Frequency Response - Part Two

Yesterday we discussed what a frequency response graph is and what it can tell you about the performance of a speaker or subwoofer.

Today, it is what the graph can not tell you.

The most common misconception is a frequency response graph somehow indicates the maximum output capabilities of a speaker. The frequency response graph only represents how evenly the speaker or subwoofer reproduces the input signal over the frequency range measured. This has no correlation to maximum output capabilities.

The frequency response graph cannot tell you if the speaker is a good design that will accurately reproduce music and film source material. It CAN tell you if the speaker is poorly designed. If the frequency response graphs shows unusually large deviations across its intended operating bandwidth....chances are very good it won't sound very good. At least not compared to a similar product with a a relatively smooth frequency response graph. However a smooth frequency response by itself isn't enough information to decide if the speaker or subwoofer is well designed.

Another misconception is that the frequency response graph is what you will be hearing sitting in your home theater room. Not quite. Not even close actually....at least not without room acoustical treatments and/or electrical equalization.(which will both be covered in future "Tips of the Day"). First, the frequency response graphs is taken "on axis" from the speaker both in terms of the vertical and the horizontal microphone placement. If you are sitting "off axis" the speaker's frequency response will change. The more off-axis you are, the larger the change. This is why you see some audio systems with main speakers "toed in" toward the center of the room. If you haven't experimented with toeing in your speakers yet it is worth spending a little time with. The changes usually aren't dramatic but they can be audible. Second, the speaker's frequency response is measured in a non reflective environment. An anechoic chamber for example. Or, the input stimulus is "gated"(limited to a very short period of time) so that any potential reflective surfaces don't alter the measurements. When the speaker is placed in a typical home, all of your walls, ceiling and floor will alter the response before it arrives at your seating position(s). Does this mean an accurate frequency response graph is not important? No. You should always strive to start with the most accurate presentation possible.

Tomorrow, tips on how to fairly compare different frequency response graphs from different sources.

Tom V.
Power Sound Audio

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