'd suggest drilling a small hole perfectly perpendicular through the panel then use a compass to draw a perfect circle so that the exciter can be perfectly aligned in the exact same spot on both sides of the panel. The mounting situation would need the same level of care to ensure that no pressure on the panel is changed in any place between tests.
For most of my panels I have 2" thick XPS that I slice down to 3/4". I do try to take the center region of the 2" thickness because the outside surface appears to be less expanded than the inside. When I slice the first 1/4" off the top of a panel both sides bow after cutting, but that 1/4" slice can really bow quite a lot with the exterior side being shorter than the interior side. The exterior surface is cooled in the mold first while the inside has more time to expand, that's what I'm thinking anyway. It's a lot like a loaf of bread - firm crust with very tiny bubbles in it but in the center of the loaf the bubbles are much larger. The whole thing is a gradient of density with crust being heaviest and center being lightest. For foam this is quite uniform across the thickness though, so if you aren't slicing a panel through its thickness then it will not cause one side to be any different than the other.
Hello Leob,
I have recently tests the different suspension configurations I have seen in this thread. Maybe it was not accurate enough in the way it was made in a changeable arrangement and only for one panel. Considering distortion, energy absorption, FR smoothness, a full perimeter light suspension seems to give good results. A possible solution for a light suspension is to use an EPDM D shape weather strip. The straight part of the D on the frame, the belly of the D to the panel for example. To have an even lighter suspension, I think to cut one side of the D shape.
Christian
Hello,
What can be seen mainly when the central area is rigid is a peak in the 2/3kHz range (called in previous posts exciter noise) coming from the back due to the air trapped in the voice coil volume. It gives a peak in the FR from the front side and looking at the spectrogram, it appears as high level delayed at that frequency. A FR with the back side pointing to the mic shows this peak in the direct wave front.
Christian
The side that has the driver mounted on it (the 'back' side) will definitely sound and measure differently to the front side.
This is especially true of any thickness of EPS which does not transmit HF very well.
It's a good test, when testing panels, to measure both the front and the back, as the difference between the measurements will tell you how much HF you're losing due to panel material properties.
I've used all kinds of EPS. I've skinned it with paper, 80gsm kraft paper, mylar, aluminum foil, 22gsm carbon fibre, 60gsm kevlar and dyneema, and 0.5mm veneer; I've used all kinds of PVA, diluted PVA, epoxy resins and polyurethane glues; I've tested all of the above on 25mm EPS, all the way down to 3mm EPS.
I can confidently say that EPS is pretty much the last on my list of preferred materials. Because of its softness, it's simply unable to produce enough HF to be useable.
The best result I got, with the flattest response, was to attach the driver to a 100mm polycarb puck attached by low compliance legs to a hole in the panel. The pics are somewhere on this thread.
I can confidently say that EPS is pretty much the last on my list of preferred materials. Because of its softness, it's simply unable to produce enough HF to be useable.
The best result I got, with the flattest response, was to attach the driver to a 100mm polycarb puck attached by low compliance legs to a hole in the panel. The pics are somewhere on this thread.
You have not noticed any difference in efficiency when using full perimeter?
I initially used foam strip for sealing windows, which resulted in light suspension, but found that the more sponge like materials will degrade with time. However the D shape strips seems to be solid rubber rather than foam though, and should be stable while still soft. I think EPDM has quite similar properties to the TPU I use, but actually should be even better at handling compression over time.
what did the top end of these panels look like? I am assuming they that they are stiffer than the meat tray panels I mentioned? Thanks Steve.