I am going to attempt to re-build my LXmini speakers using a CLD approach.
I was going to slide a 140mm PVC pipe (ID=125mm) over the top of the existing 4" pipe, then fill the cavity with Green Glue (Damping compound)
Each speaker would require 1.4 litres of Green glue.
Whereas the 4" pipe slots into the end cap, the 140mm pipe conveniently slides over the outside of the end cap and thus seals the cavity.
The fernco coupler also slides into the 140mm pipe (just).
Would this be enough to achive a CLD design?
I was going to slide a 140mm PVC pipe (ID=125mm) over the top of the existing 4" pipe, then fill the cavity with Green Glue (Damping compound)
Each speaker would require 1.4 litres of Green glue.
Whereas the 4" pipe slots into the end cap, the 140mm pipe conveniently slides over the outside of the end cap and thus seals the cavity.
The fernco coupler also slides into the 140mm pipe (just).
Would this be enough to achive a CLD design?
An externally hosted image should be here but it was not working when we last tested it.
Was going to pump a load in and hope for the best.
Gravity I suppose, does warming green glue make it less viscous?
I also realise that there would be a short circuit bewteen the two pipes, at the end cap so would need to re-think this area.
Would wrapping the inner pipe with 5mm bitumen or butyl sheet work as well as filling with latex caulk?
Gravity I suppose, does warming green glue make it less viscous?
I also realise that there would be a short circuit bewteen the two pipes, at the end cap so would need to re-think this area.
Would wrapping the inner pipe with 5mm bitumen or butyl sheet work as well as filling with latex caulk?
Well, I am committed now, have just taken delivery of 3m of both 4" and 140mm PVC pipe.
The ID of the 140mm measures 128mm so will clear the end cap without touching.
Will have to get it cut to length on a Band saw for nice straight cuts.
The ID of the 140mm measures 128mm so will clear the end cap without touching.
Will have to get it cut to length on a Band saw for nice straight cuts.
An externally hosted image should be here but it was not working when we last tested it.
How about a heavy duty glazing silicone adhesive - I think the combination of adhesion and resilience after curing would suit the task?
I don't have any personal experience with this type of product, but this was the first that popped up in my Google search.
CSL339 Fast Cure Silicone Window Sealant
I don't have any personal experience with this type of product, but this was the first that popped up in my Google search.
CSL339 Fast Cure Silicone Window Sealant
I was thinking of silicone or latex caulk to fill the void.
Here is what it might look like assembled...
Green shows the damping in the void between two pipes, blue is the end cap, orange is the MDF base and the black sections are Fernco couplers (1002-44) on top and bottom.
Here is what it might look like assembled...
Green shows the damping in the void between two pipes, blue is the end cap, orange is the MDF base and the black sections are Fernco couplers (1002-44) on top and bottom.
An externally hosted image should be here but it was not working when we last tested it.
I've never built a CLD project, so this is all conjecture - but wouldn't what appears to remain as direct connection between the blue end cap at bottom, black coupling adaptors at both ends and the internal / external pipes short circuit the attempt at isolation?
perhaps:
-shorten the outside layer so as to not directly contact the Fernco couplers,
- couplers with ID to accommodate the OD of the larger outside pipe - this would leave additional gap between the end cap and coupler that could be filled with the Green Glue or other compliant adhesive.
- isolate the blue end cap from MDF plinth with thick rubber / Sorbothane spacers?
perhaps:
-shorten the outside layer so as to not directly contact the Fernco couplers,
- couplers with ID to accommodate the OD of the larger outside pipe - this would leave additional gap between the end cap and coupler that could be filled with the Green Glue or other compliant adhesive.
- isolate the blue end cap from MDF plinth with thick rubber / Sorbothane spacers?
Maybe a slow curing mould / mold making silicone would give a long enough working time to fill every void and get any air bubbles out.
https://www.acc-silicones.com/products/mouldingrubbers.ashx
https://www.acc-silicones.com/products/mouldingrubbers.ashx
The Fernco couplers are made from "flexible PVC" which I assumed had high damping coefficient like rubber or other polymers.
How can you find out if a material has high or low damping qualities, or just be holding it?
I Like the idea of a liquid pour to fill the void, it may even be strong enough when cured to hold the outer pipe in place with no need for additional support.
The outer does clear the PVC end cap with a 2mm gap so could do away with the lower coupler.
This made for an interesting read... http://wings.buffalo.edu/academic/department/eng/mae/cmrl/Materials for vibration damping.pdf
My understanding is a material with high damping has a high Loss tangent.
Out of the polymers tested, PTFE had highest damping capacity/loss tangent but PMMA had the highest loss modulus.
Would be good if there were a list of other materials to compare.
How can you find out if a material has high or low damping qualities, or just be holding it?
I Like the idea of a liquid pour to fill the void, it may even be strong enough when cured to hold the outer pipe in place with no need for additional support.
The outer does clear the PVC end cap with a 2mm gap so could do away with the lower coupler.
This made for an interesting read... http://wings.buffalo.edu/academic/department/eng/mae/cmrl/Materials for vibration damping.pdf
My understanding is a material with high damping has a high Loss tangent.
Out of the polymers tested, PTFE had highest damping capacity/loss tangent but PMMA had the highest loss modulus.
Would be good if there were a list of other materials to compare.
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It is not a problem I am aware of, but I fancied a go at making a CLD LXmini.
The best I could hope for is an audible comparison as I wouldn't know how to measure any differences.
I think my first attempt will be wrapping the outside of the inner pipe with 5mm butyl rubber sheet and the slide the outer pipe over that. Epoxy could be poured in to fill any remaining gaps.
