Third article in a series describing different safety features and construction aspects of classroom headphones and headsets.
Over the past several weeks, we’ve blogged about the importance of some of the built-in safety features within headphones and even about the cord connection into the earcups themselves. Appreciating some of these fundamentals before purchasing a classroom headphone makes the difference between having a headphone which will still be in use at the end of a school year, or opting for a “consumer brand” that may not even last until the Winter Break. This installment will introduce some of the key performance considerations of headphones.
The technical specifications of a headphone varies from one to the next but there are certain aspects that support how well a headphone sounds and operates. Oftentimes the specs can be confusing or not very descriptive. Knowing what the individual specs are and understanding their meaning can help teachers help students benefit from proper headphone use in any type of learning environment. Below are the most common headphone specifications to consider when purchasing headphones.
Frequency Response: The range of frequencies that the headphones can reproduce effectively. The audible bandwidth for the human ear is 20 Hz – 20,000 Hz (or 20kHz), which is what Califone® headphones, both wired and wireless, and headsets typically have. Outside that range (above or below), most sounds are not audible to human ears. Ultra-low frequencies (less than 20Hz) are more often felt rather than heard.
Distortion: How accurately the headphones reproduce sounds and given in a percentage of signal distorted. Lower is better – 1% distortion or less (at maximum power). Tests have shown that 1% distortion is at the threshold of audibility. Headphones have less distortion at loud levels than speakers.
Sensitivity (loudness): A measure of headphone efficiency in decibals (shown as “dBs” SPL (sound pressure level) per milliwatt of input. A low number means that the headphones need more power to sound as loud as those which have a higher sensitivity. Headphones for portable media players such as boomboxes, cassette players / recorders as well as CD and MP3 players need to be fairly sensitive because of the lower power output of these stereo units. Modern dynamic headphones have sensitivity ratings of 90 dB or more.
Impedance: A measure of a headphone’s load on an amplifier (how much work is required) is stated in Ohms. This factor is less important with solid state amplifiers, which can drive most headphone impedances, but can be significant with tube amplifiers, which are more sensitive to load impedances. Headphones and headsets specifically manufactured for school use generally have impedances ranging from 25 Ohms, like the 2800 and 2810 Listening First™ series, 3064AV and 3064USB headsets, to 600 Ohms for headphones in the 2924 series. The 3066AV headsets are rated at 300 Ohms.