So you decide to get a Brand new Component speaker system from the Brand of your Choice. As soon as you open the packing you find a slew of papers - Manuals, Warranty Information, Specs Sheets, Ads sheets and maybe Stickers. Typically, in Indian scenario;
80% of the people dont even bother to have a look at them.
15% of the remaining give a glance inside before throwing them out
About 3% remaning, try to make sense of various specifics describing the Speaker, but give up when it comes to hardcore parameters like T/S or the Frequency response Graph.
Only 2% can make sense of the Response Graph, but not on all aspects mentioned in the same.
The last 1% are the ones who really understand in and out of a response graph.
Why is Response Graph important ?
Frequency response curves, tell you a lot about the nature, character and sound of a loudspeaker. Response Graphs when understood properly give a quick, but extremely effective way of describing various aspects related to a Speaker.
A Typical Response Graph
A typical response graph is one which is a computer generated graph between a parameter in Vertical axis and another Parameter in Horizontal axis. The vertical axis is usually the sound level in dB. Louder sounds are higher up, while quieter sounds are lower at any given frequency. What is important in a frequency response curve is not what the actual numbers are, but how much they vary from frequency to frequency.
To understand this we need to understand a bit about the dB or "decibel". The dB uses a logarithmic scale since this correlates fairly well with human hearing. As a rough rule of thumb, a change of 3 dB at 'mid' frequencies is just noticeable by the average person. Now some people are either trained themselves or have gifted ears to hear much more subtle differences. typically, a well trained audio engineer or audiophile can detect subtle differences in frequency response as small as 1 dB at certain frequencies. However, the average person will probably not notice changes until they are atleast around the 3 dB different point. This ability to detect differences gets worse for everyone at both low and high frequencies.
Most folks get confused with interpreting change in db. A larger change on the order of 10 dB is needed for something to sound "twice as loud" at mid frequencies. This gets more and more when it comes to low and High frequencies. The way it is this way is becasue the ear / brain combination interprets sound very differently.
For example if i want my sound system to play twice louder and buy a 200 watt amplifier to replace my existing 100 watt amplifier, it will not be twice louder at all, Infact i wont even be able to notice much of a difference at all as the level increase is just 3 dB. In order to get the sound system to sound twice as loud, I would have to buy a 1000 watt amplifier to replace the original 100 watt model which will then contribute to a 10 dB increase in level.
Note that the important thing on the vertical axis is not how much the curve appears to go up and down, but the number of dB it goes up or down. Be careful when comparing curves to look at the dB scale. If no dB scale is given, then the curve is close to be termed meaningless.
The next thing to look at is the horizontal axis that shows the frequency. The usual numbers given for the range of human hearing is from 20 Hz to 20,000 Hz (20 kHz). This range can be expected to hold true for healthy young people who have not been exposed to excessively loud sounds. Most of us lose some of our hearing starting at the frequency extremes as we age. An average human would be able to hear frequncies from 30hz to 17Khz well.
The Key aspect to look for in this axis is the Range. A Typical Sub would cover freq below 400 hz well. A typical Midbass would cover freq from 80 Hz to 5Khz well. a Typical Tweeter will cover freq above 4Khz pretty well. However there are quite a number of exceptions to these stated numbers. Most High end Woofers take down from 700 hz also. Few Competition grade Midbass do an easy 60 Hz to 5Khz. Few High end tweeters take things from as low as 1khz all the way beyond the 20khz range !
A Typical Response Graph looks like this;
On Axis, Off Axis Response:
Every audio device has its own "color" and "texture" which the skilled engineer uses to produce a pleasing result. Ofcourse ultimatley a flat and linear curve is what would be an ideal scenario. But then in reality it is quite impractical to get a perfect flat line. Second, most frequency response curves are only of the response directly in front (on-axis or zero degrees) of the device being tested. Even if the on-axis frequency response were flat, that would not tell us what the response was like at different angles. Most loudspeakers will have very different responses at different angles. The minimum set of curves needed to characterize a microphone's variation in frequency response and level at different angles is on-axis, 90 degrees off-axis (directly to one side), 60 degrees off-axis (angled to one side), 30 degrees off-axis (steeply angleed to one side)and 180 degrees on-axis (directly to the rear).
Remember with each type of axis, you will find the response not only varying in db but sometimes in range also. It is important you understand what axis is the response curve measured at before arriving at a final conclusion.
Sometimes, an impedance graph is also represented along with the freq range graph. The sudden peaking of the impedance in a response graphs is the Resonant Freq of the Driver.
Listed Below are Few of the Response Graphs of popular Drivers and Speakers.
DLS Scandinavia 6 Midbass
Dynaudio MD142 Mid Range
Morel CDM 88 Mid Range
Seas Reference RT27F Tweeter
Focal PolyGlass V30 Components
These curves help a lot when it comes to positioning of tweeters. So, the next time around, do understand the graphs before making a buy. Happy reading