Speaker Frequency Range and Frequency Response

What is the difference between frequency response and frequency range of a speaker?

How do we measure frequency range and frequency response?

• By the way, this question is probably more at home on sound.stackexchange.com – Fizz Oct 13 '15 at 17:03

Frequency range is a largely useless marketing term.

Frequency response is a real engineering term. It tells you the input voltage to output sound power across the audio frequency range (20 Hz to 20 kHz). From that you can decide what "frequency range" the speaker has, but based on the parameters you actually care about.

For example, for demanding high end audio applications, you might want the frequency response to be within 3 dB of flat. You look at the frequency response graph and see over what frequency range that is true for. On the other hand, if this is a less demanding application, like a public address system, you might care more about efficiency or maximum sound output power within some distortion limit.

To summarize, frequency response is the raw facts. Frequency range is someone else looking at the raw facts, deciding what's important or what they can get away with, and telling you the min/max frequency the speaker is good for, whatever "good" means.

• For what frequencies high end applications usually have flat frequency response (in other terms what is the frequency range)? Do you have any pictures of frequency response for high end audio and for low cost speaker? – Hemus San Oct 13 '15 at 16:38
• @Day: Really really good would be within 3 dB from 20 Hz to 20 kHz. Take a look at some actual speaker datasheets. – Olin Lathrop Oct 13 '15 at 21:44

Frequency response is the more practical/useful value because it tells you the "range" but within certain criteria i.e. 40 Hz to 18 kHz +/- 3dB. The +/- 3 dB is important because if the speaker spec just said 40 Hz to 18 kHz you wouldn't know that the loudness wasn't down by 30 dB at the end points of the spectrum. Neither would you know that within the pass-band there wasn't some really bad resonant point that would make listening to music an obscene act!

Just specifying a range is meaningless. You need SPL (sound pressure level) versus frequency and if you can get a graph all the better: -

An SPL frequency response tells you that a speaker can deliver a certain loudness as well telling you how "flat" the response is in the passband.

See this for extra info.

Regarding measurement, there are various standards, e.g. quoting a summary of IEC 268-5 (more recently renamed IEC 60268-5):

1) The frequency response of the loudspeaker is measured along the reference axis using a sine signal. 2) At the maximum sound pressure level, the volume level is averaged at one octave. This mean output level is termed the sensitivity. 3) The frequency response is given as the range of frequencies at which the volume level of the loudspeaker drops 10 dB below the sensitivity level. Dips in the frequency response narrower than 1/9 of an octave can be discounted.

Also notable in this regard [measurement] is the [US] AES2-2012 standard. This is a bit too long to summarize here because it concerns the components that go into a loudspeaker, with different procedures/recommendations for high vs low frequency drivers, enclosures etc.

You should also beware that manufacturer's measurements may include conditions that you surely don't have at home, for example, one loudspeaker datasheet has in the fine print

Frequency response and range measured on-axis with recommended active EQ in an anechoic environment

Anechoic environment is probably an anechoic chamber. (These are pretty expensive, by the way.) As for their "recommended active EQ", who knows... but I suspect a way to get better stats.

I should add that on-axis response, while a useful measure, if by no means a complete charcterization of a loudspeaker. The off-axis response matters quite a bit in practice, and for consumer devices this is hardly ever detailed (or even summarized)... the reason being that it would take a small book to do it (in detail) and the summarization methods require a bit of expertise to interpret. The 3D graph shown below is hard to interpret without being able to rotate it interactively etc., so that's usually not what you get, even for professional product, but instead you get a series of cross-sectional (sometimes polar in the angle) plots at some frequencies. One can argue that manufacturers could make detailed available on the internet, but alas they don't.

Also note that this example includes only one (plane) angle, actual 3D characterization needs two angles (vertical and horizontal), so that's 4D data. For datasheet examples that are somewhat decent in terms of providing this kind of off-axis data (in cross-sectional form), you can look at DAS. By no means the norm though for consumer products.

• "The frequency response is given as the range of frequencies at which the volume level of the loudspeaker drops 10 dB below the sensitivity level." - What exactly is sensitivity level and how it is measured? – Hemus San Oct 13 '15 at 16:51
• It says in the previous sentence "At the maximum sound pressure level, the volume level is averaged at one octave. This mean output level is termed the sensitivity [level]." – Fizz Oct 13 '15 at 16:56