The best I could hope for is an audible comparison as I wouldn't know how to measure any differences.
I think my first attempt will be wrapping the outside of the inner pipe with 5mm butyl rubber sheet and the slide the outer pipe over that. Epoxy could be poured in to fill any remaining gaps.
Here is a quick sketch of what I have planned...
Inner pipe keyed with 40 gritt then wrapped in 5mm Butyl rubber sheet and stuck with epoxy.
Outer pipe slides over and remaining gap filled with epoxy.
A gasket ring made from the butyl rubber sits between outer pipe and MDF base to de-couple.
Inner pipe keyed with 40 gritt then wrapped in 5mm Butyl rubber sheet and stuck with epoxy.
Outer pipe slides over and remaining gap filled with epoxy.
A gasket ring made from the butyl rubber sits between outer pipe and MDF base to de-couple.
An externally hosted image should be here but it was not working when we last tested it.
Step back for a moment and consider that the 4" nominal Schedule 40 pipe used in LXmini has a design working pressure limit of 220 PSI (1500 kPa). That means that it is sufficiently stiff that it maintains structural integrity and dimensional stability to that pressure and well beyond given working safety factors. This stiffness is probably two orders of magnitude higher than typical box speaker construction and it is uniform given the circular cross section of the pipe.
The Seas L16RN-SL has a cone area of 104 cm^2 and a maximum coil travel of 22 mm p-p so in compression (cone traveling downward) the maximum displaced volume is 104x1.1 or 229 cm^3. The LXmini pipe has an internal volume of 389.6 in^3 or 6384 cc. Ignoring the action of the vent in the tube and the Acousta-stuff that ballparks the maximum static pressure in the tube at sea level at +/- 0.5 PSI or 0.2% of the rated working pressure of the tube.
So it seems to me you are going to enormous effort chasing a phantom (my LXminis exhibit no notable sound radiation from the quite stiff pipe wall) but if you must I would adjust your formula. Butyl rubber sheet is relatively soft and flexible while cured epoxy resin is fairly stiff and hard. Maintaining a bond between the two is unlikely. A better though admittedly messy combination would be a polysulfide caulk and butyl rubber. Better yet build the LXmini to spec and find out if there is any need for this modification as it can be retrofit with little more difficulty that building from scratch this way!
The Seas L16RN-SL has a cone area of 104 cm^2 and a maximum coil travel of 22 mm p-p so in compression (cone traveling downward) the maximum displaced volume is 104x1.1 or 229 cm^3. The LXmini pipe has an internal volume of 389.6 in^3 or 6384 cc. Ignoring the action of the vent in the tube and the Acousta-stuff that ballparks the maximum static pressure in the tube at sea level at +/- 0.5 PSI or 0.2% of the rated working pressure of the tube.
So it seems to me you are going to enormous effort chasing a phantom (my LXminis exhibit no notable sound radiation from the quite stiff pipe wall) but if you must I would adjust your formula. Butyl rubber sheet is relatively soft and flexible while cured epoxy resin is fairly stiff and hard. Maintaining a bond between the two is unlikely. A better though admittedly messy combination would be a polysulfide caulk and butyl rubber. Better yet build the LXmini to spec and find out if there is any need for this modification as it can be retrofit with little more difficulty that building from scratch this way!
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I have never fully understood the mechanism for panel vibration, is it purely a function of rigidity? If it were made from 4" Aluminium pipe would it still not ring or am I getting confused?
I built the LXmini when they were first released and have been in my living room ever since.
I fancied fettling with them a little and thought CLD might be interesting.
I built the LXmini when they were first released and have been in my living room ever since.
I fancied fettling with them a little and thought CLD might be interesting.
Vibration is a complex subject but in general the resonant frequency of a structure is a function of the relationship between its mass and stiffness. Large masses with low stiffness resonate at lower frequencies and small masses with high stiffness resonate at higher frequencies. I'm ignoring the cavity pipe resonance of the air column in the tube here which is integral to the design of the speaker.
The key to minimizing unwanted vibration is to design a structure so that its resonant modes are not at frequencies at which it is excited in use. So compare the high stiffness and relatively low mass of the pipe walls in LXmini with the much larger masses and lower stiffness of the panels in a typical speaker box (imagine the result of pressurizing the box to 220 PSI) and you will appreciate that in the important modes (when LXminis pipe walls are flexing laterally to produce unwanted sound) LXmini has enormous advantages over the walls of a typical speaker enclosure which will have multiple resonant modes in the lower audio band.
So applying CLD to the LXmini pipe is using a tool made to cover a key weakness of speaker box enclosures where that weakness was engineered out of LXmini by its fundamental design. It's sort of like gluing 1/2"plywood to the top and bottom of a 12" steel I-beam to increase its load carrying capability!
The key to minimizing unwanted vibration is to design a structure so that its resonant modes are not at frequencies at which it is excited in use. So compare the high stiffness and relatively low mass of the pipe walls in LXmini with the much larger masses and lower stiffness of the panels in a typical speaker box (imagine the result of pressurizing the box to 220 PSI) and you will appreciate that in the important modes (when LXminis pipe walls are flexing laterally to produce unwanted sound) LXmini has enormous advantages over the walls of a typical speaker enclosure which will have multiple resonant modes in the lower audio band.
So applying CLD to the LXmini pipe is using a tool made to cover a key weakness of speaker box enclosures where that weakness was engineered out of LXmini by its fundamental design. It's sort of like gluing 1/2"plywood to the top and bottom of a 12" steel I-beam to increase its load carrying capability!
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