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DIY reflection filter idea
Old 1 week ago
  #1
DIY reflection filter idea

Was wondering if those environmentally unfriendly dish cleaning sponges (with the scouring layer) could be used to make a DIY reflection filter?

Maybe 2 to 4 layers of them (depending on the thickness of the ones used.

Is there anyway of knowing/guessing/testing what sort of absorption they would offer? Are they comparable to acoustic foam you can buy (I know they are different from each other)? I realise these reflection filters are not that amazing anyway, just wondered if we could save the planet a little by repurposing these things?

Thanks
Old 1 week ago
  #2
Lives for gear
My guess is that, depending on their thickness, type of foam used, reflectivity of the outer surface, foam density etc it's actually going to be a combination of reflector and absorber. If the outer surface is dimpled or pyramidical then any reflections are going to be scattered/randomised...which is a desirable quality.

Another factor is going to be the nature of the frame the sponge foams are bonded to...if it's both parabolic and reflective, this might tend to redirect sound back to the rear of the mic, rather than the intended outcome of absorbing and scattering. To that end, the frame and backing material should perhaps be corrugated or V/W shaped in profile, to facilitate wave trapping ?

It could be worth glueing sponges to the frame at a variety of angles, as well as cutting them up into multiple shapes before use...as well as disinfecting them, if they are used !!

At the end of the day, it will probably be better than not having one...but in the absence of knowledgeable application of acoustics theory and associated materials science, the result will probably be frequency-variable, unpredictable and largely subject to chance ?

As a starting point, do a Google Image search for anechoic chambers, to begin formulating a design to aim for (at much smaller scale).....it's going to be largely an experimental fun project, particularly since the jury's out as to whether the commercial designs (SE et al) even work as claimed....

Last edited by studer58; 1 week ago at 01:45 PM..
Old 1 week ago
  #3
Quote:
Originally Posted by studer58 View Post
My guess is that, depending on their thickness, type of foam used, reflectivity of the outer surface, foam density etc it's actually going to be a combination of reflector and absorber. If the outer surface is dimpled or pyramidical then any reflections are going to be scattered/randomised...which is a desirable quality.

Another factor is going to be the nature of the frame the sponge foams are bonded to...if it's both parabolic and reflective, this might tend to redirect sound back to the rear of the mic, rather than the intended outcome of absorbing and scattering. To that end, the frame and backing material should perhaps be corrugated or V/W shaped in profile, to facilitate wave trapping ?

It could be worth glueing sponges to the frame at a variety of angles, as well as cutting them up into multiple shapes before use...as well as disinfecting them, if they are used !!

At the end of the day, it will probably be better than not having one...but in the absence of knowledgeable application of acoustics theory and associated materials science, the result will probably be frequency-variable, unpredictable and largely subject to chance ?

As a starting point, do a Google Image search for anechoic chambers, to begin formulating a design to aim for (at much smaller scale).....it's going to be largely an experimental fun project, particularly since the jury's out as to whether the commercial designs (SE et al) even work as claimed....
Yes, I was thinking that it could work as a diffuser/absorber by having the sponges placed both vertically and horizontally and at varying thicknesses. I'll give it more thought.

Thanks
Old 1 week ago
  #4
Lives for gear
I don't think these reflection filters work well at all - in some cases they make matters worse. You'd be better off making some sort of temporary booth with quilts and perhaps curtain lines and/or mic stands providing the structure. ie sing out of the booth into the room space, the booth will prevent the hard to control sound bouncing around the room from being picked up by the singer's side of the usual cardiod/hyper-cardiod vocal mic. Hanging another quilt or blanket on the wall you're singing toward will help too, I wouldn't face straight on either - hit the opposite wall at an angle.

I've got a reflection filter - tried it with three or four different mics and it now has a new duty as pointless dust collector.
Old 1 week ago
  #5
Lives for gear
Quote:
Originally Posted by Mr Funk View Post
Yes, I was thinking that it could work as a diffuser/absorber by having the sponges placed both vertically and horizontally and at varying thicknesses. I'll give it more thought.

Thanks
An additional idea, if using a curved frame of chicken wire or similar lightweight and rigid yet porous material, think about lining it with a mass-y dampening material, like thick felt cloth, old blanket or heavy carpet underlay (similar to the blankets used by furniture-moving trucks, maybe a bit thinner though) Then use a hot glue gun to attach your sponge segments in the randomised horizontal & vertical alignments you mentioned in your reply above

I'm presuming this will be used for vocal recording in a sub-optimal room....if so consider using a fig 8 mic, since the reflector/absorber will partially or fully dampen the rear sector mic pickup, while the fig 8's nulls should additionally damp or kill the nearby early reflections from the floor and ceiling above/below the mic, leaving the voice direction pickup as the predominant zone of sensitivity. A shaggy rug/carpet on the floor between singer and mic will additionally help negate floor bounce interaction and combing with the primary direct vocal
Old 1 week ago
  #6
I was also thinking of hanging moving blankets (this type https://www.ebay.co.uk/itm/Moving-Pa...71e0a78cd261a7) on two clothing rails, one a few feet behind the mic and one a few feet behind the vocalist. I'm sure these reflection filters are not that great, I just like to think of useful ways to recycle!
Old 1 week ago
  #7
Lives for gear
Yes the moving blankets mass will tend to absorb the energy of bass frequencies you want to quell, but I'd worry that the reflective nature of the outer covering would tend to reflect rather than absorb the mid and higher frequencies.....which is what you're trying to avoid.

If you hang the blankets so they make folds or corrugations rather than a straight face or a curve, they will tend to break up the reflections. If you hot-glued the sponges directly onto the blankets you'd probably get the ideal combination of trapping, absorption and reflections...and your idea of one blanket behind the singer and another behind the mic is a good one. Fig 8 mic pattern would simply capitalise on these characteristics, as mentioned earlier
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