he rate of airflow is measured by the volume of air moved per unit of time. The common unit of measurement is Cubic Feet per Minute (CFM). The efficiency of various fans can be compared by looking at their CFM ratings. StudioTech offers a variety of fan kits as accessories for our Ultra cabinets, with CFM ratings that range between 40 and 100 CFM.

Hypothetical calculations

A fan’s CFM rating is a maximum figure. It indicates the highest airflow it can produce, which is always taken from its performance in open air. In a cabinet enclosure both air friction and turbulence reduce the flow rate.

On a fan panel with multiple fans, the ratings of the individual fans combine. A panel of four 50 CFM fans has a capacity of 4 x 50 = 200 CFM, for instance.

It is possible to calculate the hypothetical cooling requirements of a component system from the amount of power the system consumes.

• 1 watt of current outputs 3.413 BTU (British Thermal Units) of heat per hour
• 12,000 BTU/Hour requires 1 “ton” of air conditioning
• 1 “ton” of air conditioning is typically accomplished with 400 CFM of airflow

Complication of getting the real data

Getting the correct measurements to make this formula conform to reality is complicated, however. Most electronic components convert their entire power consumption into heat. Thus their heat output can be calculated easily based on their power requirements. But the biggest heat generators are amplifiers, and amplifiers do not convert power to heat in the same straightforward fashion.

The heat output of amplifiers depends on a complex multitude of factors, which have to do with not only the circuit design of the amplifier itself, but also the speaker load, the type of power supply, and even the type of music you play. Amplifiers come in different classes of efficiency. The most common types convert around 50% of their power consumption into heat, but different classes of amplifiers range from as low as 10% to as high as 80% heat output.

Also, 400 CFM of airflow is not accomplished by simply putting fans with a capacity of 400 CFM in the system. The stated capacity of a fan is a measure of its maximum performance in an open air setting. Its efficiency in a cabinet enclosure can be reduced by as much as 60%, all depending on the internal airflow characteristics of the system layout.

Rule-of-thumb approximation

As a rough-and-ready approximation, 600 watt of power consumption creates a need for 100 CFM of ventilation.