Most of us know what frequency is; The high or low tones of sound. But some have asked what frequency response is and how it relates to the quality of an audio product.
What does it mean?
Frequency response is a graph of voltage gain or loss versus frequency. As an audio product reaches its limits in the frequency range it may have a voltage gain or loss. The frequency limits and the gain or loss is the frequency response.
Most specs give a low and high frequency and the gain or loss that can be expected at those limits. These specs typically look like:
50-20k Hz. at +/-1dB
Let?s break down the specs. The "50" is the low end of the frequency spectrum that the unit is rated at. The "20k" (20,000) is the high end of the frequency spectrum that the unit is rated at. "Hz" is the abbreviation for hertz, the unit of frequency. Some spec have "-", "+" or "+/-", this is the loss (-) or gain (+) that the unit has at the listed frequency. The "1dB" is the amount of gain or loss. If the unit has "+/-", is means that there may be a gain or loss at the end frequencies.
As a signal reaches one of the end frequencies, the signal strength will start to change. Ideally the unit will start to roll off or have a voltage loss. This is especially good on the high frequency end. By rolling, off the gain drops and filters out high frequency that is unwanted and unneeded. High frequency can cause oscillations in the system that you may not be able to hear. The rolling off of the low end is most of a concern now days with the desire of the low booms in today?s music. Most people can hear between 20 Hz. and 20,000 Hz. The reason the loss or gain in voltage has many factors is based on the design, manufacturing and material that is used.
Testing:
Testing a unit for frequency response varies on the type of product, but the basics are all the same. I will use the testing of an audio matching transformer with a 1 to 1 ratio as a sample. This will make it a bit easier to understand. First, the transformer takes about a 1 volt input.
As you increase the frequency the signal stays at 0 dB until it gets to about 18,000 Hz. and starts to drop. At 20,000 Hz. it drops to -1dB. The frequency response of this matching transformer would be 50-20k Hz, -1dB.
What frequency response do I want?
This is a tricky question. First what is the audio system being used for? If you are looking for a public address or paging system then the frequency response is not a major factor. Human speech is typically around 300 to 5,000 Hz, so you do not need a system that goes up to 20,000 Hz or down to 30 Hz.
For background music, the frequency response is a little more important. Background music is in an environment that you want a soft and relaxing sound. The music is played to break the silence of a waiting room, office, store etc. and to relax. Because of this the frequency response is not a major importance. The typical frequency response is about 100-15K Hz, +/-2dB.
For the home entertainment system, frequency response is a major factor. From the earth shattering explosions in the latest DVD to the low base in modern pop music to the high pitch of the violin in that classical music. Typical high end audio systems run about 30 to 20,000 Hz. Anything greater, in my opinion, is overkill and just another selling pitch. Over the years I have seen more and more people installing higher end audio systems for background music in stores. Most of this is due to the pop music craze as a selling point.
Another thing to think about is what the frequency response of whole system is. If you have a speaker that only goes down to 50 Hz. with a -1 dB, then you do not need an amplifier that can go to 30 Hz. When you are designing a system or adding on to one, a chain is only as good as its weakest link.
I hope this helps you a little in knowing the role frequency response plays and what to look for.
