Abstract: A tensioning device for a sheet of material that includes a first ring with protrusions, a second ring, and a shaft. The first ring and the second ring are positioned such that the sheet of material can be clamped between the first ring and the second ring. The shaft has an outer surface, the outer surface includes a spiral race such that the protrusions of the first ring follow the spiral race, allowing the first ring and the second ring to displace linearly causing the sheet of material to be stretched. The spiral race includes a plurality of notches that correspond to the protrusions.

Abstract: An acoustic metamaterial aural protection device ear cup which includes a dome having an opening, an interchangeable membrane stretched across the opening of the dome such that an airtight cavity is created, and a one-way vacuum valve; the valve is mounted to the dome, such that air can be removed from the cavity such that the membrane acts as an acoustic metamaterial, resulting in higher attenuation values at different frequencies.

Abstract: A tensioning device for a sheet of material that includes a first ring with protrusions, a second ring, and a shaft. The first ring and the second ring are positioned such that the sheet of material can be clamped between the first ring and the second ring. The shaft has an outer diameter, the outer diameter includes a spiral race such that the protrusions of the first ring follow the spiral race, allowing the first ring and the second ring to displace linearly causing the sheet of material to be stretched. The spiral race includes a plurality of notches that correspond to the protrusions.

Abstract: An impedance tube and sample tube holder that includes a hollow tube, a first tube, a second tube, and a spool. The hollow tube has two halves which are detachable and can hold spacers and a sample. The first tube includes a first tube speaker end and a first tube spool end. The first tube has a speaker disposed at the first tube speaker end and microphones. The second tube includes an anechoic terminator tube end and a second tube spool tube. The second tube has microphones and an anechoic terminator at the anechoic terminator tube end. The spool holds the hollow tube with the spacers and the sample. The spool is attachable to the first tube spool end and the second tube spool end such that the sample is perpendicularly orientated to an incoming sound wave produced by the speaker.