Rubber sheets

[oublie]

Um bit of an odd one,

I was just thinking - what would be the down sides of making a baffle out of rubber?

I'm thinking rubber sheeting attached to the circumference of the driver and then stretched to hold the driver tight for open baffle but not baffleless?

I know some folks have been using straps etc to hold their drivers in place but im thinking of using a sheet of the stuff thin or think enough to hold the driver but not ring?

Is this feasible or would there be obvious issues that i havent considered?

[twest820]

If it's thin and has to be stretched I'd bet it'll warp with the weight of the driver and probably need to slope forward rather than be vertical to get the driver vertical. Bit of a problem mechanically and for vertical directivity plus the tension will raise the resonant frequency of the suspension and increase the coupling. The physics are not unlike a drum head so my guess managing the sheet's Sd and associated linear and nonlinear distortion will be challenging. My guess would be it'd be a bit of a mess and challenging to get performing well.

Thicker, higher durometer stuff you could work more like a traditional baffle seems more tractible. You'd likely end up with a resonant frequency on the driver suspension not greatly lower than that of a traditional baffle, just with more damping in the baffle itself. It'd probably help with baffle vibration but not so much vibrations within the basket---reducing basket vibration favors supporting the driver at the magnet and not at the flange. So I'm not immediately seeing a strong value proposition here either. MDF might actually have more damping; haven't looked too hard here.

I'm not aware of any dipole baffles built with constrained layer damping (CLD) more sophisticated than using damping glue between a couple sheets of MDF. I don't know CLD physics well enough to know if it'd be worth using a rubber sheet in the middle instead.

[Top Shelf]

Maybe to help the backwards tilt of the driver you could use a second rubber ring on the magnet with its own support ring that is attached to the main baffle?

[twest820]

Hard to do that with further obstructing the back wave. Every time I consider this sort of thing I end up thinking the most straightforward solution is to clamp the magnet at the bottom and balance the driver on isolation mounts. Hanging's popular because it's a cheap and effective isolation mount.

[oublie]

thanks twest,

that makes sense, theres really no benefit. I quite like the idea of magnet mounting with a 'suspended' baffle i think ill have a play around with that, i think it's been done so ill have a search.

[twest820]

Like the gapped baffle mige0 tried on his 12G40 in his Beautiful Swingin' Speaker thread? A drawing would be helpful to indicate the concept.

[oublie]

here we go very rough idea of what i mean - tubular chrome support structure and think rubber sheeting bolted to both the frame and the woofer mounting holes.

Might need to support the magnet as well.

What do you think?

i would use the support bolts to tighten the rubber.

[twest820]

Less likely to be sonically problematic than a solid sheet, more likely to be mechanically problematic. If the rubber's stiff enough to hold the driver without magnet support I'd expect a fairly high resonant frequency in the suspension with the driver that close to the frame.

[sreten]

Hi,

You'd want the suspension frequency to be below the bandwidth of the driver.

To avoid local stress you need to glue the sheeting around the peripherary of
the driver. To keep it simple you could let it self tension, i.e. with the driver
held up and flat and the baffle flat simply glue and staple the sheet in place
with some tension. Then add a rubbber strap to the back of the magnet that
affixes to an adjustable point above the driver to vertically align it.

You will end up with a decoupled driver. Given the arrangement a clamping
ring might be needed to prevent the rubber slowly peeling off the surround,
This could be a chamfered square or ring and driver cutout, with the rubber
glued to the front or back of the square / ring around the cutout and the
driver bolted to the front or rear to hold the rubber in place.

rgds, sreten.