ProFit Sub Enclosures are designed in-house based on the lower of the two loudest bass resonant frequencies of each vehicle tested. Sweeping the vehicle to determine the lower of the two frequencies we can conclude the frequency which plays louder in a given environment. This, along with the mechanical and electrical properties (Thiele Small Parameters) of a given subwoofer, the optimum port tuning frequency can be achieved for each ProFit Enclosure.
ProFit Sub Enclosures are manufactured through a rotational/centrifugal casting process combined with a chemical curing procedure which utilizes an exothermic reaction.
An exothermic reaction is a chemical reaction that releases heat. It gives net energy to its surroundings. That is, the energy needed to initiate the reaction is less than the energy released.
When the medium in which the reaction is taking place collects heat, the reaction is exothermic. When using a calorimeter, the total amount of heat that flows into (or through) the calorimeter is the negative of the net change in energy of the system.
When optimum exotherm is achieved the centrifugal RPM is increased i.e., starting off slow and increasing the speed of rotation (RPM's) to avoid lifting or falling of layered material during the cure process.
The absolute amount of energy in a chemical system is difficult to measure or calculate. The enthalpy change, ΔH, of a chemical reaction is much easier to work with. The enthalpy change equals the change in internal energy of the system plus the work needed to change the volume of the system against constant ambient pressure. A bomb calorimeter is very suitable for measuring the energy change, ΔH, of a combustion reaction. Measured and calculated ΔH values are related to bond energies by:
- ΔH = (energy used in forming product bonds) − (energy released in breaking reactant bonds)
In an exothermic reaction, by definition, the enthalpy change has a negative value:
- ΔH < 0
since a larger value (the energy released in the reaction) is subtracted from a smaller value (the energy used for the reaction). For example, when hydrogen burns:
- 2H2 (g) + O2 (g) → 2H2O (g)
- ΔH = −483.6 kJ/mol of O2 [3]
In an adiabatic system, the temperature raise due to enthalpy change can be expressed as
- −ΔH298.15 K = ∫T1
T0Cp, pdT + ∫T0
298 K(Cp, p−Cp, r)dT[4]
where ΔH298.15 K is the standard enthalpy of reaction at 298 K, T0 and T1 are the initial and final temperature of the system, respectively, and Cp,p and Cp,r are the heat capacities of the product and reactant, respectively.
Assuming the heat capacity of the system remains as a constant value Cp,p=Cp,r=Cp, the change of temperature ΔT=T1−T0 can be expressed as
- −ΔH298.15 K = ∫T0+ΔT
T0Cp, pdT = ΔTCp, p[4]
The most commonly available hand warmers make use of the oxidation of iron to achieve an exothermic reaction:
- 4Fe (s) + 3O2 (g) → 2Fe2O3 (s).
In controlling the exothermic reaction over a longer period of time i.e, over the activated complex period, we were able to achieve a more consistent wall thickness throughout our molds thus eliminating the requirements of hand laying fiberglass.
