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In Reply to: RE: Maggie slap / Mylar Stretched posted by pistonengine08 on July 30, 2016 at 05:36:50
I have a design for a full-length clamp which puts even but minimal pressure on the entire edge of the driver. Between driver and frame should go something like Teflon tape. I have this and it is Scotch #5181 which is 6.5 mil. NOT the stuff you wrap on pipe threads. The idea is to 'float' the panel in the frame.One other note: Mylar is VERY low stretch and temp / chem stable.
Too much is never enough
Edits: 07/30/16Follow Ups:
The heat input on the mylar is quite large if it is painted black as here. Also the difference between a clear mylar and black can cause strange shrinking then we have a metal frame which also gets a heat input. I also think that the bolt with the washer tends to twist the frame outside, lay something under the washer so you get the wanted pressure with no twist to the frame.
Black mylar? You mean the EDGE which may be painted? How much heat input does the metal frame get? It's only exposed on a small part of it, the rest will RADIATE heat. I'd have to figure out the mylar physical data to see how HOT and how much STRETCH it gets.
I agree totally with the bolt / washer idea. It is BAD. I've got a design (thanks SketchUp) for a full-length low pressure clamp for driver to frame. In my design a SPRING applies pressure and between driver and frame is THICK Teflon adhesive tape, a Scotch product. Minimal amount of metal are used.
Small amount of pressure over a larger areas is good.
Too much is never enough
It can be a high pressure clamping just that it mus not distort the intended shape of the frame including not altering the curvature of the magnet board. The washers and screws definitely will not do it right.
No, it should definitely not be a high-pressure clamping scheme. There is no need for that, and if implemented as such you could incur similar problems to those already experienced by the OP.
The panel should be allowed to "float" in whatever frame it's installed. A spring-loaded scheme would probably be okay.....as long as the perimeter spring pressure was minimal.
Dave.
Many mod projects shown here used high pressure clamping without distorting the drivers' shapes, so why is high pressure something to be avoided? It would be beneficial for draining the frame of excess vibrational energy - PG's bolting technique does this in a rather brute force manner but is very successful in clearing up the midrange of the MMGs and 1.6's, as his fans attest.
Maybe you should define "high" pressure?
The transducer units have a "curvature" to them, and if any securing method aggressively removes that and/or creates a twist and/or creates a vice-like grip on any portion of the edges a user can run into problems.
I'm not sure many users are appreciating the forces involved here when fabricating different frames for their speakers.
Dave.
My favored approach is viscoelastic damping on one side and clamping with vertical Al or or wood "L" forms bolted to the wood frame in multiple locations along its length. That would be on the sides where there is no curvature. The bolts should screw to finger tight with the screwdriver and you can tune the spring loading from there by adjusting with extra torque..
Did you look closely at the sandwich construction scheme I used on my MMG's a few years back? It's a much preferable setup to your favored approach.
It provides coupling to both sides, very even tension across the full perimeter, requires less fabrication of special pieces, has no finicky screw tension to worry about, requires no drilling of the transducers, etc, etc, etc.
Dave.
Actually I don't remember it specifically.I will look it up.
Thanks
Screenshot, above is an idea I had to use bend wood for the spring. The clamp shown is also a non-starter and was substantially changed in the next revision.
We aren't talking a LOT of energy here. A firm clamping with no 'pressure' points is the way to go.
IMO, the secret is in the SPRING. No coils. No 'torsion' springs. I don't know what it's called, but a spring that is flat and 'wavey', maybe 1/2"wide and the length of each side. Use adjustable clamps and a torque wrench and adjust tension by ear. The correct name is 'Linear Wave Spring'.
Between the panel and the frame should be the 'float' in the form of easily source TEFLON tape. This is thick stuff made by Scotch.Scroll down to the drawings.
Too much is never enough
Edits: 07/31/16
Actually, the energy dissipation/pass through required may be a significant minority of the power input. A wave spring is not a bad idea for absorbing some of the energy, but it could have a narrow freq of max absorption rather than a broad range of freq the way a CLD damper would. but I am sure you can choose the compression pressure to provide a broader range.
The hard rigid contact for energy transfer to drain the driver frame (and magnet board) to the side struts would be my choice considering how well that is reported to work in PG's design..
I'm not going to have 'side struts'. I have a unique triangulated design using a SINGLE strut.
The trianulation provides incredible rigidity without additional metal AND at the same time a single path to a mechanical ground plane.
the key is ratio of length of the elements. And the mounting points on the frame.The including drawing is my first generation 'noodle' for what I intend. This has also been changed since than. This drawing is for proportion / geometry ONLY. NOTE: The roller under the panel. The strut includes a VARIABLE tilt mechanism built-in and also acts in a manner similar to SPIKES do on box speakers.
Too much is never enough
Edits: 08/01/16
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